BIOCHEMICAL AND MORPHOLOGICAL EFFECTS OF TESTOSTERONE TREATMENT ON DEVELOPING SYMPATHETIC NEURONS

Abstract— Neonatal rats were treated with testosterone propionate (TP) or isoproterenol (ISO) to determine whether (1) increases in salivary gland mass are associated with alteration of developing sympathetic neurons and (2) whether effects on neuron growth are secondary to altered target mass itself or to increases in salivary growth factors. TP treatment is known to result in salivary tubule hypertrophy and elevated nerve growth factor (NGF) content whereas IS0 treatment results in acinar hypertrophy and no known alteration in NGF. TP treatment increased submaxillary gland weight as well as tyrosine hydroxylase (T-OH) activity, adrenergic neuron numbers and total protein in the innervating superior cervical ganglion (SCG). Unilateral sialectomy prevented the increase in T-OH activity in the SCG, suggesting that the salivary glands were necessary for this effect. T-OH activity and total protein were elevated in the distant sixth lumbar sympathetic ganglion after TP treatment, suggesting that sympathetic development as a whole was affected and that humoral factors may be involved. Salivary gland weight was also elevated following ISO administration, but T-OH activity in the SCG was not affected. These observations suggest that TP treatment increases T-OH activity and sympathetic neuron numbers by alteration of specific salivary humoral growth factor(s).     

Serum catecholamines desensitize beta-adrenergic receptors of cultured C6 glioma cells

C6 glioma cells grown in medium containing fetal bovine serum have a decreased beta-adrenergic receptor number and beta-receptor-stimulated cyclic AMP accumulation as compared to cells grown in a serum-free, defined medium. The decreased number of receptors and decreased cAMP accumulation are attributable to a suppression of receptor binding and response by serum as opposed to increases produced by growth in the defined medium. Serum, when added to cells grown in the absence of serum, stimulated cellular cyclic AMP levels to 2-3 times basal levels. This direct stimulatory effect was blocked by incubation of the cells with the beta-adrenergic antagonist propranolol and was partially reversed by dialysis of the serum. In contrast, addition of serum to cells that have been grown with serum fails to stimulate cyclic AMP accumulation. The decrease in receptors following growth in serum can be mimicked by growing cells in serum-free medium in the presence of beta-adrenergic agonists such as isoproterenol or norepinephrine. Radioenzymatic assays indicate that fetal bovine serum contains approximately 0.3 nM norepinephrine and lower concentrations of epinephrine. It thus appears that growth of C6 cells in serum-containing media desensitizes the beta-adrenergic receptor/cyclic AMP system of these cells. This desensitized state appears to result primarily from the action of catecholamines present in serum. These data indicate that retained catecholamines are one component in serum that can modify expression of beta-adrenergic receptors and hormonal response of cultured glioma cells.     

The circadian clock starts ticking at a developmentally early stage

Although overt diurnal rhythms of behavior do not begin until well after birth, molecular studies suggest that the circadian clock may begin much earlier at a cellular level: mouse embryonic fibroblasts, for example, already possess robust clocks. By multiple criteria, we found no circadian clock present in mouse embryonic stem cells. Nevertheless, upon their differentiation into neurons, circadian gene expression was observed. In the first steps along the pathway from ES cells to neurons, a neural precursor cell (NPC) line already showed robust circadian oscillations. Therefore, at a cellular level, the circadian clock likely begins at the very earliest stages of mammalian development.