Effect of acute and prolonged tianeptine administration on the 5-HT transporter: electrophysiological, biochemical and radioligand binding studies in the rat brain.

In the present study, in vivo extracellular unitary recordings, in vitro [3H]5-HT uptake and [3H]cyanoimipramine binding assays were used to assess the effect of acute and prolonged administration of the putative antidepressant tianeptine, on the 5-hydroxytryptamine (5-HT) transporter. Microiontophoretic application of tianeptine onto dorsal hippocampus CA3 pyramidal neurons, as well as its intravenous administration (2 mg/kg), increased their firing frequency. Following intracerebroventricular administration of 5,7-dihydroxytryptamine, the activation induced by the microiontophoretic application of tianeptine remained unchanged, thus suggesting that the 5-HT carrier is not involved in this effect. Furthermore, in spite of its activating effect on CA3 pyramidal neuron firing frequency, the intravenous administration of tianeptine did not alter the time of recovery of these neurons from microiontophoretic applications of 5-HT, an index of 5-HT uptake activity. In keeping with this observation, the acute administration of tianeptine did not change the effectiveness of the 5-HT reuptake blocker paroxetine (1 mg/kg, i.v.) in prolonging the suppressant effect of microiontophoretically-applied 5-HT. However, in rats that had received tianeptine for 14 days (20 mg/kg/day, s.c.), the recovery time from the suppressant effect of microiontophoretic applications of 5-HT was reduced by 40% and the effectiveness of paroxetine (1 mg/kg, i.v.) was decreased. These effects were no longer observed following a 48 h washout period. In a second series of experiments, the ability of tianeptine to interfere with the uptake blocking capacity of paroxetine was assessed in vitro, using hippocampal slices obtained from rats that had been treated with tianeptine for 14 days (20 mg/kg/day, s.c.; by minipump).(ABSTRACT TRUNCATED AT 250 WORDS)