BRAIN-MEDIATED RESPONSES TO VAGINOCERVICAL STIMULATION IN SPINAL CORD-TRANSECTED RATS - ROLE OF THE VAGUS NERVES

The present study was designed to ascertain whether the vagus nerves c onvey functional sensory activity from the reproductive tract in rats. Previously, vaginocervical mechanostimulation (VS) was shown to incre ase pupil diameter (PD) and the threshold of vocalization to tail shoc k (Voc-T). These responses were attenuated but not abolished by combin ed bilateral transection of the 'genito-spinal' nerves (i.e. pelvic, h ypogastric and pudendal). Subsequent bilateral vagotomy further reduce d or abolished the residual responses. In the present study, spinal co rd transection above the known level of entry of the genito-spinal ner ves was combined with bilateral vagotomy. In ovariectomized rats, afte r spinal cord transection at thoracic 7 (T7X), lumbar 5 (L5X) levels, or sham surgery (Sh), responses to VS were measured, the vagus nerves were then transected bilaterally, and responses to VS were again measu red. VS significantly increased Voc-T and PD after sham procedure or s pinal cord transection at either level. Subsequent bilateral vagotomy abolished the VS-induced increase in PD in the T7X group. Due to low s urvival rate, the effect of vagotomy on Voc-T could not be determined. Consequently, we performed a second experiment. In non-ovariectomized rats, VS significantly increased PD but reduced Voc-T in the T7X grou p compared to the Sh group, and subsequent bilateral vagotomy abolishe d both responses. These findings provide evidence that, in the rat, th e vagus nerves provide a functional sensory pathway from the reproduct ive tract directly to the medulla oblongata of the brain, bypassing th e spinal cord.