CAUDAL PORTIONS OF THE SPINAL TRIGEMINAL COMPLEX ARE NECESSARY FOR AUTONOMIC RESPONSES AND DISPLAY FOS-LIKE IMMUNOREACTIVITY AFTER CORNEAL STIMULATION IN THE CAT

Corneal input to the spinal trigeminal nucleus (Vsp) was assessed by e xamining Fos-like immunoreactivity (Fos-LI) after chemical irritant st imulation by mustard oil in chloralose-anesthetized cats. The distribu tion of Fos-LI within the ipsilateral Vsp was bimodal: a dominant grou p of cells within the superficial laminae at caudal levels of subnucle us caudalis and a second group of cells within the ventrolateral pole of Vsp at obex levels and within the adjacent interstitial islands. Fe w Fos-positive cells were seen within the Vsp rostral to the mid-porti on of subnucleus interpolaris or within the contralateral Vsp. To asse ss the involvement of caudal portions of the Vsp in mediating the adre nal and autonomic responses to corneal stimulation, mustard oil was ap plied before and after lidocaine blockade of the Vsp at obex levels in a second group of cats. Corneal stimulation alone increased significa ntly (P < 0.001) the adrenal secretion of catecholamines, adrenal bloo d flow, mean arterial pressure and heart rate. With the exception of h eart rate, the adrenal and autonomic responses to mustard oil were gre atly attenuated or abolished by lidocaine blockade of the ipsilateral Vsp at the level of the obex, a region that displayed a high number of Fos-positive cells after corneal stimulation. These results indicate that neurons within the Vsp at or more caudal than the level of the ob ex process chemical irritant input from the cornea and are necessary f or corneal-evoked changes in adrenal and autonomic function.