The effects of sciatic nerve section on the contraction force of gastrocnemius muscle in cats

Abstract

The experiments were performed on anaesthetised cats gastrocnemiur muscles. Both muscles were stimulated directly through silver plate electrodes by brief trains (0.33 s) of rectangular-wave electrical impulses (0.1 ms, 100 Hz) once every 2 s. The muscles contracted in steady state conditions with force 25-30% of max contraction force. The svmnathetic nervous system was treated with ganglion _ biockator benzohexony (2.5%; 13.5-68.2 mg 2.2-15.5 mg/kg). Subsequent injection of 0.3 ml Novocain (2%) in the sciatic nerve after 30 min caused an increase of muscle contraction force (MCF) in 7 of 9 experiments by 26+4% (n=7). After section of sciatic nerve at the place of novocainization in the next 30 min the MCF further increased to 29*5% (n=5). The putting of a tourniquet on the thigh for 7 min (ischemic conditions) caused an transient increase of MCF by lOI* 1.4% (n=l7). This reaction appeared with 34k1.4 s latency and persisted for 7lk3.9 s (n=l7). The denervation of these muscles resulted in the increase of the reaction to the application of tourniquet: MCF rised by 180*3.7% (n=6); the duration of enhanced reaction was 182+19.2 sand the latent period was 144+21.4 s. Cardiac arrest by injection of air into thk v,jugularis induced a greater effect in denervated muscles (increase of MCF bv 169-205%. duration 202-306 s) as compared to that in inehated muscles (increase of MCF II l-151%, duration 98-240 s). The fast elevated effect caused by denervation is thought to result from (i) recruitment of additional neiromotor units; (ii) the rise of adrenergetic chemosensitivity of extrajunctional area; (iii) additional loss of [Ca2’], from intracellular stores.