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.

Involvement of opioidergic and nitrergic systems in memory acquisition and exploratory behaviors in cholestatic mice.

Bile duct ligation (BDL) is an animal model used in cholestatic disease research. Both opioidergic and nitrergic systems are known to be involved in cholestasis. The aim of this study was to investigate the possible interaction between these two systems in BDL-induced memory formation and exploratory behaviors in mice. Male mice weighing 25-30 g were divided into nonoperated controls, sham-operated, and BDL groups. One-trial step-down and hole-board paradigms were used to assess memory acquisition and exploratory behaviors, respectively. Cholestasis did not alter memory acquisition while increasing exploratory behaviors 7 days after BDL. A pretraining intraperitoneal injection of L-arginine (50, 100, and 200 mg/kg), L-NG-nitroarginine methyl ester (L-NAME) (5, 10, 20, and 40 mg/kg), or naloxone (0.125, 0.25, and 0.5 mg/kg) did not alter memory acquisition or exploratory behaviors, whereas morphine (5 and 7.5 mg/kg) decreased memory acquisition in sham-operated animals. Moreover, although injection of L-NAME and naloxone exerted no effect on memory acquisition in the 7 days post-BDL mice, L-arginine (100 and 200 mg/kg) and morphine (2.5, 5, and 7.5 mg/kg) injection reduced it. In contrast, L-NAME and naloxone, but not morphine or L-arginine, reduced the BDL-induced exploratory behaviors. Coadministration of subthreshold doses of morphine (1.25 mg/kg) and L-arginine (50 mg/kg) caused a memory deficit in 7 days post-BDL mice. However, the memory deficit induced by the effective doses of morphine (2.5 mg/kg) or L-arginine (200 mg/kg) in these mice was restored by the administration of either naloxone (0.5 mg/kg) or L-NAME (40 mg/kg). In addition, naloxone and L-NAME reduced the exploratory behaviors in L-arginine-pretreated mice but not in morphine-pretreated mice. We conclude that there appears to be a synergistic effect between opioidergic and nitrergic systems on memory acquisition and exploratory behaviors in cholestatic mice.

Evaluation of functional relationship between mouse hippocampal cholinergic and nitrergic systems in anxiogenic-like behavior.

Although a body of evidence shows the crucial role of hippocampal nitrergic and cholinergic systems in the modulation of anxiety, little is known about their functional relationship with regard to anxiety. The present study investigated the relationship between intra-CA1 administration of a nicotinic acetylcholine receptor antagonist (mecamylamine) and a nitric oxide synthase inhibitor [Nω-nitro-L-arginine methyl ester (L-NAME)] or its precursor (L-arginine) in anxiety-related behaviors. Mice received bilateral intra-CA1 injections of either L-NAME or L-arginine in the presence of mecamylamine and were subsequently tested in the elevated plus maze. A dose of 0.5 µg/0.5 µl mecamylamine bilaterally administered into CA1 did not change the percentage of open arm time (%OAT) or the percentage of open arm entries (%OAE) in the elevated plus maze task and thus was considered as a subeffective dose. Intra-CA1 administration of either L-arginine (1 and 1.5 µg/0.5 µl, bilaterally) or L-NAME (at 60 ng/0.5 µl, bilaterally) decreased %OAT, which represents an anxiogenic-like effect. Coadministration of the subeffective dose of mecamylamine together with the lower doses of L-NAME (10 and 30 ng/0.5 µl, bilaterally) or L-arginine (0.5 µg/0.5 µl, bilaterally) led to a decrease in %OAT and %OAE. Thus, both L-NAME and L-arginine showed anxiogenic-like effects, but the effects of mecamylamine were too small to support a functional relationship between the hippocampal cholinergic and nitrergic systems.

Involvement of nitrergic system of CA1in harmane induced learning and memory deficits.

Harmane (HA) is a ß-carboline alkaloid derived from the Peganum harmala plant which induces memory impairment. On the other hand some of the investigations showed that ß-carboline alkaloids inhibit NO production. Thus, the aim of the present study was to investigate the role of nitrergic system of the dorsal hippocampus (CA1) in HA-induced amnesia in male adult mice. One-trial step-down passive avoidance and hole-board apparatuses were used for the assessment of memory retrieval and exploratory behaviors respectively. The data indicated that pre-training intraperitoneal (i.p.) administration of HA (12 and 16 mg/kg) decreased memory acquisition. Sole pre-training or pre-testing administration of L-NAME, a nitric oxide synthesis inhibitor (5, 10 and 15 µg/mice, intra-CA1) did not alter memory retrieval. On the other hand, pre-training (10 and 15 µg/mice, intra-CA1) and pre-testing (5, 10 µg/mice, intra-CA1) injections of L-NAME restored HA-induced amnesia (16 mg/kg, i.p.). Furthermore, neither sole pre-training nor pre-testing administration of l-arginine, a NO precursor (3, 6 and 9 µg/mice, intra-CA1), altered memory retrieval. In addition, pre-testing (6 and 9 µg/mice, intra-CA1), but not pre-training, injection of l-arginine increased HA-induced amnesia (16 mg/kg, i.p.). These results suggest that the nitrergic system of CA1 is involved in HA-induced amnesia.

The effects of nicotine on nitric oxide induced anxiogenic-like behaviors in the dorsal hippocampus.

Nicotine, an active tobacco derived alkaloid, regulates the activity of the neuronal nitric oxide synthase (nNOS) as well as the release of nitric oxide (NO) in the nervous system. Nicotinic acetylcholine receptors and nNOS are abundantly co-expressed in the hippocampal neurons and are found to alter anxiety-like behaviors in rodents. Dorsal hippocampus may be a site for modulation of anxiety. Therefore, in this study, we investigated the possible interactions between nicotine and NO systems of the dorsal hippocampus and the resultant effect on anxiety-like behaviors. The elevated plus-maze (EPM) test has been used to test the anxiety. Intraperitoneal administration of nicotine (0.5mg/kg) decreased the open arm time percentage (%OAT) and open arm entries percentage (%OAE) but not the locomotor activity, indicating an anxiogenic-like response. Intra-CA1 injection of l-arginine (a NO precursor) or l-NAME (a NOS inhibitor) also caused anxiogenic-like effects. On the other hand, injection of the low dose nicotine before different doses of l-arginine or l-NAME blocked the anxiogenic-like response induced by the drugs. Our results suggested that, both NO and nicotinic cholinergic systems not only play a part in the modulation of the anxiety in mice dorsal hippocampus, but also demonstrate a complex interaction in this respect.

Influence of nitric oxide agents in the dorsal hippocampus of mice on anxiogenic-like effect induced by histamine.

Histaminergic receptors and neuronal nitric oxide synthase (nNOS) are co-expressed at high levels in the hippocampal neurons and alter anxiety-like behaviors in rodents. Since the dorsal hippocampus may be involved in modulation of anxiety-like behaviors, the aim of the present study was to assess whether the nitric oxide (NO) system in the dorsal hippocampus affects anxiety-like behaviors induced by histaminergic agents in mice. The effects of the NO precursor, L-arginine and NOS inhibitor, L-nitro-amino-methyl-ester (L-NAME) on histamine, pyrilamine and ranitidine responses in elevated plus maze (E.P.M.) in mice were investigated. Intra-CA1 microinjection of histamine (9 µg/mouse) or H1 receptor antagonist, pyrilamine (3, 6 and 9 µg/mouse), but not H2 receptor antagonist, ranitidine decreased the percentage of open arm time (%OAT) and open arm entries (%OAE), without affecting locomotor activity, suggesting an anxiogenic-like response. Both L-arginine (0.4 and 0.8 µg/mouse) and L-NAME (40 ng/mouse) when injected into the dorsal hippocampus induced anxiety-like behaviors, but the drugs reversed the anxiogenic response induced by the effective dose of histamine (9 µg/mouse) or pyrilamine (9 µg/mouse). Our results also indicated that intra-CA1 administration of L-arginine and L-NAME, in the presence or absence of ranitidine, exerted an anxiogenic effect. The results may indicate a modulatory role for NO in the dorsal hippocampus in the anxiogenic-like response induced by histamine or pyrilamine.

Nitric oxide in the nucleus accumbens is involved in retrieval of inhibitory avoidance memory by nicotine.

In the present study, the possible effect of nitric oxide agents injected into the nucleus accumbens (NAc) in the presence or absence of nicotine on morphine state-dependent memory in adult male Wistar rats was investigated. As a model of memory, a step-through type inhibitory avoidance task was used. Post-training injection of morphine (4 and 6mg/kg) dose dependently induced the impairment of memory retention. Administration of morphine (4 and 6mg/kg) before retention induced state-dependent retrieval of the memory acquired under post-training morphine (6mg/kg) influence. Injection of nicotine before retention (0.25 and 0.5mg/kg) alone and nicotine (0.1, 0.25 and 0.5mg/kg) plus an ineffective dose of morphine (2mg/kg) reversed the post-training morphine-induced memory impairment. The amnesia elicited by morphine (6mg/kg) was also prevented by pre-retention intra-NAc administration of a nitric oxide synthase (NOS) inhibitor, l-NAME (0.24µg/rat, intra-NAc). Interestingly, an ineffective dose of nicotine (0.1mg/kg) in combination with low doses of l-NAME (0.06 and 0.12µg/rat, intra-NAc) synergistically improved memory performance impaired by morphine given after training. It is important to note that intra-NAc administration of l-NAME before retention impaired memory retrieval by itself. In contrast, pre-retention administration of l-arginine, a nitric oxide (NO) precursor (0.25 and 0.5µg/rat, intra-NAc), which had no effect alone, prevented the nicotine reversal of morphine effect on memory. The results suggest a possible role for nitric oxide of nucleus accumbens in the improving effect of nicotine on the morphine-induced amnesia and morphine state-dependent memory.

Modulation of WIN55,212-2 state-dependent memory by α2-adrenergic receptors of the dorsal hippocampus.

BACKGROUND: An overlapping distribution of α2-adrenergic receptors with cannabinoid receptors has been reported in certain brain structures such as the dorsal hippocampus. Thus, functional interactions between cannabinoid and α2-adrenergic systems in cognitive control seem possible. In the present study, we examine the possible role of α2-adrenergic receptors of the dorsal hippocampus on WIN55,212-2 state-dependent learning. METHODS: Adult male Wistar rats were bilaterally implanted with chronic cannulae in the CA1 regions of their dorsal hippocampi trained in a step-down type inhibitory avoidance task and tested 24 hr after training, to measure step-down latency. RESULTS: Post-training or pre-test intra-CA1 administration of the cannabinoid receptor agonist, WIN 55,212-2 (0.25 and 0.5 µg/rat) induced amnesia. Amnesia produced by post-training WIN55,212-2 (0.5 µg/rat) was reversed by pre-test administration of WIN55,212-2, that was due to a state-dependent effect. Pre-test intra-CA1 microinjections of clonidine (0.25, 0.5 and 1 µg/rat) or yohimbine (0.5, 0.75, and 1 µg/rat) did not affect memory retrieval per se. Pre-test intra-CA1 administration of clonidine (0.5 and 1 µg/rat) or clonidine (0.25, 0.5, and 1 µg/rat) with an ineffective dose of WIN 55,212-2 (0.25 µg/rat) reversed post-training WIN55,212-2 (0.5 µg/rat,intra-CA1) induced memory impairment. Pre-test intra-CA1 microinjection of yohimbine (1 µg/rat) before administration of WIN55,212-2 (0.5 µg/rat, intra-CA1), however, dose-dependently inhibited WIN55,212-2 state-dependent memory. CONCLUSION: Modulation of α2-adrenergic receptors in the dorsal hippocampal CA1 regions can influence WIN55,212-2 induced amnesia and WIN55,212-2 state-dependent learning of an inhibitory avoidance task by pre- or post-synaptic mechanism(s).

Effects of cholinergic system of dorsal hippocampus of rats on MK-801 induced anxiolytic-like behavior.

RATIONALE: Some investigations have shown that the glutamate receptors play a critical role in cognitive processes such as learning and anxiety. OBJECTIVES: The possible involvement of the cholinergic system of the dorsal hippocampus in the anxiolytic-like response induced by MK-801, NMDA receptor antagonist, was investigated in the present study. METHODS: Male Wistar rats were used in the elevated plus maze apparatus to test the parameters: open arm time (%OAT), open arm entries (%OAE), close arm time (%CAT), close arm entries (%CAE) and other exploratory behaviors (locomotor activity, grooming, rearing and defecation) of anxiety-like response. RESULTS: The data indicated that intra-CA1 administration of MK-801 increased %OAT (2µg/rat) and %OAE (1 and 2µg/rat) while decreased %CAT and %CAE and did not alter other exploratory behaviors, indicating an anxiolytic-like effect. Moreover, intra-hippocampal injections of mecamylamine, a cholinergic receptor antagonists (2µg/rat) and scopolamine (4µg/rat), by themselves, 5min before testing, increased %OAT and %OAE but decreased %CAT and %CAE and did not alter locomotor activity and other exploratory behaviors, suggesting an anxiolytic-like effect. On the other hand, intra-CA1 co-administration of an ineffective dose of scopolamine (3µg/rat), but not mecamylamine (1µg/rat), with an ineffective dose of MK-801 (0.5µg/rat) increased %OAT and %OAE and decreased %CAT and %CAE. The data may indicate the possible involvement of the cholinergic system of the CA1 in the anxiolytic-like response induced by MK-801.

Influence of intracerebral administration of NO agents in dorsal hippocampus (CA1) on cannabinoid state-dependent memory in the step-down passive avoidance test.

In the present study, the effects of nitric oxide agents on WIN55, 212-2 induced state-dependent memory of passive avoidance task were examined in mice. One-trial step-down paradigm was used for the assessment of memory retention in adult male NMRI mice. Post-training intra-CA1 administration of CB1 and CB2 receptor agonists, WIN55, 212-2 (0.25, 0.5 and 1 microg/mouse), dose-dependently decreased memory retrieval. The memory impairment induced by post-training administration of WIN55, 212-2 (1 microg/mouse) was restored by pre-test administration of the same dose of the drug (1 microg/mouse, intra-CA1), showing the WIN55, 212-2 state-dependent memory. Single intra-CA1 administration of L-arginine (0.3, 1 and 3 microg/mouse) or L-NAME (0.3, 1 and 3 microg/mouse), 5 min pre-test could not alter memory retrieval. On the other hand, in the animals in which retrieval was impaired due to post-training administration of WIN55, 212-2 (1 microg/mouse), pre-test intra-CA1 administration of l-arginine (1 and 3 microg/mouse), but not L-NAME (0.3, 1 and 3 microg/mouse) 24h after training restored memory retrieval. Also, in the animals which received both post-training (1 microg/mouse) and pre-test injections of WIN55, 212-2 (1 microg/mouse), the injection of L-NAME (3 microg/mouse, intra-CA1), 2 min before pre-test administration decreased retrieval. Furthermore, in the animals under the influence of post-training administration of WIN55, 212-2 (1 microg/mouse), pre-test co-administration of non-effective doses of WIN55, 212-2 (0.25 microg/mouse) and L-arginine (0.3 and 1 microg/mouse), increased the restoration of memory by pre-test WIN55, 212-2. These findings may demonstrate the involvement of NO in state-dependent memory induced by intra-CA1 administration of WIN55, 212-2.

Involvement of dopamine D1/D2 receptors on harmane-induced amnesia in the step-down passive avoidance test.

Ingestion of harmane and other alkaloids derived from plant Peganum harmala has been shown to elicit profound behavioural and toxic effects in humans, including hallucinations, excitation, feelings of elation, and euphoria. These alkaloids in the high doses can cause a toxic syndrome characterized by tremors and convulsions. Harmane has also been shown to act on a variety of receptor systems in the mammalian brain, including those for serotonin, dopamine and benzodiazepines. In animals, it has been reported to affect short and long term memory. In the present study, effects of dopamine D1 and D2 receptor antagonists on the harmane (HA)-induced amnesia and exploratory behaviors were examined in mice. One-trial step-down and hole-board paradigms were used for the assessment of memory retention and exploratory behaviors in adult male NMRI mice respectively. Intraperitoneal (i.p.) administration of HA (5 and 10 mg/kg) immediately after training decreased memory consolidation, while had no effect on anxiety-like behavior. Memory retrieval was not altered by 15- or 30 min pre-testing administration of the D1 (SCH23390, 0.025, 0.05 and 0.1 mg/kg) or D2 (sulpiride 12.5, 25 and 50 mg/kg) receptor antagonists, respectively. In contrast, SCH23390 (0.05 and 0.1 mg/kg) or sulpiride (25 and 50 mg/kg) pre-test administration fully reversed HA-induced impairment of memory consolidation. Finally, neither D1 nor D2 receptor blockade affected exploratory behaviors in the hole-board paradigm. Altogether, these findings strongly suggest an involvement of D1 and D2 receptors modulation in the HA-induced impairment of memory consolidation.

Involvement of dorsal hippocampal alpha-adrenergic receptors in the effect of scopolamine on memory retrieval in inhibitory avoidance task.

The present study evaluated the possible role of alpha-adrenergic receptors of the dorsal hippocampus on scopolamine-induced amnesia and scopolamine state-dependent memory in adult male Wistar rats. The animals were bilaterally implanted with chronic cannulae in the CA1 regions of the dorsal hippocampus, trained in a step-through type inhibitory avoidance task, and tested 24h after training to measure step-through latency. Results indicate that post-training or pre-test intra-CA1 administration of scopolamine (1 and 2 microg/rat) dose-dependently reduced the step-through latency, showing an amnestic response. Amnesia produced by post-training scopolamine (2 microg/rat) was reversed by pre-test administration of the scopolamine that is due to a state-dependent effect. Interestingly, pre-test intra-CA1 microinjection of alpha1-adrenergic agonist, phenylephrine (1 and 2 microg/rat) or alpha2-adrenergic agonist, clonidine improved post-training scopolamine (2 microg/rat)-induced retrieval impairment. Furthermore, pre-test intra-CA1 microinjection of phenylephrine (0.25, 0.5 and 1 microg/rat) or clonidine (0.25, 0.5 and 1 microg/rat) with an ineffective dose of scopolamine (0.25 microg/rat), synergistically improved memory performance impaired by post-training scopolamine. On the other hand, pre-test injection of alpha1-receptors antagonist prazosin (1 and 2 microg/rat) or alpha2-receptors antagonist yohimbine (1 and 2 microg/rat) prevented the restoration of memory by pre-test scopolamine. It is important to note that pre-test intra-CA1 administration of the same doses of prazosin or yohimbine, alone did not affect memory retrieval. These results suggest that alpha1- and alpha2-adrenergic receptors of the dorsal hippocampal CA1 regions may play an important role in scopolamine-induced amnesia and scopolamine state-dependent memory.

Anxiety-like behavior induced by histaminergic agents can be prevented by cannabinoidergic WIN55,212-2 injected into the dorsal hippocampus in mice.

In the present study, we investigate the effects of the histaminergic system and cannabinoid receptor agents on anxiety-related behaviors and their interactions using the hole-board test on mice. Bilateral intra-CA1 administration of the CB1/CB2 receptor agonist, WIN55, 212-2 (0.1-0.5microg/mouse) did not modify exploratory behaviors in mice. On the other hand, intra-CA1 administration of CB1 receptor antagonist, AM251 (25 and 50ng/mouse) or histamine, pyrilamine and ranitidine (5-10microg/mouse) decreased the amount of head-dipping and increased the first head-dip, suggesting an anxiogenic-like response. Furthermore, our present data indicated that the co-administration of WIN55, 212-2 (0.25microg/mouse) with histaminergic agents, decreased the anxiogenic-like response of an effective dose (5microg/mouse) of histamine and pyrilamine, but not that of ranitidine. In addition, the results demonstrated that co-administration of an ineffective dose of AM251 (15ng/mouse) with histaminergic drugs did not alter the response induced by an ineffective dose (3.75microg/mouse) of either histamine or pyrilamine and ranitidine. In all experiments and doses, locomotor activity and other exploratory behaviors were not significantly changed. In conclusion, our results showed that there is a chance of partial interaction between the cannabinoidergic and the histaminergic systems of the dorsal hippocampus on anxiogenic/anxiolytic-like behaviors in hole-board test.