Effects of fibroblast growth factors and platelet-derived growth factor on food intake in rats

In the present study, the relations between acidic and basic fibroblast growth factors (aFGF and bFGF, respectively), platelet-derived growth factor (PDGF), and food intake were studied. When aFGF-, bFGF-, and PDGF-like activity in cerebrospinal fluid (CSF) was examined by bioassay, the activity of those factors significantly increased in postfeeding CSF, compared to prefeeding CSF. Injections of aFGF, bFGF, aFGF (synthetic amino-terminal peptide of aFGF), and PDGF into the third cerebral ventricle decreased food intake, and injections of anti-aFGF, anti-bFGF, and anti-aFGF antibodies into the lateral hypothalamus (LHA) increased food intake. The activity of LHA glucose-sensitive neurons was inhibited by electrophoretic application of aFGF. These results suggest that aFGF, bFGF and PDGF have in vivo physiological roles in the central nervous system, distinct from those as mitogens.     

Effects of various N-terminal fragments of glucagon-like peptide-1(7–36) on food intake in the neonatal chick

Recently, the suppressive effect on food intake by the central administration of glucagon-like peptide-1 (GLP-1) has been confirmed in both rats and chicks. The importance of the N-terminal amino acid, histidine, for the bioactivity of GLP-1(7–36) in the central nervous system was suggested, though the role for C-terminal amino acids in the central nervous system has not been reported. The present study was done to elucidate the central effect of N-terminal fragments of GLP-1(7–36) on food intake of the neonatal chick. Intracerebroventricular (i.c.v.) administration of mammalian GLP-1(7–36) inhibited food intake of chicks, but the fragments of GLP-1(7–16) and GLP-1(7–26) did not show the suppressive effect on food intake. Furthermore, the extended fragments, GLP-1(7–30) and GLP-1(7–33), also had no effects on food intake. It is concluded that C-terminal amino acids of GLP-1(7–36) have an important role for the bioactivity in the central nervous system with special reference to feeding behavior.     

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.     

Intracerebroventricular injection of exendin (5–39) increases food intake of layer-type chicks but not broiler chicks

To clarify the involvement of endogenous glucagon-like peptide-1 (GLP-1) on feeding in chicks, we examined the central effect of GLP-1 antagonist, exendin (5–39) on food intake. Intracerebroventricular co-injection of exendin (5–39) with GLP-1 attenuated the anorexigenic effect of GLP-1 in layer-type chicks. Furthermore, exendin (5–39) enhanced food intake of layer-type chicks under ad libitum feeding. However, this effect was not observed in broiler chicks. Therefore, endogenous GLP-1 may be important in the regulation of feeding in layer-type chicks but not in broiler chicks.     

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.     

Increased binding at 5-HT1A, 5-HT1B, and 5-HT2A receptors and 5-HT transporters in diet-induced obese rats

5-Hydroxytryptamine (5-HT, serotonin), synthesized in midbrain raphe nuclei and released in various hypothalamic sites, decreases food intake but the specific 5-HT receptor subtypes involved are controversial. Here, we have studied changes in the regional density of binding to 5-HT receptors and transporters and the levels of tryptophan hydroxylase, in rats with obesity induced by feeding a palatable high-energy diet for 7 weeks. We mapped binding at 5-HT receptor subtypes and transporters using quantitative autoradiography and determined tryptophan hydroxylase protein levels by Western blotting. In diet-induced obese (DiO) rats, specific binding to 5-HT_1A receptors ([³H]8-OH-DPAT) was significantly increased in the dorsal and median raphe by 90% (P<0.01) and 132% (P<0.05), respectively, compared with chow-fed controls. 5-HT_1B receptor binding sites ([¹²⁵I]cyanopindolol) were significantly increased in the hypothalamic arcuate nucleus (ARC) of DiO rats (58%; P<0.05), as were 5-HT_2A receptor binding sites ([³H]ketanserin) in both the ARC (44%; P<0.05) and lateral hypothalamic area (LHA) (121%; P<0.05). However, binding to 5-HT_2C receptors ([³H]mesulgergine) in DiO rats was not significantly different from that in controls in any hypothalamic region. Binding to 5-HT transporters ([³H]paroxetine) was significantly increased (P<0.05) in both dorsal and median raphe, paraventricular nuclei (PVN), ventromedial nuclei (VMH), anterior hypothalamic area (AHA) and LHA of DiO rats, by 47%–165%. Tryptophan hydroxylase protein levels in the raphe nuclei were not significantly different between controls and DiO rats. In conclusion, we have demonstrated regionally specific changes in binding to certain 5-HT receptor subtypes in obesity induced by voluntary overeating of a palatable diet. Overall, these changes are consistent with reduced 5-HT release and decreased activity of the 5-HT neurons. Reduction in the hypophagic action of 5-HT, possibly acting at 5-HT_1A, 5-HT_1B and 5-HT_2A receptors, may contribute to increased appetite in rats presented with highly palatable diet.     

Anorexic action of a new potential neuropeptide Y antagonist [ -Tyr, -Thr]-NPY (27–36) infused into the hypothalamus of the rat

Neuropeptide Y (NPY) produces a vigorous feeding response in several species when it is injected into hypothalamic structures involved in eating behavior. The purpose of this study was to determine whether a unique carboxy terminal fragment of NPY would alter the pattern of eating induced in the rat either by NPY injected into the hypothalamus or by a 24-h period of food deprivation. In this case, two -tyrosine residues and one t.-threonine residue of the NPY_27–36 fragment were transformed to their D-conformation to produce [ -Tyr^27,36, -Thr³²]-NPY (27–36), i.e., D-NPY_27–36. Guide cannulae for microinjection were implanted stereotaxically just dorsal to the paraventricular nucleus (PVN) or ventromedial hypothalamus (VMH) of 24 adult male Sprague-Dawley rats. Following postoperative recovery, a microinjection of artificial CSF or 1.1 jig or 3.3 μg of a peptide was made directly into the PVN or VMH as follows; native NPY; D-NPY_27–36; or [L-Tyr^27,36 L-Thr³²]-NPY (27–36), i.e., L-NPY_27–36. Food intakes were measured at intervals of 0.25, 0.5, 1.1, 2.0, 4.0, and 24 h. When D-NPY_27–36 was microinjected at NPY reactive sites in the PVN or VMH of the rat 15 min before a similar microinjection of NPY, the intense eating response induced by the peptide was reduced significantly. Not only was the effect dose dependent, but D-NPY_27–36 also augmented the latency to feed. A mixture of the two doses of NPY and DNPY_27–36 injected at the same hypothalamic loci did not attenuate the intake of food but tended to enhance the feeding response in the rats. After the rats were deprived of food for 24 h, D-NPY_27–36 microinjected in the same hypothalamic sites similarly caused a dose-dependent suppression of normal feeding behavior. However, the CSF control vehicle and L-NPY_27–36 microinjected in the PVN or VMH were without effect on the pattern of eating. Further, D-NPY_27–38 injected in the same hypothalamic sites affected neither body temperature nor water intakes of the rats significantly. These results demonstrate that the D substitution of this C-fragment of the NPY molecule, i.e., D-NPY_27–36, serves to inhibit feeding evoked in the rat by hypothalamic NPY as well as the natural eating response to food deprivation. Thus, the D-NPY_27–36 molecule may act as an antagonist at one or more subtypes of the NPY receptor in the brain of the rat.     

Excitatory amino acid receptor subtype agonists induce feeding in the nucleus accumbens shell in rats: opioid antagonist actions and interactions with μ-opioid agonists

Administration of μ-opioid receptor subtype agonists into the nucleus accumbens shell elicits feeding which is dependent upon the normal function of μ-, δ- and κ-opioid receptors, D₁ dopamine receptors and GABA_B receptors in the nucleus accumbens shell for its full expression. Whereas the AMPA antagonist, DNQX administered into the nucleus accumbens shell elicits a transient, though intense feeding response, feeding is elicited by excitatory amino acid agonists administered into the lateral hypothalamus. The present study examined whether excitatory amino acid agonists elicited feeding following administration into the nucleus accumbens shell of rats, whether such feeding responses were altered by opioid antagonist pretreatment, and whether such feeding responses interacted with feeding elicited by μ-opioid agonists. Both AMPA (0.25–0.5 μg) and NMDA (1 μg) in the nucleus accumbens shell significantly and dose-dependently increased food intake over 4 h. Both feeding responses were blocked by naltrexone pretreatment in the nucleus accumbens shell. The μ-opioid agonist, [D-Ala²,NMe-Phe⁴,Gly-ol⁵]-enkephalin in the nucleus accumbens shell significantly increased food intake which was significantly enhanced by AMPA cotreatment. This enhanced feeding response was in turn blocked by pretreatment with either general or μ-selective opioid antagonists. In contrast, cotreatment of NMDA and the μ-opioid agonist in the nucleus accumbens shell elicited feeding which was significantly less than that elicited by either treatment alone. These data indicate the presence of important interactions between excitatory amino acid receptors and μ-opioid receptors in the nucleus accumbens shell in mediating feeding responses in nondeprived, ad libitum-fed rats.     

Different central opioid receptor subtype antagonists modify maltose dextrin and deprivation-induced water intake in sham feeding and sham drinking rats

Different central opioid receptor subtypes participate in the mediation of intakes of simple (sucrose: μ, κ₁ and complex (maltose dextrin: μ) carbohydrates as well as deprivation-induced water intake (μ) under real-feeding and real-drinking conditions. An identical pattern of μ and κ₁ mediation of sucrose intake was observed in sham-feeding rats as well, suggesting their actions on orosensory mechanisms supporting sucose intake. The present study examined whether centrally administered general (naltrexone: 1–50 μg), μ (β-funaltrexamine: 1–20 μg), μ₁ (naloxonazine: 50 μg), κ₁ (nor-binaltorphamine: 1–20 μg), δ₁ ([d-Ala², Leu⁵, Cys⁶]-enkephalin: 10–40 μg) or δ₂2 (naltrindole isothiocyanate: 20 μg) opioid subtype antagonists altered either maltose dextrin (10%) intake during sham feeding or deprivation (24 h)-induced water intake during sham drinking in rats with gastric fistulas. Sham feeding significantly increased maltose dextrin intake (180%) and sham drinking significantly increased deprivation-induced water intake (256%) over a 60 min time course. Naltrexone significantly and dose-dependently reduced maltose dextrin intake (78%) in sham feeding rats, and deprivation-induced water intake (51%) in sham drinking rats. Maltose dextrin intake in sham feeding rats was significantly reduced by either κ₁ (69%) or δ₁ (59%) opioid antagonism, was significantly increased by μ₁ antagonism (43%), and was not significantly affected by either μ or δ₂ opioid antagonism. Deprivation-induced water intake in sham drinking rats was significantly reduced by either μ (41%), μ₁ (28%), δ₁ (48%) or δ₈ (28%) opioid antagonism, but was not significantly affected by κ₁ opioid antagonism. The difference in opioid receptor subtype mediation of maltose dextrin intake in real feeding and sham feeding conditions suggest that κ₁ and δ₁ receptors are involved in the orosensory mechanisms supporting maltose dextrin intake, while μ receptors are involved in the ingestive and post-ingestive mechanisms supporting maltose dextrin intake. The different patterns of opioid involvement in sucrose and maltose dextrin intake in sham feeding and real feeding conditions provide further support for the hypothesis that at least two different carbohydrate taste systems exist. The difference in opioid receptor subtype mediation of deprivation-induced water intake in real drinking and sham drinking conditions may reflect the removal in the sham drinking condition of a μ-mediated prerestorative satiety mechanism, and the unmasking of other opioid-mediated signalling mechanisms.     

Aminoglucose-induced feeding suppression is regulated by hypothalamic neuronal histamine in rats

Central mechanisms involved in feeding suppression produced by 1-deoxy-d-glucosamine (1-DGlcN) and1-deoxy-N-acetylglucosamine (1- DGlcNAc) are unclear. To clarify the mechanisms, we investigated the role of hypothalamic neuronal histamine (HA) in feeding suppression induced by 1-DGlcN and 1-DGlcNAc in rats. Food intake was suppressed for 3 days after a single infusion of 24 μmol 1-DGlcN into the third cerebroventricle (i.c.v.) Depletion of presynaptic HA due to intraperitoneal infusion (i.p.) of α-fluoromethylhistidine (FMH), a specific inhibitor of the HA synthesizing enzyme histidine decar☐ylase (HDC), abolished feeding suppression completely. Blockade of postsynaptic H₁-receptors by i.p. injection of 26 μmol chlorpheniramine also abolished the suppression. Oral administration of 2.4 mmol 1-DGlcNAc suppressed food intake. However, depletion of neuronal HA due to FMH did not affect the suppression. I.c.v. infusion of 24 μmol 1-DGlcN increased turnover rate of HA at 1 h after the infusion. Hypothalamic HA concentration, but not that of tele-methylhistamine (t-MH), increased at 24 h after i.c.v. infusion of 1-DGlcN, which suggests a correlation between HA concentration and the behavioral response. These results indicate that 1-DGlcN, but not 1-DGlcNAc, modulates feeding suppression through HA neurons in the hypothalamus. Differences in mechanisms of feeding suppression by these aminoglucoses may depend on the principal sites of acton in the brain and/or peripheral organs.     

The orexinergic neural pathway from the lateral hypothalamus to the nucleus accumbens and its regulation of palatable food intake

ObjectiveTo explore the orexinergic pathway from the lateral hypothalamus (LHA) to the nucleus accumbens (NAc) and its regulation on the palatable food intake.MethodsFluorescent gold retrograde tracing combined with fluoro-immunohistochemical staining were used to observe the projection of orexinergic neurons from LHA to NAc. The orexin-A expression in LHA and c-Fos in NAc were studied after electrical stimulation of LHA. The firing rates of neurons were monitored by single-unit extracellular electric discharge recording and the palatable food intake were measured after orexin microinjection in NAc or electrical stimulation of LHA.Results(1) Fluorescent gold retrograde tracing combined with fluoro-immunohistochemical staining showed some orexinergic neural projection from the LHA to the NAc shell. (2) Electrical stimulation of LHA significantly enhanced the expression of orexin-A in LHA and the expression of c-Fos in NAc (P < .05). (3) The results of single-unit extracellular discharge recording showed that the microinjection of orexin in NAc or electrical stimulation of LHA significantly increased the discharge activity of gastric distension responsive neurons in NAc, and the effect could be partly blocked by pretreatment of orexin-A receptor inhibitor SB334867 in NAc (P < .05). (4) Microinjection orexin-A in NAc or electrical stimulation of LHA significantly increased the palatable food intake in rats, and the effect also was partly inhibited by pretreatment of SB334867 in NAc (P < .05).ConclusionThere is an orexinergic pathway from LHA to NAc, which may have potential regulatory effects on food reward and obesity.     

Intracerebroventricular galanin and N-terminal galanin fragment enhance the morphine-induced analgesia in the rat

Summary Behavioral effect of galanin and its fragments, galanin_1–15 and galanin_16–29 (200 ng, 1 and 5 g), after intracerebroventricular (i.c.v.) administration was studied in rats. The number of crossings and pippings and the time of locomotion (an open field test) showed a similar sedative action of galanin and galanin_16–29, with no significant effect of galanin_1–15. Galanin and its fragments, injected in doses of 200 ng, 1 and 5 g, did not affect nociception, as measured by a tail-flick and paw pressure test. Galanin and galanin_1–15, but not galanin_16–29 (5 g i.c.v.), injected together with morphine (2.5 g i.c.v.), significantly potentiated the analgetic effect of morphine assessed by a paw pressure test; a similar tendency was also observed in a tail-flick test. Galanin and its two fragments injected in doses of 200 ng, 1 and 5 g, did not change the effect of morphine given in a dose of 1 g. These data suggest that galanin, having no effect when given alone, potentiate the analgetic effect of morphine. The fact that the N-terminal fragment of galanin acts like a natural peptide suggests a receptor mediated action.In conclusion, the analgesic effect of morphine was potentiated by galanin and its N-terminal fragment galanin_1–15. On the other hand, behavioral study showed a similar sedative action of galanin and C-terminal fragment galanin_16–29. This suggests that the N- and C-terminal fragments of galanin are differentially involved in behavioral effects of the peptide.     

Microinjection of the α1-agonist methoxamine into the paraventricular hypothalamus induces anorexia in rats

Adrenergic receptors within the paraventricular hypothalamus (PVN) play a prominent role in the control of food intake: stimulation of α2-adrenoceptors induces food intake whereas stimulation of α1-adrenoceptors suppresses food intake. This study further examines the role of PVN α1-adrenoceptors hy examining the effects on food and water intake of the α1-adrenergic agonist methoxamine (100, 200, 400 nMol) microinjected into the rat paraventricular hypothalamus. Methoxamine suppressed food intake but not water intake. Doses of 100, 200, and 400 nMol methoxamine suppressed food intake by 47%. 64%, and 96%, respectively. These results further confirm the hypothesis that administration of α1-agonists into the PVN acts to significantly suppress food intake; an action that is in opposition to the facilitory effects of α2-adrenergic agonists on food intake.     

Developmental time course of acidic and basic fibroblast growth factors' expression in distinct cellular populations of the rat central nervous system

Acidic and basic fibroblast growth factors (aFGF and bFGF, respectively) are expressed in high levels in adult central nervous system (CNS). We report the time course of developmental appearance and distribution of these factors and of two FGF receptors, FGFR-1 and FGFR-2, in the CNS of rats ranging in age from embryonic day 16 to adult. Immunohistochemical analysis showed that sensory neurons in the midbrain were the first cells to contain detectable aFGF immunoreactivity at embryonic day 18. The next cell group to contain aFGF were motor neurons, which were found to be aFGF-positive at the day of birth. A number of other subcortical neuronal populations were observed to contain aFGF immunoreactivity after postnatal day 7. Adult levels and distribution patterns of aFGF were reached in all CNS areas by postnatal day 28. Basic FGF immunoreactivity was observed at postnatal day 0 in neurons in the CA2 subfield of hippocampus. Astrocytes contained detectable bFGF immunoreactivity, starting at postnatal day 7. Adult levels and patterns of distribution of bFGF were reached in all CNS areas by postnatal day 28. These immunohistochemical observations were confirmed by using bioassay and Western blot techniques. FGFR-1 and FGFR-2 mRNA were expressed in significant levels in all CNS areas at all time points analyzed. The observation that aFGF and bFGF appear in specific and distinct cellular populaitions at relatively late developmental times suggests that these FGFs may be involved in spe6ific mechanisms of CNS maturation, maintenance, and repair. © 1995 Wiley-Liss, Inc.     

Feeding pattern in obese Zucker rats after dopaminergic and serotonergic LHA grafts.

To study the role of the lateral hypothalamic area (LHA) dopamine and serotonin in the regulation of feeding pattern during obesity, embryonic dopaminergic and serotonergic neurons from mesencephalon and rombencephalon of lean rats were grafted into the LHA of adult obese Zucker rats. Compared to the pregrafting period, a smaller increase in meal size occurred in both serotonin-grafted (9%) and dopamine-grafted (31%) rats vs control rats (51%). There was also a smaller decrease in meal number in both serotonin-grafted (3%) and dopamine-grafted (13%) rats vs control rats (28%). Although the changes in feeding pattern resulted in a decrease in total food intake in serotonin-grafted rats (5%) vs control rats, no differences in body weight gain were observed in grafted vs control rats for the duration of the study. Since adult obese Zucker rats are known to have an increased meal size and decreased meal number relative to lean rats, the data indicate the involvement of LHA dopamine and serotonin in the regulation of feeding pattern during obesity.     

Down-regulation of cannabinoid-1 (CB-1) receptors in specific extrahypothalamic regions of rats with dietary obesity: a role for endogenous cannabinoids in driving appetite for palatable food?

Agonists at cannabinoid-1 (CB-1) receptors stimulate feeding and particularly enhance the reward aspects of eating. To investigate whether endogenous cannabinoids might influence appetite for palatable food, we compared CB-1 receptor density in the forebrain and hypothalamus, between rats fed standard chow (n=8) and others given palatable food (n=8) for 10 weeks to induce dietary obesity. CB-1 receptor density was significantly decreased by 30–50% (P<0.05) in the hippocampus, cortex, nucleus accumbens and entopeduncular nucleus of diet-fed rats. Furthermore, CB-1 receptor density in the hippocampus, nucleus accumbens and entopeduncular nucleus was significantly inversely correlated with intake of palatable food (r²=0.25–0.35; all P<0.05). By contrast, CB-1 receptor binding in the hypothalamus was low and not altered in diet-fed rats. CB-1 receptor down-regulation is consistent with increased activation of these receptors by endogenous cannabinoids. Acting in areas such as the nucleus accumbens and hippocampus, which are involved in the hedonic aspects of eating, cannabinoids may therefore drive appetite for palatable food and thus determine total energy intake and the severity of diet-induced obesity. However, cannabinoids in the hypothalamus do not appear to influence this aspect of eating behaviour.     

Metabolic regulation of lateral hypothalamic glucose-inhibited orexin neurons may influence midbrain reward neurocircuitry

Lateral hypothalamic area (LHA) orexin neurons modulate reward-based feeding by activating ventral tegmental area (VTA) dopamine (DA) neurons. We hypothesize that signals of peripheral energy status influence reward-based feeding by modulating the glucose sensitivity of LHA orexin glucose-inhibited (GI) neurons. This hypothesis was tested using electrophysiological recordings of LHA orexin-GI neurons in brain slices from 4 to 6 week old male mice whose orexin neurons express green fluorescent protein (GFP) or putative VTA-DA neurons from C57Bl/6 mice. Low glucose directly activated ~ 60% of LHA orexin-GFP neurons in both whole cell and cell attached recordings. Leptin indirectly reduced and ghrelin directly enhanced the activation of LHA orexin-GI neurons by glucose decreases from 2.5 to 0.1 mM by 53 ± 12% (n = 16, P < 0.001) and 41 ± 24% (n = 8, P < 0.05), respectively. GABA or neurotensin receptor blockade prevented leptin's effect on glucose sensitivity. Fasting increased activation of LHA orexin-GI neurons by decreased glucose, as would be predicted by these hormonal effects. We also evaluated putative VTA-DA neurons in a novel horizontal slice preparation containing the LHA and VTA. Decreased glucose increased the frequency of spontaneous excitatory post-synaptic currents (sEPSCs; 125 ± 40%, n = 9, P < 0.05) and action potentials (n = 9; P < 0.05) in 45% (9/20) of VTA DA neurons. sEPSCs were completely blocked by AMPA and NMDA glutamate receptor antagonists (CNQX 20 μM, n = 4; APV 20 μM, n = 4; respectively), demonstrating that these sEPSCs were mediated by glutamatergic transmission onto VTA DA neurons. Orexin-1 but not 2 receptor antagonism with SB334867 (10 μM; n = 9) and TCS-OX2-29 (2 μM; n = 5), respectively, blocks the effects of decreased glucose on VTA DA neurons. Thus, decreased glucose increases orexin-dependent excitatory glutamate neurotransmission onto VTA DA neurons. These data suggest that the glucose sensitivity of LHA orexin-GI neurons links metabolic state and reward-based feeding.     

Chemically defined projections linking the mediobasal hypothalamus and the lateral hypothalamic area

Recent studies have identified several neuropeptide systems in the hypothalamus that are critical in the regulation of body weight. The lateral hypothalamic area (LHA) has long been considered essential in regulating food intake and body weight. Two neuropeptides, melanin-concentrating hormone (MCH) and the orexins (ORX), are localized in the LHA and provide diffuse innervation of the neuraxis, including monosynaptic projections to the cerebral cortex and autonomic preganglionic neurons. Therefore, MCH and ORX neurons may regulate both cognitive and autonomic aspects of food intake and body weight regulation. The arcuate nucleus also is critical in the regulation of body weight, because it contains neurons that express leptin receptors, neuropeptide Y (NPY), α-melanin-stimulating hormone (α-MSH), and agouti-related peptide (AgRP). In this study, we examined the relationships of these peptidergic systems by using dual-label immunohistochemistry or in situ hybridization in rat, mouse, and human brains. In the normal rat, mouse, and human brain, ORX and MCH neurons make up segregated populations. In addition, we found that AgRP- and NPY-immunoreactive neurons are present in the medial division of the human arcuate nucleus, whereas α-MSH-immunoreactive neurons are found in the lateral arcuate nucleus. In humans, AgRP projections were widespread in the hypothalamus, but they were especially dense in the paraventricular nucleus and the perifornical area. Moreover, in both rat and human, MCH and ORX neurons receive innervation from NPY-, AgRP-, and α-MSH-immunoreactive fibers. Projections from populations of leptin-responsive neurons in the mediobasal hypothalamus to MCH and ORX cells in the LHA may link peripheral metabolic cues with the cortical mantle and may play a critical role in the regulation of feeding behavior and body weight. J. Comp. Neurol. 402:442–459, 1998. © 1998 Wiley-Liss, Inc.