Exploratory behaviour after intra-accumbens histamine and/or histamine antagonists injection in the rat

GABA-ergic agents modulated the effects of histamine on male mice behavior in the elevated plus-maze

NEW FINDINGS

What is the main question of this study? Is there an interaction between histamine and GABAergic system on modulation of anxiety in mice? What is the main finding and its importance? There is a synergistic anxiogenic effect between histamine and bicuculline in mice. This effect may be due to a direct or indirect effect of the histaminergic system on the GABAergic system.

ABSTRACT

There are documents that both histaminergic and GABAergic systems are participated in the neurobiology of anxiety behavior. In the current research, we investigated the effects of the histaminergic system and GABAA receptor agents on anxiety-related behaviors and their interaction using the elevated plus-maze (EPM) test in mice. Intraperitoneally (i.p.) administration of muscimol (0.12 and 0.25 mg/kg) increased the open arm time (OAT) (p < 0.001) without affecting the open arm entries (OAE) and locomotor activity, showing an anxiolytic effect. I.p. injection of bicuculline (0.5 and 1 mg/kg) decreased OAT (p < 0.001) but not OAE and locomotor activity, suggesting an anxiogenic behavior. Intracerebroventricularly (i.c.v.) microinjection of histamine (2.5 and 5 μg/mouse) declined OAT (p < 0.001) but not OAE and locomotor activity, indicating an anxiogenic response. Co-administration of histamine with GABAergic agents, muscimol (0.06 mg/kg; i.p.) and bicuculline (0.25 mg/kg; i.p.), decreased (p < 0.001) and increased (p < 0.05) the anxiogenic-like response of the effective dose (5 μg/mouse; i.c.v.) of histamine, respectively. In addition, co-treatment of effective doses of histamine (2.5 and 5 μg/mouse;i.c.v.) along with an effective dose of muscimol (0.12 mg/kg;i.p.) and not-effective dose of bicuculline (0.25 mg/kg; i.p.) significantly decreased OAT (p < 0.001), suggesting a likely interaction between the histaminergic and GABAergic systems on the regulation of anxiety. The results demonstrated a synergistic anxiogenic-like effect between histamine and bicuculline in mice. In conclusion, our results presented an interaction between the histaminergic and GABAergic systems on anxiolytic/anxiogenic-like behaviors in the EPM test. This article is protected by copyright. All rights reserved.

Central histaminergic transmission modulates the expression of chronic nicotine withdrawal induced anxiety-like and somatic behavior in mice

The present study investigated the plausible modulatory role of central histaminergic transmission on the expression of nicotine withdrawal induced anxiety and somatic behavior in mice. Abrupt cessation of chronic nicotine (2 mg/kg, i.p. × 3/day) treatment for 12 days to mice, expressed increased anxiety in light & dark test and total abstinence (somatic) score at 24 h post nicotine withdrawal time. The somatic signs includes a composite score of all behaviors such as grooming, rearing, jumping, body shakes, forelimb tremors, head shakes, abdominal constrictions, scratching, empty mouth chewing or teeth chattering, genital licking, tail licking. Mice exhibited higher expression to nicotine withdrawal induced anxiety in light & dark test at 24 h post-nicotine withdrawal time on pre-treatment centrally (i.c.v) with histaminergic agents like histamine (0.1, 50 μg/mouse), histamine H₃ receptor inverse agonist, thioperamide (2, 10 μg/mouse), histamine H₁ receptor agonist, FMPH (2, 6.5 μg/mouse) or H₂ receptor agonist amthamine (0.1, 0.5 μg/mouse) or intraperitoneally (i.p.) with histamine precursor, l-histidine (250, 500 mg/kg) as compared to control nicotine withdrawn animals. Furthermore, mice pre-treated with all these histaminergic agents except histamine H₁ receptor agonist, FMPH shows exacerbated expression to post-nicotine withdrawal induced total abstinence (somatic) score in mice. On the other hand, central injection of selective histamine H₁ receptor antagonist, cetirizine (0.1 μg/mouse, i.c.v.) or H₂ receptor antagonist, ranitidine (50 μg/mouse, i.c.v) to mice 10 min before 24 h post-nicotine withdrawal time completely alleviated the expression of nicotine withdrawal induced anxiety and somatic behavior. Thus, it can be contemplated that the blockade of central histamine H₁ or H₂ receptor during the nicotine withdrawal phase could be a novel approach to mitigate the nicotine withdrawal associated anxiety-like manifestations. Contribution of endogenous histamine via H₁ or H₂ receptor stimulation in the nicotine withdrawal induced anxiety and somatic behavior is proposed.

Satiety factor oleoylethanolamide recruits the brain histaminergic system to inhibit food intake

Key factors driving eating behavior are hunger and satiety, which are controlled by a complex interplay of central neurotransmitter systems and peripheral stimuli. The lipid-derived messenger oleoylethanolamide (OEA) is released by enterocytes in response to fat intake and indirectly signals satiety to hypothalamic nuclei. Brain histamine is released during the appetitive phase to provide a high level of arousal in anticipation of feeding, and mediates satiety. However, despite the possible functional overlap of satiety signals, it is not known whether histamine participates in OEA-induced hypophagia. Using different experimental settings and diets, we report that the anorexiant effect of OEA is significantly attenuated in mice deficient in the histamine-synthesizing enzyme histidine decarboxylase (HDC-KO) or acutely depleted of histamine via interocerebroventricular infusion of the HDC blocker α-fluoromethylhistidine (α-FMH). α-FMH abolished OEA-induced early occurrence of satiety onset while increasing histamine release in the CNS with an H3 receptor antagonist-increased hypophagia. OEA augmented histamine release in the cortex of fasted mice within a time window compatible to its anorexic effects. OEA also increased c-Fos expression in the oxytocin neurons of the paraventricular nuclei of WT but not HDC-KO mice. The density of c-Fos immunoreactive neurons in other brain regions that receive histaminergic innervation and participate in the expression of feeding behavior was comparable in OEA-treated WT and HDC-KO mice. Our results demonstrate that OEA requires the integrity of the brain histamine system to fully exert its hypophagic effect and that the oxytocin neuron-rich nuclei are the likely hypothalamic area where brain histamine influences the central effects of OEA.

Involvement of the dorsal hippocampal dopamine D2 receptors in histamine-induced anxiogenic-like effects in mice

Anxiety-related behaviors increase histamine and dopamine release in the brain. On the other hand, central histamine counteracts reward and reinforcement processes mediated by the mesolimbic dopamine system. We investigated the effects of the histaminergic system and dopamine D2 receptors agents and their interactions on anxiety-related behaviors using the elevated plus-maze (EPM). The intra-hippocampal (Intra-CA1) microinjection of histamine (10 μg/mouse) decreased the percentage of open arm time (%OAT) and open arm entries (%OAE) but not the locomotor activity, indicating an anxiogenic-like response. Quinpirole (0.5 and 2 μg/mouse) or sulpiride (0.3 and 1 μg/mouse) when injected into the dorsal hippocampus also induced anxiety-like behavior, however, the drugs reversed the anxiogenic response induced by the effective dose of histamine (10 μg/mouse). Taken together and under the present experimental design, our results indicate that activation of the dorsal hippocampal histaminergic receptors causes anxiety-like behaviors altered by dopamine D2 receptor agonist and antagonist. Histamine can decrease dopaminergic tone in the dorsal hippocampus through decreasing the endogenous dopamine release, whereas quinpirole does the same via the postsynaptic DA receptors' activation. Sulpiride however renders the same effect through autoreceptors' blockade and potentiated dopamine transmission. Thus, quinpirole and sulpiride seem to compensate the effects of the intra-CA1 injection of exogenous histamine, and tend to exert anxiolytic effects in the presence of histamine.

Histamine and motivation

Brain histamine may affect a variety of different behavioral and physiological functions; however, its role in promoting wakefulness has overshadowed its other important functions. Here, we review evidence indicating that brain histamine plays a central role in motivation and emphasize its differential involvement in the appetitive and consummatory phases of motivated behaviors. We discuss the inputs that control histaminergic neurons of the tuberomamillary nucleus (TMN) of the hypothalamus, which determine the distinct role of these neurons in appetitive behavior, sleep/wake cycles, and food anticipatory responses. Moreover, we review evidence supporting the dysfunction of histaminergic neurons and the cortical input of histamine in regulating specific forms of decreased motivation (apathy). In addition, we discuss the relationship between the histamine system and drug addiction in the context of motivation.

Withdrawal from repeated administration of morphine alters histamine-induced anxiogenic effects produced by intra-ventral hippocampal microinjection

In the present study, the influence of withdrawal from repeated administration of morphine on intra-ventral hippocampal microinjection of histamine-induced anxiety-like behavior was investigated in male Wistar rats. Three days subcutaneous administration of morphine (5-10 mg/kg) followed by five days free of the drug decreased the percentage open arm time and the percentage open arm entries. Intra-ventral hippocampal administration of histamine (2.5-7.5 microg/rat) decreased percentage open arm time and percentage open arm entries. Intra-ventral hippocampal histamine-induced anxiogenic effect was reversed in animals that had previously received the three days morphine (7.5 mg/kg) followed by five days free of the drug. Intra-ventral hippocampal administration of pyrilamine (5-20 microg/rat) or ranitidine (10-40 microg/rat) decreased percentage open arm time and percentage open arm entries. Pyrilamine- or ranitidine-induced anxiogenic effect was not changed in animals that had previously received the three days morphine (7.5 mg/kg) followed by five days free of the drug. Intra-ventral hippocampal injections of clobenpropit increased percentage open arm time. The percentage open arm time and percentage open arm entries were decreased in the morphine-treated animals compared with non-morphine-treated controls. Percentage open arm entries and locomotor activity was reduced with some doses of clobenpropit. It can be concluded that the histamine system is involved in anxiety-like behavior, and repeated injections of morphine followed by five days free of the drugs interact with histamine receptor mechanism.

Motivated exploratory behaviour in the rat: The role of hippocampus and the histaminergic neurotransmission

Exploration is one of most basic adaptive behavioural responses, giving the animal an important evolutionary advantage to survive in a changing environment. Inspection of novel environments might be come with motivated exploratory behaviour. In spite that this type of exploration in the rat is known for many years, little attention has been given to the intrinsic mechanisms or the brain structures that are involved in. In the present work the hippocampus, the neurotransmitter histamine, and the geometrical features of novel objects were examined in a model of conflictive and non-conflictive exploration in the rat which evaluates incentive-motivated exploration. Young adult intact rats were tested in a neutral non-conflictive behavioural activity detector (OVM), with (eOVM) or without (sOVM) novel objects. Three different objects were used: a box, a toy duck, and a tower. Results show that animals decrease its general motor activity (horizontal, ambulatory and non-ambulatory activity) in favor to exploration of the objects. Motivated exploration was not the same for all three objects. Rats explored significantly more the Tower and the Box objects than the Duck item. Behavioral patterns of hippocampus-implanted rats showed decreased scores in motor activity but maintained the difference in the relation of "without/with objects" exploration. When hippocampus-implanted rats were tested in a conflictive exploration device (the elevated asymmetric plus-maze), exploration of the No Wall arm, considered the most fear-inducing environment, was significantly more explored by the animal when the tower object was positioned at its end than when it was absent. Microinjection into the ventral hippocampus of histamine abolished this motivated exploratory response. Pre-treatment with pyrilamine, and not with ranitidine, was effective to block the inhibitory effect of histamine on the object motivated exploration. Results confirm that the hippocampus is involved on incentive motivated exploration, and suggest that histamine is part of an analyzing neuronal circuit of novelty incentivating behavioural responses in rats.

The effects of histaminergic agents in the ventral hippocampus of rats in the plus-maze test of anxiety-like behaviours

It has been suggested that histamine have modulatory influence on anxiety-related behaviours both in animals and humans. Ventral hippocampus (VHC) may also be an important brain site in the modulation of fear or anxiety. In the present study, the effects of histaminergic agents on anxiety-related behaviours in the rats, using plus-maze test has been investigated. Intra-VHC administration of histamine (2.5, 5 and 7.5 microg/rat) decreased %OAT and %OAE but not locomotor activity, showing an anxiogenic response. Pretreatment of animals with either pyrilamine, a H1 receptor antagonist (10 microg/rat), or ranitidine, a H2 receptor antagonist (10 microg/rat) reverse anxiogenic response of histamine (2.5, 5 and 7.5 microg/rat). However, intra-VHC microinjection of higher doses of pyrilamine (40 microg/rat) or ranitidine (20 and 40 microg/rat) alone increased anxiety-like behaviours in rats. Our results showed that histamine may modulate anxiety-like behaviours via H1 and H2 receptors in the ventral hippocampus of the rats.

The effects of histaminergic agents in the central amygdala of rats in the elevated plus-maze test of anxiety

Reports indicate that histamine and histaminergic agents can change anxiety-related behaviours in both animals and humans. The amygdala is an important brain site in the modulation of fear or anxiety. In the present study, we investigated the effects of intracentral amygdala microinjection of histaminergic agents on anxiety-related behaviours in rats, using the elevated plus-maze test of anxiety. Intracentral amygdala administration of histamine (0.01-0.5 microg/0.5 microl bilateral) decreased %open armtime and % open arm entries, but not locomotor activity, showing an anxiogenic response. Intracentral amygdala microinjection of pyrilamine (H1 receptor antagonist) and ranitidine (H2 receptor antagonist) (both at 1-20 microg/0.5 microl bilateral) did not change anxiety-related parameters in our experiments. In another series of experiments, histamine (0.5 microg/0.5 microl bilateral) was coadministrated with pyrilamine and ranitidine (both at 1-20 mg/0.5 microl bilateral). The results showed that pyrilamine but not ranitidine could significantly reverse the anxiogenic effect of histamine at doses of 10 and 20 microg/0.5 microl bilateral. The results suggest that histamine may modulate anxiety via H1 but not H2 receptors in the rat central amygdala.

Role of glutamate receptors in the nucleus accumbens on behavioural responses to novel conflictive and non-conflictive environments in the rat

The possible role of glutamic acid locally applied into the nucleus accumbens on exploratory behaviours measured in 'conflictive' and 'non-conflictive' environments was studied in adult male rats. As a model of conflictive environment, the elevated asymmetric-plus maze (APM) was used. As a model of a non-conflictive environment, a modified holeboard enriched with an object (OVM) was used. In order to characterize the possible glutamic acid receptors involved, the following antagonists were also used: AP3 (antagonist of the metabotropic glutamic acid receptor), AP7 (antagonist of NMDA glutamic acid receptor, and CNQX (antagonists of kainate/AMPA glutamic acid receptor). Results showed that injection of glutamic acid into the nucleus accumbens induced in the APM a decrease of exploration and an increase of the permanency score (non-exploratory behaviours) of the 'High and Low wall' arm. However, in the 'Two High Walls' arm, glutamic acid decreased permanency. In the OVM, no major changes in the motor activity were observed with glutamic acid. Nevertheless, the vertical activity (an index of rearing) and head-dipping were inhibited by the amino-acid treatment. In the APM, the decrease of exploration induced by glutamic acid was blocked by all three receptor antagonists. In the non-exploratory behaviours, the facilitatory effect observed in the 'High and Low walls' arm was blocked only by AP7 and CNQX. The inhibitory action of glutamic acid on the permanency score in the 'Two High Walls' arm was not blocked by the receptors antagonists. In the OVM, AP7 and CNQX were effective in blocking the inhibition of glutamic acid on the vertical activity, but in head-dipping, only AP3 and CNQX were able to block the effect of the amino acid on this behaviour. In conclusion, the present results are compatible with the concept that glutamatergic input fibres to the nucleus accumbens modulate the expression of exploratory behaviour induced by novelty in conflictive and non-conflictive conditions.

Enrichment-dependent differences in novelty exploration in rats can be explained by habituation

In rats, exploratory activity and emotional reactivity towards novel stimuli reflect independent biological functions that are modulated differently by rearing experiences. Environmental enrichment is known to improve performance in exploratory tasks, while having inconsistent effects on emotionality. This study examined the effect of environmental enrichment on the behaviour of rats in two exploratory tasks. Male rats were reared under one of four conditions, differing in social and non-social complexity. At 9 weeks of age, exploration of a novel open field, and exploration of novel objects in the same open field following 24 h habituation, was assessed. Differences in social and non-social complexity of the rearing environment had inconsistent effects on exploration in the novel open field. In contrast, when rats were faced with novel objects in an otherwise familiar environment, exploration habituated faster with increasing stimulus complexity of the non-social environment. The social environment had no effect on this latter test. These findings indicate that environmental enrichment affects exploratory activity primarily through its effect on habituation to novelty. This effect depends on relative stimulus complexity of the rearing environment, but is independent of social factors. The present results further suggest that aversive tasks can obscure the expression of enrichment-dependent differences in habituation to novelty.

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.