RAT ISOLATED PHRENIC NERVE‐DIAPHRAGM PREPARATION FOR PHARMACOLOGICAL STUDY OF MUSCLE SPINDLE AFFERENT ACTIVITY: EFFECT OF OXOTREMORINE

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Abstract
1 Muscle spindle afferent discharges exhibiting an approximately linear length-frequency relation could be recorded from the phrenic nerve in the isolated phrenic nerve-diaphragm preparation of the rat. 2 Muscle spindle afferent discharges could be identified by their characteristic ‘spindle pause’ during muscle contraction and by their response to succinylcholine. 3 Cholinergic influence on spontaneous and stretch-induced afferent discharges was indicated by the augmentation produced by physostigmine and acetylcholine. (+)-Tubocurarine, but not atropine, prevented this augmentation indicating the presence of curariform cholinoceptors in muscle spindles. 4 Acetylcholine did not appear to be involved in the genesis of spindle afferent discharges as incubation with hemicholinium-3 and (+)-tubocurarine failed to affect the rate of spontaneous and stretch-induced spindle discharges. 5 Oxotremorine markedly increased the rate of spontaneous and stretch-induced spindle afferent discharges and this effect was prevented in the presence of hemicholinium-3 and (+)-tubocurarine. 6 These results with oxotremorine are of interest in connection with the observation that muscle spindle afferents are hyperactive in Parkinsonian patients.