Br. Komisaruk et al., BRAIN-MEDIATED RESPONSES TO VAGINOCERVICAL STIMULATION IN SPINAL CORD-TRANSECTED RATS - ROLE OF THE VAGUS NERVES, Brain research, 708(1-2), 1996, pp. 128-134
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.