Dissociation between adrenal tyrosinehydroxylase and phenylethanolamine N-Methyltransferase activities following repeated experience of defeats in individually housed male DBA/2J mice

Abstract

Adrenal activities of tyrosinehydroxylase (TH) and phenylethanolamine N-methyltransferase (PNMT) were compared between individually housed defeated intruders and socially housed residents (SR) (Experiment 1), and between individually housed defeated intruders and individually housed victor residents (Experiment 2). In addition, corticosterone titers were determined and dominance status of SR (dominant, subdominant active, and subdominant passive) considered. Defeats were induced twice a week for 6 consecutive weeks in short resident-intruder encounters. The main findings were:1) within the groups of SR, TH and PNMT activities were high in dominant and low in subdominant-passive mice; 2) in Experiment 1, TH activities of individually housed defeated intruders were low like those of subdominant-passive SR whereas their PNMT activities were high like those of dominant SR; 3) in Experiment 2, TH activities were low in both categories of individually kept mice whereas PNMT activities were significantly elevated in the defeated intruders; 4) in both experiments, PNMT activities of intruders correlated signficantly with the accumulated number of attacks they had received throughout all resident-intruder tests. Findings show separate effects of permanent social stimulation and of episodic experience of defeats on adrenal catecholamine synthesis. Lack of permanent social stimulation decreased adrenal TH and PNMT activities whereas repeated episodic experience of defeats specifically increased PNMT but not TH activities in individually housed mice.