Intraspinal modulation of neuronal responses to uterine and cervix stimulation in rat L1 and L6 dorsal horn.

This two-part study examined intraspinal processing of input from the uterus, cervix and skin within the caudal spinal cord of virgin rats in estrus. The first part examined the effects of removing either pelvic or hypogastric nerve input (by appropriate dorsal rhizotomies) on neuronal responses to stimulation of uterus, cervix and skin in either the L1 or L6 dorsal horn of decerebrate, spinalized unanesthetized rats. Bilateral section of the T13-L2 roots (through which most hypogastric afferents travel) eliminated almost all responses to uterine distension in L1 and L6. Such rhizotomies also decreased the inhibitory effects of cervix input on neurons in L6. Bilateral section of the L6-S2 roots (through which most pelvic afferents travel) had no effect on responses to uterus, but decreased the inhibitory effects of cervix input on neurons in L1. Sections of both sets of roots eliminated responses to cervix stimulation in L6. The second part examined neuronal responses in T13/L1 of urethane-anesthetized rats before and after a T10 spinal transection. Transection increased the probability of observing neurons excited by uterine stimulation. Transection also increased excitatory responses and decreased inhibitory responses to cervix stimulation. These results confirm previous findings that input from the uterus to the spinal cord is mainly by way of the hypogastric nerve, while that from the cervix is by way of both the pelvic and hypogastric nerves. The results also demonstrate that descending influences in the estrous rat mainly increase the ability of cervix stimulation to inhibit spinal neuronal activity and reduce the effectiveness of uterine stimulation.(ABSTRACT TRUNCATED AT 250 WORDS)