[Modulatory effects of substance P on the membrane responses mediated by GABAA and GABAB receptors in DRG neurons].

Intracellular recordings were performed on the neurons of young rat DRG to study the modulatory effects of SP on the responses mediated by GABAA and GABAB receptors. In the majority of the neurons (20/30) the GABA induced depolarization was suppressed to 50.8 +/- 20.2% by preapplication of SP (5 x 10(-6)-4 x 10(-5) mol/L), which applied alone had no effect or only caused a slight depolarization. In addition, SP could increase APD50 by 28.7 +/- 9.1% in many neurons (10/18), and the baclofen-induced shortening of 20.6 +/- 2.9% in APD50 could abolished (4/12) or even reverse to a lengthening of 19.3 +/- 8.9% in APD50 (8/12) by the preapplication of SP. Moreover, it was found that the activation of GABAB receptors could inhibit the succeeding response mediated by GABAA receptors. Since the soma of the DRG neuron is generally considered as an accessible model for the primary afferent terminals, the results suggest that SP which is released in the dorsal horn during nociceptive stimulation can antagonize the responses mediated by GABAA and GABAB receptors.