Respiratory changes induced by activation of testicular afferents in dogs

Reportedly, more than 90% of the testicular afferents of the dog are of the polymodal type. The possible involvement of these afferents in modulation of respiration was studied using anesthetized dogs, which had been vagotomized and with both common carotid arteries ligated. Electrical stimulation of the superior spermatic nerve at an intensity of 1/5 Tc (Tc: threshold intensity for C-fiber activation) induced no substantial changes in respiration, while above 1/2 Tc it induced an increase in minute expiratory volume (VE), or a decrease followed by an increase in VE. The pattern of respiratory change was converted from the former to the latter by increasing the stimulation frequency while maintaining the same intensity. Mechanical stimulation of the testis through a stimulator with a tip of 1 cm in diameter caused an increase of VE at 200 g and a decrease followed by an increase of VE above 500 g. Intra-arterial injection of bradykinin (3 x 10(-6) M), hypertonic saline (1.5 M) and high K+ solution (180 mM) to the spermatic artery induced similar respiratory changes. Pneumograms showed a shift in end-expiratory position even at stimulus intensities without significant VE changes. Phrenic nerve recordings from some artificially ventilated dogs, revealed an prolongation of the first expiratory phase followed by augmentation of phrenic activity, mostly an increase in respiratory rate. Comparison between afferent activities and reflex respiratory changes suggests that above described two types of respiratory changes are brought about by the activities of testicular polymodal receptors.