Psychopharmacological properties of calcium channel inhibitors

Clinical management of withdrawal from benzodiazepine anxiolytic and hypnotic medications

Benzodiazepines continue to be prescribed widely in the management of patients with insomnia or anxiety disorders, despite the availability and acceptability of alternative pharmacological and psychological treatments. Many patients will experience adverse effects during treatment and considerable distress when the dosage is reduced and stopped. Management of benzodiazepine withdrawal includes measures to prevent the development of dependence, careful attention to underlying medical conditions, medication consolidation and gradual dosage reduction, accompanying psychological interventions, occasional prescription of concomitant medication, and relapse prevention with on-going support to address psychosocial stressors. There are needs for easier patient access to services with refined expertise and for further research to optimise strategies for preventing dependence and facilitating withdrawal.

Verapamil attenuates scopolamine induced cognitive deficits by averting oxidative stress and mitochondrial injury - A potential therapeutic agent for Alzheimer's Disease

Alzheimer's disease (AD) is a multifactorial disorder where amyloid beta (Aβ) plaques, Ca2+ dysregulation, excessive oxidative stress, mitochondrial dysfunction and synaptic loss operate synergistically to bring about cholinergic deficits and dementia. New therapeutic interventions are gaining prominence as the morbidity and mortality of AD increases exponentially every year. Treating AD with antihypertensive drugs is thought to be a promising intervention; however, its mechanism of action of ameliorating AD needs further investigation. In this context, the present study explores the protective effect of verapamil, an antihypertensive agent of Ca2+ channel blocker (CCB) class against scopolamine-induced in vitro neurotoxicity and in vivo cognitive impairment. Supplementation of verapamil was found to attenuate oxidative stress by preventing mitochondrial injury, and augment the expression of genes involved in the cholinergic function (mACR1), synaptic plasticity (GAP43, SYP) and Ca2+-dependent memory-related genes (CREB1, CREBBP, BDNF). Further, verapamil treatment in mice attenuated the cognitive and behavioural deficits induced by scopolamine as measured by the elevated plus maze and passive avoidance test (P < 0.05). Thus, the present study demonstrates the neuroprotective effect of verapamil against the pathogenesis of AD such as oxidative stress, mitochondrial dysfunction and cognitive decline. These observations emphasize the importance of ‛Ca2+ dysregulation' and ‛mitochondrial dysfunction' theories in AD and recommends the supplementation of compounds that regulate Ca2+ homeostasis and mitochondrial function in susceptible AD individuals.

Benzodiazepine dependence and its treatment with low dose flumazenil

Globally benzodiazepines remain one of the most prescribed medication groups, especially in the primary care setting. With such high levels of prescribing it is not surprising that benzodiazepine dependence is common, cutting across all socioeconomic levels. Despite recognition of the potential for the development of iatrogenic dependence and the lack of any effective treatment, benzodiazepines continue to be widely prescribed in general practice. Conventional dependence management, benzodiazepine tapering, is commonly a protracted process over several weeks or months. It is often associated with significant withdrawal symptoms and craving leading to patient drop out and return to use. Accordingly, there is a worldwide need to find effective pharmacotherapeutic interventions for benzodiazepine dependence. One drug of increasing interest is the GABAA benzodiazepine receptor antagonist/partial agonist, flumazenil. Multiple bolus intravenous infusions of low dose flumazenil used either with or without benzodiazepine tapering can reduce withdrawal sequelae, and/or longer term symptoms in the months following withdrawal. Preliminary data suggest that continuous intravenous or subcutaneous flumazenil infusion for 4 days significantly reduces acute benzodiazepine withdrawal sequelae. The subcutaneous infusion was shown to be tissue compatible so the development of a longer acting (i.e. several weeks) depot flumazenil formulation has been explored. This could be capable of managing both acute and longer term benzodiazepine withdrawal sequelae. Preliminary in vitro water bath and in vivo biocompatibility data in sheep show that such an implant is feasible and so is likely to be used in clinical trials in the near future.

A Bacoside containing Bacopa monnieri extract reduces both morphine hyperactivity plus the elevated striatal dopamine and serotonin turnover

Bacopa monnieri (BM) has been used in Ayurvedic medicine as a nootropic, anxiolytic, antiepileptic and antidepressant. An n-butanol extract of the plant (nBt-ext BM) was analysed and found to contain Bacoside A (Bacoside A3, Bacopaside II and Bacopasaponin C). The effects of the BM extract were then studied on morphine-induced hyperactivity as well as dopamine and serotonin turnover in the striatum since these parameters have a role in opioid sensitivity and dependence. Mice were pretreated with saline or nBt-ext BM (5, 10 and 15 mg/kg, orally), 60 min before morphine administration and locomotor activity was subsequently recorded. Immediately after testing, striatal tissues were analysed for dopamine (DA), serotonin (5HT) and their metabolites using HPLC coupled with electrochemical detection. The results indicated that nBt-ext BM significantly (p < 0.001) decreased locomotor activity in both the saline and morphine treated groups. Additionally, nBt-ext BM significantly lowered morphine-induced dopamine (DA), dihydroxyphenylacetic acid (DOPAC), homovanillic acid (HVA) and 5-hydroxyindole acetic acid (5-H1AA) upsurges in the striatum but failed to affect DA, 5-HT and their metabolites in the saline treated group. These findings suggest that nBt-ext BM has an antidopaminergic/serotonergic effect and may have potential beneficial effects in the treatment of morphine dependence.

Role of calcium in morphine dependence and naloxone-precipitated withdrawal in mice

PURPOSE

To explore the role of calcium in morphine withdrawal syndrome using various agents affecting calcium levels in cytoplasm.

METHODS

Mice were rendered dependent on morphine by subcutaneous injection of morphine, and withdrawal was induced 4 hours later by injecting the opioid antagonist, naloxone. Mice were observed for 30 minutes for signs of withdrawal, ie, characteristic jumping, hyperactivity, urination, and diarrhea. Various calcium channel blockers were injected intraperitoneally 30 minutes before naloxone to evaluate their influence on the severity of the withdrawal syndrome. We also tested the effect of combination levodopa-carbidopa pretreatment and its interaction with a selective alpha-1 blocker, terazosin, on naloxone-precipitated withdrawal in mice acutely dependent on morphine.

RESULTS

A significant dose-dependent attenuation of naloxone-induced morphine withdrawal syndrome was observed with calcium channel blockers, ie, verapamil 20 mg/kg (P < 0.05) and diltiazem 30 mg/kg (P < 0.01). Combination levodopa-carbidopa pretreatment facilitated the morphine withdrawal syndrome, and this was found to be blocked by terazosin, although not to a statistically significant (P > 0.05) extent.

CONCLUSION

The results indicate that calcium plays an important role in the genesis of morphine dependence and withdrawal, and suggest the usefulness of calcium channel blockers in the management of morphine withdrawal syndrome.

kappa-Opioid receptor signaling and brain reward function

The dynorphin-like peptides have profound effects on the state of the brain reward system and human and animal behavior. The dynorphin-like peptides affect locomotor activity, food intake, sexual behavior, anxiety-like behavior, and drug intake. Stimulation of kappa-opioid receptors, the endogenous receptor for the dynorphin-like peptides, inhibits dopamine release in the striatum (nucleus accumbens and caudate putamen) and induces a negative mood state in humans and animals. The administration of drugs of abuse increases the release of dopamine in the striatum and mediates the concomitant release of dynorphin-like peptides in this brain region. The reviewed studies suggest that chronic drug intake leads to an upregulation of the brain dynorphin system in the striatum and in particular in the dorsal part of the striatum/caudate putamen. This might inhibit drug-induced dopamine release and provide protection against the neurotoxic effects of high dopamine levels. After the discontinuation of chronic drug intake these neuroadaptations remain unopposed which has been suggested to contribute to the negative emotional state associated with drug withdrawal and increased drug intake. kappa-Opioid receptor agonists have also been shown to inhibit calcium channels. Calcium channel inhibitors have antidepressant-like effects and inhibit the release of norepinephrine. This might explain that in some studies kappa-opioid receptor agonists attenuate nicotine and opioid withdrawal symptomatology. A better understanding of the role of dynorphins in the regulation of brain reward function might contribute to the development of novel treatments for mood disorders and other disorders that stem from a dysregulation of the brain reward system.

Desipramine reduces stress-activated dynorphin expression and CREB phosphorylation in NAc tissue

The nucleus accumbens (NAc) is a critical brain area for reward and motivated behavior. Accumulating evidence suggests that altered function of the transcription factor cAMP response element binding protein (CREB) within the NAc is involved in depressive behavior. In rats, stress activates CREB within the NAc, and elevation of CREB expression in this region produces depressive-like behaviors that are accompanied by activation of CREB-regulated target genes. The depressive-like behaviors seem to be due, at least in part, to CREB-mediated increases in dynorphin function, because they are mimicked by kappa-opioid receptor (KOR) agonists and attenuated by KOR antagonists. We hypothesized that if CREB-mediated dynorphin expression in the NAc contributes to depressive behavior, then antidepressants might reduce dynorphin function in this region. Here, we demonstrate that desipramine (DMI), a norepinephrine reuptake inhibitor that has been used for decades to treat clinical depression, blocks swim stress-induced activation of prodynorphin (encodes dynorphin) in the NAc. In primary cultures of NAc and striatum, DMI decreases basal and stimulated CREB phosphorylation by causing reductions in intracellular calcium (Ca(2+)) availability that are independent of norepinephrine or other monoaminergic inputs, identifying a potential mechanism for alterations in CREB-mediated gene expression. Fluoxetine (FLX), a selective serotonin reuptake inhibitor, has similar effects in culture, suggesting a common intracellular effect of these antidepressants. These findings raise the possibility that a therapeutically relevant mechanism of action of DMI occurs through attenuation of CREB-mediated gene transcription, which is mediated via previously uncharacterized mechanisms that occur directly within the NAc.

Risk of suicide in users of cardiovascular drugs: a review of the epidemiological evidence

An association between consumption of cardiovascular drugs and increased risk of depression was first reported more than 30 years ago. More recently three observational studies have also reported an association between the use of cardiovascular drugs and risk of suicide. We review the epidemiological evidence with particular focus on bias, confounding, and chance as alternative explanations to a causal association. The results of the three studies are inconsistent with respect to the association between cardiovascular drug use and suicide. None of the studies has been able to control fully for possible confounding, in particular by the underlying disease and comorbidity. We thus conclude that the finding of an association between suicide risk and cardiovascular drug use remains dubious. A true explanation for the apparent increase in risk of suicide in users of cardiovascular drugs remains unknown. Future studies must try to reduce confounding. Meta-analyses of data from existing trials may be an approach to solve the problem of confounding.

Influence of diltiazem on the behavior of zolpidem-treated mice in the elevated-plus maze test

The present study was undertaken to investigate the effect of diltiazem, a L-type calcium channel blocker (CCB), on the behavior of zolpidem-treated mice in the elevated plus-maze (EPM). Atypical benzodiazepine zolpidem significantly increased the percentage of open arm entries without influencing the total entries and total distance and average speed at the dose of 5 mg/kg (p.o.). Co-administration of zolpidem (2 mg/kg, p.o.) and diltiazem (5, 10 and 20 mg/kg, p.o.) significantly increased both the time spent and arm entries in the open arms without influencing the total entries and spontaneous activity notwithstanding that zolpidem at dose up to 2 mg/kg (p.o.) and diltiazem at dose up to 20 mg/kg (p.o.) did not show any effects on mice behavior in EPM. Zolpidem also attenuated the anxiogenic effect of 1-(3-Chlorophenyl)piperazine (mCPP, 0.7 mg/kg, i.p.) and 5-hydroxytryptophan (5-HTP, 30 mg/kg, i.p.). Even though the zolpidem at 1 mg/kg and diltiazem at 5 mg/kg were ineffective on mCPP-induced anxiety, respectively, the co-administration of zolpidem (1 mg/kg, i.p.) and diltiazem (5 mg/kg, p.o.) showed inhibitory effect on mCPP-induced anxiety in mice. These results suggested that diltiazem, a L-type CCB may augment the anxiolytic-like effect of zolpidem and also indicated that calcium channel modulation maybe involved in the anxiolytic-like properties of zolpidem.

Effects of acute and chronic nicotine on elevated plus maze in mice: Involvement of calcium channels

The current experiments examined the anxiety-related effects of acute and repeated nicotine administration using the elevated plus maze test in mice. Nicotine (0.1 mg/kg s.c., 5 and 30 min after injection; 0.5 mg/kg, s.c., 5 min after injection) had an anxiogenic effect, shown by specific decreases in the percentage of time spent on the open arms and in the percentage of open arm entries. Tolerance developed to this anxiogenic action after 6 days of daily nicotine administration (0.1 mg/kg, s.c.). Five minutes after the seventh injection, an anxiolytic effect was observed, i.e., specific increases in the percentage of time spent on the open arms and in the percentage of open arm entries. L-type voltage-dependent calcium channel antagonists nimodipine (5 and 10 mg/kg, i.p.), flunarizine (5 and 10 mg/kg, i.p.), verapamil (5, 10, 20 mg/kg) and diltiazem (5, 10, 20 mg/kg, i.p.) were also injected prior to an acute low dose of nicotine or to each injection of chronic nicotine. Our results revealed that calcium channel blockers dose-dependently attenuated both an anxiogenic effect of nicotine as well as the development of tolerance to this effect. Our results suggest that neural calcium-dependent mechanisms are involved in the anxiety-related responses to acute and chronic nicotine injection that may ultimately lead to addiction and smoking relapse in human smokers.

Antispasmodic and bronchodilator activities of St John's wort are putatively mediated through dual inhibition of calcium influx and phosphodiesterase

The crude extract of aerial parts of St John's wort (Hypericum perforatum) (Hp.Cr) and its fractions were studied in vitro for its possible spasmolytic and bronchodilator activities to rationalize some of its medicinal uses. In rabbit jejunum preparations, Hp.Cr caused a concentration-dependent relaxation of both spontaneous and K+ (80 mm)-induced contractions at a similar concentration range (0.1-1.0 mg/mL), similar to that produced by papaverine, whereas verapamil was relatively potent against K+-induced contractions. Hp.Cr shifted the Ca2+ concentration-response curves (CRCs) to the right, similar to that caused by papaverine or verapamil and also caused leftward shift of isoprenaline-induced inhibitory CRCs, similar to papaverine. In guinea-pig tracheal preparations, Hp.Cr caused relaxation of carbachol and K+-induced contractions at similar concentrations (0.01-0.3 mg/mL) and also shifted the isoprenaline-induced inhibitory CRCs to the left, similar to that caused by papaverine. In rabbit aorta preparations at rest, Hp.Cr produced a moderate vasoconstriction, while exhibited vasodilator effect against phenylephrine and K+-induced contractions. Papaverine and verapamil also produced similar non-specific vasodilation, but were devoid of any vasoconstrictor effect. Hp.Cr caused suppression of atrial force of contractions at concentrations about 20 times higher than those that produced inhibitory effect in smooth muscle preparations, similar to papaverine. These results suggest that the spasmolytic effects of Hp.Cr are mediated through dual inhibition of calcium influx and phosphodiesterase (PDE)-like mechanisms, which might explain the medicinal use of St John's wort in the disorders of gastrointestinal and respiratory tracts. Furthermore, the presence of Ca2+ antagonist and PDE inhibitory-like constituents might also be contributing to some extent in the well established use of plant in depression.

Effects of l-tetrahydropalmatine on locomotor sensitization to oxycodone in mice

AIM

Recent studies have shown that l-tetrahydropalmatine (l-THP), an active component of Corydolis yanhusuo, can inhibit the development of the conditional place preference induced by opioid receptor agonists, but the effects of l-THP on locomotor sensitivity induced by opioid receptor agonists have not been documented. In the present study, the effects of l-THP on locomotor sensitization to oxycodone, which is an opioid receptor agonist, were studied.

METHODS

Mice treated daily for 7 d with 5 mg/kg oxycodone and challenged with the same dose after 5 days of washout showed locomotor sensitization. In order to study the effects of l-THP on locomotor sensitization induced by oxycodone, l-THP was administered at doses of 6.25, 12.5, and 18.75 mg/kg, 40 min prior to treatment of oxycodone.

RESULTS

l-THP per se did not affect the locomotor activity at the doses of 6.25, 12.5, and 18.75 mg/kg, but could antagonize the hyperactivity induced by oxycodone (5 mg/kg). Co-administration of l-THP (18.75 mg/kg), 40 min prior to oxycodone, could inhibit the development of sensitization to oxycodone. In addition, l-THP (6.25, 12.5, and 18.75 mg/kg, i.g.) dose-dependently prevented the expression of oxycodone sensitization.

CONCLUSION

These results suggested that l-THP could attenuate the locomotor-stimulating effects of oxycodone and inhibit the development and expression of oxycodone behavioral sensitization.

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.

L-type Ca(2+) channel blockers inhibit the development but not the expression of sensitization to morphine in mice

The relationship between opioid actions and L-type Ca(2+) channel blockers has been well documented. However, there is no report relevant to L-type Ca(2+) channel blockers and morphine sensitization, which is suggested to be an analog of behaviors that are characteristic of drug addiction. We now studied systematically the effects of three L-type Ca(2+) channel blockers, nimodipine, nifedipine and verapamil, on morphine-induced locomotor activity, the development and the expression of sensitization to morphine. The results showed that both nimodipine and verapamil attenuated, while nifedipine had only a tendency to decrease morphine-induced locomotor activity. All three drugs inhibited the development of sensitization to morphine. However, none of them showed any effects on the expression of morphine sensitization. These results indicate that blocking L-type Ca(2+) channel attenuates the locomotor-stimulating effects of morphine and inhibits the development but not the expression of morphine sensitization.

Effects of six anti-hypertensive medications on cognitive performance

OBJECTIVE

To describe and compare the effects of six different antihypertensive medications on cognitive performance.

DESIGN

Prospective, randomized, and double-blind with treatment cross-over.

SETTING

University hypertension clinic and neuropsychology laboratory.

PARTICIPANTS

Ninety-eight Caucasian men between 25 and 55 years of age with mild-to-moderate essential hypertension (88 of whom completed the study), and 32 normotensive men with similar socio-demographic characteristics.

INTERVENTIONS

Six-week treatment periods with atenolol, metoprolol, hydrochlorothiazide, methyldopa, enalapril and verapamil, and 2-week placebo baseline and wash-out periods.

MAIN OUTCOME MEASURES

In-depth neuropsychological assessments and several mood questionnaires were completed during placebo (baseline) periods and active treatment periods. Practice effects due to repeated neuropsychological testing were estimated from data collected concurrently in the normotensive participants.

RESULTS

The antihypertensive treatments lowered blood pressure comparably and did not affect mood or anxiety. Small treatment effects were noted in four of seven domains of cognitive performance. Irrespective of medication type, treatment reduced the simple motor speed (P < 0.001), and slowed completion of two tests measuring perceptuo-motor speed and mental flexibility (P </= 0.05). Manual dexterity declined somewhat with metoprolol and methyldopa (P = 0.01). In contrast, all antihypertensive agents favorably affected performance on several tests that require working memory (P < 0.01). Performance on other tests assessing grip strength, learning and memory, attention and executive function was not affected.

CONCLUSION

Short-term treatment with standard antihypertensive medications was associated with some small decrements in psychomotor performance and small improvements in working memory, without notable drug-class differences. Long-term effects await further study.

Evaluation of the anxiolytic-like effects of Cecropia glazioui Sneth in mice

Cecropia glazioui Sneth has been used in most Latin American countries as an antihypertensive, cardiotonic, and antiasthmatic folk medicine. In the cardiovascular studies to define its antihypertensive action it was noteworthy that animals treated with the aqueous extract (AE) of C. glazioui were much calmer than control animals. That observation prompted the present study, aimed at an investigation of the effects of AE and of two semipurified fractions on mouse behavior as evaluated in the elevated plus-maze test (EPM). Male adult Swiss mice were treated with AE (0.25-1 g/kg po) acutely (1 h) or repeatedly (24, 7, and 1.5 h before the test). After repeated administration of AE, the frequency of entries in the open arms of EPM was increased threefold. A similar profile of action was observed after treatment with the butanolic fraction (Fbut) but not with the aqueous fraction (Faq). These findings suggest that the AE of C. glazioui promotes an anxiolytic-like effect in mice. The active principles responsible for this action are present in the less polar fraction of the extract, the main constituents of which are flavonoids and terpenes, among other compounds.

Amlodipine enhances the activity of antiepileptic drugs against pentylenetetrazole-induced seizures

Amlodipine (AML), which belongs to the 1,4-dihydropyridine calcium channel antagonists, possesses pharmacological and pharmacokinetic profile that distinguishes it from other agents of this class. Pentylenetetrazole (PTZ)-induced clonic and tonic convulsions in mice were significantly reduced by administration of AML at 10 mg/kg. At this dose AML remained without influence upon the plasma level of PTZ. The ED50 value of AML against clonic seizures induced by PTZ was 5.4 mg/kg. This calcium channel antagonist (at 2.5 mg/kg) combined with ethosuximide (ETX), valproate magnesium (VPA) or phenobarbital (PB) significantly reduced their ED50 values against clonic phase of PTZ-induced seizures. AML administered alone or in combination with antiepileptic drugs (AEDs) worsened the motor performance of mice in the chimney test. However, these treatments remained without significant influence on the retention time in the passive avoidance test. Plasma levels of antiepileptics remained unchanged in the presence of AML. The results indicate that AML does not seem a good candidate for a combination therapy in epileptic patients because of its adverse potential.

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 baroreceptor reflex in anaesthetized cats

The baroreflex-induced changes in heart rate in chloralose anaesthetized and artificially ventilated cats (2.5-4.0 kg) before and after pretreatment with calcium channel blockers (CCBs) were compared. Baroreflex mediated changes in heart rate (HR) were elicited by raising and lowering the systemic blood pressure with intravenous injections of phenylephrine and sodium nitroprusside, respectively. The effects of three CCBs, verapamil, diltiazem and nifedipine administered either intravenously (i.v.) or intracisternally (i.c.) were studied. Verapamil administration markedly inhibited the reflex bradycardia as well as the tachycardia following either i.v. or i.c. administration. Intracisternally, a relatively smaller dose of verapamil produced an effect comparable in magnitude and duration, to a higher i.v. dose. The reflex bradycardia was inhibited following i.v., but not i.c. administration of nifedipine while the reflex tachycardia was not affected significantly by either i.v. or i.c. nifedipine. Intravenous diltiazem did not appear to affect the reflex bradycardia or tachycardia significantly. It is suggested that verapamil administration interacts with central cardiovascular integrating mechanisms to reduce the gain of the baroreflex function. Nifedipine and diltiazem are relatively free from this effect.

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.

Nantenine and papaverine differentially modify synaptosomal membrane enzymes

Papaverine (1-[(3,4-Dimethoxyphenyl) methyl]-6,7-dimethoxyisoquinoline) and nantenine (O-methyldomesticine) are chemically related isoquinoline alkaloids displaying similar dose-dependent sedative or convulsant effects, but seem to act differentially on synaptosomal membrane enzymes. Na+, K+-, Mg2+- and Ca2+-ATPase activities were inhibited by nantenine but not by papaverine, whereas acetylcholinesterase activity remained unchanged by nantenine but slightly enhanced by papaverine. Nantenine inhibited roughly both 20-50% Ca2+- and Mg2+-ATPase activities but 40-90% Na+, K+-ATPase activity. Kinetic analysis indicated that nantenine interacts with the substrate ATP for Ca2+-ATPase activity but that it competes with K+ for Na+, K+-ATPase activity. Given the roles of Na+, K+-ATPase and Ca2+-ATPase in cation transport and [Ca2+]i regulation, respectively, the inhibitory effect of nantenine upon these enzymes may explain its convulsant effect though not its sedative activity. The sedative action of both nantenine and papaverine is hardly attributable to an effect on the synaptosomal membrane enzymes assayed.

Calcium channel antagonists for the treatment of bipolar disorder

Calcium channel antagonists (CCAs) have many clinical applications, including their possible use in the treatment of bipolar disorder. Two justifications for this last application are some overlap in physiological activities of CCAs with those of lithium, and a possible association between bipolar disorder and calcium dysregulation. While the data from earlier studies support the use of verapamil in treating bipolar mania. more recent better-controlled trials have not. This paper reviews the available body of data regarding CCAs in the treatment of bipolar disorder, concluding there is presently limited support for their efficacy.

Discriminative and affective stimulus effects of dihydropyridine calcium channel modulators: relationship to antialcohol effects

Voltage-operated calcium channels (VOCCs) have been implicated in alcoholism. Thus, dihydropyridine (DHP) VOCC antagonists, such as nimodipine, reduce ethanol (EtOH) intake and preference in a variety of animal models of alcoholism. Paradoxically, the DHP VOCC agonist BAY k 8644 also demonstrates antialcohol effects in such models. The antialcohol effects of BAY k 8644 are stereoselective [the "agonistic" (-)-enantiomer being more potent than the "antagonistic" (+)-enantiomer], and are not blocked by pretreatment with nimodipine. The present review summarizes studies on the effects of DHPs in drug discrimination (DD), conditioned taste aversion (CTA), and conditioned place preference (CPP) paradigms, and discusses the possibility that the apparent antialcohol effect of these compounds is related to their discriminative and/or affective stimulus effects. In rats trained to discriminate nimodipine from vehicle, (-)-BAY k 8644 completely generalizes to the nimodipine cue; whereas, in rats trained to discriminate (-)-BAY k 8644, nimodipine completely generalizes to, and is unable to block, the (-)-BAY k 8644 cue. The same stereoselectivity is obtained for BAY k 8644 in DD paradigms and models of alcoholism. The apparent similarity of these profiles of activity suggests that a common neurobiological mechanism underlies the discriminative stimulus and antialcohol effects of DHPs. It appears unlikely, however, that the antialcohol effects of DHPs are based on substitution for, or blockade of, the EtOH cue, as these compounds were not found to generalize to, or block, the EtOH cue. Comparison of the effects of DHPs in CTA and CPP paradigms suggests that the affective stimulus effects of these compounds are dissimilar, and that the mechanism underlying the latter effects is probably not related to the mechanism underlying the antialcohol effects of DHP VOCC modulators.

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

The present study assessed the ability of voltage-sensitive calcium channel (VSCC) blockers to affect the behavioral effects of the noncompetitive N-methyl-D-aspartate (NMDA) receptor antagonist, dizocilpine, in male Wistar rats. Dizocilpine produced dose-dependent increases in locomotor activity. Nimodipine, verapamil, and flunarizine suppressed dizocilpine-facilitated vertical activity, while horizontal activity was attenuated by verapamil and nimodipine but not flunarizine. Repeated dizocilpine injections resulted in the development of sensitization to its locomotor stimulating properties. Development of sensitization was not context specific, and was observed following repeated exposures to 0.1 but not 0.056 or 0.3 mg/kg of dizocilpine. Nimodipine retarded the development of sensitization to dizocilpine's stimulating effects on horizontal activity, while verapamil suppressed sensitization to the vertical stimulating effects of dizocilpine. Flunarizine had no significant effects on sensitization to dizocilpine's locomotor stimulating properties. In rats trained to discriminate between injections of 0.056 mg/kg of dizocilpine and vehicle, none of the tested VSCC blockers was able to completely antagonize the discriminative stimulus properties of dizocilpine. Nimodipine, when administered in combination with the training dose of dizocilpine, modestly decreased the dizocilpine-lever selection. Dizocilpine dose dependently decreased the self-determined stimulation threshold implanted in rats with electrodes into the ventral tegmental area. Nimodipine exhibited some tendency to block the facilitating effects of dizocilpine, while verapamil and flunarizine had no effects. In summary, in the present experiments VSCC blockers exerted only modest interactions with the behavioral effects of dizocilpine, and it is unlikely that VSCC blockers have remarkable potential as adjunct treatment aimed at correcting the negative side effects of NMDA receptor antagonists (e.g., dizocilpine).

Attenuation by nimodipine of amitriptyline-induced avoidance impairment in mice

The effects of the dihydropyridine calcium channel blocker nimodipine on avoidance impairment induced by the tricyclic antidepressant amitriptyline were assessed during shuttle-box training and in previously trained mice of the DBA/2 strain. Nimodipine (0, 0.5, 1, 2.5, or 5 mg/kg) had no effect alone, but attenuated the avoidance impairment induced by 5 mg/kg amitriptyline on avoidance acquisition, as well as on a previously learned avoidance response. The avoidance improving action of the calcium channel blocker was less evident in mice receiving a larger dose (7.5 mg/kg) of the antidepressant drug. The effect of nimodipine did not appear to be specifically related to the avoidance impairment induced by amitriptyline, because the calcium antagonist also attenuated the avoidance impairing action of the neuroleptic chlorpromazine. The avoidance impairment induced by amitriptyline and chlorpromazine, and the related ameliorating action of nimodipine, seem imputable to drug effects on the performance of the avoidance response, rather than to interferences with learning processes. The results suggest that, in the case of concomitant administration, nimodipine could alleviate adverse side effects of tricyclic antidepressant, i.e., psychomotor disturbances.

Effects of Ca2+ channel blockers on apomorphine, bromocriptine and morphine-induced locomotor activity in mice

The effects of L-type voltage-dependent Ca2+ channel blockers on apomorphine, bromocriptine and morphine-induced changes in locomotor activity were examined in mice. Apomorphine (4 mg/kg) and morphine (20 mg/kg) produced locomotor stimulation. Bromocriptine (8 mg/kg) produced a biphasic effect on motor behaviour, an early depressant phase, followed by locomotor stimulation. Amlodipine (2.5 mg/kg), nicardipine (10 mg/kg), diltiazem (10 mg/kg) and verapamil (10 mg/kg), which by itself did not affect locomotor activity, inhibited the stimulant phase of bromocriptine without altering the depressant phase, while they did not affect apomorphine- and morphine-induced locomotor stimulation. Apomorphine, bromocriptine and morphine-induced locomotor stimulation was decreased by SCH 23390 (R-(+)-8-chloro-2,3,4,5-tetrahydro-3-methyl-5-phenyl-1H-3-benzazepine-7- ol) (0.05 mg/kg) or haloperidol (0.1 mg/kg). These results indicate that L-type voltage-dependent Ca2+ channels are involved in the motor stimulant effect of bromocriptine, but not in apomorphine- and morphine-induced locomotor stimulation. The effects of Ca2+ channel blockers on the dopaminergic system appears not to be directly related to dopamine receptor blockade.

Discriminative stimulus effects of ethanol: neuropharmacological characterization

Generally, compounds discriminated by animals possess psychotropic effects in animals and humans. As with many other drugs of abuse, strength of the ethanol discriminative stimulus is dose related. The majority of studies show that doses close to 1.0 g/kg are close to the minimum at which the discrimination can be learned easily. Substitution studies suggest that anxiolytic, sedative, atactic, and myorelaxant effects of ethanol all play an important role in the formation of its intercoeptive stimulus. Low doses of ethanol produce more excitatory cues, similar to amphetamine-like subjective stimuli, whereas higher doses produce rather sedative/hypnotic stimuli similar to those elicited by barbiturates. Substitution studies have shown that the complete substitution for ethanol may be exerted by certain GABA-mimetic drugs acting through different sites within the GABA(A)-benzodiazepine receptor complex (e.g., diazepam, pentobarbital, certain neurosteroids), gamma-hydroxybutyrate, and antagonists of the glutamate NMDA receptor. Among the NMDA receptor antagonists both noncompetitive (e.g., dizocilpine) and competitive antagonists (e.g., CGP 40116) are capable of substituting for ethanol. Further, some antagonists of strychnine-insensitive glycine modulatory sites among the NMDA receptor complex (e.g., L-701,324) dose-dependently substitute for the ethanol discriminative stimulus. On the other hand, neither GABA-benzodiazepine antagonists nor NMDA receptor agonists produce contradictory effects (i.e., reduce the ethanol discriminative stimulus). There is influence of a particular training dose of ethanol on the substitution pattern of different compounds. For example, 5-HT(1B/2C) agonists substitute for intermediate (1.0 g/kg) but not higher (2.0 g/kg) ethanol training doses. Discrimination studies with ethanol and drugs acting on NMDA and GABA receptors consistently indicate asymmetrical generalization. For example, ethanol is able to generalize to barbiturates and benzodiazepines, but neither the benzodiazepine nor barbiturate response generalizes to ethanol. Only a few drugs are able to antagonize, at least to some extent, the discriminative stimulus of ethanol (e.g., partial inverse GABA-benzodiazepine receptor antagonist Ro 15-4513 and the opioid antagonist naloxone). The ethanol stimulus effect may be increased (i.e., stronger recognition) by N-cholinergic drugs (nicotine), dopaminergic drugs (apomorphine), and 5-HT3 receptor agonists (m-chlorophenylbiguanide). Thus, the ethanol stimulus is composed of the several components, with the NMDA receptor and GABA(A) receptor complex being of particular importance. This suggests that a drug mixture may be more capable of substituting for ethanol (or block its stimulus) than a single compound. The ability of drugs to substitute for the ethanol discriminative stimulus is frequently, although not preclusively, associated with the reduction of voluntary ethanol consumption. The examples of positive correlation are gamma-hydroxybutyrate, possibly memantine and certain serotonergic drugs such as fluoxetine. However, it remains uncertain to what extent the discriminative stimulus of ethanol can be seen as relevant in the understanding of the complex mechanisms of dependence.

"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.

The influence of the calcium channel antagonist, verapamil and ethanol on the myocardial ultrastructure in the rat

In this study we investigated the ultrastructural changes in rat myocardium induced by the concomitant treatment of animals with ethanol and the calcium channel antagonist, verapamil. The animals were given perorally either placebo or 8 g/kg body weight ethanol in combination with 3 mg/kg verapamil for 30 days. Rats treated with ethanol and verapamil had ultrastructural myocardiocyte damage. The ultrastructural changes were present in myofibrils, mitochondria, intercalated discs and plasmalemma. Due to widespread use of verapamil for treatment of a variety of cardiological disorders and, therefore, a high risk of its interaction with ethanol the data can be of potential significance for humans.

Ketamine effects on bupivacaine local anaesthetic activity and pharmacokinetics of bupivacaine in mice

This study was designed to document possible changes in bupivacaine (B) local anaesthetic activity and pharmacokinetics in mice after a ketamine (K) injection. In the experiments, bupivacaine (8.25 mg.kg(-1)), was injected into the popliteal space of the right posterior limb: the local anaesthetic activity was assessed according to a sciatic nerve blockade method with three different doses (2, 10 and 40 mg/kg) of ketamine and the kinetics were studied after a 10 mg/kg dose. When ketamine was associated, the local anesthetic activity of bupivacaine was significantly enhanced as well as its elimination half-life. Significantly lower levels of the main metabolite, PPX, were observed, when ketamine was associated, suggesting a metabolic inhibition phenomenon. The ketamine-induced increase in the total anaesthetic effect of bupivacaine may thus be explained by kinetic modifications i.e. a possible inhibiting effect of ketamine on the metabolism of bupivacaine.

Analgesic effects of amlodipine and its interaction with morphine and ketorolac-induced analgesia

1. The antinociceptive effects of amlodipine, administered subcutaneously (s.c.), intracerebroventricularly (i.c.v.) and intrathecally (i.t.) were examined with the acetic acid writhing and tail-flick tests in mice. Amlodipine was also tested in combination with morphine and ketorolac. Isobolographic analyses were used to define the nature of functional interactions between amlodipine and morphine or ketorolac. 2. The s.c. (0.1, 1.25, 2.5, 5 and 10 mg/kg), i.c.v. (2.5, 5, 10 and 20 micrograms/mice) and i.t. (2.5, 5, 10 and 20 micrograms/mice) administration of amlodipine exhibited a dose-dependent antinociceptive effect in the writhing test but had no effect on the tail-flick latency. Isobolographic analyses revealed an additive interaction between amlodipine and morphine or ketorolac in the writhing test. 3. These results suggest that amlodipine induces antinociception and increases antinociceptive action of morphine and ketorolac, possibly through a decrease in cellular calcium availability.

Effects of dihydropyridine Ca2+ channel blockers on the discriminative stimulus and the motor impairing effects of (+/-)-Bay K 8644

Functional interactions between the dihydropyridine Ca2+ channel activator, (+/-)-Bay K 8644 (methyl-1,4-dihydro-2,6-dimethyl-3-nitro-4-(2-trifluoromethyphenyl )-pyridine-5-carboxylate), and several dihydropyridine L-type Ca2+ channel blockers were investigated on rotarod performance in mice and in rats trained to discriminate between (+/-)Bay K 8644 and saline. When administered alone, (+/-)-Bay K 8644 produced dose-dependent impairments of rotarod activity with an ED50 of 1.3 mg/kg. Pretreatment with nifedipine (10-30 mg/kg) produced dose-dependent rightward shifts of the (+/-)-Bay K 8644 dose-response curve. In contrast, pretreatment with several other dihydropyridine L-type Ca2+ channel blockers, including nicardipine, nimodipine, isradipine and nitrendipine, did not modify the (+/-)-Bay K 8644 dose-effect function. Rats learned to discriminate between (+/-)-Bay K 8644 (0.5 mg/kg) and saline in an average of 65 training sessions. In substitution tests, the Ca2+ channel activator engendered dose-related increases in the percentage of rats selecting the drug-associated lever with an ED50 of 0.19 mg/kg. Pretreatment with nifedipine (10 mg/kg) produced a rightward shift of the (+/-)-Bay K 8644 dose-response function. Pretreatment with nicardipine (2.5 mg/kg) only partially antagonised the training dose of (+/-)-Bay K 8644 whereas nimodipine (0.6-10 mg/kg) did not affect the (+/-)-Bay K 8644 discriminative stimulus. The results of the present study show that the behavioural effects of the dihydropyridine Ca2+ channel activator are differentially modified by dihydropyridine L-type Ca2+ channel blockers. These results may suggest that dihydropyridine blockers possess different intrinsic activities or act at different binding sites.

The influence of three L-type calcium channel blockers on morphine effects in healthy volunteers

Numerous animal studies and several clinical studies have shown that calcium channel blockers (CCBs) augment opioid analgesia. We sought to determine whether three CCBs from three L-type subgroups (i.e., L-CCBs) enhanced morphine analgesic effects in healthy volunteers, and whether other effects of morphine (e.g., mood-altering effects) were altered by the CCB pretreatment. We examined the effects of three L-CCBs--diltiazem (30 mg, per os [P.O.]), nimodipine (60 mg, P.O.), and verapamil (80 mg, P.O.)--on morphine (10 mg/70 kg, intravenously) effects in nine healthy volunteers. Subjects first ingested the oral drug or placebo and 120 min later were injected with morphine or saline. Dependent measures included pain ratings measured during a cold-pressor test and subjective, psychomotor, and physiological effects. The L-CCBs alone had no effect on any of the dependent measures. Morphine alone and in combination with the L-CCBs reduced pain ratings, but there were no statistically significant differences in the pain measures between the morphine alone and the L-CCB/morphine conditions. Pretreatment with the L-CCBs in most cases neither potentiated nor attenuated the other effects of morphine. L-CCBs as well as the N-type CCBs currently under drug development should continue to be investigated to determine their potential as analgesic adjuvants.

IMPLICATIONS

This study is important because the results are at odds with numerous animal studies and several clinical studies, which indicate that calcium channel blockers of the L-type increase the amount of analgesia produced by morphine. Using clinically relevant doses of L-type blockers, we could find no potentiation of morphine analgesia.

Actions of nimodipine on the serotonergic systems of rat brain

1. The effects of the serotonin (5-HT) precursor, L-5-hydroxytryptophan (L-5-HTP), or the selective 5-HT1A receptor agonist, 8-OHDPAT, on behavior or brain 5-HT metabolism or both were evaluated in rats IP pretreated with nimodipine at doses ranging from 0.31 to 40 mg/kg. 2. Nimodipine, in a wide dose range (0.6-20.0 mg/kg) potentiated the head-twitch response to L-5-HTP. 3. The effects of nimodipine on the 5-HT metabolism of rats treated with L-5-HTP did not comply with the increase in the behavioral response to this 5-HT precursor. 4. Nimodipine antagonized the effects on 5-HT metabolism induced by 8-hydroxy-2-(di-N-propyl-amino)-tetralin through stimulation of 5-HT1A autoreceptors. 5. It was concluded that the effects of nimodipine on brain 5-HT metabolism appeared to be linked to activation of serotonergic neurotransmission likely due to inhibition of the back-regulation mechanism mediated by presynaptic 5-HT1A receptors.

Nimodipine on shuttle-box avoidance learning in mice: no impairment but slight improvement

The dihydropyridine calcium channel antagonist nimodipine was tested in mice of CD-1, C57BL/6, and DBA/2 strains subjected to shuttle-box avoidance training. In contrast with some findings of other authors showing impairment of shuttle-box avoidance learning by low doses of the drug in rats, nimodipine given IP before each training session at doses of 0.25, 0.5, 1, 2.5, or 5 mg/kg never impaired avoidance acquisition in mice. On the contrary, one dose of nimodipine (1 mg/kg) significantly improved avoidance acquisition in mice of the DBA/2 strain. The drug failed to impair avoidance performance in DBA/2 mice even if given acutely in the middle (third session) or at the end (fifth session) of the training period. The results contradict studies showing cognitive impairment induced by calcium channel blockers, and may provide some limited evidence in support of improved cognitive function in normal animals, although this effect is much less evident than in aged or brain-damaged subjects.

Differential anxiolytic effects of neurosteroids in the mirrored chamber behavior test in mice

This study examined the effects of neurosteroids on the behavior of mice in the mirrored chamber test of anxiety, and determined the potential mechanisms by which neurosteroids alter the behavior in animal models of anxiety. Allopregnanolone (AP) (0.5 and 1 mg/kg) and pregnenolone sulfate (PS) (0.5 and 2 mg/kg) significantly reduced the latency to enter the chamber, and increased both number of entries and total time spent in the chamber in a dose-dependent manner, without affecting the spontaneous locomotor activity. In contrast, dehydroepiandrosterone sulfate (DHEAS) (1 and 2 mg/kg) increased motor activity and caused an anxiogenic response, i.e., an increase in latency to enter the mirrored chamber, and a decrease in the number of entries and time spent in the chamber. Progesterone (PROG) (1-10 mg/kg), a neurosteroid precursor, and 4'-chlordiazepam (4'-CD) (0.25-1 mg/kg), a specific ligand for the mitochondrial diazepam binding inhibitor (DBI) receptor (MDR), produced a clear dose-dependent anxiolytic response in the mirrored chamber. The AP-, PROG- and 4'-CD-elicited anxiolytic behavior was blocked by picrotoxin (1 mg/kg), a GABA-A chloride channel antagonist, but not by flumazenil (2 mg/kg), a selective benzodiazepine (BZD) antagonist. In contrast, the anxiolytic effect of PS was not blocked by picrotoxin. The 4'-CD-induced anxiolytic effect was prevented by pretreatment with PK11195 (2 mg/kg), a selective partial MDR antagonist. Nifedipine (2 and 5 mg/kg), a dihydropyridine-type Ca2+ channel blocker, produced a flumazenil-resistant anxiolytic effect. Combined administration of nifedipine (2 and 5 mg/kg) and PS (0.5 and 2 mg/kg) exerted a significant additive effect in the mirrored chamber test. The potent anxiolytic effect of dizocilpine (0.5 and 1 mg/kg), an NMDA receptor antagonist, was blocked by pretreatment with DHEAS (2 mg/kg). Neurosteroids evoked changes in mirrored chamber activities resembling those elicited by triazolam (0.25 and 0.5 mg/kg). However, these effects were seen at doses that did not markedly affect locomotor activity, thereby suggesting these changes in behavior represent anxiolytic actions. Together, these results provide evidence for differential behavioral actions of the neurosteroids AP, PS and DHEAS in the mirrored chamber test of anxiety. The anxiolytic effect of PROG may be imputed to its metabolism to neurosteroid AP, while the 4'-CD-induced anxiolytic response is related to its MDR-stimulated neurosteroidogenesis and subsequent modulation of GABA-A receptor. Further, these differential effects reaffirm the contention that neurosteroids could be involved in the homeostasis of stress response.

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.

Insulin-like growth factor I expression alters acute sensitivity and tolerance to ethanol in transgenic mice

We compared some biobehavioral effects of ethanol in transgenic mice that overexpress insulin-like growth factor I (IGF-I) in brain and in those that exhibit ectopic: brain expression of IGF binding protein I with those in non-transgenic littermate controls. Ethanol-induced sleep in IGF-I transgenic mice was significantly shorter, and in IGF binding protein 1 transgenic mice significantly longer, than in controls. A similar tendency, though not significant, was observed for ethanol-induced hypothermia. The groups did not differ in the degree of ethanol-induced ataxia. IGF-I transgenic mice did not acquire tolerance to either the hypothermic or hypnotic effects of ethanol following 7-day ethanol treatment. In contrast, tolerance in IGF binding protein 1 transgenic mice was significantly more pronounced than in controls. There were no significant differences among the three groups in the peak blood alcohol concentrations or the overall blood alcohol curves following acute ethanol challenge. In general, these data support the prediction made that chronically elevated exposure to IGF-I in IGF-I transgenic mice renders them less susceptible to the effects of ethanol than their non-transgenic siblings, and that overexpression of IGF binding protein 1 has the opposite effect.

Antidystonic effects of L-type Ca2+ channel antagonists in a hamster model of idiopathic dystonia

The effects of selective L-type Ca2+ channel antagonists on severity of dystonia were investigated in a mutant hamster model of idiopathic generalized dystonia. Nimodipine and diltiazem significantly decreased the severity of dystonia. Nimodipine was more potent in this respect and did not cause any behavioral side effects. The present data therefore suggest that Ca2+ channel antagonists could be useful in the treatment of idiopathic dystonia. The antidystonic effect of diltiazem and nimodipine may be based on their antidopaminergic action. However, the lack of significant effects of the L-type channel agonist (+/-)-BAY k-8644 (1-5 mg/kg; methyl-1,4-dihydro-2,6-dimethyl-3-nitro-4-(2-trifluoro-methylphenyl) -pyridine-5-carboxylate)) on severity of dystonia may indicate that voltage-gated Ca2+ channels are not critically involved in the pathophysiology of dystonia in mutant hamsters.

Role of taste aversion in calcium channel inhibitor-induced suppression of saccharin and alcohol drinking in rats

L-type calcium (Ca2+) channel inhibitors suppress drinking of highly preferred solutions of simple carbohydrates, saccharin, or alcohol. The present study was designed to examine whether this decrease in drinking behavior can be explained by the development of consummatory aversion. In the first experiment, the propensity of Ca2+ channel inhibitors to induce conditioned taste aversion (CTA) to 0.1% saccharin was examined using two saccharin/drug injection pairings in saccharin-naive rats. We compared three chemically different drugs: diltiazem, isradipine, and nicardipine. A dose-dependent CTA was observed after both conditioning sessions for all three drugs tested. Interestingly, the lowest dose of nicardipine (i.e., 1.25 mumol/kg), significantly increased saccharin intake. A nonsignificant trend to increase saccharin intake was also observed with the lowest dose of isradipine. We then examined whether nicardipine could similarly induce CTA to a novel taste of alcohol (6%, v/v). The drug failed to produce a significant effect. In the third experiment, we found that nicardipine did not induce CTA (or preference) if the saccharin taste was familar to rats. In the final experiment, the interaction of nicardipine (1.25 and 2.5 mumol/kg) with the ethanol (1.5 g/kg)-induced CTA to saccharin was investigated. The higher dose of nicardipine potentiated the aversive effect of ethanol in the test. Overall, the present results suggest that CTA does not play a major role in Ca2+ channel inhibitor-induced suppression of drinking behavior.

Effects of calcium antagonists nifedipine and flunarizine on phencyclidine-induced changes in the regional dopaminergic metabolism of the rat brain

To elucidate the psychotropic actions of calcium (Ca) antagonists, we investigated the effect of the voltage-dependent Ca channel antagonists, nifedipine and flunarizine, on phencyclidine (PCP)-induced changes in the monoamine metabolism in the regional brain areas of rats. The results indicate that the administration of nifedipine alone attenuated dopamine (DA) metabolism in the nucleus caudatus putamen while enhancing serotonin (5-HT) metabolism. By contrast, flunarizine increased DA metabolism. PCP significantly increased DA metabolite levels in the prefrontal cortex, the nucleus caudatus putamen, and the amygdala. The PCP-induced increases in DA metabolism in these regions were significantly antagonized by nifedipine, but not by flunarizine. These results indicate that nifedipine attenuates the PCP-induced hyperactivity of the dopaminergic neurons, suggesting antipsychotic properties for this drug.

Administration of antidepressants, diazepam and psychomotor stimulants further confirms the utility of Flinders Sensitive Line rats as an animal model of depression

Flinders Sensitive Line (FSL) rats have been proposed as an animal model of depression because they resemble depressed humans in that they have elevated REM sleep, reduced activity, and increased immobility and anhedonia after exposure to stressors. The present paper reviews experiments on the drug treatment of FSL and control Flinders Resistant Line (FRL) rats related to their utility as an animal model of depression, and presents new information. FSL rats exhibited exaggerated immobility in the forced swim test which is counteracted by the tricyclic antidepressants imipramine and desipramine and the serotonin reuptake blocker sertraline; the low immobility exhibited by the FRL rats is generally unaffected by these compounds. In contrast to these "therapeutic" effects of well recognized antidepressants, lithium and bright light treatment did not alter the exaggerated immobility of FSL rats. Novel data indicated that neither FSL nor FRL rats exhibited alterations in swim test immobility following chronic administration of the psychomotor stimulant amphetamine (2 mg/kg) and the anticholinergic scopolamine (2 mg/kg), which typically reduce immobility after acute administration. However, it was found that the calcium channel blockers verapamil (5 and 15 mg/kg) and nicardipine (10 mg/kg) did reduce the exaggerated immobility in FSL rats following chronic administration, suggesting that these compounds need to be evaluated further in humans. Previous studies have indicated no differences between FSL and FRL rats evaluated in the elevated plus maze, either at baseline or after the administration of diazepam, suggesting that the FSL rat may not differ from controls in anxiety-related behavior. Another recently published study showed that the FSL rat also did not differ from normal Sprague-Dawley rats in startle tests, indicating that the FSL rats do not exhibit behaviors shown in animal models of schizophrenia. These findings confirm the utility of FSL rats as an animal model of depression because the FSL rats do not appear to exhibit behaviors analogous to anxiety or schizophrenia and because they respond "therapeutically" to antidepressants and not psychomotor stimulants.

Effects of isradipine and darodipine on serotonergic system of the rat brain

Isradipine and darodipine are dihydropyridine calcium antagonists that easily pass into the brain, showing high affinity for cerebral L-type voltage-sensitive calcium channel (VSCC). These drugs were IP administered to rats to study their effects on serotonergic systems of discrete brain areas. Isradipine (0.05-5.0 mg/kg) and darodipine (0.3-20 mg/kg) increased the 5-HIAA/5-HT ratio, mostly enhancing the metabolite (5-HIAA) content in various brain areas, suggesting that serotonin (5-HT) turnover was increased. This increase appeared to depend on facilitation of serotonergic neurotransmission, because low doses of isradipine (< 0.075 mg/kg) or darodipine (< 0.6 mg/kg) enhanced the number of head twitches induced by L-5-hydroxytryptophan (L-5-HTP). However, higher doses of isradipine (1.5 mg/kg) or darodipine (5 mg/kg) also appeared to stimulate a negative feedback mechanism, which predominated over the facilitation when the serotonergic neurotransmission was strongly activated. Thus, higher drug doses decreased both the serotonin turnover and the number of head twitches on rats treated with L-5-HTP. It was speculated that the observed effects were due to brain VSCC blockade, although the studied compounds showed a peculiar profile of properties when compared to other previously studied calcium antagonists. Moreover, it was concluded that darodipine appeared to be more effective and selective than isradipine regarding the effects on brain serotonergic systems.