Effects of histamine H3-receptor ligands on brain monoamine oxidase in various mammalian species.

The effects of an H3 agonist, R-alpha-methylhistamine (alpha-MeHA), and an H3 antagonist, thioperamide, on monoamine oxidase (MAO) activity in the hypothalamus of rat, monkey and human brains were compared in vitro. The histamine H(3)-receptor ligands competitively inhibited MAO-B, but noncompetitively inhibited MAO-A in all three mammalian species. However, alpha-MeHA inhibited MAO-A more potently than MAO-B at high concentrations in all three species. The K(i) values for MAO-A of alpha-MeHA in hypothalamic homogenates of rat, monkey and human brains were estimated to be 1.1, 1.2 and 1.9 mM, respectively, suggesting that alpha-MeHA cannot behave as a substrate for the MAO inhibitor. In contrast, rat, monkey and human brain MAO-B activities were inhibited by thioperamide, with respective K(i) values of 174.6, 8.2 and 10.8 microM, more potently than MAO-A activity. These results indicate that thioperamide, which elicits a strong activation of histamine release and turnover to N-tele-methylhistamine from histamine, competitively inhibits the conversion of N-tele-methylhistamine to N-tele-methylimidazoleacetic acid in human and monkey brains where MAO-B predominates.

Staurosporine differentiated human SH-SY5Y neuroblastoma cultures exhibit transient apoptosis and trophic factor independence.

The use of chemically differentiated neuroblastoma cells in the study of neuronal function has become a common alternative to primary neuronal cell cultures in recent years, particularly in the area of cell death. Staurosporine, a nonselective protein kinase inhibitor, has been demonstrated to be a particularly strong inducer of differentiation in the SH-SY5Y human neuroblastoma cell line. However, at present, no data exist on the long-term effects of this compound. We have compared the effects of staurosporine with 12-O-tetradecanoyl phorbol-13 acetate and retinoic acid in terms of long-term cell viability and neuronal function in the SH-SY5Y cell line. In the presence of serum, staurosporine-treated cells underwent apoptosis, which ultimately resulted in total cell loss. In contrast, when cultured in defined serum-free medium, a cessation of apoptosis occurred after approximately 1 week, at which point viability could be maintained in excess of 1 month. The addition of aurintricarboxylic acid, which has been demonstrated to prevent apoptosis in a variety of cell models, completely prevented both apoptosis and differentiation in staurosporine-treated cells both under serum-supplemented and serum-free conditions. Apoptosis was not prevented by the protein synthesis inhibitor, cycloheximide. The removal of staurosporine from the culture medium after 3 weeks had no effect on cellular morphology, function, or proliferation, indicating that the attained neuronal phenotype was terminal. Voltage-gated calcium channel sensitivity, used as a measurement of neuronal function, was highest in staurosporine-treated cells. On the basis that apoptosis and neurotrophin independence are hallmarks of the maturation of dorsal root ganglion neurons, results suggest that staurosporine-differentiated SH-SY5Y cells may bear a similar phenotype to that found in vivo. Furthermore, this model may provide for an excellent means of obtaining a stable and homogenous population of postmitotic monoaminergic neurons for investigating neuronal function and differentiation.

Superoxide dismutase activity in brains from chronic alcoholics.

CuZn superoxide dismutase (SOD) and Mn SOD activities were analyzed in hypothalamus, nucleus caudatus, hippocampus and cortex gyrus cinguli from 12 chronic alcoholics and from 16 controls. The CuZn SOD activities were slightly lower and the Mn SOD activities were slightly higher in the brain pieces from chronic alcoholics compared to the controls. The slight differences found can hardly be assigned etiological importance in the degenerative processes in brain tissue connected with chronic alcoholism.

The activity of monoamine oxidase -A and -B in brains from chronic alcoholics.

The activity of monoamine oxidase--A was found to be lower in homogenates of hypothalamus and caudate nucleus, but not in cortex of the gyrus cinguli and hippocampus, from chronic alcoholics with respect to homogenates from autopsy cases without histories of alcohol abuse. The activity of monoamine oxidase--B was also lower in the alcoholics, but this could be due to the selective effect of age upon this enzyme form, since the alcoholics were younger than controls. No difference was found for either monoamine oxidase -A or -B activities in brain homogenates from an alcohol preferring (AA) strain of rats, with respect to those from a water preferring (ANA) strain.