Differential effects of muscimol upon the firing frequency of large and small amplitude antidromic dorsal root action potentials in rat spinal cord in vitro

Abstract

The effects of bath applied muscimol upon spontaneous and evoked antidromic activity recorded from lumbar dorsal roots was investigated in hemisected, isolated preparations of rat spinal cord. In magnesium free medium containing 0.1 microM 4-aminopyridine, bursts of high amplitude (up to 1 mV), dorsal root reflexes were recorded. These were blocked by low concentrations of muscimol (2-5 microM). Higher concentrations (5-20 microM) of muscimol caused a concentration-dependent increase in the frequency of small amplitude (<200 microV) spontaneous dorsal root action potentials. The possibility that the large and small amplitude extracellular action potentials reflect activity in large and small diameter dorsal root axons, and that these respond in different ways to the GABA(A) agonist muscimol, is discussed.