Neurotransmitted responses of smooth-muscle strips of complex sheep stomach after electrical field stimulation

Contractile responses to stimulation of nerve elements in smooth-muscle strips of complex sheep stomach suggest the existence of inhibitory and excitatory nerve structures in preparations from all compartments. Pharmacological analysis of the responses shows that they are mediated by cholinergic excitatory, noncholinergic excitatory and nonadrenergic inhibitory nerve elements. Comparison of the distribution of the cholinergic nerve structures shows that there are no essential differences between the different compartments. Differences are observed between strips cut in the direction of the two muscle layers, the effect of the cholinergic nerve elements being more pronounced in the longitudinal strips compared with the transverse ones. Noncholinergic excitatory effects of nerve stimulation are observed in all compartments of the complex stomach. Nonadrenergic nerve structures with inhibitory effect on the muscle strips are found in all compartments of the stomach. It is assumed that in the rumen they have spontaneous activity which inhibits the capacity of the smooth muscles in this part of the stomach for spontaneous phasic contractions.