Effects of PVN galanin on macronutrient selection

The neuropeptide galanin (GAL), after injection into the hypothalamic paraventricular nucleus (PVN), elicited a potent feeding response. In satiated rats maintained on pure macronutrient diets (protein, carbohydrate and fat), PVN GAL injection was found to cause a preferential increase in the consumption of the fat diet, with a significantly smaller increase in carbohydrate intake and no change in protein ingestion. When the fat diet was removed, GAL's stimulatory effect on carbohydrate ingestion was reliably and selectively enhanced. These effects of GAL stand in contrast to those of neuropeptide Y (NPY), which is co-localized with NE in the PVN and which induced in these animals a strong and selective enhancement of carbohydrate intake after PVN injection. Similarly, PVN NE, known to act via alpha 2-noradrenergic receptors, induced feeding specifically of carbohydrate and, to a small extent, fat. These differential results demonstrate the specificity of the effects of the peptides (GAL and NPY) and NE on macronutrient selection, all of which can be repeatedly observed in the same group of animals and which appear to be unrelated to the rats' natural 24 hr baseline preferences. However, we did observe a strong positive correlation between NE- and GAL-induced carbohydrate intake. In light of this relationship and additional pharmacological evidence linking GAL- and NE-induced feeding, it is proposed that the effects of GAL on macronutrient selection may be mediated, at least in part, by the alpha 2-noradrenergic feeding system within the PVN.     

Brain-derived neurotrophic factor in the hypothalamic paraventricular nucleus reduces energy intake

Recent studies show that brain-derived neurotrophic factor (BDNF) decreases feeding and body weight after peripheral and ventricular administration. BDNF mRNA and protein, and its receptor tyrosine kinase B (TrkB) are widely distributed in the hypothalamus and other brain regions. However, there are few reports on specific brain sites of actions for BDNF. We evaluated the effect of BDNF in the hypothalamic paraventricular nucleus (PVN) on feeding. BDNF injected unilaterally or bilaterally into the PVN of food-deprived and nondeprived rats significantly decreased feeding and body weight gain within the 0- to 24-h and 24- to 48-h postinjection intervals. Effective doses producing inhibition of feeding behavior did not establish a conditioned taste aversion. PVN BDNF significantly decreased PVN neuropeptide Y (NPY)-induced feeding at 1, 2, and 4 h following injection. BDNF administration in the PVN abolished food-restriction-induced NPY gene expression in the hypothalamic arcuate nucleus. In conclusion, BDNF in the PVN significantly decreases food intake and body weight gain, suggesting that the PVN is an important site of action for BDNF in its effects on energy metabolism. Furthermore, BDNF appears to interact with NPY in its anorectic actions, although a direct effect on NPY remains to be established.     

Nesfatin-1 influences the excitability of glucosensing neurons in the hypothalamic nuclei and inhibits the food intake

Nesfatin-1 is a recently discovered neuropeptide that has been shown to decrease food intake after lateral, third, or fourth brain ventricle, cisterna magna administration, or PVN injection in ad libitum fed rats. With regards to the understanding of nesfatin-1 brain sites of action, additional microinjection studies will be necessary to define specific nuclei, in addition to the PVN, responsive to nesfatin-1 to get insight into the differential effects on food intake. In the present study, we evaluated nesfatin-1 action to modulate food intake response upon injection into the specific hypothalamic nuclei (PVN, LHA and VMN) in freely fed rats during the dark phase. We extend previous observations by showing that the nesfatin-1 (50 pmol) injected before the onset of the dark period significantly reduced the 1 to 5 h cumulative food intake in rats cannulated into the PVN, LHA, but not in rats cannulated into the VMN. Glucosensing neurons located in the hypothalamus are involved in glucoprivic feeding and homeostatic control of blood glucose. In order to shed light on the mechanisms by which nesfatin-1 exerts its satiety-promoting actions, we examined the effect of nesfatin-1 on the excitability of hypothalamic glucosensing neurons. Nesfatin-1 excited most of the glucose-inhibited (GI) neurons and inhibited most of the glucose-excited (GE) neurons in the PVN. Of 34 GI neurons in the LHA tested, inhibitory effects were seen in 70.6% (24/34) of GI neurons. The main effects were excitatory after intra-VMN administration of nesfatin-1 in GE neurons (27/35, 77.1%). Thus, our data clearly demonstrate that nesfatin-1 may exert at least a part of its physiological actions on the control of food intake as a direct result of its role in modulating the excitability of glucosensing neurons in the PVN, LHA and VMN.     

Endorphinergic and alpha-noradrenergic systems in the paraventricular nucleus: effects on eating behavior

Brain cannulated rats were injected with the opioid peptide beta-endorphin (beta-EP) directly into the hypothalamic paraventricular nucleus (PVN) where norepinephrine (NE) is most effective in stimulating eating behavior. Beta-Endorphin (1.0 nmole) reliably increased food intake in satiated animals, and this response was blocked by local administration of the selective opiate antagonist naloxone. The eating induced by beta-EP was positively correlated in magnitude with the NE response and, like NE, was antagonized by PVN injection of the alpha-noradrenergic blocker phentolamine. Naloxone had no effect on NE-induced eating, and the dopaminergic blocker fluphenazine failed to alter either beta-EP or NE eating. When injected simultaneously, at maximally effective doses, beta-EP and NE produced an eating response which was significantly larger than either of the responses elicited separately by beta-EP or NE and was essentially equal to the sum of these two responses. The evidence obtained in this study suggests that beta-EP and NE stimulate food ingestion through their action on PVN opiate and alpha-noradrenergic receptors, respectively, and that beta-EP's action is closely related to, and in part may be dependent upon, the PVN alpha-noradrenergic system for feeding control.     

Differential effects of galanin and neuropeptide Y on extracellular norepinephrine levels in the paraventricular hypothalamic nucleus of the rat: a microdialysis study.

Evidence suggests that the peptides galanin (GAL) and neuropeptide Y (NPY) interact with the amine norepinephrine (NE) in the hypothalamic paraventricular nucleus (PVN) to stimulate feeding behavior. To directly investigate the nature of these interactions, extracellular levels of PVN NE were monitored in freely-moving rats using the microdialysis/HPLC technique. Following PVN administration of GAL (0.3 nmol), NPY (78 pmol) or Ringer's solution, local NE levels were measured at 20-min intervals for 2 hrs postinjection, under two feeding conditions, namely, in the presence or absence of food. The results demonstrate different effects of these peptides on endogenous NE levels. Following GAL administration, PVN NE levels were enhanced by 80 to 90%, up to 40 min postinjection, independent of food availability. In contrast, following NPY injection, NE levels were significantly reduced 20 min postinjection with food absent, and when food was available, NE levels tended to be enhanced. These results, consistent with pharmacological and biochemical studies, reveal different patterns of peptide-amine interactions in the PVN.     

Diurnal rhythm of galanin-like immunoreactivity in the paraventricular and suprachiasmatic nuclei and other hypothalamic areas

The peptide galanin (GAL), when injected into the rat hypothalamus, is known to stimulate feeding behavior and affect the secretion of various hormones, including insulin and the adrenal steroid, corticosterone. To determine whether endogenous peptide levels shift in relation to natural rhythms of feeding and circulating hormone levels, rats were sacrificed at different times of the light/dark cycle, and their GAL levels were measured, via radioimmunoassay, in medial hypothalamic dissections and micropunched hypothalamic areas. The results suggest the existence of two distinct diurnal rhythms for hypothalamic GAL. One rhythm, detected exclusively in the area of the SCN, is characterized by bimodal peaks of GAL, threefold higher than basal peptide levels, around the onset of the dark and light periods. The second rhythm shows a single peak of GAL towards the middle of the nocturnal feeding cycle, specifically between the third and sixth hour. This latter rhythm is evident in the dorsal region of the medial hypothalamus, localized specifically to the lateral portion of the PVN. Moreover, it is inversely related to circulating insulin but unrelated to the adrenal steroids, suggesting a possible association between this pancreatic hormone and GAL in the PVN.     

Dietary fat stimulates endogenous enkephalin and dynorphin in the paraventricular nucleus: role of circulating triglycerides

The opioid peptides enkephalin (ENK) and dynorphin (DYN), when injected into the hypothalamus, are known to stimulate feeding behavior and preferentially increase the ingestion of a high-fat diet. Studies of another peptide, galanin (GAL), with similar effects on feeding demonstrate that a high-fat diet, in turn, can stimulate the expression of this peptide in the hypothalamus. The present study tested different diets and variable periods of high- vs. low-fat diet consumption to determine whether the opioid peptides respond in a similar manner as GAL. In six experiments, the effects of dietary fat on ENK and DYN were examined in three hypothalamic areas: the paraventricular nucleus (PVN), perifornical hypothalamus (PFH), and arcuate nucleus (ARC). The results demonstrated that the ingestion of a high-fat diet increases gene expression and peptide levels of both ENK and DYN in the hypothalamus. The strongest and most consistent effect is seen in the PVN. In this nucleus, ENK and DYN are increased by 50-100% after 1 wk, 1 day, 60 min, and even 15 min of high-fat diet consumption. While showing some effect in the PFH, these peptides in the ARC are considerably less responsive, exhibiting no change in response to the briefer periods of diet intake. This effect of dietary fat on PVN opioids can be observed with diets equal in caloric density and palatability and without a change in caloric intake, body weight, fat pad weight, or levels of insulin or leptin. The data reveal a strong and consistent association between these peptides and a rise in circulating levels of triglycerides, supporting a role for these lipids in the fat-induced stimulation of opioid peptides in the PVN, similar to GAL.     

Evidence for neuropeptide Y mediation of eating produced by food deprivation and for a variant of the Y1 receptor mediating this peptide's effect.

Neuropeptide Y (NPY) elicits eating when injected directly into the paraventricular nucleus (PVN) or perifornical hypothalamus (PFH). To identify the essential regions of the NPY molecule and the relative contributions of Y1 and Y2 receptors, the eating stimulatory potency of NPY was compared to that of its fragments, analogues, and agonists when injected into the PVN or PFH of satiated rats. Additionally, antisera to NPY was injected into the cerebral ventricles (ICV) to determine whether passive immunization suppresses the eating produced by mild food deprivation. Tests with NPY fragments revealed that NPY(2-36) was surprisingly potent, nearly three times more so than intact NPY. In contrast, fragments with further N-terminal deletions were progressively less effective or ineffective, as was the free acid form of NPY. Collectively, this suggests that both N- and C-terminal regions of NPY participate in the stimulation of eating. Tests with agonists revealed that the putative Y1 agonist [Pro34]NPY elicited a strong dose-dependent feeding response, while the putative Y2 agonist, C2-NPY, had only a small effect at the highest doses. Although this suggests mediation by Y1 receptors, the uncharacteristically high potency of NPY(2-36) may additionally suggest that the receptor subtype underlying feeding is distinct from that mediating other responses. Additional results revealed that ICV injection of antisera to NPY, which should inactivate endogenous NPY, produced a concentration-dependent suppression of eating induced by mild food deprivation. This finding, along with published work demonstrating enhanced levels of hypothalamic NPY in food-deprived rats, suggests that endogenous NPY mediates the eating produced by deprivation.     

Diminished feeding responsiveness to orexin A (hypocretin 1) in aged rats is accompanied by decreased neuronal activation

Orexin A is produced in caudal lateral, posterior, perifornical, and dorsomedial hypothalamic areas. Orexin A in the rostro-dorsal lateral hypothalamic area (rLHa) stimulates feeding and activates several feeding-regulatory brain areas. We hypothesized that aging diminishes feeding and c-Fos-immunoreactivity (c-Fos-ir; marker of neuronal activation) response to orexin A. Young (3 mo), middle-aged (12 mo), and old (24 mo) male Fischer 344 rLHa-cannulated rats were injected with orexin A (0.5, 1, and 2 nmol). Food intake was measured at 1, 2, and 4 h. c-Fos-ir in hypothalamic, limbic, and hindbrain regions was measured in two additional sets of rLHa-orexin A injected rats. In a separate study, orexin A effects on feeding and c-Fos-ir were measured in 6-mo-old rats. Orexin A significantly elevated feeding in rats aged 3, 6, and 12 mo in the 0-1 and 1-2- h time intervals, whereas in old rats this was significant in the 1-2 h time interval only. At 1 h, 6-8 (of 14) brain areas showed elevated c-Fos-ir in response to orexin A in 3- and 6-mo-old rats, but 24-mo-old rats exhibited attenuated or absent c-Fos-ir response in all brain regions except the hypothalamic paraventricular nucleus (PVN) and rostral nucleus of the solitary tract (rNTS). Orexin A did not elevate c-Fos-ir in 3-mo-old rats at 2 h after injection, whereas the PVN and mediodorsal thalamic nucleus (MD) showed elevated c-Fos-ir at 2 h in 24-mo-old rats. These data suggest that delayed and diminished feeding responses in old animals may be due to ineffective neural signaling and implicate the orexin A network as one feeding system affected by aging.     

Injection of noradrenaline into the hypothalamic paraventricular nucleus produces vigorous gnawing in satiated rats

Single injections of noradrenaline (NA) into the hypothalamic paraventricular nucleus (PVN) initiate short bouts of eating in the rat. The effect of the injections of NA (40 nM) into the PVN on gnawing was studied in satiated male rats that had displayed a reliable eating response to NA. The NA injections produced numerous bouts of prolonged and vigorous gnawing of wood pieces shaped like food pellets. The gnawing response started 0.5-2 min after the injection of NA and lasted for 20-25 min. The results suggest that the increase in gnawing and eating evoked by NA might be related to facilitation of the oral responses, and a changed sensitivity to the food related stimuli, in addition to an intrinsic increase in appetite.     

PVN galanin increases fat storage and promotes obesity by causing muscle to utilize carbohydrate more than fat

To understand the function of the feeding-stimulatory peptide, galanin (GAL), in eating and body weight regulation, the present experiments tested the effects of both acute and chronic injections of this peptide into the paraventricular nucleus (PVN) of rats. With food absent during the test, acute injection of GAL (300 pmol/0.3 microl) significantly increased phosphofructokinase activity in muscle, suggesting enhanced capacity to metabolize carbohydrate, and reduced circulating glucose levels. It also decreased beta-hydroxyacyl-CoA dehydrogenase activity in muscle, indicating reduced fat oxidation, while increasing circulating non-esterified fatty acids (NEFA) and lipoprotein lipase activity in adipose tissue (aLPL). Chronic PVN injections of GAL (300 pmol/0.3 microl/injection) versus saline over 7-10 days significantly stimulated daily caloric intake and increased the weight of four dissected fat depots by 30-40%. These effects, accompanied by elevated levels of leptin, triglycerides, NEFA and aLPL activity, were evident only in rats on a diet with at least 35% fat. Thus, by favoring carbohydrate over fat metabolism in muscle and reversing hyperglycemia, PVN GAL may have a function in counteracting the metabolic disturbances induced by a high-fat diet. As a consequence of these actions, GAL can promote the partitioning of lipids away from oxidation in muscle towards storage in adipose tissue.     

Participation of galaninergic neurotransmission at the paraventricular hypothalamic nucleus in the suppression of baroreceptor reflex response by locus ceruleus in the rat

We evaluated the potential participation of galanin (GAL) at the paraventricular nucleus of hypothalamus (PVN) in the suppression of baroreceptor reflex (BRR) response by locus ceruleus (LC), using adult male Sprague-Dawley rats anesthetized with pentobarbital sodium. Microinjection of GAL (100 pmol) bilaterally into the PVN significantly depressed the BRR response. This suppressive effect was appreciably antagonized when GAL (100 pmol) and GAL antiserum (1:20) were coadministered into the bilateral PVN. Whereas bilateral microinjection of GAL antiserum into the PVN by itself elicited minimal effect, it nevertheless significantly attenuated the suppressive effect of either electrical or chemical activation of LC on the BRR response. Pretreatment with the same amount of normal rabbit serum (1:20), on the other hand, was ineffective. These results suggest that a galaninergic projection from the LC to PVN may participate in the suppression of BRR response by this dorsal pontine nucleus.     

Neuropeptide Y: stimulation of feeding and drinking by injection into the paraventricular nucleus

Neuropeptide Y (NPY), a peptide contained within numerous presynaptic terminals in the hypothalamic paraventricular nucleus (PVN), was injected directly into the PVN of satiated, brain-cannulated rats, and food and water intake were measured 0.5, 1, 2 and 4 hrs postinjection. Neuropeptide Y (24 and 78 pmoles/0.3 microliter isotonic saline) caused a dose-dependent increase in food intake, as well as a small, dose-dependent increase in water intake. This effect on feeding occurred even when food was not presented until 4 hrs postinjection. To determine the behavioral specificity of this effect, the impact of PVN injection of NPY (78 pmoles) on various behaviors was observed. With food available, only feeding and drinking behavior were affected. No change in other behaviors, including grooming, rearing, sleeping, resting or different levels of activity, was observed. With food absent, NPY still elicited drinking, suggesting that this is a primary effect, rather than secondary to the feeding. In addition to drinking, NPY reliably increased activity while decreasing sleep and grooming. These results suggest an important role for hypothalamic NPY, or a structurally-related peptide, in the regulation of feeding and drinking behavior.     

Differential effects of central administration of relaxin‐3 on food intake and hypothalamic neuropeptides in male and female rats

Relaxin‐3 (RLN3) is an orexigenic neuropeptide that produces sex‐specific effects on food intake by stronger stimulation of feeding in female compared with male rats. This study determined which hypothalamic nuclei and associated neuropeptides may be involved in the sex‐specific orexigenic effects of RLN3. Relaxin‐3 (800 pmol) or vehicle was injected into the lateral ventricle of female and male rats. Food and water intake were measured after the first injection, and rats were euthanized after the second injection to determine the mRNA expression of the hypothalamic neuropeptides. Food but not water intake showed sex‐specific effects of RLN3. Stimulation of food intake by RLN3 was significantly higher in female than in male rats. No effect of RLN3 injection was found on c‐fos mRNA expression in the arcuate, dorsomedial and ventromedial hypothalamic nuclei. Increased c‐fos mRNA expression was observed in the paraventricular hypothalamic nucleus (PVN) in both sexes and in the lateral hypothalamic area (LHA) in female rats. Relaxin‐3 injections led to a sex‐nonspecific increase in the expression of oxytocin mRNA in the magnocellular PVN. Conversely, RLN3‐induced expression of anorexigenic neuropeptide arginine vasopressin (AVP) was significantly higher in the parvocellular PVN in male compared with female rats. Finally, RLN3 administration significantly increased the expression of orexin (ORX) mRNA in the LHA in female but not in male rats. Stronger expression of anorexigenic AVP in the PVN in male rats and increased expression of ORX in the LHA in female rats may contribute to stronger orexigenic effects of RLN3 in female rats compared with male rats.     

Ghrelin is an orexigenic and metabolic signaling peptide in the arcuate and paraventricular nuclei

Ghrelin is a 28-amino acid acylated peptide and is the endogenous ligand for the growth hormone secretagogue receptor (GHS-R). The GHS-R is expressed in hypothalamic nuclei, including the arcuate nucleus (Arc) where it is colocalized with neuropeptide Y (NPY) neurons. In the present study, we examined the effects of ghrelin on feeding and energy substrate utilization (respiratory quotient; RQ) following direct injections into either the arcuate or the paraventricular nucleus (PVN) of the hypothalamus. Ghrelin was administered at the beginning of the dark cycle at doses of 15-60 pmol to male and female rats. In feeding studies, food intake was measured 2 and 4 h postinjection. Separate groups of rats were injected with ghrelin, and the RQ (VCO(2)/VO(2)) was measured using an open circuit calorimeter over a 4-h period. Both Arc and PVN injections of ghrelin increased food intake in male and female rats. Ghrelin also increased RQ, reflecting a shift in energy substrate utilization in favor of carbohydrate oxidation. Because these effects are similar to those observed after PVN injection of NPY, we then assessed the impact of coinjecting ghrelin with NPY into the PVN. When rats were pretreated with very low doses of ghrelin (2.5-10 pmol), NPY's (50 pmol) effects on eating and RQ were potentiated. Overall, these data are in agreement with evidence suggesting that ghrelin functions as a gut-brain endocrine hormone implicated in the regulation of food intake and energy metabolism. Our findings are also consistent with a possible interactive role of hypothalamic ghrelin and NPY systems.     

Feeding inhibition by urocortin in the rat hypothalamic paraventricular nucleus

Ventricular administration of urocortin (UCN) inhibits feeding, but specific site(s) of UCN action are unknown. In the current studies we examined the effect of UCN in the hypothalamic paraventricular nucleus (PVN) on feeding. We tested UCN administered into the PVN in several paradigms: deprivation-induced, nocturnal, and neuropeptide Y (NPY)-induced feeding. We compared the effect of equimolar doses of UCN and corticotrophin releasing hormone (CRH) on NPY-induced and nocturnal feeding, determined whether UCN in the PVN produced a conditioned taste aversion (CTA) and induced changes in c-Fos immunoreactivity (c-Fos-ir) after UCN and NPY administration in the PVN. UCN in the PVN significantly decreased NPY and nocturnal and deprivation-induced feeding at doses of 1, 10, and 100 pmol, respectively. UCN anorectic effects lasted longer than those attributed to CRH. Ten and thirty picomoles UCN did not induce a CTA, whereas 100 pmol UCN produced a CTA. UCN (100 pmol) in the PVN neither increased c-Fos-ir in any brain region assayed nor altered c-Fos-ir patterns resulting from PVN NPY administration. These data suggest the hypothalamic PVN as a site of UCN action.     

Aqueduct Occlusion Does Not Impair Feeding Induced by Either Third or Fourth Ventricle Galanin Injection

Exogenous galanin stimulates feeding when injected into forebrain and hindbrain sites, including the third and fourth ventricles (3V and 4V), amygdala, paraventricular nucleus of the hypothalamus (PVN), and nucleus of the solitary tract (NTS). Because the PVN and NTS border the ventricular space, it is possible that feeding stimulated by injection of galanin at these sites may be caused by the transport of galanin through the ventricular system to a remote site of action. The role of ventricular transport of galanin between the 3V and 4V in galanin-induced feeding was examined in this study. Rats were implanted with two guide cannula assemblies: one dorsal to the mesencephalic aqueduct and the other in the 3V or 4V. Feeding in response to 3V or 4V galanin injection was first measured after sham-occlusion of the aqueduct. Subsequently, flow of cerebrospinal fluid between the forebrain and hindbrain ventricles was acutely interrupted by injection of a silicone grease plug into the mesencephalic aqueduct just before assessment of the feeding response to 4V or 3V galanin injection. Aqueduct occlusion did not alter the feeding induced by either 3V or 4V galanin injection, indicating that galanin terminals in both the diencephalon and hindbrain are involved in control of food intake.     

Brain-derived neurotrophic factor in the hypothalamic paraventricular nucleus increases energy expenditure by elevating metabolic rate

Brain-derived neurotrophic factor (BDNF) decreases food intake and body weight, but few central sites of action have been identified. The hypothalamic paraventricular nucleus (PVN) is important in energy metabolism regulation, and expresses both BDNF and its receptor. We tested three hypotheses: 1) PVN BDNF reduces feeding and increases energy expenditure (EE), 2) PVN BDNF-enhanced thermogenesis results from increased spontaneous physical activity (SPA) and resting metabolic rate (RMR), and 3) PVN BDNF thermogenic effects are mediated, in part, by uncoupling protein 1 (UCP1) in brown adipose tissue (BAT). BDNF (0.5 microg) was injected into the PVN of Sprague-Dawley rats; and oxygen consumption, carbon dioxide production, food intake, and SPA were measured for 24 h in an indirect calorimeter. SPA was also measured in open-field activity chambers for 48 h after BDNF injection. Animals were killed 6 or 24 h after BDNF injection, and BAT UCP1 gene expression was measured with quantitative real-time PCR. BDNF significantly decreased food intake and body weight gain 24 h after injection. Heat production and RMR were significantly elevated for 7 h immediately after BDNF injection. BDNF had no effect on SPA, but increased UCP1 gene expression in BAT at 6 h, but not 24 h after injection. In conclusion, PVN BDNF reduces body weight by decreasing food intake and increasing EE consequent to increased RMR, which may be due, in part, to BAT UCP1 activity. These data suggest that the PVN is an important site of BDNF action to influence energy balance.     

Ghrelin microinjection into forebrain sites induces wakefulness and feeding in rats

Ghrelin, a gut-brain peptide, is best known for its role in the stimulation of feeding and growth hormone release. In the brain, orexin, neuropeptide Y (NPY), and ghrelin are parts of a food intake regulatory circuit. Orexin and NPY are also implicated in maintaining wakefulness. Previous experiments in our laboratory revealed that intracerebroventricular injections of ghrelin induce wakefulness in rats. To further elucidate the possible role of ghrelin in the regulation of arousal, we studied the effects of microinjections of ghrelin into hypothalamic sites, which are implicated in the regulation of feeding and sleep, such as the lateral hypothalamus (LH), medial preoptic area (MPA), and paraventricular nucleus (PVN) on sleep in rats. Sleep responses, motor activity, and food intake after central administration of 0.04, 0.2, or 1 mug (12, 60, or 300 pmol) ghrelin were recorded. Microinjections of ghrelin into the LH had strong wakefulness-promoting effects lasting for 2 h. Wakefulness was also stimulated by ghrelin injection into the MPA and PVN; the effects were confined to the first hour after the injection. Ghrelin's non-rapid-eye-movement sleep-suppressive effect was accompanied by attenuation in the electroencephalographic (EEG) slow-wave activity and changes in the EEG power spectrum. Food consumption was significantly stimulated after microinjections of ghrelin into each hypothalamic site. Together, these results are consistent with the hypothesis that forebrain ghrelinergic mechanisms play a role in the regulation of vigilance, possibly through activating the components of the food intake- and arousal-promoting network formed by orexin and NPY.     

Osmotic regulation of substance P and neurokinin A peptide content and substance P binding sites in distinct hypothalamic nuclei of the rat.

Quantitative receptor autoradiography using Bolton-Hunter iodinated substance P (SP) was used to localize specific sites in the rat hypothalamus. The amount of SP and neurokinin A (NkA) in extracts from discrete areas of the hypothalamus was measured using specific radioimmunoassays. A high density of SP binding sites was observed in the perimeter of the magnocellular paraventricular and supraoptic nuclei, while the magnocellular nuclei themselves possessed a low receptor density. In control animals, the number of SP binding sites was also low in the arcuate nucleus and the median eminence. Substance P and NkA peptide concentrations were highest in the paraventricular nucleus (PVN), decreasing in the following order: arcuate nucleus (Arc) greater than median eminence (ME) greater than supraoptic nucleus (SON) greater than subfornical organ (SFO). In animals given 340 mmol/l NaCl instead of tap water to drink for 12 days, significant increases in the number of SP binding sites occurred in the medial parvocellular subdivision of the PVN, periamygdaloid cortex, medial preoptic nucleus, Arc, and ME, but other hypothalamic areas were unaffected. In saline-treated animals, significant increases in SP and NkA peptide concentrations were observed in the ME, while in the SFO only the concentration of NkA increased significantly. In the SON, substance P and neurokinin A levels were doubled, whereas in the PVN and Arc no changes in peptide levels were observed. Chronic osmotic stimulation is associated with lowered circulating levels of adrenocorticotropin releasing hormone (ACTH), and the present data further substantiate the hypothesis that hypothalamic tachykinin-containing neuronal terminals are centrally involved in the inhibition of anterior pituitary ACTH release observed during chronic osmotic stimulation.