Altered adult locomotor activity in rats from phencyclidine treatment on postnatal days 7, 9 and 11, but not repeated ketamine treatment on postnatal day 7

Abstract

Neonatal ketamine (KET) or phencyclidine (PCP) treatment can trigger apoptotic neurodegeneration in rodents. Previously, we described KET- and PCP-induced altered body weight and home cage, slant board and forelimb hang behaviors in preweaning rats (Boctor et al., 2008). In that study, l-carnitine (LC) attenuated the KET-induced behavioral alterations and body weight decrements. The four subcutaneous (sc) treatment groups were: (1) saline; (2) 10 mg/kg PCP on PNDs 7, 9 and 11; (3) 20 mg/kg KET (6 injections; one every 2 h on PND 7); or (4) a regimen of KET and 250 mg/kg LC (KLC) both administered on PND 7, with additional 250 mg/kg doses of LC on PNDs 8–11. A portion of each treatment group was evaluated for postweaning behaviors which included grip strength and motor coordination (postnatal days (PNDs) 22 or 71), locomotor sensitization (PND 42), spatial alternation (PNDs 22–70) and residential running wheel activity (PNDs 72–77). On PND 42 or 78, whole and regional brain weights were measured. Grip strength and motor coordination were unaffected at either age by neonatal treatment. On PND 42, neonatally treated KET- or KLC-treated rats responded to a challenge of 5 mg/kg KET with activity similar to controls that received the same challenge. Neonatal PCP treatment, however, induced significant sensitization to a challenge of 3 mg/kg PCP on PND 42 relative to controls that received the same challenge, causing increased activity which was especially profound in females. Performance on a continuous spatial alternation task requiring a “win-shift, lose-stay” strategy appeared unaffected by neonatal KET or KLC treatment. PCP treatment, however, caused significantly increased random responding and shorter choice latencies. In addition, neonatal PCP treatment elevated light and dark period running wheel activity and reduced PND 42 and 78 body and whole brain weights. These findings provide further evidence that PCP treatment on PNDs 7, 9, and 11 causes subtle cognitive deficits and long-term alterations in activity that are unrelated to deficits in grip strength or motor coordination. Further, repeated KET treatment on PND 7 does not appear to result in severe behavioral modifications.