Neuropeptide Y: intrastriatal injections produce contralateral circling that is blocked by a dopamine antagonist in rats.

The brain is rich in neuropeptide Y (NPY) but its function is poorly understood. Previous studies have shown that intrastriatal injections of NPY stimulate dopamine (DA) release. In the present paper, behavioral studies evaluated the possibility that unilateral intrastriatal injections of NPY would produce contralateral circling that could be blocked by coinjection with a DA antagonist. Four experiments examined circling behavior in rats after unilateral intrastriatal microinjections (0.5 microliter) of: 1) amphetamine alone; 2) amphetamine with the DA antagonist cis-flupenthixol; 3) NPY alone; and 4) NPY with cis-flupenthixol. Each experiment consisted of seven test sessions; the first and seventh were preceded by no injection, the second and sixth by a control injection (saline or cis-flupenthixol with saline) and the third, fourth, and fifth by drug injections. Animals were scored during two 5-min intervals of a 20-min test session that began with the central injection and placement in a circular arena (30 cm diam.). Results indicated that the 25.0- but not the 6.0- or 12.0-micrograms doses of amphetamine and the 0.10- but not the 0.01- or 1.0-microgram doses of NPY produced contralateral circling. This directional bias was antagonized by cis-flupenthixol (20 micrograms in 0.5 microliter) in the case of amphetamine and fully blocked in the case of NPY. Results raise the intriguing possibility that contralateral circling induced by unilateral intrastriatal NPY may be mediated by DA.