Microinjection of galanin-like peptide into the medial preoptic area stimulates food intake in adult male rats

Galanin-like peptide (GALP) is a neuropeptide implicated in the regulation of feeding behaviour, metabolism and reproduction. GALP is an endogenous ligand of the galanin receptors, which are widely expressed in the hypothalamus. GALP is predominantly expressed in arcuate nucleus (ARC) neurones, which project to the paraventricular nucleus (PVN) and medial preoptic area (mPOA). Intracerebroventricular or intraparaventricular (iPVN) injection of GALP acutely increases food intake in rats. The effect of GALP injection into the mPOA on feeding behaviour has not previously been studied. In the present study, intra-mPOA (imPOA) injection of GALP potently increased 0-1-h food intake in rats. The dose-response effect of imPOA GALP administration on food intake was similar to that previously observed following iPVN administration. The effects of GALP (1 nmol) or galanin (1 nmol) on food intake were then compared following injection into the PVN, mPOA, ARC, dorsal medial nucleus (DMN), lateral hypothalamus and rostral preoptic area (rPOA). GALP (1 nmol) increased food intake to a similar degree when injected into the imPOA or iPVN, but produced no significant effect when injected into the ARC, DMN, lateral hypothalamus or rPOA. Similarly, galanin (1 nmol) significantly increased food intake following injection imPOA and iPVN. However, the effect was significantly smaller than that following administration of GALP (1 nmol). Galanin also had no significant effect on food intake when administered into the ARC, DMN, lateral hypothalamus and rPOA. These data suggest that the mPOA and the PVN may have specific roles in mediating the orexigenic effect of GALP and galanin.     

Changes in Feeding Activity, Plasma Luteinizing Hormone, and Testes Weight in Ring Doves Following Hypothalamic Injections of Prolactin

Microinjections of ovine prolactin were administered unilaterally to the ventromedial hypothalamic nucleus and the preoptic-suprachiasmatic region in adult male ring doves in an attempt to determine the site(s) at which intracranial injections of prolactin act to alter feeding behaviour and gonadotropin secretion in this species. Food intake and body weight were measured daily during a 6-day pretreatment period and the 5-day treatment period that immediately followed. During the treatment period, birds received twice daily injections (0.5 μl) of either 2.5 ng ovine prolactin or saline vehicle. An additional group of birds with cannulae in the ventromedial nucleus were given twice daily injections of 25 ng ovine prolactin. Although food consumption was unaffected by low dose prolactin treatment, birds given 25 ng prolactin injections into the ventromedial nucleus showed a significant augmentation in food intake. Injections of 25 ng prolactin into the preoptic area also increased feeding; however, the magnitude of this hyperphagic response, as expressed relative to pretreatment levels, was less than that observed following prolactin injection into the ventromedial nucleus. No differences were observed between prolactin-treated and vehicle-treated birds in either cannulation group when testes weights and plasma luteinizing hormone concentrations were compared at the end of the treatment period. However, the possibility that prolactin influenced changes in luteinizing hormone and testes weight relative to baseline values could not be assessed due to constraints imposed by the experimental paradigm used. These results suggest that prolactin-sensitive neurons in the ventromedial hypothalamic region and the preoptic area are potential sites of prolactin action in promoting hyperphagia in ring doves. However, the role of these sites in mediating prolactin-induced suppression of gonadotropin secretion in this species remains to be clarified.     

Neuropeptide-Y: a possible mediator of prolactin-induced feeding and regulator of energy balance in the ring dove (Streptopelia risoria)

Although neuropeptide-Y (NPY) has been widely reported to be a potent stimulator of feeding activity and regulator of energy homeostasis, most of the supportive evidence for such effects has been gathered in mammalian species. This study characterized the orexigenic potency of NPY in an avian species, the ring dove, and measured changes in hypothalamic NPY-immunoreactive (NPY-ir) cell numbers in response to energy state fluctuations or intracranial administration of the potent orexigenic hormone prolactin. Food intake was significantly elevated in male doves at 1 h after intracerebroventricular (i.c.v.) injection of 0.25 and 0.5 microg NPY but not after injection of a higher dose (1.0 microg). In time course studies, food intake was increased at 1 h after i.c.v. injection of 0.5 microg NPY but was not elevated at 2, 3, or 4 h. The number of NPY-ir cell bodies in the infundibular region of the dove hypothalamus increased two to four-fold following acute food deprivation, chronic food restriction, or repeated i.c.v. injections of prolactin. No additive effects were observed when food restriction and prolactin treatment were combined. These findings suggest that NPY is involved in energy homeostasis in doves and are consistent with the hypothesis that prolactin-induced hyperphagia is mediated in part by NPY.     

Changes in agouti-related peptide during the ring dove breeding cycle in relation to prolactin and parental hyperphagia

Ring doves (Streptopelia risoria) exhibit marked increases in food consumption and decreases in body weight when they are provisioning their young. This study examined changes in hypothalamic immunostaining for agouti-related peptide (AGRP), an endogenous melanocortin receptor antagonist and appetite stimulant, during the ring dove breeding cycle. Because prolactin is orexigenic in doves, and is elevated in blood at the onset of parental hyperphagia, we also explored the possibility that prolactin-induced hyperphagia is associated with AGRP changes. The numbers of AGRP-immunoreactive (ir) cells within the tuberal hypothalamus were maximal during the prelaying period of the breeding cycle but decreased dramatically during early incubation. AGRP-ir cell numbers began to increase again during late incubation and reached a peak during the early and late posthatching stages. Because posthatching elevations in AGRP-ir were temporally associated with marked elevations in parental food intake, and because AGRP is orexigenic in doves, these findings suggest that increased AGRP activity in the dove tuberal hypothalamus may contribute to parental hyperphagia. Rising prolactin secretion during late incubation and early posthatching may initiate this increase in AGRP-ir, since intracerebroventricular administration of prolactin significantly elevated food intake and AGRP-ir cell numbers in the tuberal hypothalamus of nonbreeding doves. Prolactin-induced elevations in AGRP-ir cell numbers persisted when the confounding effects of weight gain that accompany prolactin-induced hyperphagia in nonbreeding doves were eliminated by a food restriction procedure, thereby suggesting that prolactin can directly influence AGRP activity under neutral energy state conditions.     

Long-term reorganization of afferents to the mediobasal hypothalamus following retrochiasmatic knife cuts. A study using horseradish peroxidase

Retrochiasmatic knife cuts produce a series of dynamic changes across time in the luteinizing hormone-releasing hormone and catecholamine content of the mediobasal hypothalamus (MBH). We have examined the sources of afferents projecting to the mediobasal hypothalamus of female rats at 7, 60 and 90 days following retrochiasmatic frontal cut (FC) surgery using the intra-axonal retrograde transport of horseradish peroxidase (HRP) in order to better define the functional plasticity demonstrated by the MBH at these time periods after damage. Age-matched, previously unoperated, female rats served as controls. Small HRP injections placed in the ventromedial nucleus (VMN) in control animals labelled neurons within the VMN, dorsomedial nucleus (DMN) and lateral hypothalamic area (LHA). Larger injections also labelled neurons in the anterior hypothalamic area (AHA), preoptic area (POA), septal nuclei, periventricular nuclei (PVN), supraoptic nucleus (SON), zona incerta (ZI) and suprachiasmatic nucleus (Schn). Seven days after surgery, no labelled neurons could be detected rostral to the knife cut when the injection site was confined to the boundary of the glial scar. At 60 days, labelled soma were observed in LPOA, POA, AHA, PVN, SON and ZI. At 90 days only the SON contained labelled neurons rostral to the knife cut. These results suggest a dynamically changing pattern of innervation to the MBH following damage.     

Neuropeptide Y (NDY) Y1 Receptoe mRNA is Upregulated in Association with Transient Hyperphagia and Body Weight Gain: Evidence for a Hypothalamic Site for Concurrent Development of Leptin Resistance

Microinjection of colchicine (COL), a neurotoxin that blocks axoplasmic flow in the neurons, bilaterally into the ventromedial nucleus (VMN) evokes transient hyperphagia and body weight gain. These shifts in energy balance occurred in conjunction with development of increased sensitivity to neuropeptide Y (NPY), the endogenous orexigenic signal. In order to trace the aetiology of NPY supersensitivity, we have evaluated (1) NPY Y1 and Y5 receptor (R) gene expression in the hypothalamus and (2) the possibility of alterations in the inhibitory action of leptin, a hormone produced by lipocytes. Adult male rats were rendered hyperphagic with bilateral microinjections of COL (4 μg/side) into the VMN. We observed that hypothalamic NPY Y1 mRNA levels, as measured by RNAase protection assay, were significantly increased on day 2 and returned to the control level on day 4 in COL-injected rats. The effects on NPY Y5R mRNA were not as clear cut. Interestingly, serum leptin levels increased in association with the hyperphagia and body weight gain, thereby raising the likelihood of development of resistance to the suppressive effect of endogenous leptin on food intake. Indeed, intracerebroventricular injection of 7 μg human recombinant leptin, a dose that attenuated daily food intake in normal and fasted rats, was completely ineffective in attenuating hyperphagia in COL-treated rats. These results show that transient hyperphagia induced by interruption of signalling in the VMN may be caused by increased sensitivity to NPY, which may be caused, in part, by increased expression of NPY Y1R in hypothalamic sites involved in regulation of ingestive behaviour. Additionally, the observation of increased leptin release and concurrent development of leptin resistance suggest that a normally functioning VMN may be necessary for the central inhibitory effects of leptin on food 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.     

Lateral hypothalamic injection of bombesin decreases food intake in rats

STUCKEY, J. A. AND J. GIBBS. Lateral hypothalamic injection of bombesin decreases food intake in rats. BRAIN RES. BULL. 8(6)617–621, 1982.—The effect of lateral hypothalamic injections of bombesin on feeding behavior was examined. Rats equipped with stainless steel cannulas directed toward the lateral hypothalamus received bilateral injections of bombesin prior to access to a liquid test diet after a 3 hr food deprivation. Bombesin in doses of 5 ng, 50 ng and 100 ng produced significant reductions in the size of the first meal. Injection of 50 ng of the biologically weak analogue [D-Trp⁸] bombesin had no effect. Injection of 5 ng or 50 ng of bombesin had no effect on deprivation-induced water intake, and injection of 50 ng of bombesin had no effect on body temperature. The food and water intake data and direct quantitative behavioral measures indicated that lateral hypothalamic injections of bombesin specifically reduced food intake. The structure-activity relationship for this effect was similar to those for other actions of bombesin. A bombesin-like peptide in the lateral hypothalamus or its receptors may play a role in postprandial satiety.     

Role of Oestrogen α Receptors in Sociosexual Behaviour in Female Rats Housed in a Seminatural Environment

The present study investigated the role of oestrogen receptor (ER)α in the ventromedial nucleus of the hypothalamus (VMN), the preoptic area (POA), the medial amygdala (MePD) and the bed nucleus of stria terminalis (BNST) in sociosexual behaviour in female rats. This was conducted in two sets of experiments, with the VMN and POA investigated in the first set, and the MePD and BNST in the second set. The VMN and POA received intense projections from the MePD and BNST. We used a short hairpin RNA encoded within an adeno‐associated viral vector directed against the gene for ERα to reduce the number of ERα in the VMN or POA (first set of experiments) or in the BNST or MePD (second set of experiments) in female rats. The rats were housed in groups of four ovariectomised females and three males in a seminatural environment for 8 days. Compared with traditional test set‐ups, the seminatural environment provides an arena in which the rats can express their full behavioural repertoire, which allowed us to investigate multiple aspects of social and sexual behaviour in groups of rats. Behavioural observation was performed after oestrogen and progesterone injections. A reduction of ERα expression in the VMN or POA diminished the display of paracopulatory behaviours and lordosis responses compared to controls, whereas the lordosis quotient remained unaffected. This suggests that ERα in the VMN and POA play an important role in intrinsic sexual motivation. The reduction in ERα did not affect the social behaviour of the females, although the males sniffed and pursued the females with reduced ERα less than the controls. This suggests that the ERα in the VMN and POA is involved in the regulation of sexual attractiveness of females. The ERα in the MePD and BNST, on the other hand, plays no role in sociosexual behaviour.     

Short-term anorexigenic effects of central neuropeptide VF are associated with hypothalamic changes in chicks

The present study was designed to measure food and water intake, changes in hypothalamic chemistry, and other behaviour modifications after central injection of neuropeptide (NP) VF in broiler type chicks. In Experiment 1, chicks responded to central NPVF with a reduction in food intake for up to 90 min post injection. Water intake was unaffected. In Experiment 2, NPVF exerted a less potent and shorter duration of attenuated food intake than did the structurally related NPFF. In Experiment 3, 16.0 nmol NPVF reversed the prolactin-releasing peptide induced orexigenic effect. In Experiment 4, central NPVF treatment was associated with decreased c-Fos immunoreactivity in the lateral hypothalamus, whereas c-Fos immunoreactivity in the dorsomedial nucleus, infundibular nucleus (homologue to the mammalian arcuate nucleus) and ventromedial nucleus was increased. In Experiment 5, behaviours unrelated to ingestion including sit, stand, deep rest and locomotion were affected by central NPVF injection. Some of these behaviours are incompatible with ingestion and may contribute to hypothalamic associated perception of satiety after central NPVF. In conclusion, NVPF is a short-term regulator of appetite and its effects are associated with hypothalamic and behaviour changes in chicks.     

Neuroanatomical specificity of prolactin-induced hyperphagia in virgin female rats

Intracerebroventricular (i.c.v.) administration of PRL increases food intake in virgin female rats but the brain site(s) at which PRL acts to promote feeding behavior is not known. The present studies investigated the role of the paraventricular nucleus (PVN), ventromedial nucleus (VMH), and medial preoptic nucleus (MPOA) in the hyperphagic actions of PRL. Ad-libitum-fed virgin female rats received twice daily site-specific injections of PRL (800 ng) over a period of 10 days. Only subjects demonstrating regular vaginal cyclicity were included in the study. Food intake, body weight, and vaginal cyclicity were measured daily. Results showed that PRL significantly increased food intake when injected into the PVN. A nonsignificant trend towards a hyperphagic response in the last 5 days of testing was observed in rats receiving intra-VMH injections of PRL, and the MPOA was not responsive to the feeding-stimulating properties of PRL. None of the manipulations affected body weight or vaginal cyclicity as demonstrated by vaginal smears. In sum, the present results reveal that one brain site at which PRL acts to increase food intake is the PVN, but these studies do not rule out the possibility that the effects of PRL on food intake may also involve other brain areas.     

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.     

Responses to cholecystokinin in the ventromedial nucleus of the rat hypothalamus in vivo

The peptide cholecystokinin (CCK) is a short‐term satiety signal released from the gastrointestinal tract during food intake. From the periphery, CCK signalling travels via the vagus nerve to reach the brainstem from which it is relayed higher into the brain. The hypothalamus is a key integrator of appetite‐related stimuli and the ventromedial nucleus of the hypothalamus (VMN) is thought to have an important role in the regulation of satiety. We investigated the effect of intravenous injections of CCK on the spontaneous firing activity of single VMN neurons in urethane‐anaesthetised rats in vivo. We found that the predominant effect of CCK on the electrical activity in the VMN is inhibitory. We analysed the responses to CCK according to electrophysiologically distinct subpopulations of VMN neurons and found that four of these VMN subpopulations were inhibited by CCK, while five were not significantly affected. Finally, CCK‐induced inhibitory response in VMN neurons was not altered by pre‐administration of intravenous leptin.     

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.     

The role of the melanocortin system and the melanocortin-4 receptor in ring dove (Streptopelia risoria) feeding behavior

The melanocortin-4 receptor (MC4-R) is an important mediator of the effects of two melanocortin system ligands, alpha melanocyte stimulating hormone (-MSH) and agouti-related peptide (AGRP), on feeding behavior and energy balance in mammals. Although an avian homologue of the mammalian MC4-R has recently been identified, there is little information on the role of this receptor and the melanocortin system in avian feeding and body weight regulation. In these studies, we measured changes in feeding behavior in ring doves (Streptopelia risoria) following intracerebroventricular (i.c.v.) injection of various melanocortin receptor agonists and antagonists. The selective MC4-R antagonist HS014 elevated food intake within 4 h at all three doses tested (0.02, 0.2, and 2 nmol). A 1 nmol dose of the endogenous antagonist AGRP also stimulated feeding but only after a post-injection interval of 10 h. Surprisingly, the MC3-R and MC4-R antagonist SHU9119 not only failed to stimulate food intake at the same doses as HS014, but actually inhibited food intake at 8 h after injection. Whether this was due to toxicity effects or differences in the pharmacology of avian and mammalian melanocortin receptors remains to be determined. Food-deprived doves showed a fourfold increase in the number of AGRP-immunoreactive cells in the tuberal region of the hypothalamus and 5 ng of the MC3-R and MC4-R agonist MTII significantly attenuated the amount of food consumed by food-deprived birds that were allowed to re-feed. These data support a role for the melanocortin system and the melanocortin-4 receptor in the ring dove feeding behavior.     

Exogenous prolactin-releasing peptide's orexigenic effect is associated with hypothalamic neuropeptide Y in chicks

Exogenous administration of prolactin-releasing peptide (PrRP) exerts anorexigenic effects in rats while causing orexigenic effects in chicks. While the central mechanism mediating PrRP's effect on food intake in rodents is somewhat understood, in chicks information is lacking. Therefore, this study was designed to elucidate the hypothalamic mechanism of PrRP induction of hunger perception in chicks. Chicks that received intracerebroventricular (ICV) injections of PrRP dose-dependently increased their food intake with no effect on water intake or whole blood glucose concentration. The threshold of food intake stimulation was as low as 3 pmol, thus as compared to other neuropeptides PrRP is exceptionally potent. The mRNA abundance of several appetite-associated neuropeptide genes was quantified and hypothalamic neuropeptide Y (NPY) mRNA was increased in PrRP-injected chicks. Therefore, the orexigenic effects of PrRP may be associated with increased NPY-ergic tone. These results provide insight into the evolutionary aspects of appetite regulation during the course of divergent evolution of mammals and birds.     

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.     

A comparison of the effects of the 5-HT1 agonists TFMPP and RU 24969 on feeding following peripheral or medial hypothalamic injection

Experiments were conducted to compare the food intake suppressant effects of the 5-hydroxytryptamine (5-HT)₁ agonists 1-3-trifluoro-methylphenylpiperazine hydrochloride (TFMPP) and 5-methoxy-3-(1,2,3,6-tetrahydropyridinyl)1H indole (RU 24969) following either peripheral or medial hypothalamic injections. The effects of these manipulations were examined in 3 different paradigms involving the stimulation of feeding by: (1) infusion of 25 nmol noradrenaline (NA) into the medial hypothalamus, (2) adaptation to a 20 h food deprivation schedule, and (3) the presentation of a palatable wet mash diet for 1 h each day to ad libitum-fed rats. In all 3 paradigms TFMPP and RU 24969 (0.31–5 mg/kg, i.p.) induced dose-dependent reductions of food intake. Both drugs were somewhat less potent at inhibiting feeding that resulted from food deprivation. In contrast to these results medial hypothalamic infusion of TFMPP or RU 24969 (12.5–50 nmol) failed to affect food intake in any of the 3 tests. This occured in spite of the fact that both 5-HT (12.5–50 nmol) and fluoxetine (12.5–50 nmol) mildly attenuated the feeding that resulted from NA infusion into the same site. The results provide clear evidence that the food intake suppressant effects of peripherally injected TFMPP and RU 24969 are not mediated in the medial hypothalamus. They also suggest that even though manipulations of serotonergic function within the medial hypothalamus can alter food intake, this probably does not involve selective activation of 5-HT_1C and/or 5-HT_1B receptors.