Correlation between electrical and mechanical activity in myogenic and neurogenic control of the bovine retractor penis muscle

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Abstract
The electrical and mechanical activity of fine bundles of the bovine retractor penis muscle (RP) were investigated with the sucrose-gap technique. The muscle displayed prominent automaticity. It showed a vigorous and long lasting active response to stretch. Phasic contractions of the RP were associated with electrical firing while tonic contractions were not necessarily correlated to spike activity. Stimulation of excitatory nerves induced excitatory junction potentials (EJP). Single EJP could elicit spikes and repetitive firing with long lasting contraction. The EJP were abolished by phentolamine and adrenergic neuron blocking agents. Physostigmine suppressed EJP while scopolamine and atropine enhanced them and counteracted the effect of physostigmine. This points to an endogenous neurogenic prejunctional muscarinic suppression of the excitatory adrenergic neurotransmission. Inhibitory nerve stimulation could produce an inhibitory junction potential (IJP). The inhibitory nerves may also act on the contractile process without an IJP as a necessary step.