Changes in tyrosine hydroxylase mRNA expression in the rat locus coeruleus following acute or chronic treatment with valproic acid.

Valproate has proven effective in treating bipolar disorder. Though some biochemical effects of valproate are rapid, mood-stabilizing effects can take weeks, suggesting that regulatory changes in gene expression in brain neurotransmitter systems may be involved. Given a presumed role for norepinephrine (NE) in bipolar disorder, as well as the actions of mood-stabilizing drugs, we examined changes in mRNA expression for tyrosine hydroxylase (TH), the NE transporter (NET) and alpha 2A autoreceptor in the rat locus coeruleus after valproate treatment. TH mRNA increased slightly (16%) following acute treatment, and more so after chronic valproate treatment (26%), while neither NET nor alpha 2A mRNA expression changed. Further, chronic valproate treatment attenuated the elevation in TH mRNA expression induced in the LC in response to acute restraint stress. Both acute and chronic valproate treatment attenuated restraint stress-induced elevations in plasma ACTH secretion. These observations suggest that the therapeutic effects of valproate may involve regulatory alterations in TH message expression in the brain, and attenuation of stress-reactivity of the central noradrenergic system and the hypothalamic-pituitary-adrenal axis.