Social stress alters expression of large conductance calcium-activated potassium channel subunits in mouse adrenal medulla and pituitary glands.

Large conductance calcium-activated potassium (BK) channels are very prominently expressed in adrenal chromaffin and many anterior pituitary cells, where they shape intrinsic excitability complexly. Stress- and sex-steroids regulate alternative splicing of Slo-alpha, the pore-forming subunit of BK channels, and chronic behavioural stress has been shown to alter Slo splicing in tree shrew adrenals. In the present study, we focus on mice, measuring the effects of chronic behavioural stress on total mRNA expression of the Slo-alpha gene, two key BK channel beta subunit genes (beta2 and beta4), and the 'STREX' splice variant of Slo-alpha. As a chronic stressor, males of the relatively aggressive SJL strain were housed with a different unfamiliar SJL male every 24 h for 19 days. This 'social-instability' paradigm stressed all individuals, as demonstrated by reduced weight gain and elevated corticosterone levels. Five quantitative reverse transcriptase-polymerase chain assays were performed in parallel, including beta-actin, each calibrated against a dilution series of its corresponding cDNA template. Stress-related changes in BK expression were larger in mice tested at 6 weeks than 9 weeks. In younger animals, Slo-alpha mRNA levels were elevated 44% and 116% in the adrenal medulla and pituitary, respectively, compared to individually-housed controls. beta2 and beta4 mRNAs were elevated 162% and 194% in the pituitary, but slightly reduced in the adrenals of stressed animals. In the pituitary, dominance scores of stressed animals correlated negatively with alpha and beta subunit expression, with more subordinate individuals exhibiting levels that were three- to four-fold higher than controls or dominant individuals. STREX variant representation was lower in the subordinate subset. Thus, the combination of subunits responding to stress differs markedly between adrenal and pituitary glands. These data suggest that early stress will differentially affect neuroendocrine cell excitability, and call for detailed analysis of functional consequences.

Protein kinase A linked phosphorylation mediates triiodothyronine induced actin gene expression in developing brain.

In the developing rat cerebra, triiodothyronine (T3) stimulates actin mRNA by acting predominantly at the level of transcription whereas tubulin mRNA is enhanced primarily by post-transcriptional regulation. We report here that in primary cultures of rat cerebra, the T3-induced actin gene expression is mediated by phosphorylation events. Inhibition of protein kinase A (PKA), but not of protein kinase C (PKC) or tyrosine kinase, totally blocked the induction of actin mRNA by T3. Under identical conditions, induction of tubulin mRNA by T3 was virtually unaffected by all the inhibitors. Activators of PKA, but not of PKC, potentiated the T3-induced actin gene expression, both at mRNA and protein level, by about 2-fold. In the absence of T3, neither the inhibitor nor the activator of PKA had any significant effect on this induction. The involvement of PKA in mediating the induction of actin mRNA by T3 was confirmed by transfecting primary cultures of rat cerebra with an expression vector encoding the protein kinase A inhibitor which totally abolished the induction. T3 is shown to enhance the phosphorylation of the thyroid hormone receptor, TRalpha, by about 2-fold but the level of phosphorylation of TRbeta remained virtually unaffected.