EFFECTS OF GABA AND GLYCINE RECEPTOR ANTAGONISTS ON THE ACTIVITY AND PAG-INDUCED INHIBITION OF RAT DORSAL HORN NEURONS

The effects of bicuculline and strychnine on the activity and periaque ductal gray (FAG)-induced inhibition of rat dorsal horn neurons of the lumbar spinal cord were tested. Extracellular single unit recordings were from 36 dorsal horn neurons near a microdialysis fiber passed thr ough the spinal cord for drug application. The GABAA receptor antagoni st, bicuculline was tested on 19 cells, whereas the glycine receptor a ntagonist, strychnine, was tested on 17 cells. Both bicuculline and st rychnine increased the background activity and responses to mechanical stimulation (BRUSH, PRESS, and PINCH) of the skin. They also signific antly blocked the FAG-induced inhibition of responses to peripheral me chanical stimuli. This experiment suggests that the mechanism of FAG-i nduced descending inhibition of dorsal horn neuron activity involves G ABA and/or glycine release in the spinal cord and that there is tonic release of these inhibitory neurotransmitters.