We applied randomized double pulse stimulation for assessing the effects of GABA and a GABA(A) antagonist on compound action potentials in dorsal column axons isolated from adult rat. We stimulated the axons with double pulses at 0.2Hz and randomly varied interpulse intervals between 3, 4, 5, 8, 10, 20, 30, 50 and 80ms. Action potentials were measured using glass micropipettes. The first pulse was used to condition the response activated by the second test pulse. Concentrations of GABA of 1mM, 100μM and 10μM did not affect action potential amplitudes or latencies activated by conditioning pulses. In the control studies, before drug administration, test pulses induced response amplitudes that were significantly decreased at 3-, 4- and 5-ms interpulse intervals. The test action potential amplitudes were 84.6±2.5%, 89.0±3.9% and 93.3±3.6% (mean±S.E.M.) of conditioning pulse levels, respectively. At 3-ms interpulse intervals, test response latencies were prolonged to 104.3±1.0%, but were unchanged at the other interpulse intervals. The 10μM, 100μM and 1mM concentrations of GABA affected test response amplitudes. Application of 100μM GABA reduced the amplitudes of test responses at 3-, 4-, 5- and 8-ms interpulse intervals, to 59.2±3.0%, 70.0±3.0%, 80.2±1.1% and 88.6±3.6% of the conditioning pulse amplitudes, respectively. At both 100μM and 1mM concentrations, GABA significantly prolonged the latencies of test responses. Treatment with 100μM GABA prolonged the latencies of test responses at 3-, 4- and 5-ms interpulse intervals, to 119.3±3.1%, 107.3±2.8% and 105.5±2.5% of conditioning pulse latencies, respectively. The addition of 100μM bicuculline methochloride, a GABA(A) antagonist, eliminated the effects of 100μM GABA. The combined application of GABA and bicuculline (both 100μM) did not affect amplitudes or latencies of test responses.These results suggest that GABA(A) receptor subtypes are present on the spinal dorsal column axons of adult rat, and that they modulate the excitability of the axons. The randomized double pulse methods reveal that GABA increases refractoriness of adult rat dorsal column axons. Copyright (C) 1999 IBRO.
All Science Journal Classification (ASJC) codes
- Adult rat
- Dorsal column
- Randomized double pulse