Effects of apomorphine and piribedil on pentylenetetrazol-induced seizures in mice

Based on previous work examining the effects of dextroamphetamine on pentylenetetrazol (PTZ)-induced clonic seizure threshold, the objective of the present study was to determine the effects of two other dopamine agonists, apomorphine (AP) and piribedil, on PTZ seizures. TD50 and LD50 values for CD-1 mice were determined initially for the two drugs. Subsequently, dose-and time-response analyses established that AP decreased PTZ seizure threshold 15 min after administration, but increased the threshold at 60 min. Piribedil elevated the seizure threshold, but like AP, did not exhibit a clear dose-response relationship. Subsequent blocker studies with phentolamine, (-)sotalol, pimozide, and atropine suggested the possible neurotransmitter systems involved in the modulation of the PTZ-induced seizures by AP and piribedil. Pimozide blocked the changes in seizure threshold induced by both drugs. Atropine also decreased the AP-induced increase in threshold at 60 min. The pattern of inhibition of seizure threshold changes induced by the neurotransmitter blockers suggested that piribedil blocked seizures by means of indirect actions on several neurotransmitters.