Abstract: The experiments were carried on anesthetized and immobilized rats, and the change of spinal field potentials (SFP) was observed when L-5HTP or 5-HT was given. No change was seen in SFP during intraperi-tonial injection of L-5HTP solution. The amplitudes of waves N and P reduced or increased in equal number following intravenous injection of L-5HTP.Only decrease in magnitude of waves N and P was shown when 5-HT was locally applied. No change in wave A's amplitude could be observed in all experimental groups. The results indicate that 5-HT may influence formation of waves N and P mainly via suppression of the activity of interneurons as well as pre-and/or postsynaptic inhibition.

Key words: 5-hydroxytryptamine, spinal field potential, spinal interneurons, pre-and/or postsynaptic inhibition