procedure. and immediately postmortem to verify the stage of the estrous cycle. Measurement of local cerebral glucose utilization. Local CMRglU values were ...
Journal of Cerebral Blood Flol\' and Me/aholism © Raven Press. New York
5:393-400
1985
Local Cerebral Glucose Utilization in Normal Female Rats: Variations During the Estrous Cycle and Comparison with Males
Astrid Nehlig, Linda J. Porrino, Alison M. Crane, and Louis Sokoloff Laboratory of Cerebral Metabolism. National Institute of Mental Health, U.S. Public Health Service, Department of Health and Human Services, Bethesda, Maryland, U.S.A.
Summary: The quantitative 2-[14C]deoxyglucose autora diographic method was used to study the fluctuations of energy metabolism in discrete brain regions of female rats during the estrous cycle. A consistent though statistically nonsignificant cyclic variation in average glucose utili zation of the brain as a whole was observed. Highest levels of glucose utilization occurred during proestrus and metestrus, whereas lower rates were found during estrus and diestrus. Statistically significant fluctuations were found specifically in the hypothalamus and in some limbic
structures. Rates of glucose utilization in the female rat brain were compared with rates in normal male rats. Sta tistically significant differences between males and fe males at any stage of the estrous cycle were confined mainly to hypothalamic areas known to be involved in the control of sexual behavior. Glucose utilization in males and females was not significantly different in most other cerebral structures. Key Words: Deoxyglucose Estrous cycle- Female-Local cerebral glucose utili zation-Male.
T he quantitative 2-[14C]deoxyglucose autoradio graphic method (Sokoloff et aI., 1977) has been ex tensively used to determine local CMRg1u in discrete areas of the brain in a variety of physiologic, phar macologic, and behavioral states (Sokoloff, 1981). Although there is generally equal interest in the ef fects of these experimental conditions in both sexes, males have been routinely used to avoid pos sible complications arising from the cyclicity in fe males of both reproductive and nonreproductive be haviors. In the female rat, the 4- to 5-day estrous cycle consists of four well-defined stages that are regu lated by interactions of brain, pituitary, and ovaries and by the hormones produced by each. Briefly, during metestrus, levels of estrogen and proges terone are low, as are levels of luteinizing hormone
(LH) and prolactin. At this time, follicle-stimulating hormone acts to stimulate growth of the ovarian follicles. During the following stage, diestrus, the follicles develop and begin to secrete estrogen. During the proestrous stage, estrogen levels peak, stimulating the hypothalamus to release luteinizing hormone releasing hormone. T his hormone acts on the anterior pituitary to release LH, which causes the ovarian follicles to develop further until one of them ruptures and ovulation occurs. During this es trous stage of the cycle, progesterone is released from the ruptured follicle or corpus luteum, acti vating sexual receptivity. T he present studies were carried out to determine whether there are corresponding changes in local cerebral glucose utilization accompanying the gross behavioral, hormonal, and physiological changes that occur during the estrous cycle and also to com pare these rates in normal female with those in normal male rats.
Received January 16. 1985; accepted April I, 1985. Address correspondence and reprint requests to Dr. L. J. Por rino at Laboratory of Cerebral Metabolism, National Institute of Mental Health, 36/lA-05, 9000 Rockville Pike, Bethesda, MD 20205. U. S.A. Dr. A. Nehlig's present address is Laboratoire de Biochimie Pharmacologique, Universite de Nancy I, 30 Rue Lionnois, 54001 Nancy-Cedex, France. Abbreviations used: E2, estradiol; LH. luteinizing hormone.
MATERIALS AND METHODS Animals
Experiments were performed on 24 adult females (200260 g) and 6 adult male (300-350 g) Sprague-Dawley rats.
393
394
A. NEHLIG ET AL.
All animals were maintained on a 12: 12 h light/dark cycle (lights on at 06:00 h). Food and water were available ad libitum. Vaginal smears were obtained and evaluated at approximately the same time daily. Only those animals that exhibited at least two consecutive 4-day cycles were used. On the day of the experiment. vaginal smears were performed before the surgery. at the end of the surgical procedure. and immediately postmortem to verify the stage of the estrous cycle.
Measurement of local cerebral glucose utilization
Local CMRglU values were measured by the 2[14Cldeoxyglucose method (Sokoloff et al.. 1977). The rats were lightly anesthetized with a mixture of � 1-1.5% halothane and 70% nitrous oxide, and polyethylene cath eters were inserted into one femoral artery and vein. An imals were then placed in loose-fitting plaster casts around the lower abdomen and pelvis and allowed to re cover from the effects of anesthesia for at least 3 h before initiation of the measurement of local cerebral glucose utilization. All experiments were conducted at � 1300 h. The 2-[14Cldeoxyglucose (125 [LCi/kg. specific activity 50-55 mCi/mmol; New England Nuclear, Boston. MA,
U.S.A.) was injected as an intravenous pulse. and timed arterial samples were drawn during the following 45 min. The blood samples were immediately centrifuged in a Beckman Microfuge B (Beckman Instruments, Inc., Ful
lerton. CA. U.S.A.), and the plasma was assayed for [14Cldeoxyglucose concentration by liquid scintillation counting and for glucose concentration by means of a Beckman Glucose Analyzer 2 (Beckman Instruments).
An additional plasma sample was taken during the ex periment from each female rat for radioimmunoassay
(Hazleton Laboratories, Inc.. Arlington. VA. U.S.A.) of estradiol (E,) and LH levels to confirm the stage of the estrous cycle. At the end of the 45-min experimental pe riod. the animals were killed by the intravenous injection of sodium pentobarbital. The brains were rapidly re moved and frozen in isopentane chilled to - 45°C. coated
with embedding medium. and stored at -70°C in plastic bags until sectioned. The brains were cut into 20-[Lm sections at -22°C in a cryostat and autoradiographed on Kodak OM I film along with calibrated [14C Jmethylmethacrylate standards as previously described (Sokoloff et aI., 1977). Adjacent sections were stained with thionin for histological iden tification of the structures examined in the autoradio graphs.
The autoradiographs were analyzed by quantitative densitometry with a computerized image-processing system (Goochee et al.. 1980) or a manual densitometer (Densichron Model PPD; Sargent-Welch, Skokie, IL, U.S.A.). Optical density measurements for each struc ture, anatomically defined according to the rat brain atlas of Paxinos and Watson (1982), were made bilaterally in a minimum of four brain sections. All densitometry was
conducted without knowledge of the stage of the estrous cycle or sex of the animal. Tissue 14C concentrations were determined from the optical densities of the autoradio graphic representations of the neural structures and a cal ibration curve obtained by densitometric analysis of the autoradiographs of the calibrated standards. CMRglli was then calculated from the local tissue concentration of 14C, the time courses of the plasma 2-[14Cldeoxyglucose and glucose concentrations, and the appropriate constants ac-
J Cereb Blood Flow Metabol, Vol. 5, No.3, 1985
cording to the operational equation of the method (So koloff et aI., 1977).
Physiological variables
An assessment of the physiologic state of each animal was made just prior to the administration of the 2[14Cldeoxyglucose. Arterial blood pressure was measured with an air-damped mercury manometer and body tem perature with a rectal probe thermometer (Model 73;
Yellow Springs Instruments, Yellow Springs, OH. U.S.A.). Arterial blood pH. Peoe, and P02 were mea sured with an ILS Model 213 Blood Gas Analyzer (In strumentation Laborat ory, Inc., Lexington, MA. U.S.A.).
Statistical analysis
Local CMRglu was determined in 55 cerebral structures in four groups of female and one group of male rats. Local CMRglu values of animals in each stage of the estrous cycle were compared with those for animals in the im mediately following stage by means of Bonferroni mul tiple comparison procedures (Kirk, 1968). Local CMRglu values for rats in each stage were also compared with values in a group of normal male rats by means of Dun nett's procedure for multiple comparisons (Dunnett, 1955). Conservative multiple comparison procedures were chosen to reduce the likelihood of Type II errors in view of the large number of statistical procedures per formed.
RESULTS Physiological variables and plasma hormone concentrations
No statistically significant differences in any of the recorded physiological variables with respect to either the sex or the stage of the estrous cycle in the female rats were found (Table 1). Plasma levels of E2 and LH were determined to confirm the stage of the estrous cycle. E2 levels were lowest during estrous and metestrous stages; small increases occurred during diestrus, but peak E2 levels were found in proestrus (Table 2). Plasma concentrations of LH followed the same pattern: Low levels were found throughout estrus, metes trus, and diestrus, with peak levels present during proestrus (Table 2). T hese patterns of hormone fluc tuations are consistent with the known character istics of the estrous cycle (Brown-Grant et aI., 1970; Naftolin et aI. , 1972; Butcher et aI. , 1974). Variations in local cerebral glucose utilization with the estrous cycle
Local glucose utilization varied throughout the brain in females as a function of the estrous cycle (Tables 3-8). Local CMRglu values tended to be higher in all structures examined during proestrus and metestrus as compared with the rates observed during estrus and diestrus. T hese fluctuations were reflected in the average rates of glucose utilization
395
LOCAL CMRfil1l IN FEMALE RATS
TABLE 1. Physiological variables during the estrous cycle: comparison with males Females Proestrus (n = 6) pHa Peo2 (mm Hg) a P02 (mm Hg)" Body temperature (0C) Blood pressure (mm Hg) Hematocrit (%) Plasma glucose (mg%)
7. 46 35 85 37. 3 113 46 174
± ± ± ± ± ± ±
Estrus (n = 7)
0. 03 1 2 0. 3 3 2 7
7. 39 35 83 36. 9 116 45 164
± ± ± ± ± ± ±
Metestrus (n = 7)
0. 03 1 I 0. 2 2 1 II
7. 47 36 85 37.5 114 42 172
± ± ± ± ± ± ±
7. 42 36 83 37. 0 116 46 169
0. 02 1 1 0. 4 3 2 11
Values are means ± SEM of the number of animals in parentheses, except for variables marked rats in the female groups.
of the brain as a whole, weighted for the relative sizes of its component parts (Fig. I A). Although many of these changes were not statistically signif icant, significant differences in glucose utilization across stages of the estrous cycle were found in hypothalamic structures, including the medial and lateral preoptic areas, anterior and anterolateral hy pothalamus, and arcuate nucleus (Table 5; Fig. IB). Statistically significant cyclic changes in glucose utilization were also evident in the entorhinal cortex (Table 3; Fig. IB), nucleus accumbens and hippo campus (Table 4; Fig. IB), medial geniculate nu cleus (Table 6), substantia nigra pars reticulata (Table 7), and superior colliculus (Table 7; Fig. I B). Comparative local CMR 1u values in male and g female rats
In most of the structures examined, the CMRg1u values in males did not differ significantly from those in females at any stage of the estrous cycle (Tables 3-8). T he differences that were found, how ever, were specifically related to both the structure and the stage of the cycle. In one group of struc tures, local CMR g1u was significantly higher in female rats, but only in the proestrous and/or met estrous stages. T hese structures included the hypo thalamic medial preoptic area, ventromedial nu cleus, dorsomedial nucleus, arcuate nucleus, and median eminence (Table 5), as well as the entorhinal
Males (n = 6)
Diestrus (n = 4)
(/,
± ± ± ± ± ± ±
7. 42 36 84 37. 0 117 48 148
0. 04 1 4 0. 1 2 2 \3
± ± ± ± ± ± ±
0. 01 1 2 0. 3 2 1 6
which were determined in four
and olfactory cortices (Table 3), the substantia nigra pars reticulata, and the superior colliculus (Table 7). In another group of structures, glucose utilization in the female rats was significantly lower than in the male rats, but only in the estrous and/or diestrous stages. T hese structures included the frontal cortex (Table 3), the nucleus accumbens (Table 4), the lat eral nucleus of the thalamus, and the medial genic ulate body (Table 6). DISCUSSION
T he results of the present studies represent, to our knowledge, the first measurements of glucose utilization throughout the estrous cycle in normal conscious female rats. T he most striking finding is the demonstration of dynamic changes in the rates of glucose utilization in a number of cerebral struc tures through the various stages of the estrous cycle, with peaks in metabolic activity found during proestrus and metestrus. Although the changes were statistically significant in only a few specific structures, all the cerebral regions examined showed the identical pattern. T his was reflected in the cyclic fluctuation in the average rates of glucose utilization in the brain as a whole. T hese global al terations are reminiscent of the circadian variation found when rates of glucose utilization measured during the day are compared with those measured
TABLE 2. Serum levels of estradiol and luteinizing hormone in female rats throughout
the estrous cycle Proestrus (n = 6) Estradiol (pg/m!) Luteinizing hormone (ng/m!) Values are means
±
Estrus (n = 7)
Metestrus (n = 7)
Diestrus (n = 4)
68
±
9
21
±
1
24
±
4
37
±
7
53
±
16
14
±
4
12
±
2
14
±
3
SEM of the number of animals in parentheses.
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A. NEHLIG ET AL.
396
TABLE 3. Local glucose utilization in the cerehral cortex of adult male and adult female rats at different stages of
the estrous cycle Female rats Region Medial prefrontal cortex Frontal cortex Anterior cingulate cortex Sensorimotor cortex Olfactory cortex Parietal cortex Auditory cortex Entorhinal cortex Visual cortex
Proestrus (n = 6) 124 107 128 115 105 112 165 73 117
± ± ± ± ± ± ± ± ±
6 6 8 8 5 7 9 4 6
Estrus (n = 7) 109 93 112 103 90 99 144 65 104
± ± ± ± ± ± ± ± ±
4 4 4 6 4 4 6 3" 6
127 105 126 112 102 108 158 76 116
± ± ± ± ± ± ± ± ±
Male rats (n = 6)
Diestrus (n = 4)
Metestrus (n = 7)
113 102 100 99 87 93 13 5 58 101
6 3 4 4 4 5 6 2" 4
± ± ± ± ± ± ± ± ±
114 110 113 112 88 106 159 64 117
5 5 5 1 5 4 2 1" 3
± ± ± ± ± ± ± ± ±
4 5" 6 3 3h( 5 8 3' 6
Values are means ± SEM of the number of animals in parentheses, expressed as /Lmoi/IOO g/min. " Statistically significant differences between male rats and female rats at the estrous stage (p < 0.05). h Statistically significant differences between male rats and female rats at the proestrous stage (p < 0. 05). C Statistically significant differences between male rats and female rats at the metestrous stage (p < 0. 05). d Statistically significant differences from one stage of the estrous cycle to the following one (p < 0. 05). e Statistically significant differences from one stage of the estrous cycle to the following one. (p < 0. 01).
levels of estrogen are highest. In contrast, treat ment with a combination of estrogen and proges terone to mimic the hormonal events that trigger the estrous phase results in lower CMRg1u, partic ularly in the hypothalamus (Porrino et aI. , 1982), similar to the rates found here in the estrous stage. One can conclude from the results of the present experiments that hormones can play a role in the regulation of cerebral energy metabolism and that these effects are not confined solely to areas in which receptors for these hormones are found, but throughout the central nervous system. T his global influence is significant in that a wide variety of be haviors, including those not related to reproductive function, have been shown to fluctuate across the estrous cycle (Beatty, 1979). Statistically significant changes in CMRg1u were found in structures, such as the preoptic and ar cuate portions of the hypothalamus and the hippo campus, known to be rich in estrogen-concentrating
at night (Crane et aI. , 1980; Jay-Nowaczyk and Des Rosiers, 1984). Variation in overall levels of brain energy metabolism appear, then, to be associated with normal biological rhythms. Furthermore, these data serve to illustrate the significant influence that hormones can have on functional activity in the brain. Measurements of local cerebral glucose utilization in ovariectomized females, i.e. , those in which the source of estrogen and progesterone production has been removed, tend to show uniformly lower rates than those in animals receiving hormone treatment (Porrino et aI. , 1982; Namba and Sokoloff, 1984). Local cere bral energy metabolism in the ovariectomized fe males most closely resembles that in the diestrous stage in which low levels of estrogen and proges terone are found. Estrogen replacement, either in low or high doses, causes widespread increases in glucose utilization, which correlates well with the high rates found during the proestrous stage when
TABLE 4. Local glucose utilization in the forehrain of adult male and adult female rats at different stages of the
estrous cycle Female rats Region Nucleus accumbens Caudate-putamen Globus pallidus Septal area Amygdala Hippocampus, CA3 Dentate gyrus
Proestrus (n = 6) 72 117 45 69 52 77 58
± ± ± ± ± ± ±
4" 9 2 5 2 3 3
Estrus (n = 7) 59 106 39 60 46 69 53
± ± ± ± ± ± ±
3" 3 3 2 3 3" 2
Metestrus (n = 7) 69 116 46 67 48 82 60
± ± ± ± ± ± ±
2 5 3 2 2 2" 2
Diestrus (n = 4) 65 104 40 63 42 67 54
± ± ± ± ± ± ±
Values are means ± SEM of the number of animals in parentheses, expressed as /Lmo1/100 g/min. a Statistically significant differences from one stage of the estrous cycle to the following one (p < 0. 05) . b Statistically significant differences between male rats and female rats a t the estrous stage ( p < 0. 05) .
J Cereb Blood Flow Metabol, Vol. 5, No.3, 1985
3 4 1 2 I 3 5
Male rats (n = 6) 70 III 42 63 44 76 59
± ± ± ± ± ± ±
3b 3 2 2 I 4 2
LOCAL CMR /1I IN FEMALE RATS g
397
TABLE 5. Local glucose utilization in the hypothalamus of adult male and adult female rats at different stages of
the estrous cycle Female rats Region Medial preoptic area Lateral preoptic area Magnocellular preoptic area Suprachiasmatic nucleus Anterior hypothalamus Anterolateral hypothalamus Paraventricular nucleus Ventromedial nucleus Dorsomedial nucleus Arcuate nucleus Median eminence Median forebrain bundle Posterior hypothalamus Mamillary body
Proestrus (n = 6) 55 74 93 77 57 72 60 54 63 50 65 65 63 121
± ± ± ± ± ± ± ± ± ± ± ± ± ±
Estrus (n = 7)
2" 3h 4 5 3" 4h
44 64 81 66 46 59 54 46 53 40 51 57 55 109
4 3 3 3h 4 3 3 9
± ± ± ± ± ± ± ± ± ± ± ± ± ±
Metestrus (n = 7)
2h 3" 5 3 2h
50 78 92 76 56 69 59 54 60 48 63 65 63 116
3 3 3 4 2 4 3 I 3
± ± ± ± ± ± ± ± ± ± ± ± ± ±
Diestrus (n = 4)
I 2 3 4 2 3 2 I 2 2 3 3 2 4
46 68 79 63 49 58 52 47 57 46 59 56 57 107
± ± ± ± ± ± ± ± ± ± ± ± ± ±
I" 2 3 2 2 Ih 3 2 3 I 4 3 3 4
Male rats (n = 6) 43 73 86 77 52 67 52 45 51 42 48 56 62 118
± ± ± ± ± ± ± ± ± ± ± ± ± ±
I cd 3 3 7 2 2 2 2eI 2" 2e I'I 3 I 7
Values are means ± SEM of the number of animals in parentheses, expressed as fLmol/lOO g/min. a Statistically significant differences from one stage of the estrous cycle to the following one (p < 0.01). b Statistically significant differences from one stage of the estrous cycle to the following one (p < 0.05). C Statistically significant differences between male rats and female rats at the proestrous stage (p < 0.01). d Statistically significant differences between male rats and female rats at the metestrous stage (p < 0.01). e Statistically significant differences between male rats and female rats at the proestrous stage (p < 0.05) . I Statistically significant differences between male rats and female rats at the metestrous stage (p < 0.05).
hippocampus (Swanson and Cowan, 1979) and ol factory cortex with the amygdala and hypothalamus (Powell et aI. , 1965). T he fluctuations in glucose utilization during the estrous cycle observed in the present studies can be compared with the results of studies in which cerebral metabolism was measured with other methods. Average oxygen uptake of the brain as a whole, as measured in vitro, has been reported not to vary significantly during the estrous cycle (Mo guilevsky and Malinow, 1964). In the hypothal amus, however, some evidence of cyclic variation in energy metabolism has been reported (Moguil-
cells (Pfaff and Keiner, 1973; Rainbow et aI. , 1982) as well as to contain cells responsive to proges terone (Sar and Stumpf, 1973; Warembourg, 1978; Parsons et aI. , 1982). T he changes in glucose utili zation in these hypothalamic and limbic areas during the estrous cycle are consistent with the role of these nerve cell groupings in controlling sex ste roid-dependent functions, such as reproductive be haviour and gonadotropin release. Other areas in which glucose utilization varied significantly have, for the most part, strong anatomic interconnections with hormone-concentrating brain regions, e. g. , en torhinal cortex and nucleus accumbens with the
TABLE 6. Local glucose utilization in the thalamus of adult male and adult female rats at different stages of the
estrous cycle Female rats Region Lateral nucleus Ventral nucleus Mediodorsal nucleus Medial geniculate Lateral geniculate Medial habenula Lateral habenula, medial part Lateral habenula, lateral part
Proestrus (n = 6)
Estrus (n = 7)
108 95 95 133 93 74 107 133
96 87 91 114 83 72 104 122
± ± ± ± ± ± ± ±
5 6 6 9 7 2 6 10
± ± ± ± ± ± ± ±
4 3 3 5 6 2 4 4
Metestrus (n = 7) liD 97 96 127 90 74 108 127
± ± ± ± ± ± ± ±
4 2 3 5 4 3 3 6
Diestrus (n = 4) 94 84 83 106 82 70 102 115
± ± ± ± ± ± ± ±
2 2 3 4b 4 4 8 11
Male rats (n = 6) 111 98 98 137 95 73 114 141
± ± ± ± ± ± ± ±
2a 4 3 6ac 3 5 6 6
Values are means ± SEM of the number of animals in parentheses, expressed as fLmolll00 g/min. a Statistically significant differences between male rats and female rats at the diestrous stage (p < 0.05). b Statistically significant differences from one stage of the estrous cycle to the following one (p < 0.05) . C Statistically significant differences between male rats and female rats at the estrous stage (p < 0.05).
J Cereb Blood Flow Metabol, Vol. 5, No.3, 1985
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A. NEHLlG ET AL.
TABLE 7. Local glucose utilization in midbrain and pons of adult male and adult female rats at different stages of
the estrous cycle Female rats Proestrus (n = 6)
Region Substantia nigra, pars reticulata Substantia nigra, pars compacta Ventral tegmental area Red nucleus Subthalamic nucleus Interpeduncular nucleus Superior colliculus Inferior colliculus Medial raphe Dorsal raphe Locus ceruleus Lateral lemniscus Pontine gray Superior olive Cerebellar cortex
61
±
73 65 81 88 106 97 207 99 92 71 116 61 156 58
± ± ± ± ± ± ± ± ± ± ± ± ± ±
Estrus (n = 7)
211
53
±
I
3 4 5 5 6 3d II 6 7 2 9 4 II 3
61 55 71 75 98 79 194 87 82 64 104 53 136 53
±
3 3 4 3 6 2" 10 5 4 4 7 2 7 I
± ± ± ± ± ± ± ± ± ± ± ± ±
Metestrus (n = 7)
60 70 60 81 85 110 91 210 98 92 69 106 59 146 57
Male rats (n = 6)
Diestrus (n = 4)
±
2
53
±
2
51
±
2hc
±
3 3 2 5 4 2 10 3 4 3 6 3 6 3
62 59 67 78 87 80 184 88 82 65 91 53 129 51
±
3 2 2 1 5 4" 9 4 2 3 3 4 8 3
66 57 77 90 101 86 223 95 87 65 118 60 142 54
±
3 4 3 4 7 2b 14 5 6 2 6 2 9 3
± ± ± ± ± ± ± ± ± ± ± ± ±
± ± ± ± ± ± ± ± ± ± ± ± ±
± ± ± ± ± ± ± ± ± ± ± ± ±
Values are means ± SEM of the number of animals in parentheses, expressed as f.LmollIOO g/min. Statistically significant differences from one stage of the estrous cycle to the following one (p < 0.05). b Statistically significant differences between male rats and female rats at the proestrous stage (p < 0.05). C Statistically significant differences between male rats and female rats at the metestrous stage (p < 0.05). d Statistically significant differences from one stage of the estrous cycle to the following one (p < 0.01).
U
evsky and Malinow, 1964; Moguilevsky et aI. , 1968). In the hypothalamus, cyclic (Packman et aI. , 1977) as well as estrogen-dependent (Luine et al. , 1974) changes in the levels of various enzymes con cerned with energy metabolism have also been found. T he results of the present studies with the 2-[14C]deoxyglucose method, which permits in vivo measurement of brain energy metabolism in indi vidual structures in conscious animals, agree for the most part with the results of these other studies of brain metabolism. Furthermore, we have extended the previous work by identifying specific areas of the central nervous system in which glucose utili zation varies with the estrous cycle. T here were few significant differences between local CMRglu values in males and those of females
across the various stages of the estrous cycle, ex cept in hypothalamic areas known to be involved in reproductive behavior. T he clearest differences were apparent in the ventromedial nucleus and preoptic area. Electrical or chemical stimulation of the ventromedial nucleus facilitates feminine sexual behavior (Lisk, 1962; Barfield and Chen, 1977; Pfaff and Sakuma, 1979), but does not alter masculine sexual behavior (Dorner et aI. , 1968). T he medial preoptic area, besides having opposite roles in mas culine and feminine sexual behavior (Heimer and Larsson, 1966; Malsbury, 1971; Powers and Valen stein, 1972), has been shown to contain a sexually dimorphic nucleus larger and more cell dense in males than in females (Gorski et aI. , 1978). Fur thermore, these two hypothalamic regions exhibit
TABLE 8. Local glucose IItilization in white matter q{ adult male and adult female rats
at different stages of the estrous cycle Female rats Region Genu of the corpus callosum Internal capsule Cerebellar white
Proestrus (n = 6) 33 35 39
± ± ±
2 I 2
Estrus (n = 7) 31 33 38
± ± ±
2 2 2
Metestrus (n = 7) 35 36 41
± ± ±
I 2 2
Diestrus (n = 4) 31 34 35
± ± ±
2 2 2
Male rats (n = 6) 28 32 37
± ± ±
I" 2 3
Values are means ± SEM of the number of animals in parentheses, expressed as f.LmollIOO g/min. Statistically significant differences between male rats and female rats at the metestrus stage (p < 0.05). a
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Cereh Blood Flo\\' Metahol, Vol. 5, No.3, 1985
LOCAL CMR/illl IN FEMALE RATS
z 0
A
� ..:
N ..J
....
:>
e
E
w C. -;; ..J " CI 0 ..J E
..: �
a: III w a: w I)
WEIGHTED
399
AVERAGE
80
+
70
60
0
1 B
FIG. 1. A: Variation in the average local CMRglu in female rats across stages of the
REPRESENTA TlVE STRUCTURES
estrous cycle and comparison with that of males. B: Variation in local CMR lu in q some representative brain areas, dem onstrating significant changes across
,.
100
stages of the estrous cycle of female rats and comparison with those of males. t indicates statistically significant differ z 0
80
.... ..:
N ::;
S Col
e
� ,E :>
W ..J CI ..J
Hpc
CI 0
� , " ..
Acc 60
0 E
..: �
a: III w a: w I)
�
?
AH
+
M Pos
•
ences from one stage of the estrous cycle to the following one. Glucose utilization is expressed as the mean ± SEM of six
animals in proestrus, seven in estrus, seven in metestrus, four in diestrus, and six males. S Col, superior colliculus; Hpc, hippocampus; Acc, nucleus accumbens; AH, anterior hypothalamus; M Poa, me dial preoptic area.
40
o
l�
__�,
__
Diestrus
__�'�____r' ____-"______,�____� Dlestru. Proestrus Estrus Metestrus FEMALES
changes in local CMRglu in response to estrogen and progesterone treatment in ovariectomized rats (Por rino et aI. , 1982). T he pattern of sex differences in local CMRglu values was not a uniform one. Some areas in males displayed rates similar to peak rates in females during proestrus and metestrus, whereas in other areas the rates were more similar to those in fe males during estrus and diestrus. T his variable pat tern may help to account for the inconsistency that is sometimes apparent in assessing sexually di morphic behaviors, particularly those that are non reproductive in nature. REFERENCES Barfield RJ, Chen 11 (1977) Activation of estrous behavior in ovariectomized rats by intracerebral implants of estradiol benzoate. Endocrinology 101: 1716-1725
MALES
Beatty W W (1979) Gonadal hormones and sex differences in nonreproductive behaviors in rodents: organizational and activational influences. Horm Behav 12: 112-163 Brown-Grant K, Exley 0, Naftolin F (1970) Peripheral plasma oestradiol and luteinizing hormone concentrations during the oestrus cycle of the rat. J Endocrinol 48: 295-296 Butcher RL, Collins W E, Fugo NW (1974) Plasma concentra tions of LH, FSH, prolactin, progesterone and estradiol-1713 throughout the 4-day estrous cycle of the rat. Endocrinology 94: 1704 Crane DO, Braun LD, Cornford EM, Nyerges AM, Oldendorf W H (1980) Cerebral cortical glucose utilization in the con scious rat: evidence for a circadian rhythm. J Neurochem 34: 1700-1706 Dorner G, Docke F, Moustafa S (1968) Differential localization of a male and a female hypothalamic mating centre. J Re prod Ferti! 17: 583-586 Dunnett CW (1955) A multiple comparison procedure for com paring several treatments with a control. J Am Stat Assoc 50: 1096-1121 Goochee C. Rasband W, Sokoloff L (1980) Computerized den sitometry and color coding of [14CJdeoxyglucose autoradio graphs. Ann Neurol 7: 359-370 Gorski RA. Gordon JH, Shryne JL, Southam AM (1978) Evi-
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