Chronic phencyclidine treatment decreases phencyclidine and dopamine receptors in rat brain.

Chronic phencyclidine treatment (10 mg/kg/day, SC for 14 days) significantly decreased the number of [3H]phencyclidine and [3H]spiperone binding sites in rat brain. [3H]Dihydromorphine binding was not affected by the same treatment. An acute treatment with phencyclidine (10 mg/kg, SC) did not modify any of the binding sites under study. These results suggest that a chronic phencyclidine treatment induces a down-regulation of phencyclidine and dopamine receptors without affecting opiate receptors. These reductions in the number of phencyclidine and dopamine binding sites might be related to the development of tolerance and/or dependence to phencyclidine.