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-chlorophenylalanine (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.