Chronic individual housing-induced stress decreased expression of catecholamine biosynthetic enzyme genes and proteins in spleen of adult rats.

Objective: Social isolation is regarded as one of the most relevant causes of diseases in mammalian species. The activation of the sympathoneural system represents one of the key components of the stress response. The sympathetic nervous system is one of the major pathways involved in immune-neuroendocrine interactions. The aim of the present study was to determine plasma epinephrine and norepinephrine in individually housed rats, as well as to find out whether splenic gene expression of catecholamine synthesizing enzymes and their protein levels are affected by chronic psychosocial stress.

Methods: Tyrosine hydroxylase (TH), dopamine-beta-hydroxylase (DBH) and phenylethanolamine N-methyltransferase (PNMT) mRNA levels were quantified by quantitative real-time RT-PCR. The TH, DBH and PNMT immunoproteins were assayed by Western blot.

Results: Chronic social isolation of adult male rats produced a significant increase in plasma catecholamine levels and a decrease in splenic TH mRNA, DBH mRNA and PNMT mRNA. Protein levels of TH, DBH and PNMT were also reduced.

Conclusion: These results suggest that increased plasma catecholamines and decreased gene expression and protein levels of catecholamine biosynthetic enzymes in the spleen of chronically individually housed animals might reduce catecholamine synthesis, thus leaving the immunocompetent tissues depleted of catecholamines and consequently leading to an impairment of immune response.