The present experiment was conducted to identify changes in hippocampal after discharge (AD) parameters following administration of subconvulsant dosages (half of the convulsant dosage) of analeptics with known pharmacological action. Long Evans rats (N=104) with chronic bipolar electrodes implanted in the dorsal hippocampus were injected with saline (0 mg/kg), caffeine (75 mg/kg), picrotoxin (2 mg/kg) or pentylenetetrazol (20 mg/kg) 15 minutes before testing. A differential effect of caffeine administration was observed in the dramatic prolongation of the rebound AD, without an accompanying change noted in the duration of the primary AD. Because caffeine blocks adenosine receptors at physiological concentrations, adenosine action is implicated in the termination of the second, but not the first, spike train. Picrotoxin and pentylenetetrazol had no influence on EEG parameters. A decrease in wet dog shake frequency, was associated with picrotoxin. The results suggest that GABA is involved minimally, if at all, in the hippocampal AD sequence.