Organization of blood pressure reflexes elicited by low intensity stimulation of cutaneous and muscular afferents in cats.

The incidence and patterns of blood pressure reflexes elicited by sustained (3--4 min) low intensity electric stimulation (0.5--4 V, 0.1 ms, 4 Hz) of cutaneous and muscular afferents of high or low spinal segmental input levels were investigated in immobilized (gallamine) and artificially ventilated conscious or anaesthesized (chloralose-urethan) cats. In a part of the experiments, subconvulsive doses of picrotoxin and/or strychnine were used as pharmacological disinhibitors. The results suggest that (1) the variability of the responses in conscious animals may be due to the varying degree of spinal inhibition, especially of that associated with cutaneous inputs; (2) intraspinal irradiation of excitation plays an important role in the integration of the reflexes; (3) the preferred direction of irradiation seems to be different in the projection zones of cutaneous and muscular afferents. Comparison of the results with previous data points to the possibility that the different response patterns seen after intense stimulation might be the result of the suppression of spinal inhibitions, due to C-fibre activation.