Vas deferens sympathetic activity homeostasis involving capsaicin-sensitive neurons

Resumen

The evidence indicates the presence of crossed histamine-containing neuronal pathways at the level of the sympathetic ganglionic clusters of the vas deferens, which are involved in a peripheral short-loop reflex, in which noradrenergic neurons interact with contralateral sympathetic ganglionic histamine-containing neurons. The latter cause a contralateral reciprocal inhibitory modulation of vas deferens sympathetic activity. This short loop reflex requires the presence of interneurons which convey the message of the sympathetic discharge from one vas deferens to the contralateral ganglionic histaminergic neurons. In this work, we are presenting evidence concerning the possible peptidergic nature, distribution, and functioning of these interneurons. Sprague-Dawley rats were subjected to axotomy induced by capsaicin applied at the prostatic end of the vas deferens. For selective decentralization, capsaicin was locally applied to the preganglionic hypogastric nerve. After the surgery, animals received reserpine intraperitoneally to assess changes of sympathetic activity in the vas deferens. Our findings demonstrate that capsaicin-induced selective postganglionic axotomy does not affect noradrenaline or histamine levels in the vas deferens. The local application of capsaicin to the ipsilateral preganglionic sympathetic nerve did not alter sympathetic activity in the vas deferens. Capsaicin applied locally to only one sympathetic ganglion, caused the facilitation of sympathetic activity in both vasa deferentia. Capsaicin-induced postganglionic selective axotomy caused similar local facilitation of the sympathetic activity in the presence of normal histamine levels. Facilitation of sympathetic activity induced by surgical ganglionectomy was similar in magnitude as the one induced by capsaicin selective postganglionic axotomy. Furthermore, the combination of capsaicin-induced postganglionic selective axotomy plus surgical contralateral ganglionectomy, caused similar facilitation on the sympathetic activity as either one alone, suggesting that both inhibitory components of the reflex are sharing the same mechanism to damp down sympathetic activity in the vas deferens. Our results indicate that peripheral neuropeptidergic, as well as histaminergic neurons, are important components of the peripheral compensatory reflex of sympathetic activity, thus contributing to maintaining homeostasis of the sympathetic activity.