Some behavioral effects of repeated administration of calcium channel antagonists

L-type calcium channel regulation of depression, anxiety and anhedonia-related behavioral phenotypes following chronic stress exposure

Exposure to chronic and unpredictable stressors can precipitate mood-related disorders in humans, particularly in individuals with pre-existing mental health challenges. L-type calcium channels (LTCCs) have been implicated in numerous neuropsychiatric disorders, as LTCC encoding genes have been identified as candidate risk factors for neuropsychiatric illnesses. In these sets of experiments, we sought to examine the ability of LTCC blockade to alter depression, anxiety, and anhedonic-related behavioral responses to chronic unpredictable stress (CUS) exposure in female and male rats. Rats first underwent either 21 days of CUS or no exposure to chronic stressors, serving as home cage controls (HCC). Then rats were examined for anhedonia-related behavior, anxiety and depression-like behavioral responses as measured by the sucrose preference test (SPT), elevated plus maze (EPM), and forced swim test (FST). CUS exposed females and males showed anhedonic and anxiogenic-like behavioral responses on the SPT and EPM, respectively, when compared to HCCs. In female and male rats, systemic administration of the LTCC blocker isradipine (0.4 mg/kg and 1.2 mg/kg, I.P.) attenuated the CUS-induced decrease in sucrose preference and reversed the CUS-induced decrease in open arm time. In the FST, systemic isradipine decreased immobility time across all groups, consistent with an antidepressant-like response. However, there were no significant differences in forced swim test immobility time between HCC and CUS exposed animals. Taken together, these data point to a role of LTCCs in the regulation of mood disorder-related behavioral phenotype responses to chronic stress exposure.

Nimodipine activates TrkB neurotrophin receptors and induces neuroplastic and neuroprotective signaling events in the mouse hippocampus and prefrontal cortex

The L-type calcium channel blocker nimodipine improves clinical outcome produced by delayed cortical ischemia or vasospasm associated with subarachnoid hemorrhage. While vasoactive mechanisms are strongly implicated in these therapeutic actions of nimodipine, we sought to test whether nimodipine might also regulate neurotrophic and neuroplastic signaling events associated with TrkB neurotrophin receptor activation. Adult male mice were acutely treated with vehicle or nimodipine (10 mg/kg, s.c., 1.5 h) after which the phosphorylation states of TrkB, cyclic-AMP response element binding protein (CREB), protein kinase B (Akt), extracellular regulated kinase (ERK), mammalian target of rapamycin (mTor) and p70S6 kinase (p70S6k) from prefrontal cortex and hippocampus were assessed. Nimodipine increased the phosphorylation of the TrkB catalytic domain and the phosphoslipase-Cγ1 (PLCγ1) domain, whereas phosphorylation of the TrkB Shc binding site remained unaltered. Nimodipine-induced TrkB phosphorylation was associated with increased phosphorylation levels of Akt and CREB in the prefrontal cortex and the hippocampus whereas phosphorylation of ERK, mTor and p70S6k remained unaltered. Nimodipine-induced TrkB signaling was not associated with changes in BDNF mRNA or protein levels. These nimodipine-induced changes on TrkB signaling mimic those produced by antidepressant drugs and thus propose common mechanisms and long-term functional consequences for the effects of these medications. This work provides a strong basis for investigating the role of TrkB-associated signaling underlying the neuroprotective and neuroplastic effects of nimodipine in translationally relevant animal models of brain trauma or compromised synaptic plasticity.

Psychostimulants, antidepressants and neurokinin-1 receptor antagonists ('motor disinhibitors') have overlapping, but distinct, effects on monoamine transmission: the involvement of L-type Ca2+ channels and implications for the treatment of ADHD

Both psychostimulants and antidepressants target monoamine transporters and, as a consequence, augment monoamine transmission. These two groups of drugs also increase motor activity in preclinical behavioural screens for antidepressants. Substance P-preferring receptor (NK1R) antagonists similarly increase both motor activity in these tests and monoamine transmission in the brain. In this article, the neurochemical and behavioural responses to these three groups of drugs are compared. It becomes evident that NK1R antagonists represent a distinct class of compounds ('motor disinhibitors') that differ substantially from both psychostimulants and antidepressants, especially during states of heightened arousal or stress. Also, all three groups of drugs influence the activation of voltage-gated Ca(v)1.2 and Ca(v)1.3 L-type channels (LTCCs) in the brain, albeit in different ways. This article discusses evidence that points to disruption of these functional interactions between NK1R and LTCCs as a contributing factor in the cognitive and behavioural abnormalities that are prominent features of Attention Deficit Hyperactivity Disorder (ADHD). Arising from this is the interesting possibility that the hyperactivity and impulsivity (as in ADHD) and psychomotor retardation (as in depression) reflect opposite poles of a behavioural continuum. A better understanding of this pharmacological network could help explain why psychostimulants augment motor behaviour during stress (e.g., in preclinical screens for antidepressants) and yet reduce locomotor activity and impulsivity in ADHD. This article is part of the Special Issue entitled 'CNS Stimulants'.

CACNA1C (Cav1.2) in the pathophysiology of psychiatric disease

One of the most consistent genetic findings to have emerged from bipolar disorder genome wide association studies (GWAS) is with CACNA1C, a gene that codes for the α(1C) subunit of the Ca(v)1.2 voltage-dependent L-type calcium channel (LTCC). Genetic variation in CACNA1C have also been associated with depression, schizophrenia, autism spectrum disorders, as well as changes in brain function and structure in control subjects who have no diagnosable psychiatric illness. These data are consistent with a continuum of shared neurobiological vulnerability between diverse-Diagnostic and Statistical Manual (DSM) defined-neuropsychiatric diseases. While involved in numerous cellular functions, Ca(v)1.2 is most frequently implicated in coupling of cell membrane depolarization to transient increase of the membrane permeability for calcium, leading to activation and, potentially, changes in intracellular signaling pathway activity, gene transcription, and synaptic plasticity. Ca(v)1.2 is involved in the proper function of numerous neurological circuits including those involving the hippocampus, amygdala, and mesolimbic reward system, which are strongly implicated in psychiatric disease pathophysiology. A number of behavioral effects of LTCC inhibitors have been described including antidepressant-like behavioral actions in rodent models. Clinical studies suggest possible treatment effects in a subset of patients with mood disorders. We review the genetic structure and variation of CACNA1C, discussing relevant human genetic and clinical findings, as well as the biological actions of Ca(v)1.2 that are most relevant to psychiatric illness.

Nifedipine-morphine interaction: a further investigation on nociception and locomotor activity in mice

Nociception and locomotor activity were tested in mice (C57BL/6 and DBA/2 strains), receiving the dihydropyridine calcium-channel blocker nifedipine, alone or combined with morphine. The calcium antagonist did not change the reaction time to thermal stimulation (tail-flick test), when administered alone, but combinations of nifedipine and morphine prolonged tail-flick latencies less than did the opiate alone. Nifedipine decreased locomotion in both strains, reduced the hypermotility induced by morphine in C57 mice, and enhanced the locomotor depression induced by the opiate in DBA mice. A comparison of the effects of nifedipine with those of the non-calcium antagonist vasodilator, hydralazine, suggests that the interactions with morphine were not exclusively related to neuronal changes produced by calcium channel blockade, but also to haemodynamic factors. In fact, except for the lack of interference with morphine-induced hypermotility in C57 mice, hydralazine, given alone or in combination with morphine, produced effects similar to those of nifedipine.

A double-blind comparative study of clinical efficacy of verapamil versus lithium in acute mania

Objectives. The importance of intracellular calcium ions to processes that may be involved in mania and the calcium antagonist action of mood stabilizers suggest a role of verapamil in the treatment of mania. This study was undertaken to compare the clinical efficacy and tolerability of verapamil versus lithium in manic patients. Methods. Patients with acute mania were randomized to receive lithium (N =25) or verapamil (N =25) in a 4-week double-blind comparative study. Both groups were homogeneous with regard to demographic and disease variables. The primary efficacy measures were the mean change from the baseline to the last assessment in BRMS (Bech-Raefelson Mania Rating Scale) and YMRS (Young-Mania Rating scale) total score. The rating scales were administered to the patients on day 1, 3, 5, 7, 11, 13, 17, 21, 28 of the study. Attendant's assessment of relief and adverse events were recorded during the study. Results. Both treatment groups showed significant decrease in mean BRMS and YMRS score assessed at different points of time. The study showed an equal efficacy of verapamil compared with lithium in the treatment of mania. The findings were supported by good tolerability of verapamil treatment. Conclusion. This study found equal benefit of verapamil over lithium in treating acute mania.

Prevention of diazepam withdrawal syndrome by nifedipine—behavioural and neurochemical studies

Our studies aimed at investigating whether the dihydropyridine calcium antagonist, nifedipine, could prevent anxiogenic-like consequences of diazepam withdrawal in rats. Animals withdrawn from chronic diazepam (2 mg/kg/day i.p. for 2 weeks) drank significantly less water than did control rats in the unfamiliar arm of a Y maze. This anxiogenic-like effect could be prevented by acute administration of nifedipine (at 10 mg/kg i.p., but not at lower doses), which, on its own, did not change water intake in naive rats. Given chronically in combination with diazepam for the second half of a 2-week treatment with this drug, nifedipine (at the daily dose of 5 mg/kg i.p.) also suppressed the reduction of water intake normally observed on diazepam withdrawal. Biochemical measurements showed that acutely, as well as chronically, administered nifedipine increased 5-HT turnover in the hippocampus of diazepam-treated rats, thereby suggesting that the prevention of diazepam withdrawal-induced anxiogenic behaviour by the calcium antagonist might be underlain by serotoninergic mechanisms.

The L-type calcium channel blocker nimodipine mitigates "learned helplessness" in rats

We assessed the effect of nimodipine, an L-type calcium channel blocker, on the escape deficit induced by prior exposure to inescapable shock in rats in four experiments. In Experiment 1, we injected rats at each of three time points (i.e., before shock exposure, after shock exposure, and before shuttle escape testing) with one of four doses of nimodipine (0, 0.5, 2.5, 5.0 mg/kg). The 5.0-mg/kg dose was most effective, acting to reduce shuttle escape latencies of inescapably shocked rats to a level comparable with nonshocked controls. No benefit occurred in Experiment 2, however, when nimodipine was administered at only one of the three time points used in the first experiment. Moreover, escape performance did not improve when rats received injections of nimodipine on the 2 days prior the experiment, and then one additional injection at one of the three time points identified above in Experiment 3. Finally, administration of nimodipine at two of the three time points did improve escape responding, but only when injected immediately prior both to shock exposure and the shuttle escape test.

Modulation of serotonin2A receptor function in rats after repeated treatment with dexamethasone and L-type calcium channel antagonist nimodipine

1. It has been conceivable that the hypothalamic-pituitary-adrenal (HPA) axis hyperactivity plays an important role in the pathophysiology of depression. In the present study, we have investigated the effect of repeated treatment with dexamethasone on serotonin (5-HT) 1A, 5-HT2A and alpha1-adrenergic receptors in the rat frontal cortex. Moreover, several studies have suggested the effectiveness of L-type calcium channel antagonist nimodipine for the treatment of depression. We also investigated the effect of repeated treatment with nimodipine on 5-HT2A receptor in rats with repeated dexamethasone treatment. 2. Repeated treatment with dexamethasone (1 mg/kg/day for 14 days) increased the density of 5-HT2A receptor, but not 5-HT1A and alpha1-adrenergic receptors in the rat frontal cortex. 3. The density of 5-HT2A receptor in the rat frontal cortex was significantly increased 1 day after repeated treatment with dexamethasone, but was not increased 7 or 14 days after repeated treatment. Wet dog shakes (WDS) induced by (+/-)-1-(4-iodo-2,5-dimethoxyphenyl)-2-aminopropane hydrochloride (DOI), a 5-HT2A receptor agonist, in rats were significantly enhanced 1, 7 and 14 days after repeated treatment with dexamethasone, although the frequency of WDS gradually decreased after repeated treatment. 4. Repeated treatment with nimodipine (5 mg/kg/day for 14 days) attenuated DOI-induced WDS enhanced by repeated treatment with dexamethasone (1 mg/kg/day for 14 days), however, it did not change the density of 5-HT2A receptor. Repeated treatment with dexamethasone decreased locomotor activity and body weight, but repeated treatment with nimodipine did not recover these parameters. 5. The results of the present study suggest that repeated treatment with dexamethasone may selectively increase the 5-HT2A receptor in the rat frontal cortex and affect 5-HT2A receptor-mediated signal transduction. In addition, the intracellular calcium homeostasis by blocking calcium influx through L-type calcium channel may play an important role in the regulation of the 5-HT2A receptor function by dexamethasone.

Antidepressant drugs inhibit glucocorticoid receptor-mediated gene transcription - a possible mechanism

1. Antidepressant drugs are known to inhibit some changes evoked by glucocorticoids, as well as a hyperactivity of hypothalamic-pituitary-adrenal (HPA) axis, often observed in depression. 2. The aim of present study was to investigate effects of various antidepressant drugs on the glucocorticoid-mediated gene transcription in fibroblast cells, stably transfected with an MMTV promoter (LMCAT cells). 3. The present study have shown that antidepressants (imipramine, amitriptyline, desipramine, fluoxetine, tianeptine, mianserin and moclobemide), but not cocaine, inhibit the corticosterone-induced gene transcription in a concentration- and a time-dependent manner. 4. Drugs which are known to augment clinical effects of medication in depressed patients (lithium chloride, amantadine, memantine), do not affect the inhibitory effects of imipramine on the glucocorticoid receptor (GR)-mediated gene transcription. 5. Inhibitors of phospholipase C (PLC), protein kinase C (PKC), Ca(2+)/calmodulin-dependent protein kinase (CaMK) and antagonists of the L-type Ca(2+) channel also inhibit the corticosterone-induced gene transcription. 6. Inhibitors of protein kinase A (PKA) and protein kinase G (PKG) are without effect on the GR-induced gene transcription. 7. Phorbol ester (an activator of PKC) attenuates the inhibitory effect of imipramine on the GR-induced gene transcription. 8. Imipramine decreases binding of corticosterone-receptor complex to DNA. 9. It is concluded that antidepressant drugs inhibit the corticosterone-induced gene transcription, and that the inhibitory effect of imipramine depends partly on the PLC/PKC pathway.

"Atypical" neuromodulatory profile of glutapyrone, a representative of a novel 'class' of amino acid-containing dipeptide-mimicking 1,4-dihydropyridine (DHP) compounds: in vitro and in vivo studies

Glutapyrone, a disodium salt of 2-(2,6-dimethyl-3,5-diethoxycarbonyl-1,4-dihydropyridine-4-carboxamido)- glutaric acid, is a representative of a novel 'class' of amino acid-containing 1,4-dihydropyridine (DHP) compounds developed at the Latvian Institute of Organic Synthesis, Riga, Latvia. Conceptually, the glutapyrone molecule can be regarded as a dipeptide-mimicking structure formed by the "free" amino acid (glutamate) moiety and "crypto" (built into the DHP cycle) amino acid ("GABA") elements. Both of these amino acids are joined by the peptide bond. This compound unlike classical DHPs lacks calcium antagonistic or agonistic properties. Our previous studies revealed a profound and long-term anticonvulsant, stress-protective and neurodeficit-preventive activities of glutapyrone. In view of structural properties the role of glutamatergic mechanisms in the mediation of central effects of glutapyrone was considered. In the present study glutapyrone at the concentration range of 1 microM(-1) mM failed to effect both NMDA ([3H]TCP) and non-NMDA ([3H]KA and [3H]AMPA) receptor ligand binding in the rat cortical membranes in vitro. The compound markedly enhanced motor hyperactivity induced by the NMDA antagonist PCP and the dopamine releasing compound D-amphetamine in the rats. Glutapyrone displayed activity in a variety of animal models relevant for affective/depressive disorders in humans i.e. reserpine-induced ptosis and hypothermia, forced swimming test and open field test. These data indicate that the unusually "broad" pharmacological spectrum of glutapyrone might involve concomitant actions on multiple neurotransmitter systems, particularly, GABA-ergic and the catecholamines. It is discussed whether these functional properties are secondary to action on intracellular events, predominantly, G protein-related since glutapyrone appears to lack direct interactions with a number of receptors including ionotropic glutamate and GABA(A)/Bzd receptors.

Open field behavior in nucleus basalis magnocellularis-lesioned rats treated with physostigmine and verapamil

The present study was done to investigate and compare the effect of acetylcholinesterase inhibitor, physostigmine (0.030, 0.045, 0.060 and 0.075 mg/kg sc) and Ca-antagonist, verapamil (1.0, 2.5, 5.0 and 10.0 mg/kg sc) on open field behavior in male Wistar rats with bilateral electrolytic lesions of nucleus basalis magnocellularis (NBM). NBM-lesions produced a significant increase and decrease of ambulation and number of inner squares entered, and defecation, respectively, with no influence on grooming in rats exposed to novel environment. Physostigmine and verapamil in all tested doses, given 30 min before the test did not affect the open field behavior in control animals. In contrast to that, physostigmine (0.045, 0.060 and 0.075 mg/kg) and verapamil (2.5 and 5.0 mg/kg) significantly reduced ambulation and number of inner squares entered in NBM-lesioned rats. Also, physostigmine in a dose of 0.060 mg/kg significantly decreased defecation and in doses of 0.060 and 0.075 mg/kg the grooming, as well. On the other hand, verapamil only in a dose of 2.5 mg/kg significantly increased defecation. It could be concluded that lesions of NBM in rats induced disturbances in the open field behavior, which might be successfully ameliorate by physostigmine and verapamil treatment.

Effects of nimodipine and nifedipine upon behavior and regional brain monoamines in the rat

The effects of single and repeated (9 times) administration of two dihydropyridines (DHPs), nimodipine (NIM) and nifedipine (NIF) (5 mg/kg per 12 h and 2.5 mg/kg per 12 h, IP), on the behavior of male adult rats in the holeboard and in the plus-maze, were investigated. Besides, the effects of repeated administration of the drugs on the levels of dopamine (DA), serotonin (5-HT), and their respective major metabolites in several regions of the central nervous system (CNS) were also assessed. The effects of single and repeated administration of the drugs were similar. Both DHPs caused a significant decrease in general motor activity which was evident in both tests and more marked, with the higher doses. The two exploratory parameters measured in the holeboard, i.e. head-dipping frequency and duration, were dissociated under pharmacological treatment. The drug-treated animals did not show an increased emotionality in the holeboard. However, in the plus-maze, NIF (5 mg/kg) and to a lesser extent NIM, appeared to induce some anxiety-related responses which may be secondary, at least in part, to the depressing effect on activity and exploration. Repeated administration of NIM and NIF caused an increase in striatal DA and DOPAC levels, whilst no effects were found on serotonergic system in any of the regions of the CNS analyzed.

The effect of repeated combined treatment with nifedipine and antidepressant drugs or electroconvulsive shock on the hippocampal corticosteroid receptors in rats

The effect of nifedipine, a calcium channel antagonist, on changes in the density of glucocorticoid (GR) and/or mineralocorticoid receptors (MR), induced by long-term treatment with antidepressant drugs (imipramine and amitriptyline) or electroconvulsive shock (ECS) was investigated in the rat hippocampus. Long-term treatment with imipramine or amitriptyline significantly increased the density of GR, while chronic ECS significantly elevated the density of both GR and MR. Nifedipine administered repeatedly had no effect on the basal GR and MR levels, however when the rats were pretreated with nifedipine, the antidepressant drugs and ECS were unable to increase the density of GR, or GR and MR, respectively. These results indicate that, unlike in other models, nifedipine blocks the effects of antidepressant drugs and ECS on GR and/or MR. They also show, that antidepressant drugs and ECS differ in their effect on the density of GR and MR.

Ca2+ antagonists effect an antidepressant-like adaptation of the NMDA receptor complex

Chronic, but not acute treatment of mice with nimodipine and diltiazem produce significant increases in the IC50 of glycine to inhibit [3H]5,7-dichlorokynurenic acid binding in cerebral cortex. Such adaptive changes in the ligand binding properties of the NMDA receptor complex are also manifested following chronic treatment with antidepressants from every principal therapeutic class. These findings indicate voltage-dependent calcium channel antagonists would be strong candidates for rigorous clinical trials in depressive disorders.

Facilitation of shuttle-box avoidance behaviour in mice treated with nifedipine in combination with amphetamine

The dihydropyridine calcium channel antagonist nifedipine, tested in mice of CD-1, C57BL/6 and DBA/2 strains, at doses of 2.5, 5 and 10 mg/kg IP, had no significant effect on shuttle-box avoidance acquisition. Nifedipine also failed to affect performance retention in CD-1 mice subjected to a one-trial passive avoidance task (step-through). While ineffective alone, nifedipine strongly enhanced the shuttle-box avoidance facilitating action of amphetamine (1 and 2 mg/kg IP) in low performing CD-1 mice. The results indicate that although calcium channel blockers do not affect learning in avoidance paradigms in normal animals, they can interfere with the effects of other centrally acting drugs. Calcium antagonists might interfere with neuronal changes induced by amphetamine, but at present it is difficult to explain the strong avoidance facilitation produced by combinations of nifedipine and amphetamine. A possibility that the action of nifedipine on cerebral circulation is involved in the amphetamine-nifedipine interaction cannot be excluded.

Psychopharmacological properties of calcium channel inhibitors

The previous decade has witnessed a major expansion of knowledge of the role played by voltage-sensitive calcium channels in the function of the central nervous system. Significant progress in the field has been made possible with the broadening use of organic calcium channel inhibitors (CCIs, Ca2+ antagonists), until recently considered almost exclusively as peripherally active antianginal and antiarrhythmic drugs. CCIs, however, do penetrate the blood-brain barrier from the periphery. Autoradiographic studies have established a highly heterogeneous distribution of CCI recognition sites within the brain. The existing evidence suggests that CCIs have marked psychotropic properties. The profile of their central activity is unique and spans a wide range of effects. Nevertheless, question regarding potentially confounding potent peripheral effects of these drugs remain. This paper reviews the psychopharmacology of CCIs, concentrating on preclinical data, but including supportive clinical and biochemical evidence as well. It focuses on these drugs' antidepressant, antidopaminergic (neuroleptic-like), anxiolytic and anticonvulsant effects. CCIs may also modify the reinforcing properties of some addictive drugs.

Some central pharmacological effects of the calcium channel antagonist flunarizine

Our earlier studies showed that dihydropyridine calcium channel antagonists have some central pharmacological effects. Flunarizine is considered to be a calcium channel antagonist; therefore this study was aimed at investigating the effect of flunarizine (given in single doses of 5, 10 and 20 mg/kg p.o.) in behavioural models in which calcium channel antagonists of the dihydropyridine type were previously studied. Flunarizine inhibited the apomorphine-induced stereotypy and yawning behaviour in rats. It decreased the hypothermia induced by a low dose of apomorphine in mice, but not that one induced by high dose of it. The quinpirole-induced hypothermia was also reduced. In the tests used for evaluation of the effect on the serotonergic system, flunarizine decreased the 5-HTP-induced head twitches and partly antagonized the fenfluramine- and quipazine-induced hyperthermias (at a high ambient temperature). In the forced swimming test flunarizine was inactive in mice and rats. The obtained results indicate that flunarizine exerts central antagonistic effects on the dopaminergic and serotonergic systems and has no antidepressant activity. Flunarizine differs from calcium channel antagonists of the dihydropyridine type, which have no dopamine-antagonistic activity and show anti-depressant-like properties.

Chronic oral treatment with diltiazem or verapamil decreases isolation-induced activity impairment in elevated plus maze

Adult male Wistar rats were either socially isolated or group-housed for 6 weeks and then tested in an elevated plus maze. During isolation the rats received either water or two concentrations of the calcium channel inhibitors, diltiazem or verapamil, in drinking solutions (approximately 5 and 10 mg/kg daily). Isolated rats showed a significantly lower total number of arm entries, a lower percentage of open arm entries and negligible time spent therein than did group-housed animals. Verapamil, in the higher dose, prevented that effect of isolation. Treatment with diltiazem brought about a similar tendency, though the effect did not reach statistical significance. Chronic treatment of group-housed rats with either drug failed to influence their behavior in the plus maze. We conclude that certain calcium channel inhibitors may decrease the behavioral deficit in the elevated plus maze that follows chronic social isolation.