Concurrent treatment with verapamil prevents diazepam withdrawal-induced anxiety, in the absence of altered calcium flux in cortical synaptosomes

Up-regulation of L-type high voltage-gated calcium channel subunits by sustained exposure to 1,4- and 1,5-benzodiazepines in cerebrocortical neurons

The aim of this study is to examine how sustained exposure to two 1,4-benzodiazepines (BZDs) with different action period, diazepam and brotizolam, and a 1,5-BZD, clobazam, affects L-type high voltage-gated calcium channel (HVCC) functions and its mechanisms using primary cultures of mouse cerebral cortical neurons. The sustained exposure to these three BZDs increased [(45)Ca2+] influx, which was due to the enhanced [(45)Ca2+] entry through L-type HVCCs but not through of Cav2.1 and Cav2.2. Increase in [(3)H]diltiazem binding after the exposure to these three BZDs was due to the increase in the binding sites of [(3)H]diltiazem. Western blot analysis showed increase of Cav1.2 and Cav1.3 in association with the increased expression of alpha2/delta1 subunit. Similar changes in [(3)H]diltiazem binding and L-type HVCC subunit expression were found in the cerebral cortex from mouse with BZD physical dependence. These results indicate that BZDs examined here have the potential to increase L-type HVCC functions mediated via the enhanced expression of not only Cav1.2 and Cav1.3 but also alpha2/delta1 subunit after their sustained exposure, which may participate in the development of physical dependence by these BZDs.

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 Animals withdrawn from chronic diazepam (2 mg/kg/day i.p. for 2 weeks) drank significantly less water than did control rats in the unfamiliar arm of a Y maze.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.

Diazepam withdrawal-induced anxiety and place aversion in the rat: differential effects of two chronic diazepam treatment regimes

The ability of the benzodiazepine antagonist flumazenil to precipitate a withdrawal subjective state in rats receiving chronic diazepam was investigated in a biased conditioned place aversion (CPA) procedure. Conditioning with flumazenil (10 mg/kg i.p.) in rats receiving chronic diazepam subcutaneously (s.c. in oil, 15 mg/kg/day for 28 days) but not intraperitoneally (i.p., 5 mg/kg for 28 days) resulted in the formation of a conditioned place aversion. These results indicate that precipitated withdrawal from diazepam injected s.c. but not i.p. produces a negative subjective state and that the conditioned place aversion paradigm may be useful in detecting the negative subjective effects of diazepam withdrawal. In parallel studies, the same s.c. treatment protocol produced an anxiogenic effect in the elevated plus-maze on spontaneous diazepam withdrawal, whereas rats treated with the i.p. protocol displayed no signs of withdrawal anxiety. The results of the present study are consistent with the interpretation that rats withdrawn from chronic i.p. diazepam did not demonstrate a CPA due to the 'repeated withdrawal' experiences induced by the i.p. injection route attenuating the subsequent ability of flumazenil to precipitate a subjective withdrawal state. Pharmacokinetic evidence and previous evidence showing that repeated withdrawal from diazepam in mice attenuates the aversive effects of the withdrawal experience in a conditioned taste aversion (CTA) paradigm support this interpretation.

Tolerance to acute anxiolysis but no withdrawal anxiogenesis in mice treated chronically with 5-HT1A receptor antagonist, WAY 100635

Anxiolytic-like activity in the mouse elevated plus-maze has recently been demonstrated for a range of compounds varying in degree of selectivity as 5-HT1A receptor antagonists. As tolerance and dependence liability are among the major clinical disadvantages of benzodiazepine therapy, the present study examined the effects of acute drug challenge on the plus-maze profiles of mice following daily treatment for 20 days with saline, chlordiazepoxide (CDP; 10.0 mg/kg) or the selective 5-HT1A receptor antagonist, WAY 100635 (0.1-1.0 mg/kg). To assess the development of physical dependence (withdrawal anxiogenesis), the study incorporated independent groups of animals tested on the maze 24 h after the final dose. Challenge with CDP or WAY 100635 produced behavioural changes indicative of anxiety reduction in mice that had received daily handling/saline for 20 days, thereby demonstrating that the chronic injection regimen per se had not compromised the acute efficacy of either agent. The absence of a similar response to acute drug challenge in mice treated chronically with CDP or WAY 100635 suggested the development of tolerance to the acute anxiolytic effects of both compounds under present test conditions. Despite these observations, however, no signs of enhanced anxiety were evident 24 h following discontinuation of chronic treatment with either compound. In a further experiment, the absence of withdrawal anxiogenesis at 24 h was replicated and extended to discontinuation periods of 36 and 48 h for both drugs. Although present results show that tolerance develops to the acute anxiolytic effects of CDP and WAY 100635 in the murine plus-maze, they also suggest that enhanced anxiety is not an inevitable consequence of abrupt cessation of chronic treatment with either compound.

Evidence suggesting that gonadal hormones influence benzodiazepine withdrawal-induced weight loss in rats

1. In experimental animals, benzodiazepine (BZ) withdrawal syndrome includes anorexia and acute weight loss. The literature shows several sex-based differences in the expression of BZ dependence; however, the authors did not find studies dealing with the influence of gonadal hormones on BZ withdrawal-induced weight loss. Thus, this study was designed to investigate the effects of castration on diazepam (DZ) withdrawal-induced weight loss in rats. 2. Male (260-330 g) or female (220-260 g) Wistar rats were anesthetized with ether and submitted to surgical castration or sham-operation. Seven days later, recovered from the surgery, the animals were injected i.p. with DZ (4 mg kg-1 day-1) or appropriate vehicle (VEH; 2 ml kg-1 kg-1 day-1) for 28 days. In the next 7 days, the rats received the same doses of DZ (four groups) or VEH (eight groups). Weights of all animals were recorded daily to the nearest gram at 09:00 h. To assess the degree of weight loss and make statistical comparisons, weights over days 29-34 were expressed as percentage of those recorded in the morning of day 28. 3. Sham-operated female rats from the group DZ-VEH showed a small but statistically significant weight loss on days 29 and 30 (P < 0.05) when compared with groups VEH-VEH and DZ-DZ. Ovariectomized rats, however, did not show any significant change in body weight from days 29-34. 4. Sham-operated male rats did not exhibit any significant weight loss after DZ withdrawal. Orchidectomized animals, however, showed a small but statistically significant weight loss on day 31 (P < 0.05) when compared with groups VEH-VEH and DZ-DZ. 5. These results show a gonadal influence on DZ withdrawal-induced weight loss in Wistar rats; in particular, they also suggest that female hormones (progesterone and/or estrogen) facilitate whilst male hormones inhibit this phenomenon.

Effects of calcium channel inhibitors on ethanol effects and pharmacokinetics in healthy volunteers

Previous studies have shown that calcium channel antagonists alter the effects of alcohol in animals and humans. We selected a phenylalkylamine, verapamil, and a dihydropyridine, nimodipine, to determine whether these drugs would affect the subjective or psychomotor effects of ethanol in humans. Subjects ingested verapamil (80 mg, PO), nimodipine (30 and 60 mg, PO), or placebo 60 min before drinking an alcohol (0.7 g/kg) or placebo beverage. Subjects' mood, psychomotor performance, physiological status, and blood alcohol levels were assessed up to 3 h after beverage ingestion. Alcohol increased "drunk" ratings and impaired psychomotor performance (p < 0.05). Blood alcohol levels were decreased by nimodipine pretreatment, but not by verapamil pretreatment. Subjective and psychomotor effects of alcohol were not altered as a function of nimodipine or verapamil pretreatment. Nimodipine, verapamil, and alcohol, either alone or in combination, had no effect on blood pressure or heart rate.

Concurrent nimodipine attenuates the withdrawal signs and the increase of cerebral dihydropyridine binding after chronic morphine treatment in rats

The effect of chronic administration of dihydropyridine calcium channel antagonist nimodipine (1 mg/kg/day) given concurrently with morphine on the signs of morphine withdrawal and on the [3H]nitrendipine binding in the rat brain has been investigated. Chronic morphine administration in increasing daily doses from 20 mg/kg to 70 mg/kg for 24 days and consequent withdrawal for 24 h induced loss of body weight, wet dog shakes, episodes of writhing and yawning behaviour. The density of [3H]nitrendipine binding was elevated in the cortex and limbic structures but not in the striatum after chronic morphine treatment. Chronic concurrent administration of nimodipine prevented the loss of body weight and reduced the scores of wet dog shakes and writhing, but did not affect yawning behaviour at 24 h after morphine withdrawal. The concurrent nimodipine treatment also prevented the rise in the density of central dihydropyridine binding sites which occurred upon chronic morphine treatment. These results suggest that chronic nimodipine treatment attenuates the development of the withdrawal signs which occur upon the termination of chronic morphine treatment by preventing the up-regulation of the central dihydropyridine-sensitive binding sites.

Calcium agonists and antagonists of the dihydropyridine type: effect on nicotine-induced antinociception and hypomotility

The influence of a calcium agonist (BAYK 8644) and several calcium channel blockers on nicotine-induced antinociception was investigated in mice. The effect of nicotine was sharply increased by BAYK 8644. This potentiation by BAYK 8644 was blocked by pretreating the animals with nifedipine at 2 and 10 mg/kg. The calcium channel antagonists, nifedipine and nimodipine at doses that had no effect on tail-flick time, reduced significantly the antinociception induced by nicotine (1.5 mg/kg, s.c.). However, the effect of verapamil on nicotine was not significant. These results indicate that DHP calcium channels (type L-channel) play a role in some of the pharmacological effects of nicotine, particularly, locomotor activity and antinociception.

Raised [3H]-5-HT release and 45Ca2+ uptake in diazepam withdrawal: inhibition by baclofen

The effect of diazepam withdrawal (2 mg/kg/day) on release of [3H]-5-hydroxytryptamine(5-HT) and [14C]-GABA from rat cortical and hippocampal slices was studied. No changes in [14C]-GABA release (basal, K(+)-evoked, uptake) from slices of either region were observed. Similarly, all parameters of [3H]-5-HT release were unchanged in cortical slices. However, during diazepam withdrawal, depolarised [3H]-5-HT release from hippocampal slices was raised with no changes in basal release or uptake into the slices being found. This increase could be prevented by in vivo administration of 1 mg/kg baclofen--this dose having no significant effect on [3H]-5-HT release from hippocampal slices of control rats. To further investigate this effect, 45Ca2+ uptake into hippocampal synaptosomes was examined and found to be increased during withdrawal. This was blocked by in vitro addition of 10 microM (-)baclofen, which had no effect on 45Ca2+ uptake in controls. Inhibition of 45Ca2+ uptake by (-)baclofen was also enhanced in nonwithdrawn diazepam-treated rats, but not in rats treated acutely with diazepam. The results from both studies indicate that chronic diazepam treatment increases neuronal sensitivity to baclofen. These results are discussed with reference to the anxiogenic state during diazepam withdrawal and a recent report of reversal of this behaviour by baclofen.

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.