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 i n estrus. The first part examined the effects of removing either pelvi c or hypogastric nerve input (by appropriate dorsal rhizotomies) on ne uronal responses to stimulation of uterus, cervix and skin in either t he L1 or L6 dorsal horn of decerebrate, spinalized unanesthetized rats . Bilateral section of the T13-L2 roots (through which most hypogastri c afferents travel) eliminated almost all responses to uterine distens ion in L1 and L6. Such rhizotomies also decreased the inhibitory effec ts of cervix input on neurons in L6. Bilateral section of the L6-S2 ro ots (through which most pelvic afferents travel) had no effect on resp onses 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 respons es in T13/L1 of urethane-anesthetized rats before and after a T10 spin al transection. Transection increased the probability of observing neu rons excited by uterine stimulation. Transection also increased excita tory responses and decreased inhibitory responses to cervix stimulatio n. These results confirm previous findings that input from the uterus to the spinal cord is mainly by way of the hypogastric nerve, while th at from the cervix is by way of both the pelvic and hypogastric nerves . The results also demonstrate that descending influences in the estro us rat mainly increase the ability of cervix stimulation to inhibit sp inal neuronal activity and reduce the effectiveness of uterine stimula tion. Intersegmental effects between L1 and L6 as well as effects from distant roots within each segment on the processing of input from the cervix are similarly generally inhibitory. The challenge now is to un derstand how these interacting, mainly inhibitory effects sculpt the a ctions of neurons for various aspects of reproduction and other functi ons.