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.     

Anorexia is Associated with Stress‐Dependent Orexigenic Responses to Exogenous Neuropeptide Y

Chicken lines that have been divergently selected for either low (LWS) or high (HWS) body weight at 56 days of age for more than 57 generations have different feeding behaviours in response to a range of i.c.v. injected neurotransmitters. The LWS have different severities of anorexia, whereas the HWS become obese. Previously, we demonstrated that LWS chicks did not respond, whereas HWS chicks increased food intake, after central injection of neuropeptide Y (NPY). The present study aimed to determine the molecular mechanisms underlying the loss of orexigenic function of NPY in LWS. Chicks were divided into four groups: stressed LWS and HWS on day of hatch, and control LWS and HWS. The stressor was a combination of food deprivation and cold exposure. On day 5 post‐hatch, each chick received an i.c.v. injection of vehicle or 0.2 nmol of NPY. Only the LWS stressed group did not increase food intake in response to i.c.v. NPY. Hypothalamic mRNA abundance of appetite‐associated factors was measured at 1 h post‐injection. Interactions of genetic line, stress and NPY treatment were observed for the mRNA abundance of agouti‐related peptide (AgRP) and synaptotagmin 1 (SYT1). Intracerebroventricular injection of NPY decreased and increased AgRP and SYT1 mRNA, respectively, in the stressed LWS and increased AgRP mRNA in stressed HWS chicks. Stress was associated with increased NPY, orexin receptor 2, corticotrophin‐releasing factor receptor 1, melanocortin receptor 3 (MC3R) and growth hormone secretagogue receptor expression. In conclusion, the loss of responsiveness to exogenous NPY in stressed LWS chicks may be a result of the decreased and increased hypothalamic expression of AgRP and MC3R, respectively. This may induce an intensification of anorexigenic melanocortin signalling pathways in LWS chicks that block the orexigenic effect of exogenous NPY. These results provide insights onto the anorexic condition across species, and especially for forms of inducible anorexia such as human anorexia nervosa.     

Neuroanatomical evidence for reciprocal regulation of the corticotrophin-releasing factor and oxytocin systems in the hypothalamus and the bed nucleus of the stria terminalis of the rat: Implications for balancing stress and affect

Activation of corticotrophin releasing factor (CRF) neurons in the paraventricular nucleus of the hypothalamus (PVN) is necessary for establishing the classic endocrine response to stress, while activation of forebrain CRF neurons mediates affective components of the stress response. Previous studies have reported that mRNA for CRF2 receptor (CRFR2) is expressed in the bed nucleus of the stria terminalis (BNST) as well as hypothalamic nuclei, but little is known about the localization and cellular distribution of CRFR2 in these regions. Using immunofluorescence with confocal microscopy, as well as electron microscopy, we demonstrate that in the BNST CRFR2-immunoreactive fibers represent moderate to strong labeling on axons terminals. Dual-immunofluorescence demonstrated that CRFR2-fibers co-localize oxytocin (OT), but not arginine-vasopressin (AVP), and make perisomatic contacts with CRF neurons. Dual-immunofluorescence and single cell RT-PCR demonstrate that in the hypothalamus, CRFR2 immunoreactivity and mRNA are found in OT, but not in CRF or AVP-neurons. Furthermore, CRF neurons of the PVN and BNST express mRNA for the oxytocin receptor, while the majority of OT/CRFR2 neurons in the hypothalamus do not. Finally, using adenoviral-based anterograde tracing of PVN neurons, we show that OT/CRFR2-immunoreactive fibers observed in the BNST originate in the PVN. Our results strongly suggest that CRFR2 located on oxytocinergic neurons and axon terminals might regulate the release of this neuropeptide and hence might be a crucial part of potential feedback loop between the hypothalamic oxytocin system and the forebrain CRF system that could significantly impact affective and social behaviors, in particular during times of stress.     

Effects of Gold Thioglucose Treatment on Central Corticotrophin‐Releasing Hormone Systems in Mice

Systemic administration of gold thioglucose (GTG) causes a hypothalamic lesion that extends from the ventral part of the ventromedial hypothalamus (VMH) to the dorsal part of the arcuate nucleus (ARC), resulting in hyperphagia and obesity in mice. In the present study, we used in situ hybridisation histochemistry to explore the effects of GTG on the central corticotrophin‐releasing hormone (CRH) system, which regulates feeding and energy homeostasis. Type 2 CRH receptor (CRHR‐2) mRNA expression decreased by 40% at 8 weeks in the VMH and by 40–60% at 2 and 8 weeks in the ARC after GTG injection. By contrast, CRHR‐2 mRNA expression in the hypothalamic paraventricular nucleus (PVN) and lateral septum was unchanged. Urocortin (Ucn) 3 mRNA expression in the perifornical area and medial amygdala decreased, whereas CRH mRNA expression in the PVN increased at 2 and 8 weeks after GTG injection. Ucn 1 mRNA expression in the Edingher–Westphal nucleus and Ucn 2 mRNA expression in the PVN were unchanged. Because Ucn 3 is an anorexigenic and a possible endogenous ligand for VMH CRHR‐2, our results suggest that decreased Ucn 3 expression and decreased VMH CRHR‐2 expression contribute, in part, to GTG‐induced hyperphagia and obesity. To determine whether VMH CRHR‐2 mediates the anorexigenic effects of Ucn 3, Ucn 3 was administered i.c.v. and food intake was measured 8 weeks after GTG treatment. Ucn 3 decreased cumulative food intake on days 4–7 after surgery compared to i.c.v. administration of vehicle in control mice. By contrast, the anorexigenic effects of i.c.v. Ucn 3 were abolished in GTG‐treated mice. Taken together, our results indicate that the Ucn 3 pathway, which innervates the VMH, is involved in appetite regulation via CRHR‐2. It remains to be determined whether CRHR‐2 in the ARC has additional roles in appetite regulation by Ucn 3.     

Differential stress‐induced alterations of colonic corticotropin‐releasing factor receptors in the Wistar Kyoto rat

Background A growing body of data implicates increased life stresses with the initiation, persistence and severity of symptoms associated with functional gut disorders such as irritable bowel syndrome (IBS). Activation of central and peripheral corticotropin‐releasing factor (CRF) receptors is key to stress‐induced changes in gastrointestinal (GI) function. Methods This study utilised immunofluorescent and Western blotting techniques to investigate colonic expression of CRF receptors in stress‐sensitive Wistar Kyoto (WKY) and control Sprague Dawley (SD) rats. Key Results No intra‐strain differences were observed in the numbers of colonic CRFR1 and CRFR2 positive cells. Protein expression of functional CRFR1 was found to be comparable in control proximal and distal colon samples. Sham levels of CRFR1 were also similar in the proximal colon but significantly higher in WKY distal colons (SD: 0.38 ± 0.14, WKY: 2.06 ± 0.52, P < 0.01). Control levels of functional CRFR2 were similar between strains but sham WKYs samples had increased CRFR2 in both the proximal (SD: 0.88 ± 0.21, WKY: 1.8 ± 0.18, P < 0.001) and distal (SD: 0.18 ± 0.08, WKY: 0.94 ± 0.32, P < 0.05) regions. Exposure to open field (OF) and colorectal distension (CRD) stressors induced decreased protein expression of CRFR1 in SD proximal colons, an effect that was blunted in WKYs. CRD stimulated decreased expression of CRFR2 in WKY rats alone. Distally, CRFR1 is decreased in WKY rats following CRD but not OF stress without any apparent changes in SD rats. Conclusions & Inferences This study demonstrates that psychological and physical stressors alter colonic CRF receptor expression and further support a role for local colonic CRF signalling in stress‐induced changes in GI function.     

The central anorexigenic mechanism of adrenocorticotropic hormone involves the caudal hypothalamus in chicks

Adrenocorticotropic hormone (ACTH), consisting of 39 amino acids, is most well-known for its involvement in an organism's response to stress. It also participates in satiety, as exogenous ACTH causes decreased food intake in rats. However, its anorexigenic mechanism is not well understood in any species and its effect on appetite is not reported in the avian class. Thus, the present study was designed to evaluate central ACTH's effect on food intake and to elucidate the mechanism mediating this response using broiler chicks. Chicks that received intracerebroventricular (ICV) injection of 1, 2, or 4 nmol of ACTH reduced food intake, under both ad libitum and 180 min fasted conditions. Water intake was also reduced in ACTH-injected chicks under both feeding conditions, but when measured without access to feed it was not affected. Blood glucose was not affected in either feeding condition. Following ACTH injection, c-Fos immunoreactivity was quantified in key appetite-associated hypothalamic nuclei including the ventromedial hypothalamus (VMH), dorsomedial hypothalamus, lateral hypothalamus (LH), arcuate nucleus (ARC) and the parvo- and magno-cellular portions of the paraventricular nucleus. ACTH-injected chicks had increased c-Fos immunoreactivity in the VMH, LH, and ARC. Hypothalamus was collected at 1 h post-injection, and real-time PCR performed to measure mRNA abundance of some appetite-associated factors. Neuropeptide Y, pro-opiomelanocortin, glutamate decarboxylase 1, melanocortin receptors 2–5, and urocortin 3 mRNA abundance was not affected by ACTH treatment. However, expression of corticotropin releasing factor (CRF), urotensin 2 (UT), agouti-related peptide (AgRP), and orexin (ORX), and melanocortin receptor 1 (MC1R) mRNA decreased in the hypothalamus of ACTH-injected chicks. In conclusion, ICV ACTH causes decreased food intake in chicks, and is associated with VMH, LH, and ARC activation, and a decrease in hypothalamic mRNA abundance of CRF, UT, AgRP, ORX and MC1R.     

Role of the posterodorsal medial amygdala in predator odour stress‐induced puberty delay in female rats

Puberty onset is influenced by various factors, including psychosocial stress. The present study investigated cat‐odour stress on puberty onset and oestrous cyclicity in rats. Female weanling rats were exposed to either soiled cat litter or fresh unused litter for 10 consecutive days. Following vaginal opening (VO), rats were smeared for 14 days to determine oestrous cyclicity. Anxiety‐like behaviour was assessed using standard anxiety tests. Brains were collected to determine corticotrophin‐releasing factor (CRF), CRF receptor 1 (CRF‐R1) and CRF receptor 2 (CRF‐R2) mRNA in the paraventricular nucleus (PVN), as well as the central nucleus of the amygdala (CEA) and the medial nucleus of the amygdala (MEA). Cat odour delayed VO and first oestrus, disrupted oestrous cycles and caused anxiogenic responses. Cat odour elicited increased CRF mRNA expression in the PVN but not in the CeA. CRF‐R1 and CRF‐R2 mRNA levels in the PVN and CeA were unaffected by cat odour; however, CRF‐R1 mRNA levels were decreased in the MeA. The role of CRF signalling in the MeA, particularly its posterodorsal subnucleus (MePD), with respect to pubertal timing was directly examined by unilateral intra‐MePD administration of CRF (0.2 nmol day^‐1 for 14 days) via an osmotic mini‐pump from postnatal day 24 and was shown to delay VO and first oestrus. These data suggest that CRF signalling in the MePD may be associated with predator odour‐induced puberty delay.     

Differential appetite-related responses to central neuropeptide S in lines of chickens divergently selected for low or high body weight

The anorexigenic 20 amino acid neuropeptide S (NPS) has not been studied in an animal model of hypo- or hyperphagia. The present study aimed to elucidate whether central NPS appetite-related effects are different in lines of chickens that had undergone long-term divergent selection for low (LWS) or high (HWS) body weight and that were hypo- and hyperphagic, respectively. It took a longer time for food intake to be reduced in LWS than HWS chicks administered the lowest dose of NPS tested (0.14 nmol) and, at the highest dose tested (0.56 nmol), they had a greater reduction in food intake than did HWS chicks. HWS chicks responded with a similar magnitude of food intake reduction that was independent of NPS dose. Although water intake was reduced concurrently with food intake after central NPS in both lines, blood glucose concentrations were not affected. Hypothalamic signalling was different between the lines. Although both lines respond to central NPS with decreased c-Fos immunoreactivity in the lateral hypothalamus, the periventricular nucleus had increased c-Fos immunoreactivity in LWS but not HWS chicks. After central NPS treatment, there was increased c-Fos immunoreactivity in the paraventricular nucleus in HWS but not LWS chicks. These data support the notion of differences in the central NPS system between the LWS and HWS lines and infer that central NPS may differentially affect appetite-related processes in other species that contain hypo- and hyperphagic individuals.     

5-HT(2A/2C) receptor antagonists in the paraventricular nucleus attenuate the action of DOI on NPY-stimulated eating.

Hypothalamic neuropeptide Y (NPY) and serotonin (5-HT)-containing neurons are believed to exert an interactive effect on ingestive behavior. The present study examined the ability of two serotonergic antagonists, spiperone (SPIP), a 5-HT2A antagonist, and mianserin (MIAN), a 5-HT(2A/2C) antagonist, to block the inhibitory action of the 5-HT(2A/2C) receptor agonist 1-(2,5-dimethoxy-4-iodophenyl)-2-aminopropane (DOI) on NPY-stimulated eating. Drugs were injected directly into the paraventricular nucleus (PVN), the perifornical (PFH) or the ventromedial hypothalamus (VMH) at the onset of the dark cycle. PVN, PFH and VMH injections of NPY potentiated food intake although only PVN pretreatment with DOI (5-20 nmol) suppressed NPY-induced eating. SPIP or MIAN, injected immediately prior to PVN DOI, reversed the suppressive effect of DOI on NPY feeding. These findings are consistent with other recent data showing that 5-HT2A receptors within the PVN modulate NPY's effect on food intake at the start of the nocturnal period.     

Involvement of hypothalamic neuropeptide Y in pentazocine induced suppression of food intake in rats

The potent orexigenic peptide neuropeptide Y (NPY) has been considered as a possible endogenous ligand for a subpopulation of sigma receptors (SigR). However, their mutual interaction with reference to feeding behavior remains poorly understood. In the present study, we explored the possible interaction between sigma1 receptors (Sig1R) agonist, pentazocine, and NPY on food intake in satiated rats. While pentazocine dose-dependently reduced the food intake, NPY significantly increased it at 2, 4 and 6 h post injection time points. In combination studies, pretreatment with NPY (0.1 nmol/rat, intra-PVN) normalized the inhibitory effect of pentazocine (60 μg/rat, intra-PVN) on food intake. Similarly, pre-treatment with pentazocine (30 μg/rat, intra-PVN) significantly antagonized the orexigenic effect of NPY (0.5 and 1.0 nmol/rat, intra-PVN). Moreover, pentazocine treatment decreased NPY immunoreactivity in arcuate (ARC), paraventricular (PVN), dorsomedial (DMH) and ventromedial (VMH) nuclei of hypothalamus. However, no change was observed in lateral hypothalamus (LH). Study implicates the reduced NPY immunoreactivity for the anorectic effect observed following pentazocine injections. Therefore, the concomitant activation of the NPYergic system along with the Sig1R agonist treatment may serve a useful purpose in the management of the unwanted side effects related to energy homeostasis.     

Corticotropin-releasing factor type-1 receptor mRNA is not induced in mouse hypothalamus by either stress or osmotic stimulation

In rats, acute stress substantially increases corticotropin-releasing factor (CRF) type 1 receptor (CRFR-1) mRNA expression in the paraventricular nucleus (PVN) and osmotic stimulation induces both CRF and CRFR-1 mRNA in magnocellular PVN and supraoptic nucleus (SON). However, these phenomena have not been analysed in other species. We compared CRF and CRFR-1 expression in rat and mouse hypothalamus. Male C57BL/6 mice and Wistar rats were exposed to acute restraint stress for 3 h, or to hypertonic saline ingestion for 7 days. Restraint stress increased CRF and c-fos mRNA expression in both rat and mouse PVN. CRFR-1 mRNA was barely detectable in controls, whereas restraint stress substantially increased CRFR-1 mRNA in rat PVN, but not in mouse. Hypertonic saline ingestion induced CRF mRNA in magnocellular PVN and SON of the rat, but did not alter CRF mRNA levels in mouse hypothalamus. CRFR-1 mRNA was also induced in magnocellular PVN and SON of the rat in response to osmotic stimulation, but not in mouse. Immunohistochemistry demonstrated that CRFR-1-like immunoreactivity (ir) was distributed within parvocellular and magnocellular PVN of mouse and rat. CRFR-1-ir in rat PVN was increased by acute stress and osmotic stimulation. By contrast, these treatments did not alter CRFR-1-ir in mouse PVN. Combined immunohistochemistry and in situ hybridization revealed that CRFR-1-ir was most frequently colocalized to CRF in mouse PVN, whereas only a small percentage of oxytocin and vasopressin-producing cells coexpressed CRFR-1-ir. These results indicate that (i) by contrast to rats, neither acute stress nor osmotic stimulation induces CRFR-1 mRNA expression in the mouse PVN; (ii) osmotic stimulation does not alter CRF mRNA expression in parvocellular and magnocellular neurones of mouse PVN; and (iii) acute stress increases c-fos and CRF mRNA to a similar degree in mouse and rat PVN. Thus, differences may exist between mouse and rat in the regulation of CRF and CRFR-1 gene expression in hypothalamus following stress and osmotic stimulation.     

Anorexigenic effects of substance P in Coturnix japonica

Substance P (SP) is an 11-amino acid tachykinin-related peptide that has anorexigenic effects in birds and mammals although the central mechanism is not well understood. Hence, the objective was to identify appetite-associated hypothalamic mechanisms in Japanese quail (Coturnix japonica). Seven days post-hatch, quail were intracerebroventricularly injected with 0, 0.25, 0.5 or 1.0 nmol of SP and monitored for 180 min. On a cumulative basis, quail that received 0.5 and 1.0 nmol of SP consumed less food for 90 min post-injection. On a non-cumulative basis, food intake was reduced in 0.5 nmol-injected birds at 30 min post-injection. Water intake was not affected. A comprehensive behavior analysis was performed, revealing that SP-injected chicks displayed less feeding pecks and reduced locomotion compared to vehicle-injected birds. To identify molecular mechanisms, the hypothalamus was isolated at 1 h post-injection and real-time PCR was performed to measure mRNA. Agouti-related peptide (AgRP) mRNA was reduced in SP-injected chicks. Immunohistochemistry was used to quantify c-Fos-expressing cells in appetite-associated hypothalamic nuclei. There were more reactive cells in the lateral hypothalamus (LH) and the paraventricular nucleus (PVN) of SP- than vehicle-injected chicks. The LH and PVN were collected for gene expression analysis. Corticotropin-releasing factor (CRF) and urotensin 2 (UTS2) mRNAs were greater in SP- than vehicle-injected chicks in the PVN. In the LH, CRF receptor sub-type 2 (CRFR2) mRNA was greater and kappa opioid receptor mRNA was reduced in SP- compared to vehicle-injected quail. Thus, SP induces a potent anorexia in quail that coincides with increased LH-specific CRFR2 mRNA and increased UTS2 mRNA in the PVN. Future studies will evaluate whether SP-induced anorexigenic effects are mediated through CRF receptors.     

Substance P is associated with hypothalamic paraventricular nucleus activation that coincides with increased urotensin 2 mRNA in chicks

Exogenous administration of substance P (SP) exerts anorexigenic effects in both chicks and rats, but the central mechanism mediating this response is poorly understood. Therefore, this study was designed to elucidate mechanisms of SP-induced anorexia using chicks as models. Chicks that received intracerebroventricular (ICV) injections of SP dose-dependably reduced their food intake with no effect on water intake. Next, the diencephalon was isolated from SP-injected chicks and mRNA expression of neuropeptide Y (NPY), corticotropin releasing factor (CRF), urocortin 3 (UCN 3) and CRF receptors were measured but were not affected. When measured in the hypothalamus, mRNA abundance of these and NPY receptors, urotensin 2 (UTS2) and melanocortin receptor 4 (MCR4) were not affected by SP-injection. Quantification of c-Fos immunoreactivity in appetite-associated hypothalamic nuclei demonstrated that the paraventricular nucleus (PVN) was activated in SP-injected chicks. Finally, in the PVN isolated from SP-injected chicks, there was increased expression of UTS2 mRNA while CRF and UCN3 were not affected. Thus, the anorexigenic effects of SP appear to be mediated by PVN activation and may involve UTS2.     

Leptin effects on the expression of type-2 CRH receptor mRNA in the ventromedial hypothalamus in the rat

The product of the ob gene, leptin, is thought to act in the hypothalamus to reduce food intake and body weight (b.w.) in rats and mice; however, the mechanisms of leptin action in the brain have not been fully elucidated. Corticotropin-releasing hormone (CRH) is a potent anorectic neuropeptide, and its type-2 receptor (CRHR-2) in the ventromedial hypothalamus (VMH) appears to play an important role in the expression of this anorectic effect. We explored here the impact of systemic leptin administration on CRH mRNA expression in the hypothalamic paraventricular nucleus (PVN) and CRHR-2 mRNA expression in the VMH in male rats, using in-situ hybridization histochemistry. The expression of CRH mRNA in the PVN and CRHR-2 mRNA in the VMH were increased at 2 h and 6 h, respectively, after a single intraperitoneal injection of leptin (1.0 mg/kg). Continuous subcutaneous infusion of leptin (1.2 mg/kg/day) via an osmotic minipump for 5 days increased the expression of CRHR-2 mRNA in the VMH, but not the expression of CRH mRNA in the PVN, compared with vehicle treatment. The rats that received the single or continuous administration of leptin showed reductions of food intake and b.w. compared with vehicle-treated rats. These results are consistent with our previous findings that the expression of CRHR-2 mRNA in the VMH is positively correlated with plasma leptin concentrations under various conditions, and highlight the importance of circulating leptin for the regulation of VMH CRHR-2 mRNA. The present results also raise the possibility that leptin reduces food intake and b.w. at least partially due to the enhancement of the anorectic effect of CRH via increased PVN CRH expression and/or VMH CRHR-2 expression.     

Disruption of arcuate/paraventricular nucleus connections changes body energy balance and response to acute stress.

The mediobasal hypothalamus regulates functions necessary for survival, including body energy balance and adaptation to stress. The purpose of this experiment was to determine the contribution of the arcuate nucleus (ARC) in controlling these two functions by the paraventricular nucleus (PVN). Circular, horizontal cuts (1.0 mm radius) were placed immediately above the anterior ARC to sever afferents to the PVN. In shams the knife was lowered to the same coordinates but was not rotated. Food intake and body weight were monitored twice daily, at the beginning and end of the light cycle, for 1 week. On the final day the animals were restrained for 30 min. Lesioned animals had increased food intake in light and dark periods, higher weight gain per day, and more body fat as compared with shams. There was no difference in caloric efficiency. Unlike shams, lesioned rats had no predictable relationship between plasma insulin and leptin. Plasma ACTH was increased at 0 min in lesioned rats but was decreased 15 and 30 min after restraint as compared with shams. There was no difference in plasma corticosterone. Immunostaining revealed that alpha-melanocortin (alphaMSH) and neuropeptide Y (NPY) accumulated below the cuts, and both were decreased in PVN. Food intake and body weight were correlated negatively to alphaMSH, but not NPY in PVN. There was no difference in proopiomelanocortin (POMC) mRNA, but NPY mRNA was reduced in the ARC of lesioned animals. We conclude that ARC controls body energy balance in unstressed rats, possibly by alphaMSH input to PVN, and that ARC also is necessary for PVN regulation of ACTH.     

Corticotrophin-Releasing Factor Alters the Timing of Puberty in the Female Rat

Puberty is a developmental process that is dependent upon activation of the hypothalamic gonadotrophin-releasing hormone (GnRH) pulse generator. It is well established that the stress neuropeptide, corticotrophin-releasing factor (CRF), has a profound inhibitory action on GnRH pulse generator frequency. Although stress is known to affect the timing of puberty, the role of CRF is unknown. The present study aimed to test the hypothesis that CRF plays a critical role in the timing of puberty. On postnatal day (pnd) 28, female rat pups were chronically implanted with i.c.v. cannulae and received 14 days of administration of either CRF, CRF receptor antagonist (astressin-B) or artificial cerebrospinal fluid via an osmotic mini-pump. A separate group of rats served as nonsurgical controls. As a marker of puberty, rats were monitored for vaginal opening and first vaginal oestrus. Levels of CRF , CRF receptor types 1 and 2 ( CRF-R1 , CRF-R2 ) mRNA expression in micropunches of the medial preoptic area (mPOA), hypothalamic paraventricular nucleus (PVN) and arcuate nucleus (ARC) were determined across pubertal development; brain tissue was collected from a naive group of rats on pnd 14, 32, on the day of vaginal opening, and pnd 77 (Adult). Administration of CRF resulted in a delay in the onset of puberty, whereas astressin-B advanced pubertal onset. Additionally, CRF and CRF-R1 mRNA expression was reduced in the mPOA, but not ARC, at puberty. In the PVN, expression of CRF , but not CRF-R1 mRNA, was reduced at the time of puberty. These data support the hypothesis that CRF signalling may play an important role in modulating the timing of puberty in the rat.     

Feeding and drinking elicited by central injection of neuropeptide Y: Evidence for a hypothalamic site(s) of action

Neuropeptide Y (NPY), which exists in very high concentrations in the brain, has been shown to elicit a powerful feeding response and a small drinking response in satiated rats. In order to delineate the brain sites sensitive to these effects, NPY was injected through chronic guide cannulas into seven different brain regions, and the food and water intake of satiated rats was measured one hr postinjection. Injection of NPY (78 pmoles) into hypothalamic areas, namely the paraventricular nucleus (PVN), ventromedial hypothalamus (VMH), and lateral hypothalamus (LH), elicited a strong feeding response; in contrast, injections into extra-hypothalamic areas, namely the amygdala, thalamus, and periaqueductal gray, were completely ineffective. Administration of NPY into the PVN and VMH also elicited a small drinking response; however, all other areas, including the LH, were insensitive to this effect. The findings that NPY was effective in the hypothalamus, as opposed to sites anterior, posterior, lateral or dorsal to this structure, suggest a hypothalamic site(s) of action for this neuropeptide.