Differential regional zif268 messenger RNA expression in an escalating dose/binge model of amphetamine-induced psychosis

Abstract

Amphetamine-induced psychosis is most often associated with a high-dose multiple binge pattern of stimulant abuse. To simulate these conditions in rats, we used an escalating dose/binge administration paradigm. Animals were pretreated with escalating doses of amphetamine (1.0–8.0 mg/kg) over four days, then exposed to nine daily binges (8.0 mg/kg every 2 h; four injections/day). Other animals received either multiple injections of saline, saline followed by acute amphetamine (8.0 mg/kg) or single daily injections of amphetamine (8.0 mg/kg) in parallel with the escalating dose/binge treatment. One hour after the last injection, all animals were decapitated and regional brain activation patterns were assessed using in situ hybridization with antisense probes for zif268. Acute amphetamine resulted in a significant elevation of zif268 messenger RNA in both the nucleus accumbens and dorsal striatum. However, whereas after single daily amphetamine treatment this index was no longer elevated above control levels in the dorsal striatum, multiple binge exposures were required for the nucleus accumbens to return to baseline. Agranular insular cortex and medial olfactory tubercle zif268 messenger RNA expression was also markedly increased after acute amphetamine treatment but, unlike the nucleus accumbens and dorsal striatum, this increase was not significantly attenuated by either single daily injection or multiple binge treatment. Zif268 messenger RNA expression in the lateral nucleus of the amygdala also remained elevated above baseline after binge treatment. The possible relationships of these changes in zif268 messenger RNA regional expression patterns to the development of psychosis in high-dose stimulant abusers are discussed.