The tuberomammillary nucleus region as a reinforcement inhibiting substrate: facilitation of ipsihypothalamic self-stimulation by unilateral ibotenic acid lesions

Targeting Histamine and Histamine Receptors for Memory Regulation: An Emotional Perspective

Histamine has long been accepted as a pro-cognitive agent. However, lines of evidence have suggested that the roles of histamine in learning and memory processes are much more complex than previously thought. When explained by the spatial perspectives, there are many contradictory results. However, using emotional memory perspectives, we suspect that the histaminergic system may interplay with stress, reward inhibition, and attention to modulate emotional memory formation. The functional diversity of histamine makes it a viable target for clinical management of neuropsychiatric disorders. Here, we update the current knowledge about the functions of histamine in emotional memory and summarize the underlying molecular and neural circuit mechanisms. Finally, we review the main clinical studies about the impacts of histamine-related compounds on memory and discuss insights into future research on the roles of histamine in emotional memory. Despite the recent progress in histamine research, the histaminergic emotional memory circuits are poorly understood, and it is also worth verifying the functions of histamine receptors in a more spatiotemporally specific manner.

Histamine receptors, agonists, and antagonists in health and disease

Histamine in the brain is produced by a group of tuberomamillary neurons in the posterior hypothalamus and a limited number of mast cells in different parts of the brain. Four G-protein-coupled receptors mediate the effects of histamine. Two of these receptors, H3 and H4 receptors, are high-affinity receptors in the brain and immune system, respectively. The two classic histamine receptors, H1 receptor and H2 receptor, are well known as drug targets for allergy and gastric ulcer, respectively. These receptors have lower affinity for histamine than the more recently discovered H3 and H4 receptors. The H1 and H2 receptors are important postsynaptic receptors in the brain, and they mediate many of the central effects of histamine on, e.g., alertness and wakefulness. H3 receptor is a pre- and postsynaptic receptor, which regulates release of histamine and several other neurotransmitters, including serotonin, GABA, and glutamate. H4 receptor is found in cerebral blood vessels and microglia, but its expression in neurons is not yet well established. Pitolisant, a H3 receptor antagonist, is used to treat narcolepsy and hypersomnia. H1 receptor antagonists have been used to treat insomnia, but its use requires precautions due to potential side effects. H2 receptor antagonists have shown efficacy in treatment of schizophrenia, but they are not in widespread clinical use. H4 receptor ligands may in the future be tested for neuroimmunological disorders and potentially neurodegenerative disorders in which inflammation plays a role, but clinical tests have not yet been initiated.

The effect of quetiapine (Seroquel™) on conditioned place preference and elevated plus maze tests in rats when administered alone and in combination with (+)-amphetamine

RATIONALE

Recent case reports describe recreational use of quetiapine and drug-seeking behaviour to obtain quetiapine, an atypical antipsychotic.

OBJECTIVE

We examined the hypothesis that quetiapine (10, 20 or 40 mg/kg) alone or co-administered with (+)-amphetamine (0.25, 0.5, 0.75 or 2.0 mg/kg) will affect reward and/or decrease anxiety in rats, as measured by conditioned place preference (CPP) and elevated plus maze (EPM) test, respectively.

RESULTS

Quetiapine (20 mg/kg) produced greater open arm time and entries in the EPM test compared to 10 and 40 mg/kg, and quetiapine (10 mg/kg) significantly increased open arm entries and time when co-administered with (+)-amphetamine (0.5 mg/kg) compared to (+)-amphetamine (0.5 mg/kg) alone, suggesting decreased anxiety. Quetiapine (10, 20 or 40 mg/kg) produced no CPP when administered alone; the lowest dose of quetiapine (10 mg/kg) reduced CPP produced by a low dose of (+)-amphetamine (0.25 mg/kg), but had no significant effect on CPP produced by a higher dose (0.5 mg/kg).

DISCUSSION

The quetiapine-induced anxiolytic effect in the EPM might explain why humans are misusing quetiapine and combining it with (+)-amphetamine. It is possible that humans experience an anxiolytic effect of the combined drugs and relatively unaltered rewarding effects of (+)-amphetamine. The results shed some light on the question of why humans are abusing and misusing quetiapine, despite its dopamine (DA) D2 receptor antagonism; it will be the task of future studies to identify the pharmacological mechanism mediating this behaviour.

JNJ-39220675, a novel selective histamine H3 receptor antagonist, reduces the abuse-related effects of alcohol in rats

RATIONALE

A few recent studies suggest that brain histamine levels and signaling via H(3) receptors play an important role in modulation of alcohol stimulation and reward in rodents.

OBJECTIVE

The present study characterized the effects of a novel, selective, and brain penetrant H(3) receptor antagonist (JNJ-39220675) on the reinforcing effects of alcohol in rats.

METHODS

The effect of JNJ-39220675 on alcohol intake and alcohol relapse-like behavior was evaluated in selectively bred alcohol-preferring (P) rats using the standard two-bottle choice method. The compound was also tested on operant alcohol self administration in non-dependent rats and on alcohol-induced ataxia using the rotarod apparatus. In addition, alcohol-induced dopamine release in the nucleus accumbens was tested in freely moving rats.

RESULTS

Subcutaneous administration of the selective H(3) receptor antagonist dose-dependently reduced both alcohol intake and preference in alcohol-preferring rats. JNJ-39220675 also reduced alcohol preference in the same strain of rats following a 3-day alcohol deprivation. The compound significantly and dose-dependently reduced alcohol self-administration without changing saccharin self-administration in alcohol non-dependent rats. Furthermore, the compound did not change the ataxic effects of alcohol, alcohol elimination rate, nor alcohol-induced dopamine release in nucleus accumbens.

CONCLUSIONS

These results indicate that blockade of H(3) receptor should be considered as a new attractive mechanism for the treatment of alcoholism.

Effects of histamine H3 receptor ligands on the rewarding, stimulant and motor-impairing effects of ethanol in DBA/2J mice

Histamine H3 receptor (H3R) antagonists are currently being investigated for the possible therapeutic use in various cognitive deficits such as those in schizophrenia, attention deficit hyperactivity disorder and Alzheimer's disease. Our previous studies suggest a role for H3Rs in ethanol-related behaviors in rat and mice. Here we have examined the role of different H3R ligands on the effects of ethanol in conditioned place preference (CPP) paradigm, stimulation of locomotor activity and motor impairment in rotarod and balance beam in male DBA/2J mice. We found that H3R antagonists ciproxifan and JNJ-10181457 inhibited the ethanol-evoked CPP whereas H3R agonist immepip did not alter ethanol-induced place preference. Acute stimulatory response by ethanol was also modulated by H3R ligands. Ciproxifan increased ethanol activation when ethanol was given 1g/kg but not at 1.5g/kg dose. Immepip pretreatment diminished ethanol stimulation and increased motor-impairing effects of ethanol on the balance beam. In conclusion, these findings give further evidence of the involvement of H3R in the regulation of the effects of ethanol. The inhibition of ethanol reward by H3R antagonism implies that H3R might be a possible target to suppress compulsory ethanol seeking. This article is part of a Special Issue entitled 'Trends in neuropharmacology: in memory of Erminio Costa'.

Involvement of the brain histaminergic system in addiction and addiction-related behaviors: a comprehensive review with emphasis on the potential therapeutic use of histaminergic compounds in drug dependence

Neurons that produce histamine are exclusively located in the tuberomamillary nucleus of the posterior hypothalamus and send widespread projections to almost all brain areas. Neuronal histamine is involved in many physiological and behavioral functions such as arousal, feeding behavior and learning. Although conflicting data have been published, several studies have also demonstrated a role of histamine in the psychomotor and rewarding effects of addictive drugs. Pharmacological and brain lesion experiments initially led to the proposition that the histaminergic system exerts an inhibitory influence on drug reward processes, opposed to that of the dopaminergic system. The purpose of this review is to summarize the relevant literature on this topic and to discuss whether the inhibitory function of histamine on drug reward is supported by current evidence from published results. Research conducted during the past decade demonstrated that the ability of many antihistaminic drugs to potentiate addiction-related behaviors essentially results from non-specific effects and does not constitute a valid argument in support of an inhibitory function of histamine on reward processes. The reviewed findings also indicate that histamine can either stimulate or inhibit the dopamine mesolimbic system through distinct neuronal mechanisms involving different histamine receptors. Finally, the hypothesis that the histaminergic system plays an inhibitory role on drug reward appears to be essentially supported by place conditioning studies that focused on morphine reward. The present review suggests that the development of drugs capable of activating the histaminergic system may offer promising therapeutic tools for the treatment of opioid dependence.

Histamine and H3 receptor-dependent mechanisms regulate ethanol stimulation and conditioned place preference in mice

RATIONALE

Neuronal histamine has a prominent role in sleep-wake control and body homeostasis, but a number of studies suggest that histamine has also a role in higher brain functions including drug reward.

OBJECTIVE

The present experiments characterized the involvement of histamine and its H3 receptor in ethanol-related behaviors in mice.

MATERIALS AND METHODS

Male histidine decarboxylase knockout (HDC KO) and control mice were used to study the role of histamine in ethanol-induced stimulation of locomotor activity, impairment of motor coordination, and conditioned place preference (CPP). Male C57BL/6Sca mice were used to study the effects of H3 receptor antagonist in the effects of ethanol on locomotor activity.

RESULTS

The HDC KO mice displayed a weaker stimulatory response to acute ethanol than the wild-type (WT) mice. No differences between genotypes were found after ethanol administration on accelerating rotarod. The HDC KO mice showed stronger ethanol-induced CPP than the WT mice. Binding of the GABA(A) receptor ligand [(3)H]Ro15-4513 was not markedly changed in HDC KO mouse brain and thus could not explain altered responses in KO mice. Ethanol increased the activity of C57BL/6Sca mice, and H3 receptor antagonist ciproxifan inhibited this stimulation. In CPP paradigm ciproxifan, an H3 receptor inverse agonist potentiated ethanol reward.

CONCLUSIONS

Histaminergic neurotransmission seems to be necessary for the stimulatory effect of ethanol to occur, whereas lack of histamine leads to changes that enhance the conditioned reward by ethanol. Our findings also suggest a role for histamine H3 receptor in modulation of the ethanol stimulation and reward.

The role of antihistaminic effects in the misuse of quetiapine: a case report and review of the literature

Recent case reports and case series suggest that the atypical antipsychotic quetiapine has the potential for misuse. This includes drug-seeking behaviors motivated by quetiapine as well as inappropriate (intranasal or intravenous) administration. We present an additional case of quetiapine misuse and review other published cases. In general, quetiapine misuse is associated with prior CNS depressant use and is more common in forensic settings. The mechanism of reinforcement for this misuse is unknown, but we hypothesize that it is related to quetiapine's pharmacological profile as an antihistamine with a relative low affinity for dopamine receptors. The risks to individuals and society of exaggerating/simulating symptoms to obtain high-dose quetiapine in the absence of a clinical indication are discussed. This includes the unwelcome possibility of restricting access to this effective medication.

Involvement of the histaminergic system on appetitive learning and its interaction with haloperidol in goldfish

This study investigated the actions of the histaminergic system on appetitive learning and memory, and its interaction with the dopaminergic system in goldfish. It consisted of nine sessions, in which fish were tested in a four-arm tank. On day 1, the animals were habituated for 10 min. On day 2, they were placed in one arm and had to find food at the left or the right arm. Time to begin feeding was recorded, and the procedure repeated for more 3 days (training phase). On training day 4, seven groups were injected with saline, seven with haloperidol (2.0 mg/kg) and one with DMSO solution before training and after feeding, three groups received saline, six chlorpheniramine (CPA) (1.0, 4.0 and 8.0 mg/kg), and six l-histidine (LH) (25, 50 and 100 mg/kg). Saline groups were considered as control of CPA and LH treated groups and DMSO as control of haloperidol. A non-injected group was also included. Testing occurred after 24 h. A reversal procedure was conducted 24h after testing and repeated for 3 days. The groups receiving CPA at 1.0 and 8.0 mg/kg and LH at 25, 50 and 100 mg/kg differed between Test and Reversal day 1. Pre-treatment with haloperidol plus 8.0 mg/kg of CPA and 25 and 50 mg/kg of LH reverted the treatment effect. However, in the groups treated with 1.0 mg/kg of CPA and 100 mg/kg of LH, the difference remained. This study confirmed the interaction between the histaminergic and the dopaminergic systems on memory process in goldfish.

Histamine in the brain: Beyond sleep and memory

A few decades elapsed between the attribution of unwanted side effects of classic antihistamine compounds to the blockade of central H(1) receptors, and the acceptance of the concept that the histaminergic system commands general states of metabolism and consciousness. In the early 80s, two laboratories discovered independently that histaminergic neurons are located in the posterior hypothalamus and project to the whole CNS [Panula P, Yang HY, Costa E. Histamine-containing neurons in the rat hypothalamus. Proc Natl Acad Sci 1984;81:2572-76, Watanabe T, Taguchi Y, Hayashi H, Tanaka J, Shiosaka S, Tohyama M, Kubota H, Terano Y, Wada H. Evidence for the presence of a histaminergic neuron system in the rat brain: an immunohistochemical analysis. Neurosci Lett 1983;39:249-54], suggesting a global nature of histamine regulatory effects. Recently, functional studies demonstrated that activation of the central histaminergic system alters CNS functions in both behavioral and homeostatic contexts, which include sleep and wakefulness, learning and memory, anxiety, locomotion, feeding and drinking, and neuroendocrine regulation. These actions are achieved through interactions with other neurotransmitter systems, and the interplay between histaminergic neurons and other neurotransmitter systems are becoming clear. Hence, numerous laboratories are pursuing novel compounds targeting the three known histamine receptors found in the brain for various therapeutic indications. Preclinical studies are focusing on three major areas of interest and intense research is mainly oriented towards providing drugs for the treatment of sleep, cognitive and feeding disorders. This commentary is intended to summarize some of the latest findings that suggest functional roles for the interplay between histamine and other neurotransmitter systems, and to propose novel interactions as physiological substrates that may partially underlie some of the behavioral changes observed following manipulation of the histaminergic system.

Lesion of the tuberomammillary nucleus E2-region attenuates postictal seizure protection in rats

Postictal seizure protection (PSP) is an endogenous anticonvulsant phenomenon that follows an epileptic seizure and inhibits the induction of further seizures. The tuberomammillary nucleus (TM), located in the posterior hypothalamus, consists of five subregions and is the sole source of histaminergic neurons in the brain. To determine whether the TM is involved in PSP in rats, we tested the effects of bilateral electrolytic lesions of the TM E2-region on seizures induced by intermittent maximal electroshock (MES). The TM E2-region lesions significantly attenuated PSP during the intermittent MES procedure. Furthermore, intracerebroventricular injection of alpha-fluoromethylhistidine (100 microg), a selective and irreversible histidine decarboxylase inhibitor, mimicked the attenuation of PSP induced by the lesion of TM E2-region. In addition, neurochemical experiments revealed that the TM E2-region lesions markedly decreased basal histamine levels in the cortex, hippocampus, brainstem and hypothalamus, but had no significant effect on basal glutamate and GABA levels. Moreover, intermittent MES induced a persistent decrease of brain histamine levels in both sham-operated and lesioned rats. These results indicate that through its intrinsic histaminergic system, the TM may exert powerful inhibitory function during the intermittent MES procedure and actively participate in the mechanisms of PSP.

The psychostimulant and rewarding effects of cocaine in histidine decarboxylase knockout mice do not support the hypothesis of an inhibitory function of histamine on reward

RATIONALE AND OBJECTIVES

Lesion studies have shown that the tuberomammillary nucleus (TM) exerts inhibitory effects on the brain reward system. To determine whether histamine from the TM is involved in that reward inhibitory function, we assessed the stimulant and rewarding effects of cocaine in knockout mice lacking histidine decarboxylase (HDC KO mice), the histamine-synthesizing enzyme. If histamine actually plays an inhibitory role in reward, then it would be expected that mice lacking histamine would be more sensitive to the behavioral effects of cocaine.

MATERIALS AND METHODS

The first experiment characterized spontaneous locomotion and cocaine-induced hyperactivity (0, 8, and 16 mg/kg, i.p.) in wild-type and HDC KO mice. The rewarding effects of cocaine were investigated in a second experiment with the place-conditioning technique.

RESULTS

The first experiment demonstrated that histidine decarboxylase mice showed reduced exploratory behaviors but normal habituation to the test chambers. After habituation to the test chambers, HDC KO mice were slightly, but significantly, less stimulated by cocaine than control mice. This finding was replicated in the second experiment, when cocaine-induced activity was monitored with the place-conditioning apparatus. Furthermore, a significant place preference was present in both genotypes for 8 and 16 mg/kg cocaine, but not for 2 and 4 mg/kg.

CONCLUSIONS

Our data confirm previous results demonstrating that HDC KO mice show reduced exploratory behaviors. However, contrary to the hypothesis that histamine plays an inhibitory role in reward, histamine-deficient mice were not more responsive to the psychostimulant effects of cocaine.

Endogenous histamine inhibits the development of morphine-induced conditioned place preference

AIM

The conditioned place preference (CPP) paradigm was used to investigate the effects of endogenous histamine on the processes leading to morphine-induced reward-seeking behavior in Sprague-Dawley rats.

METHODS

The model of CPP was used to assess the rewarding effect of morphine. The levels of histamine, glutamate, gamma-aminobutyric acid (GABA), dopamine (DA) and 3, 4-dihydroxyphenylacetic acid (DOPAC) in rat brains were measured with high-performance liquid chromatography. Immunohistochemistry technique was used to observe the morphological changes of neurons.

RESULTS

Intraperitoneal injection of morphine (2, 5 or 10 mg/kg) induced the development of CPP in a dose-dependent manner. In addition, morphine administrations (10 mg/kg) decreased the histamine content and reduced the number and size of histaminergic neurons in the tubero-mammillary nucleus (TM), as well as markedly increasing the DOPAC/DA ratios in the ventral tegmental area (VTA) and nucleus accumbens (NAc). Intraperitoneal injection of histidine (50, 100 or 200 mg/kg) dose-dependently inhibited the development of morphine-induced CPP. Bilateral lesions of the TM, which decreased the histamine levels in the VTA and NAc, potentiated the development of CPP induced by morphine (1 mg/kg, a dose that produced no appreciable effect when given alone) and increased the DOPAC/DA ratios in the VTA and NAc, but did not change the glutamate or GABA levels in these nuclei. Histidine reversed the effects of the TM lesions.

CONCLUSION

These results indicate that endogenous histamine plays a role in inhibiting the development of morphine-induced reward-seeking behavior, and the inhibition may involve the modulation of dopaminergic activity.

The H3 antagonist thioperamide reveals conditioned preference for a context associated with an inactive small dose of cocaine in C57BL/6J mice

The histaminergic system has been speculated to be involved in the inhibitory control of drug reward, H1 and H2 antagonists having been found to potentiate conditioned place preference induced by morphine or cocaine. In contrast, the role of H3 receptors in cocaine-induced place preference is still unknown. The present study tested the effects of thioperamide (0, 10 and 20 mg/kg, i.p.), an H3 autoreceptor antagonist, on the development of a conditioned place preference induced by cocaine (0, 2 and 8 mg/kg, i.p.) in C57BL/6J mice. Thioperamide was injected 10 min before each cocaine-pairing session. The activity scores recorded on the first cocaine-pairing session were also used to test the effects of thioperamide on cocaine-induced locomotor activity. Thioperamide alone had no reinforcing effects and did not affect the conditioned place preference induced by 8 mg/kg cocaine. However, thioperamide dose-dependently revealed a conditioned place preference induced by 2 mg/kg cocaine, a dose that was inactive per se. Finally, thioperamide dose-dependently potentiated the stimulant effects of cocaine, in spite of its slight hypolocomotor effect when given alone. Our results strongly suggest that H3 antagonists potentiate the stimulant and reinforcing effects of cocaine in mice.

Tracing the Neuroanatomical Profiles of Reward Pathways with Markers of Neuronal Activation

Functional neuroanatomical tools have played an important role in proposing which structures underlie brain stimulation reward circuitry. This review focuses on studies employing metabolic markers of neuronal and glial activation, including 2-deoxyglucose, cytochrome oxidase, and glycogen phosphorylase, and a marker of cellular activation, the immediate early gene c-fos. The principles underlying each method, their application to the study of brain stimulation reward, and their strengths and limitations are described. The usefulness of this strategy in identifying candidate structures, and the degree of overlap in the patterns of activation arising from different markers is addressed in detail. How these data have contributed to an understanding of the organization of reward circuitry and directed our thinking towards an alternative framework of neuronal arrangement is discussed in the final section.

The physiology of brain histamine

Histamine-releasing neurons are located exclusively in the TM of the hypothalamus, from where they project to practically all brain regions, with ventral areas (hypothalamus, basal forebrain, amygdala) receiving a particularly strong innervation. The intrinsic electrophysiological properties of TM neurons (slow spontaneous firing, broad action potentials, deep after hyperpolarisations, etc.) are extremely similar to other aminergic neurons. Their firing rate varies across the sleep-wake cycle, being highest during waking and lowest during rapid-eye movement sleep. In contrast to other aminergic neurons somatodendritic autoreceptors (H3) do not activate an inwardly rectifying potassium channel but instead control firing by inhibiting voltage-dependent calcium channels. Histamine release is enhanced under extreme conditions such as dehydration or hypoglycemia or by a variety of stressors. Histamine activates four types of receptors. H1 receptors are mainly postsynaptically located and are coupled positively to phospholipase C. High densities are found especially in the hypothalamus and other limbic regions. Activation of these receptors causes large depolarisations via blockade of a leak potassium conductance, activation of a non-specific cation channel or activation of a sodium-calcium exchanger. H2 receptors are also mainly postsynaptically located and are coupled positively to adenylyl cyclase. High densities are found in hippocampus, amygdala and basal ganglia. Activation of these receptors also leads to mainly excitatory effects through blockade of calcium-dependent potassium channels and modulation of the hyperpolarisation-activated cation channel. H3 receptors are exclusively presynaptically located and are negatively coupled to adenylyl cyclase. High densities are found in the basal ganglia. These receptors mediated presynaptic inhibition of histamine release and the release of other neurotransmitters, most likely via inhibition of presynaptic calcium channels. Finally, histamine modulates the glutamate NMDA receptor via an action at the polyamine binding site. The central histamine system is involved in many central nervous system functions: arousal; anxiety; activation of the sympathetic nervous system; the stress-related release of hormones from the pituitary and of central aminergic neurotransmitters; antinociception; water retention and suppression of eating. A role for the neuronal histamine system as a danger response system is proposed.

Dopaminergic effects of histamine administration in the nucleus accumbens and the impact of H1-receptor blockade

The mesolimbic dopamine system is thought to play a critical role in reward-related processes. A number of studies have shown that lesion or inhibition of histaminergic neurons acting through H1 receptors can potentiate the effects of drug-induced reward (e.g., psychostimulants and opioids) and can enhance the reinforcing effects of electrical stimulation of the brain. Since dopamine transmission in the nucleus accumbens is thought to provide a crucial link in these histaminergic actions, we examined the effects of local histamine application (0.1, 1.0 and 10.0 micromol/l) on dopamine and its metabolites in the nucleus accumbens of anesthetized rats by means of unilateral reverse dialysis. To study the influence of H1 receptors, we also applied the H1-receptor antagonist pyrilamine (10.0 and 20.0 mg/kg, intraperitoneally) 20 min before histamine administration (1 mmol/l). Finally, pyrilamine (0.1, 1.0 and 10.0 micromol/l) was locally administered into the nucleus accumbens. The data show that histamine can enhance extracellular dopamine levels in the nucleus accumbens in a dose-dependent way. This increase was partially antagonized by prior peripheral administration of 10 mg/kg, and was completely blocked by 20 mg/kg, of pyrilamine. Finally, intra-accumbens administration of pyrilamine locally decreased dopamine and increased dihydroxyphenylacetic acid and homovanillic acid levels. These data are discussed with respect to the possible interactions between dopaminergic and histaminergic mechanisms in the mesolimbic system and their relation to mechanisms of reinforcement.

Food-deprived activity stress decreased the activity of the histaminergic neuron system in rats

The hypothalamus, which is rich in histaminergic neurons, is highly sensitive to aversive stimuli such as stress. Histamine H3 receptors, which regulate histamine release from the presynaptic site, are associated with stress-induced brain activity. In this study, we investigated the changes of histamine content and histamine H1 and H3 receptors in the brains of rats subjected to stress induced through food deprivation and physical activity on a running wheel (food-deprived activity stress). For purposes of comparison, we also examined the stressful effects of forced swimming on the histaminergic neuron system of rats. The H3 receptor density rapidly declined in the acute phase of stress but gradually returned to the control level in the chronic phase. On the other hand, the H1 receptor slowly decreased and remained at a low level during the chronic phase. These results reveal that there is a discrepancy between the levels of H1 and H3 receptors in the acute and chronic phases of stress. Brain histamine content gradually increased during the late phase of both food-deprived activity stress and forced swimming stress. These changes presumably resulted in the inhibition of histaminergic neuronal activity in the chronic stress condition. In accordance with this hypothesis, the intraventricular administration of histamine significantly reduced the hyperactivity caused by food-deprived activity stress. Since extensive exercise and restricted feeding are thought to be associated with anorexia nervosa, the abnormalities in the histaminergic neuron system might contribute to trait status in anorexia nervosa.

Analysis of the role of histamine in inhibitory avoidance in goldfish

1. Teleost fish have histaminergic cell bodies on the posterior part of the basal hypothalamus. It was suggested that they are homologous to the tuberomammillary E group in rats. However, unlike in rats, fish have fewer ascending fibers. The main projection runs through the ventral telencephalic area reaching the dorsal telencephalon. This projection is considered homologous to the prosencephalic forebrain bundle. 2. The aim of this study was to verify if the histaminergic system has an inhibitory action on learning and memory in goldfish, as suggested previously for higher vertebrates. 3. A two-compartment aquarium with a central sliding door was used. The animals were placed in one of them, the central door was opened after 30 sec and the time spend for crossing between compartments was recorded. After the fish dorsal fin crossed the line between the compartments a 45 g weight was dropped into the compartment the fish entered. 4. On the training day this procedure was done 3 times. Immediately after the 3rd trial the fish was injected i.p. with either vehicle (2 ml/kg), chlorpheniramine (CPA; 1.0, 4.0 and 8.0 mg/kg) or histidine (500 mg/kg). On the next day, fishes were placed in the start compartment and the latency to cross between compartments was again recorded. 5. The group treated with CPA at the dose of 8 mg/kg, presented a significant increase in the latency to leave the start compartment (Wilcoxon rank sum test, p<0.0232). On the other hand, the vehicle and 1-histidine (500 mg/kg) treated groups, presented a decrease in test latency. 6. Thus, we suggest that also in fish, the histaminergic system has an inhibitory role on learning and memory.

Differential sensitivity of the caudal and rostral nucleus accumbens to the rewarding effects of a H1-histaminergic receptor blocker as measured with place-preference and self-stimulation behavior

A recent series of studies in rats has demonstrated positively reinforcing and memory enhancing effects following lesions of the nucleus tuberomammillaris, which is the only known source of neuronal histamine. The aim of the present experiments was to assess whether inhibition of histaminergic neurotransmission in the ventral striatum has positively reinforcing effects. In Experiment 1 rats with chronically-implanted cannulae were injected with the H1 receptor blocker d-( + )-chlorpheniramine at doses of 0.1, 1.0 and 10.0 microg into the rostral or caudal parts of the nucleus accumbens, a brain region known to be involved in reward-related processes. Immediately after the treatment the animals were placed into one of four restricted quadrants of a circular open field (closed corral) for a single conditioning trial. During the drug-free test for conditioned place preference, when a choice among the four quadrants was provided, those rats injected with 10.0 microg chlorpheniramine in the caudal nucleus accumbens spent more time in the treatment corral, indicative of a positively rewarding drug action. In Experiment 2 the question was posed whether injection of chlorpheniramine into the nucleus accumbens influences electrical self-stimulation of the lateral hypothalamus. For this purpose rats were chronically implanted with two bipolar electrodes aimed at the lateral-hypothalami and with two additional guide cannulae aimed either at the rostral or caudal nucleus accumbens. After having established reliable self-stimulation behavior at one of the two electrode sites the animals were allowed to self-stimulate for one hour (baseline). Then they were unilaterally injected with 10.0 microg chlorpheniramine or vehicle and allowed to self-stimulate for another hour (test). On the next day the same procedure took place, except for the difference that the animals received an injection aimed at the hemisphere not treated so far. Animals treated with chlorpheniramine in the caudal and in the rostral nucleus accumbens displayed higher rates of ipsihemispheric self-stimulation behavior. Moreover, the animals treated with the H1 receptor blocker in the caudal nucleus accumbens displayed higher rates of ipsihemispheric self-stimulation than those having received an injection in the rostral pole. Upon completion of this part of the experiment all animals received an additional intraperitoneal treatment with chlorpheniramine (20 mg/kg) or vehicle, respectively, and were tested in the same way described above. This treatment also resulted in an amplification of intracranial self-stimulation behavior. These results support the hypothesis that histaminergic neurotransmission is involved in the inhibitory control of a central system subserving reward-related processes. The present data also further highlight the nucleus accumbens as functionally heterogenous along its rostrocaudal axis, with the caudal-shell subregion being more sensitive to antihistaminic induced reward than the rostral entity.

Post-trial administration of H1 histamine receptor blocker improves appetitive reversal learning and memory in goldfish, Carassius auratus

Based on the hypothesis that neuronal histamine exerts an inhibitory influence on learning and reinforcement, goldfish were tested for post-trial effects of the H1 receptor blocker chlorpheniramine (CPA) on learning the location of a food source in one of two compartments, one black the other white, with a feeder located in each compartment. Testing was carried out over 6 days. On the training day a food pellet was placed into the feeder of one of the compartments. After consumption of the food the fish were injected i.p. with either vehicle or CPA either immediately after training or 3 h later. Twenty-four-hours later, food was placed in the same compartment and the time to begin feeding was recorded. On the next day the location of the food pellet was reversed, and testing was continued for 4 days. On the first test day the time to begin feeding was significantly longer for the vehicle injected fish as compared with those injected with CPA. The vehicle group also took longer to begin feeding than the CPA group on the first reversal test day. The results of the 3-h delay groups indicated no significant differences between vehicle and drug for any experimental session. These results suggest that post-trial blockade of the H1 histamine receptor can affect appetitive learning in goldfish either by improving long-term memory consolidation and/or by the additive reinforcing effects of CPA (known from previous studies) on behavior.

Memory improvement by post-trial injection of lidocaine into the tuberomammillary nucleus, the source of neuronal histamine

Brain histamine is exclusively contained within and released from neurons whose cell bodies are clustered in the tuberomammillary nucleus (TM) of the posterior hypothalamus. This experiment examined the effects of a transient inactivation of the TM on inhibitory avoidance learning. Rats with chronically implanted cannulae were tested on a 1-trial step-through avoidance task. Immediately following training, the rats received unilateral intra-TM infusions (0.5 microl) of lidocaine (5 or 20 microg). Control groups included vehicle-injected rats and a group given an injection of 20 microg lidocaine 5 h after training. When tested 24 h later, rats treated with 20 microg lidocaine exhibited longer step-through latencies than vehicle-treated controls, indicative of superior learning of the task. The failure of the delayed post-trial injection of lidocaine to significantly influence step-through latencies indicates that the compound influenced learning by modulating memory storage processes rather than by acting on performance variables during retrieval of the task. Thus, inactivation of the TM by lidocaine can exert facilitatory effects on mnemonic processing, which might be related to a temporary reduction of histaminergic activity during the early phase of memory consolidation.

Enhanced learning by posttrial injection of H1-but not H2-histaminergic antagonists into the nucleus basalis magnocellularis region

The aim of this study was to examine the effects of histaminergic antagonists on memory upon injection into the region of the nucleus basalis magnocellularis (NBM). In experiment 1, rats with chronically implanted cannulae were trained on the uphill avoidance task, which involves a punishment of a high-probability turning response on a tilted platform (negative geotaxis). Immediately after the training trial, that is, after a tail shock was administered upon performing the response, rats received one microinjection (0.5 microliter) of H1-receptor blocker chlorpheniramine (dose range 0.1 to 20 microgram) or the H2-receptor blocker ranitidine (same dose range) or saline into the NBM region. When tested 24 h later, rats treated with chlorpheniramine (20 micrograms) had significantly longer uphill latencies than vehicle controls and ranitidine-treated animals, indicative of superior learning of the avoidance response. In experiment 2, a test for possible proactive effects of posttrial chlorpheniramine on performance during the retention trial was performed. Animals were injected with either 20 micrograms chlorpheniramine or saline immediately after the training trial of the uphill task. One chlorpheniramine control group was treated with a delay of 5 h. Additional groups which received chlorpheniramine or vehicle after the training trial but no trail shock were included. When tested 24 h later, rats injected with 20 micrograms chlorpheniramine again exhibited significantly longer uphill latencies than did vehicle-injected rats. Retention latencies for the rats of the chlorpheniramine 5-h delayed group did not differ from those of the vehicle-injected rats, ruling out proactive effects of chlorpheniramine on performance. In summary, the histaminergic H1-blocker chlorpheniramine can enhance mnemonic functioning in addition to its reinforcing effects upon NBM injection as reported previously.

Regional differences in desensitization of c-Fos expression following repeated self-stimulation of the medial forebrain bundle in the rat

The acute self-stimulation of the medial forebrain bundle was reported to induce the expression of c-Fos, the protein product of c-fos, an immediate early gene, in the central nervous system. In the present study, we examined regional changes in c-Fos expression in several reward-related areas of rat brain in response to short- and long-term exposure to self-stimulation of the medial forebrain bundle. Short-term one-hour stimulation of the medial forebrain bundle for one day after training, which evoked steady self-stimulation behavior, significantly increased the number of c-Fos-positive neurons bilaterally in all of 15 brain structures assayed, as compared to the non-stimulation control. Among them, structures showing a larger number of the stained neurons on the stimulated side were the anterior olfactory nucleus, amygdala, medial caudate-putamen complex, lateral septum, bed nucleus of the stria terminals, ventral pallidum, substantia innominata, lateral preoptic area, medial preoptic area, lateral hypothalamus rostral to the stimulating electrodes, and substantia nigra. Long-term stimulation of the medial forebrain bundle once daily for five successive days, which maintained consistently stable self-stimulation behavior, also increased the number of c-Fos-positive neurons in the aforementioned structures, as compared to the control. However, the long-term rewarding stimulation diminished the increased number of labeled neurons, as compared to the short-term rewarding stimulation. Seven areas, medial caudate-putamen complex, ventral pallidum, substantia innominata, lateral preoptic area, medial preoptic area, rostral lateral hypothalamus and substantia nigra, showed asymmetrical, ipsilateral predominance after the short- and long-term stimulation. However, the stained neuron count in those areas after the long-term stimulation was reduced to less than 50% of that found after the short-term stimulation with the exception of lateral preoptic area and rostral lateral hypothalamus. The results suggest that the development of desensitization of c-Fos response may differ among the reward-relevant brain regions as a consequence of repeated self-stimulation. They also indicate that a larger portion of neurons in the lateral preoptic area and rostral lateral hypothalamus may be implicated in both short- and long-term self-stimulations of the medial forebrain bundle.

Stress-induced release of anterior pituitary hormones: effect of H3 receptor-mediated inhibition of histaminergic activity or posterior hypothalamic lesion

The effect of stress- or lipopolysaccharide (LPS) endotoxin-induced release of ACTH, beta-endorphin (beta-END) and prolactin (PRL) was investigated in two groups of conscious male rats: (1) Rats pretreated with different H3 receptor agonists, which inhibit neuronal histamine (HA) synthesis and release, and (2) rats with bilateral posterior hypothalamic lesion, which destroys the histaminergic perikarya exclusively localized in the mammillary nuclei. The H3 receptor agonists R(alpha)methyl-HA, BP 2-94 or imetit injected intraperitoneally (ip) had no effect on basal secretion of ACTH or PRL but inhibited the ACTH and PRL responses to restraint stress and the ACTH response to LPS endotoxin. LPS had no effect on PRL secretion. The inhibitory effect of the agonists was prevented by prior ip administration of the H3 receptor antagonist thioperamide. Bilateral lesion of the posterior hypothalamus inhibited the ACTH, beta-END and PRL responses to restraint stress, ether stress and LPS endotoxin, whereas sham operation had no effect compared to nonoperated control rats. In addition, posterior hypothalamic lesion inhibited the PRL response but not the ACTH and beta-END responses to activation of serotonergic neurons induced by ip administration of the 5-HT precusor 5-hydroxytryptophan in combination with the 5-HT re-uptake inhibitor fluoxetine. Thus, serotonergic pathways were not damaged by the lesions. The present results support our previous findings that inhibition of neuronal HA synthesis by alpha-fluoromethylhistidine as well as blockade of H1 or H2 receptors inhibit the ACTH, beta-END and PRL responses to stress and LPS endotoxin and further substantiate an important role of histaminergic neurons in the mediation of the stress-induced release of pituitary stress hormones. Furthermore, in accordance with our previous findings, the lesion experiments indicated the existence of an interaction between the histaminergic and serotonergic system in regulation of the stress- and LPS-induced PRL release.

The H1- and H2-histamine blockers chlorpheniramine and ranitidine applied to the nucleus basalis magnocellularis region modulate anxiety and reinforcement related processes

This study examined the effects of the H1-antagonist chlorpheniramine and the H2-antagonist ranitidine on reinforcement and anxiety-parameters following unilateral injection into the vicinity of the nucleus basalis magnocellularis (NBM). In Experiment 1, rats with chronically implanted cannulae were injected with chlorpheniramine or ranitidine (each at doses of 0.1, 1, 10 and 20 microg) and were placed into one of four restricted quadrants of a circular open field (closed corral) for a single conditioning trial. During the test for conditioned corral preference, when provided a choice between the four quadrants, only those rats injected with 10 or 20 microg chlorpheniramine spent more time in the treatment corral, indicative of a positively reinforcing action. None of the other doses of chlorpheniramine or of the H2-antagonist influenced rats' preference behavior. In Experiment 2, the elevated plus-maze (EPM) was used to gauge possible anxiolytic or anxiogenic effects of intra-basalis injection of chlorpheniramine or ranitidine (each at doses of 0.1, 1, 10 and 20 microg). A single injection of chlorpheniramine at 0.1 or 20 microg as well as ranitidine at 20 microg was found to exert anxiolytic-like effects in the EPM. Both compounds elevated the time spent on the open arms and increased scanning over the edge of an open arm. None of the other doses of the H1- and H2-antagonist influenced rats' behavior in the EPM. In sum, these findings show that H1- and H2-receptor antagonists differentially modulate reinforcement and fear-related processes in the NBM and thus, provide the first evidence for a behavioral relevance for the histaminergic innervation of this brain site.

Differential modulation of hippocampal signal transfer by tuberomammillary nucleus stimulation in freely moving rats dependent on behavioral state

Tuberomammillary histamine neurons (TM) in the posterior hypothalamus project to extensive parts of the brain, including the hippocampal formation. The purpose of the present experiments was to investigate whether activation of the TM modulates signal transfer from the perforant pathway (PP) or ventral hippocampal commissure (VHC) to the dentate gyrus (DG) in freely moving rats. Paired pulses of electrical stimulation were delivered to PP or VHC, and evoked field potentials (fEPSPs and pop spikes) were recorded in the DG. Before activating PP or VHC, the TM was triggered by electrical stimulation. Experimentation was performed during four behavioral conditions: exploration, grooming, awake immobility, and slow-wave sleep. Electrical activation of the TM was found to modify dentate fEPSPs evoked by PP or VHC stimulation without generating a field potential by itself. Train stimulation of the TM (100 Hz, 500 ms) preceding paired pulses on the hippocampus by 50 ms decreased dentate fEPSPs in dependence of the ongoing behavior and the pathway stimulated. During exploration but not consummatory behavior, the PP signal was reduced when preceded by TM stimulation; during consummatory behavior but not exploration, the VHC signal was reduced. In contrast to other hippocampal afferents which increase pop spikes but leave fEPSPs unchanged, TM stimulation decreased dentate fEPSPs without affecting pop-spike activity. Thus, the TM-histaminergic system seems to modulate signal processing in the dentate gyrus in a specific way, exerting an inhibitory action on the entorhinal input only during learning-related exploratory behavior.

Conditioned place-preference analysis in the goldfish with the H1 histamine antagonist chlorpheniramine

The aim of this study was to investigate whether the histamine H1-receptor blocker, chlorpheniramine (CPA), has a reinforcing effect in goldfish. We used a place-preference procedure in an aquarium with two chambers colored black and white. On day 1, the animals were placed in the test chamber for 10 min for habituation. On day 2, they were placed in the start compartment for 30 s, the sliding doors were opened, and the time spent in each compartment was recorded over the 10 min to determine the natural compartment preference for each animal. On day 3, they were injected either with 0.1, 0.4, 1.0, or 4.0 mg/kg of CPA or only with vehicle and placed in the less preferred compartment for 25 min. On day 4, the animals were placed in the start compartment and the time spent in each compartment during the 10-min test period was recorded again. The groups treated with 1.0 and 4.0 mg/kg of CPA, spent significantly more time in the compartment in which they experienced the drug effect than the group treated with vehicle. On the other hand, the group treated with 0.4 mg/kg spent significantly less time in the drug-paired compartment. The results indicate a biphasic effect of CPA. Considering that there is evidence that low doses of CPA can also block H3-receptors, we suggest that in goldfish the histaminergic neural system has an inhibitory role in the reinforcing process.

Unilateral lesion of dorsal hippocampus enhances reinforcing lateral hypothalamic stimulation in the contralateral hemisphere

Whereas convincing evidence exists for an important role of the hippocampus in mechanisms underlying memory and encoding of location in space, the contribution of the hippocampus to the system underlying central processes of reinforcement is less well established. Scattered data suggesting that hippocampal ablation increases the effectiveness of positive reinforcers have alternatively been interpretated in terms of general and unspecific behavioral disinhibition, which results in higher levels of activity and rates of responding. In the present experiment, 22 Wistar rats were either given a neurotoxic or a sham lesion in the CA1 region of the hippocampus, and the effect on lateral hypothalamic self-stimulation behavior was assessed. To control for nonspecific performance effects rates of lever pressing were assessed ipsi- and contralateral to the lesioned hemisphere as well as under condition of extinction (current set to zero). Following the neurotoxic lesion the animals displayed significant higher rates of self-stimulation at the electrode sites in the hypothalamus situated contralateral but not ipsilateral to the hemisphere with the lesion compared with controls. The increase in self-stimulation commenced on the third day postlesion and was maintained over the 8 days of testing. The lesion did not change the animals' behavior under extinction. Thus, the hippocampal lesion led to an amplification of rewarding lateral hypothalamic self-stimulation behavior, indicative of a lesion induced disinhibition of the brain's reinforcement system.

The histamine H1-antagonist chlorpheniramine facilitates learning in aged rats

The effect of the histamine H1-receptor antagonist chlorpheniramine on inhibitory avoidance conditioning was investigated in 31-month-old rats, using a one-trial step-through avoidance task. Immediately after the learning trial, old rats were injected intraperitoneally with 5 or 10 mg/kg d-chlorpheniramine. Control groups included vehicle-injected old and adult (4-month-old) rats and a group of aged animals given an injection of 10 mg/kg chlorpheniramine 5 h after the training trial. When tested 24 h after training, aged rats receiving 10 mg/kg chlorpheniramine exhibited longer step-through latencies than vehicle-treated old controls, indicative of superior learning of the task. The hypermnestic effects of 10 mg/kg chlorpheniramine were no longer evident when injection was performed 5 h, rather than immediately after the learning trial, ruling out enduring proactive effects of the treatment on test performance. Furthermore, vehicle-treated old rats showed poorer inhibitory avoidance performance than vehicle-treated adult controls. Thus, the improvement in performance after the 10 mg/kg dose of chlorpheniramine can be interpreted in terms of a compensation of performance deficits in the old rats.

The tuberomammillary nucleus projections in the control of learning, memory and reinforcement processes: evidence for an inhibitory role

The tuberomammillary nucleus (TM), a cluster of magnocellular cells in the posterior hypothalamus, is the main source of neuronal histamine in the brain. Although this nucleus is well described in terms of anatomy and neurochemistry, only little is known about its function. Our earlier work showed that the TM projection system may be involved in behavioral asymmetries and behavioral recovery after unilateral manipulations of the brain. Using horseradish peroxidase (HRP) labeling we found an increase in strength (structure and/or activity) in the crossed and uncrossed tuberomammillary-striatal projections in the course of recovery from behavioral asymmetries produced by unilateral removal of the rats' vibrissae, which were in the same direction as the asymmetries found in projections from the substantia nigra to the striatum. Experiments performed with unilateral lesions of the TM region provide evidence for an involvement of the TM system in reinforcement mechanisms. Unilateral destruction of the TM with direct current (DC) or ibotenic acid was found to increase the rate of lateral hypothalamic self-stimulation ipsilateral to the lesion site, suggesting that the TM (particularly the E2 subgroup in its rostral part) may function as a reinforcement inhibiting neural substrate. Experiments performed with bilateral DC or ibotenic acid lesions of the TM region suggest a role of the nucleus in learning and mnemonic processes. A bilateral electrolytic or neurotoxic lesion of the TM region was found to facilitate the performance of adult and behaviorally impaired aged rats in a variety of learning tasks, including a habituation paradigm, aversively motivated learning tasks and water mazes. Examination of the site of the neurotoxic lesion in the TM region with immunohistochemical techniques revealed a marked decline of histamine-staining neurons mainly in the rostral part of the TM nucleus, suggesting that the facilitatory effects on reinforcement and mnemonic processes might be related to the destruction of TM intrinsic histaminergic cells. In summary, the present results indicate that the TM nucleus is involved in neural plasticity and functional recovery following damage to the CNS and may function as an inhibitory neural substrate in the control of reinforcement and mnemonic processes.

Lateralized attenuation of hypothalamic self-stimulation after injecting histamine synthesis blocker alpha-FMH into the E2 tuberomammillary subnucleus

The tuberomammillary nucleus (TM), located in the posterior hypothalamic region, is the only known source of neuronal histamine. Unilateral lesions in the rostroventral part of this nucleus enhanced ipsihemispheric lateral hypothalamic self-stimulation behavior, suggesting that this region exerts inhibitory control over the neuronal systems related to reward or reinforcement processes. To examine whether the amplification of reinforcing stimulation following lesions of histamine synthesizing neurons is indeed histamine mediated, we blocked histamine synthesis unilaterally by injection of 200 microg alpha-fluoromethylhistidine into the E2 region of the TM, and assessed the effects on electrical self-stimulation behavior in the lateral hypothalamus (LH) of rats. Based on the finding that TM lesions facilitated such self-stimulation behavior, we hypothesized that this treatment would have similar effects. Unexpectedly, there was a sharp decrease in the rate of ipsihemispheric lateral hypothalamic self-stimulation following the injection of alpha-FMH compared to the contralateral hemisphere of treated animals as well as compared to the vehicle group. Response rates were most strikingly attenuated 1 h postinjection, but remained low over the whole 7 days of testing. Opposite behavioral effects of TM lesions and alpha-FMH application have been reported previously, and the effectiveness of alpha-FMH in reducing brain histamine levels is known to differ between brain regions. The fact that the alpha-FMH injection affected self-stimulation only in the ipsilateral hemisphere rules out an interpretation of the results in terms of unspecific effects of the treatment on arousal and other performance variables, and, instead, indicates a functional interaction with a subsystem linked to lateral hypothalamic reinforcement processes.

Tuberomammillary nucleus lesion facilitates two-way active avoidance retention in rats

To evaluate whether the tuberomammillary nucleus might be involved in the acquisition and/or retention of a two-way active avoidance conditioning, rats were given a unilateral lesion of the tuberomammillary nucleus (E2 region) 24 h prior to the first conditioning session. Four learning sessions were performed: one acquisition and 3 retention sessions (short-term, 24 h; and long-term, 8 and 18 days). Results showed that the lesion facilitated the long-term retention of conditioning, but no effects were observed on acquisition and short-term retention. Since rewarding intracranial electrical stimulation seems to be a consistent way to facilitate learning and memory processes, and tuberomammillary lesion has been shown to improve intracranial self-stimulation behavior (ICSS), we suggest that lesions in the present experiment could have facilitated two-way active avoidance retention by enhancing the function of brain reward mechanisms.

Functional sexual dimorphism of the nucleolar organizer regions in the tuberomamillary nucleus

The tuberomamillary nucleus (TM) is a cluster of magnocellular neurons that are located close to the mamillary recess or basal surface of the mamillary body (MBs) and is the only known source of histamine (HA). The nucleolar organizer regions (NORs) of the nervous cells of the subnuclei E1, E2 and E3 of the TM are quantified in this paper to discern the existence of possible sexual differences in the overall neuronal protein synthesis between male and female rats in two phases of the oestrous cycle (oestrous-dioestrous). We have used the argentic impregnation technique of the NORs (AgNORs) in both bilateral nuclei of the TM and found functional bilateral symmetry in its AgNORs. Furthermore, we demonstrate the existence of significant differences (P < 0.001) between sexes and between two phases of the oestrous cycle studied (oestrous-dioestrous) in the parameter of number of AgNORs per neuron. Hormonal manipulation of the TM in the rat during the two periods, postnatal or adult, shows the importance of the activational effect of the hormones on the activity of cellular protein synthesis.

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.

Facilitation of learning in adult and aged rats following bilateral lesions of the tuberomammillary nucleus region

In the present experiment, adult (3-month-old) and aged (31-month-old) rats received bilateral DC or sham-lesions in the region of the tuberomammillary (TM) nucleus before they were trained and tested on a one-trial step-through inhibitory avoidance task. Bilateral lesions of the TM nucleus led to significantly longer latencies in the step-through response during retention test in both adult and aged rats, indicative of superior learning of the task. Thus, lesions of the TM nucleus may have a facilitatory effect on learning and mnemonic functioning which is possibly related to a lesion-induced disinhibition or facilitation of reinforcement processes ("stamping-in") as revealed in previous studies.