NEGATIVE FEEDBACK OF CORTICOSTERONE ON THE PITUITARY-ADRENAL AXIS IS MAINTAINED AFTER INHIBITION OF SEROTONIN SYNTHESIS WITH PARACHLOROPHENYLALANINE

The role of the serotonergic transmission on the negative feedback of corticosterone on the pituitary-adrenal (PA) axis was studied in adult male rats. Animals were given p-chlorophenylalaine (PCPA) and 24 h later were administered corticosterone, 2 h before being subjected to 20 min of noise stress. The main results were as follows: First. PCPA administration increased resting levels of both corticotropin (ACTH) and corticosterone but did not alter PA response to noise stress: second. ACTH response to stress was eliminated in rats given PCPA: third, corticosterone reduced ACTH levels in nonstressed rats only and this effect was maintained after PCPA administration. Taken together. the present results suggest a mediator role for serotonin in the noise-stress-induced PA hormone release but no role in the negative feedback of corticosterone on the PA axis.