Effects of psychoactive drugs on operant responding and non-operant activity of rats with hippocampal system damage

The effects of various psychoactive drugs (methylphenidate, 0.2-8.0 mg/kg; pentobarbital, 0.5-10.0 mg/kg; caffeine, 3.2-32.0 mg/kg; imipramine, 1.0-20.0 mg/kg; d-amphetamine, 0.1-1.0 mg/kg) on the operant and non-operant behavior rates of adult male Sprague-Dawley rats with various lesion types localized in the septal-hippocampal area were tested in an appetative operant paradigm utilizing both a response contingent (VI50 sec) and a response non-contingent (VT50 sec) schedule. In general, both pentobarbital and imipramine reduced the rate of both behavioral measures in a dose-dependent manner while the psychomotor stimulants tended to decrease operant rates and increase non-operant rates to varying degrees in all groups. There were differential drug effects among the various lesion types which would indicate specific drug responsivity patterns. These results are discussed in terms of their usefulness in understanding the therapeutic effects of these drugs in treating possible hippocampal dysfunction.