Ionic regulation of antagonist binding to the human muscarinic cholinergic receptor of caudate nucleus

Internalization of neuropeptide Y Y1 and Y5 and of pancreatic polypeptide Y4 receptors is inhibited by lithium in preference to sodium and potassium ions

The receptor-linked internalization of [125I] human neuropeptide Y (NPY) in Chinese hamster ovary (CHO) cells expressing the guinea-pig Y1 receptors or in human endometrial carcinoma-1B (Hec-1B) cells expressing the human Y5 receptor, as well as the receptor-linked internalization of human pancreatic polypeptide (hPP) receptor expressed in CHO cells, is selectively inhibited by low molarities of the Li+ cation. The Na+ and K+ cations decreased the receptor-linked internalization of agonist peptides only at high molar inputs, and largely in proportion to the reduction of cell surface binding of Y ligand peptides, dependent on ion concentration and the type of Y receptor examined. With particulates isolated from disrupted cells, there was no preferential inhibition by Li+ relative to Na+ in the binding of type-specific ligand peptides to Y receptors of any type. The observed difference could be connected to the known ability of Li+ to modify active conformations of signal transducers, which may also directly or indirectly affect the internalization motors. The decrease in the rate of Y receptor internalization by Li+ also points to a possible alteration of Y receptor signaling in vivo by lithium at acute therapeutically employed dose levels.

Loss of muscarinic cholinergic receptors from the temporal cortex of alcohol abusers

It is currently controversial whether all the brain damage in alcohol abusers in the result of thiamine deficiency (Wernicke-Korsakoff's disease) or whether, in addition, alcohol abuse may affect the brain by other mechanisms as well. The purpose of this study was to determine if alcohol abuse affects muscarinic cholinergic and benzodiazepine receptors in histologically normal brains obtained at autopsy in a general hospital population. Patients were excluded from this study if they had clinical brain diseases (including Wernicke's disease), died in coma, or had liver disease, significant brain atrophy, or dementia severe enough to require institutionalization. We found that muscarinic cholinergic synaptic receptor density determined with [3H] quinuclidinly benzilate was decreased by 40% in homogenates of the tempeoral cortex of 26 alcohol abusers compared with 26 matched nonalcoholic controls. The affinities of the muscarinic receptors were not significantly different between the two groups. In contrast, receptor densities and affinities of benzodiazepine receptors determined with [3H]flunitrazepam were not significantly different in the two groups. Age and death-autopsy time interval had no significant effects on either wet tissue protein concentrations, yields of protein after centrifugation, or receptor binding. The contributions of age and time interval were each less than 2% of the total variance of protein concentrations and receptor binding. When patients were excluded or included who had received cholinergic, anticholinergic, or benzodiazepine medications before death, no significant effects on the final results were observed. Pneumonia, known to be associated with acute hypoxia, and chronic obstructive pulmonary disease, known to be associated with chronic hypoxia, where approximately equally distributed between the two groups and had no significant effects on the results reported here. The loss of muscarinic and the sparing of benzodiazepine receptors occurs in the temporal cortex of histologically normal brains in the absence of significant atrophy and of gross dementia. This means that these changes are early in the development of an alcohol encephalopathy. We have previously reported a decrease in both muscarinic and benzodiazepine receptor binding in the frontal cortex and a decreasing muscarinic but not benzodiazepine receptors in the temporal cortex of alcohol abusers. Taken together, these findings suggest that alcohol neurotoxicity does not simply result in a random loss of neurons and or their associated synapses with their receptors. Instead, different types of receptors, depending upon their location in different brain regions, are specifically affected or spared. This suggests the involvement of region- and receptor-specific mechanisms in chronic alcohol toxicity.(ABSTRACT TRUNCATED AT 400 WORDS)

Loss of muscarinic and benzodiazepine neuroreceptors from hippocampus of alcohol abusers

Thiamine deficiency (Wernicke-Korsakoff's disease) may not be the only mechanism whereby chronic alcohol abuse affects the brain and not all alcohol-related changes may be evident morphologically. The purpose of this study was to determine if alcohol abuse affects muscarinic cholinergic and benzodiazepine receptors in the hippocampus of histologically normal brains obtained at autopsy in a general hospital population. Because patients were excluded who had significant brain atrophy and/or dementia severe enough to require institutionalization, the reported findings are presumed to be early changes in the development of an alcohol encephalopathy. In addition, patients were excluded from this study if they had clinical brain diseases (including Wernicke's disease), died in coma, had liver disease, or received medications that could potentially alter receptor binding. The reported changes in receptor binding were therefore presumed to be related to alcohol abuse per se and not an alcohol-associated condition. We found that muscarinic cholinergic synaptic receptor density determined with 3[H] quinuclidinyl benzilate was decreased by 30% in homogenates of the hippocampus of 25 alcohol abusers compared with 25 matched nonalcoholic controls. Similarly, densities of benzodiazepine receptors determined with 3[H] flunitrazepam were also decreased by approximately 30% in alcohol abusers. The affinities of both receptor types were not affected by alcohol abuse. Age and death-autopsy time interval had no significant effects on either wet tissue protein concentrations, yields of protein after centrifugation, or receptor binding. The contributions of age and time interval were each less than 2% of the total variance of protein concentrations and receptor binding.(ABSTRACT TRUNCATED AT 250 WORDS)

Decrease of benzodiazepine receptors in frontal cortex of alcoholics

We hypothesize that chronic alcohol abuse results in a loss of neurons and their associated synaptic receptors. This encephalopathy may be a precursor of brain atrophy and end-stage dementia. Autopsies were performed on normal brains of 27 alcoholics (mean age 62.5) and 30 nonalcoholic matched controls (mean age 64.4) free of other brain and liver diseases. None had recently received benzodiazepine medications. Gross brain atrophy was slight and equal in both groups. Benzodiazepine receptor densities and affinities in homogenates of frontal cortex were determined using [3H]flunitrazepam. Bmax specific binding was reduced by 20% in alcoholics compared with nonalcoholic controls of comparable age and with similar death-autopsy time intervals. The affinity was slightly less in the alcoholics. Wet tissue brain protein concentrations and their yields of 50,000-g pellet proteins were similar. Aging, death-autopsy time intervals, pneumonia and chronic obstructive pulmonary disease (diseases usually associated with hypoxia) had no significant effect on brain proteins, receptor densities, or affinities. We conclude that chronic alcoholism is associated with a loss of benzodiazepine receptor densities. Alcohol abuse may affect the results of post-mortem neurochemical investigations of other diseases.

A review of the biochemical and neuropharmacological actions of lithium

The pharmacological actions central to the therapeutic effects of lithium have not yet been established, despite almost 40 years of clinical use and scientific investigation. We review the biochemical and neuropharmacological data relating to this problem and attempt to identify profitable areas for further research.