Aphagia and adipsia after preferential destruction of nerve cell bodies in hypothalamus

Lateral hypothalamic glutamatergic inputs to VTA glutamatergic neurons mediate prioritization of innate defensive behavior over feeding

The lateral hypothalamus (LH) is involved in feeding behavior and defense responses by interacting with different brain structures, including the Ventral Tegmental Area (VTA). Emerging evidence indicates that LH-glutamatergic neurons infrequently synapse on VTA-dopamine neurons but preferentially establish multiple synapses on VTA-glutamatergic neurons. Here, we demonstrated that LH-glutamatergic inputs to VTA promoted active avoidance, long-term aversion, and escape attempts. By testing feeding in the presence of a predator, we observed that ongoing feeding was decreased, and that this predator-induced decrease in feeding was abolished by photoinhibition of the LH-glutamatergic inputs to VTA. By VTA specific neuronal ablation, we established that predator-induced decreases in feeding were mediated by VTA-glutamatergic neurons but not by dopamine or GABA neurons. Thus, we provided evidence for an unanticipated neuronal circuitry between LH-glutamatergic inputs to VTA-glutamatergic neurons that plays a role in prioritizing escape, and in the switch from feeding to escape in mice.

Optimization of whole-brain rabies virus tracing technology for small cell populations

The lateral hypothalamus (LH) is critically involved in the regulation of homeostatic energy balance. Some neurons in the LH express receptors for leptin (LepRb), a hormone known to increase energy expenditure and decrease energy intake. However, the neuroanatomical inputs to LepRb-expressing LH neurons remain unknown. We used rabies virus tracing technology to map these inputs, but encountered non-specific tracing. To optimize this technology for a minor cell population (LepRb is not ubiquitously expressed in LH), we used LepRb-Cre mice and assessed how different titers of the avian tumor virus receptor A (TVA) helper virus affected rabies tracing efficiency and specificity. We found that rabies expression is dependent on TVA receptor expression, and that leakiness of TVA receptors is dependent on the titer of TVA virus used. We concluded that a titer of 1.0–3.0 × 10⁷ genomic copies per µl of the TVA virus is optimal for rabies tracing. Next, we successfully applied modified rabies virus tracing technology to map inputs to LepRb-expressing LH neurons. We discovered that other neurons in the LH itself, the periventricular hypothalamic nucleus (Pe), the posterior hypothalamic nucleus (PH), the bed nucleus of the stria terminalis (BNST), and the paraventricular hypothalamic nucleus (PVN) are the most prominent input areas to LepRb-expressing LH neurons.

Weight gain and neuroadaptations elicited by high fat diet depend on fatty acid composition

Overconsumption of food is a major health concern in the western world. Palatable food has been shown to alter the activity of neural circuits, and obesity has been linked to alterations in the connectivity between the hypothalamus and cortical regions involved in decision-making and reward processing, putatively modulating the incentive value of food. Outlining neurophysiological adaptations induced by dietary intake of high fat diets (HFD) is thus valuable to establish how the diet by itself may promote overeating. To this end, C57BL/6 mice were fed HFD rich in either saturated fatty acids (HFD-S) or polyunsaturated fatty acids (HFD-P), or a low-fat control diet (LFD) for four weeks. Food and energy intake were monitored and ex vivo electrophysiology was employed to assess neuroadaptations in lateral hypothalamus (LH) and corticostriatal circuits, previously associated with food intake. In addition, the effects of dietary saturated and polyunsaturated fatty acids on the gene expression of NMDA, AMPA and GABA_A receptor subunits in the hypothalamus were investigated. Our data shows that mice fed HFD-P had increased daily food and energy intake compared with mice fed HFD-S or LFD. However, this increase in energy intake had no obesogenic effects. Electrophysiological recordings demonstrated that HFD-P had a selective effect on glutamatergic neurotransmission in the LH, which was concomitant with a change in mRNA expression of AMPA receptor subtypes Gria1, Gria3 and Gria4, with no effect on the mRNA expression of NMDA receptor subtypes or GABA_A receptor subtypes. Furthermore, while synaptic output from corticostriatal subregions was not significantly modulated by diet, synaptic plasticity in the form of long-term depression (LTD) was impaired in the dorsomedial striatum of mice fed HFD-S. In conclusion, this study suggests that the composition of fatty acids in the diet not only affects weight gain, but may also modulate neuronal function and plasticity in brain regions involved in food intake.

A hypothalamus-habenula circuit controls aversion

Encoding and predicting aversive events are critical functions of circuits that support survival and emotional well-being. Maladaptive circuit changes in emotional valence processing can underlie the pathophysiology of affective disorders. The lateral habenula (LHb) has been linked to aversion and mood regulation through modulation of the dopamine and serotonin systems. We have defined the identity and function of glutamatergic (Vglut2) control of the LHb, comparing the role of inputs originating in the globus pallidus internal segment (GPi), and lateral hypothalamic area (LHA), respectively. We found that LHb-projecting LHA neurons, and not the proposed GABA/glutamate co-releasing GPi neurons, are responsible for encoding negative value. Monosynaptic rabies tracing of the presynaptic organization revealed a predominantly limbic input onto LHA Vglut2 neurons, while sensorimotor inputs were more prominent onto GABA/glutamate co-releasing GPi neurons. We further recorded the activity of LHA Vglut2 neurons, by imaging calcium dynamics in response to appetitive versus aversive events in conditioning paradigms. LHA Vglut2 neurons formed activity clusters representing distinct reward or aversion signals, including a population that responded to mild foot shocks and predicted aversive events. We found that the LHb-projecting LHA Vglut2 neurons encode negative valence and rapidly develop a prediction signal for negative events. These findings establish the glutamatergic LHA-LHb circuit as a critical node in value processing.

Hypocretin as a Hub for Arousal and Motivation

The lateral hypothalamus is comprised of a heterogeneous mix of neurons that serve to integrate and regulate sleep, feeding, stress, energy balance, reward, and motivated behavior. Within these populations, the hypocretin/orexin neurons are among the most well studied. Here, we provide an overview on how these neurons act as a central hub integrating sensory and physiological information to tune arousal and motivated behavior accordingly. We give special attention to their role in sleep-wake states and conditions of hyper-arousal, as is the case with stress-induced anxiety. We further discuss their roles in feeding, drug-seeking, and sexual behavior, which are all dependent on the motivational state of the animal. We further emphasize the application of powerful techniques, such as optogenetics, chemogenetics, and fiber photometry, to delineate the role these neurons play in lateral hypothalamic functions.

Presynaptic Regulation of Leptin in a Defined Lateral Hypothalamus-Ventral Tegmental Area Neurocircuitry Depends on Energy State

Synaptic transmission controls brain activity and behaviors, including food intake. Leptin, an adipocyte-derived hormone, acts on neurons located in the lateral hypothalamic area (LHA) to maintain energy homeostasis and regulate food intake behavior. The specific synaptic mechanisms, cell types, and neural projections mediating this effect remain unclear. In male mice, using pathway-specific retrograde tracing, whole-cell patch-clamp recordings and post hoc cell type identification, we found that leptin reduces excitatory synaptic strength onto both melanin-concentrating hormone- and orexin-expressing neurons projecting from the LHA to the ventral tegmental area (VTA), which may affect dopamine signaling and motivation for feeding. A presynaptic mechanism mediated by distinct intracellular signaling mechanisms may account for this regulation by leptin. The regulatory effects of leptin depend on intact leptin receptor signaling. Interestingly, the synaptic regulatory function of leptin in the LHA-to-VTA neuronal pathway is highly sensitive to energy states: both energy deficiency (acute fasting) and excessive energy storage (high-fat diet-induced obesity) blunt the effect of leptin. These data revealed that leptin may regulate synaptic transmission in the LHA-to-VTA neurocircuitry in an inverted "U-shape" fashion dependent on plasma glucose levels and related to metabolic states.SIGNIFICANCE STATEMENT The lateral hypothalamic area (LHA) to ventral tegmental area (VTA) projection is an important neural pathway involved in balancing whole-body energy states and reward. We found that the excitatory synaptic inputs to both orexin- and melanin-concentrating hormone expressing LHA neurons projecting to the VTA were suppressed by leptin, a peptide hormone derived from adipocytes that signals peripheral energy status to the brain. Interestingly, energy states seem to affect how leptin regulates synaptic transmission since both the depletion of energy induced by acute food deprivation and excessive storage of energy by high-fat diet feeding dampen the suppressive effect of leptin on synaptic transmission. Together, these data show that leptin regulates synaptic transmission and might be important for maintaining energy homeostasis.

Lateral Hypothalamic Control of the Ventral Tegmental Area: Reward Evaluation and the Driving of Motivated Behavior

The lateral hypothalamus (LH) plays an important role in many motivated behaviors, sleep-wake states, food intake, drug-seeking, energy balance, etc. It is also home to a heterogeneous population of neurons that express and co-express multiple neuropeptides including hypocretin (Hcrt), melanin-concentrating hormone (MCH), cocaine- and amphetamine-regulated transcript (CART) and neurotensin (NT). These neurons project widely throughout the brain to areas such as the locus coeruleus, the bed nucleus of the stria terminalis, the amygdala and the ventral tegmental area (VTA). Lateral hypothalamic projections to the VTA are believed to be important for driving behavior due to the involvement of dopaminergic reward circuitry. The purpose of this article is to review current knowledge regarding the lateral hypothalamic connections to the VTA and the role they play in driving these behaviors.

An Inhibitory Septum to Lateral Hypothalamus Circuit That Suppresses Feeding

Feeding behavior is orchestrated by neural circuits primarily residing in the hypothalamus and hindbrain. However, the relative influence of cognitive and emotional brain circuits to the feeding circuitry in the hypothalamus and hindbrain remains unclear. Here, using the cell-type selectivity of genetic methods, circuit mapping, and behavior assays, we sought to decipher neural circuits emanating from the septal nucleus to the lateral hypothalamus (LH) that contribute to neural regulation of food intake in mice. We found that chemogenetic and optogenetic activation of septal vesicular GABA transporter (vGAT)-containing neurons or their projections in the LH reduced food intake in mice. Consistently, chemogenetic inhibition of septal vGAT neurons increased food intake. Furthermore, we investigated a previously unknown neural circuit originating from septal vGAT neurons to a subset of vGAT neurons in the LH, an area involved in homeostatic and hedonic control of energy states. Collectively, our data reveal an inhibitory septohypothalamic feeding circuit that might serve as a therapeutic target for the treatment of eating disorders such as anorexia nervosa.

SIGNIFICANCE STATEMENT

Our results demonstrate that top-down projections from the septum to the hypothalamus control food intake negatively. Given the known role for both of these brain regions in the control of feeding and emotion-related behaviors, these findings reveal previously unknown neural circuitry that is likely implicated in emotional aspects of food intake and provide new insights into the development of therapeutic targets for the treatment of eating disorders.

Food-Anticipatory Circadian Rhythms in Rats with Paraventricular and Lateral Hypothalamic Ablations

Neural mechanisms generating food-anticipatory circadian rhythms in rats are sep arate from the suprachiasmatic nuclei, a putative circadian pacemaker for light-entrainable circadian rhythms. We attempted to localize these mechanisms using lesions focused on the paraventricular and lateral hypothalamic areas, two regions that have functional properties likely to characterize a food-entrainable circadian oscillator. Rats with complete radiofre quency ablation of the paraventricular and suprachiasmatic nuclei or ibotenic acid destruction of the lateral hypothalamus showed anticipatory circadian rhythms to a 2-hr daily mealtime, as measured by locomotor activity or activity directed toward a food bin. The long-term continued function of the meal-associated oscillator was also unaffected by the lesions, as demonstrated by a reappearance of activity at the former mealtime during 3 days of starvation after 11 or 12 days of ad libitum feeding. Several rats with total or partial paraventricular lesions failed to exhibit anticipatory locomotor activity, but did show anticipatory food- bin-related activity. These hypothalamic lesions may alter the probability of particular antic ipatory behaviors, but they do not eliminate the food-entrainable circadian timekeeping func tion.

Inhibitory Input from the Lateral Hypothalamus to the Ventral Tegmental Area Disinhibits Dopamine Neurons and Promotes Behavioral Activation

Projections from the lateral hypothalamus (LH) to the ventral tegmental area (VTA), containing both GABAergic and glutamatergic components, encode conditioned responses and control compulsive reward-seeking behavior. GABAergic neurons in the LH have been shown to mediate appetitive and feeding-related behaviors. Here we show that the GABAergic component of the LH-VTA pathway supports positive reinforcement and place preference, while the glutamatergic component mediates place avoidance. In addition, our results indicate that photoactivation of these projections modulates other behaviors, such as social interaction and perseverant investigation of a novel object. We provide evidence that photostimulation of the GABAergic LH-VTA component, but not the glutamatergic component, increases dopamine (DA) release in the nucleus accumbens (NAc) via inhibition of local VTA GABAergic neurons. Our study clarifies how GABAergic LH inputs to the VTA can contribute to generalized behavioral activation across multiple contexts, consistent with a role in increasing motivational salience. VIDEO ABSTRACT.

Distinct Types of Feeding Related Neurons in Mouse Hypothalamus

The last two decades of research provided evidence for a substantial heterogeneity among feeding-related neurons (FRNs) in the hypothalamus. However, it remains unclear how FRNs differ in their firing patterns during food intake. Here, we investigated the relationship between the activity of neurons in mouse hypothalamus and their feeding behavior. Using tetrode-based in vivo recording technique, we identified various firing patterns of hypothalamic FRNs, which, after the initiation of food intake, can be sorted into four types: sharp increase (type I), slow increase (type II), sharp decrease (type III), and sustained decrease (type IV) of firing rates. The feeding-related firing response of FRNs was rigidly related to the duration of food intake and, to a less extent, associated with the type of food. The majority of these FRNs responded to glucose and leptin and exhibited electrophysiological characteristics of putative GABAergic neurons. In conclusion, our study demonstrated the diversity of neurons in the complex hypothalamic network coordinating food intake.

Lateral hypothalamic circuits for feeding and reward

In experiments conducted over 60 years ago, the lateral hypothalamic area (LHA) was identified as a critical neuroanatomical substrate for motivated behavior. Electrical stimulation of the LHA induces voracious feeding even in well-fed animals. In the absence of food, animals will work tirelessly, often lever-pressing thousands of times per hour, for electrical stimulation at the same site that provokes feeding, drinking and other species-typical motivated behaviors. Here we review the classic findings from electrical stimulation studies and integrate them with more recent work that has used contemporary circuit-based approaches to study the LHA. We identify specific anatomically and molecularly defined LHA elements that integrate diverse information arising from cortical, extended amygdala and basal forebrain networks to ultimately generate a highly specified and invigorated behavioral state conveyed via LHA projections to downstream reward and feeding-specific circuits.

Reduction in 50-kHz call-numbers and suppression of tickling-associated positive affective behaviour after lesioning of the lateral hypothalamic parvafox nucleus in rats

The parvafox nucleus is located ventrolaterally in the lateral hypothalamic area (LHA). Its core and shell are composed of neurons expressing the calcium-binding protein parvalbumin (PV) and the transcription factor Foxb1, respectively. Given the known functions of the LHA and that the parvafox nucleus receives afferents from the lateral orbitofrontal cortex and projects to the periaqueductal gray matter, a functional role of this entity in the expression of positive emotions has been postulated. The purpose of the present study was to ascertain whether the deletion of neurons in the parvafox nucleus influenced the tickling-induced 50-kHz calls, which are thought to reflect positive affective states, in rats. To this end, tickling of the animals (heterospecific play) was combined with intracerebral injections of the excitotoxin kainic acid into the parvafox nucleus. The most pronounced surgery-associated reduction in 50-kHz call-numbers was observed in the group of rats in which, on the basis of PV-immunoreactive-cell counts in the parvafox nucleus, bilateral lesions had been successfully produced. Two other parameters that were implemented to quantify positive affective behaviour, namely, an approach towards and a following of the hand of the tickling experimenter, were likewise most markedly suppressed in the group of rats with bilaterally successful lesions. Furthermore, positive correlations were found between each of the investigated parameters. Our data afford evidence that the parvafox nucleus plays a role in the production of 50-kHz calls in rats, and, more generally, in the expression of positive emotions.

To ingest or rest? Specialized roles of lateral hypothalamic area neurons in coordinating energy balance

Survival depends on an organism’s ability to sense nutrient status and accordingly regulate intake and energy expenditure behaviors. Uncoupling of energy sensing and behavior, however, underlies energy balance disorders such as anorexia or obesity. The hypothalamus regulates energy balance, and in particular the lateral hypothalamic area (LHA) is poised to coordinate peripheral cues of energy status and behaviors that impact weight, such as drinking, locomotor behavior, arousal/sleep and autonomic output. There are several populations of LHA neurons that are defined by their neuropeptide content and contribute to energy balance. LHA neurons that express the neuropeptides melanin-concentrating hormone (MCH) or orexins/hypocretins (OX) are best characterized and these neurons play important roles in regulating ingestion, arousal, locomotor behavior and autonomic function via distinct neuronal circuits. Recently, another population of LHA neurons containing the neuropeptide Neurotensin (Nts) has been implicated in coordinating anorectic stimuli and behavior to regulate hydration and energy balance. Understanding the specific roles of MCH, OX and Nts neurons in harmonizing energy sensing and behavior thus has the potential to inform pharmacological strategies to modify behaviors and treat energy balance disorders.

The role of the lateral hypothalamus and orexin in ingestive behavior: a model for the translation of past experience and sensed deficits into motivated behaviors

The hypothalamus has been recognized for its involvement in both maintaining homeostasis and mediating motivated behaviors. The present article discusses a region of the hypothalamus known as the lateral hypothalamic area (LHA). It is proposed that brain nuclei within the LHA including the dorsal region of the lateral hypothalamus (LHAd) and perifornical area (PeF) provide a link between neural systems that regulate homeostasis and those that mediate appetitive motivated behaviors. Functional and immunohistochemical data indicate that the LHA promotes many motivated behaviors including food intake, water intake, salt intake, and sexual behavior. Anatomical tracing experiments demonstrate that the LHA is positioned to receive inputs from brain areas involved in regulating body fluid and energy homeostasis. Regions within the LHA send dense projections to the ventral tegmental area (VTA), providing a pathway for the LHA to influence dopaminergic systems generally recognized to be involved in motivated behaviors and their reinforcement. Furthermore, the LHA contains neurons that synthesize orexin/hypocretin, a neuropeptide that promotes many appetitive motivated behaviors. The LHA also receives inputs from brain areas involved in reward-related learning and orexin neuron activation can become conditioned to environmental stimuli that are associated with rewards. Therefore, it is hypothesized that the LHA integrates signaling from areas that regulate body fluid and energy balance and reward-related learning. In turn, this information is “fed into” mesolimbic circuitry to influence the performance of motivated behaviors. This hypothesis may foster experiments that will result in an improved understanding of LHA function. An improved understanding of LHA function may aid in treating disorders that are associated with an excess or impairment in the expression of ingestive behavior including obesity, anorexia, impairments in thirst, salt gluttony, and salt deficiency.

Differential involvement of two cortical masticatory areas in submandibular salivary secretion in rats

To evaluate the role of the masticatory area in the cerebral cortex in the masticatory-salivary reflex, we investigated submandibular salivary secretion, jaw-movement trajectory and electromyographic activity of the jaw-opener (digastric) and jaw-closer (masseter) muscles evoked by repetitive electrical stimulation of the cortical masticatory area in anesthetized rats. Rats have two cortical masticatory areas: the anterior area (A-area) in the orofacial motor cortex, and the posterior area (P-area) in the insular cortex. Our defined P-area extended more caudally than the previous reported one. P-area stimulation induced vigorous salivary secretion (about 20 µl/min) and rhythmical jaw movements (3-4 Hz) resembling masticatory movements. Salivary flow persisted even after minimizing jaw movements by curarization. A-area stimulation induced small and fast rhythmical jaw movements (6-8 Hz) resembling licking of solutions, but not salivary secretion. These findings suggest that P-area controls salivary secretion as well as mastication, and may be involved in the masticatory-salivary reflex.

Relation of autonomic and cardiac abnormalities to ventricular fibrillation in a rat model of epilepsy

Cardiac autonomic, conduction, and structural changes may occur in epilepsy and may contribute to sudden unexpected death in epilepsy (SUDEP), e.g. by increasing the risk for ventricular fibrillation (VF). In a model of chronic seizures in rats, we sought to study (1) cardiac and autonomic derangements that accompany the epileptic state, (2) whether chronically seizing rats experienced more significant cardiac effects after severe acute seizures, and (3) the susceptibility of chronically seizing rats to VF arising from autonomic and hypoxemic changes, which commonly occur during seizures. Sprague-Dawely rats were injected with saline or kainic acid to induce chronic seizures. At 2-3 months or 7-11 months after injection, these rats were studied with both 12-lead electrocardiography (to assess heart rate variability and QT dispersion) and echocardiography under ketamine/xylazine or urethane anesthesia. Hearts were subsequently excised, weighed, and examined histologically. Epileptic rats exhibited decreased vagal tone, increased QT dispersion, and eccentric cardiac hypertrophy without significant cardiac fibrosis, especially at 7-11 months post-injection. Of these three findings, vagal tone was inversely correlated with heart weights. Epileptic rats exhibited diminished systolic function compared to controls after severe acute seizures. However, animals with long-standing chronic seizures were less susceptible to autonomic/hypoxemia-driven VF, and their susceptibility inversely correlated with mean left ventricular wall thickness on histology. On the basis of this model, we conclude that cardiac changes accompany epilepsy and these can lead to significant seizure-associated cardiac performance decreases, but these cardiac changes actually lower the probability of VF.

Differential effects of electrical stimulation of the central amygdala and lateral hypothalamus on fos-immunoreactive neurons in the gustatory brainstem and taste reactivity behaviors in conscious rats

Projections from the central amygdala (CeA) and lateral hypothalamus (LH) modulate the activity of gustatory brainstem neurons, however, the role of these projections in gustatory behaviors is unclear. The goal of the current study was to determine the effects of electrical stimulation of the CeA or LH on unconditioned taste reactivity (TR) behaviors in response to intra-oral infusion of tastants. In conscious rats, electrical stimulation of the CeA or LH was delivered with and without simultaneous intra-oral infusion of taste solutions via an intra-oral cannula. Immunohistochemistry for the Fos protein was used to identify neurons in the gustatory brainstem activated by the electrical and/or intra-oral stimulation. In the absence of intra-oral infusion of a tastant, electrical stimulation of either the CeA or the LH increased the number of ingestive, but not aversive, TR behaviors performed. During intra-oral infusions of taste solutions, CeA stimulation tended to increase aversive behaviors whereas LH stimulation dramatically reduced the number of aversive responses to quinine hydrochloride (QHCl). These data indicate that projections from the CeA and LH alter TR behaviors. A few of the behavioral effects were accompanied by changes in the number of Fos-immunoreactive neurons in the gustatory brainstem, suggesting a possible anatomical substrate for these effects.

Lateral hypothalamus contains two types of palatability-related taste responses with distinct dynamics

The taste of foods, in particular the palatability of these tastes, exerts a powerful influence on our feeding choices. Although the lateral hypothalamus (LH) has long been known to regulate feeding behavior, taste processing in LH remains relatively understudied. Here, we examined single-unit LH responses in rats subjected to a battery of taste stimuli that differed in both chemical composition and palatability. Like neurons in cortex and amygdala, LH neurons produced a brief epoch of nonspecific responses followed by a protracted period of taste-specific firing. Unlike in cortex, however, where palatability-related information only appears 500 ms after the onset of taste-specific firing, taste specificity in LH was dominated by palatability-related firing, consistent with LH's role as a feeding center. Upon closer inspection, taste-specific LH neurons fell reliably into one of two subtypes: the first type showed a reliable affinity for palatable tastes, low spontaneous firing rates, phasic responses, and relatively narrow tuning; the second type showed strongest modulation to aversive tastes, high spontaneous firing rates, protracted responses, and broader tuning. Although neurons producing both types of responses were found within the same regions of LH, cross-correlation analyses suggest that they may participate in distinct functional networks. Our data shed light on the implementation of palatability processing both within LH and throughout the taste circuit, and may ultimately have implications for LH's role in the formation and maintenance of taste preferences and aversions.

Lateral hypothalamus contains two types of palatability-related taste responses with distinct dynamics

The taste of foods, in particular the palatability of these tastes, exerts a powerful influence on our feeding choices. Although the lateral hypothalamus (LH) has long been known to regulate feeding behavior, taste processing in LH remains relatively understudied. Here, we examined single-unit LH responses in rats subjected to a battery of taste stimuli that differed in both chemical composition and palatability. Like neurons in cortex and amygdala, LH neurons produced a brief epoch of nonspecific responses followed by a protracted period of taste-specific firing. Unlike in cortex, however, where palatability-related information only appears 500 ms after the onset of taste-specific firing, taste specificity in LH was dominated by palatability-related firing, consistent with LH's role as a feeding center. Upon closer inspection, taste-specific LH neurons fell reliably into one of two subtypes: the first type showed a reliable affinity for palatable tastes, low spontaneous firing rates, phasic responses, and relatively narrow tuning; the second type showed strongest modulation to aversive tastes, high spontaneous firing rates, protracted responses, and broader tuning. Although neurons producing both types of responses were found within the same regions of LH, cross-correlation analyses suggest that they may participate in distinct functional networks. Our data shed light on the implementation of palatability processing both within LH and throughout the taste circuit, and may ultimately have implications for LH's role in the formation and maintenance of taste preferences and aversions.

CART peptide and the mesolimbic dopamine system

Over the past decade, CART peptide has been commonly associated with the rewarding and reinforcing properties of drugs of abuse and natural rewards such as food. The mesolimbic dopamine system is the predominant pathway involved in mediating reward and reinforcement. Many behavioral and neuroanatomical studies have been conducted in order to further elucidate the importance of CART-containing neurons within the mesolimbic dopamine system. This chapter will review the current knowledge of the localization, synaptic connectivity and neurochemical content of CART peptidecontaining neurons in nuclei of the mesolimbic reward pathway. These nuclei include the nucleus accumbens (NA), ventral midbrain, and the lateral hypothalamus (LH). In conclusion, an interconnected CART-containing loop between the NA, ventral midbrain and LH has evolved from these neuroanatomical studies that may have functional implications for CART peptide's involvement in reward and reinforcement.

Water deprivation increases the expression of neuronal nitric oxide synthase (nNOS) but not orexin-A in the lateral hypothalamic area of the rat

The discovery that the lateral hypothalamic area (LHA) might be important in modulating drinking behavior and fluid balance has led to numerous studies aimed at identifying the key neurotransmitters/neuromodulators and pathways involved. While past studies have demonstrated the presence of neuronal nitric oxide synthase (nNOS) within the LHA, its role in the regulation of fluid homeostasis is not known. In light of this, and the mounting evidence suggesting a role for nitric oxide in osmotic regulation within the hypothalamus, this study sought to determine the effects of 24- and 72-hours of water deprivation on nNOS protein expression within the LHA of the rat with immunohistochemistry. In euhydrated control animals we observed nNOS-like immunoreactivity throughout all levels of the LHA. Following 24 hours of dehydration the number of nNOS-like immunopositive neurons was significantly increased in the rostral but not the caudal regions of LHA. Seventy-two hours of water deprivation lead to further increases in nNOS-like immunoreactivity at different levels of the LHA. Interestingly, however, we observed increased nNOS-like immunoreactivity in the caudal regions of the LHA that was not evident after 24 hours of water deprivation. Double-labeling immunofluorescence histochemistry revealed that the nNOS-like immunoreactive neurons were not colocalized with the orexin-A-containing neurons. These results suggest that an osmotic challenge leads to an upregulation of nNOS immunoreactivity within discrete areas of the LHA. This altered neurochemistry within the LHA further highlights the potential importance of nitric oxide and the LHA in central regulation of fluid homeostasis.

Dual roles in feeding for AMPA/kainate receptors: receptor activation or inactivation within distinct hypothalamic regions elicits feeding behavior

We have previously shown that hypothalamic injections of glutamate, or agonists of its ionotropic receptors (iGluRs), elicit intense feeding responses in satiated rats [Brain Res. 613 (1993) 88, Brain Res. 630 (1993) 41]. While attempting to clarify the role of the AMPA and kainate (KA) receptor subtypes in glutamatergic feeding systems, we discovered that lateral hypothalamic (LH) injection of high doses of the competitive AMPA/KA receptor antagonist, NBQX (10 and 30 nmol), elicited a pronounced feeding response. We questioned whether this effect was due to inactivation of AMPA or possibly KA receptors. To determine whether other AMPA/KA antagonists can also elicit feeding, we tested whether injection of CNQX, another AMPA/KA receptor antagonist, also stimulates eating and whether these feeding stimulatory effects were due to antagonists' actions in the LH or in other hypothalamic sites. Here we report that NBQX and CNQX elicit feeding in a dose dependent manner and are most effective when injected into the perifornical hypothalamus (PFH), or into the paraventricular nucleus (PVN) and, to a lesser extent, into the LH of satiated rats. In contrast, AMPA was most effective in stimulating feeding when injected into the LH, confirming previous reports. These data suggest that either activation or inactivation of AMPA/KA receptors in distinct but overlapping hypothalamic sites may be sufficient to induce feeding behavior, indicating a broadened role for glutamate in hypothalamic feeding mechanisms.

The feeding response to melanin-concentrating hormone is attenuated by antagonism of the NPY Y(1)-receptor in the rat

Melanin-concentrating hormone (MCH) and NPY are orexigenic peptides localized in the lateral hypothalamic area and arcuate nucleus, respectively. Although both NPY- and MCH-containing fibers innervate areas of the hypothalamus implicated in feeding, the extent to which the regulation of appetite is dependent on interactions between these peptides is unknown. Daytime feeding responses to 2 nmol MCH, 1 nmol NPY, or vehicle were investigated in male Sprague Dawley rats previously implanted with intracerebroventricular cannulas. The effects of prior administration of the Y(1)-receptor antagonists BIBO 3304 (20 nmol) or GR231118 (5 nmol) on these responses were examined. NPY and MCH stimulated food intake relative to vehicle (4 h intake, 5.9 +/- 0.7 and 3.6 +/- 0.2 g, respectively; P < 0.0001). BIBO 3304 and GR231118 significantly inhibited MCH- induced feeding by 73% (P < 0.01) and 86% (P < 0.01), respectively, at 2 h. Coadministration of NPY and MCH did not increase food intake above that in response to NPY alone; however, prior administration of BIBO 3304 resulted in a less marked inhibition of feeding (P < 0.05, 30 min only). Inhibition of MCH-induced feeding by two structurally different NPY Y(1)-receptor antagonists provides strong evidence that the orexigenic action of MCH involves the Y(1)-receptor.

Dopamine-acetylcholine interaction in the rat lateral hypothalamus in the control of locomotion

Pharmacological, neurochemical, and behavioral techniques were used to characterize DA-ACh interaction within the lateral hypothalamus (LH) in the context of locomotion, feeding behavior, and reinforcement. In Experiment 1, the muscarinic agonist carbachol injected in the LH increased locomotor activity in proportion to dose. In Experiment 2, the same doses of carbachol proportionately increased exctracellular DA in the nucleus accumbens (Nac) as monitored by brain microdialysis. Dihydroxyphenylacetic acid (DOPAC) and homovanillic acid (HVA) also increased. In Experiment 3, LH infusion by reverse microdialysis of the D(2) receptor blocker sulpiride released ACh in the LH in a dose-response manner. This suggested that sulpiride disinhibits ACh release via D(2) receptors in the LH and thereby facilitates behavior. Confirming this in Experiment 4, local LH atropine 5 min before sulpiride suppressed the locomotor response to sulpiride for about 20 min. These results suggest that sulpiride acts in the LH by disinhibiting a hypothalamic locomotor mechanism that is cholinergically driven and connected with the mesoaccumbens dopamine pathway. Given prior results that local sulpiride in the LH can induce hyperphagia and reward, this system may be involved in searching for food and rewarding feeding behavior. In conclusion, DA acts in the LH via D(2) receptors to inhibit cholinergic neurons or terminals that are part of an approach system for eating.

Leptin differentially regulates NPY and POMC neurons projecting to the lateral hypothalamic area

Recent studies have reinforced the view that the lateral hypothalamic area (LHA) regulates food intake and body weight. We identified leptin-sensitive neurons in the arcuate nucleus of the hypothalamus (Arc) that innervate the LHA using retrograde tracing with leptin administration. We found that retrogradely labeled cells in the Arc contained neuropeptide Y (NPY) mRNA or proopiomelanocortin (POMC) mRNA. Following leptin administration, NPY cells in the Arc did not express Fos but expressed suppressor of cytokine signaling-3 (SOCS-3) mRNA. In contrast, leptin induced both Fos and SOCS-3 expression in POMC neurons, many of which also innervated the LHA. These findings suggest that leptin directly and differentially engages NPY and POMC neurons that project to the LHA, linking circulating leptin and neurons that regulate feeding behavior and body weight homeostasis.

Cells of origin of the trigeminohypothalamic tract in the rat

Recent studies have demonstrated that a large number of spinal cord neurons convey somatosensory and visceral nociceptive information directly from cervical, lumbar, and sacral spinal cord segments to the hypothalamus. Because sensory information from head and orofacial structures is processed by all subnuclei of the trigeminal brainstem nuclear complex (TBNC) we hypothesized that all of them contain neurons that project directly to the hypothalamus. In the present study, we used the retrograde tracer Fluoro-Gold to examine this hypothesis. Fluoro-Gold injections that filled most of the hypothalamus on one side labeled approximately 1,000 neurons (best case = 1,048, mean = 718 +/- 240) bilaterally (70% contralateral) within all trigeminal subnuclei and C1-2. Of these neurons, 86% were distributed caudal to the obex (22% in C2, 22% in C1, 23% in subnucleus caudalis, and 18% in the transition zone between subnuclei caudalis and interpolaris), and 14% rostral to the obex (6% in subnucleus interpolaris, 4% in subnucleus oralis, and 4% in subnucleus principalis). Caudal to the obex, most labeled neurons were found in laminae I-II and V and the paratrigeminal nucleus, and fewer neurons in laminae III-IV and X. The distribution of retrogradely labeled neurons in TBNC gray matter areas that receive monosynaptic input from trigeminal primary afferent fibers innervating extracranial orofacial structures (such as the cornea, nose, tongue, teeth, lips, vibrissae, and skin) and intracranial structures (such as the meninges and cerebral blood vessels) suggests that sensory and nociceptive information originating in these tissues could be transferred to the hypothalamus directly by this pathway.

Orphan neurones and amine excess: the functional neuropathology of Parkinsonism and neuropsychiatric disease

The aetiology and treatment of Parkinsonism is currently conceptualised within a dopamine (DA) deficiency-repletion framework. Loss of striatal DA is thought to cause motor impairment of which tremor, bradykinaesia and rigidity are prominent features. Repletion of deficient DA should at least minimise parkinsonian signs and symptoms. In Section 2, based on extensive pre-clinical and clinical findings, the instability of this approach to Parkinsonism is scrutinised as the existing negative findings challenging the DA deficiency hypothesis are reviewed and reinterpreted. In Section 3 it is suggested that Parkinsonism is due to a DA excess far from the striatum in the area of the posterior lateral hypothalamus (PLH) and the substantia nigra (SN). This unique area, around the diencephalon/mesencephalon border (DCMCB), is packed with many ascending and descending fibres which undergo functional transformation during degeneration, collectively labelled 'orphan neurones'. These malformed cells remain functional resulting in pathological release of transmitter and perpetual neurotoxicity. Orphan neurone formation is commonly observed in the PLH of animals and in man exhibiting Parkinsonism. The mechanism by which orphan neurones impair motor function is analogous to that seen in the diseased human heart. From this perspective, to conceptualise orphan neurones at the DCMCB as 'Time bombs in the brain' is neither fanciful nor unrealistic [E.M. Stricker, M.J. Zigmond, Comments on effects of nigro-striatal dopamine lesions, Appetite 5 (1984) 266-267] as the DA excess phenomenon demands a different therapeutic approach for the management of Parkinsonism. In Section 4 the focus is on this novel concept of treatment strategies by concentrating on non-invasive, pharmacological and surgical modification of functional orphan neurones as they affect adjacent systems. The Orphan neurone/DA excess hypothesis permits a more comprehensive and defendable interpretation of the interrelationship between Parkinsonism and schizophrenia and other related disorders.

The hypocretins: hypothalamus-specific peptides with neuroexcitatory activity

We describe a hypothalamus-specific mRNA that encodes preprohypocretin, the putative precursor of a pair of peptides that share substantial amino acid identities with the gut hormone secretin. The hypocretin (Hcrt) protein products are restricted to neuronal cell bodies of the dorsal and lateral hypothalamic areas. The fibers of these neurons are widespread throughout the posterior hypothalamus and project to multiple targets in other areas, including brainstem and thalamus. Hcrt immunoreactivity is associated with large granular vesicles at synapses. One of the Hcrt peptides was excitatory when applied to cultured, synaptically coupled hypothalamic neurons, but not hippocampal neurons. These observations suggest that the hypocretins function within the CNS as neurotransmitters.

The hypothalamic ventromedial nuclei couple activity in the hypothalamo-pituitary-adrenal axis to the morning fed or fasted state

Function in the adrenocortical system is markedly altered by availability of food. Basal activity is lowest and stress responsivity highest in the morning when nocturnal rats eat approximately 90% of their daily calories during the dark. After an overnight fast, basal corticotrophin and corticosteroid levels are elevated, and responsivity to stressors is decreased. Central neural sites that control these changes are unidentified. The hypothalamic ventromedial nuclei (VMN) appear to signal satiety; lesions result in increased food intake, obesity, and elevated basal insulin and corticosteroids. Thus, the VMN are good candidates for calorically mediated control of adrenocortical system function in satiated rats. We injected colchicine into the VMN to cause reversible inhibition of activity (Avrith and Mogenson, 1978) and tested the effects on basal and stimulated function in the adrenocortical system. Colchicine-injected rats that fed ad libitum exhibited increased basal but reduced corticotrophin and corticosterone responses to restraint in the morning compared with controls. By contrast, after an overnight fast, control rats had increased basal adrenocortical hormones and decreased stress responses that did not differ from colchicine-injected rats. Colchicine was visualized within cells in the VMN for up to 5 d using fluorescein/colchicine, and the treatment did not cause increased gliosis; moreover, the functional effects of the injections were reversed within 15 d. We conclude that (1) the VMN serve to couple activity in the adrenocortical system to energy intake and (2) discrete colchicine injections provide a behaviorally and neuroendocrinologically useful period of inhibition without causing permanent functional damage.

Distribution and time course of appearance of "dark" neurons and EEG activity after amygdaloid kainate lesion

To determine the extent and time course of local and distant neuronal damage produced by microiontophoretic administration of kainic acid (KA) into the central amygdaloid nucleus, distribution of neuronal damage was compared in various brain areas after different survival times. For demonstration of damaged, so-called "dark" neurons, a newly developed silver stain was employed. In addition, silver staining method was used to visualize microglia cells. In a separate experiment, electroencephalographic (EEG) activity was recorded from the amygdaloid body, hippocampus, and the frontal cortex before and after microiontophoretic KA lesion of the central amygdaloid nucleus. It was observed that (1) even a minute amount of KA into this nucleus caused transient neuronal damage in distant brain areas; (2) the hippocampal formation, subiculum, entorhinal cortex, piriform cortex, and lateral septum were consistently affected; (3) the extent and time course of neuronal damage and appearance of microglia cells varied from area to area; (4) the KA neurotoxicity in distant brain areas appeared to depend on specific excitatory circuits, especially in the hippocampal formation; (5) the appearance and time course of pathologic EEG activity paralleled the appearance of dark neurons; and (6) the absence of pathologic EEG activity and the lack of massive neuronal loss or microglia proliferation in distant brain areas of rats surviving longer than 48 h suggested that these areas may have recovered both morphologically and functionally. Although details of cellular mechanism responsible for development of "dark" degeneration of neurons are not known, the silver method employed in the present study proved to be sensitive, useful tool for fine histological analyses of early and distant consequences of excitotoxic lesions.

Organization of projections from the dorsomedial nucleus of the hypothalamus: a PHA-L study in the rat

The axonal projections of the dorsomedial nucleus of the hypothalamus were investigated by using Phaseolous vulgaris-leucoagglutinin. The main conclusion of this work is that these projections are largely intrahypothalamic, with smaller components directed toward the brainstem and telencephalon. Although the intrahypothalamic pathways are very complex and intermix at various levels, we conclude that dorsomedial nucleus outputs follow three distinct ascending pathways: periventricular, coursing through the hypothalamic periventricular zone; ventral, traveling beneath the medial zone; and lateral, ascending in medial parts of the lateral hypothalamic area. Within the hypothalamus, the most densely innervated areas are the paraventricular nucleus, other dorsal regions of the periventricular zone, the preoptic suprachiasmatic nucleus, and the parastrial nucleus. Other significant terminal fields include the median preoptic, anteroventral periventricular, lateral part of the medial preoptic, and anteroventral preoptic nuclei; and the retrochiasmatic (including perisuprachiasmatic) area. Descending projections follow two pathways that also converge at various levels: a dorsal pathway in the midbrain periventricular system travels through, and primarily innervates, the periaqueductal and pontine gray, and a ventral pathway extends through ventromedial regions of the brainstem. Although sparse, fibers in the later pathway can be traced as far caudally as the nucleus of the solitary tract. The results are discussed relative to the pathways and properties of nearby hypothalamic medial zone nuclei. Dorsomedial nucleus projections are similar to certain other nuclei (e.g., anteroventral periventricular and parastrial) with predominantly intrahypothalamic projections, and different from those arising in the medial zone nuclei (medial preoptic, anterior hypothalamic, ventromedial, and mammillary.

Mediation of dehydration-induced peptidergic gene expression in the rat lateral hypothalamic area by forebrain afferent projections

We have previously shown in dehydrated rats that cellular levels of the mRNAs encoding the precursor peptides for corticotropin-releasing hormone and neurotensin/neuromedin N significantly increase in a restricted region of the lateral hypothalamic area (Watts, 1992, Brain Res. 581:208-216). The experiments reported here address the role that forebrain osmosensitive cells groups or regions associated with autonomic regulation play in developing this mRNA response. The first experiment showed that unilateral knife cuts placed between the rostral forebrain and the lateral hypothalamic area (LHA) will unilaterally attenuate the mRNA response in the LHA to dehydration. In a second experiment, small injections of the retrograde tracer Fluorogold into the region of the LHA containing these mRNAs revealed a direct input from the osmosensitive median preoptic nucleus and subfornical organ and from the fusiform nucleus of the bed nuclei of the stria terminalis, which is part of a complex of cell groups associated with autonomic regulation. We found that at least 30% of the neurons in the median preoptic nucleus and subfornical organ and 14% of the neurons in the fusiform nucleus of the bed nuclei of the stria terminalis that project to the LHA responded to a rapid increase in plasma osmolality with increased c-fos mRNA levels. In the final experiment, injections of Fluorogold into the LHA were made simultaneously with ipsilateral rostral knife cuts. Here the numbers of neurons accumulating Fluorogold in the median preoptic nucleus, subfornical organ, and the fusiform nucleus were all significantly decreased concomitantly with attenuated mRNA responses in the LHA to dehydration. We conclude that the LHA receives direct and functional projections from the median preoptic nucleus, subfornical organ, and the fusiform nucleus. These projections appear capable of mediating a substantial part of the response of peptidergic mRNAs in the LHA to dehydration.

Kainic acid versus carbachol induced emotional-defensive response in the cat

The emotional-defensive response (EDR) and accompanied neurotoxic and electroencephalographic (EEG) effects induced by injection of kainic acid (KA, 0.1; 0.2 microgram) into the midbrain periaqueductal grey region (PAG) and antero-medial hypothalamus (AMH) in the cat were examined and compared with EDR and accompanied neurotoxic and EEG effects induced by injection of cholinergic agent, carbachol (CCH), into the same sites. The injections of KA (0.2 microgram) into the PAG induced EDR which closely resembled the defense behavior typically observed after administration of CCH. However, in contrast to CCH-induced EDR, the defensive response induced by KA was found to be accompanied by EEG symptoms of epileptiform activity in the limbic cortex and a massive cell loss in the site of injection. It is proposed that KA-induced EDR and seizure activity may have resulted from the activation of different cell populations localized either in the vicinity of the injection (i.e., PAG region) and in the area remote from the injection loci, the limbic cortex. KA induced activation of PAG neuronal network would trigger the 'local response' (emotional-defensive response) and produce a remote effect-epileptiform activity.

The lateral hypothalamic area revisited: ingestive behavior

This article discusses the role of the lateral hypothalamic area (LHA) in feeding and drinking and draws on data obtained from lesion and stimulation studies and neurochemical and electrophysiological manipulations of the area. The LHA is involved in catecholaminergic and serotonergic feeding systems and plays a role in circadian feeding, sex differences in feeding and spontaneous activity. This article discusses the LHA regarding dietary self-selection, responses to high-protein diets, amino acid imbalances, liquid and cafeteria diets, placentophagia, "stress eating," finickiness, diet texture, consistency and taste, aversion learning, olfaction and the effects of post-operative period manipulations by hormonal and other means. Glucose-sensitive neurons have been identified in the LHA and their manipulation by insulin and 2-deoxy-D-glucose is discussed. The effects on feeding of numerous transmitters, hormones and appetite depressants are described, as is the role of the LHA in salivation, lacrimation, gastric motility and secretion, and sensorimotor deficits. The LHA is also illuminated as regards temperature and feeding, circumventricular organs and thirst and electrolyte dynamics. A discussion of its role in the ischymetric hypothesis as an integrative Gestalt concept concludes the review.

Dopamine-deficient mice are severely hypoactive, adipsic, and aphagic

Mice unable to synthesize dopamine (DA) specifically in dopaminergic neurons were created by inactivating the tyrosine hydroxylase (TH) gene then by restoring TH function in noradrenergic cells. These DA-deficient (DA-/-) mice were born at expected frequency but became hypoactive and stopped feeding a few weeks after birth. Midbrain dopaminergic neurons, their projections, and most characteristics of their target neurons in the striatum appeared normal. Within a few minutes of being injected with L-dihdroxyphenylalanine (L-DOPA), the product of TH, the DA-/- mice became more active and consumed more food than control mice. With continued administration of L-DOPA, nearly normal growth was achieved. These studies indicate that DA is essential for movement and feeding, but is not required for the development of neural circuits that control these behaviors.

Medial forebrain bundle stimulation in rats activates glycogen phosphorylase in layers 4, 5b and 6 of ipsilateral granular neocortex

Functional activation in human brain produces an increase in glycolytic metabolism. Animal studies suggest activation-induced glycolysis is coupled to brain glycogenolysis. Medial forebrain bundle (MFB) stimulation activates the release of neurotransmitters which promote neocortical glycogenolysis in vitro. In the present study, active glycogen phosphorylase (GP), an index of glycogenolysis, is assessed histochemically in rat brain after 15 min of MFB self-stimulation. Active GP increased significantly in layers 4, 5b and 6 of granular neocortex ipsilateral to MFB self-stimulation. Restriction of increased glycogenolysis to granular neocortex suggests an important functional interaction between sensory neocortical processing and ascending MFB systems.

The lateral hypothalamus: a primary site mediating excitatory amino acid-elicited eating

Lateral hypothalamic (LH) injections of the excitatory neurotransmitter glutamate, or its excitatory amino acid (EAA) agonists, kainic acid (KA), D,L-alpha-amino-3-hydroxy-5-methyl-isoxazole propionic acid (AMPA), or N-methyl-D-aspartic acid (NMDA), can rapidly elicit an intense feeding response in satiated rats. To determine whether the LH is the actual locus of this effect, we compared these compounds' ability to stimulate feeding when injected into the LH, versus when injected into sites bracketing this region. Food intake in groups of adult male rats was measured 1 h after injection of glutamate (30-900 nmol), KA (0.1-1.0 nmol), AMPA (0.33-3.3 nmol), NMDA (0.33-33.3 nmol) or vehicle, through chronically implanted guide cannulas, into one of seven brain sites. These sites were: the LH, the anterior and posterior tips of the LH, the thalamus immediately dorsal to the LH, the amygdala just lateral to the LH, or the paraventricular and perifornical areas medial to the LH. The results show that across doses and agonists the eating-stimulatory effects were largest with injections into the LH. In the LH, glutamate between 300 and 900 nmol elicited a dose-dependent eating response of up to 5 g within 1 h (P < 0.01). Each of the other agonists at doses of 3.3 nmol or less elicited eating responses of at least 10 g with injections into this site. Injections into the other brain sites produced either no eating, or occasionally smaller and less consistent eating responses.(ABSTRACT TRUNCATED AT 250 WORDS)

Neuronal histamine in the hypothalamus suppresses food intake in rats

Using probes to manipulate hypothalamic neuronal histamine, we report here that changes in neuronal histamine modulate physiological feeding behavior in rats. Infusion of alpha-fluoromethylhistidine (FMH), a "suicide" inhibitor of histidine decarboxylase (HDC), into the third cerebroventricle induced feeding in the early light phase when the histamine synthesis was most accelerated. FMH at an optimum 2.24 mumol dose elicited feeding in 100% of rats. Treatment of FMH specifically and selectively decreased concentration of histamine without affecting concentrations of catecholamines in the hypothalamus. Immediately before the dark phase, when the histamine synthesis was normally lower, FMH infusion did not affect feeding-related parameters such as meal size, meal duration or latency to eat. Conversely, thioperamide, which facilitates both synthesis and release of neuronal histamine by blocking presynaptic autoinhibitory H3 receptors, significantly decreased food intake after infusion of a 100-nmol dose into the third cerebroventricle. The effect of thioperamide was abolished with i.p. injection of 26 mumol/kg chlorpheniramine, an H1antagonist. FMH at 224 nmol was microinfused bilaterally into the feeding-related nuclei in the hypothalamus. The ventromedial nucleus (VMH) and the paraventricular nucleus (PVN), but not the lateral hypothalamus, the dorsomedial hypothalamus or the preoptic anterior hypothalamus were identified as the active sites for the modulation. Neuronal histamine may convey suppressive signals of food intake through H1 receptors in the VMH and the PVN with diurnal fluctuation.

Where does damage lead to enhanced food aversion: the ventral pallidum/substantia innominata or lateral hypothalamus?

It is well known that lesions of the lateral hypothalamus (LH) produce aphagia. Several previous studies have reported that lateral hypothalamus damage produces food aversion in addition to aphagia. However, damage to other regions near the LH also produce aphagia and enhanced aversion. The purpose of this study was to resolve where the site or sites for aversion-inducing lesions is/are located. Small, bilateral excitotoxin lesions (QUIN, 10 micrograms in 1 microliter or IBO, 15 micrograms in 1 microliter) or bilateral sham injections of vehicle were made into the globus pallidus (GP), the ventral pallidum/substantia innominata (VP/SI) or the lateral hypothalamus (LH). Affective reactions to taste were elicited by infusing sucrose solutions (1 M) into the mouth via chronic oral cannulae. The number of aversive responses (gapes, chin-rubbing, head-shaking and forelimb flails) emitted was tallied. Individual lesions were mapped and a single 'necessary and sufficient' site for damage-induced aversion was identified (the area of overlapping damage common to all rats that showed enhanced aversive reactions). To identify the lesions, two lesion-mapping techniques were used: (1) a conventional neuron-counting procedure in which an attempt is made to count all neurons within a brain region, and (2) a new modified 'fractionator' procedure consisting of exhaustive 400 x magnification counts at point locations within a brain region. Results indicated that aversive reactions to food are enhanced only following bilateral neuron loss (> 70%) from the caudal ventromedial VP/SI alone. This shared site has a lateral diameter of 1.0 mm, a dorsoventral diameter of 0.5 mm and a rostrocaudal diameter of 1.0 mm. Damage restricted to the LH never produced enhanced aversion even when it produced aphagia. The crucial region for aversion is located ventral and medial to the globus pallidus and dorsal and lateral to the lateral hypothalamus.

Effect of ACE inhibitors on atrial natriuretic factor in the brains of rats with reduced renal mass

We tested the effect of renal insufficiency, with and without angiotensin (Ang) converting enzyme (ACE) inhibition, on blood and brain atrial natriuretic factor (ANF) in rats. Two ACEs, one which penetrates into the CNS and one which does not, were used to distinguish between peripheral and central ACE effects. Rats underwent 5/6 nephrectomy (5/6-NPX) by ligation of renal arterial branches. After seven days, 28 5/6-NPX rats received lisinopril 20 mg/kg/day and 28 5/6-NPX rats received quinapril 30 mg/kg/day orally for five days, while 28 5/6-NPX control rats and 28 sham rats did not. Body weight, blood pressure, drinking and urine volume were monitored. At sacrifice, urine, plasma, and brain tissue was collected. ANF in 16 brain areas was measured by radioimmunoassay. 5/6-NPX resulted in increased blood pressure, increased urine volume, proteinuria, and increased drinking. Both ACEs lowered blood pressure to sham values and decreased proteinuria. Both ACEs increased plasma renin activity and decreased plasma ANF. However, only lisinopril decreased drinking and urine volume. 5/6-NPX increased ANF values in six brain areas, namely the periventricular preoptic nucleus, the arcuate nucleus, the perifornical nucleus, the periventricular hypothalamic nucleus, the paraventricular nucleus, and the dorsal raphe nucleus compared to sham rats. These same increases in brain ANF were also observed in 5/6-NPX rats given quinapril, compared to shams. However, lisinopril lowered ANF to sham levels in the periventricular preoptic nucleus, the arcuate nucleus, and the perifornical nucleus. In the three additional brain areas, namely the periventricular hypothalamic nucleus, the paraventricular nucleus, and the dorsal raphe nucleus, lisinopril did not effect the elevated ANF concentrations.(ABSTRACT TRUNCATED AT 250 WORDS)