Methamphetamine- and 3,4-Methylenedioxymethamphetamine–Induced Behavioral Changes in Histamine H3–Receptor Knockout Mice

The role of heterodimers formed by histamine H3 receptors and dopamine D1 receptors on the methamphetamine-induced conditioned place preference

RATIONALE

The rewarding effect of Methamphetamine (METH) is commonly believed to play an important role in METH use disorder. The altered expression of dopamine D1 receptor (D1R) has been suggested to be essential to the rewarding effect of METH. Notably, D1R could interact with histamine H3 receptors (H3R) by forming a H3R-D1R heteromer (H3R-D1R).

OBJECTIVES

This study was designed to specifically investigate the involvement of H3R-D1R in the rewarding effect of METH.

METHODS

C57BL/6 mice were treated with intraperitoneal injections of a selective H3R antagonist (Thioperamide, THIO; 20 mg/kg), an H1R antagonist (Pyrilamine, PYRI; 10 mg/kg), or microinjections of cytomegalovirus (CMV)-transmembrane domain 5 (TM5) into the nucleus accumbens (NAc). The animal model of Conditioned Place Preference (CPP) was applied to determine the impact of H3R-D1R on the rewarding effect of METH.

RESULTS

METH resulted in a significant preference for the drug-associated chamber, in conjunction with increased H3R and decreased D1R expression in both NAc and the ventral tegmental area (VTA). THIO significantly attenuated the rewarding effect of METH, accompanied by decreased H3R and increased D1R expression. In contrast, pyrilamine failed to produce the similar effects. Moreover, the inhibitory effect of THIO on METH-induced CPP was reversed by SKF38393, a D1R agonist. Furthermore, SCH23390, a D1R antagonist, counteracted the ameliorative effect of SKF38393 on THIO. Co-immunoprecipitation (CO-IP) experiments further demonstrated the specific interaction between H3R and D1R in METH CPP mice. The rewarding effect of METH was also significantly blocked by the interruption of CMV-transmembrane domain 5 (TM5), but not CMV-transmembrane domain 7 (TM7) in NAc.

CONCLUSION

These results suggest that modulating the activity of H3R-D1R complex holds promise for regulating METH use disorder and serves as a potential drug target for its treatment.

Histamine H3 and H4 receptors modulate Parkinson's disease induced brain pathology. Neuroprotective effects of nanowired BF-2649 and clobenpropit with anti-histamine-antibody therapy

Military personnel deployed in combat operations are highly prone to develop Parkinson's disease (PD) in later lives. PD largely involves dopaminergic pathways with hallmarks of increased alpha synuclein (ASNC), and phosphorylated tau (p-tau) in the cerebrospinal fluid (CSF) precipitating brain pathology. However, increased histaminergic nerve fibers in substantia nigra pars Compacta (SNpc), striatum (STr) and caudate putamen (CP) associated with upregulation of Histamine H3 receptors and downregulation of H4 receptors in human cases of PD is observed in postmortem cases. These findings indicate that modulation of histamine H3 and H4 receptors and/or histaminergic transmission may induce neuroprotection in PD induced brain pathology. In this review effects of a potent histaminergic H3 receptor inverse agonist BF-2549 or clobenpropit (CLBPT) partial histamine H4 agonist with H3 receptor antagonist, in association with monoclonal anti-histamine antibodies (AHmAb) in PD brain pathology is discussed based on our own observations. Our investigation shows that chronic administration of conventional or TiO₂ nanowired BF 2649 (1mg/kg, i.p.) or CLBPT (1mg/kg, i.p.) once daily for 1 week together with nanowired delivery of HAmAb (25μL) significantly thwarted ASNC and p-tau levels in the SNpC and STr and reduced PD induced brain pathology. These observations are the first to show the involvement of histamine receptors in PD and opens new avenues for the development of novel drug strategies in clinical strategies for PD, not reported earlier.

Metoprine, a histamine N-methyltransferase inhibitor, attenuates methamphetamine-induced hyperlocomotion via activation of histaminergic neurotransmission in mice

Metoprine increases the content of histamine in brain by inhibiting histamine N-methyltransferase (HMT), a centrally acting histamine degrading enzyme. We present data demonstrating that pretreatment with metoprine attenuates the hyperlocomotive effects of METH in mice using a multi-configuration behavior apparatus designed to monitor four behavioral outcomes [horizontal locomotion, appetitive behavior (food access), and food and water intake]. Metoprine pretreatment itself induced hyperlocomotion in mice challenged with saline during the large part of light phase. The trend was also observed during the following dark phase. This is the first report that metoprine has a long-lasting locomotor stimulating property. Similarly, in a tail suspension test, a single injection of metoprine significantly reduced total time of immobility in mice, consistent with the idea that metoprine possesses motor stimulating properties. Metoprine pretreatment did not affect other aspects of behavior. Metoprine did not affect the appetitive and drinking behavior while exerted an effect on stereotypy. No stereotyped behavior was observed in mice pretreated with vehicle followed by METH, while stereotyped sniffing was observed in mice pretreated with metoprine followed by METH. The metoprine pretreatment attenuated METH-induced hyperlocomotion during the first 2 h of light phase, suggesting that metoprine-induced locomotor stimulating property might be different from that of METH. The hypothalamic content of histamine (but not its brain metabolite) was increased after metoprine or METH administration. Both METH and metoprine reduced dopamine and histamine turnover in the striatum and the nucleus accumbens and the hypothalamus, respectively, and there is a significant metoprine pretreatment x METH challenge interaction in the histamine turnover. It is likely that metoprine may attenuate METH-induced hyperlocomotion via activation of histaminergic neurotransmission. Metoprine also might induce a long-lasting locomotor stimulating effect via a putative mechanism different from that whereby METH induces the locomotor stimulating effect.

Of mice and men on MDMA: A translational comparison of the neuropsychobiological effects of 3,4-methylenedioxymethamphetamine ('Ecstasy')

MDMA (3,4-methylendioxymethamphetamine), also known as Ecstasy, is a stimulant drug recreationally used by young adults usually in dance clubs and raves. Acute MDMA administration increases serotonin, dopamine and noradrenaline by reversing the action of the monoamine transporters. In this work, we review the studies carried out over the last 30 years on the neuropsychobiological effects of MDMA in humans and mice and summarise the current knowledge. The two species differ with respect to the neurochemical consequences of chronic MDMA, since it preferentially induces serotonergic dysfunction in humans and dopaminergic neurotoxicity in mice. However, MDMA alters brain structure and function and induces hormonal, psychomotor, neurocognitive, psychosocial and psychiatric outcomes in both species, as well as physically damaging and teratogen effects. Pharmacological and genetic studies in mice have increased our knowledge of the neurochemical substrate of the multiple effects of MDMA. Future work in this area may contribute to developing pharmacological treatments for MDMA-related disorders.

Interleukin-18-deficient mice develop hippocampal abnormalities related to possible depressive-like behaviors

Interleukin-18 (IL-18) is an inflammatory cytokine linked to major depressive disorder (MDD). MDD is closely related to metabolic disorders, such as diabetes mellitus (DM) and obesity. Moreover, DM is associated with cognitive impairment and promotes apoptosis of hippocampal cells by activating pro-apoptotic and inhibiting anti-apoptotic factors. IL-18-deficient (Il18^-/-) mice are obese and have DM. Therefore, we hypothesized a close relationship between IL-18 and death of hippocampal cells, affecting neurogenesis related to behavioral changes such as MDD. Il18^-/- male mice were generated on the C57Bl/6 background and Il18^+/+ mice were used as controls. Behavioral, histopathological, and molecular responses, as well as responses to intracerebral recombinant IL-18 administration, were examined. Compared with Il18^+/+ mice, Il18^-/- mice had impaired learning and memory and exhibited lower motivation. In the Il18^-/- mice, degenerated mitochondria were detected in synaptic terminals in the molecular layer, the polymorphic layer, and in mossy fibers in the dentate gyrus, suggesting mitochondrial abnormalities. Because of the degeneration of mitochondria in the dentate gyrus, in which pro-apoptotic molecules were upregulated and anti-apoptotic factors were decreased, apoptosis inducers were not cleaved, indicating inhibition of apoptosis. In addition, neurogenesis in the dentate gyrus and the maturity of neuronal cells were decreased in the Il18^-/- mice, while intracerebral administration of recombinant IL-18 promoted significant recovery of neurogenesis. Our findings suggested that IL-18 was indispensable for mitochondrial homeostasis, sustaining clearance of degenerative neural cells, and supporting neurogenesis, normal neuronal maturation and hippocampal function.

The novel non-imidazole histamine H3 receptor antagonist DL77 reduces voluntary alcohol intake and ethanol-induced conditioned place preference in mice

It has become clear that histamine H3 receptors (H3R) have been implicated in modulating ethanol intake and preference in laboratory animals. The novel non-imidazole H3R antagonist DL77 with excellent selectivity profile shows high in-vivo potency as well as in-vitro antagonist affinity with ED50 of 2.1 ± 0.2 mg/kg and pKi=8.08, respectively. In the present study, and applying an unlimited access two-bottle choice procedure, the anti-alcohol effects of the H3R antagonist, DL77 (0, 3, 10 and 30 mg/kg; i.p.), were investigated in adult mice. In this C57BL/6 line, effects of DL77 on voluntary alcohol intake and preference, as well as on total fluid intake were evaluated. Results have shown that DL77, dose-dependently, reduced both ethanol intake and preference. These effects were very selective as both saccharin and quinine, used to control for taste sensitivity, and intakes were not affected following DL77 pre-application. More importantly, systemic administration of DL77 (10 mg/kg) during acquisition inhibited ethanol-induced conditioned-place preference (EtOH-CPP) as measured using an unbiased protocol. The anti-alcohol activity observed for DL77 was abrogated when mice were pretreated with the selective H3R agonist R-(α)-methyl-histamine (RAMH) (10 mg/kg), or with the CNS penetrant H1R antagonist pyrilamine (PYR) (10mg/kg). These results suggest that DL77 has a predominant role in two in vivo effects of ethanol. Therefore, signaling via H3R is essential for ethanol-related consumption and conditioned reward and may represent a novel therapeutic pharmacological target to tackle ethanol abuse and alcoholism.

Histamine H3 receptor antagonist JNJ-39220675 modulates locomotor responses but not place conditioning by dopaminergic drugs

RATIONALE

Brain histaminergic system is involved in the regulation of the dopaminergic circuitry. The role of histamine H3 receptor (H3R) in behaviors linked to amphetamine addiction and other behaviors induced by dopaminergic compounds has remained unclear.

OBJECTIVE

Our aim was to study whether H3R antagonist JNJ-39220675 inhibits amphetamine-induced stimulation and reward. The effects of JNJ-39220675 on dopamine D2-like receptor (D2R-like) agonist quinpirole-induced behaviors were also investigated in order to clarify whether the possible effects of H3R antagonists are D2R-like dependent.

METHODS

The effects of JNJ-39220675 on amphetamine and quinpirole-induced behavioral responses in mice were studied assessing the locomotor activation after both acute and repeated administrations of amphetamine and quinpirole. The place conditioning paradigm was also used as a measure of reward or aversion.

RESULTS

JNJ-39220675 inhibited amphetamine-induced stimulation acutely but not after repeated administrations. Amphetamine (2 mg/kg) induced conditioned place preference that was not affected by either of the tested doses of JNJ-39220675 (1 and 10 mg/kg). Quinpirole (0.5 mg/kg) induced conditioned place aversion to which the pretreatment by JNJ-39220675 (10 mg/kg) had no effect. In repeated administration, JNJ-39220675 did, however, inhibit quinpirole-induced tolerance to hypokinesia.

CONCLUSIONS

Our results show that although H3R antagonists inhibit ethanol reward, they may not possess the same ability on psychostimulants, such as amphetamine. However, if H3R antagonists will become clinically available, it is of importance that these compounds potentiate neither the rewarding nor aversive effects of other drugs.

Role of histamine H3 receptor in glucagon-secreting αTC1.6 cells

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Histamine H₃ receptor is expressed in pancreatic α-cells.

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Histamine H₃ receptor negatively regulates glucagon secretion from αTC1.6 cells.

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Immepip, a selective H₃ receptor agonist, decreases serum glucagon concentration in rats.

Pancreatic α-cells secrete glucagon to maintain energy homeostasis. Although histamine has an important role in energy homeostasis, the expression and function of histamine receptors in pancreatic α-cells remains unknown. We found that the histamine H₃ receptor (H₃R) was expressed in mouse pancreatic α-cells and αTC1.6 cells, a mouse pancreatic α-cell line. H₃R inhibited glucagon secretion from αTC1.6 cells by inhibiting an increase in intracellular Ca²⁺ concentration. We also found that immepip, a selective H₃R agonist, decreased serum glucagon concentration in rats. These results suggest that H₃R modulates glucagon secretion from pancreatic α-cells.

Preclinical evaluation of the abuse potential of Pitolisant, a histamine H₃ receptor inverse agonist/antagonist compared with Modafinil

BACKGROUND AND PURPOSE

Pitolisant, a histamine H₃ receptor inverse agonist/antagonist is currently under Phase III clinical trials for treatment of excessive daytime sleepiness namely in narcoleptic patients. Its drug abuse potential was investigated using in vivo models in rodents and monkeys and compared with those of Modafinil, a psychostimulant currently used in the same indications.

EXPERIMENTAL APPROACH

Effects of Pitolisant on dopamine release in the nucleus accumbens, on spontaneous and cocaine-induced locomotion, locomotor sensitization were monitored. It was also tested in three standard drug abuse tests i.e. conditioned place preference in rats, self-administration in monkeys and cocaine discrimination in mice as well as in a physical dependence model.

KEY RESULTS

Pitolisant did not elicit any significant changes in dopaminergic indices in rat nucleus accumbens whereas Modafinil increased dopamine release. In rodents, Pitolisant was without any effect on locomotion and reduced the cocaine-induced hyperlocomotion. In addition, no locomotor sensitization and no conditioned hyperlocomotion were evidenced with this compound in rats whereas significant effects were elicited by Modafinil. Finally, Pitolisant was devoid of any significant effects in the three standard drug abuse tests (including self-administration in monkeys) and in the physical dependence model.

CONCLUSIONS AND IMPLICATIONS

No potential drug abuse liability for Pitolisant was evidenced in various in vivo rodent and primate models, whereas the same does not seem so clear in the case of Modafinil.

Histamine H₃ receptors, the complex interaction with dopamine and its implications for addiction

Histamine H₃ receptors are best known as presynaptic receptors inhibiting the release of histamine, as well as other neurotransmitters including acetylcholine and dopamine. However, in the dorsal and ventral striatum, the vast majority of H₃ receptors are actually located postsynaptically on medium sized spiny output neurons. These cells also contain large numbers of dopamine (D₁ and D₂) receptors and it has been shown that H₃ receptors form heterodimers with both D₁ and D₂ receptors. Thus, the anatomical localization of H₃ receptors suggests a complex interaction that could both enhance and inhibit dopaminergic neurotransmission. Dopamine, especially within the striatal complex, plays a crucial role in the development of addiction, both in the initial reinforcing effects of drugs of abuse, as well as in maintenance, relapse and reinstatement of drug taking behaviour. It is, therefore, conceivable that H₃ receptors can moderate the development and maintenance of drug addiction. In the present review, we appraise the current literature on the involvement of H₃ receptors in drug addiction and try to explain these data within a theoretical framework, as well as provide suggestions for further research.

The expression and function of histamine H₃ receptors in pancreatic beta cells

BACKGROUND AND PURPOSE

Histamine and its receptors in the CNS play important roles in energy homeostasis. Here, we have investigated the expression and role of histamine receptors in pancreatic beta cells, which secrete insulin.

EXPERIMENTAL APPROACH

The expression of histamine receptors in pancreatic beta cells was examined by RT-PCR, Western blotting and immunostaining. Insulin secretion assay, ATP measurement and calcium imaging studies were performed to determine the function and signalling pathway of histamine H₃ receptors in glucose-induced insulin secretion (GIIS) from MIN6 cells, a mouse pancreatic beta cell line. The function and signalling pathway of H₃ receptors in MIN6 cell proliferation were examined using pharmacological assay and Western blotting.

KEY RESULTS

Histamine H₃ receptors were expressed in pancreatic beta cells. A selective H₃ receptor agonist, imetit, and a selective inverse H₃ receptor agonist, JNJ-5207852, had inhibitory and facilitatory effects, respectively, on GIIS in MIN6 cells. Neither imetit nor JNJ-5207852 altered intracellular ATP concentration, or intracellular calcium concentration stimulated by glucose and KCl, indicating that GIIS signalling was affected by H3 receptor signalling downstream of the increase in intracellular calcium concentration. Moreover, imetit attenuated bromodeoxyuridine incorporation in MIN6 cells. The phosphorylation of cAMP response element-binding protein (CREB), which facilitated beta cell proliferation, was inhibited, though not significantly, by imetit, indicating that activated H₃ receptors inhibited MIN6 cell proliferation, possibly by decreasing CREB phosphorylation.

CONCLUSIONS AND IMPLICATIONS

Histamine H₃ receptors were expressed in mouse beta cells and could play a role in insulin secretion and, possibly, beta cell proliferation.

Influence of the novel histamine H₃ receptor antagonist ST1283 on voluntary alcohol consumption and ethanol-induced place preference in mice

RATIONALE

Growing evidence supports a role for the central histaminergic system to have a modulatory influence on drug addiction in general and alcohol-use disorders in particular through histamine H3 receptors (H3R).

OBJECTIVE

In the present study, the effects of systemic injection of the newly synthesized H3R antagonist ST1283 on ethanol (EtOH) voluntary intake and EtOH-conditioned reward in mice have been investigated.

METHODS

Oral EtOH, saccharin, and quinine intake was assessed in a two-bottle choice paradigm using escalating concentrations of alcohol or tastant solutions. EtOH-induced place preference (CPP), EtOH-induced locomotor activity, and blood ethanol concentration (BEC) were also measured.

RESULTS

Following administration of the H3R antagonist (2.5, 5, and 10 mg/kg, i.p.), there was a significant dose-dependent decrease in alcohol consumption and preference. Importantly, vehicle- and ST1283 (5 mg/kg)-treated mice showed similar consumption and preference to increasing concentration of both sweet and bitter tastes. More interestingly, systemic administration of ST1283 inhibited EtOH-CPP and EtOH-enhanced locomotion. This inhibition was blocked when mice were pretreated with the selective H3R agonist R-(alpha)-methyl-histamine (10 mg/kg). Finally, vehicle- and ST1283-treated mice had similar BECs.

CONCLUSION

Our results show that ST1283 may decrease voluntary EtOH consumption and EtOH-CPP by altering its reinforcing effects, suggesting a novel role for histamine signaling in regulation of alcoholism. Lastly, the results add to the growing literature on H3R modulation in the pharmacotherapy of EtOH addiction.

Histamine h3 receptor: a novel therapeutic target in alcohol dependence?

The brain histaminergic system is one of the diffuse modulatory neurotransmitter systems which regulate neuronal activity in many brain areas. Studies on both rats and mice indicate that histamine H3 receptor antagonists decrease alcohol drinking in several models, like operant alcohol administration and drinking in the dark paradigm. Alcohol-induced place preference is also affected by these drugs. Moreover, mice lacking H3R do not drink alcohol like their wild type littermates, and they do not show alcohol-induced place preference. Although the mechanisms of these behaviors are still being investigated, we propose that H3R antagonists are promising candidates for use in human alcoholics, as these drugs are already tested for treatment of other disorders like narcolepsy and sleep disorders.

Activation of metabotropic glutamate 2/3 receptors attenuates methamphetamine-induced hyperlocomotion and increase in prefrontal serotonergic neurotransmission

RATIONALE

Metabotropic glutamate (mGlu) 2/3 receptor agonists inhibit amphetamine- and phencyclidine-induced hyperlocomotion. The mechanism for the antipsychotic effect of mGlu2/3 receptor agonists was studied in a hypoglutamatergic model, but not a hyperdopaminergic model.

OBJECTIVES

To study the mechanism for the antipsychotic effect of the agonist in the hyperdopaminergic model, this study examined the effects of the selective mGlu2/3 receptor agonist MGS0028 on methamphetamine-induced hyperlocomotion and the increases in extracellular levels of serotonin, dopamine, noradrenaline, and glutamate in the prefrontal cortex and nucleus accumbens of mice.

RESULTS

Systemic administration of MGS0028 attenuated methamphetamine-induced hyperlocomotion in a dose-dependent manner. Microdialysis studies showed that MGS0028 significantly inhibited methamphetamine-induced increases in the extracellular serotonin, but not dopamine and noradrenaline, levels in the prefrontal cortex, and it did not affect methamphetamine-induced increases in the extracellular amine levels in the nucleus accumbens. Methamphetamine did not affect the glutamate release in the prefrontal cortex and nucleus accumbens. Local application of MGS0028 into the prefrontal cortex also attenuated methamphetamine-induced hyperlocomotion and increases in the extracellular serotonin levels in the prefrontal cortex. Moreover, MGS0028 did not affect methamphetamine-induced hyperlocomotion in the mice pretreated with p-chlorophenylalanine, a serotonin synthesis inhibitor.

CONCLUSIONS

Activation of prefrontal mGlu2/3 receptors inhibits the psychomotor stimulant effect of methamphetamine in mice, and the prefrontal serotonergic system may be involved in this effect. The finding provides evidence that prefrontal mGlu2/3 receptors are functionally coupled with the serotonergic system.

Evidence for the role of histamine H3 receptor in alcohol consumption and alcohol reward in mice

Recent research suggests that histamine H3 receptor (H3R) antagonism may diminish motivational aspects of alcohol dependence. We studied the role of H3Rs in alcohol-related behaviors using H3R knockout (KO) mice and ligands. H3R KO mice consumed less alcohol than wild-type (WT) mice in a two-bottle free-choice test and in a 'drinking in the dark' model. H3R antagonist ciproxifan suppressed and H3R agonist immepip increased alcohol drinking in C57BL/6J mice. Impairment in reward mechanisms in H3R KO mice was confirmed by the lack of alcohol-evoked conditioned place preference. Plasma alcohol concentrations of H3R KO and WT mice were similar. There were no marked differences in brain biogenic amine levels in H3R KO mice compared with the control animals after alcohol drinking. In conclusion, the findings of this study provide evidence for the role of H3R receptor in alcohol-related behaviors, especially in alcohol drinking and alcohol reward. Thus, targeting H3Rs with a specific antagonist might be a potential means to treat alcoholism in the future.

Histamine-dependent behavioral response to methamphetamine in 12-month-old male mice

Methamphetamine (MA) use is a large problem across the United States. Effects of MA include hyperactivity and increased anxiety. Using a mouse model system, we examined behavioral performance in the open field and elevated zero maze and shock-startle response of 12-month-old wild-type mice injected with MA once (1 mg/kg) 30 min prior to behavioral testing. MA treatment resulted in behavioral sensitization in the open field, consistent with studies in younger mice. There was an increased activity in the elevated zero maze and an increased shock-startle response 30 and 60 min post-injection. Since histamine mediates some effects of MA in the brain, we assessed whether 12-month-old mice lacking histidine decarboxylase (Hdc⁻/⁻), the enzyme required to synthesize histamine, respond differently to MA than wild-type (Hdc+/+) mice. Compared to saline treatment, acute and repeated MA administration increased activity in the open field and measures of anxiety, though more so in Hdc⁻/⁻ than Hdc+/+ mice. In the elevated zero maze, opposite effects of MA on activity and measures of anxiety were seen in Hdc+/+ mice. In contrast, MA similarly increased the shock-startle response in Hdc⁻/⁻ and Hdc+/+ mice, compared to saline-treated genotype-matched mice. These results are similar to those in younger mice, suggesting that the effects are not age-dependent. Overall, single or repeated MA treatment causes histamine-dependent changes in 12-month-old mice in the open field and elevated zero maze, but not in the shock-startle response.

Histamine and H3 receptor in alcohol-related behaviors

Data from rat models for alcohol preference and histidine decarboxylase knockout (HDC KO) mice suggest that brain histamine regulates alcohol-related behaviors. Histamine levels are higher in alcohol-preferring than in alcohol-nonpreferring rat brains, and expression of histamine H(3) receptor (H(3)R) is different in key areas for addictive behavior. H(3)R inverse agonists decrease alcohol responding in one alcohol-preferring rat line. Conditioned place preference induced by alcohol is stronger in HDC KO mice than in control mice. The HDC KO mice display a weaker stimulatory response to acute alcohol than the wild-type (WT) mice. In male inbred C57BL/6 mice the H(3)R antagonist ciproxifan inhibits ethanol-evoked stimulation of locomotor activity. Ciproxifan also potentiates the ethanol reward, but does not alone result in the development of place preference. At least in one rat model developed to study alcohol sensitivity high histamine levels are characteristic of the alcohol-insensitive rat line, and lowering brain histamine with a HDC inhibitor increases alcohol sensitivity in the tilting plane test. However, the motor skills of HDC KO mice do not seem to differ from those of the WT mice. Current evidence suggests that the histaminergic system is involved in the regulation of place preference behavior triggered by alcohol, possibly through an interaction with the mesolimbic dopamine system. Histamine may also interact with dopamine in the regulation of the cortico-striato-pallido-thalamo-cortical motor pathway and cerebellar mechanisms, which may be important in different motor behaviors beyond alcohol-induced motor disturbances. H(3)R ligands may have significant effects on alcohol addiction.

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.