Commentary on: Saper CB, Loewy AD, Swanson LW, Cowan WM. (1976) Direct hypothalamo-autonomic connections. Brain Research 117:305-312.

The 1970s saw the introduction of new technologies for tracing axons both anterogradely and retrogradely. These methods allowed us to visualize fine, unmyelinated pathways for the first time, such as the hypothalamic pathways that control the autonomic nervous system. As a result, we were able to identify the paraventricular nucleus and lateral hypothalamus as the key sites that provide direct inputs to the autonomic preganglionic neurons in the medulla and spinal cord. These findings revolutionized our understanding of hypothalamic control of the autonomic nervous system.

Bilateral descending hypothalamic projections to the spinal trigeminal nucleus caudalis in rats.

Several lines of evidence suggest that the hypothalamus is involved in trigeminal pain processing. However, the organization of descending hypothalamic projections to the spinal trigeminal nucleus caudalis (Sp5C) remains poorly understood. Microinjections of the retrograde tracer, fluorogold (FG), into the Sp5C, in rats, reveal that five hypothalamic nuclei project to the Sp5C: the paraventricular nucleus, the lateral hypothalamic area, the perifornical hypothalamic area, the A11 nucleus and the retrochiasmatic area. Descending hypothalamic projections to the Sp5C are bilateral, except those from the paraventricular nucleus which exhibit a clear ipsilateral predominance. Moreover, the density of retrogradely FG-labeled neurons in the hypothalamus varies according to the dorso-ventral localization of the Sp5C injection site. There are much more labeled neurons after injections into the ventrolateral part of the Sp5C (where ophthalmic afferents project) than after injections into its dorsomedial or intermediate parts (where mandibular and maxillary afferents, respectively, project). These results demonstrate that the organization of descending hypothalamic projections to the spinal dorsal horn and Sp5C are different. Whereas the former are ipsilateral, the latter are bilateral. Moreover, hypothalamic projections to the Sp5C display somatotopy, suggesting that these projections are preferentially involved in the processing of meningeal and cutaneous inputs from the ophthalmic branch of the trigeminal nerve in rats. Therefore, our results suggest that the control of trigeminal and spinal dorsal horn processing of nociceptive information by hypothalamic neurons is different and raise the question of the role of bilateral, rather than unilateral, hypothalamic control.

Sexual experience changes sex hormones but not hypothalamic steroid hormone receptor expression in young and middle-aged male rats.

Testosterone is well known to regulate sexual behavior in males, but this is dependent upon prior sexual experience. Aging is associated with decreased libido and changes in testosterone, but the role of experience in these age-related processes has not been systematically studied. We examined effects of age and sexual experience on serum hormones (total testosterone, free testosterone, estradiol, LH) and on numbers of androgen receptor (AR) and estrogen receptor alpha (ERalpha) immunoreactive cells in the hypothalamus. Extensive sexual experience was given to male rats at 4 months of age. Rats were euthanized at either 4 months (young) or 12 months (middle-aged (MA)). Comparable sexually naïve male rats were handled and placed into the testing arena but did not receive any sexual experience. Thus, we had four groups: young-naïve, young-experienced, MA-naïve and MA-experienced. Serum hormone levels were assayed, and numbers of AR and ERalpha cells were quantified stereologically in the medial preoptic nucleus (MPN) and the anteroventral periventricular nucleus (AVPV). Sexually experienced males had significantly elevated serum testosterone and free testosterone in both age groups. Both total and free testosterone were higher, and estradiol lower, in middle-aged than young rats. Experience did not alter either AR or ERalpha expression in the preoptic brain regions studied. Aging was associated with increased expression of AR, but no change in ERalpha. These results show that sexual experience can induce short-term and long-term alterations in serum hormones but these effects are not manifested upon their receptors in the hypothalamus.

Characterization of the projections to the hypothalamic paraventricular and periventricular nuclei in the female sheep brain, using retrograde tracing and immunohistochemistry.

The paraventricular nucleus (PVN) and the periventricular nucleus (Pe) are important neuroendocrine centers, but the neuronal input to these regions is poorly defined in nonrodent species. We utilized the retrograde transport of injected tracers to determine the neural input to these two nuclei in the ovine brain. Adult Corriedale ewes were studied following FluoroGold injection into either the PVN (n = 5) or the Pe (n = 3). Both the PVN and the Pe were found to receive neuronal input from a number of hypothalamic nuclei. Projections to the PVN from the lateral hypothalamic area were from neurons that produce melanin-concentrating hormone or orexins and a subset of those from the arcuate nucleus were immunopositive for neuropeptide Y and gamma-melanocyte stimulating hormone. This pathway was verified by staining of terminals in the PVN. Input to the PVN from the brain stem was seen to originate from the catecholaminergic and serotoninergic neurons. The projections to the PVN and Pe from hypothalamic and brain stem regions in the sheep brain are generally similar to those in the rat, with some minor differences. These studies highlight the differences in the afferent input to these two closely related nuclei in the ovine brain.

Brief daily suckling shifts locomotor behavior and induces PER1 protein in paraventricular and supraoptic nuclei, but not in the suprachiasmatic nucleus, of rabbit does.

Nursing in the rabbit is a circadian event during which mother and pups interact for a period of < 5 min every day. Here we explored behavioral and neuronal changes in the mother by analyzing the suprachiasmatic nucleus (SCN), and oxytocinergic (OT) neurons in the paraventricular nucleus (PVN) and the supraoptic nucleus (SON). We maintained lactating does in a light-dark cycle (lights on at 07 : 00 hours; ZT0); they were scheduled to nurse during either the day (ZT03) or the night (ZT19). Groups of intact and nursing females was perfused, one at each 4-h point through a 24-h cycle. We explored, by immunohistochemistry, the PER1 expression and double-labeling, with OT antibody, of neurons in the PVN and SON at lactation on day 7. In the SCN, intact and lactating groups had peak PER1 expression at ZT11; however, there was a reduction in PER1 at peak time in the nursing groups. There was a locomotor activity rhythm with increased activity around the time of lights-on in intact subjects and around the time of suckling in lactating does. There was an induction of PER1 in OT cells in the PVN and SON that shifted in phase with timing of nursing. We further explored the maintenance of the PER1 expression in OT cells in nursing-deprived does and found a significant decrease at 24 and 48 h after the last nursing. We conclude that suckling induced PER1 in the PVN and SON, but not in the SCN, in nursing does, and also shifted their locomotor behavior.

Differential expression of hypothalamic CART mRNA in response to body weight change following different dietary interventions.

Cocaine- and amphetamine-regulated transcript (CART) peptide is widely expressed in the hypothalamus and is involved in the central regulation of energy balance. Using in situ hybridization, this study examined the roles of CART peptide in the hypothalamus of diet-induced obese (DIO) or diet-resistant (DR) mice under different dietary interventions including high-fat (HF), low-fat (LF) and pair-feeding (PF) diet for 6 weeks. Pair feeding the energy intake of the DIO and DR mice was used to determine whether there is an inherent difference in baseline CART expression that may cause the DIO and DR phenotypes. The results demonstrated that CART mRNA expression in the hypothalamus of the DIO mice responded differently on the high-fat diet compared to DR mice. The arcuate nucleus and paraventricular nucleus showed a significant reduction in CART mRNA expression in DIO mice compared to DR mice on the HF diet (-19.6%, p=0.019; -26.1%, p=0.003); whilst a profound increase in CART mRNA expression was observed in the dorsomedial nucleus and lateral hypothalamic area (+44.5%, p=0.007; +37.4%, p=0.033). Our study suggests that the decrease of CART mRNA expression in Arc and PVN regions of DIO mice may contribute to the development of high-fat diet-induced obesity. In addition, CART in the dorsomedial nucleus (DM) of hypothalamus and lateral hypothalamus (LH) may be involved in the activation of an orexigenic effect. Since pair feeding of the high-fat diet eliminated both the body weight and CART mRNA differences between the DIO and DR mice, it is likely that their alterations in gene expression were a consequence of their dissimilar body weight levels.

Pituitary atrial natriuretic peptide of paraventricular nucleus origin.

Atrial natriuretic peptide-synthesizing neurons in the hypothalamic paraventricular nucleus constitute the major sources of ANP in the three lobes of the pituitary gland. Complete transection of the pituitary stalk eliminated 93% of ANP from the intermediate lobe, 47 and 77% from the anterior and the posterior lobes, respectively. Meantime, increased levels of immunoreactive ANP were measured in the median eminence, due to the accumulation of the peptide in the transected axons centrally to the transected stalk and in the paraventricular nucleus. It is likely that ANP neurons in the paraventricular nucleus innervate the pituitary, but those in the periventricular (median) preoptic nucleus and the organum vasculosum laminae terminalis may not contribute to the ANP innervation of the pituitary gland.

The use of heat-induced hydrolysis in immunohistochemistry on angiotensin II (AT1) receptors enhances the immunoreactivity in paraformaldehyde-fixed brain tissue of normotensive Sprague-Dawley rats.

The research on components of the renin-angiotensin system delivered a broad image of angiotensin II-binding sites. Especially, immunohistochemistry (IHC) provided an exact anatomical localization of the AT(1) receptor in the rat brain. Yet, controversial results between in vitro receptor autoradiography and IHC as well as between immunohistochemical studies using various antisera started a vehement discussion concerning specificity and cross-reactivity of these antisera. In particular the magnocellular subdivision of the paraventricular nucleus (PVN) and the supraoptic nucleus (SON) provided controversial results on the localization of AT(1) receptors. Both areas are known for angiotensin II-induced release of vasopressin (VP) and oxytocin (OXT). To evaluate the significance of the appropriate method of antigen retrieval and its relevance for the detection of AT(1) receptors we performed IHC on AT(1) receptors in paraformaldehyde-fixed and paraffin-embedded brain tissue of Sprague-Dawley rats using either the detergent Triton X-100 or microwave oven heating. This study demonstrates that heat-induced hydrolysis enhances the quality and quantity of immunoreactivity (IR) in IHC on AT(1) receptors. In the organum vasculosum lamina terminalis and in the parvocellular subdivisions of the PVN we report a distribution of AT(1)-like-IR similar to that observed with other methods. However, in addition, we provide evidence that distinct AT(1)-like-IR is also localized in few magnocellular neurons of the PVN and in few parvocellular neurons of the dorsal SON but not in magnocellular neurons of the SON. Moreover, parallel IHC indicates that few magnocellular OXT- or VP-releasing neurons of the PVN as well as parvocellular OXT-releasing neurons of the SON do also contain AT(1) receptors.

Anatomical distribution and biochemical characterization of the novel RFamide peptide 26RFa in the human hypothalamus and spinal cord.

26RFa is a novel RFamide peptide originally isolated in the amphibian brain. The 26RFa precursor has been subsequently characterized in various mammalian species but, until now, the anatomical distribution and the molecular forms of 26RFa produced in the CNS of mammals, in particular in human, are unknown. In the present study, we have investigated the localization and the biochemical characteristics of 26RFa-like immunoreactivity (LI) in two regions of the human CNS--the hypothalamus and the spinal cord. Immunohistochemical labeling using specific antibodies against human 26RFa and in situ hybridization histochemistry revealed that in the human hypothalamus 26RFa-expressing neurons are located in the paraventricular and ventromedial nuclei. In the spinal cord, 26RFa-expressing neurons were observed in the dorsal and lateral horns. Characterization of 26RFa-related peptides showed that two distinct molecular forms of 26RFa are present in the human hypothalamus and spinal cord, i.e. 26RFa and an N-terminally elongated form of 43 amino acids designated 43RFa. These data provide the first evidence that 26RFa and 43RFa are actually produced in the human CNS. The distribution of 26RF-LI suggests that 26RFa and/or 43RFa may modulate feeding, sexual behavior and transmission of nociceptive stimuli.

Habituation to repeated restraint stress is associated with lack of stress-induced c-fos expression in primary sensory processing areas of the rat brain.

Rats repeatedly exposed to restraint show a reduced hypothalamic-pituitary-adrenal axis response upon restraint re-exposure. This hypothalamic-pituitary-adrenal axis response habituation to restraint does not generalize to other novel stressors and is associated with a decrease in stress-induced c-fos expression in a number of stress-reactive brain regions. We examined whether habituation to repeated restraint is also associated with adaptation of immediate early gene expression in brain regions that process and relay primary sensory information. These brain regions may not be expected to show gene expression adaptation to repeated restraint because of their necessary role in experience discrimination. Rats were divided into a repeated restraint group (five 1-hour daily restraint sessions) and an unstressed group (restraint naïve). On the sixth day rats from each group were either killed with no additional stress experience or at 15, 30 or 60 min during restraint. Immediate early gene expression (corticotrophin-releasing hormone heteronuclear RNA, c-fos mRNA, zif268 mRNA) was determined by in situ hybridization. A reduction in stress-induced hypothalamic-pituitary-adrenal axis hormone secretion (plasma corticosterone and adrenocorticotropic hormone) and immediate early gene expression levels in the paraventricular nucleus of the hypothalamus, the lateral septum and the orbital cortex was observed in repeated restraint as compared with restraint naïve animals. This reduction was already evident at 15 min of restraint. Unexpectedly, we also found in repeated restraint rats a reduction in restraint-induced c-fos expression in primary sensory-processing brain areas (primary somatosensory cortex, and ventroposteriomedial and dorsolateral geniculate nuclei of thalamus). The overall levels of hippocampal mineralocorticoid receptor heteronuclear RNA or glucocorticoid receptor mRNA were not decreased by repeated restraint, as may occur in response to severe chronic stress. We propose that repeated restraint leads to a systems-level adaptation whereby re-exposure to restraint elicits a rapid inhibitory modulation of primary sensory processing (i.e. sensory gating), thereby producing a widespread attenuation of the neural response to restraint.

Gravity stress elevates the nociceptive threshold level with immunohistochemical changes in the rat brain.

Young Wistar male rats were exposed to 2G hypergravity by continuous centrifugation for 15 minutes. The nociceptive threshold was measured by using the von Frey type filament on the rat skin surfaces after hypergravity exposure. Following the hypergravity exposure, rats were sacrificed with anesthesia, then perfused and fixed for immunohistochemical examination. The 2G hypergravity elevated the nociceptive threshold up to 2-fold and induced analgesic effects on rats that remained for 2 hours after termination of centrifugation. Expression of Fos-immunoreactive proteins was prominently induced by 2G hypergravity in the arcuate nucleus and the paraventricular nucleus of the hypothalamus. The 15-minute flash exposure to 2G hypergravity induced pain suppression in rats, which might be attributed to change of neuronal activity in rat hypothalamus.

Relationship between sexual behavior and sexually dimorphic structures in the anterior hypothalamus in control and prenatally stressed male rats.

The present study was designed to examine the effects of prenatal stress on the morphological development of sexually dimorphic structures in the anterior hypothalamus in male rats and to determine if there is a relationship between morphologic development of the brain and copulatory behavior in individual animals. Dams in the stress group were subjected to treatments of heat-light restraint during the third trimester of gestation (day 14 to parturition) three times daily for 45-min periods. At 90 days of age, prenatally stressed and control male offspring were tested during the dark cycle for spontaneous male sexual behavior. Volumes of the sexually dimorphic nucleus of the preoptic area (SDN-POA) and the anteroventral periventricular nucleus (AVPV) were measured. Comparisons were made between copulatory behavior and hypothalamic nuclear volumes. SDN-POA volumes were significantly reduced (feminized; males have a larger SDN-POA than females) in prenatally stressed males that did not copulate, whereas, SDN-POA volumes in prenatally stressed males that copulated were not altered. The few control males that did not copulate (sexually non-active) also had significantly reduced SDN-POA volumes compared to the control males that did copulate (sexually active). The volume of the AVPV was significantly increased (feminized; males have a smaller AVPV than females) in prenatally stressed males that were sexually non-active compared to AVPV volumes in sexually active males. The results obtained in this study provide a strong positive relationship between sexual behavior and the morphology of the two sexually dimorphic structures measured.

Activation by hypotension of neurons in the hypothalamic paraventricular nucleus that project to the brainstem.

To investigate the involvement of neuronal nitric oxide (NO) in the response of the brain to changes in blood pressure, we studied the activation of putative NO-producing neurons in the paraventricular nucleus of the hypothalamus (PVN) in rats whose mean arterial pressures (MAPs) were decreased by 40-50% with hemorrhage (HEM) or infusion of sodium nitroprusside (NP). Activation was assessed on the basis of expression of the immediate early gene, c-fos; putative NO-producing neurons were identified with the histochemical stain for nicotinamide adenine dinucleotide phosphate-diaphorase (NADPH-d); and the proportions of neurons projecting to the nucleus of the tractus solitarius (NTS) and/or caudal ventrolateral medulla (CVLM) were determined with retrograde tracing techniques. No differences were found for results obtained from HEM and NP animals. Three to four percent of activated PVN neurons projected to the NTS or CVLM. Conversely, approximately 33% and 16% of neurons projecting to the NTS and CVLM, respectively, were activated. About 43% of NADPH-d neurons in the PVN were activated. Of PVN neurons projecting to the NTS or CVLM, 38% and 32%, respectively, were NADPH-d positive. About 11% of NADPH-d PVN neurons projected to the NTS or CVLM. An average of 3 NADPH-d neurons per section were activated and projected to either target. Finally, 7 PVN cells per section sent collateral branches to the NTS and CVLM; 2 or 3 of these cells per section were also activated by decreases in arterial pressure. No NADPH-d cells were found that sent collateral branches to the NTS and CVLM. This study shows that decreases in MAP activate PVN neurons that project, singly and through collaterals, to the NTS and CVLM. A relatively high proportion of the singly projecting neurons is NADPH-d positive. These results support the contention that descending projections from the PVN to the brainstem play an important role in the physiological response to decreases in arterial pressure and suggest that NO may participate in this response.

Immunohistochemical localization of corticotropin-releasing factor, [arginine8]-vasopressin and oxytocin neurons in the goat hypothalamus.

Distribution patterns of corticotropin-releasing factor (CRF), [arginine8]-vasopressin (AVP) and oxytocin (OXY) neurons were examined immunohistochemically in the female goat hypothalamus. The majority of the CRF immunoreactive (-IR) cells were located in the parvocellular part of the paraventricular nucleus (PVN) with smaller population found in the magnocellular part of the PVN. CRF-IR cells were also found in the suprachiasmatic nucleus, the preoptic area and around the fornix in the caudal part of the hypothalamus. AVP- and OXY-IR cells were similarly distributed in the hypothalamus. The majority of AVP- and OXY-IR cells were observed in the magnocellular part of PVN and the supraoptic nucleus. Smaller numbers of AVP- and OXY-IR cells were found in the parvocellular part of the PVN and lateral hypothalamic area. AVP-IR but not OXY-IR cells were located in the suprachiasmatic nucleus. CRF-IR fibers were concentrated in the external palisade zone of the median eminence (ME) with a few fibers found in the internal palisade zone of the ME, whereas AVP- and OXY-IR fibers were concentrated in the internal palisade zone of the ME with a few fibers found in the external zone. These results support the view that not only CRF but also AVP and OXY are released into the hypophysial portal blood and involved in the control of pituitary endocrine function in ruminant species.

Vasopressin- and oxytocin-immunoreactive nerve cells in the aging rat hypothalamus.

Immunohistochemistry and morphometry were used to study the age-related changes in the vasopressin (AVP) and oxytocin (OXT) nerve cells in the paraventricular (PVN), supraoptic (SON) and suprachiasmatic (SCN) nuclei of 3-, 11- and 28-month-old rats. The results showed a statistically significant reduction in the mean number of AVP cells in the PVN, SON and SCN, and of OXT cells in the PVN with advancing age. Different age-related changes in the mean size of the immunoreactive cells were found in the three nuclei: a significant and transitory increase in the AVP and OXT cell sizes in the PVN, a tendency towards increasing the AVP and OXT cell sizes in the SON, and a significant and gradual decrease in the AVP cell size in the SCN. The combination of the morphometric data and staining patterns of the AVP and OXT perikarya and fibers in the PVN and SON pointed to an increased transport of AVP and OXT in 11-month-old rats as well as to a decreased production of these peptides in the PVN of 28-month-old rats. Taken together the staining pattern and the morphometric results showed a progressive loss of AVP cells in the SCN in aging.

Changes in hypothalamic prostaglandin E2 may predict the occurrence of sleep or wakefulness as assessed by parallel EEG and microdialysis in the rat.

Prostaglandin (PG) E2 is produced by mammalian hypothalamus and when administered exogenously prolongs wakefulness. In order to study the relation of endogenous hypothalamic PGE2 to sleep and wakefulness, we have used microdialysis in freely moving rats associated with EEG recording. Male Wistar rats were implanted with three cortical electrodes and with a guide cannula for microdialysis in the space between the paraventricular nucleus (PVN) and the ventromedial hypothalamus (VMH). PGE2 was measured by RIA in 3- or 6-min dialysates 15 days after surgery, when sleep patterns were normal again and PGE2 production stabilised. PGE2 levels were significantly higher during wakefulness (601 +/- 35 pg/ml, 5 experiments, 35 samples) than during slow-wave sleep (487 +/- 24 pg/ml, 5 experiments, 49 samples). Samples corresponding to paradoxical sleep showed a tendency towards higher PGE2 values compared to slow-wave sleep but lower compared to wakefulness. In epochs of wakefulness or sleep lasting at least 12 min, high PGE2 levels in the middle of wakefulness regularly dropped, thus announcing the occurrence of sleep. During sleep, PGE2 first went on dropping and then reincreased towards the values that characterize early periods of wakefulness. In its turn, this reincrease in PGE2 announced the end of sleep and the imminent occurrence of wakefulness. It is the first study to our knowledge showing that the evolvement in endogenous PG profile may predict the occurrence of sleep or wakefulness.

Ineffectiveness of hypothalamic serotonin to block neuropeptide Y-induced feeding.

A variety of recent research has suggested that the feeding associated with enhanced neuropeptide Y (NPY) activity within the hypothalamus may operate in part by interacting antagonistically with other neural processes responsive to serotonin (5-hydroxytryptamine or 5-HT). To test this possibility further, experiments were performed to determine if the magnitude of feeding produced by injecting NPY into the paraventricular nucleus (PVN) or the perifornical hypothalamus (PFH) was diminished by coinjections of 5-HT into these two sites or peripheral injections of the 5-HT agonist, d-fenfluramine. Adult male Sprague-Dawley rats were implanted unilaterally with stainless steel cannulae aimed to terminate either in the PVN or the PFH. In both studies, NPY (235 pmol) produced significant feeding in both sites either 1 or 2 h after injection when compared to saline. This enhanced feeding response was significantly greater in the PFH 2 h after injection (40% in the central study; 70% in the peripheral study). Coinjection of 5-HT (6.3, 12.5, or 25.0 nmol) into either site had no effect on the induction of this NPY-induced feeding response. However, peripherally injected d-fenfluramine (0.32, 0.63, or 1.25 mg/kg) produced strong dose-dependent attenuation both 1- and 2-h food intake elicited by 235 pmol NPY in either site, with the PFH being proportionately more sensitive to this effect. Viewed together, these results suggest that the feeding-suppressant effects of systemic fenfluramine on hypothalamic NPY-induced feeding may operate largely via peripheral mechanisms and/or central ones that have little to do with its 5-HT agonistic effects within the PVN or PFH.

Cranial and cerebral-ventricular landmarks for accurate stereotaxic approach to hypothalamic nuclei in the goat brain.

This paper describes a new stereotaxic coordinate system for the goat brain based on cranial landmarks. An osseous triangle (a-b-c) formed by the point of junction of the crista galli with the caudal ventral part of the frontal sinus septum (a), the external occipital protuberance (b), and the midsagittal projection of the external acoustic meatus (c), was measured using lateral radiographs and ventriculographs and showed a constant mathematical relation. The rostral angle was 20.3 +/- 1.0 (mean +/- SD) degree in 23 goats studied regardless of their cranial size which varied considerably from one animal to another. The hypotenuse length (a-b distance) was found to be a good predictor of the rostral nuchal position of the anterior commissure (AC) and the infundibular recess of the third ventricle (INF), by which the individual variance of the stereotaxic coordinates for a given hypothalamic structure could be compensated. The anterior-posterior distances from the external acoustic meatus was highly correlated with the a-b distance for AC (r = 0.88) and INF (r = 0.90). Using these cranial landmarks and the method outlined in this paper, uncertainty in coordinate values for AC and INF in the goat brain was reduced considerably in comparison to deviation observed when the ordinary Horsley-Clarke axis (Reid's plane) was employed.

Anorexic action of a new potential neuropeptide Y antagonist [D-Tyr27,36, D-Thr32]-NPY (27-36) infused into the hypothalamus of the rat.

Neuropeptide Y (NPY) produces a vigorous feeding response in several species when it is injected into hypothalamic structures involved in eating behavior. The purpose of this study was to determine whether a unique carboxy terminal fragment of NPY would alter the pattern of eating induced in the rat either by NPY injected into the hypothalamus or by a 24-h period of food deprivation. In this case, two L-tyrosine residues and one L-threonine residue of the NPY27-36 fragment were transformed to their D-conformation to produce [D-Tyr27,36,D-Thr32]-NPY (27-36), i.e., D-NPY27-36. Guide cannulae for microinjection were implanted stereotaxically just dorsal to the paraventricular nucleus (PVN) or ventromedial hypothalamus (VMH) of 24 adult male Sprague-Dawley rats. Following postoperative recovery, a microinjection of artificial CSF or 1.1 microgram or 3.3 micrograms of a peptide was made directly into the PVN or VMH as follows: native NPY; D-NPY27-36; or [L-Tyr27,36, L-Thr32]-NPY (27-36), i.e., L-NPY27-36. Food intakes were measured at intervals of 0.25, 0.5, 1.1, 2.0, 4.0, and 24 h. When D-NPY27-36 was microinjected at NPY reactive sites in the PVN or VMH of the rat 15 min before a similar microinjection of NPY, the intense eating response induced by the peptide was reduced significantly. Not only was the effect dose dependent, but D-NPY27-36 also augmented the latency to feed. A mixture of the two doses of NPY and D-NPY27-36 injected at the same hypothalamic loci did not attenuate the intake of food but tended to enhance the feeding response in the rats.(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of prolonged social isolation on responses of neurons in the bed nucleus of the stria terminalis, preoptic area, and hypothalamic paraventricular nucleus to stimulation of the medial amygdala.

The studies presented demonstrate changes in hypothalamo-pituitary-adrenocortical secretion, and in electrical activity and synaptic responses of neurons in the bed nucleus of the stria terminalis, preoptic area, and hypothalamic paraventricular nucleus of rats exposed to early, long-term social isolation. Rats isolated from all social contact from an early preweaning time showed reduced basal plasma corticosterone concentrations, compared with littermate controls raised under social conditions. Isolated animals also exhibited a selective decrease in the spontaneous electrical activity of neurons within the hypothalamic paraventricular nucleus and lateral preoptic area, but not in adjacent structures. Moreover, isolation also altered the response of neurons in certain nuclei to electrical stimulation of the medial amygdala. Thus, a reduction in excitatory responses, and an increase in inhibition and nonresponsiveness, of preoptic area and paraventricular nucleus neurons was recorded, compared with control rats. Neurons in the bed nucleus of the stria terminalis were less affected, but showed an increase in the duration of excitatory responses following medial amygdala stimulation. These results, obtained from urethane-anesthetized rats, together with the reduced basal plasma corticosterone concentrations, suggest a reduction in limbic-hypothalamo-pituitary-adrenocortical (LHPA) activity following maternal deprivation and prolonged social isolation. This may result from altered limbic activity, specifically in the amygdala and its pathways to the paraventricular nucleus (PVN). Such alterations may include the stria terminalis, in so much as increased efficacy of inhibitory components and reduced efficacy of excitatory components was observed. The neural mechanisms underlying these alterations could involve an altered synaptology of the regions examined and/or a disruption of glucocorticoid feedback events.