Acute and chronic phencyclidine administration: Effects on the conversion of³H-tryptophan to³H-serotonin in rat forebrain

Acute administration of phencyclidine hydrochloride (PCP) resulted in a dose-responsive decrease in the conversion of³H-tryptophan to³H-serotonin (³H-5-HT) in rat forebrain. Subsequent experiments measured the effect of a subthreshold dose of PCP (4 mg/kg) daily for one, seven, or fourteen days on this index of 5-HT turnover. Although single administration again had no effect at this dose, repeated administration for seven days resulted in a 37% decrease in 5-HT turnover. However, after fourteen days of administration this index was not significantly different from saline controls. The possible significance of these findings are discussed in relation to reported alterations in PCP-induced behaviors observed with chronic administration.