Alcohol impairs age-dependent adaptation of human lymphocyte beta-adrenergic receptors

Alcohol and the brain: setting the benefit/risk balance

This article reviews the literature and presents some unpublished data on the CNS effects of alcohol at doses not producing tolerance and dependence. The available evidence indicates that the effect of low doses of ethanol may qualitatively differ from those produced in animal models mimicking alcoholism. For example, rats exposed for two months to alcohol in drinking water at a concentration (3%) not inducing tolerance or dependence, as assessed by lack of withdrawal signs upon treatment suspension, appear to be less stressed in the two-way avoidance-learning tests. Accordingly, the treated rats perform better and learn faster than sucrose-fed controls, while this behavior is disrupted by high levels of ethanol intake. These initial observations suggest that discontinuity may exist between the effects of low and high doses of this substance and underscore the need to expand research on the effects of alcohol on the CNS to include the bottom end of the dose-response curve.

The aging brain: protein phosphorylation as a target of changes in neuronal function

There is evidence that senescence affects neurotransmission at different levels. In particular, this review summarizes the studies on age-dependent modifications in protein phosphorylation, which represents the final pathway in the action of transmitters and hormones at neuronal level. Cyclic AMP-dependent protein kinase and protein kinase C have been reported to be modified during aging in various cerebral areas; the changes may involve either enzyme activity or substrate availability. These findings can be related to the alterations in neurotransmitter function and synaptic efficiency observed in the senescent brain. The activity of the other types of protein kinases (tyrosine-, cGMP-, calcium/calmodulin-dependent) during aging needs to be explored. An emerging point is the role of protein phosphorylation in the transfer of membrane signals to the nucleus, for the activation or disactivation of specific genes responsible for long-term neuronal events. Along this view, alterations in protein kinase pathway during senescence would ultimately affect gene expression, resulting in long term modifications of cell function. The reviewed literature opens the perspective of restoring some of the deficits associated with senescence by modulating protein phosphorylation pathway.

Studies on leukocyte beta-adrenergic receptors in depression: a critical appraisal

Alterations in beta-adrenergic receptors (BAR) of human mononuclear leukocytes (MNL) are considered to reflect changes in central noradrenergic function and have been studied in a number of diseases. This paper critically reviews the results of recent studies on MNL-BAR in depression, with particular emphasis on the biochemical and clinical methodologies used. Despite considerable differences in these methods, a number of laboratories report consistent decreases in MNL-BAR density and significantly reduced functional response in patients as compared to controls. These studies used MNL, isolated from patients who had a greater than 14 day drug washout, and BAR-densities were measured in membrane preparations, using full Scatchard analyses, and 125I-ICYP or 3H-DHA as the ligand. Functional response of MNL-BARs was assessed by the determination of isoproterenol-stimulated cyclic AMP accumulation. A comparison of methods used by these groups further indicates that additional biochemical parameters such as lymphocyte preparation and standardized experimental conditions for the binding assays are also important for obtaining consistent results. The clinical methods in rigorous study designs also include clearly stated inclusion/exclusion criteria for patients, and age-, and gender-matched patient-control populations. Whether the reduced MNL-BAR density and function is an inherited abnormality in depressed patients, or results from downregulation by elevated catecholamines is at present not known. Studies are needed to characterize further the changes in MNL-BARs in depression and to evaluate the effects of caetcholamines and hormones on this system. Based on critical assessment of the methods reviewed we propose specific biochemical and clinical guidelines, and recommend, that these be followed in future studies on MNL-BARs in this disease.