MAP OF SPINAL NEURONS ACTIVATED BY CHEMICAL-STIMULATION IN THE NUCLEUS RAPHE MAGNUS OF THE UNANESTHETIZED RAT

The expression of the proto-oncogene c-fos was used as a cellular mark er of spinal cord neurons activated by microinjection of kainic acid i nto the medullary nucleus raphe magnus of awake and drug-free Sprague- Dawley rats. The c-FOS protein was detected by immunocytochemistry. We found increased immunoreactivity bilaterally in laminae I-VI of the d orsal horn. The strongest c-FOS expression was observed within the inn er layer of lamina II near its border with lamina III. In the ventral horn no c-FOS immunoreactivity was observed. Thus, the present results provide evidence for a descending excitation of neurons predominantly in inner lamina II, possibly mediating nucleus raphe magnus-induced i nhibition of neurons in other laminae.