Prevention of diazepam withdrawal syndrome by nifedipine—behavioural and neurochemical studies
Introduction
Benzodiazepines are the most commonly prescribed anxiolytic drugs, being effective against a wide spectrum of anxiety disorders. However, addiction, tolerance, and dependence/withdrawal may develop with these drugs, as well as adverse side effects that include sedation, cognitive and psychomotor impairments, and anterograde amnesia. Benzodiazepine withdrawal in human is associated with increased anxiety, insomnia, sensory disturbances, and even seizures (Ladewig, 1984). Similar symptoms have been observed in animals withdrawn from chronic benzodiazepine treatment (for review, see File, 1990). The cellular and molecular mechanisms underlying the withdrawal syndrome are still poorly understood. There is growing evidence that limbic structures and neurotransmitters, such as noradrenaline, serotonin (5-hydroxytryptamine, 5-HT), and GABA, are implicated. In particular, benzodiazepines are well known to act at allosteric sites on GABA A receptors to potentiate GABA-mediated opening of the receptor-chloride channel. Chronic modulation of GABA-benzodiazepine receptor complex plays a major role in central nervous system dysregulation during benzodiazepine abstinence (Malcolm, 2003). It thus appears that withdrawal symptoms stem, in part, from a resulting decrease in GABAergic inhibitory neurotransmission. However, increases in the activity of other neurotransmitters' systems also seem to play a role in benzodiazepine-withdrawal syndrome (Malcolm, 2003). In particular, the activation of the noradrenergic system has been shown to mediate benzodiazepine withdrawal-induced locomotor hyperactivity (Kunchandy and Kulkarni, 1986), but not the associated anxiogenic response (Baldwin et al., 1989). The increased anxiety associated with benzodiazepine withdrawal is more probably related to excessive ‘rebound’ 5-HT activity. Indeed, there is abundant experimental evidence supporting the idea that the median raphe nucleus–dorsal hippocampal 5-HT pathway mediates diazepam withdrawal-induced anxiety (Andrews et al., 1997). Moreover, withdrawal from chronic diazepam treatment has been shown to induce an increase in both [3H]5-HT release from and 45Ca2+ uptake into hippocampal slices, and these changes could be prevented by in vivo administration of the GABA B agonist, baclofen (Andrews and File, 1993). By acting at terminal GABA B heteroreceptors, baclofen antagonizes the raise in calcium uptake that normally occurs during diazepam withdrawal, thereby preventing Ca2+-dependent elevation in [3H]5-HT release. On this basis, we postulated that calcium channel antagonists (CCAs) might block or reverse the increased anxiety observed during benzodiazepine withdrawal, possibly through some effects on serotoninergic neurotransmission.
Indeed CCAs appear to have some efficacy in the treatment of mood disorders (Post et al., 1998). In animal studies, the administration of CCAs has been reported to exert an anxiolytic-like effect in the four-plate test (Chopin and Briley, 1987), the elevated plus-maze (Pucilowski and Kostowski, 1991), and in the paradigm consisting of measuring water intake by animals placed in a novel, anxiogenous, environment (Tazi et al., 1992). Furthermore, the CCA nitrendipine was shown to dose-dependently reduce the convulsions induced by withdrawal from flurazepam (Dolin et al., 1988), which raises the possibility that CCAs may prevent the benzodiazepine withdrawal syndrome (Hitchcott et al., 1992, Gupta et al., 1996).
In a previous study, we demonstrated that the anxiolytic-like effects of another potent CCA, nifedipine, could be modulated by the 5-HT1A receptor agonist, ipsapirone (El Ganouni et al., 1998). Accordingly, we postulated that the anxiolytic-like effects of CCA may be mediated by the 5-HT system. To further assess this hypothesis, we herein examined whether nifedipine affected 5-HT turnover in selected brain regions under conditions when this drug effectively prevents and/or reverses axiogenic-like behaviour in rats withdrawn from diazepam. In addition, activity of the hypothalamo–pituitary–adrenal (HPA) axis was also assessed in these animals.
Section snippets
Animals and drugs
Male Wistar rats weighing 250–290 g and housed 3–4 per cage were used. The rat room was lit with dim light from 08:00 to 20:00 h and maintained at 22±1 °C. Food and water were freely available to all animals. The experimental procedures used in this study were conducted in conformity with the institutional guidelines that are in compliance with international laws and policies (the UK Animals ‘Scientific Procedures ‘Act, 1986, and its associated guidelines).
Diazepam (Roche, Morocco), obtained
Results
Fig. 1 shows the effects of acute and chronic administration of nifedipine on water consumption by rats subjected to the Y maze paradigm. Vehicle-treated animals exhibited a marked decrease in water intake during the test session (day 8) compared with the last training day (day 7; 2.02±0.99 vs. 10.02±0.27 ml; means±S.E.M., n=10 in each group; p<0.001). Analysis of variance on mean water consumption during the test session indicated a significant group effect [F(3,36)=7.25, p<0.0001]. Post hoc
Discussion
Previous data from our laboratory have shown that acute administration of CCAs increased water intake by rats placed in a novel environment, indicating an anxiolytic-like effect of these drugs (El Ganouni et al., 1998). We confirmed herein that one of these drugs, nifedipine, dose dependently increased water intake by rats in a novel environment, and we also demonstrated that this effect was more striking after subchronic (for 8 days) than after acute administration of this drug. In contrast,
Acknowledgements
This research has been supported by grants from INSERM, Faculty of Sciences and Technics of Settat-Morocco, and the Comité Mixte Inter-Universitaire Franco-Marocain AI n° MA/02/53.
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