Hypothalamic mechanisms associated with corticotropin-releasing factor-induced anorexia in chicks

Central administration of corticotropin-releasing factor (CRF), a 41-amino acid peptide, is associated with potent anorexigenic effects in rodents and chickens. However, the mechanism underlying this effect remains unclear. Hence, the objective of the current study was to elucidate the hypothalamic mechanisms that mediate CRF-induced anorexia in 4 day-old Cobb-500 chicks. After intracerebroventricular (ICV) injection of 0.02 nmol of CRF, CRF-injected chicks ate less than vehicle chicks while no effect on water intake was observed at 30 min post-injection. In subsequent experiments, the hypothalamus samples were processed at 60 min post-injection. The CRF-injected chicks had more c-Fos immunoreactive cells in the arcuate nucleus (ARC), dorsomedial nucleus (DMN), ventromedial hypothalamus (VMH), and paraventricular nucleus (PVN) of the hypothalamus than vehicle-treated chicks. CRF injection was associated with decreased whole hypothalamic mRNA abundance of neuropeptide Y receptor sub-type 1 (NPYR1). In the ARC, CRF-injected chicks expressed more CRF and CRF receptor sub-type 2 (CRFR2) mRNA but less agouti-related peptide (AgRP), NPY, and NPYR1 mRNA than vehicle-injected chicks. CRF-treated chicks expressed greater amounts of CRFR2 and mesotocin mRNA than vehicle chicks in the PVN and VMH, respectively. In the DMN, CRF injection was associated with reduced NPYR1 mRNA. In conclusion, the results provide insights into understanding CRF-induced hypothalamic actions and suggest that the anorexigenic effect of CRF involves increased CRFR2-mediated signaling in the ARC and PVN that overrides the effects of NPY and other orexigenic factors.     

Food intake elicited by central administration of orexins/hypocretins: identification of hypothalamic sites of action

Orexin A and B, a recently identified pair of neuropeptides, are produced in perikarya located in the lateral and perifornical hypothalamus (LH and PFH). Immunoreactive fibers from these neurons innervate several nuclei in the hypothalamus. Orexin A and orexin B stimulate feeding when administered intracerebroventricularly to rats. To identify the specific sites of orexin action, orexin A and B were microinjected into a number of hypothalamic and extrahypothalamic sites in rats. Orexin A was found to enhance food intake when injected into four hypothalamic sites, the paraventricular nucleus (PVN), the dorsomedial nucleus (DMN), LH and the perifornical area, but was ineffective in the arcuate nucleus (ARC), the ventromedial nucleus (VMN), and the preoptic area (POA) as well as the central nucleus of the amygdala (CeA) and nucleus of the tractus solitarius (NTS). Orexin B was not effective at any site tested. These findings demonstrate that orexin A receptive sites for stimulation of food intake exist primarily in a narrow band of neural tissue within the hypothalamus that is known to be involved in control of energy homeostasis.     

ICV galanin-like peptide stimulates non-contact erections but not touch-based erections in adult,sexually experienced male rats

Galanin-like peptide (GALP) is a neuropeptide transcribed only within the arcuate nucleus of the hypothalamus and is thought to be a mediator between energetics and reproductive function. Intracerebroventricular (ICV) injection of GALP is known to have effects on feeding, and to significantly increase gonadotropin releasing hormone- (GnRH-) mediated luteinizing hormone (LH) secretion. Furthermore, ICV GALP is known to stimulate fos production in the medial pre-optic area (mPOA) and to a lesser extent, the paraventricular nucleus (PVN). ICV injection of 5.0 nmol GALP profoundly stimulates male rat sexual behavior. It is not known if GALP's effects on sex behavior are due to an increase in appetitive or mechanical (erectile) aspects of male sexual behavior. To determine this, sexually experienced male rats were cannulated in the lateral ventricle and injected with 5.0 nmol GALP or vehicle. Immediately after injections, male rats were placed in an arena connected to a second arena via a tube with a fan. The second arena contained a steroid-primed female and her bedding. The male rat had olfactory but not visual or tactile contact with the female. We analyzed the amount of time the male rats spent investigating the air intake and the number of non-contact erections (NCEs) in a 30 minute test. ICV GALP significantly (p < 0.05) increased both the amount of time of olfactory investigations and NCEs compared to vehicle. In a second set of animals, we tested if ICV GALP could stimulate touch-based erections. GALP had no significant effect on touch-based erections compared to vehicle. These data suggest that GALP's activation of fos within the mPOA is indicative of its action to stimulate the appetitive aspects of male sexual behavior.     

The effects of galanin-like peptide on energy balance, body temperature and brain activity in the mouse and rat are independent of the GALR2/3 receptor

Galanin-like peptide (GALP) is a neuropeptide that is thought to act on the galanin receptors GALR1, GALR2 and GALR3. In rats, i.c.v. injection of GALP has dichotomous actions on energy balance, stimulating feeding over the first hour, but reducing food intake and body weight at 24 h, as well as causing an increase in core body temperature. In mice, GALP only induces an anorexic action, and its effects on core body temperature are unknown. One aim of the present study was to determine the effects of GALP on core body temperature in mice. Intracerebroventricular injection of GALP into conscious mice had no effect on feeding over 1 h, but caused a significant reduction in food intake and body weight at 24 h. It also caused an immediate drop in core body temperature, which was followed by an increase in body temperature. To understand these different effects of GALP on energy balance in mice compared to rats, and to determine the involvement of GALR2 and GALR3, immunohistochemistry was performed to localise c-Fos, a marker of cell activation. Intracerebroventricular injection of GALP induced c-Fos expression in the parenchyma surrounding the ventricles, the ventricular ependymal cells and the meninges in mice and rats. GALP also induced c-Fos expression in the supraoptic nucleus, dorsomedial hypothalamic nucleus, lateral hypothalamus and nucleus tractus solitarius in rats but not in mice. Central administration of a GALR2/3 agonist in rats did not induce c-Fos in any of the brain regions that expressed this protein after GALP injection, and had no effect on food intake, body weight and body temperature in rats or mice. These data suggest that GALP induces differential effects on energy balance and brain activity in mice compared to rats, which are unlikely to be due to activation of the GALR2 or GALR3 receptor.     

Differential sensitivity of specific neuronal populations of the rat hypothalamus to prolactin action

Prolactin stimulates dopamine release from neuroendocrine dopaminergic (NEDA) neurons in the hypothalamic arcuate nucleus (ARC) to maintain low levels of serum prolactin. Elevated prolactin levels during pregnancy and lactation may mediate actions in other hypothalamic regions such as the paraventricular nucleus (PVN) and rostral preoptic area (rPOA). We predicted that NEDA neurons would be more sensitive prolactin targets than neurons in other regions because they are required to regulate basal prolactin secretion. Moreover, differences in the accessibility of the ARC to prolactin in blood may influence the responsiveness of this population. Therefore, we compared prolactin-induced signaling in different hypothalamic neuronal populations following either systemic or intracerebroventricular (icv) prolactin administration. Phosphorylation of the signal transduction factor, STAT5 (pSTAT5), was used to identify prolactin-responsive neurons. In response to systemic prolactin, pSTAT5-labeled cells were widely observed in the ARC but absent from the rPOA and PVN. Many of these responsive cells in the ARC were identified as NEDA neurons. The lowest icv prolactin dose (10 ng) induced pSTAT5 in the ARC, but with higher doses (>500 ng) pSTAT5 was detected in numerous regions, including the rPOA and PVN. NEDA neurons were maximally labeled with nuclear pSTAT5 in response to 500 ng prolactin and appeared to be more sensitive than dopaminergic neurons in the rPOA. Subpopulations of oxytocin neurons in the hypothalamus were also found to be differentially sensitive to prolactin. These data suggest that differences in the accessibility of the arcuate nucleus to prolactin, together with intrinsic differences in the NEDA neurons, may facilitate homeostatic feedback regulation of prolactin release.     

Hypothalamic sites of neuronal histamine action on food intake by rats

To identify sites of histaminergic modulation of food intake, histamine H₁-receptor antagonist was microinfused into the rat hypothalamus, the ventromedial hypothalamus (VMH), the lateral hypothalamus (LHA), the paraventricular nucleus (PVN), the dorsomedial hypothalamus (DMH), or the preoptic anterior hypothalamus (POAH), during the early light period. Feeding, but not drinking, was elicited in 100% of the rats (P<0.01) that were bilaterally microinfused with 26 nmol chlorpheniramine into the VMH. Unilateral infusion into the VMH did not affect food intake at doses of 26 or 52 nmol. Feeding was also induced by bilateral microinfusion into the PVN, but only the 52 nmol dose was effective. Bilateral infusions into the LHA, the DMH or the POAH did not affect ingestive behavior. Feeding induced by an H₁-antagonist was completely abolished in all 7 rats tested when endogenous neuronal histamine was decreased by pretreatment with α-fluoromethylhistidine (100 mg/kg). The findings suggest that H₁-receptors in the VMH and the PVN, but not in the LHA, the DMH or the POAH, may be involved in histaminergic suppression of foof intake.     

Intraperitoneal injection of ghrelin induces Fos expression in the paraventricular nucleus of the hypothalamus in rats

Ghrelin is a 28-amino acid peptide hormone secreted from the stomach that acts as a gut-brain peptide with potent stimulatory effects on food intake. The aim of the present study was to investigate the effects of peripheral ghrelin (1 and 10 nmol/rat) injected intraperitoneally (i.p.) on food intake and neuronal activity in the hypothalamus and brain stem, as assessed by c-Fos-like-immunoreactivity (c-FLI), using a confocal laser scanning microscope (cLSM) as a sensitive microscopic technique to detect c-FLI-positive neurons. Cumulative food intake was significantly increased 5.3- and 3.7-fold for the 4-h period after i.p. injection of ghrelin at both doses. The number of c-FLI-positive neurons in the paraventricular nucleus of the hypothalamus (PVN) was significantly increased after peripheral administration of ghrelin (1 nmol i.p.; median: 41.8) compared with i.p. saline (median: 17.5). As described before, c-fos expression was increased in the arcuate nucleus of the hypothalamus (ARC). In the nucleus of the solitary tract (NTS) or the area postrema (AP), there was no significant change in the density of c-FLI-positive neurons. Our data suggest that an activation of the arcuate-paraventricular axis may be part of the brain circuits involved in the orexigenic effect of peripheral ghrelin.     

Effect of hypothalamic administration of growth hormone-releasing factor (GRF) on feeding behavior in rats.

To examine the role and working site of growth hormone-releasing factor (GRF) in feeding behavior, we first tested the effect of the intracerebroventricular (i.c.v.) injection of GRF on food intake after 24 h of food deprivation. Cumulative food intake was measured 1, 3 and 6 h after injection. A lower dose of GRF stimulated food intake in a dose dependent manner (3 h; GRF 100 pmol 8.64 +/- 1.06 g vs saline 5.50 +/- 0.60 g, P less than 0.05), while a higher dose (1 nmol, 500 pmol) suppressed food intake (3 h; GRF 1 nmol 2.65 +/- 0.70 g vs saline 5.50 +/- 0.60 g, P less than 0.01). Second, the effect of i.c.v. injection of 100 pmol of GRF on peripheral metabolites was examined. The subsequent levels of plasma insulin, glucagon, glucose and non-esterified fatty acid showed no significant difference from those of saline administration. Third, the effect of microinjection of GRF (5 pmol) into several hypothalamic areas on food intake was examined. Injection into the ventromedial hypothalamic nucleus (VMN) stimulated food intake (3 h; GRF 5 pmol 10.32 +/- 1.04 g vs saline 6.92 +/- 0.32 g, P less than 0.05), but no significant effect was observed following injection either into the lateral hypothalamic area (LHA), paraventricular nucleus (PVN) or medial preoptic area (MPOA). Finally, we tested the stimulatory effect of GRF on food intake in bilateral VMN lesioned rats. I.c.v. injection in these animals had no more significant effect on food intake than did saline injection in VMN lesioned rats (3 h; GRF 100 pmol 6.27 +/- 0.87 g vs saline 5.34 +/- 0.44 g).(ABSTRACT TRUNCATED AT 250 WORDS)     

Functional mapping of neural sites mediating prolactin-induced hyperphagia in doves

Microinjections of prolactin (PRL) into the ventromedial nucleus of the hypothalamus (VMN) or the preoptic area (POA) have been previously shown to increase food intake and body weight in ring doves. In an attempt to corroborate these results and to provide a more complete map of PRL-sensitive brain sites mediating the orexigenic action of PRL, a microinjection procedure was employed in the present study that delivered PRL or saline vehicle in extremely small volumes (10 nl/injection) to a variety of diencephalic sites in dove brain that had been previously demonstrated to contain high concentrations of PRL receptors. Estimates obtained from one female subject given a single 10 nl injection of [¹²⁵I]ovine PRL into the VMN supported the claim that such injection volumes resulted in limited diffusion, as 80% of the tissue radioactivity was found within a 280 mm area surrounding the injection site at 30 min after injection. Food intake of cannulated male doves in the mapping study was monitored daily during a 6 day baseline period, an initial 4 day treatment period, a 6–12 day post-treatment recovery period, and a second 4 day treatment period. Approximately half of the birds received PRL injections (50 ng/10 nl twice daily) and saline vehicle injections (10 nl twice daily) during the first and second treatment periods, respectively, while remaining birds received these treatments in the reverse order. No significant changes in food intake across baseline, vehicle, post-treatment, or PRL treatment periods were observed in birds with injection sites in the lateral POA, paraventricular nucleus of the hypothalamus (PVN), or the medial-basal hypothalamic region between the tuberal hypothalamus (TU) and VMN. In contrast, injections of PRL into the VMN area, medial POA, or TU resulted in average daily food intake values that significantly exceeded those recorded during other periods. The most robust feeding response was seen in the VMN group, where PRL injections resulted in a 58% increase in food intake over that recorded during injection of vehicle. This increase was significantly greater than that observed following PRL injections into the mPOA (26%) or the TU (32%). These findings suggest that the VMN may be a primary site of PRL action in promoting hyperphagia in this species, although PRL effects at other diencephalic loci, such as the mPOA and TU, may also contribute to the orexigenic action of this hormone.     

Mapping of hypothalamic sites involved in the effects of NPY on body temperature and food intake

The objective of the present study was to identify hypothalamic sites that might be implicated in the effects of neuropeptide Y (NPY) on both body temperature and food intake. For this purpose, the effects of direct microinjections of NPY in several doses (0.156–20 μg) into discrete hypothalamic nuclei on body temperature were examined in rats. To examine specificity of effects, food consumption of animals following injections was also measured. Results indicate that the influence of NPY on body temperature varies with the hypothalamic region where the peptide is administered. NPY had no effect on temperature after administration into the ventromedial (VMH) and the perifornical hypothalamus (PeF). However, a significant hypothermia was seen following administration into the preoptic (POA) and arcuate nucleus (Arc), and hyperthermia was seen after injection into the paraventricular nucleus (PVN). Finally, a biphasic effect was observed after injection into the lateral hypothalamus (LH): hyperthermia with relatively small doses and hypothermia with higher doses. Similar effects were obtained when administred into the third ventricle (3V) but in an inverted dose-related fashion: hypothermia at low and hyperthermia at higher doses. For feeding, NPY consistently increased food intake in all regions examined, with the strongest effect obtained after administration into the PeF. The present results clearly dissociate the effects of NPY on food intake and body temperature, and demonstrate that these effects are related to specific hypothalamic nuclei.     

Leptin Responsive and GABAergic Projections to the Rostral Preoptic Area in Mice

The adipocyte‐derived hormone leptin plays a critical role in the control of reproduction via signalling in hypothalamic neurones. The drivers of the hypothalamic‐pituitary‐gonadal axis, the gonadotrophin‐releasing hormone (GnRH) neurones, do not have the receptors for leptin. Therefore, intermediate leptin responsive neurones must provide leptin‐to‐GnRH signalling. We investigated the populations of leptin responsive neurones that provide input to the rostral preoptic area (rPOA) where GnRH cell bodies reside. Fluorescent retrograde tracer beads (RetroBeads; Lumafluor Inc., Naples, FL, USA) were injected into the rPOA of transgenic leptin receptor enhanced green fluorescent protein (Lepr‐eGFP) reporter mice. Uptake of the RetroBeads by Lepr‐eGFP neurones was assessed throughout the hypothalamus. RetroBead uptake was most evident in the medial arcuate nucleus (ARC), the dorsomedial nucleus (DMN) and the ventral premammillary nucleus (PMV) of the hypothalamus. The uptake of RetroBeads specifically by Lepr‐eGFP neurones was highest in the medial ARC (18% of tracer‐labelled neurones Lepr‐eGFP‐positive). Because neurones that are both leptin responsive and GABAergic play a critical role in the regulation of fertility by leptin, we next focussed on the location of these populations. To address whether GABAergic neurones in leptin‐responsive hypothalamic regions project to the rPOA, the experiment was repeated in GABA neurone reporter mice (Vgat‐tdTomato). Between 10% and 45% of RetroBead‐labelled neurones in the ARC were GABAergic, whereas uptake of tracer by GABAergic neurones in the DMN and PMV was very low (< 5%). These results show that both leptin responsive and GABAergic neurones from the ARC project to the region of the GnRH cell bodies. Our findings suggest that LEPR‐expressing GABA neurones from the ARC may be mediators of leptin‐to‐GnRH signalling.     

Neuronal histamine in the hypothalamus suppresses food intake in rats

Using probes to manipulate hypothalamic neuronal histamine, we report here that changes in neuronal histamine modulate physiological feeding behavior in rats. Infusion of α-fluoromethylhistidine (FMH), a “suicide” inhibitor of histidine decar☐ylase (HDC), into the third cerebroventricular induced feeding in the early light phase when the histamine synthesis was most accelerated. FMH at an optimum 2.24 μmol dose elicited feeding in 100% of rats. Treatment of FMH specifically and selectively decreased concentration of histamine without affecting concentrations of catecholamines in the hypothalamus. Immediately before the dark phase, when the histamine synthesis was normally lower, FMH infusion did not affect feeding-related parameters such as meal size, meal duration or latency to eat. Conversely, thioperamide, which facilitates both synthesis and release of neuronal histamine by blocking presynaptic autoinhibitory H₃ receptors, significantly decreased food intake after infusion of a 100-nmol dose into the third cerebroventricle. The effect of thioperamide was abolished with i.p. injection of 26 μmol/kg chlorpheniramine, an H₁ antagonist. FMH at 224 nmol was microinfused bilaterally into the feeding-related nuclei in the hypothalamus. The ventromedial nucleus (VMH) and the paraventricular nucleus (PVN), but not the lateral hypothalamus, the dorsomedial hypothalamus or the preoptic anterior hypothalamus were identified as the active sites for the modulation. Neuronal histamine may convey suppressive signals of food intake through H₁ receptors in the VMH and the PVN with diurnal fluctuation.     

Centrally administered galanin-like peptide modifies food intake in the rat: a comparison with galanin

Galanin-like peptide (GALP) is a recently identified neuropeptide that shares sequence homology with the orexigenic neuropeptide, galanin. In contrast to galanin, GALP is reported to bind preferentially to the galanin receptor 2 subtype (GalR2) compared to GalR1. The aim of this study was to determine the effect of GALP on feeding, body weight and core body temperature after central administration in rats compared to the effects of galanin. Intracerebroventricular (i.c.v.) injection of GALP (1 micro g-10 micro g) significantly stimulated feeding at 1 h in both satiated and fasted Sprague-Dawley rats. However, 24 h after GALP injection, body weight gain was significantly reduced and food intake was also usually decreased. In addition, i.c.v. GALP caused a dose-related increase in core body temperature, which lasted until 6-8 h after injection, and was reduced by peripheral administration of the cyclooxygenase inhibitor, flurbiprofen (1 mg/kg). Similar to GALP, i.c.v. injection of galanin (5 micro g) significantly increased feeding at 1 h in satiated rats. However, there was no difference in food intake and body weight at 24 h, and galanin only caused a transient rise in body temperature. Thus, similar to galanin, GALP has an acute orexigenic effect on feeding. However, GALP also has an anorectic action, which is apparent at a later time. Therefore, GALP has complex opposing actions on energy homeostasis.     

Amygdala enterostatin induces c-Fos expression in regions of hypothalamus that innervate the PVN

Enterostatin selectively inhibits the intake of the dietary fat after both central and peripheral administration. Our previous studies have shown that a central site of action is the central nucleus of amygdala. Serotonergic agonists administered into the paraventricular nucleus (PVN) inhibit fat intake and serotonergic antagonists block the feeding suppression induced by amygdala enterostatin, suggesting that there are functional connections between the PVN and amygdala that affect the feeding response to enterostatin. Our purpose was to identify the anatomic and functional projections from the amygdala to the PVN and hypothalamic area that are responsive to enterostatin, by using a retrograde tracer fluorogold (FG) and c-Fos expression. Rats were injected with fluorogold unilaterally into the PVN and a chronic amygdala cannula was implanted ipsilaterally. After 10 days recovery, rats were injected with either enterostatin (0.1 nmol) or saline vehicle (0.1 microl) into the amygdala and sacrificed 2 h later by cardiac perfusion under anesthesia. The brains were subjected to dual immunohistochemistry to visualize both FG and c-Fos-positive cells. FG/c-Fos double-labeled cells were found in forebrain regions including the PVN, amygdala, lateral hypothalamus (LH), ventral medial hypothalamus (VMH) and arcuate nucleus (ARC). The data provides the first anatomical evidence that enterostatin activates amygdala neurons that have functional and anatomic projections directly to the PVN and also activates neurons in the arcuate, LH and VMH, which innervate the PVN.     

The neural pathway of galanin in the hypothalamic arcuate nucleus of rats: activation of beta-endorphinergic neurons projecting to periaqueductal gray matter

We have previously shown that microinjection of galanin into the arcuate nucleus of hypothalamus (ARC) produced antinociceptive effects in rats (Sun et al., 2003a). In this study, the neural pathway of galanin from ARC to midbrain periaqueductal gray (PAG) in nociceptive modulation was investigated. The hindpaw withdrawal latencies (HWLs) with noxious thermal and mechanical stimulation were assessed by the hotplate and the Randall Selitto tests. Intra-ARC administration of 0.1, 0.5, or 1 nmol of galanin induced significant increases in HWLs of rats. The galanin-induced increases in HWLs were inhibited by injection of 10 microg of the opioid receptor antagonist naloxone or 1 nmol of the mu-opioid receptor antagonist beta-funaltrexamine (beta-FNA) into PAG, suggesting that the antinociceptive effects induced by intra-ARC injection of galanin occur via the neural pathway from ARC to PAG. Furthermore, our results demonstrate that the galaninergic fibers directly innervated the beta-endorphinergic neurons in ARC by immunofluorescent methods. Taken together, our results suggest that galanin produces antinociceptive effects in the ARC of rats by activating the beta-endorphinergic pathway from ARC to PAG.     

Evidence for a mu-opioid-opioid connection between the paraventricular nucleus and ventral tegmental area in the rat

The paraventricular nucleus (PVN) and the ventral tegmental area (VTA) have been shown to be involved in opioid mediated feeding behavior. The present study examined whether mu-opioid signalling between the PVN and VTA affected feeding behavior. Male Sprague-Dawley rats were cannulated with one cannula placed in the PVN and two cannulae placed in the VTA, which allowed for co-administration of the mu-opioid receptor agonist [D-Ala(2), NMe-Phe(4), Gly-ol(5)]-enkephalin (DAMGO) in one site and the opioid antagonist naltrexone (NTX) in the other site. Bilateral administration of DAMGO (1.2, 2.4 and 4.9 nmol) into the VTA stimulated feeding dose dependently at 2.4 and 4.9 nmol (P<0.05). The DAMGO (2.4 nmol)-induced increase of food intake following injection into the PVN was blocked by bilateral injection of NTX (6.6, 13.2 and 26.5 nmol) into the VTA at 2 and 4 h (P<0.05). In the reverse situation, the DAMGO (2.4 nmol)-induced increase of food intake following injection into the VTA was blocked by injection of NTX (13.2 and 26.5 nmol) into the PVN at 2 and 4 h (P<0.05). The present study suggests that a bidirectional mu-opioid-opioid signalling pathway exists between the PVN and the VTA which influences feeding.     

c-fos expression in the rat brain following central administration of neuropeptide Y and effects of food consumption

Administration of neuropeptide Y (NPY) intracerebroventricularly (i.c.v.) results in the release of a number of hypothalamic and pituitary hormones and stimulation of feeding and suppression of sexual behavior. In this study, we sought to identify cellular sites of NPY action by evaluating perikaryal Fos-like immunoreactivity (FLI), a marker of cellular activation, in those hypothalamic and extrahypothalamic sites previously implicated in the control of neuroendocrine function and feeding behavior. Additionally, we compared the topography of FLI in these brain sites when food was either available ad libitum or withheld after NPY injection (1 nmol/3 μl, i.c.v.). The results showed that one hour after NPY injection a large number of cells in the parvocellular region of the paraventricular nucleus (PVN) were FLI-positive in the absence of food consumption. However, in association with food intake, a significant number of cells were intensely stained in the magnocellular region of the PVN. An analogous increase in FLI in association with feeding was apparent in the supraotic nucleus (SON), the dorsomedial nucleus and the bed nucleus of the stria terminalis in the hypothalamus. Anong the extrahypothalamic sites, feeding facilitated FLI in a large number of cells located in the lateral subdivision of the central amygdaloid nucleus and the lateral subdivision of the solitary tract. FLI was observed in a moderate number of cells in the hypothalamic arcuate nucleus (ARC) and ventromedial nucleus, and this response was not changed by feeding. Cumulatively, these results show that neurons in a number of discrete hypothalamic and extrahypothalamic sites, previously implicated in the control of neuroendocrine function and feeding behavior, are activated by NPY and further, a divergent pattern of c-fos expression emerged in some of these sites if feeding occurs after NPY injection. Stimulation of FLI in cells of the PVN, SON and ARC by NPY imply the presence of NPY target cells that play a role in the neuroendocrine control of pituitary function. The finding that NPY induced FLI in cells located in the parvocellular subdivision of the PVN even in the absence of feeding, imply that cells involved in initiation of food intake by NPY may reside in this subdivision of the PVN. On the other hand, the appearance of Fos-cells in the magnocellular subdivision of the PVN in response to feeding, suggests neural mechanisms that operate during the post-ingestion period, including those associated with termination of NPY-induced feeding, may impinge upon this subdivision of the PVN.     

Efferents from medial basal forebrain and hypothalamus in the rat. II. An autoradiographic study of the anterior hypothalamus.

Using tritiated amino acid autoradiography, the efferent projections of the anterior hypothalamic area (AHA) were studied in albino rats. Axons from AHA neurons were not confined to local projections in the hypothalamus. Ascending AHA axons ran through the preoptic region, joined the diagonal band and distributed in the lateral septum. Descending AHA efferents within the hypothalamus coursed in a bundle ventromedial to the fornix. Projections were observed to the dorsomedial, ventromedial, arcuate and dorsal premammillary nuclei, and to the median eminence. Sweeping dorsomedially in the posterior hypothalamus, some AHA axons distributed in the central grey. AHA axons staying ventral projected to the supramammillary region, ventral tegmental area, raphe nuclei and midbrain reticular formation. Other AHA efferents distributed to the periventricular thalamus, to the medial amygdala via the stria terminalis or supraoptic commissure, and to the lateral habenula through the stria medullaris. For comparison with the AHA, efferent projections from the paraventricular nucleus (PVN) and from the ventromedial nucleus and adjacent basal hypothalamus (VMR) were studied. Projections from PVN neurons were not restricted to the median eminence and neurohypophysis. PVN efferents also distributed to many of the same regions as did those of the AHA but had somewhat different fiber trajectories and longer descending projections. VMR efferents were more widespread than those of the AHA, with projections extending into the lateral zona incerta and pontine reticular formation. Projections from the AHA were distinct from those of the medial preoptic area (mPOA). For example, while AHA axons descended in a bundle ventromedial to the fornix, mPOA axons ran in the medial forebrain bundle. Such anatomical differences may underlie experimentally demonstrated functional differences between the mPOA and AHA, for instance, in mediation of male and female sex behaviors.