Amphetamine microinjections into distinct striatal subregions cause dissociable effects on motor and ingestive...

The mammalian striatum, although cytoarchitecturally consistent throughout its extent, is considered heterogeneous with regard to functional subregions. The present study investigated the behavioral effects of amphetamine microinjections into specific subregions within the striatum. These three sites, the nucleus accumbens (N.Acc), ventrolateral striatum (VLS) and dorsolateral striatum (DLS), were selected on the basis of their differential afferent projections. Three groups of rats were implanted with guide cannulae aimed at these sites, and were tested in their home cages following intrastriatal administration of saline, 0.1, 1.0, or 5.0 micrograms amphetamine (0.5 microliters bilaterally). Spontaneous motor and ingestive behaviors (the rats were maintained ad libitum) were observed and recorded over a 40-min session. Amphetamine injected into the N.Acc produced a dose-dependent increase in locomotion and rearing and decreased the average duration of rears. No effects were found on feeding or drinking. Amphetamine injected into the VLS had no overall effects on motor behavior, except to decrease locomotion and rearing in the first 10 min following the high dose. During this period, however, VLS amphetamine-treated animals showed increased levels of feeding, with no effects on drinking. At the higher doses of amphetamine infused into the VLS, some rats showed a marked but short-lasting stereotyped biting of the forepaws. Amphetamine injected into the DLS resulted in no measurable changes in behavior. Findings are interpreted as evidence for the diversity of the striatal dopamine system, based on its limbic and cortical connections, and suggest in particular that the ventrolateral striatum may critically mediate oral behavior.