Central renin injections: effects on drinking and expression of immediate early genes

This study investigated the drinking response and the expression of Fos- and Egr-1-immunoreactivity (Fos-ir; Egr-1-ir) in the brain induced by endogenous angiotensin generated by intracerebroventricular (i.c.v.) injection of renin. Renin induced Fos-ir in the subfornical organ (SFO), median preoptic (MnPO), supraoptic and paraventricular nuclei (SON and PVN), area postrema (AP), nuclei of the solitary tract (NTS) and lateral parabrachial nuclei (LPBN). Renin-induced Egr-1-ir exhibited a similar pattern of distribution as that observed for Fos-ir. The dose of i.c.v. renin that induced expression of immediate early gene (IEG) product immunoreactivity also produced vigorous drinking. When renin-injected rats were pretreated with captopril, an angiotensin converting enzyme inhibitor, drinking was blocked. With the same captopril pretreatment, both Fos- and Egr-1-ir in the SFO, MnPO, SON, PVN, AP and LPBN were also significantly reduced.     

Expression of Fos immunoreactivity in rat brain during dehydration: effect of duration and timing of water deprivation

Water deprivation induces expression of the immediate early gene c-fos in specific brain regions, most likely as a result of the activation of cells that are responsive to changes in osmolality and/or blood volume. We hypothesized that the magnitude of c-fos expression would be a function of both the duration of water deprivation and the time of day at which the deprivation started. This study was designed to examine the pattern of Fos-like immunoreactivity (FLI) following water deprivation in rats under normal light/dark conditions (nLD) and reverse light/dark conditions (rLD). Rats were deprived of water but not food either for 0, 5, 16, 24 or 48 h. As expected, hematocrit ratio (HCT), osmolality (OSM), plasma renin activity (PRA) and weight loss increased as a function of duration of water deprivation. In non-deprived rats (0 h), very little FLI was observed in most brain regions. The number of cells showing FLI increased with duration of water deprivation in the supraoptic nucleus (SON), paraventricular nucleus (PVN), organum vasculosum laminae terminalis (OVLT), median preoptic nucleus (MnPO) and subfornical organ (SFO) in both nLD and rLD conditions. However, the pattern of FLI differed between nLD and rLD conditions. Compared to corresponding nLD groups after 5 or 24-h water deprivation, rLD groups had significantly more FLI in SON and PVN, and higher PRA and HCT. Also, weight loss and FLI in the MnPO were greater after 5 h, and FLI in the SFO was greater after 24 h under rLD compared to nLD conditions. Our findings indicate that the magnitude of c-fos expression, and change in weight and plasma parameters were a function of both the duration of water deprivation and the time of day at which the deprivation started. This may result from ingestion of food early in the deprivation periods during the rLD tests, thus producing greater change in osmolality and blood volume.     

Kappa-opioid antagonist strongly attenuates drinking of genetically polydipsic mice.

Effects of opioid antagonists on the genetic polydipsia of the STR/N strain of mice were investigated. Naltrexone (0.5-5.0 mg/kg) injected subcutaneously before dark period attenuated spontaneous drinking for the first 3 h after injection only in the inbred polydipsic mice (STR/N), whose water intake was 5 times that of controls (non-polydipsic mutant, STR/1N, and Swiss/Webster mice). The highest dose (5 mg/kg) of naltrexone administration reduced drinking also during the next 3-6 h period and overnight feeding. Cerebroventricular (i.c.v.) injection of naltrexone, 1.0 and 2.5 micrograms (per mouse), suppressed drinking only in the polydipsic mice, while the higher dose (5.0 micrograms) attenuated drinking and feeding of both the polydipsic mice and their controls. However, i.c.v. injection of specific kappa-receptor antagonist, nor-binaltorphimine (nor-BNI, 0.5-2.5 micrograms), suppressed drinking only in the polydipsic strain of mice at one-half dose of that needed for naltrexone. Furthermore, even a higher dose of nor-BNI administration was without effect on food intake in all strains. These findings suggest that the central opioid system plays an important role in causing the polydipsia in the STR/N mice, probably through the kappa-opioid receptor.     

Regional differences in the expression of Fos-like immunoreactivity after central salt loading in conscious rats: modulation by endogenous vasopressin and role of the area postrema

In this study, we examined the quantitative relationship between centrally administered hypertonic saline (HS) concentrations and the expression of Fos-like immunoreactivity (FLI) in brain regions involved in the homeostasis of body fluids. The regions examined were the organum vasculosum laminae terminalis (OVLT), the median preoptic nucleus (MnPO), the subfornical organ (SFO), the paraventricular nucleus (PVN), the supraoptic nucleus of the hypothalamus, the nucleus of the solitary tract (NTS), and the area postrema (AP). The experiments were performed in conscious rats with attention to the actual changes in central [Na(+)]. Hypertonic saline (0.3, 0.67, or 1.0 M) was delivered at 1 microl/min for 20 min. The changes in cerebrospinal fluid [Na(+)] during i.c.v. administration of 0.3 M hypertonic saline were compatible with those expected for thermal dehydration. FLI increased in a dose-dependent manner in the dorsomedial cap of the PVN and NTS. Although the pressor responses during central salt loading were not significantly affected by pretreatment with the peripheral vasopressin V(1) receptor antagonist OPC-21268, FLI expression in the PVN was significantly augmented. In addition, in AP-lesioned rats, FLI expression in the lateral magnocellular part of the PVN and NTS was significantly enhanced after central salt loading. These results suggest that the peripheral vasopressin system participates in negative feedback to modulate neuronal activities in the PVN, probably through the AP or direct action at the PVN in response to central osmotic and/or Na(+) stimulation.     

Mortality over a 20-year period in patients with primary polydipsia associated with schizophrenia: a retrospective study

Primary polydipsia, excessive fluid intake without medical cause, is present in over 20% of seriously and persistently ill psychiatric inpatients. The long-term effects of primary polydipsia on longevity have not previously been examined. Inpatients in a psychiatric hospital were screened for polydipsia in 1985. Those identified to be polydipsic, the majority of whom suffered from schizophrenia, were re-evaluated in 2005 and compared with a control group of non-polydipsic patients. Chart reviews were conducted and follow-up data were obtained. Of 172 patients at the time of screening, 48 suffering from schizophrenia either had or went on to develop polydipsia; 42 non-polydipsic patients with schizophrenia from the original survey were randomly selected as controls. Primary polydipsia had a significant negative effect on longevity. The median age at death (age at which 50% of cases have died) was 59 years for polydipsic patients and 68 for non-polydipsic control patients. Adjusting for duration of schizophrenia, smoking, and diagnosis, a patient with polydipsia had a 74% greater chance of dying before a non-polydipsic patient (a hazard ratio of 2.84 [95% Confidence Interval (CI): 1.22-6.64]). Outcome was worst in patients with severe polydipsia: the median age at death was 57 years and a patient with severe polydipsia had a 75% greater chance of dying before a non-polydipsic patient (hazard ratio of 3.36 [95% CI: 1.31-8.60]). When polydipsia is associated with schizophrenia, mortality is increased in comparison to that in patients with schizophrenia who do not drink water to excess.     

Quantitative autoradiography of 125I-[Sar1, Ile8]-angiotensin II binding in the brain of spontaneously hypertensive rats

The brain contains its own angiotensin II (AII) system. To better understand the role of central AII in cardiovascular regulation, we used 125I-[Sar1, Ile8]-AII (125I-SI-AII), radioactive AII antagonist, to autoradiographically localize putative AII receptor binding in many parts of the central nervous system of the spontaneously hypertensive (SHR) and normotensive Wistar-Kyoto (WKY) rats. With 125I-SI-AII binding on brain membrane preparations. Scatchard analysis indicated that Kd values were from 0.10 +/- 0.04 nM to 0.13 +/- 0.05 nM, whereas Bmax values (femtomol/mg protein) were found to be from 6.95 +/- 1.60 to 15.52 +/- 4.99 among brain regions studied. Various SI-AII receptor binding activities among brain regions revealed in this study were therefore most likely due to differences in AII receptor density with high affinity binding of 125I-AII. Using 125I-SI-AII, specific binding for SI-AII was found in the nucleus tractus solitarius (NTS), paraventricular hypothalamic nucleus (PVN), subfornical organ (SFO), suprachiasmatic nucleus (SCN), area postrema, the dorsal motor nucleus of the vagus (DMX), and the nucleus of spinal tract of the trigeminal system (NSV). With quantitative receptor autoradiography in conjunction with radioactive standards, we have observed that the NTS possesses the highest SI-AII binding, followed by the PVN, SFO, NTS, DMX, and NSV. No significant differences were observed between the SHR and WKY rats in the SI-AII binding within the SFO, PVN and NTS. However, SHR at early hypertensive (7 weeks) and established hypertensive (16 weeks) stages contained significantly higher SI-AII bindings in the NSV, as compared to age-matched WKY rats.(ABSTRACT TRUNCATED AT 250 WORDS)     

Hypothalamic cholinergic regulation of body temperature and water intake in rats.

Without disturbing the behavior of unanesthetized rats, the perfusion of neostigmine through microdialysis probe into the anterior hypothalamus (AH), paraventricular nucleus (PVN) and lateral ventricle (LV) decreased body temperature and increased water intake. On the other hand, the perfusion into the supraoptic nucleus (SON) increased the body temperature. The perfusion of neostigmine increased the extracellular concentration of acetylcholine in the perfusion sites except LV. Changes, both decrease and increase, in body temperature and increase in water intake were correlated with increases in c-fos-like immunoreactivity (Fos-IR) in the hypothalamus, pons and medulla. Distinct Fos-IR was found in the PVN, SON, median preoptic nucleus (MnPO), locus coeruleus (LC), area postrema and nucleus of the solitary tract (NTS). Co-administration of atropine with neostigmine completely suppressed the changes in the body temperature, water intake and Fos-IR, all of which were induced by the neostigmine perfusion into AH, PVN and SON. In the LV-perfused rats, on the other hand, co-administration of atropine and neostigmine only partially prevented body temperature reduction and still induced significant hypothermia. These results suggest that muscarinic receptor activation in specific regions of the hypothalamus and the activation of LC and NTS are implicated in the regulation of body temperature and water intake. Other receptor processes are involved in the LV-induced changes.     

The median preoptic nucleus participates in the control of paraventricular vasopressin neurons by the subfornical organ in the rat

Extracellular single-unit activity was recorded from phasically firing neurohypophyseal neurons (n = 41) in the hypothalamic paraventricular nucleus (PVN) of urethane-anesthetized male rats. Electrical stimulation of the subfornical organ (SFO) produced orthodromic long-duration (n = 18) or short-duration (n = 10) excitation or inhibition (n = 8) of the activity of PVN neurons. The long-duration excitatory response of about half (n = 7) the neurons (n = 15) tested was reversibly abolished by microinjection of the local anesthetic lidocaine into the median preoptic nucleus (MnPO), whereas neither the short-duration excitatory (n = 7) nor inhibitory (n = 6) responses were affected. These results suggest that the SFO efferents through the MnPO to the PVN may transmit the neuromodulatory signals which evoke long-duration increases in the excitability of putative vasopressin (VP)-secreting neurons in the PVN.     

Fos expression in the brain induced by peripheral injection of CCK or leptin plus CCK in fasted lean mice

We previously reported a synergistic interaction between leptin and cholecystokinin (CCK) to reduce food intake through CCK-A receptors in lean mice fasted for 24 h. To identify the activated neuronal pathways, we investigated changes in Fos expression in brain nuclei 2 h after single or combined intraperitoneal (i.p.) injections of leptin (120 μg/kg) and sulfated CCK-8 (3.5 μg/kg) in male lean mice (C57BL/6) fasted for 24 h using immunohistochemistry for Fos, the protein product of the early gene, c-fos. Leptin did not increase Fos expression in the brain compared with vehicle-treated mice. CCK increased the numbers of Fos-positive neurons in the nucleus of the solitary tract (NTS)/area postrema (AP), central nucleus of the amygdala (CeA) and, to a smaller extent, in the paraventricular nucleus of the hypothalamus (PVN) (5.2-, 2.3- and 0.3-fold respectively). Injections of leptin–CCK further enhanced Fos expression by 40% in the PVN compared with that induced by CCK alone, but not in the other nuclei. Devazepide (a CCK-A receptor antagonist, 1 mg/kg, i.p.) prevented the increase in Fos expression induced by leptin–CCK in the PVN and by CCK alone in the PVN, CeA and NTS/AP. These results indicate that in fasted mice, i.p. injection of CCK increases Fos expression in specific brain nuclei through CCK-A receptors while leptin alone had no effect. Leptin in conjunction with CCK selectively enhanced Fos expression in the PVN. The PVN may be an important site mediating the synergistic effect of leptin–CCK to regulate food intake.     

Fos-like immunoreactivity and thirst following hyperosmotic loading in rats with subdiaphragmatic vagotomy

If receptors in the gut relay information about increases in local osmolality to the brain via the vagus nerve, then vagotomy should diminish this signaling and reduce both thirst and brain Fos-like immunoreactivity (Fos-ir). Water intake in response to hypertonic saline (i.p. or i.g., 1 M NaCl, 1% BW; i.g., 0.6 M NaCl, 0.5% BW) was reduced during 120 min in rats with subdiaphragmatic vagotomy (VGX) compared to sham-VGX rats. Brain Fos-ir was examined in response to both i.g. loads. After the smaller load, VGX greatly reduced Fos-ir in the supraoptic nucleus (SON) and the magnocellular and parvocellular areas of the paraventricular nucleus (PVN). Fos-ir in the subfornical organ (SFO) and nucleus of the solitary tract (NTS) was not affected. After the larger load, VGX significantly reduced Fos-ir in the parvocellular PVN and in the NTS, but not in the other regions. Thus, decreased water intake by VGX rats was accompanied by decreased Fos-ir in the parvocellular PVN after the same treatments, indicating a role for the abdominal vagus in thirst in response to signaling from gut osmoreceptors. The decreased water intake in the VGX group was not reflected as a decrease in Fos-ir in the SFO. Absorption of the larger i.g. load may have activated Fos-ir through more rapidly increasing systemic osmolality, thereby obscuring a role for the vagus at this dose in the SON and magnocellular PVN.     

Vasopressin- and oxytocin-immunoreactive hypothalamic neurones of inbred polydipsic mice

In the late 1950s the inbred polydipsic mice, STR/N, was discovered. The early studies indicated that the extreme polydipsia was not due to a lack of vasopressin but probably due to innate thirst of unknown origin. Because the recent investigation has revealed the presence of some functional abnormality in the brain of the STR/N mouse, we now investigated, using immunohistochemical techniques, distribution of vasopressin (AVP)- and oxytocin (OXT)-containing neurones in the hypothalamus of polydipsic strain of mouse and compared with that of the control. The pattern of distribution of AVP- and OXT-immunoreactive neurones in the paraventricular (PV), supraoptic (SO), and suprachiasmatic nuclei (SCN) of the STR/N polydipsic mouse was similar to that of the control, but the number of AVP-immunoreactive neurones was more numerous in the PVN and SON and less in the SCN in the polydidipsic mouse than in the control. In addition, a discrete group of AVP- and OXT-containing neurones that was not clearly seen in the control was discovered in the STR/N. These results implicate that abnormal distribution in the brain AVP and OXT contribute to the mechanism responsible for the polydipsia shown by the strain STR/N.     

Effects of the opiates on the paraventricular nucleus in genetically polydipsic mice

The inbred mice, STR/N, are known to possess extreme polydipsia with no known abnormality in vasopressin system and the kidney function. Our previous studies indicate that the opiate antagonists given intracerebroventricularly strongly attenuated spontaneous drinking. To determine the site(s) of action, the present study was undertaken. Microinjections of naltrexone methobromide and a selective kappa-receptor antagonist, nor-binaltorphimine (nor-BNI), into the paraventricular nucleus of the hypothalamus (PVN) greatly attenuated drinking of the STR/N for 0.5 to 16 h after injections, while in the two control groups, non-polydipsic STR/1N and Swiss/Webster strains, drinking was not affected by the injections. Food intake was not much altered in all groups. Studies of PVN neurons in vitro (n = > 160 for each group) showed that basal firing rates and patterns were similar in the STR/N and the control groups. Morphine added to the medium inhibited some but excited none in all strains tested. The threshold for the inhibitory action was higher in the polydipsic STR/N mice (10(-8) M), compared to that in the control, S/W mice (10(-9) M). Further, a proportion of neurons inhibited by morphine in the PVN was significantly smaller (P < 0.01) in the STR/N (41.7%), compared to that in the control (64.9%). Dynorphin had very similar effect to that of morphine, but the proportion of cells inhibited was 25.4% in the STR/N, and 70.4% in the S/W. Prior applications of naloxone to the medium prevented the action of both morphine and dynorphin. Under the synaptic blockade (in a low Ca2+ and high Mg2+ medium) the inhibitory effect of the opiates persisted. We concluded that the PVN is at least one of the possible sites where the opiates are acting to cause the polydipsia in the STR/N mice.     

Expression of Fos in rat brain in relation to sodium appetite: furosemide and cerebroventricular renin

Two experiments were performed to investigate the relationship between the expression of sodium appetite and the appearance of Fos-like immunoreactivity (Fos-IR) in the brain of rats. In the first experiment, rats were depleted of sodium by treatment with furosemide 24 h prior to sacrifice and without access to either food or sodium solution. Some rats had access to distilled water, and others had no fluids available during the 24 h. All of the furosemide-treated rats showed Fos-IR in both the subfornical organ (SFO) and around the organum vasculosum laminae terminalis (OVLT). Rats with access to distilled water during the depletion period showed no Fos-IR in the supraoptic (SON) or paraventricular hypothalamic nuclei (PVN) and, in parallel behavioral studies, comparably-treated rats consumed only 0.3 M NaCl solution at the end of the 24 h. In rats that had no fluids during the deprivation period, only about one half showed Fos-IR in SON and PVN and, in parallel behavioral studies, comparably treated rats consumed both water and 0.3 M NaCI solution at the end of 24 h. In a second experiment, cerebroventricular administration of renin stimulated short latency intake of 0.3 M NaCI and water. The relative intakes of water and NaCl were comparable at a low dose of renin, but intake of water exceeded that of NaCl after higher doses. Renin induced Fos-IR in SFO, MnPO, peri-OVLT region, SON and PVN. Both Fos-IR and fluid intake were antagonized by administration of losartan, an angiotensin 11 type 1 receptor antagonist. Thus, only the circumventricular organs of the lamina terminalis showed Fos-IR during each natriorexigenic regimen in these studies. These data support the view that Ang 11 of both central and peripheral origin activates the SFO and/or peri-OVLT region and contributes to sodium appetite.     

Reduced dipsogenic response induced by angiotensin II activation of subfornical organ projections to the median preoptic nucleus in estrogen-treated rats

The present study was carried out to investigate whether estrogen modulates the drinking response induced by activation of angiotensinergic neural pathways from the subfornical organ (SFO) to the median preoptic nucleus (MnPO). Microinjection of angiotensin II (ANG II, 10(-10) M, 0.2 microl) into the SFO elicited drinking in ovariectomized (OVX) female rats that were treated with either propylene glycol (PG) vehicle or estrogen benzoate (EB). The amount of water intake induced by the ANG II injection was significantly greater in the PG-treated than in the EB-treated animals. In both groups of female rats, previous injections of saralasin (Sar, 10(-10) M, 0.2 microl), a specific ANG II antagonist, into the MnPO resulted in the significant attenuation of the drinking response to ANG II, showing that the ANG II-induced drinking response may be mediated in part by the angiotensinergic SFO projections to the MnPO. Injections of ANG II (10(-10) M, 0.2 microl) into the MnPO caused drinking in both groups, while no significant difference was found between the groups in the amount of water intake. These results suggest that increases in the circulating level of estrogen may attenuate the drinking response induced by ANG II activation of the SFO projections to the MnPO.     

Effects of unilateral or bilateral lesions within the anteroventral third ventricular region on c-fos expression induced by dehydration or angiotensin II in the supraoptic and paraventricular nuclei of the hypothalamus

This paper reports the effects of AV3V lesions on the pattern of c-fos induced by 24 h dehydration. As expected, bilateral electrolytic lesions within the AV3V region (the ventral median preoptic nucleus) suppressed water intake following 24 h water deprivation. C-fos expression was also suppressed in the supraoptic (SON) and (less completely) in the paraventricular (PVN) nuclei, but not in the subfornical organ (SFO). Unilateral lesions of the AV3V region suppressed c fos expression in the ipsilateral SON, but this selective ipsilateral effect was less in the PVN. The SFO was again unaffected. Unilateral lesions also suppressed c-fos expression in the ipsilateral SON and PVN (to a lesser degree) following intraventricular infusions of angiotensin 11 (250 pmol). These results suggest that the cellular response of supraoptic neurons to osmotic stimuli require inputs from the AV3V region, but that this is less absolute for the PVN; that the projection from the ventral AV3V area to the SON is ipsilateral, but that to the PVN may be less lateralised. Activation of the SFO by dehydration is not dependent upon the integrity of the ventral AV3V region. These results are closely comparable to the effects of similar lesions on c-fos expression following intraventricular infusions of angiotensin 11, and suggest that the effect of dehydration on forebrain c-fos expression may be related to the central actions of angiotensin II.     

迷走神经切断对胃肠道给予大鼠伤寒杆菌诱发的下丘脑室旁核和视上核Fos表达的影响

为研究迷走神经在自然感染状态下向脑传递免疫信息的作用。应用免疫组织化学方法,观察了切断隔下迷走神经对大鼠消化道内给予鼠伤寒杆菌刺激诱发的下丘脑室旁核和视上核的Fos表达变化的影响。结果发现,接受细菌刺激的动物与仅给予生理盐水的动物相比,回肠和肠系膜淋巴结有明显炎症存在,室旁结果发现,接受细菌刺激的动物与仅给予生理盐水的动物相比,回肠和肠系膜淋巴结有明显炎症存在,室旁核外侧部和视上核背侧部的Fos阳性细胞数增加;膈下迷走神经切断后,手术 细菌组与假手术 细菌组相比,室旁核的外侧部和视上核背部Fos表达减少。因此迷走神经途径在自然感染性免疫应答过程中,特别是在其早期阶段可能是传递腹腔免疫信息的重要途径之一。     

Angiotensin II receptors are upregulated by estradiol and progesterone in the locus coeruleus, median preoptic nucleus and subfornical organ of ovariectomized rats

Angiotensin II (Ang II) receptors in specific brain areas and in the anterior pituitary are controlled by reproductive hormones. Since Ang II also plays a role in controlling reproductive functions, such as luteinizing hormone and prolactin secretion, the objective of the present study was to evaluate the regulation of Ang II receptors by estradiol (E(2)) and progesterone (P) in areas of the brain involved in homeostatic and reproductive functions, such as the locus coeruleus (LC), median preoptic nucleus (MnPO) and subfornical organ (SFO). Adult female rats were ovariectomized under anesthesia and divided into 2 groups after 2 weeks: OVX plus E(2)/P replacement (OVXE(2)P) and OVX plus oil vehicle (OVX). E(2) was injected for 3 consecutive days followed by an injection of P on the 4th day. Animals were killed by decapitation and the brains were removed and frozen. Consecutive coronal brain sections were cut in a cryostat and Ang II receptors were quantified by autoradiography in the MnPO, LC and SFO. Treatment of OVX rats with E(2) and P induced a significant increase in the Ang II receptor binding (fmol/mg protein) in the MnPO (OVX: 4.48 +/- 0.58 and OVXE(2)P: 9.89 +/- 1.65), LC (OVX: 2.72 +/- 0.37 and OVXE(2)P: 8.03 +/- 0.9) and SFO (OVX: 5.45 +/- 0.66 and OVXE(2)P: 10.73 +/- 1.79) compared to OVX animals treated with the vehicle, P < 0.05. In conclusion, these results show that Ang II receptors are upregulated by E(2) and P in the LC, MnPO and SFO of ovariectomized rats.     

Effect of fasting and immobilization stress on estrogen receptor immunoreactivity in the brain in ovariectomized female rats

The present study examined the effect of 48-h fasting and 1-h immobilization on estrogen receptor immunoreactivity in selected hypothalamic areas and the nucleus of the solitary tract (NTS) in ovariectomized rats. Fasting induced an increase in ER-immunoreactive cells in the paraventricular nucleus (PVN), paraventricular nucleus (PeVN) and NTS compared with the unfasted control group. Similarly, immobilization caused an increase in ER-positive cells in the same areas, PVN, PeVN and NTS, versus the non-immobilized group. There was no significant increase in the number of ER-immunoreactive cells in the preoptic area (POA), arcuate nucleus (ARC) or ventromedial hypothalamic nucleus (VMH) following fasting and immobilization. Our previous work in ovariectomized rats with estrogen microimplants in the brain revealed that the PVN and A2 region of the NTS are the feedback sites of estrogen in activating the neural pathway to suppress pulsatile LH secretion during 48-h fasting. The result in the food-deprived rats suggests that estrogen modulation of the suppression of LH secretion during fasting is partly due to the increase in estrogen receptors in the PVN and A2 region. The physiological significance of the increase in neural ER following immobilization remains to be elucidated.