Neuromodulatory role of 5-hydroxytryptamine type 1A receptors on the excitability of Renshaw cells in the rat spinal cord

Serotonin modulates neurotransmission at synapses between various spinal neurons and, thus, may either facilitate or depress the information processed in the circuits and ultimately modulate the final motor output. A possible neuromodulatory role of 5-hydroxytryptamine type 1A (5-HT1A) receptors on the excitability of lumbar spinal Renshaw cells was explored in anesthetized rats spinalized at T4 level. Intravenous administration of the specific 5-HT1A agonist (2R)-(+)-8-hydroxy-2-(di-n-propylamino)tetralin hydrobromide (8-OH-DPAT) (0.1 mg/kg) decreased the Renshaw cell burst response by 20–45%. This effect was completely antagonized by the specific 5-HT1A antagonist (S) -N-tert-butyl-3- (4-(2 -methoxyphenyl) - piperazin-1-yl) -2 -phenylpropanamide dihydrochloride [(S)-WAY 100135] (0.1 mg/kg, intravenous), although this drug per se had no effect on the Renshaw cell burst response. These results suggest that 8-OH-DPAT-induced decrease in Renshaw cell burst firing was mediated by 5-HT1A receptors located either presynaptically or postsynaptically.