Journal of Neurochemistry, 1977. Vol. 29, pp. 13-26. Pergamon Press. Printed in Great Britain.

SHORT REVIEW

 

RELATION BETWEEN PHYSIOLOGICAL FUNCTION
AND ENERGY METABOLISM IN THE
CENTRAL NERVOUS SYSTEM

Louts SOKOLOFF

Laboratory of Cerebral Metabolism, U.S. Department of Health, Education, and Welfare,
Public Health Service, Bethesda, MD 20014, U.S.A.

THE BRAIN is a complex organ composed of many
structural and functional components with markedly
different and independently regulated levels of func-
tional and metabolic activity. In more homogeneous
organs that do readily recognizable physical and
chemical work, such as the heart, skeletal muscle, and
kidney, a close relationship between functional ac-
tivity and energy metabolism is well established. The
existence of a similar relationship in the tissues of
the CNS has been more difficult to prove, partly
because of uncertainty about the nature of the work
associated with nervous functional activity, but

mainly because of the difficulty in assessing the levels ,

of functional and metabolic activities in the same
functional component of the brain at the same time.
Pathological and pharmacological conditions with
gross and diffuse effects on cerebral functional ac-
tivity, particularly those that alter the level of con-
sciousness, have been shown to be associated with
changes in overall cerebral metabolic rate (KETY,
1950, 1957; LASSEN, 1959; SOKOLOFF, 1976), but such
associations could reflect separate independent conse-
quences of cellular dysfunction rather than a direct
relationship between cerebral functional activity and
energy metabolism. Changes in the metabolic rate of
the brain as a whole have generally not been found
during physiological alterations of cerebral functional
activity (LASSEN, 1959; SoOKOLOFF, 1969, 1976). What
has clearly been needed is a method that measures
the rates of energy metabolism in specific discrete
regions of the brain in normal and altered states of
functional activity. The recently developed
[!*C]deoxyglucose technique (SoKOLOFF et al., 1977)
appears to fulfill this need. It can be used to measure
quantitatively the local rates of glucose utilization
simultaneously in all the macroscopically visible
structures of the brain. It can be applied to normal
conscious animals as well as those under experimen-
tally altered states of cerebral activity. Furthermore,

 

Abbreviations used: DG, 2-deoxy-p-glucose; DG-6-P,
2-deox y-D-glucose-6-phosphate.

13

the ['*C]deoxyglucose method employs an auto-
radiographic technique which provides pictorial
representations of the relative rates of glucose utiliza-
tion throughout the various components of the brain;
even without quantification these autoradiographs
provide clearly visible markers that map cerebral
regions with increased or decreased rates of energy
metabolsim in altered physiological, pharmacological,
and pathological states. This method has provided
unequivocal evidence of a close relationship between
functional activity and energy metabolism in discrete
structural and/or functional units of the nervous sys-
tem.

METHODOLOGY

A full, detailed, and comprehensive description of
the theoretical basis of the ['*C]deoxyglucose
method has recently been published (ScKOLOFF et al.,
1977). A brief summary of its essential principles is
necessary, however, to clarify the salient features of
its design, its rigid procedural requirements, and the
limitations on its applications.

The method was designed to take advantage of the
extraordinary spatial resolution afforded by a quanti-
tative autoradiographic technique that was originally
developed for the measurement of local cerebral
blood flow (LANDAU et al., 1955; REIvICH et al., 1969).
The dependence on autoradiography prescribed the
use of radioactive substrates for energy metabolism,
the labeled products of which could be assayed in
the tissues by the autoradiographic technique.
Although oxygen consumption is the most direct
measure of energy metabolism, the volatility of
oxygen and the short physical half-life of its radioac-
tive isotopes precluded measurement of oxidative
metabolism by the autoradiographic technique. In
most circumstances glucose is almost the sole sub-
strate for cerebral oxidative metabolism, and its utili-
zation is stoichiometrically related to oxygen con-
sumption (Kety, 1957; SoKoLorr, 1976). Radidactive
glucose is, however, not fully satisfactory because its
labeled products have too short a biological half-life
and are lost too rapidly from the cerebral tissues. The
14 Louis SOKOLOFF

labeled analogue of glucose, 2-deoxy-b-['*C] glucose,
was, therefore, selected because it has some special
biochemical properties that make it particularly
appropriate to trace glucose metabolism and to
measure the local rates of cerebral glucose utilization
by the autoradiographic technique.

Theory

The method is derived from a model based on the
biochemical properties of 2-deoxyglucose (SOKOLOFF
et al., 1977). 2-Deoxyglucose is transported bi-direc-
tionally between blood and brain by the same carrier
that transports glucose across the blood-brain barrier
(BIDDER, 1968; BACHELARD, 1971; OLDENDORF, 1971).
In the cerebral tissues it is phosphorylated by hexo-
kinase (EC 2.7.1.1) to 2-deox yglucose-6-phosphate
(SoLs & CRANE, 1954). Deoxyglucose and glucose are,
therefore, competitive substrates for both blood-brain
transport and hexokinase-catalyzed phosphorylation.

 

during the interval of time equals the steady state
flux of glucose through the hexokinase-catalyzed step
times the duration of the interval, and the net rate
of flux of glucose through this step equals the rate
of glucose utilization.

These relationships can be mathematically defined
and an operational equation derived if the following
assumptions are made: (1) a steady state for glucose
(ie. constant plasma glucose concentration and con-
stant rate of glucose consumption) throughout the
period of the procedure; (2) homogencous tissue com-
partment within which the concentrations of
[!4C]DG and glucose are uniform and exchange di-
rectly with the plasma; and (3) tracer concentrations
of [!4C]DG (ie. molecular concentrations of free
[!4C]DG essentially equal to zero). The operational .
equation which defines R;, the rate of glucose con-
sumption per unit mass of tissues, i, in terms of
measurable variables is as follows:

T
CHT) — kee 8187 | Che" de
Oo

 

R=

®V,Ki

 

ve 7 '
(LPEEs | I crrcerae— ero (CHIC at |
0 0

 

Unlike glucose-6-phosphate, however, which is meta-
bolized further eventually to CO, and water and to
a lesser degree via the hexosemonophosphate shunt,
deoxyglucose-6-phosphate cannot be converted to fruc-
tose-6-phosphate and is not a substrate for glucose-
6-phosphate dehydrogenase (SOLS & CRANE, 1954).
There is very little glucose-6-phosphatase activity in
brain (Hers, 1957) and even less deoxyglu-
cose-6-phosphatase activity (SOKOLOFF et al., 1977).
Deox yglucose-6-phosphate, once formed, is, therefore,
essentially trapped in the cerebral tissues, at least long
enough for the duration of the measurement. The
half-lives of ['*C]deoxyglucose-6-phosphate in the
various cerebral tissues have been experimentally esti-
mated: the average half-lives are 7,7 (s.D. = +1.6) and
9.7 (.D. = +2.6) h in gray and white matter, respect-
ively (SOKOLOFF ef al., 1977). The shortest half-life is
6.th in the inferior colliculus (SOKOLOFF et al., 1977).

If the interval of time is kept short enough, for
example, less than 1h, to allow the assumption of
negligible loss of ('“C]DG-6-P from the tissues, then
the quantity of ['4C]DG-6-P accumulated in any cer-
ebral tissue at any given time following the introduc-
tion of [!*C]DG into the circulation is equal to the
integral of the rate of ['*C]DG- phosphorylation by
hexokinase in that tissue during that interval of time.
This integral is in turn related to the amount of glu-
cose that has been phosphorylated over the same in-
terval, depending on the time courses of the relative
concentrations of [!“C]DG and glucose in the pre-
cursor pools and the Michaelis-Menten kinetic con-
stants for hexokinase with respect to both ['*C]DG
and glucose. With cerebral glucose consumption in
a steady state, the amount of glucose phosphorylated

(1)

where C* (T) equals the combined concentrations of
[!4C]DG and ['*C}DG-6-P in the tissue, i, at time,
T, determined by quantitative autoradiography; C
and Cp equal the arterial plasma concentrations of
[)4C]DG and glucose, respectively; k%, k&%, and k¥
are the rate constants for the transport from the
plasma to the tissue precursor pool, for the transport
back from tissue to plasma, and for the phosphoryla-
tion of free ['*CJDG in the tissue, respectively; A
equals the ratio of the distribution volume of
[!4C]DG in the tissue to that of glucose; @ equals
the fraction of glucose which once phosphorylated
continues down the glycolytic pathway; and K%, and
V*,., and K,, and Via, are the familiar Michaelis—
Menten kinetic constants of hexokinase for ['*C]DG
and glucose, respectively.

The rate constants are determined in a separate
group of animals by a non-linear, iterative process
which provides the least squares best-fit of an equa-
tion which defines the time course of total tissue 4c
concentration in terms of the time, the history of the
plasma concentration, and the rate constants to the
experimentally determined time courses of tissue and
plasma concentrations of '*C (SOKOLOFF et al., 1977).
The rate constants have thus far been determined
only in normal conscious albino rats; the values
obtained for kt, k%, and k$ and their standard errors
are 0.189 + 0.012, 0.245 + 0.040, and 0.052 +.0.010
per min in gray matter and 0.079 + 0.008,
0.133 + 0.046, and 0.020 + 0.020 per min in white
matter, respectively (SOKOLOFF et al., 1977). Prelimi-
nary estimates indicate that the values are quite simi-
lar in the conscious monkey (Kennedy, Sakurada,
Shinohara, & Sokoloff, unpublished observations).
Function and energy metabolism in CNS 15

The 4, @, and the enzyme kinetic constants are
grouped together to constitute a single, lumped con-
stant (see equation). It can be shown mathematically
that this lumped constant is equal to the asymptotic
value of the product of the ratio of the cerebral
extraction ratios of ['*C]DG and glucose and the
ratio of the arterial blood to plasma specific activities
when the arterial plasma ['*C]DG concentrations is
maintained constant. The. lumped constant is also
determined in a separate group of animals from arter-
ial and cerebral venous blood samples drawn during
a programmed intravenous infusion which produces
and maintains a constant arterial plasma ['*C]DG
concentration (SOKOLOFF et al., 1977). Thus far it has
been determined only in the albino rat and the mon-
key. Values are 0.483 (SEM. = +0.022) in the rat
(SoKoLorF et al., 1977) and 0.344 (8.6.M. = +0.036)
in the monkey (Kennedy, Sakurada, Shinohara &
Sokoloff, unpublished observations). The lumped con-
stant appears to be characteristic of the species and
does not appear to change significantly in a wide
range of conditions (SOKOLOFF et al., 1977).

Despite its complex appearance, equation (1) is
really nothing more than a general statement of the
standard relationship by which rates of enzyme-cata-
lyzed reactions are determined from measurements
made with radioactive tracers. The. numerator of the
equation represents the amount of radioactive
product formed in a given interval of time; it is equal
to C#, the combined concentrations of ['*C]DG and
['+C]DG-6-P in the tissue at time, 7, measured by
the quantitative autoradiographic technique, less a
term that represents the free unmetabolized ()*C]DG
still remaining in the tissue. The denominator rep-
resents the integrated specific activity of the precursor
pool times a factor, the lumped constant, which is
equivalent to a correction factor for an isotope effect.
The term with the exponential factor in the denomi-
nator takes into account the lag in the equilibration
of the tissue precursor pool with the plasma.

Procedure

Because local rates of cerebral glucose utilization
are calculated by means of equation (1), this equation
dictates the variables to be measured. The specific
procedure employed is designed to evaluate these
variables and to minimize potential errors that might
occur in the actual application of the method. If the
rate constants, k%, k%, and k%, are precisely known,
then equation (1) is generally applicable with any
mode of administration of ['*C]DG and for a wide
range of time intervals. At the present time the rate
constants have been determined only in the conscious
rat. These rate constants can be expected to vary with
the condition of the animal, however, and for most
accurate results should be re-determined for each con-
dition studied. The structure of equation (1) suggests
a more practicable alternative. All the terms in the
equation. that contain the rate constants approach
zero with increasing time if the ['*C]DG is so admin-

istered that the plasma ['*C]DG concentration also
approaches zero. From the values of the rate con-
stants determined in normal animals and the usual
time course of the clearance of ['*C]DG from the
arterial plasma following a single intravenous pulse
at zero time, an interval of 30-45 min is adequate
for these terms to become sufficiently small that con-
siderable latitude in inaccuracies of the rate constants
is permissible without appreciably increased error in
the estimates of local glucose consumption (SOKOLOFF
et al, 1977). An additional advantage derived from
the use of a single pulse of [’*C]DG followed by
a relatively long interval before killing the animal for
measurement of local tissue '*C concentration is that
by then most of the free ['*C]DG in the tissues has
been either converted to {'*C]DG-6-P or transported
back to the plasma; the optical densities in the auto-
radiographs then represent mainly the concentrations
of ['4C]DG-6-P and, therefore, reflect directly the
relative rates of glucose utilization in the various cere-
bral tissues.

The experimental procedure is to inject a pulse of
['*C]DG intravenously at zero time and to decapi-
tate the animal at a measured time, T, 30-45 min
later; in the interval timed arterial samples are taken
for the measurement of plasma ['*C]DG and glucose
concentrations. Tissue '*C concentrations, C¥, are
measured at time, 7; by the quantitative autoradio-
graphic technique. Local cerebral glucose utilization
is calculated by equation (1) (SOKOLOFF ef al., 1977).

RATES OF LOCAL CEREBRAL GLUCOSE
UTILIZATION IN THE NORMAL
CONSCIOUS RAT

Thus far quantitative measurements of local cere-
bral glucose utilization have been completed only in
the albino rat. These values are presented in Table
1. The rates of local cerebral glucose utilization in
the normal conscious rat vary widely throughout the
brain. The values in white structures tend to group
together and are always considerably below those of
gray structures. The average value in gray matter is
approx 3 times that of white matter, but the indivi-
dual values vary from approx 50 to 200 pmol of glu-
cose/100 g/min. The highest values are in the struc-
tures involved in auditory functions with the inferior
colliculus clearly the most metabolically active struc-
ture in the brain.

Quantitative determinations of local cerebral glu-
cose utilization in the normal conscious monkey are
currently being carried out in this laboratory, and
the values should be available soon. The results thus
far indicate similar heterogeneity in the monkey
brain, but the values are considerably lower, approxi-
mately one-third to one-half those in the rat, probably
because of the lower cellular packing density and
greater amounts of white matter (Kennedy, Sakurada,
Shinohara & Sokoloff, unpublished observations).
16 Louis SOKOLOFF

EFFECTS OF GENERAL ANESTHESIA

In the albino rat thiopental anesthesia reduces the
rates of glucose utilization in all structures of the
brain (Table 1). The effects are not uniform; the per-
cent effects in white matter are relatively small com-
pared to those in most gray structures. Anesthesia
also markedly reduces the heterogeneity normally
present within gray matter, an effect clearly visible
in the autoradiographs (SOKOLOFF et al.,.1977). These
results are in agreement with those of previous studies
in which anesthesia has been found to decrease the
cerebral metabolic rate of the brain as a whole (KETy,
1950; Lassen, 1959; SOKOLOFF, 1976).

Preliminary studies indicate that thiopental anes-
thesia has effects in the rhesus monkey like those in
the rat (SHAPIRO et al., 1975). The effects of halothane
anesthesia in the monkey are similar, except that it
appears to leave the basal ganglia unaffected (SHAPIRO
et al., 1975). In contrast, phencyclidine, which is often
used as an anesthetic agent but is probably a convul-
sant, causes 10-50% increases in glucose consumption
in all gray structures, except the inferior colliculus,
pontine nuclei, and cerebellar cortex where significant
decreases are observed (SHAPIRO et al., 1975).

RELATION BETWEEN LOCAL FUNCTIONAL
ACTIVITY AND ENERGY METABOLISM

The results of a variety of applications of the

method demonstrate a clear relationship between
local cerebral functional activity and glucose con-
sumption. The most striking demonstrations of the
close coupling between function and energy metabo-
lism are seen with experimentally induced local alter-
ations in functional activity that are restricted to a
few specific areas in the brain. The effects on local
glucose consumption are then so pronounced that
they are not only observed in the quantitative results
but can be visualized directly on the autoradiographs
which are really pictorial representations of the rela-

tive rates of glucose utilization in the various struc- .

tural components of the brain.

Effects of increased functional activity

Effects of sciatic nerve stimulation. Electrical stimu-
lation of one sciatic nerve in the rat under barbiturate
anesthesia causes pronounced increases in glucose
consumption (i.e. increased optical density in the
autoradiographs) in the ipsilateral dorsal horn of the
lumbar spinal cord (KENNEDY ef al., 1975).

Effects of olfactory stimulation. The ['*C]deoxyglu-
cose method has been used to map the olfactory sys-
tem of the rat (SHARP et al., 1975). Olfactory stimu-
lation with amyl acetate has been found to produce
increased labeling in localized regions of the olfactory
bulb. Preliminary results obtained with other odors,
such as camphor and cheese, suggest different spatial
patterns of increased metabolic activity with different
odors.

Effects of experimental focal seizures. The local in-
jection of penicillin into the hand-face area of the
motor cortex of the rhesus monkey has been shown
to induce electrical discharges in the adjacent cortex
and to result in recurrent focal seizures involving the
face, arm, and hand on the contralateral side (Cave-
NESS, 1969). Such seizure activity causes selective in-
creases in glucose consumption in areas of motor cor-
tex adjacent to the penicillin locus and in small dis-
crete regions of the putamen, globus pallidus, caudate
nucleus, thalamus, and substantia nigra of the same
side (Fig. 1) (KENNEDY et al., 1975). Similar studies
in the rat have led to comparable results and pro-
vided evidence on the basis of an evoked metabolic
response of a ‘mirror’ focus in the motor cortex con-
tralateral to the penicillin-induced epileptogenic focus
(COLLINS et al., 1976).

Effects of decreased functional activity

Decrements in functional activity result in reduced
rates of glucose utilization. These effects are particu-
larly striking in the auditory and visual systems of
the rat and the visual system of the monkey.

Effects of auditory deprivation. In the albino rat
some of the highest rates of local cerebral glucose
utilization are found in components of the auditory
system, i.e. auditory cortex, medial geniculate gang-
lion, inferior colliculus, lateral lemniscus, superior
olive, and cochlear nucleus (Table 1). The high meta-
bolic activities of some of these structures are clearly
visible in the autoradiographs (Fig. 2). Bilateral audi-
tory deprivation by occlusion of both external audi-
tory canals with wax markedly depresses the meta-
bolic activity in all of these areas (Fig. 2) (Des Rosiers,
Kennedy & Sokoloff, unpublished observations). The
reductions are symmetrical bilaterally and range from
35 to 60% Unilateral auditory deprivation also
depresses the glucose consumption of these structures
but to a lesser degree, and some of the structures
are asymmetrically affected. For example, the meta-
bolic activity of the ipsilateral cochlear nucleus equals
75% of the activity of the contralateral nucleus. The
lateral lemniscus, superior olive, and medial genicu-
late ganglion are slightly lower on the contralateral
side while the contralateral inferior colliculus is mark-
edly lower in metabolic activity than the ipsilateral
structure (Fig. 2). These results demonstrate that there
is somé degree of lateralization and crossing of audi-
tory pathways in the rat.

Visual deprivation in the rat. In the rat, the visual
system is 80-85% crossed at the optic chiasma
(LasHiey, 1934; MONTERO & GUILLERY, 1968), and
unilateral enucleation removes most of the visual in-
put to the central visual structures of the contralateral
side. In the conscious rat studied 24h after unilateral
enucleation, there are marked decrements in glucose
utilization in the contralateral superior colliculus,
lateral geniculate ganglion, and visual cortex as com-
pared to the ipsilateral side (Fig. 3) (KENNEDY et al.,
17

 

Fic. 1. Effects of focal seizures produced by local application of penicillin to motor cortex on local
cerebral glucose utilization in the rhesus monkey. The penicillin was applied to the hand and face
area of the left motor cortex. The left side of the brain is on the left in each of the autoradiographs
in the figure. The numbers are the rates of local cerebral glucose utilization in pmol/100 g tissue/min.
Note the following: Upper left, motor cortex in region of penicillin application and corresponding
region of contralateral motor cortex; Lower left, ipsilateral and contralateral motor cortical regions
remote from area of penicillin applications; Upper right, ipsilateral and contralateral putamen and
globus pallidus; Lower right, ipsilateral and contraiateral thalamic nuclei and substantia nigra. From
KENNEDY et al. (1975).
 

Fic. 2. Effects of auditory deprivation on cerebral glucose utilization of some components of the
auditory system of the albino rat. Upper. autoradiograph of section of brain from normal conscious
rat with intact bilateral hearing in ambient noise of laboratory. The autoradiograph shows the inferior
colliculi, the lateral lemnisci, and the superior olives, all of which exhibit bilateral’ symmetry of optical
densities. Middle, autoradiograph of comparable section of brain from rat with bilateral occlusion
of external auditory canals with wax and kept in sound-proof room. Note the virtual disappearance
of the inferior colliculi, lateral lemnisci, and superior olives. Lower, autoradiograph of comparable
section of brain from rat with one external auditory canal blocked. Note the asymmetry of the inferior
colliculi, and the almost symmetrical intermediate reductions of densities in the lateral lemnisci and
superior olives. The ear that was blocked was contralateral to the inferior colliculus that was markedly
depressed. From Des Rosiers, Kennedy & Sokoloff (unpublished observations).
 

 

 

 

Fic. 3. Effects of unilateral enucleation on ['*C]deoxyglucose uptake in components of the visual

system in the rat. In the normal rat with both eyes intact the uptakes in the lateral geniculate bodies

(LG), superior colliculi (SC) and striate cortex (STR C) are approximately equal on both sides (A

and C). In the unilaterally enucleated rat there are marked decreases in optical densities in the areas

corresponding to these structures on the side contralateral to the enucleation (B and D). From KENNEDY
et al. (1975).
20

 

e——
5.0mm

Fic. 4. Autoradiographs of coronal brain sections from rhesus monkeys at the level of the lateral
geniculate bodies. Large arrows point to the lateral geniculate bodies; small arrows point to oculomotor
nuclear complex. (A) Animal with intact binocular vision. Note the bilateral symmetry and relative
homogeneity of the lateral geniculate bodies and oculomotor nuclei. (B) Animal with bilateral visual
occlusion. Note the reduced relative densities, the relative homogeneity, and the bilateral symmetry
of the lateral geniculate bodies and oculomotor nuclei. (C) Animal with right eye occluded. The left
side of the brain is on the left side of the photograph. Note the laminae and the inverse order of
the dark and light bands in the two lateral. geniculate bodies. Note also the lesser density of the
oculomotor nuclear complex on the side contralateral to the occluded eye. From KENNEDY et al.
(1976). ,
21

 

 

Cc

5.0mm

Fic. 5. Autoradiographs of coronal brain sections from rhesus monkeys at the level of the striate
cortex. (A) Animal with normal binocular vision. Note the laminar distribution of the density; the
dark band corresponds to Layer IV. (B) Animal with bilateral visual deprivation. Note the almost
uniform and reduced relative density, especially the virtual disappearance of the dark band correspond-
ing to Layer IV. (C) Animal with right eye occluded. The half-brain on the left side of the photograph
represents the left hemisphere contralateral to the occluded ‘eye. Note the alternate dark and light
striations, each approx 0.3-0.4 mm in width, representing the ocular dominance columns. These columns
are most apparent in the dark lamina corresponding to Layer IV but extend through the entire thickness
of the cortex. The arrows point to regions of bilateral asymmetry where the ocular dominance columns
are absent. These are presumably areas with normally only monocular input. The one on left, contra-
lateral to occluded eye, has a continuous dark lamina corresponding to Layer IV which is completely
absent on the side ipsilateral to the occluded eye. These regions are believed to be the loci of the
cortical representations of the blind spots. From KENNEDY ef al. (1976).
Function and energy metabolism in CNS

23

TABLE 1. NORMAL VALUES FOR LOCAL CEREBRAL GLUCOSE UTILIZATION IN THE CON-
SCIOUS AND THIOPENTAL-ANESTHETIZED ALBINO RAT*§

 

Local cerebral glucose utilization

(umol/100 g/min)

 

Structure Control (6)t Anesthetized (8)t % Effect
Gray matter
Visual cortex Wi+5 644+ 3 -—42
Auditory cortex 157 + 5 81+3 —48
Parietal cortex 107 + 3 65+2 —39
Sensory-motor cortex 118 + 3 67+2 —43
Lateral geniculate body 924+2 53 +3 —42
Medial geniculate body 126+ 6 63 +3 —50
Thalamus: lateral nucleus 108 + 3 58 +2 —46
Thalamus: ventral nucleus 98 +3 55+1 —44
Hypothalamus 63 + 3 4342 —32
Caudate-putamen 1i+t4 72+3 —35
Hippocampus: Ammon’s horn 7941 564+ 1 —29
Amygdala 56+4 4142 —27
Cochlear nucleus 12447 79+5 —36
Lateral lemniscus {1447 75+4 —34
Inferior colliculus 198 +7 13148 —34
Superior olivary nucleus 141 +5 104+7 —26
Superior colliculus 99 + 3 59 +3 —-40
Vestibular nucleus 133 +4 81+4 —39
Pontine gray matter 69 +3 46+ 3 —33
Cerebellar cortex 66 +2 4442 —33
Cerebellar nucleus 106 + 4 715+4 —29
White matter
Corpus callosum 4242 30 +2 —29
Genu of corpus callosum 3545 30 +2 —14
Internal capsule 35+2 294+2 -17
Cerebellar white matter 384+2 29 +2 —24

 

* Determined at 30 min following pulse of ['*C]deoxyglucose.
+The values are the means + standard errors obtained in the number of animals
indicated in parentheses. All the differences are statistically significant at the P < 0.05

level.
§ From SoKoLorF et al. (1977).

1975). In the rat with both eyes intact, no asymmetry
in the autoradiographs is observed (Fig. 3).

Visual deprivation in the monkey. In animals with
binocular visual systems, such as the rhesus monkey,
there is only approx 50°% crossing of the visual path-
ways, and the structures of the visual system on each
side of the brain receive equal inputs from both
retinae. Although each retina projects more or less
equally to both hemispheres, their projections remain
segregated and terminate in six well-defined laminae
in the lateral geniculate ganglia, three each for the
ipsilateral and contralateral eyes (HUBEL & WIESEL,
1968, 1972; WlesEL et al., 1974; Raxic, 1976). This
segregation is preserved in the optic radiations which
project the monocular representations of the two eyes
for any segment of the visual field to adjacent regions
of Layer IV of the striate cortex (HUBEL & WIESEL,
1968, 1972). The cells responding to the input of each
monocular terminal zone are distributed transversely
through the thickness of the striate cortex resulting
in a mosaic of columns, 0.3-0.5 mm in width, alter-
nately representing the monocular inputs of the two
eyes. The nature and distribution of these occular
dominance columns have previously been character-
ized by electrophysiological techniques (HUBEL &

WIESEL, 1968), Nauta degeneration methods (HUBEL
& Wiese, 1972), and by autoradiographic -visualiza-
tion of axonal and transneuronal transport of
[3H]proline- and (*H]fucose-labeled protein and/or
glycoprotein (WieseL et al., 1974; RAKIC, 1976). Bila-
teral or unilateral visual deprivation. either by enuc-
leation or by the insertion of opaque plastic discs,
produce consistent changes in the pattern of distribu-
tion of the rates of glucose consumption, all clearly
visible in the autoradiographs, that coincide closely
with the changes in functional activity expected from
known physiological and anatomic properties of the
binocular visual system (KENNEDY et al., 1976).

In animals with intact binocular vision no bilateral
asymmetry is seen in the autoradiographs of the
structures of the visual system (Figs. 4A, 5A). The
lateral geniculate ganglia and oculomotor nuclei
appear to be of fairly uniform density and essentially
the same on both sides (Fig. 4A). The visual cortex
is also the same on both sides (Fig. 5A), but through-
out all of Area 17 there is heterogeneous density dis-
tributed in a characteristic laminar pattern. These
observations indicate that in animals with binocular
visual input the rates of glucose consumption in the
visual pathways are essentially equal on both sides
24 Louis SOKOLOFF

of the brain and relatively uniform in the oculomotor
nuclei and lateral geniculate ganglia, but, markedly
different in the various layers of ‘te “hate “Cottey:

Autoradiographs from animals with both eyes
occluded exhibit generally decreased labeling of all
components of the visual system, but the bilateral
symmetry is fully retained (Figs. 4B, 5B), and the den-
sity within each lateral geniculate body is for the most
part fairly uniform (Fig. 4B). In the striate cortex,
however, the marked differences in the densities of
the various layers seen in the animals with intact bila-
teral vision (Fig. 5A) are virtually absent so that,
except for a faint delineation of a band within Layer
IV, the concentration of the label is essentially homo-
geneous throughout the striate cortex (Fig. 5B).

Autoradiographs from monkeys with only monocu-
lar input because of unilateral visual occlusion exhibit
markedly different patterns from those described
above. Both lateral geniculate bodies exhibit exactly
inverse patterns of alternating dark and light bands
corresponding to the known laminae representing the
regions receiving the different inputs from the retinae
of the intact and occluded eyes (Fig. 4C). Bilateral
asymmetry is also seen in the oculomotor nuclear
complex; a lower density is apparent in the nuclear
complex contralateral to the occluded eye (Fig. 4C).
In the striate cortex the pattern of distribution of the
['*C]DG-6-P appears to be a composite of the pat-
terns seen in the animals with intact and bilaterally
occluded visual input. The pattern found in the
former regularly alternates with that of the latter in
columns oriented perpendicularly to the cortical sur-
face (Fig. 5C). The dimensions, arrangement, and dis-
tribution of these columns are identical to those of
the ocular dominance columns described by Hubel
and Wiesel (HUBEL & WIESEL, 1968, 1972; WIESEL et
al., 1974). These columns reflect the interdigitation of
the representations of the two retinae in the visual
cortex. Each element in the visual fields is represented
by a pair of contiguous bands in the visual cortex,
one for each of the two retinae or their portions that
correspond to the given point in the visual fields.
With symmetrical visual input bilaterally, the
columns representing the two eyes are equally active
and, therefore, not visualized in the autoradiographs
(Fig. SA). When one eye is blocked, however, only
those columns representing the blocked eye become
metabolically less active, and the autoradiographs
then display the alternate bands of normal and
depressed activities corresponding to the regions of
visual cortical representation of the two eyes (Fig.
SC).

There can be seen in the autoradiographs from the
animals with unilateral visual deprivation a pair of
regions in the folded calcarine cortex that exhibit bila-
teral asymmetry (Fig. SC). The ocular dominance
columns are absent on both sides, but on the side
contralateral to the occluded eye this region has the
appearance of visual cortex from an animal with nor-
mal bilateral vision, and on the ipsilateral side this

Yas

region looks like cortex from an animal with both
eyes occluded (Fig. 5). These regions are the loci of
the ddHichl répréséntdtion of the blind spots of the
visual fields and normally have only monocular input
(KENNEDY et al, 1975, 1976). The area of the optic
dise in the nasal half of each retina cannot transmit
to this region of the contralateral striate cortex which,
therefore, receives its sole input from an area in the
temporal half of the ipsilateral retina. Occlusion of
one eye deprives this region of the ipsilateral striate
cortex of all input while the corresponding region of
the contralateral striate cortex retains uninterrupted
input from the intact eye. The metabolic reflection
of this ipsilateral monocular input is seen in the
autoradiograph in Fig. 5C.

The results of these studies with the ['*C]deoxyglu-
cose method in the binocular visual system of the
monkey represent the most dramatic demonstration
of the close relationship between physiological
changes in functional activity and the rate of energy
metabolism in specific components of the CNS.

PHARMACOLOGICAL STUDIES

The ability of the ['*C]deoxyglucose method to
map the entire brain for localized regions of altered
functional activity on the basis of changes in energy
metabolism offers a potent tool to identify the neural
sites of action of agents with neuropharmacological
and psychopharmacological actions. The method is
still too new to have been extensively used for this
purpose, but a number of such studies have been in-
itiated, and preliminary reports have appeared.

The inhalation of 5—10° CO,. which increases cer-
ebral blood flow and produces desynchronization and
a shift to higher frequency activity in the electroence-
phalogram, causes in the conscious rat moderate but
diffuse reductions in local cerebral glucose utilization
(Des Rosters et al., 1976).

y-Hydroxybutyrate and -butyrolactone, which is
hydrolyzed to y-hydroxybutyrate in plasma, produce
trance-like behavioral states associated with marked
suppression of  electroencephalographic activity
(GIARMAN & Rotu, 1964). These effects are reversible,
and these drugs have been used clinically as anesthe-
tic adjuvants. There is evidence that these agents
lower neuronal activity in the nigrostriatal pathway
and may act by inhibition of dopaminergic synapses
(RotH, 1976). Studies in rats with the ('*C]deoxyglu-
‘cose technique have demonstrated that y-butyrolac-
tone produces profound dose-dependent reductions of
glucose utilization throughout the brain (WOLFSON et
al., 1976). At the highest doses studied, 600 mg/kg
of body weight, glucose utilization was reduced by
approx 75% in gray matter and 33% in white matter,
but there was no obvious further specificity with re-
spect to the local cerebral structures affected. The
reversibility of the effects and the magnitude and dif-
fuseness of the depression of cerebral metabolic rate
suggests that this drug might be considered as a
chemical substitute for hypothermia in conditions in
Function and energy metabolism in CNS 25

which profound reversible reduction of cerebral meta-
bolism is desired.

Ascending dopaminergic pathways appear to have

a potent influence on glucose utilization in the fore-
brain of rats. Electrolytic lesions placed unilaterally
in the lateral hypothalamus or pars compacta of the
substantia nigra caused marked ipsilateral reductions
of glucose metabolism in numerous forebrain struc-
tures rostral to the lesion, particularly the frontal cer-
ebral cortex, caudate-putamen, and parts of the tha-
lamus (SCHWARTZ et al., 1976). Similar lesions in the
locus coeruleus had no such effects.

Enhancement of dopaminergic synaptic activity by
administration of the agonist of dopamine, apomor-
phine (WOLFSON & Brown, 1976). or of amphetamine
(Wechsler, Savaki & Sokoloff, unpublished observa-
tions), which stimulates release of dopamine at the
synapse, produces marked increases in glucose con-
sumption in some of the components of the extrapyr-
amidal system known or suspected to contain dopa-
mine-receptive cells. With both drugs, the greatest in-
creases noted were in the zona reticulata of the sub-
stantia nigra and the subthalamic nucleus. Surpris-
ingly, the caudate nucleus was unaffected, and reduc-
tions were noted in the suprachiasmatic nucleus of
the hypothalamus and the habenula (Wechsler,
Savaki & Sokoloff, unpublished observations).

The effects of the potent psychotomimetic agent
p-lysergic acid diethylamide, have been examined in
the rat (SHINOHARA et al., 1976). In doses of 12.5-125
ug/kg, it caused dose-dependent reductions in glucose
utilization in a number of cerebral structures. With
increasing dosage more structures were affected and
to a greater degree. There was no pattern in the distri-
bution of the effects, at least none discernible at the
present level of resolution, that might contribute to
the understanding of the drug’s psychotomimetic
actions.

Acute morphine administration depresses glucose
utilization in many areas of the brain, but the specific
effects of morphine could not be distinguished from
those of the hypercapnia produced by the associated
respiratory depression (SAKURADA et al., 1976). In
contrast, morphine addiction, produced within 24h
by a single subcutaneous injection of 150 mg/kg of
morphine base in an oil emulsion, reduces glucose
utilization in a large number of gray structures in
the absence of changes in arterial pCO,. White matter
appears to be unaffected. Naloxone (1 mg/kg subcu-
taneously) reduces glucose utilization in a number of
structures when administered to normal rats, but
when given to the morphine-addicted animals pro-
duces an acute withdrawal-syndrome and reverses the
reductions of glucose utilization in several of the
structures, most strikingly in the habenula (SAKURADA
et al.. 1976).

SUMMARY

The results of studies with the ['*C]deoxyglucose
technique unequivocally estabiish that functional ac-

tivity in specific components of the CNS is, as in
other tissues, closely. coupled to the local rate of
energy metabolism. Stimulation of functional activity
increases the local rate of glucose utilization; reduced
functional activity depresses it. These changes are so
profound that they can be visualized directly in auto-
radiographic representations of local tissue concen-
trations of [!4C]deoxyglucose-6-phosphate. Indeed,
the existence of such evoked metabolic responses to
experimentally induced alterations in local functional
activity, together with the ability to visualize them
by the [!4C]deoxyglucose method, has become the
basis of a potent technique for the mapping of func-
tional pathways in the CNS (KENNEDY et al., 1975,
1976; PLum et al. 1976). The potential usefulness of
this technique would be greatly advanced by techno-
logical improvements in the autoradiographic pro-
cedure that improve the spatial resolution to the
microscopic or even the single-cell level.

Acknowledgements—The author wishes to express his
appreciation to SUZANNE M. Cook for her valuable assist-
ance in the preparation of this manuscript.

REFERENCES

BACHELARD H. S. (1971) J. Neurochem. 18, 213-222.

Bipper T. G. (1968) J. Neurochem. 15, 867-874.

Caveness W. F. (1969) in Basic Mechanisms of the Epilep-

’ sies (JASPER H. H., Warp A. A. & Pope A., eds.) pp.
517-534. Little, Brown, Boston.

Coitins R. C., KENNEDY C., SoKoLorF L. & PLuM F.
(1976) Arch Neurol. 33, 536-542.

Des Rosters M. H., KENNEDY C., SHINOHARA M. & SOKO-
LOFF L. (1976) Neurology 26, 346.

GIARMAN N. J. & Rotu R. H. (1964) Science 145, 583-584.

Hers H. G. (1957) Le Métabolisme du Fructose. p. 102.
Editions Arscia, Bruxelles.

Huse, D. H. & Wiese, T. N. (1968) J. Physiol. 195,
215-243.

Huser D. H. & Wiese T. N. (1972) J. comp. Neurol. 146,
421-450.

Kennepy C., Des Rosiers M. H., ReivicH M., SHARP F.,
JEHLE J. W. & SoKOLOFF L. (1975) Science 187, 850-853.

KeENneDY C., Des Rosters M. H., SAKURADA O., SHINO-
HARA M., REIVICH M., JEHLE J. W. & SOKOLOFF L. (1976)
Proc. natn. Acad. Sci., U.S.A. 73, 4230-4234.

Kery S. S. (1950) Am. J. Med. 8, 205-217.

Kety S. S. (1957) in The Metabolism of the Nervous System
(RICHTER D., ed.) pp. 221-237. Pergamon Press, London.

LANDAU W. H., FREYGANG W. H., ROWLAND L. P., SOKO-
Lorr L. & Kety S. S. (1955) Trans. Am. Neurol. Ass.
80, 125-129.

LasHLey K. S. (1934) J. comp. Neurol. 59, 341-373.

LASSEN N. A. (1959) Physiol. Rev. 39, 183-238.

Montero V. M. & GuILLery R. W. (1968) J. comp. Neurol.
134, 211-242.

OLDENDORF W. H. (1971) Am. J. Physiol, 221, 1629-1638.

PLuM F., GseDvE A. & SAMSON F. E. (1976) Neurosci. Res.
Prog. Bull. 14, 457-518.

Rakic P. (1976) Nature 261, 467-471.

Reivicu M., JeHLe J. W., SOKOLOFF L. & KETyY S. S. (1969)
J. Appl. Physiol. 27, 296-300.
6 Louis SOKOLOFF

Rotu R. H. (1976) Pharmac. Ther. 2. 71-88.

SAKURADA O., SHINOHARA M., KLEE W. A. KENNEDY
C. & SOKOLOFF L. (1976) Neurosci. Abstr. 2 (Part 4).
613.

ScHwartz W. J., SHARP F. R., GUNN R. H. & EvartTs
E. V. (1976) Nature 261, 155-157.

Sapiro H. M., GREENBERG J. H., REIVICH M., SHiPKo E.,
VAN Horn K. & SoxovorF L. (1975) in Blood F low and
Metabolism in the Brain (HARPER A. M., JENNETT W.
B., MILLER J. D. & Rowan J. O., eds.) pp. 9.42-9.43.
Churchill Livingstone, Edinburgh.

Suarp F. R., KAUER J. S. & SHEPHERD G. M. (1975) Brain
Res. 98. 596-600.

SHINOHARA M., SAKURADA O., JEHLE J. & SOKOLOFF L.
(1976) Neurosci. Abstr. 2 (Part 1), 615.

Reprinted by the

SOKOLOFF L. (1969) in Psychochemical Research in Man
(MANDELL A. J. & MANDELL M. P., eds.) pp. 237-252.
Academic Press, New York.

SoKOLOFF L. (1976) in Basic Neurochemistry (SiEGEL G. J.,
Avpers R. W., Katzman R. & AGRANOFF B. W., eds.)
2nd ed, pp. 388-413. Little, Brown, Boston.

SoKOLorF L., REIVICH M., KENNEDY C., Des ROSIERS M.
H., PatLak C. S., PeTTiGRew K. D., SAKURADA oO. &
SHINOHARA M. (1977) J. Neurochem. 28, 897-916.

Sots A. & CRANE R. K. (1954) J. biol. Chem. 210, 581-595.

Wiese. T. N., Huser D. H. & Lam D. M. K. (1974) Brain
Res. 79, 273-279.

WOLFSON L. I. & BROWN L. (1976) Neurosci. Abstr. 2 (Part
1), 510.

WOLFSON L. I., SAKURADA O. & SOKOLOFF L. (1976) Trans.
Am. Soc. Neurochem. 7, 165.

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