The role of melanin concentrating hormone (MCH) in the central chemoreflex: a knockdown study by siRNA in the lateral hypothalamus in rats

Melanin concentrating hormone (MCH), a neuropeptide produced mainly in neurons localized to the lateral hypothalamic area (LHA), has been implicated in the regulation of food intake, energy balance, sleep state, and the cardiovascular system. Hypothalamic MCH neurons also have multisynaptic connections with diaphragmatic motoneurons and project to many central chemoreceptor sites. However, there are few studies of MCH involvement in central respiratory control. To test the hypothesis that MCH plays a role in the central chemoreflex, we induced a down regulation of MCH in the central nervous system by knocking down the MCH precursor (pMCH) mRNA in the LHA using a pool of small interfering RNA (siRNA), and measured the resultant changes in breathing, metabolic rate, body weight, and blood glucose levels in conscious rats. The injections of pMCH-siRNA into the LHA successfully produced a ∼62% reduction of pMCH mRNA expression in the LHA and a ∼43% decrease of MCH levels in the cerebrospinal fluid relative to scrambled-siRNA treatment (P = 0.006 and P = 0.02 respectively). Compared to the pretreatment baseline and the scrambled-siRNA treated control rats, knockdown of MCH resulted in: 1) an enhanced hypercapnic chemoreflex (∼42 & 47% respectively; P < 0.05) only in wakefulness; 2) a decrease in body weight and basal glucose levels; and 3) an unchanged metabolic rate. Our results indicate that MCH participates not only in the regulation of glucose and sleep-wake homeostasis but also the vigilance-state dependent regulation of the central hypercapnic chemoreflex and respiratory control.

Voluntary enhancement of neural signatures of affiliative emotion using FMRI neurofeedback

In Ridley Scott's film "Blade Runner", empathy-detection devices are employed to measure affiliative emotions. Despite recent neurocomputational advances, it is unknown whether brain signatures of affiliative emotions, such as tenderness/affection, can be decoded and voluntarily modulated. Here, we employed multivariate voxel pattern analysis and real-time fMRI to address this question. We found that participants were able to use visual feedback based on decoded fMRI patterns as a neurofeedback signal to increase brain activation characteristic of tenderness/affection relative to pride, an equally complex control emotion. Such improvement was not observed in a control group performing the same fMRI task without neurofeedback. Furthermore, the neurofeedback-driven enhancement of tenderness/affection-related distributed patterns was associated with local fMRI responses in the septohypothalamic area and frontopolar cortex, regions previously implicated in affiliative emotion. This demonstrates that humans can voluntarily enhance brain signatures of tenderness/affection, unlocking new possibilities for promoting prosocial emotions and countering antisocial behavior.

The lateral hypothalamic parvalbumin-immunoreactive (PV1) nucleus in rodents

In the lateral hypothalamus, groups of functionally related cells tend to be widely scattered rather than confined to discrete, anatomically distinct units. However, by using parvalbumin (PV)-specific antibodies, a solitary, compact cord of PV-immunoreactive cells (the PV1-nucleus) has been identified in the ventrolateral tuberal hypothalamus in various species. Here we describe the topography, the chemo-, cyto-, and myeloarchitectonics, and the ultrastructure of this PV1-nucleus in rodents. The PV1-nucleus is located within the ventrolateral division of the medial forebrain bundle. In the horizontal plane, it has a length of 1 mm in mice and 2 mm in rats. PV-immunoreactive perikarya fall into two distinct size categories and number (~800 in rats and ~400 in mice). They are intermingled with PV-negative neurons and coarse axons of the medial forebrain bundle, some of which are PV-positive. Symmetric and asymmetric synapses, as well as PV-positive and PV-negative fiber endings, terminate on the perikarya of both PV-positive and PV-negative neurons. PV-positive neurons of the PV1-nucleus express glutamate, not γ-aminobutyric acid (GABA), the neurotransmitter that is usually associated with PV-containing nerve cells. Although we could not find evidence that PV1 neurons express either catecholamines or known neuropeptides, they sometimes are interspersed with the fibers and terminals of such cells. From its analogous topographical situation, the PV1-nucleus could correspond to the lateral tuberal nucleus in humans. We anticipate that the presence of the marker protein PV in the PV1-nucleus of the rodent hypothalamus will facilitate future studies relating to the connectivity, transcriptomics, and function of this entity.

Stimulation of lateral hypothalamic AMPA receptors may induce feeding in rats

Glutamate or its ionotropic receptor (iGluR) agonists, N-methyl-D-aspartate (NMDA), alpha-amino-3-hydroxy-5-methyl-4-isoxale propionate (AMPA), and kainate (KA) elicit feeding when microinjected into the lateral hypothalamus (LH) of satiated rats. In the present study we investigated the contributions of AMPA and KA receptors (AMPARs and KARs) to feeding initiation. Intense feeding was elicited by LH injection of RS-AMPA (1 and 10 nmol) but not by the isolated, inactive R-AMPA enantiomer (1 and 10 nmol). Further, LH pretreatment with either the non-selective AMPAR/KAR antagonist, 6-cyano-7-nitroquinoxaline-2,3-dione (CNQX, 4 nmol) or the selective AMPAR antagonist, GYKI 52466 (10 nmol), suppressed AMPA-elicited food intake and, when combined, blocked AMPA-elicited food intake. These findings suggest that LH AMPARs mediate AMPA injection-elicited feeding with a possible contribution by KARs. In contrast, CNQX or GYKI 52466 injected into the LH at the onset of the nocturnal period or into fasted rats did not suppress the feeding produced by either condition. RS-AMPA injected into the LH of fasted or nocturnal feeding subjects elicited eating in both conditions; however, the magnitude of the increase was greater in fasted rats. These data suggest that selective stimulation of AMPAR in the LH is sufficient to elicit feeding. In contrast, the results did not provide evidence that AMPAR stimulation is necessary for deprivation-induced or nocturnal eating; however, they did suggest that modulatory interactions may exist between these receptors and these forms of naturally occurring eating behavior.

Caudal hindbrain lactate infusion alters glucokinase, SUR1, and neuronal substrate fuel transporter gene expression in the dorsal vagal complex, lateral hypothalamic area, and ventromedial nucleus hypothalamus of hypoglycemic male rats

While in vitro studies show that the oxidizable energy substrate, lactate, is a preferred fuel for CNS neurons during states of energy crisis, and that lactate may regulate neuronal glucose uptake under those conditions, its role in neuronal function in vivo remains controversial. Glucose-excited neurons in hindbrain dorsal vagal complex (DVC) monitor both glucose and lactate, and express both the glucose sensor, glucokinase (GK), and the SUR1 subunit of the plasma membrane energy transducer, K(ATP). Fourth ventricular lactate infusion exacerbates insulin-induced hypoglycemia (IIH) and IIH-associated patterns of DVC neuronal activation. We investigated the hypothesis that during glucoprivation, lactate regulates neuronal monocarboxylate and glucose transporter gene transcription in the DVC, and adjustments in these gene profiles are correlated with altered GK and SUR1 mRNA expression. We also examined whether caudal hindbrain lactate repletion alters the impact of hypoglycemia on substrate fuel uptake and metabolic sensing functions in other characterized metabolic monitoring sites, e.g., the ventromedial hypothalamic nucleus (VMH) and lateral hypothalamic area (LHA). qPCR was used to measure MCT2, GLUT3, GLUT4, GK, and SUR1 transcripts in the microdissected DVC, VMH, and LHA from groups of male rats treated by continuous infusion of aCSF or lactate into the caudal fourth ventricle (CV4), initiated prior to injection of Humulin R or saline. Blood glucose was decreased in response to insulin, a response that was significantly augmented by CV4 lactate infusion. IIH alone did not alter mean DVC MCT2, GLUT3, GLUT4, GK, or SUR1 mRNA levels, but these transcripts were increased in the lactate plus insulin group, relative to both euglycemic and aCSF-infused hypoglycemic rats. IIH decreased MCT2, GLUT3, and SUR1 gene profiles in the VMH; CV4 lactate infusion during IIH further diminished these transcripts, and suppressed GLUT4 and GK mRNA levels in this site. In LHA, IIH increased GLUT3 and SUR1 gene expression to an equal extent, with or without lactate, while GLUT4, MCT2, and GK mRNA levels were elevated only in response to lactate plus insulin. These studies show that caudal hindbrain-targeted delivery of exogenous lactate during IIH upregulates neuronal monocarboxylate and glucose transporter, GK, and SUR1 gene profiles in the DVC, and results in increased or decreased GLUT4 and GK mRNA in LHA and VMH, respectively. These data suggest that lactate and glucose utilization by DVC neurons may be enhanced in response to local lactate surfeit, alone or relative to glucose deficiency, and that increases in intracellular glucose and net energy yield may be correlated with elevated GK and SUR1 gene transcription, respectively, in local glucose sensing neurons. The results also imply that GLUT4- and GK-mediated glucose uptake and glucose sensing functions in the VMH and LHA may be reactive to DVC signaling of relative lactate abundance within the caudal hindbrain, and/or to physiological sequelae of this fuel augmentation, including amplified hypoglycemia.

Ingestive effects of NMDA and AMPA-kainate receptor antagonists microinjections into the lateral hypothalamus of the pigeon (Columba livia)

This study examined the ingestive and behavioral effects of NMDA- and AMPA/kainate glutamatergic receptor blockade in the lateral hypothalamic area (LHy) of free-feeding pigeons (Columba livia). Injections of MK-801 (NMDA receptor antagonist; 6 nmol) or CNQX (AMPA/kainate receptor antagonist; 25.8 nmol) into the LHy of free-feeding pigeons induced significant increases in food intake and in feeding duration, as well as reductions in the latency to start feeding. Duration, latency and volume of water intake, as well as duration of sleep-like behavior, alert immobility, locomotion and preening were not changed by these treatments in the LHy. These results indicate that glutamatergic inputs to cells containing NMDA and/or AMPA receptors located in the LHy could modify both the beginning of a feeding bout (or the end of a period of satiety) and its duration (satiation). Our data also suggest that these inhibitory glutamatergic influences on feeding behavior are tonically active in the LHy.

Sleep-active neurons in the preoptic area project to the hypothalamic paraventricular nucleus and perifornical lateral hypothalamus

The lamina terminalis consists of the organum vasculosum of the lamina terminalis (OVLT), median preoptic nucleus (MnPO) and subfornical organ. The MnPO and ventrolateral preoptic area (vlPOA) are known to contain high densities of neurons that are sleep active. The prevalence of sleep-active neurons in the OVLT and subfornical organ is unknown. The vlPOA and subdivisions of the lamina terminalis project to hypothalamic regions involved in the control of behavioral, electrographic or autonomic arousal, including the lateral hypothalamic area (LHA) and paraventricular nucleus (PVN). The extent to which projection neurons are active during sleep is unknown. We quantified c-Fos protein immunoreactivity (IR) in the lamina terminalis and vlPOA in sleeping and awake rats that received injections of retrograde tracer into either the LHA or PVN. Fos IR was also examined in lamina terminalis neurons following tracer injections into the vlPOA. Significantly more projection neurons from the MnPO, OVLT and vlPOA to the LHA were Fos-immunoreactive in sleeping vs. awake animals. Waking Fos IR was more prevalent in lamina terminalis neurons projecting to the PVN although a subset of MnPO projection neurons in sleeping rats was Fos-immunoreactive. Almost 50% of vlPOA-PVN projection neurons expressed Fos IR during sleep, compared with 3% during waking. Significantly more neurons in the OVLT and MnPO projecting to the vlPOA were Fos-immunoreactive in sleeping vs. awake rats. Inhibition of LHA and PVN neurons arising from OVLT, MnPO and vlPOA neurons may contribute to suppression of behavioral, electroencephalographic and sympathetic nervous system activation during sleep.

Lesions of tuberomammillary nuclei induce differential polydipsic and hyperphagic effects

This study aimed to examine the function of the tuberomammillary complex in water and food intake of Wistar rats. The results show that lesions restricted to tuberomammillary subnuclei: caudal ventral tuberomammillary nucleus (E1), rostral ventral tuberomammillary nucleus (E2), medial ventral tuberomammillary nucleus (E3) or medial dorsal tuberomammillary nucleus (E4), induce a strong and persistent polydipsia with specific characteristics for each nucleus. Interestingly, the distribution of tuberomammillary hyperdipsia throughout the day was similar to that in non-lesioned animals, in contrast to the lack of rhythmicity observed in rats with anodic lesion to median eminence. This polydipsia appears to be independent of food intake, as food deprivation for 22 h did not significantly reduce the water intake. Finally, lesions in ventral tuberomammillary nuclei E1 and E2 induce hyperphagia, confirming a possible role for the tuberomammillary complex in food intake. This increase in food intake is not observed after lesions in medial subnuclei E3 and E4. These results are interpreted in terms of the hypothalamic systems involved in the consumption of both food and water.

Comparison of melanin-concentrating hormone and hypocretin/orexin mRNA expression patterns in a new parceling scheme of the lateral hypothalamic zone

A high-resolution spatial distribution analysis of hypothalamic neurons expressing melanin-concentrating hormone or hypocretin/orexin was performed in adult male rats with in situ hybridization cytochemistry. For the analysis, a new parcellation of the lateral zone with some two-dozen regions was used, and distributions were plotted on 15 transverse reference levels through the hypothalamus. Qualitatively the results confirm earlier, much lower resolution mapping studies, although some discrepancies are clarified. Previous work indicates that each of these cell populations is far from homogeneous, and the present results should help establish a framework for clarifying more precisely how they are differentiated and organized in terms of axonal input-output relationships and gene expression patterns, and for defining precise relationships with other hypothalamic neuron populations.

Dopaminergic regulation of orexin neurons

Orexin/hypocretin neurons in the lateral hypothalamus and adjacent perifornical area (LH/PFA) innervate midbrain dopamine (DA) neurons that project to corticolimbic sites and subserve psychostimulant-induced locomotor activity. However, it is not known whether dopamine neurons in turn regulate the activity of orexin cells. We examined the ability of dopamine agonists to activate orexin neurons in the rat, as reflected by induction of Fos. The mixed dopamine agonist apomorphine increased Fos expression in orexin cells, with a greater effect on orexin neurons located medial to the fornix. Both the selective D1-like agonist, A-77636, and the D2-like agonist, quinpirole, also induced Fos in orexin cells, suggesting that stimulation of either receptor subtype is sufficient to activate orexin neurons. Consistent with this finding, combined SCH 23390 (D1 antagonist)-haloperidol (D2 antagonist) pretreatment blocked apomorphine-induced activation of medial as well as lateral orexin neurons; in contrast, pretreatment with either the D1-like or D2-like antagonists alone did not attenuate apomorphine-induced activation of medial orexin cells. In situ hybridization histochemistry revealed that LH/PFA cells rarely express mRNAs encoding dopamine receptors, suggesting that orexin cells are transsynaptically activated by apomorphine. We therefore lesioned the nucleus accumbens, a site known to regulate orexin cells, but this treatment did not alter apomorphine-elicited activation of medial or lateral orexin neurons. Interestingly, apomorphine failed to activate orexin cells in isoflurane-anaesthetized animals. These data suggest that apomorphine-induced arousal but not accumbens-mediated hyperactivity is required for dopamine to transsynaptically activate orexin neurons.

Cardiovascular responses to the injection of l-glutamate in the lateral hypothalamus of unanesthetized or anesthetized rats

The present experiment was designed to compare the cardiovascular effects of injections of 0.1 M L-glutamate (50, 100 or 500 nL) into the anterior (LHa), tuberal (LHt) or posterior (LHp) regions of the lateral hypothalamus (LH) of either unanesthetized or anesthetized male Wistar rats. In unanesthetized rats, L-glutamate caused significant depressor responses without significant heart rate (HR) effects. L-Glutamate caused similar depressor responses when injected into the different LH subregions. A positive trend was observed between depressor response intensity and injected volume. In urethane-anesthetized rats, L-glutamate caused either depressor responses or biphasic responses, characterized by a significant initial depressor component followed by a secondary pressor response which was significant only after the injection of L-glutamate in 500 nL. The depressor component was accompanied by significant bradycardia only when the LHa or LHt were stimulated. Similar depressor responses were observed after L-glutamate microinjection into the different LH subregions. A positive trend was observed between depressor response intensity and injected volume. The present results suggest that: 1) lateral hypothalamic L-glutamate-sensitive neurons are involved in cardiovascular control and may have a wide and homogeneous distribution throughout the LH; 2) these neurons are mainly associated to the expression of hypotensive responses in unanesthetized rats; and 3) bradycardiac responses are evidenced when L-glutamate is microinjected into the LHa and the LHt in urethane-anesthetized rats.

Hypothalamic circadian organization in birds. I. Anatomy, functional morphology, and terminology of the suprachiasmatic region

In mammals, the "master clock" controlling circadian rhythmicity is located in the hypothalamic suprachiasmatic nuclei (SCN). Until now, no comparable structure has been unambiguously described in the brain of any nonmammalian vertebrate. In birds, early anatomical and lesioning studies described a SCN located in the anterior hypothalamus, but whether birds possess a nucleus equivalent to the mammalian SCN remained controversial. By reviewing the existing literature it became evident that confusion in delineation and nomenclature of hypothalamic cell groups may be one of the major reasons that no coherent picture of the avian hypothalamus exists. In this review, we attempt to clarify certain aspects of the organization of the avian hypothalamus by summarizing anatomical and functional studies and comparing them to immunocytochemical results from our laboratory. There is no single cell group in the avian hypothalamus that combines the morphological and neurochemical features of the mammalian SCN. Instead, certain aspects of anatomy and morphology suggest that at least two anatomically distinct cell groups, the SCN and the lateral hypothalamic nucleus (LHN), bear some of the characteristics of the mammalian SCN.

Hypothalamic circadian organization in birds. II. Clock gene expression

While the site of the major circadian pacemaker in mammals, the suprachiasmatic nucleus (SCN) of the hypothalamus, is very well characterized, little is known about hypothalamic circadian organization in birds. This paper reviews recent findings on clock gene expression in the hypothalamus of several bird species focusing on circadian pPer2 expression in the house sparrow. In contrast to mammals, rhythmic Per2 gene expression in the house sparrow hypothalamus is not restricted to a single cell group but occurs in two distinct hypothalamic nuclei, the SCN and the lateral hypothalamic nucleus (LHN). The complex temporal and spatial distribution of pPer2 expression suggests a longitudinal compartmentalization of the SCN with period gene expression being initiated in the most rostral portion before lights on. In the lateral hypothalamus, phasing of pPer2-rhythmicity appeared delayed. In pinealectomized house sparrows, the overall circadian pPer2 expression pattern is maintained indicating that rhythmic pPer2 transcription in the SCN and LHN of the house sparrow are not driven by the pineal gland. Rather, they reflect the activity of autonomous hypothalamic circadian oscillators. Certain changes in peak expression levels and the expression phase, however, suggest that the pineal melatonin rhythm affects both the phase and the amplitude of rhythmic hypothalamic pPer2 expression.

Peptides that regulate food intake: regional, metabolic, and circadian specificity of lateral hypothalamic orexin A feeding stimulation

Orexin A (OX-A) administered in the lateral hypothalamus (LH) increases feeding in a dose-dependent manner. The LH is a relatively large neural structure with a heterogeneous profile of neural inputs, efferent projections, and orexin receptor distribution. We sought to determine the LH region most sensitive to the feeding stimulatory effect of OX-A injection. Fifty-six male Sprague-Dawley rats were fitted with cannulas 1 mm above four separate LH regions approximately 1 mm apart in the rostral-caudal direction. There were 14-16 animals/LH region. After recovery, animals received either artificial cerebrospinal fluid or OX-A (250, 500, or 1,000 pmol). To determine whether there is a circadian effect of LH OX-A on the feeding response, we performed injections at 0200, 0900, 1400, and 2100. Food intake was measured at 1, 2, and 4 h after injection. The most rostral extent of the LH was the only region in which injection of OX-A significantly stimulated feeding. Within this region, feeding was increased at all times of the day, although the most robust and only significant feeding response occurred after the afternoon injection (1400) of OX-A. To determine the extent to which the metabolic status of the rat contributed to the circadian specificity of orexin-induced feeding, animals were placed on a restricted diet and injected with OX-A in the most rostral region of the LH. Under these conditions, OX-A significantly increased feeding and more robustly when compared with animals on a nonrestricted diet. These data suggest that the rostral LH is the only region of the LH sensitive to the injection of OX-A, and the metabolic status of the animal at the time of injection may influence the feeding response to OX-A.

Descending influences from the lateral hypothalamus and amygdala converge onto medullary taste neurons

The lateral hypothalamus (LH) and the central nucleus of the amygdala (CeA) exert an influence on many aspects of ingestive behavior. These nuclei receive projections from several areas carrying gustatory and viscerosensory information, and send axons to these nuclei as well, including the nucleus of the solitary tract (NST). Gustatory responses of NST neurons are modulated by stimulation of the LH and the CeA, and by several physiological factors related to ingestive behavior. We investigated the effect of both LH and CeA stimulation on the activity of 215 taste-responsive neurons in the hamster NST. More than half of these neurons (113/215) were modulated by electrical stimulation of the LH and/or CeA; of these, 52 cells were influenced by both areas, often bilaterally. The LH influenced more neurons than the CeA (101 versus 64 cells). Contralateral stimulation of these forebrain areas was more often effective (144 responses) than ipsilateral (74). Modulatory effects were mostly excitatory (102 cells); 11 cells were inhibited, mostly by ipsilateral LH stimulation. A subset of these cells (n = 25) was examined for the effects of microinjection of DL-homocysteic acid (DLH), a glutamate receptor agonist, into the LH and/or CeA. The effects of electrical stimulation were completely mimicked by DLH, indicating that cell somata in and around the stimulating sites were responsible for these effects. Other cells (n = 25) were tested for the effects of electrical stimulation of the LH and/or CeA on the responses to taste stimulation of the tongue (32 mM sucrose, NaCl and quinine hydrochloride, and 3.2 mM citric acid). Responses to taste stimuli were enhanced by the excitatory influence of the LH and/or CeA. These data demonstrate that descending influences from the LH and CeA reach many of the same cells in the gustatory NST and can modulate their responses to taste stimulation.

Hypothalamic inferior lobe and lateral torus connections in a percomorph teleost, the red cichlid (Hemichromis lifalili)

The neuroanatomic connections of the inferior lobe and the lateral torus of the percomorph Hemichromis lifalili were investigated by 1,1', dioctadecyl-3,3,3',3'-tetramethylindo-carbocyanine perchlorate (DiI) tracing. The inferior lobe and the lateral torus both receive afferents from the secondary gustatory nucleus. Additional afferents reach the inferior lobe from the nucleus glomerulosus, nucleus suprachiasmaticus, dorsal and central posterior thalamic nucleus, nucleus lateralis valvulae, magnocellular part of the magnocellular nucleus of the preoptic region, caudal nucleus of the preglomerular region, posterior tuberal nucleus, area dorsalis of the telencephalon, and a tegmental nucleus (T2). Efferents from the inferior lobe and the lateral torus terminate in the dorsal hypothalamic neuropil and corpus mamillare. Furthermore, the inferior lobe projects to the medial nucleus of the lateral tuberal hypothalamus and perhaps makes axo-axonal synapses in the tractus tectobulbaris rectus. The inferior lobe and the torus lateralis have reciprocal connections with the preglomerular tertiary gustatory nucleus and posterior thalamic nucleus and are also mutually interconnected. The inferior lobe is also reciprocally connected with the medial nucleus of the preglomerular region, reticular formation and sparsely with the anterior dorsal thalamic and the ventromedial thalamic nuclei. Thus, whereas the lateral torus is exclusively connected with the gustatory system, the inferior lobe is of a multisensory nature. In comparison with the goldfish (Carassius auratus), the connectivity pattern of the inferior lobe of Hemichromis lifalili reflects its specialization with respect to the visual system, as it receives qualitative (i.e., dorsal posterior, anterior, and ventromedial thalamic nuclei) as well as quantitative (i.e., nucleus glomerulosus) additional visual input.

Contrasting effects of dopamine antagonists and frequency reduction on Fos expression induced by lateral hypothalamic stimulation

To help further identify the reward-relevant regions activated by electrical stimulation of the lateral hypothalamus, Fos expression was quantified in 23 brain regions in naïve, awake rats following non-contingent stimulation with a frequency that supports self-stimulation (100 Hz), a frequency that supports only minimal responding (50 Hz) and a frequency that does not support self-stimulation (25 Hz). Fos expression was also examined in stimulated and unstimulated rats pretreated with SCH 23390 (a dopamine D1 antagonist) or spiperone (a D2-like antagonist), at doses known to greatly inhibit responding for self-stimulation. Lowering the stimulation frequency from 100 to 50 Hz reduced Fos labelling in all areas, except for a few cells immediately surrounding the electrode tip. No differences were observed between unstimulated rats and those receiving 25 Hz stimulation. This suggests that a critical threshold of stimulation is required before other reward-relevant regions in the midbrain and forebrain are recruited with higher frequency stimulation. Pretreatment with SCH 23390 (0.1 mg/kg) inhibited stimulation-induced Fos expression in some key dopamine terminal areas, such as the nucleus accumbens (core and shell) and medial caudate-putamen, but not in directly driven neurons near the stimulation site. In contrast, spiperone (0.1 mg/kg) did not affect the pattern of stimulation-induced Fos expression, but induced immunolabelling in the dorsolateral caudate-putamen, an area associated with the extrapyramidal side-effects of antipsychotic drugs. These results reveal the utility of Fos immunohistochemistry to show how different treatments that alter the rewarding impact of electrical brain stimulation achieve their effects at the neural level.

Dynamic changes in cytochrome oxidase activity in the amygdala following lesions of rewarding sites in the lateral hypothalamus

The aim of this study was to evaluate neural changes in oxidative metabolism in amygdaloid sub-nuclei following unilateral electrolytic lesions of lateral hypothalamic sites that supported brain stimulation reward. A histochemical analysis of cytochrome oxidase activity, comparing lesioned to non-lesioned sides in the amygdala, revealed a significant reduction of oxidative metabolism in the cortical nucleus and, to a lesser degree, in the adjacent piriform cortex; this effect was observed 2-4 weeks after the lesion, with complete recovery by the eighth week in the case of the cortical nucleus only. No particular pattern in cytochrome oxidase activity was detected in other amygdaloid sub-nuclei that were examined, including the basolateral and medial nucleus. Within both structures, the most pronounced decreases in metabolic activity were observed at roughly the same level, corresponding to the posterolateral and posteromedial levels of the cortical nucleus and just anterior to the amygdalopiriform transition. These results suggest that within the amygdaloid complex, the cortical sub-nuclei and possibly the neighbouring piriform cortex contribute more to modulating lateral hypothalamic self-stimulation than components of the central extended amygdala.

Anatomical correlates of the lateral hypothalamic influence on waking-sleep relationship in the rat

Restricted electrolytic lesions of the lateral hypothalamus (LH) evoke sleeplessness in the rat. The present study was aimed to analyze a possible anatomical substrate of the LH hyposomnia within the hypothalamus. In a group of electrolytically lesioned LH rats the intensity of sleep disturbances, assessed on the basis of EEG records from the neocortex and the hippocampus, was confronted with the localization and the extent of destruction of the LH area and with the topography of known fiber systems of the medical forebrain bundle (MFB). In separate experiments the effects of the destruction of LH cell bodies by means of bilateral ibotenic acid (IBO) injections and inhibition of LH neuronal elements by bilateral muscimol (MUSC) administration were also tested. It was found that pronounced hyposomnia follows electrolytic but not IBO lesions of the LH/MFB area. The effective LH damage might have been localized at every level of its antero-posterior axis, from the preoptic area up to the posterior hypothalamus, suggesting involvement of fiber system(s) rather than a localized group of neuronal pericaria. The most effective lesions transsected projections descending from the preoptic/anterior hypothalamic area, olfactory structures, ventral striatum and the central amygdaloid nucleus as well as fibers connecting LH with the brainstem reticular formation, many of them using GABA as a neurotransmitter. Bilateral MUSC injections caused a dose-dependent, bicuculline-reversible, increase in waking time, most pronounced at a dose of 50 ng, which ressembled the effect of the electrolytic lesion. These results indicate that LH hyposomnia is not attributable to the damage to the intrahypothalamic neurons and suggest the participation of GABA-ergic transmission in LH in waking-sleep regulation.

The lateral hypothalamic syndrome in the weanling rat: bone geometry and biomechanics

Male weanling Sprague-Dawley rats received bilateral electrolytic lesions in the lateral hypothalamic area (LHAL). One group of sham-operated controls was fed ad lib (CON-ADLIB), another was pair fed to the LHAL group (CON-PF). The experiment was terminated 1 month after surgery. At that time, LHAL rats were 49% and CON-PF rats were 41% lighter than CON-ADLIB. Carcass protein in LHAL rats was significantly reduced in LHAL: versus CON-ADLIB. Linear growth was significantly reduced by 18% in LHAL versus CON-ADLIB, as well as LHAL: versus CON-PF by 6%. Mean caloric intake was significantly reduced by 48% in LHAL versus CON-ADLIB, as was caloric efficiency (body weight gained per calories eaten) by 36%, as well as, in CON-PF versus CON-ADLIB by 20%. LHAL rats showed a significantly shorter (10%), narrower (15%) and thinner (25 %) cortex at midshaft of the femur. Resistance to torsional loads was reduced by 25% in both LHAL and CON-PF, but this did not reach statistical significance, in comparison to CON-ADLIB. There was no statistical significance among the groups in stiffness and maximal angular displacement. We conclude that the reduced bone geometrical and biomechanical properties in both LHAL rats and CON-PF versus CON-ADLIB are similar because both former groups of rats were greatly subcaloric. Thus, the changes here observed are not due to a specific neuroendocrine/autonomic lesion effect but may be attributable to the reduced food intake, i.e., nutritional factors.

Effects of NMDA lesions of the medial basal forebrain on LH and VTA self-stimulation

Rewarding stimulation of the medial forebrain bundle (MFB) increases Fos-like immunoreactivity in many brain areas, including an ipsilateral, basal forebrain region extending from the medial preoptic area (MPO) to the lateral preoptic area, and substantia innominata. Excitotoxic lesions of the lateral portion of this region have been found to produce large sustained or transient increases in the number of pulses required to maintain half-maximal lever-pressing (required number of pulses) for MFB stimulation. In the present study, changes in self-stimulation of the lateral hypothalamus and ventral tegmental area were assessed following excitotoxic lesions of more medial structures, including the MPO and bed nucleus of the stria terminalis. Increases in the required number of pulses (up to 0.16 log10 units) were seen in only 2 of 10 subjects. In two other rats, the reward effectiveness of the stimulation was moderately increased after the lesion as manifested in decreases of up to 0.14 log10 units in the required number. No appreciable change from baseline was seen in the remaining six subjects. The simplest interpretation of these results is that neurons with cell bodies in the medial portion of the basal forebrain may make a smaller contribution to the rewarding effect of MFB stimulation than neurons in the lateral portion.

A search for the metabolic signal that sensitizes lateral hypothalamic self-stimulation in food-restricted rats

Food deprivation and restriction increase the rewarding potency of food, drugs of abuse, and electrical brain stimulation. Based on evidence that the rewarding effects of these stimuli are mediated by the same neuronal circuitry, lateral hypothalamic self-stimulation (LHSS) was used to investigate the involvement of various metabolic signals in the sensitization of reward. In Experiment 1, glucoprivation with 2-deoxy-d-glucose (150 mg/kg, intraperitoneally (i.p.)) and lipoprivation with nicotinic acid (150 mg/kg, subcutaneously (s.c.)), individually and in combination, failed to affect the LHSS threshold in ad lib.-fed rats. These results suggest that signals associated with acute shortage of metabolic substrate do not sensitize reward. Because numerous responses to more prolonged negative energy balance are mediated by neuropeptide Y (NPY), the effect of exogenous neuropeptide Y upon LHSS was investigated in Experiment 2. Intraventricular infusion of orexigenic neuropeptide Y doses (2.0, 5.0, and 12.5 g), in ad lib.-fed rats, had no effect on LHSS threshold. In Experiment 3, other concomitants of prolonged negative energy balance--high circulating levels of free fatty acids (FFA) and beta-hydroxybutyrate (HDB)-were investigated. Nicotinic acid (250 mg/kg, s.c.), which suppressed serum HDB and FFA levels, had no effect on LHSS in food-restricted or ad lib.-fed rats. Mercaptoacetate (68.4 mg/kg, i.p.), which suppressed serum HDB levels and exacerbated the elevation of FFA levels, also had no effect. Thus, the brain reward system, if modulated by these substances, is not affected by transient, though marked, changes in their levels. To investigate the effect of a sustained increase in levels of FFA and HDB, a "ketogenic" diet was employed. Although this diet produced a fourfold increase in serum HDB levels, it had no effect on LHSS thresholds. Moreover, the failure of mercaptoacetate (68.4 mg/kg, i.p.) to decrease LHSS thresholds in these rats supports the conclusion that acute shortage of metabolic substrate does not sensitize reward. Other possible mechanisms of reward sensitization, including sustained decreases in circulating insulin and leptin and increases in corticosterone, are discussed.

The second messenger cAMP elicits eating by an anatomically specific action in the perifornical hypothalamus

We have previously shown that a membrane-permeant analog of cAMP, 8-bromo-cAMP (8-br-cAMP), elicits a vigorous eating response when microinjected into the perifornical hypothalamus (PFH) or lateral hypothalamus (LH) of satiated rats, suggesting that increases in cAMP in these areas may be important in the neural control of eating. To determine the locus of this effect, we compared the ability of 8-br-cAMP (1-100 nmol/0.3 microl) to elicit eating after microinjection into the PFH, LH, or the following bracketing areas: the anterior and posterior LH, paraventricular nucleus of the hypothalamus, thalamus, and amygdala. 8-br-cAMP at 50 nmol elicited eating (>/=3.4 gm in 2 hr) exclusively in the PFH and LH. At 100 nmol, 8-br-cAMP elicited a larger response in these areas and elicited a smaller, more variable response in the thalamus. We similarly mapped the feeding-stimulatory effects of compounds that increase endogenous cellular cAMP in naive rats. Combined microinjection of matched doses (300 nmol) of 3-isobutyl-1-methylxanthine and 7-deacetyl-7-O-(N-methylpiperazino)-gamma-butyryl-forskolin was effective exclusively in the PFH, eliciting an average 2 hr food intake of 8.4 +/- 2.0 gm. Collectively, these results suggest that increases in cellular cAMP within a specific brain site, the PFH, may play a role in the neural stimulation of eating.

Medullary catecholaminergic neurons projecting to lateral hypothalamic area and expressing Fos after chemical stimulation of the stomach in the rat

Catecholaminergic neurons in the medulla projecting to lateral hypothalamic area (LH) and expressing Fos were investigated in the rat by a triple labelling method, in which horseradish peroxidase (HRP) was injected into the LH, and visceral noxious stimulation was induced by formalin injection into the stomach, sections of the medulla were stained histochemically for HRP and immunohistochemically for Fos and tyrosine hydroxylase (TH). Some neurons labeled with HRP and showing both Fos- and TH-like immunoreactivities were mainly found in the nucleus tractus solitarii (NTS) and ventrolateral medulla (VLM) at the middle and caudal levels of medulla, only a few of them were located in the reticular formation between NTS and VLM. These results indicated that some medullary catecholaminergic neurons projected to the LH and some of them might be involved in the transmissing processes of stress responses to the visceral nociceptive information produced by chemical stimulation.

Antinociceptive effects of stimulation of discrete sites in the rat hypothalamus: evidence for the participation of the lateral hypothalamus area in descending pain suppression mechanisms

The sites in the rat hypothalamus where microinjection of morphine (5 micrograms/0.5 microliters) or electrical stimulation depresses the tail withdrawal reflex to noxious heating of the skin were examined. Among other hypothalamic sites found to be sensitive to morphine or to an electrical stimulus, the posterior part of the lateral hypothalamic area (LHA) was the only portion of the hypothalamus that was strongly sensitive to both manipulations. A 15-sec period of 35 microA sine-wave stimulation of the LHA significantly increased the latency of the tail reflex for periods up to 30 min. The effects of intraperitoneal administration of antagonists to opioids (naloxone), 5-hydroxytryptamine (methysergide), noradrenaline (phenoxybenzamine), dopamine (haloperidol), and acetylcholine (atropine and mecamylamine) on the antinociceptive effects of LHA stimulation were also examined. Naloxone, methysergide, and atropine (all given at doses of 0.5 and 1.0 mg/kg) attenuated the effects of LHA stimulation in a dose-dependent manner. Phenoxybenzamine but not haloperidol (both at the dose of 1.0 mg/kg), was also effective but dose-dependent curves could not be constructed. Mecamylamine (1.0 mg/kg) reduced the duration but not the peak effect of stimulating the LHA. We conclude that antagonism at the level of opioid, serotonergic, adrenergic, and muscarinic cholinergic receptors, but not dopamine or nicotinic cholinergic receptors, reduces the antinociceptive effects of LHA stimulation. This may imply that antinociception evoked from the LHA depends on the activation of descending pathways that relay in the mesencephalic periaqueductal gray matter and then in the nucleus raphe magnus and/or nucleus reticularis paragigantocellularis.

Effects of excitotoxic lesions of the basal forebrain on MFB self-stimulation

Electrolytic lesions of the anterior medial forebrain bundle (MFB) have been shown to attenuate the rewarding impact of stimulating more caudal MFB sites. In the present study, excitotoxic lesions were employed to determine the relative contribution of somata or fibers of passage contributing to that effect. Changes in reward efficacy were inferred, at three currents, from lateral displacements of the curve relating the rate of responding to the number of stimulation pulses per train. After baseline data were collected from stimulation sites in the lateral hypothalamus (LH) and the ventral tegmental area (VTA), 70 nmol of N-methyl-D-aspartic acid was injected via cannulae aimed at basal forebrain sites. Three subjects were injected with vehicle and served as controls. In 5 out of 15 cases, lesions encompassing the lateral preoptic area, anterior LH, and substantia innominata resulted in long-lasting, large increases (0.2-0.47 log10 units) in the number of pulses required to maintain half-maximal rates of self-stimulation for low currents delivered via the LH electrode; smaller increases (0.08-0.33 log10 units) were noted at moderate and high currents. Seven rats with similar or more dorsally located damage showed moderate or transient increases in the number of pulses required to maintain half-maximal rates of LH or VTA self-stimulation. Vehicle injections did not affect behaviour. Varying degrees of demyelination were seen, mostly removed from the electrode tip, and in locations that varied substantially across subjects manifesting similar changes in self-stimulation. These results support the notion that somata in the basal forebrain give rise to some of the directly activated fibers subserving self-stimulation of the MFB.

Physiological measures of conduction velocity and refractory period for putative reward-relevant MFB axons arising in the rostral MFB

Extracellular recordings were obtained, in urethane-anesthetized rats, from 44 neurons in the rostral bed nuclei of the medial forebrain bundle (MFB). These cells were antidromically activated by stimulation of MFB sites that typically support self-stimulation. Recording sites included the magnocellular preoptic nucleus, substantia innominata, ventral pallidum, olfactory tubercle, and horizontal limb of the diagonal band. Refractory period estimates ranged from 0.35 to 1.20 ms (mean +/- SD = 0.72 +/- 0.30 ms, n = 15) for stimulation sites in the lateral hypothalamic and ventral tegmental areas when using currents of twice threshold and procedures designed to estimate excitability at or near the site of stimulation. Interelectrode conduction velocity estimates ranged from 1.48 to 20.0 m/s (mean +/- SD = 9.26 +/- 7.22 m/s, n = 11) and were obtained by dividing the interelectrode distance by the difference in the response latency from the two MFB stimulation sites. The refractory period and conduction velocity estimates for these neurons overlap the psychophysically derived estimates for MFB reward neurons. These data are consistent with the hypothesis that neurons arising in the rostral bed nucleus of the MFB compose at least part of the directly activated substrate for MFB self-stimulation.

Measurement issues in curve-shift analysis of apomorphine effects on rewarding brain stimulation

The direct dopamine agonist apomorphine has been reported to reduce the rewarding efficacy of lateral hypothalamic (LH) self-stimulation. This effect has been claimed to support the notion that dopamine mediates the rewarding effects of LH self-stimulation. Using a standard rate-frequency curve-shift paradigm with ascending order of frequency presentation, we also found that apomorphine (0.1-0.8 mg/kg, SC) appeared to decrease LH self-stimulation reward. These apparent rightward curve shifts were exacerbated by shortening the test duration, which also produced a number of sessions in which the subjects did not respond at all. When the presentation order of stimulation frequencies was reversed, apomorphine did not produce large reward decreases. These results suggest that the previously reported effects of apomorphine on LH self-stimulation were the result of artifact, perhaps related to apomorphine-induced stereotypical behavior combined with rapid pharmacological recovery.

Curve-shift analysis of self-stimulation in food-restricted rats: relationship between daily meal, plasma corticosterone and reward sensitization

Chronic food restriction lowers the threshold for lateral hypothalamic electrical self-stimulation (LHSS). This effect has previously been interpreted to reflect a sensitization of reward. In the present study a curve-shift method was used to explicitly differentiate effects of food restriction on brain stimulation rewarding efficacy and performance. Food restriction consistently shifted rate-frequency curves to the left, lowering the M-50 and Theta-0 parameters of rewarding efficacy. Asymptotic rates of reinforcement and slopes of rate-frequency functions were unaffected, confirming that food restriction does not facilitate LHSS by enhancing performance. In this and previous studies, LHSS in food-restricted rats was measured in the period immediately preceding the daily meal when hunger (i.e., period since last meal) and plasma corticosterone are at peak levels. In the light of evidence that corticosterone may regulate sensitivity of the mesolimbic dopamine pathway and account for the sensitizing effect of stress on psychomotor effects of opiates and stimulants, LHSS and corticosterone were measured in the immediate pre-and post-meal periods. While all food-restricted rats displayed elevated corticosterone levels in the pre-meal period and generally displayed a decline to control levels in the post-meal period, the sensitization of reward was not reversed in the post-meal period. These results indicate that chronic food restriction produces a sensitization of reward that does not depend upon the acute state of hunger that precedes the daily meal and does not vary with dynamic changes in plasma corticosterone level.

Rats self-inject a dopamine antagonist in the lateral hypothalamus where it acts to increase extracellular dopamine in the nucleus accumbens

Local injection of sulpiride to block dopamine (primarily D2-type) receptors in the perifornical lateral hypothalamus (pf-LH) can induce locomotion, feeding, and drinking, and in the present study, local sulpiride induced reward and dopamine (DA) release in the nucleus accumbens. Sulpiride injected bilaterally (4, 8, and 16 micrograms/0.3 microliters), ipsilaterally, or contralaterally (8 micrograms) in the pf-LH increased extracellular levels of DA and its metabolites in the accumbens. Bilateral sulpiride injected posterior and medial to the pf-LH controlled for diffusion to the ventricle or ventral midbrain. Rats self-injected sulpiride (210 ng/21 nl/2 s) in the pf-LH (111 resp/2 h on drug lever vs. 20 resp on a blank lever). Thus, cells in the pf-LH establish connections with mesolimbic DA neurons involved in the behavior reinforcement process. Evidently hypothalamic cells with DA receptors normally inhibit aspects of behavior reinforcement. Disinhibition with hypothalamic sulpiride is reward for self-injection and cause of overeating that can lead to obesity.

Cranial and cerebral-ventricular landmarks for accurate stereotaxic approach to hypothalamic nuclei in the goat brain

This paper describes a new stereotaxic coordinate system for the goat brain based on cranial landmarks. An osseous triangle (a-b-c) formed by the point of junction of the crista galli with the caudal ventral part of the frontal sinus septum (a), the external occipital protuberance (b), and the midsagittal projection of the external acoustic meatus (c), was measured using lateral radiographs and ventriculographs and showed a constant mathematical relation. The rostral angle was 20.3 +/- 1.0 (mean +/- SD) degree in 23 goats studied regardless of their cranial size which varied considerably from one animal to another. The hypotenuse length (a-b distance) was found to be a good predictor of the rostral nuchal position of the anterior commissure (AC) and the infundibular recess of the third ventricle (INF), by which the individual variance of the stereotaxic coordinates for a given hypothalamic structure could be compensated. The anterior-posterior distances from the external acoustic meatus was highly correlated with the a-b distance for AC (r = 0.88) and INF (r = 0.90). Using these cranial landmarks and the method outlined in this paper, uncertainty in coordinate values for AC and INF in the goat brain was reduced considerably in comparison to deviation observed when the ordinary Horsley-Clarke axis (Reid's plane) was employed.

Dose-discrimination performance of mice for self-administration of morphine into the lateral hypothalamus

Two experiments were performed in BALB/c mice implanted bilaterally with guide cannulae. In the first experiment, the tips of the guide cannulae were positioned 1.5 mm above the lateral hypothalamus (LH). On each experimental day, injection cannulae were inserted into each side of the LH. The experiment, carried out in a Y-maze, was composed of two phases. During the initial acquisition period, which lasted 4 days, animals were allowed to self-inject, successively, on alternate days, one dose of morphine into one side of the LH and a different dose in the other side. From the fifth day, the subjects were given the possibility of choosing between these two doses by entering into a given arm of the Y-maze. When the two doses available were 5 ng and 50 ng or 15 ng and 50 ng, the subjects rapidly discriminated them and preferentially triggered the injection of the higher dose (50 ng). When the two doses available were 30 ng and 50 ng, the mice triggered indifferently the two doses during the first three sessions. A discrimination between these two doses began to become apparent from the fourth session, with the subjects preferring to trigger the dose of 50 ng. In a second experiment, the tips of the guide cannulae were positioned either 1.5 mm or 2.6 mm above the LH, the bilateral injection cannulae consequently being inserted either into the LH or into the overlying ventral thalamus (TH). Experimental conditions were the same as that of Experiment 1.(ABSTRACT TRUNCATED AT 250 WORDS)

Afferent projections to the lateral and dorsomedial hypothalamus in a lizard, Gekko gecko

Afferent projections to the lateral hypothalamic area and dorsomedial hypothalamic nucleus of the lizard Gekko gecko were studied after applications of wheat germ agglutinin conjugated to horseradish peroxidase. Large applications into the hypothalamus labeled several telencephalic populations not observed after smaller injections. These included the rostrolateral area of the dorsal cortex, a sheet of cells deep to the caudal pole of the lateral cortex, the external amygdala, and part of the dorsal ventricular ridge. Other populations were labeled in the diencephalon, including the supraoptic nucleus and nucleus ovalis; in the medulla the medial reticular area was labeled. Injections into the lateral hypothalamic area labeled neurons in the rostrolateral dorsal cortex, anterior, lateral, and dorsal septal nuclei, the striatoamygdalar area, nucleus accumbens, vertical limb of the diagonal band, nucleus of the accessory olfactory tract, the interstitial, ventral anterior, and ventral posterior amygdalar nuclei, several hypothalamic nuclei, and the posteroventral thalamic nucleus. Labeled brainstem populations included the ventral tegmental area, torus semicircularis, parvocellular and ventral isthmal nuclei, superior raphe, and the solitary nucleus. Injections in the dorsomedial hypothalamic nucleus labeled neurons in the rostral and caudolateral poles of the dorsal cortex, anterior septal nucleus, horizontal limb of the diagonal band, nucleus of the anterior commissure, several hypothalamic areas, the lateral habenula, the posteroventral thalamic nucleus, and cells scattered around the dorsolateral anterior thalamic nuclei. Labeled brainstem populations included the torus semicircularis, ventral tegmental area, superior raphe, parvocellular and ventral isthmal nuclei, and the lateral dorsal tegmental nucleus. The results of these studies are compared with findings in amphibians and mammals.

Ascorbic acid concentration in the lateral hypothalamus is related to plasma osmolality

Microdialysis was used to measure extracellular ascorbic and uric acid concentrations in the lateral hypothalamus of water-restricted rats as they drank distilled water or 1.5% NaCl. Other water-restricted rats, not implanted with microdialysis probes, were decapitated 2 h after beginning to drink these fluids. Rats were inverted and their blood was collected for measurements of plasma osmolality and percent hematocrit. Results showed that drinking distilled water produced a significant increase in the ascorbic acid concentration but not in the uric acid concentration. Drinking 1.5% NaCl produced a significant decrease in the uric acid concentration but not in the ascorbic acid concentration. Drinking distilled water decreased mean osmolality from 306.0 to 291.5 mOsm/kg, whereas drinking 1.5% NaCl maintained mean osmolality at water-restricted levels. These results indicate that the extracellular fluid concentration of ascorbic acid in the lateral hypothalamus rises in response to a fall in plasma osmolality.

Effects of morphine injection into the parabrachial area on saccharin preference: modulation by lateral hypothalamic neurons

The aim of the present study was to analyze the effects of morphine injected into the second relay station of the gustatory input pathways, the parabrachial area, on preference for saccharin over water. This study was carried out using both rats whose lateral hypothalamic neurons had been lesioned by ibotenic acid and sham-lesioned rats. As already shown, an 0.3 mM solution of the sweetener, which was clearly preferred over water by the sham-lesioned animals, was neutral for the lesioned rats. The injection of 50 ng of morphine into each parabrachial area transformed this neutral response of the lesioned rats to a clear preference for the sweetener, whereas the preference of sham-lesioned rats for the same solution was converted to an aversive response. Likewise, with a more palatable solution of saccharin (2.5 mM), the injection of 50 ng of morphine decreased the preference of the nonlesioned rats but increased the preference of the lesioned animals. Using the 2.5 mM solution of saccharin, the intraparabrachial injection of higher doses of morphine (100 and 500 ng) did not greatly modify the preference for the sweetener but induced a significant decrease in total fluid intake that was still observed 11 h after the injection of the opiate. These results are discussed: the morphine-induced aversion observed in the nonlesioned rats could be explained either by a specific influence on certain opioid receptors in the parabrachial area or, more probably, by the stimulation of pathways involved in taste or visceral aversive processes and relaying in the parabrachial area.(ABSTRACT TRUNCATED AT 250 WORDS)

Somatic parameters, organ growth, and plasma substrates in weanling rats with lateral hypothalamic lesions one month postoperatively

Somatic and some metabolic aspects of the syndrome that follows bilateral destruction of the lateral hypothalamic area (LHA) have been studied primarily in mature rats. Fewer data are available for the weanling rat. Weanling Sprague-Dawley rats received small (10 mC) bilateral electrolytic lesions (LHAL). Sham-operated controls were pair-gained to LHAL rats (CON-PG) or fed ad lib (CON-ADLIB). All rats were killed 1 month after LHAL. Both LHAL and CON-PG weighed less, had less carcass fat, and were shorter than CON-ADLIB. Also, LHAL were somewhat, but significantly (SIGN), shorter than CON-PG. Rats with LHAL has less carcass protein than CON-ADLIB in percent but not in absolute terms. Liver, epididymal fat pads, diaphragm, kidneys adrenals, testes, spleen, and heart grew SIGN smaller in LHAL vs. CON-ADLIB, but in no instance was there a SIGN difference between LHAL and CON-PG. In body weight percentage, some of these differences (liver, kidneys, heart) were not SIGN. Both LHAL and CON-PG had larger adrenals than CON-ADLIB and both LHAL and CON-PG had SIGN less protein in their livers, epididymal fat pads, and diaphragm than CON-ADLIB. In organ weight percentage, however, LHAL rats had more protein in their livers and fat pads than CON-ADLIB and LHAL rats had less protein in fat pads than CON-PG in absolute but not in percent organ weight terms. Plasma glucose was similar in all groups, but LHAL had SIGN lower triglycerides and total cholesterol than CON-ADLIB.(ABSTRACT TRUNCATED AT 250 WORDS)

Catecholaminergic projections from the solitary tract nucleus to the perifornical hypothalamus

The source of adrenergic and other catecholaminergic fibers innervating the perifornical lateral hypothalamus was localized in the medulla after combination of Fluoro-Gold retrograde tracing and immunohistochemistry for either tyrosine-hydroxylase or phenylethanolamine-N-methyltransferase. Following perifornical injections, Fluoro-Gold-labeled neurons were observed mainly in regions including the noradrenergic and adrenergic cell groups. In the caudal solitary tract nucleus, two kinds of doubly labeled neurons were found: a) numerous noradrenergic neurons in the A2 group at the level of, or caudal to the area postrema; b) some adrenergic neurons in the C2 group at a level immediately rostral to the area postrema. These catecholaminergic neurons connecting the caudal solitary tract nucleus to the perifornical hypothalamus might convey feeding relevant information such as glycemic level or satiety signals.

Sources of cortical, hypothalamic and spinal serotonergic projections: topical organization within the nucleus raphe dorsalis

Retrograde axonal transport of fluorescent tracers (primuline, FluoroGold and Nuclear Yellow) from the spinal cord, frontal cortex, lateral hypothalamus to various neuronal groups of the midbrain periventricular gray substance (periaqueductal gray matter) and to the dorsolateral pontine tegmentum in the rat has been studied. Two large groups of serotonin-containing neurons have been found to be localized in the dorsomedial region of the nucleus raphe dorsalis. They are sources of projections into the thoracic segments of the spinal cord. A part of these neurons gives divergent axon collaterals to the frontal cortex and to the spinal cord. Non-collateral projections of the dorsolateral pontine tegmental catecholaminergic neurons to the spinal cord and the frontal cortex have been revealed. The data obtained give support to the fact that antinociceptive effect of stimulation of the "pure analgesic zone" [Fardin et al. (1984) Brain Res. 306, 105-123.] of the midbrain periaqueductal gray matter may be due to direct involvement of the nucleus raphe dorsalis into a descending control over transmitting nociceptive stimuli at the spinal cord level. Neurotransmissive and neuroregulatory roles of separate cortical, hypothalamic and spinal serotonergic projections of the nucleus raphe dorsalis neurons are discussed.

Hypothalamic involvement in stress-induced hypocalcemia in rats

Although hormonal regulation of blood calcium homeostasis has been intensively investigated in the peripheral organs, the involvement of the central nervous system in calcium regulation is still poorly understood. In the present study, we found that (1) bilateral lesions of the ventromedial nucleus of the hypothalamus (VMH), but not those of the paraventricular hypothalamic nucleus or the lateral hypothalamic area, eliminated immobilization (IMB)-induced hypocalcemia, and (2) electrical stimulation of the VMH decreased the blood calcium level. The results suggest that the VMH has a hypocalcemic function and plays a role in IMB-induced hypocalcemia.

Identification, partial characterization, and hypothalamic distribution of kappa, mu, and delta opioid receptors in a passerine songbird (Junco hyemalis)

Brain tissues obtained from a passerine songbird (dark-eyed junco, Junco hyemalis) were used to identify and partially characterize central opioid receptors. We found that [3H]EKC (putative kappa ligand), [3H]DAMGO (putative mu ligand), and [3H]DPDPE and [3H]pCl-DPDPE (two putative delta ligands) bind to brain tissue preparations specifically, in a time-dependent fashion, and with a high affinity (Kd's < or = 5 nM). Binding sites are present at low concentrations (Bmax < 120 fmol/mg protein), and they are pharmacologically selective. In vitro autoradiography studies revealed a high density of delta receptors in hypothalamic regions (ventromedial and lateral hypothalamus) that regulate feeding behavior. Together with previous studies, these observations suggest that the central influence of opioids on avian food consumption depends on mechanisms located in hypothalamic regions.

The lateral hypothalamic area revisited: neuroanatomy, body weight regulation, neuroendocrinology and metabolism

This article reviews findings that have accumulated since the original description of the syndrome that follows destruction of the lateral hypothalamic area (LHA). These data comprise the areas of neuroanatomy, body weight regulation, neuroendocrinology, neurochemistry, and intermediary metabolism. Neurons in the LHA are the largest in the hypothalamus, and are topographically well organized. The LHA belongs to the parasympathetic area of the hypothalamus, and connects with all major parts of the brain and the major hypothalamic nuclei. Rats with LHA lesions regulate their body weight set point in a primary manner and not because of destruction of a "feeding center". The lower body weight is not due to finickiness. In the early stages of the syndrome, catabolism and running activity are enhanced, and so is the activity of the sympathetic nervous system (SNS) as shown by increased norepinephrine excretion that normalizes one mo later. The LHA plays a role in the feedback control of body weight regulation different from ventromedial (VMN) and dorsomedial (DMN). Tissue preparations from the LHA promote glucose utilization and insulin release. Although it does not belong to the classical hypothysiotropic area of the hypothalamus, the LHA does affect neuroendocrine secretions. No plasma data on growth hormone are available following electrolytic lesions LHA but electrical stimulation fails to elicit GH secretion. Nevertheless, antiserum raised against the 1-37 fragment of human GHRF stains numerous perikarya in the dorsolateral LHA. The plasma circadian corticosterone rhythm is disrupted in LHA lesioned rats, but this is unlikely due to destruction of intrinsic oscillators. Stimulation studies show a profound role of the LHA in glucose metabolism (glycolysis, glycogenesis, gluconeogenesis), this mechanism being cholinergic. Its role in lipolysis appears not to be critical. In general, stimulation of the VMN elicits opposite effects. Lesion studies in rats show altered in vitro glucose carbon incorporation into several tissue fractions both a few days, and one mo after lesion production. Several of these changes may be due to the reduced food intake, others appear to be due to a "true" lesion effect.

Functional and anatomical organization of cardiovascular pressor and depressor sites in the lateral hypothalamic area. II. Ascending projections

Microinjections of L-glutamate or D,L-homocysteic acid were used to stimulate cell bodies in the region of the lateral hypothalamic area (LHA) selectively. Subsequent iontophoretic injections of Phaseolus vulgaris-leucoagglutinin or pressure injections of wheat germ agglutinin-horseradish peroxidase were made into regions containing identified pressor and depressor sites and their connections with the forebrain and cerebral cortex were traced. The results indicate that decreases in blood pressure (10-45 mm Hg) and heart rate (20-70 bpm) could be elicited from tuberal (LHAt) and posterior (LHAp) sites in the LHA and that these regions have ascending projections to the insular cortex, the ventral forebrain including the septal-diagonal band of Broca complex, the ventral palladium, substantia innominata, amygdala, and the lateral preoptic area. In contrast, increases in blood pressure (10-40 mm Hg) and heart rate (20-70 bpm) were elicited primarily from neurons located adjacent to the fornix in the perifornical area (PFA). Injections of tract tracers into this region produced terminal labeling that differed markedly from the pattern seen following injections of tracer into depressor sites in the LHA. In addition, the pattern of anterograde labeling seen following injections of tracer into the anterior PFA differed from that seen following injections of tracer into the posterior PFA. Injections of tracer into the anterior PFA resulted in dense terminal labeling in the medial preoptic area and the parvicellular paraventricular nucleus of the hypothalamus whereas injections into the posterior PFA resulted in dense terminal labeling in the lateral septal nucleus, nucleus accumbens, bed nucleus of the stria terminalis, as well as the medial preoptic area and the parvocellular paraventricular nucleus of the hypothalamus. The results demonstrate that the posterolateral hypothalamus of the rat contains two regions with specific cardiovascular function and highly organized connections with diencephalic, forebrain, and cortical structures.

Chronic food restriction and weight loss produce opioid facilitation of perifornical hypothalamic self-stimulation

Electrical stimulation frequency thresholds for lateral hypothalamic (LH) self-stimulation were monitored throughout a 3 week period of food restriction and a subsequent 3 week period of re-feeding. Rats with electrodes placed in the perifornical LH were sensitive to this dietary manipulation as evidenced by a high positive correlation between body weight and self-stimulation threshold. Rats with electrodes in the zona incerta/subincertal region or ventral hypothalamus displayed little or no change in threshold. Lateral ventricular injection of naltrexone (200.0 nM) reversed the decline in threshold that was otherwise present during food restriction in rats with perifornical placements. Naltrexone had no effect on thresholds of rats with placements outside the perifornical region. These findings suggest that food restriction and weight loss activate an opioid mechanism that facilitates perifornical LH self-stimulation. The documented association of perifornical LH with the phenomenon of stimulation-induced feeding, and the reciprocal connections between this region and gustatory structures, supports the hypothesis that facilitation of self-stimulation by food restriction is related to the natural phenomenon of positive alliesthesia (i.e. the hunger-dependency of food reward).

Hypothalamic melanin-concentrating hormone and alpha-neoendorphin-immunoreactive neurons project to the medial part of the rat parabrachial area

Neurons in the middle and posterior parts of the lateral hypothalamus project to the parabrachial area, and in particular to the gustatory relay-station located in the medial part of this area. In the present study we have examined some of the neuropeptide immunoreactivities of the lateral hypothalamus neurons that project to the gustatory region of the parabrachial area. By coupling retrograde transport and immunohistochemistry, we found that 50-60% of medial parabrachial area-projecting cells located in the juxta-capsular region of the posterior lateral hypothalamus are labeled by rat melanin-concentrating hormone antiserum, while 28% of the retrogradely labeled neurons located in the perifornical lateral hypothalamus are visualized with alpha-neoendorphin antiserum. Moreover, a large number of terminals distributed throughout the parabrachial nucleus are immunoreactive to melanin-concentrating hormone or alpha-neoendorphin antisera. These immunoreactivities are not co-localized within the same lateral hypothalamic neurons. The potential role of these peptidergic projections in the reward mechanisms elicited in the medial parabrachial area and in the control of palatability is discussed.

Amplification of rewarding hypothalamic stimulation following a unilateral lesion in the region of the tuberomammillary nucleus

The tuberomammillary nucleus, a cluster of cells in the posterior hypothalamus, is the only known source of brain histamine. Although this nucleus is well described in terms of anatomy and neurochemistry, only little is known about its function. In the present study, the effect of a lesion in the region of this nucleus on intracranial self-stimulation was examined. Rats were implanted bilaterally with stimulating electrodes in the lateral hypothalamus and unilaterally with one lesion electrode in the region of this nucleus. After three days of baseline testing, half of the animals were given an electrolytic lesion. The animals were retested for six consecutive days, and thereafter weekly for another seven weeks. From the second day postlesion on, we unexpectedly found a gradual increase in response rate, which peaked on day 13 in the ipsilateral hemisphere only. Although there was no further increase over subsequent days, response rates remained elevated during the following seven weekly tests. The observed increase in lateral hypothalamic self-stimulation after an electrolytic lesion of the tuberomammillary nucleus is discussed in terms of an inhibitory system, possibly located in the region of this nucleus which, when removed by the lesion, increased reinforcing effects of the electrical brain stimulation. The fact that the effects on self-stimulation were lateralized to one hemisphere rules out an interpretation in terms of unspecific "performance" variables that could influence rate of lever pressing.

A detailed autoradiographic mapping of histamine H3 receptors in rat brain areas

[3H](R)alpha-methylhistamine, a selective histamine H3-receptor ligand, was used to perform binding studies with membranes and generate light microscopic autoradiograms in sections of the rat brain. High densities of H3 receptors were found in membranes from the anterior part of the cerebral cortex, the accumbens nucleus, the striatum, the olfactory tubercles and the substantia nigra. Autoradiography of sagittal and frontal sections evidenced specific labelling in a number of gray matter areas over a very low background, as determined using thioperamide, a selective H3-receptor antagonist, as competing drug. Labelled areas were identified by comparison with adjacent Nissl-stained sections and their labelling was rated visually. H3 receptors are heterogeneously distributed among areas known to receive histaminergic projections. In the cerebral cortex, H3 receptors are present in all areas and layers, with a rostrocaudal gradient and a higher density in deep layers (laminae IV-VI). In the hippocampal formation, H3 receptors are the most abundant in the dentate gyrus and the subiculum. In the amygdaloid complex, the highest densities are found in the central, lateral and basolateral groups of nuclei. In the basal forebrain, the accumbens nucleus, the striatum, the olfactory tubercles and the globus pallidus are highly labelled. In the thalamus in which histaminergic fibres are scarce, H3 receptors are present in a rather high density, particularly in the midline, median and intralaminar groups of nuclei. In the hypothalamus, where the densest network of histaminergic fibres is found, H3 receptors occur in moderate density, being slightly more abundant in the anterior and medial part. They are also present at the level of the tuberomammillary nuclei where they may reside on histaminergic perikarya. In mesencephalon and lower brainstem, H3 receptors are abundant in the reticular part of the substantia nigra and central gray. They are present in low density in areas of noradrenergic and serotoninergic perikarya and in the spinal cord, where a faint specific labelling is detected in the gray matter, particularly in the external layers of the dorsal horn. In the cerebellum and pituitary gland, H3 receptors are scarce. Kainic acid infusions into the striatum were followed by marked local decreases in H3 receptors evidenced in both membrane binding and autoradiographic studies. Unilateral interruption of the ascending histaminergic pathways via electrocoagulation of the lateral hypothalamic area was followed by ipsilateral increase in striatal [3H](R)alpha-methylhistamine binding, a process consistent with denervation up regulation of postsynaptic H3 receptors.(ABSTRACT TRUNCATED AT 400 WORDS)

Infection specific prion protein (PrP) accumulates on neuronal plasmalemma in scrapie infected mice

Prion protein (PrP) is an abundant membrane-associated host protein which accumulates in abnormal, relatively protease-resistant forms in the brains of animals with scrapie and related diseases. Using correlative light and electron microscopy we determined the sites of subcellular localisation of PrP in mice infected with the 87V strain of scrapie. Disease specific accumulation of PrP was observed at light microscopy as amyloid plaques or as diffuse or granular staining within the neuropil, often clearly associated with individual neurons. Serial electron microscopical preparations were immunostained for PrP by the immunogold method. Gold particles were located on amyloid fibrils and on the plasmalemma of neurites at the periphery of plaques and in the neuropil, irrespective of the morphological form of PrP accumulation when viewed by light microscopy. This suggests that amyloid fibrils are formed following the accumulation and aggregation of sub-unit proteins at the plasmalemma and, furthermore, that normal PrP may be converted to its pathological form at this site.

Glucose utilization and insulin binding in discrete brain areas of obese rats

The present study was carried out to determine whether genetically obese Zucker rats present changes in brain glucose utilization and/or insulin binding when compared to their lean counterparts. Glucose utilization in the whole brain, determined by measurement of 2-deoxy(1-3H)glucose-6-phosphate, was significantly lower in obese than in lean Zucker rats. In order to precise the structure involved, we then used quantitative autoradiography methods after either (1-14C) 2-deoxyglucose injection or 125I-insulin incubation. In obese rats, local cerebral glucose utilization (LCGU) was significantly decreased in the external plexiform layer (-37%, p < 0.05), in the lateral hypothalamus (-23%, p < 0.05), and in the basolateral amygdaloid nucleus (-30%, p < 0.05). In contrast, no difference in specific insulin binding was found between the two genotypes in any of the areas studied. These results are consistent with some data showing a decrease of LCGU in hyperinsulinemic rats. All together, these data show perturbations of glucose utilization, particularly in structures linked to the regulation of body weight and food intake in obese Zucker rats.