CONNECTIVITY BETWEEN BRAIN-STEM AUTONOMIC STRUCTURES AND EXPRESSION OF C-FOS FOLLOWING ELECTRICAL-STIMULATION OF THE CENTRAL NUCLEUS OF THEAMYGDALA IN RAT

Combinations of retrograde tracing with detection of Fos (the protein product of the immediate early gene c-fos) following electrical stimul ation of the central nucleus of the amygdala were used to explore: (1) the connectivity of activated (Fos-positive) neurons in the ventrolat eral medulla with the nucleus of the solitary tract; (2) the connectiv ity of activated neurons in the nucleus of the solitary tract with the ventrolateral medulla; (3) the proportion of activated catecholaminer gic neurons that project to the nucleus of the solitary tract or to th e ventrolateral medulla. Retrograde tracer was injected into the nucle us of the solitary tract or the ventrolateral medulla. After 5 days, s timulation for 60 min induced a statistically significant increase in the number of Fos-immunoreactive neurons in the ventrolateral medulla that project to the nucleus of the solitary tract and in the number of Fos-positive neurons in the nucleus of the solitary tract that projec t to the ventrolateral medulla. Of the neurons activated by stimulatio n of the central nucleus of the amygdala, 20% in the ventrolateral med ulla and 3% in the nucleus of the solitary tract contained the retrogr ade tracer and were also immunopositive for tyrosine hydroxylase, the enzyme responsible for synthesis of catecholamines.