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 deficit of avoidance accompanied by a reduction in the basal levels of extraneuronal dopamine and in dopamine accumulation in the nucleus accumbens shell after acute uptake inhibition. Such a condition is similar to that of an experimental model of depression induced by exposing rats to a chronic stress procedure. Rats exposed to chronic stress are also unable to acquire an appetitive behavior sustained by a highly palatable food. Thus, it was studied whether rats fed a diet containing lithium would develop an appetitive behavior induced by a pure hedonic stimulus. Rats on the lithium diet developed a clear-cut escape deficit condition accompanied by a decreased dopamine output in the nucleus accumbens shell; nevertheless, they learned the appetitive 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 the 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.