Effect of pentylenetetrazol and anticonvulsants on neurotrasmitter release into the caudate nucleus of rats: In vivo differential pulse voltammetric study

The release of indoleamine and catecholamine within the caudate nucleus of freely moving and immobilized rats during convulsions induced by pentylenetetrazol (PTZ) was investigated by in vivo differential pulse voltammetry. In voltammograms obtained from the caudate nucleus, there were two distinct oxidation peaks: one at 130mV (peak P(2)) and the other at 300mV (peak P(3)). Thier potentials are characteristic of the oxidation of 3, 4-dihydroxyphenylacetic acid (DOPAC) and 5-hydroxyindoleacetic acid (5-HIAA), respectively. During tonic convulsions induced by 60 mg/kg of PTZ i.p., the amplitude of peak P(2) obtained from the caudate nucleus of freely moving rats significantly decreased to 75 % of the peak height recorded prior to the injection of PTZ, and recovered to normal within 60 min of the end of tonic convulsions. The amplitude of peak P(3) showed almost no change during and after tonic convulsions. These results suggest that the release of dopamine (DA) in this region of freely moving rats during tonic convulsions is induced by PTZ. The heights of peaks P(2) and P(3) were not influenced by phenobarbital (10-80 mg/kg, i.p.) or diazepam (10 mg/kg, i.p.) administration. In voltammograms from the caudate nucleus of immobilized rats, the amplitude of peak P(2) significantly increased during seizures. The increase lasted for 3 to 6 min after the seizures induced by PTZ (60-90 mg/kg, i.p.). This data suggests that DA release was increased in this region of immobilized rats during EEG-verified convulsions induced by PTZ. As the height of peak P(3) increased somewhat during seizures, so the release of serotonin increased during convulsions induced by PTZ. Although the changes in the DA release during convulsions were opposite in freely moving and immobilized rats, changes in DA and serotonin release in the caudate nucleus might participate in the development of convulsions induced by PTZ