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Biomedical subjects

D C Mash

Publications and source records attributed to D C Mash.

98 records · Page 6Linked to original sources
PubMed1986

Autoradiographic localization of M1 and M2 muscarine receptors in the rat brain.

The distribution of M1 and M2 muscarine receptors in the rat brain was investigated by in vitro autoradiography. Muscarine receptors were visualized after complete receptor uncoupling in ethylenediaminetetraacetic acid buffer containing 1 mM N-ethyl maleimide and saturation with the ligand [3H]quinuclidinyl benzilate. Pirenzepine, an M1-selective antagonist, was used in our assays as a counter ligand to occlude M1 sites, allowing the primary ligand, [3H]quinuclidinyl benzilate, to label the remaining M2 muscarine receptors. In adjacent section, M1 muscarine receptors were labelled with [3H]quinuclidinyl benzilate in the presence of sufficient carbachol, and M2-selective agonist, to inhibit the binding to M2 sites. Our results reveal a heterogeneous distribution of M1 and M2 receptors. Increased densities of carbachol-resistant and pirenzepine-sensitive sites (M1 receptor subtype) were apparent over many forebrain structures including the olfactory tubercle, caudate-putamen, nucleus accumbens, hippocampus, amygdala and cerebral cortex. In contrast, pirenzepine-resistant and carbachol-sensitive sites (M2 receptor subtype) were distributed throughout the brain with increased densities apparent over regions known to contain large numbers of cholinergic cell bodies. M2 receptor localization patterns were largely coincident with the regional distribution and intensity of acetylcholinesterase positive sites. Since the M2 receptor pattern appears to parallel regional innervation densities, we conclude that the M2 receptor may serve as a marker for cholinergic pathways. The findings also suggest that M1 muscarine receptors are involved in the presumptive postsynaptic actions of acetylcholine in many forebrain structures.

Acetylcholine↗
PubMed1986

Characterization of L-[3H]nicotine binding in human cerebral cortex: comparison between Alzheimer's disease and the normal.

Putative nicotine receptors in the human cerebral cortex were characterized with L-[3H]nicotine, L-[3H]Nicotine binding was enhanced by the addition of Ca2+ and abolished in the presence of Na3EDTA. Association and dissociation of the ligand were rapid at 25 degrees C with t1/2 values of 2 and 3 min, respectively. Saturation binding analysis revealed an apparent single class of sites with a dissociation constant of 5.6 nM and a Hill coefficient of 1.05. There was no effect of postmortem interval on the density of binding sites assayed up to 24 h in rat frontoparietal cortex. Nicotine binding in human cortical samples was also unaltered by increasing sampling delay. In human cortical membranes, binding site density decreased with normal aging. Receptor affinity and concentration in samples of frontal cortex (Brodmann area 10) from patients with Alzheimer's disease were comparable to age-matched control values. Samples of infratemporal cortex (Brodmann area 38) from patients with Alzheimer's disease had a 50% reduction in the number of L-[3H]nicotine sites. Choline acetyltransferase activity was significantly decreased in both cortical areas. Enzyme activities in the temporal pole were reduced to 20% of control values. These data indicate that postsynaptic nicotine receptors are spared in the frontal cortex in Alzheimer's disease. In the infratemporal cortex, significant numbers of receptors remain despite the severe reduction in choline acetyltransferase activity. Replacement therapy directed at these sites may be warranted in Alzheimer's disease.

Adult↗
PubMed1986

The effect of altered 5-hydroxytryptamine levels on beta-endorphin content in rat brain.

The purpose of the present study was to examine the effect of altering the concentration of 5-hydroxytryptamine (5-HT) on beta-endorphin (beta-Ep) content in the hypothalamus, thalamus, and periaqueductal gray (PAG)-rostral pons regions of the rat brain. The selective 5-HT reuptake inhibitor, fluoxetine (10 mg/kg), significantly lowered beta-Ep content in the hypothalamus and the PAG. Parachlorophenylalanine, which inhibits 5-HT synthesis, significantly elevated beta-Ep in all brain parts studied. Intracisternal injections of the neurotoxin, 5',7'-dihydroxytryptamine, with desmethylimipramine pretreatment, significantly increased beta-Ep content in the hypothalamus and the PAG. In adrenalectomized rats, fluoxetine significantly decreased beta-Ep levels in the hypothalamus and increased the levels in the PAG. The results indicate that 5-HT may modulate the levels of brain beta-Ep.

5,7-Dihydroxytryptamine↗
PubMed1985

Loss of M2 muscarine receptors in the cerebral cortex in Alzheimer's disease and experimental cholinergic denervation.

Cerebral cortex samples from patients with Alzheimer's disease and from rats after experimental cholinergic denervation of the cerebral cortex exhibited reductions in the presynaptic marker choline acetyltransferase activity and in the number of M2 muscarine receptors, with no change in the number of M1 receptors. These results are in keeping with evidence that M2 receptors function in cholinergic nerve terminals to regulate the release of acetylcholine, whereas M1 receptors are located on postsynaptic cells and facilitate cellular excitation. New M1-selective agonists and M2-selective antagonists directed at post- or presynaptic sites deserve consideration as potential agents for the treatment of the disease.

Aged↗
PubMedDate not supplied

Localization of nerve growth factor receptors in the normal human brain and in Alzheimer's disease.

NGF receptors were visualized in human brain sections with an immunohistochemical procedure using a monoclonal antibody. This method results in the selective visualization of a population of neurons in the medial septal nucleus, the nucleus of the diagonal band of Broca, and the nucleus basalis of Meynert. Several lines of evidence indicate that this neuronal population is identical to the cholinergic neurons of the basal forebrain. NGF receptor immunohistochemistry therefore represents a sensitive and reliable procedure to selectively visualize forebrain cholinergic neurons for post-mortem analysis. NGF receptors were found to be expressed during the entire life span. However, the intracellular staining intensity was reduced in normal aging, suggesting the tentative conclusion that NGF receptor synthesis may decline in the aged brain. In Alzheimer's disease, the number of NGF receptor-positive cells was decreased. The morphological characteristics of surviving neurons were similar to immuno-positive neurons visualized in normal aged brains.

Adult↗
PubMedDate not supplied

Vesicular acetylcholine transporter density and Alzheimer's disease.

We have evaluated the vesamicol analogue meta-[125I]iodobenzyltrozamicol {(+)-[125I]MIBT} as a probe to assess cholinergic terminal integrity in the human temporal cortex. Saturation binding analysis, using 5-aminobenzovesamicol (ABV) to define nonspecific binding, revealed a high-affinity binding site with a Kd value of 4.3 +/- 1.2 nM in the temporal cortex of the young control subjects. Similar affinity values were observed for (+)-[125I]MIBT binding in aged control subjects (Kd = 3.4 +/- 0.5 nM) and AD patients (Kd = 3.0 +/- 0.8 nM). In contrast, Bmax values for young subjects, aged controls and AD patients were 31.2 +/- 6.3, 17.0 +/- 2.0 and 9.4 +/- 1.6 pmol/g, respectively, clearly reflecting significant reductions in (+)-[125I]MIBT binding site density with aging and age-related neuropathology. Moreover, the decrease in (+)-[125I]MIBT binding was correlated with choline acetyltransferase activities (r = 0.72) in the AD temporal cortex. These results suggest that when selective ligands are used, the vesicular acetylcholine transporter can be a useful marker protein for assessing the loss of cholinergic projections in AD and related disorders.

Acetylcholine↗