Evidence for a role of the shell of the nucleus accumbens in oral behavior of freely moving rats.

Behavioral effects of intra-accumbens administration of the dopamine DAi receptor agonist (3,4-dihydroxyphenylimino)-2-imidazoline (DPI) were studied in freely moving rats. Three distinct areas were examined: core, shell and "shore," namely, the border region of the core and shell. DPI (5 micrograms) administered into the shell, but not areas ventral to the shell, increased chewing, tongue protrusion, sniffing, and grooming; it also induced abnormal oral behavior, namely, large-amplitude chewing. A similar dose of DPI administered into the core did not affect any (peri-)oral behavior, except sniffing. Because of methodological constraints the receptor specificity of the DPI effects was studied in rats with cannulas directed at the shore. DPI (5.0-10.0 micrograms) administered into the shore increased oral behavior dose dependently; however, the dose-effect curve varied per distinct type of oral behavior. The dopamine DAi receptor antagonist ergometrine attenuated the effect of DPI on tremor, chewing, and sniffing frequencies. Taken together, the data show that the effects of DPI were DAi receptor specific. It is concluded that stimulation of dopamine DAi receptors in the shell modulates and induces (peri-)oral behaviors in freely moving rats.