Development and characterization of glucocorticoid receptors in rat superior cervical ganglion

Glucocorticoids have many effects on the development and regulation of catecholamine systems in sympathetic neurons. Although it has been suggested that some of these effects may be mediated by cytoplasmic steroid receptors, the presence of high affinity glucocorticoid receptors in sympathetic cells has not been established. To determine whether such receptors are present and whether receptor levels change during development, glucocorticoid binding was measured in the superior cervical ganglion (SCG) of perfused rats 24 h after adrenalectomy using [³H]dexamethasone ([³H]Dex). Binding was optimal when [³H]Dex was added directly to tissue homogenates in the presence of 20 mM molybdate prior to preparing cytosol fractions. In the SCG of adult rats, 5.3 ± 0.9 x 10^-15 mol of [³H]Dex was bound/ganglion. The affinity and specificity of the SCG receptors were characteristic of cytosolic glucocorticoid receptors in other tissues. Binding of [³H]Dex was completely inhibited by dexamethasone and corticosterone, partially inhibited by progesterone, and not inhibited by estradiol or testosterone. The K(d) was estimated to be 1-2.5 nM from IC₅₀ values. The ontogeny of glucocorticoid receptor binding was measured at 2, 10 and 60 days of age. Receptor concentration was highest at 2 days, 99 ± 9 x 10^-15 mol/mg protein, and decreased to 29 ± 4 x 10^-15 mol/mg protein at 60 days. This decrease was entirely accounted for by the developmental increase in ganglion protein, whereas total binding remained constant at approximately 5 x 10^-15 mol/ganglion at all ages. The possibility that receptors are localized in principal neurons was examined by treating rats at birth with 6-hydroxydopamine (6-OHDA), a toxin which selectively destroys these neurons. 6-OHDA had no significant effect on total binding, suggesting that principal sympathetic neurons are not glucocorticoid target cells. Moreover, decentralization of ganglia 2 weeks prior to sacrifice had no significant effect on total ganglion binding of [³H]Dex, suggesting that glucocorticoid receptors are not present on presynaptic nerve endings. These data demonstrate that high affinity glucocorticoid receptors are present in sympathetic ganglia and suggest that these receptors may be localized in cells other than principal neurons, possibly glial or small, intensely fluorescent (SIF) cells.