Sensitisation of withdrawal signs following repeated withdrawal from a benzodiazepine: differences between measures of anxiety and seizure sensitivity

Abstract

Three experiments examined the effect of either withdrawal from diazepam, or repeated treatment with the convulsant, pentylenetetrazol (PTZ), on behaviour and seizure threshold. The behaviours measured were on the elevated plus maze and in the four-plate test; seizure threshold was measured as dose of PTZ infused via the tail vein to the first clonic twitch. In experiment 1, we examined the effect of either single or repeated withdrawal from diazepam using a procedure in which the drug was administered SC in a slow release depot. Three cycles of withdrawal from diazepam were compared to a single withdrawal experience. A single withdrawal from diazepam following chronic treatment gave rise, 72 h following the last dosing, to behavioural changes, suggestive of anxiety, in both tests, but did not result in a reduced convulsant threshold. In contrast, repeated withdrawal resulted in a reduction in sensitivity in several measures of anxiety, but sensitised the mice to the convulsive effects of the PTZ. The unexpected failure to find an increased sensitivity to a convulsive agent following a single withdrawal from SC diazepam was examined in experiment 2. The seizure threshold following a single withdrawal of mice which had received diazepam chronically IP in aqueous vehicle was significantly reduced relative to vehicle-treated controls, whereas that of animals receiving the same dose SC in oil, was not. It is argued that the difference may arise from the animals treated repeatedly with IP diazepam unintentionally experiencing repeated withdrawal, since the half-life of the drug by this route is short. In experiment 3, repeated sub-convulsant PTZ treatment reduced the convulsant threshold (the dose of PTZ required to give rise to the first clonic twitch), but had no significant effect on the behavioural measures of anxiety compared to a single dose of PTZ or vehicle controls. The results suggest that repeated withdrawal from chronic treatments with diazepam sensitises mice to convulsant stimuli in a manner resembling the effects of repeated administration of sub-convulsant doses of PTZ, but that neither repeated PTZ nor repeated diazepam withdrawal results in increased sensitivity to anxiogenic stimuli; rather, repeated withdrawal from diazepam may reduce the susceptibility of mice to behavioural measures of anxiety.

Differential Effects of Two Chronic Diazepam Treatment Regimes on Withdrawal Anxiety and AMPA Receptor Characteristics

“…It is therefore possible that the rats experience daily spontaneous withdrawal events during the course of the chronic DZP treatment. This is consistent with evidence from mouse studies, which showed that repeated previous experience of withdrawal from DZP ameliorates the anxiogenic effect of withdrawal, while lowering seizure thresholds (Dunworth and Stephens, 1998;Ward and Stephens, 1998). Thus, in the present study, the rats undergoing the i.p.…”

“…DZP increases AMPA receptor binding in mouse hippocampus and amygdala (Allison et al, 2005) consistent with a hypothesis that neuroadaptive changes at the level of the AMPA receptor are involved in the differential effects of these treatment regimes on behavioral measures of withdrawal (Ward and Stephens, 1998;Dunworth and Stephens, 1998;Dunworth et al, 2000). However, neurochemical measures were not directly correlated with behavior in this study and changes in AMPA receptor subunit expression that could affect the functionality of the receptor were not investigated.…”

“…These effects on withdrawal anxiety and aversion may be the result of these treatment regimens producing either a single withdrawal event (s.c. treatment) or repeated withdrawal events (i.p. treatment), based on pharmacokinetic evidence in rats (Friedman et al, 1986;Fernandes et al, 1999;Allison et al, 2002) and behavioral evidence in mice that repeated withdrawal from DZP results in amelioration of the anxiogenic effects of withdrawal (Dunworth and Stephens, 1998;Ward and Stephens, 1998).…”

“…All animals were killed immediately after the test period and their brains were removed and frozen in isopentane before being stored at À701C until required for receptor autoradiography and in situ hybridization (ISH). The chronic s.c. DZP treatment regimen employed (15 mg/kg/day s.c. for 28 days) is based on studies by other groups in both rats (Fernandes et al, 1999;Arnot et al, 2001) and mice Ward and Stephens, 1998;Dunworth et al, 2000), with the intention of producing relatively more stable plasma levels of DZP than the i.p. treatment regimen.…”

“…Assuming that this i.p. protocol evokes similar repeated withdrawal experiences as that in mice, resulting in reduced anxiety but enhanced seizure susceptibility (Ward and Stephens, 1998;Dunworth and Stephens, 1998) In similarity with the hippocampus, the amygdala has functional overlaps with respect to anxiety behaviors and seizure activity. Stimulation of the amygdala in animals provokes fear behaviors and defensive reactions (see Davis, 1992aDavis, , b, 1994 for reviews) and amygdaloid lesions reduce the expression of signs of fear and anxiety (Treit et al, 1993).…”