THE EFFECT OF GABA AND 5-HT RECEPTOR ANTAGONISTS ON RAT DORSAL-ROOT POTENTIALS

The prolonged dorsal root potential (DRP) and its associated primary a fferent depolarisation and presynaptic inhibition had been shown in pr evious studies to be reduced by GABAA antagonists. However we show her e that picrotoxin only reduces the rat DRP to 60% of its control ampli tude. We have therefore searched for antagonists to other neurotransmi tters that might also contribute to the DRP. The GABA(B) antagonist CG P 36742 had no significant effect. Similarly, antagonists specific to the serotonin (S-HT)(1A) receptor (MDL73005EF) and to the 5-HT3 recept or (granisetron) had no significant effect. However, methysergide sign ificantly reduced the DRP to 71% of its control level. Combined methys ergide and picrotoxin reduced the DRP to 20% of control level. We ther efore propose that both GABA(A) and 5-HT2 receptor mechanisms may play a role in generating the DRP.