DISTRIBUTION OF FOS-LIKE IMMUNOREACTIVITY IN THE CAUDAL MEDULLARY RETICULAR-FORMATION FOLLOWING NOXIOUS FACIAL STIMULATION IN THE RAT

To investigate the topographic organization of nociceptive neurons in the caudal medullary reticular formation, the distribution of cells th at exhibit c-fos expression was examined following a unilateral noxiou s facial stimulus: subcutaneous injection of formalin into the vibriss al pad of awake rats. Labelling for Fos-like immunoreactivity was pres ent in a somatotopic distribution in a region of the lateral reticular formation adjacent to trigeminal nucleus caudalis, which corresponds approximately to lamina V of the medullary dorsal horn. Labelling in a djacent regions of the reticular formation showed no somatotopy but wa s predominantly ipsilateral. Contralateral labelling was concentrated ventrolaterally around the lateral reticular nucleus and dorsally near the nucleus of the solitary tract.