The effects of central myorelaxants on synaptically-evoked primary afferent depolarization in the immature XXXX spinal cord in vitro.

@entity308 @entity1338 @entity3175 @entity21819 @entity9006 @entity5757 @entity35 @entity1772 @entity7233
1. In the immature @entity35 in vitro hemisected spinal cord preparation the dorsal root-evoked depolarizing potential recorded from an adjacent dorsal root DR-DRP had a mean peak amplitude (+/- s.e.mean, n = 27) of 2.9 +/- 0.2 mV and a mean latency to peak amplitude of 106 +/- 3 ms. The DR-DRP amplitude was maximal with a stimulus intensity of four times the threshold intensity required to activate the lowest threshold fibres. The peak amplitude and/or integral over a time-source of 0.5 s were used to assess the effects of applied drugs. 2. The DR-DRP was abolished by @entity1772 (mean IC50 190 +/- 46 nM, n = 7). The depressant effect of @entity1772 was reversed by @entity7233 (1 mM). The mean apparent Kd value calculated from dose-ratios was 16.7 +/- 6.4 microM (n = 3). 3. At a maximally effective concentration, @entity21819 (1 microM) produced at the most only a 14% @entity308 of the DR-DRP (n = 4). @entity1338 (0.3 microM) had an effect similar to that of @entity21819 . These depressant effects were reversed by @entity9006 (1 microM). 4. The DR-DRP was potentiated by @entity3175 in a @entity5757 (1 microM)-reversible manner. A maximal potentiation of 23.2 +/- 2.7% (n = 5) was produced by 1 microM @entity3175 . 5. @entity3175 (1 microM) induced a mean bicuculline- (10 microM, n = 2) and @entity5757 - (1 microM, n = 8) sensitive depolarization in the dorsal root of 0.25 +/- 0.03 mV (n = 8). However, @entity3175 failed to depolarize dorsal roots (n = 3) which had been excised from the spinal cord. 6. Comparison of the above effects with previously reported depressant effects of these drugs on the synaptic output from ventral roots suggests that actions on presynaptic inhibition, as reflected in the DR-DRP, are of subsidiary importance in explaining the muscle relaxant actions of @entity21819 or @entity3175 .
