Effects of calcium channel blockers on behaviors induced by the N-methyl-D-aspartate receptor antagonist, dizocilpine, in rats

Dantrolene blockade of ryanodine receptor impairs ethanol-induced behavioral stimulation, ethanol intake and loss of righting reflex

Calcium has been characterized as one of the most ubiquitous, universal and versatile intracellular signals. Among other substances with the ability to alter intracellular calcium levels, ethanol has been described as particularly relevant because of its social and economic impact. Ethanol effects on calcium distribution and flux in vitro have been widely studied, showing that acute ethanol administration can modulate intracellular calcium concentrations in a dose dependent manner. Intracellular calcium released from the endoplasmic reticulum plays a determinant role in several cellular processes. In this study, we aim to assess the effect of dantrolene, a ryanodine receptor antagonist, on three different ethanol-elicited behaviors: locomotor activity, loss of righting reflex and ethanol intake. Mice were challenged with an injection of dantrolene (0-5 mg/kg, i.p.) 30 min before ethanol (0-4 g/kg, i.p.) administration. Animals were immediately placed in an open field cylinder to monitor distance travelled horizontally or in a V-shaped trough to measure righting reflex recovery time. For ethanol intake, dantrolene (0-5mg/kg, i.p.) was administered 30 min before ethanol (20%, v/v) exposure, following a drinking in the dark paradigm. Our results showed that dantrolene selectively reduces ethanol-induced stimulation, loss of righting reflex, and ethanol intake in a dose dependent manner. Together, these data suggest that intracellular calcium released from the endoplasmic reticulum may play a critical role in behavioral effects caused by ethanol, and point to a calcium-dependent pathway as a possible cellular mechanism of action for ethanol.

Participation of L-type calcium channels in ethanol-induced behavioral stimulation and motor incoordination: effects of diltiazem and verapamil

Calcium flux through voltage gate calcium channels (VGCC) is involved in many neuronal processes such as membrane depolarization, gene expression, hormone secretion, and neurotransmitter release. Several studies have shown that either acute or chronic exposure to ethanol modifies calcium influx through high voltage activated channels. Of special relevance is the L-type VGCC. Pharmacological manipulation of L-type calcium channels affects ethanol intake, ethanol discrimination and manifestations of withdrawal syndrome. The present study investigates the role of L-type channels on the psychomotor effects (stimulation and sedation/ataxia) of ethanol by testing the effects of different L-type calcium channel blockers (CCB) on such behaviors. Mice were pretreated intraperitoneally with the CCB, diltiazem (0-40 mg/kg) or verapamil (0-30 mg/kg) 30 min before ethanol (0-3.5 g/kg). Locomotion was measured in an open field chamber for 20 min immediately after ethanol. The two CCB tested prevented locomotor stimulation, but not locomotor suppression produced by ethanol. Doses of the two CCB which reduced ethanol stimulation, did not alter spontaneous locomotion. The ataxic effects of ethanol (1.25 g/kg), measured with an accelerating rotarod task, were not affected by diltiazem (20mg/kg) or verapamil (15 mg/kg). In addition, our results indicated that ethanol is more sensitive to the antagonism of L-type calcium channels than other drugs with stimulant properties; doses of the two CCB that reduced ethanol stimulation did not reduce the psychomotor effects of amphetamine, caffeine or cocaine. In conclusion, these data provide further evidence of the important involvement of L-type calcium channels in the behavioral effects produced by ethanol.

Lowered brain stimulation reward thresholds in rats treated with a combination of caffeine and N-methyl-D-aspartate but not alpha-amino-3-hydroxy-5-methyl-4-isoxazole propionate or metabotropic glutamate receptor-5 receptor antagonists

Previous studies suggested that adenosine A1 and A2A receptor agonists counteract behavioral effects of N-methyl-D-aspartate (NMDA) receptor antagonists while adenosine receptor antagonists may produce opposite effects enhancing the actions of NMDA receptor antagonists. To further evaluate the effects of combined administration of adenosine receptor antagonist caffeine and various NMDA and non-NMDA glutamate receptor antagonists on brain stimulation reward (discrete-trial threshold current intensity titration procedure), rats with electrodes implanted into the ventral tegmental area were tested after pretreatment with NMDA receptor channel blocker MK-801 (0.01-0.3 mg/kg), competitive antagonist D-CPPene (0.3-5.6 mg/kg), glycine site antagonist L-701,324 (1.25-5 mg/kg), alpha-amino-3-hydroxy-5-methyl-4-isoxazole propionate (AMPA) receptor antagonist GYKI-53655 (1-10 mg/kg), metabotropic glutamate receptor 5 (mGluR5) antagonist MPEP (1-10 mg/kg) alone and in combination with caffeine (1-30 mg/kg). MK-801 (0.056 and 0.1 mg/kg) was the only tested glutamate antagonist that lowered self-stimulation thresholds, while D-CPPene (5.6 mg/kg) and MPEP (5.6 and 10 mg/kg) had the opposite effects. Threshold-increasing effects of D-CPPene, but not of MPEP, however, were associated with marked impairment of operant performance, reflected by longer latencies to respond and higher rates of responding during the inter-trial intervals. Operant performance was also disrupted by the highest dose of MK-801 (0.3 mg/kg). For subsequent experiments, caffeine (1-30 mg/kg) was combined with the highest doses of NMDA receptor antagonists that did not lower the brain stimulation reward thresholds and did not impair operant performance. Caffeine had no appreciable effects on self-stimulation behavior when given alone. A low dose of caffeine (3 mg/kg) significantly lowered self-stimulation thresholds only when given together with MK-801 (0.03 mg/kg) or D-CPPene (3 mg/kg). Combined with the same antagonist drugs, higher doses of caffeine (10 and 30 mg/kg) facilitated time-out responding. These results indicate that, within a limited dose range, caffeine in combination with an NMDA receptor channel blocker and a competitive antagonist significantly lowers brain stimulation reward thresholds in rats.

NMDA or AMPA/kainate receptor blockade prevents acquisition of conditioned place preference induced by D(2/3) dopamine receptor stimulation in rats

RATIONALE

Recent experiments from this laboratory demonstrated synergistic effects of AMPA/kainate receptor blockade and D(2/3) dopamine (DA) receptor stimulation on brain stimulation reward and locomotor activity.

OBJECTIVES

Using place conditioning, this study explored further the interaction between DA and glutamate (Glu) using the N-methyl-D-aspartate (NMDA) receptor antagonist MK-801, the AMPA/kainate receptor antagonist NBQX, and the D(2/3) DA receptor agonist 7-OH-DPAT.

METHODS

Effects of these compounds, alone and combined, were measured in male Sprague--Dawley rats using an unbiased two-compartment place conditioning procedure.

RESULTS

7-OH-DPAT (0.03--5.0 mg kg(-1), s.c.) administered immediately prior to conditioning was ineffective; when administered 15 min prior to conditioning, only the highest dose (5.0 mg kg(-1), s.c.) induced conditioned place preference (CPP). Acquisition of 7-OH-DPAT-induced CPP was blocked by MK-801 (0.06 or 0.13 mg kg(-1), i.p.) or NBQX (0.5 microg) microinjected into the nucleus accumbens (NAS) shell subregion. Intra-NAS shell administration of 7-OH-DPAT (5.0 microg) or NBQX (0.5 microg), alone or combined, failed to induce place conditioning, and this lack of effect was not due to state dependency. Administration of MK-801 or 7-OH-DPAT (5.0 mg kg(-1)) during the conditioning phase acutely increased horizontal activity, but neither compound, alone or combined, induced conditioned locomotor effects.

CONCLUSIONS

Acquisition of place conditioning induced by systemic administration of 7-OH-DPAT is blocked by systemic NMDA receptor antagonism by MK-801 or by the AMPA/kainate receptor antagonist NBQX microinjected into the NAS shell subregion.

Atypical antipsychotic profile of flunarizine in animal models

RATIONALE

Flunarizine is known as a calcium channel blocker commonly used in many countries to treat migraine and vertigo. Parkinsonism has been described as one of its side-effects in the elderly, which is in agreement with its recently characterized moderate D2 receptor antagonism.

OBJECTIVES

To perform a pre-clinical evaluation of flunarizine as a potential antipsychotic.

METHODS

We evaluated the action of orally administered flunarizine in mice against hyperlocomotion induced by amphetamine and dizocilpine (MK-801) as pharmacological models of schizophrenia, induction of catalepsy as a measure for extrapyramidal symptoms and impairment induced by dizocilpine on the delayed alternation task for working memory.

RESULTS

Flunarizine robustly inhibited hyperlocomotion induced by both amphetamine and dizocilpine at doses that do not reduce spontaneous locomotion (3-30 mg/kg). Mild catalepsy was observed at 30 mg/kg, being more pronounced at 50 mg/kg and 100 mg/kg. Flunarizine (30 mg/kg) improved dizocilpine-induced impairment on the delayed alternation test.

CONCLUSIONS

These results suggest a profile comparable to atypical antipsychotics. The low cost, good tolerability and long half-life (over 2 weeks) of flunarizine are possible advantages for its use as an atypical antipsychotic. These results warrant clinical trials with flunarizine for the treatment of schizophrenia.

Calcium channel antagonists attenuate cross-sensitization to the rewarding and/or locomotor effects of nicotine, morphine and MK-801

The present study focused on the evaluation of behavioural cross-sensitization, particularly in locomotor activities and conditioned rewarding effects, between nicotine and morphine, cocaine, amphetamine or MK-801. Nicotine (0.5 mg kg(-1))-experienced mice manifested an enhanced locomotor response to morphine (5 mg kg(-1)) or MK-801 (0.3 mg kg(-1)). No cross-sensitization was observed between nicotine and amphetamine (2 mg kg(-1)) or cocaine (15 mg kg(-1)). Additionally, the L-type voltage-dependent calcium-channel antagonists, nimodipine and verapamil, but not diltiazem, at a dose of 20 mg kg(-1) injected before morphine or MK-801 challenge, blocked the expression of this cross-sensitization. In the second test, an enhancement of morphine place conditioning in rats pre-exposed to nicotine (0.5 mg kg(-1), injected daily for 5 days) was demonstrated. After two conditioning sessions, morphine (5 mg kg(-1)) induced a clear place preference only in animals that had previously received nicotine injections. The administration of nimodipine (10 and 20 mg kg(-1)), verapamil (10 and 20 mg kg(-1)) and diltiazem (10 and 20 mg kg(-1)) prior to nicotine dose-dependently prevented this sensitization to the rewarding effect of morphine produced by prior injections of nicotine. These findings support the hypothesis that similar neural calcium-dependent mechanisms are involved in the appetitive effects of nicotine and morphine and in the sensitized locomotor stimulant effects of nicotine and morphine or MK-801.

Morphine-induced dependence and sensitization are altered in mice deficient in AMPA-type glutamate receptor-A subunits

AMPA-type glutamate receptors have been suggested to be involved in the neurobiological mechanisms of drug addiction. We have made use of two mouse lines, which both have modulated AMPA receptor responses. The first line is entirely deficient in glutamate receptor-A (GluR-A) subunits (A-/- knock-out line) and, in the second one, the Q582 residue of GluR-A subunits is replaced by an arginine residue (R/R mutants), which reduces the calcium permeability and channel conductance of the receptors containing this mutated subunit. Mice of both lines are healthy, but they show slightly increased locomotor activity. Acute morphine administration enhanced locomotor activity of the GluR-A-/- and GluR-A(R/R) mice, at least as much as that of their wild-type littermates. Only in the GluR-A-/- mice did we observe reduced tolerance development in tail-flick antinociception and less severe naloxone-precipitated withdrawal symptoms after treatment with increasing morphine doses, without differences in plasma and brain morphine levels when compared with wild type. Repeated daily morphine administration sensitized the locomotor activity responses in the GluR-A-/- and GluR-A(R/R) mice only when given in the measuring cages, whereas the wild-type mice showed slightly increased responses also when the repeated treatment was given in their home cages. Normal or even enhanced context-dependent sensitization was observed also with repeated amphetamine administration in the GluR-A subunit-deficient mice. The results indicate that AMPA receptors are involved in the acute and chronic effects of morphine, including context-independent sensitization, and that the GluR-A subunit itself is important for morphine tolerance and dependence.

Behavioural and anti-psychotic effects of Ca2+ channel blockers in rhesus monkey

The potential utility of Ca2+ channel blockers in the treatment of various psychiatric disorders has been recently suggested. In the present study, the behavioural and anti-psychotic effects of Ca2+ channel blockers were investigated in unrestrained rhesus monkeys (Macaca mulatta) living together in a colony. The different behaviours categorised as social, solitary and abnormal were video recorded and analysed. Graded doses of verapamil (5-20 mg/kg, i.m.) and nimodipine (7.5-30 mg/kg, p.o.) produced a mild decrease in social and solitary behaviour without producing any cataleptic posture in the tested monkeys. In order to determine potential antipsychotic effects, Ca2+ channel blockers were studied in the model of amphetamine-induced psychosis. Amphetamine, at the dose of 2 mg/kg, i.m., induced suppression of approach, contact, grooming, and feeding, whilst vigilance (checking), stereotyped behaviour and oral hyperkinesia were increased in the monkeys. Pre-treatment with verapamil (10 and 20 mg/kg, i.m.) significantly suppressed amphetamine-induced hypervigilance, stereotypy, oral hyperkinesia and tachypnoea but was unable to reverse other amphetamine-induced behavioural effects. Nimodipine showed insignificant anti-psychotic effects at both 15 and 30 mg/kg doses. These results suggest that verapamil has a definite antipsychotic effect without any extrapyramidal side effects and thus may be of clinical significance in the treatment of psychosis.

Effect of calcium channel blockers on stress-induced visceral, endocrinological and immune responses

In the present study effects of five commonly used calcium channel blockers (CCBs) belonging to different chemical classes have been investigated on stress-induced modulation of some visceral, endocrinological and immunological parameters in rats and mice. Restraint stress (RS) produced gastric mucosal lesions, increased plasma corticosterone levels and reduced antiSRBC antibody titre, a measure of humoral immune response and % leucocyte migration inhibition (% LMI) and foot pad thickness, measures of cell-mediated immunity. Nimodipine (10, 20 40 mg/kg, i.p.) and flunarizine (10, 20, 40 mg/kg, i.p.) antagonised the effect of RS on gastric ulcerogenesis and plasma corticosterone levels but failed to modulate the stress-induced suppression of both humoral and cell-mediated immune responses. Thus, CCBs appear to modulate stress-induced visceral, endocrinological and immune responses, albeit in a differential manner.