Release of [3H]norepinephrine from synaptic vesicles isolated from rat brain after the intracisternal administration of [3H]norepinephrine: influence of nucleotides, ions and drugs, and destabilization of transmitter storage caused by acute or chronic lithium administration

Chronic lithium chloride injection increases glucocorticoid receptor but not mineralocorticoid receptor mRNA expression in rat brain

Lithium has been used clinically for the treatment of bipolar disorders. However, the brain mechanisms, by which lithium acts, are still unclear. An impaired hypothalamic-pituitary-adrenal (HPA) axis has been implicated in the pathogenesis of mood disorders. In this study, we investigated the effects of chronic lithium on the corticosteroid receptors in the brain. Male Wistar rats were injected with LiCl (1.5 mEq/kg) or saline intraperitoneally (i.p.) once a day for 14 days. Twenty-four hours after the last injection, the expressions of mRNA for glucocorticoid receptor (GR) and mineralocorticoid receptor (MR) in the brain were determined by non-radioactive in situ hybridization. Chronic administration of LiCl increased the expression of GR mRNA in the hippocampus and paraventricular nucleus of the hypothalamus (PVN). However, no significant changes were observed in the expression of either MR mRNA in the hippocampus or GR mRNA in the locus ceruleus. Since the hippocampus and PVN mediate negative feedback regulation of the HPA axis, an increased expression of GR mRNA in these regions may normalize HPA axis activity in mood disorders. Thus, the effect of chronic lithium on GR function may be involved in its antimanic and/or prophylactic activity in bipolar disorders.

Vesicular and ganglionic norepinephrine in the rat: progressive increase with age

This study analyzed dopamine (DA) and norepinephrine (NE) in the synaptic vesicles and cytoplasm of brains of rats of 2 months and 14 months. The data revealed a clear NE increase in the synaptic vesicles of the 14-month-old rats, contrasting with NE in the cytoplasmic fraction of the rat brain, which remained unchanged with age. Synaptic vesicles from different regions of rat brain, including those from the striatum, consistently exhibited higher NE than DA concentrations, suggesting that they are predominantly noradrenergic. In the brain, DA concentrations in vesicular and cytoplasmic fractions did not vary with age, whereas in the superior cervical ganglia DA and NE concentrations increased in the older rats. L-3,4-Dihydroxyphenylalanine administration significantly increased DA without affecting NE in the ganglia of rats of all ages. In the brain, such a treatment significantly raised DA only in the synaptic vesicles of the older rats, suggesting an increased facilitation of DA transport into the synaptic vesicles with age, which may account for the higher vesicular NE in the older rats.

Temperature-induced lysis of chromaffin granules provides evidence against the two-pool hypothesis of catecholamine storage

The temperature-dependent release of core constituents from isolated chromaffin granules in isotonic sucrose has been a controversial and puzzling phenomenon that has been interpreted either as selective catecholamine efflux from different catecholamine pools or as temperature-dependent lysis. We have analysed the kinetics, temperature dependence and physical basis of this process. Our results demonstrate that, upon increasing the ambient temperature, chromaffin granules show a shift in their osmotic fragility to higher osmolarities, which is linearly dependent on temperature and leads to measurable lysis in 0.26 M buffered sucrose at temperatures above 12 degrees C. It is possible to demonstrate both protein and dopamine beta-hydroxylase release when lysis as a function of temperature is measured in 0.26 M buffered sucrose. Real time measurements of the lysis kinetics were recorded on cassettes and analysed by a computer program for exponential decay kinetics. It is shown that the temperature-dependent lysis proceeds in two separate phases, the fast one of which is associated with temperature-dependent shift in the osmotic fragility curve. It has no characteristics of any exponential decay kinetics. The slow phase, when followed over several hours, leads to complete lysis of the granules in a sigmoidal time course at 30 degrees C. We conclude from the absence of exponentiality that there is no basis on which to assume the existence of different catecholamine pools. The fast phase of temperature-dependent lysis can be best explained as a simple temperature-dependent increase of the granule core solution's osmotic pressure, while the slow phase is probably caused by sucrose permeation into the granules. On the basis of these results, we warn against any efflux experiments measuring the temperature-dependent transmitter release from secretory vesicles with highly concentrated core solutions.