Acquisition of an appetitive behavior reverses the effects of long-term treatment with lithium in rats

Rats exposed to a long-term treatment with lithium chloride develop a defic it of avoidance accompanied by a reduction in the basal levels of extraneur onal dopamine and in dopamine accumulation in the nucleus accumbens shell a fter acute uptake inhibition. Such a condition is similar to that of an exp erimental model of depression induced by exposing rats to a chronic stress procedure. Rats exposed to chronic stress are also unable to acquire an app etitive behavior sustained by a highly palatable food. Thus, it was studied whether rats fed a diet containing lithium would develop an appetitive beh avior induced by a pure hedonic stimulus. Rats on the lithium diet develope d a clear-cut escape deficit condition accompanied by a decreased dopamine output in the nucleus accumbens shell; nevertheless, they learned the appet itive behavior within a similar period to controls. The development of the appetitive behavior coincided with the recovery of the capacity to avoid a noxious stimulus and with the return of the dopaminergic transmission in th e nucleus accumbens shell to values similar to those of control rats. It may be concluded that the mechanism of action underlying the behavioral and neurochemical sequelae of a chronic stress is distinct from that of the analogous effects produced by lithium. (C) 2000 IBRO. Published by Elsevie r Science Ltd. All rights reserved.