We have shown that stimulation of cardiopulmonary sympathetic afferent fibers activates relays in upper cervical segments to suppress activity of lumbosacral spinal cells. The purpose of this study was to determine if chemical excitation (glutamate) of upper cervical cell bodies changes the spontaneous activity and evoked responses of lumbosacral spinal cells to colorectal distension (CRD). Extracellular potentials were recorded in pentobarbital-anesthetized male rats. CRD (80 mmHg) was produced by inflating a balloon inserted in the descending colon and rectum. A total of 135 cells in the lumbosacral segments (L6-S2) were activated by CRD. Seventy-five percent (95/126) of tested cells received convergent somatic input from the scrotum, perianal region, hindlimb, and tail; 997135 (73%) cells were excited or excited/inhibited by CRD; and 36 (27%) cells were inhibited or inhibited/excited by CRD. A glutamate (1 M) pledget placed on the surface of C1-C2 segments decreased spontaneous activity and excitatory CRD responses of 33/56 cells and increased spontaneous activity of 13/19 cells inhibited by CRD. Glutamate applied to C6-C7 segments decreased activity of 10/18 cells excited by CRD, and 9 of these also were inhibited by glutamate at C1-C2 segments. Glutamate at C6-C7 increased activity of 4/6 cells inhibited by CRD and excited by glutamate at C1-C2 segments. After transection at rostral C1 segment, glutamate at C1-C2 still reduced excitatory responses of 7/10 cells. Further, inhibitory effects of C6-C7 glutamate on excitatory responses to CRD still occurred after rostral C1 transection but were abolished after a rostral C6 transection in 4/4 cells. These data showed that C1-C2 cells activated with glutamate primarily produced inhibition of evoked responses to visceral stimulation of lumbosacral spinal cells. Inhibition resulting from activation of cells in C6-C7 segments required connections in the upper cervical segments. These results provide evidence that upper cervical cells integrate information that modulates activity of distant spinal neurons responding to visceral input.
|Number of pages||11|
|Journal||Journal of Neurophysiology|
|State||Published - 1 Dec 1999|