Research reportAttenuation of benzodiazepine withdrawal anxiety in the rat by serotonin antagonists
Introduction
Anxiety disorders are common affecting approximately 13% of the population at any one time [26]. Benzodiazepines are often a first-line treatment for anxiety but chronic administration may result in physiological dependence, and when treatment is terminated, a severe withdrawal syndrome can occur [22]. Animal models can be used for the study of the withdrawal syndrome, as comparisons can be made without confounding pre-existing anxiety. The use of animal models has resulted in the identification of dosages, frequencies, and durations of treatment required for inducing withdrawal symptoms [8]. They also allow examination of possible treatment regimes that may alleviate the withdrawal symptoms.
Two common behavioural models used to evaluate the potential anxiolytic activity of compounds are the elevated plus maze and the social interaction test. In the elevated plus maze, it has been demonstrated that animals treated with anxiolytic drugs spend significantly less time in the perceived safety of the dark arms and venture more often into the open arm environment [30]. The social interaction test evaluates the time spent by two con-specifics in interaction for example sniffing, chasing and crawling over each other [12]. This test has been successfully used as both, a screen for anxiolytic compounds and as a model of anxiety [1], [9] and is considered to be a sensitive drug discovery paradigm for the evaluation of novel anxiolytic compounds [13]. Both models have been shown to be sensitive to anxiety arising in the context of benzodiazepine withdrawal [21], [29].
In this paper, we investigate the relationship between the GABAergic and serotonergic systems during withdrawal using pharmacological models. This is based on the notion that benzodiazepines exert their anxiolytic activity via the GABAergic system and evidence that the withdrawal of these drugs results in changes to the serotonergic system [1]. Elevated levels of hippocampal 5-HT in animals suffering from a withdrawal syndrome have been measured compared to control and chronically diazepam-treated animals [2]. Increases in amygdala 5-HT levels have also been demonstrated in withdrawal [6]. Additionally, animals that failed to show an anxiogenic response in withdrawal also failed to demonstrate an increase in hippocampal 5-HT concentrations [1]. A role for serotonin antagonists in alleviating anxiety is suggested from these studies The current study utilised the specific, but non-selective, 5-HT2 antagonists mianserin and ritanserin in the treatment of benzodiazepine withdrawal syndrome. While neither drug displays selectivity for 5-HT2 receptor subtypes, it is as yet unclear which subtypes may exert anxiolytic effects in animal models. Several studies suggest that 5HT2C antagonists when administered alone are anxiolytic in various animal models [17], [18], [19], [28]. On the other hand, the evidence for anxiolytic activity of 5HT2A antagonists is more controversial [15]. In some models, these antagonists are clearly anxiolytic [24] while in others there is a suggestion of anxiogenesis[28]. This may be related to the effects of some agents at other receptor subtypes, for example acting as partial agonists at 5HT2C receptors [4]. Nevertheless, activity in the model would imply a role for 5-HT2 receptors in mediating benzodiazepine withdrawal as well as suggesting further exploration of this system with more selective antagonists.
Section snippets
Animals
A total of 100 male Wistar rats (200–250 g) were used in the current studies. The animals were individually housed in a 24 h light/dark cycle. The light cycle started at 08:00 h and ended at 20:00 h, the temperature was maintained at 22 ± 1 °C. Standard laboratory chow and tap water was available ad libitum.
Chemicals
The compounds used in the experiment were Diazepam hydrochloride (a gift from Roche Products, Australia, Pty Ltd.), Ritanserin hydrochloride (Sigma, Pharmaceuticals, Sydney, Australia) and
Experiment 1
The effects of benzodiazepine withdrawal on behaviour in the social interaction test are shown in Fig. 1. A one-way ANOVA was conducted on the social interaction data with a significant main effect of drug condition found (F2, 45 = 36.97, p < 0.001). A post-hoc Student–Newman–Keuls (SNK) analysis revealed that both vehicle and diazepam-treated groups had significantly more interactions than the withdrawn animals. There were no statistically significant differences between vehicle- and chronic
Discussion
The study shows that abrupt withdrawal of diazepam led to the development of a characteristic anxiety response that was associated with significantly less interaction in the social interaction test, and significantly less exploratory behaviour in the elevated plus maze (as measured by open arm entries and time spent in the open arms). Animals exhibiting this syndrome also spent significantly more time in the closed arms of the elevated plus maze than control or diazepam-treated animals. The
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2007, European Journal of PharmacologyCitation Excerpt :The phenomenon is generally mild to moderate and it develops slowly, making it difficult to emulate in acute mammalian models. Typical treatment regimens to induce physical dependence in mice, rats, cats, dogs, or baboons involve administration of a benzodiazepine for days or weeks and the withdrawal signs often do not develop until hours or even days after the discontinuation of the drug (e.g., Ryan and Boisse, 1983; McNicholas et al., 1983; Rosenberg and Chiu, 1982, 1985; Pokk and Zharkovsky, 1998; Kaminski et al., 2003; Begg et al., 2005; Listos et al., 2005). In the present study, we report induction of physical dependence and abstinence-induced withdrawal in planarians using two benzodiazepines (midazolam and clorazepate (chlorazepate)) and a non-benzodiazepine benzodiazepine-receptor agonist (zolpidem).