Effects of gamma-aminobutyrate and bicuculline on primary afferent depolarization of cutaneous fibres in the cat spinal cord.

The excitability of single cutaneous primary afferent fibres (sural nerve) was tested by focal stimulation in the dorsal horn of the cat spinal cord, and recording the antidromically conducted action potential in the peripheral nerve. To induce primary afferent depolarization, which is an expression of presynaptic inhibition, the superficial peroneal nerve was stimulated. The primary afferent depolarization was measured as the concomitant excitability change in the antidromically excited sural fibre. This primary afferent depolarization was reduced by 32% during microelectrophoretic release of bicuculline methochloride near the microstimulation electrode in the dorsal horn. Microelectrophoresis of gamma-aminobutyrate increased excitability in sural nerve fibres which correlated with the primary afferent depolarization induced by stimulation of the superficial peroneal nerve. The results suggest a possible role for gamma-aminobutyrate in presynaptic inhibition of cutaneous afferent fibres in the cat.