FIMBRIA-FORNIX LESIONS DO NOT BLOCK SENSITIZATION TO THE PSYCHOMOTOR ACTIVATING EFFECTS OF AMPHETAMINE

The repeated, intermittent administration of amphetamine produces a lo ng-lasting sensitization to its behavioral activating effects. Excitat ory amino acid receptors in the striatum have been implicated in the d evelopment of amphetamine sensitization, and one source of excitatory amino acid input to the striatum is the hippocampus. The purpose of th is experiment, therefore, was to determine if an intact hippocampal sy stem is necessary for either the development or expression of sensitiz ation to the psychomotor activating effects of amphetamine. Rats recei ved either fimbria-fornix lesions or sham lesions and approximately 2 weeks later received 10 injections of 3.0 mg/kg d-amphetamine or salin e (IP) every other day. Rotational behavior was quantified as an index of amphetamine's psychomotor stimulant effects. Animals with a fimbri a-fornix lesion were hyperresponsive to an acute injection of amphetam ine, but animals with a fimbria-fornix lesion and control animals did not differ in the development of sensitization (i.e., the rate of sens itization). Furthermore, both groups expressed comparable sensitizatio n (relative to their respective saline-pretreated control groups) when given a challenge injection of amphetamine. These results suggest an intact hippocampal system is not necessary for the development or expr ession of amphetamine sensitization.