Selective antagonists provide evidence that M1 muscarinic receptors may mediate carbachol-induced drinking in the rat

The present study served to investigate the ability of seven selective muscarinic antagonists to inhibit carbachol-induced drinking in the rat. The muscarinic antagonists were given by intracerebroventricular (i.c.v.) injection 1 min before the i.c.v. injection of carbachol (1 microgram/rat). The M2 antagonist, methoctramine, was inactive up to 80.3 nmol/rat. The M3 antagonist, p-fluoro-hexahydro-sila-difenidol, elicited a modest (42%) but statistically significant inhibition of drinking only at 80 nmol/rat. On the other hand, the selective M1 antagonists, (R)-trihexphenidyl, o-methoxy-sila-hexocyclium and pirenzepine, produced a marked and dose-dependent inhibition of carbachol-induced drinking, their ID50 values being 0.51, 7.36 and 9.31 nmol/rat. Also the M1/M3 antagonists, 4-diphenylacetoxy-N-methylpiperidine methiodide and hexahydro-sila-difenidol, were potent inhibitors of carbachol-induced drinking, their ID50 values (0.28 and 11.09 nmol/rat) being related to their pA2 values for M1 receptors in rabbit vas deferens. These data suggest that carbachol-induced drinking may be mediated by activation of muscarinic M1 receptors.     

Methoctramine, a selective M2 alpha muscarinic receptor antagonist, does not inhibit carbachol-induced drinking in the rat

Methoctramine, a selective M2 alpha muscarinic receptor antagonist, was examined for its ability to inhibit carbachol-induced drinking in the rat. Intracerebroventricularly (i.c.v.) administered methoctramine was devoid of activity up to a dose of 100 nmol/rat, whereas higher doses were toxic under our experimental conditions. 4-DAMP, pirenzepine and hexahydrosiladifenidol were also tested. The rank potency order for the compounds (4-DAMP greater than pirenzepine = hexahydrosiladifenidol) was similar to that for their affinity at M1 receptors, as found in experiments in vitro. The putative M1 agonist McN-A-343 was inactive up to doses of 13.9 micrograms/rat. Our data suggest that M2 alpha receptors do not mediate cholinergic drinking in the rat. The question whether M1 or M2 beta muscarinic receptors are involved in this response still awaits a firm answer.     

Age and sex influence on oxidative damage and functional status in human skeletal muscle

A reduction in muscle mass, with consequent decrease in strength and resistance, is commonly observed with advancing age. In this study we measured markers of oxidative damage to DNA, lipids and proteins, some antioxidant enzyme activities as well Ca²⁺ transport in sarcoplasmic reticulum membranes in muscle biopsies from vastus lateralis of young and elderly healthy subjects of both sexes in order to evaluate the presence of age- and sex- related differences. We found a significant increase in oxidation of DNA and lipids in the elderly group, more evident in males, and a reduction in catalase and glutathione transferase activities. The experiments on Ca²⁺ transport showed an abnormal functional response of aged muscle after exposure to caffeine, which increases the opening of Ca²⁺ channels, as well a reduced activity of the Ca²⁺ pump in elderly males. From these results we conclude that oxidative stress play an important role in muscle aging and that oxidative damage is much more evident in elderly males, suggesting a gender difference maybe related to hormonal factors.This revised version was published online in September 2005 with corrections to the Cover Date.     

Effect of nociceptin on alcohol intake in alcohol-preferring rats

The present study investigated the effect of nociceptin (NC), the endogenous ligand of the opioid-like orphan receptor ORL1, on ethanol intake in genetically selected Marchigian Sardinian alcohol-preferring (msP) rats. Acute intracerebroventricular (ICV) injection of 250 or 500 ng/rat of NC, just before access to 10% ethanol (offered 2 h/day), significantly increased ethanol intake. Subchronic (7 days) ICV injection of 500 ng/rat of NC, given just before access to 10% ethanol (for 30 min/day), resulted in a progressive decrease in ethanol consumption. After the end of NC treatment, rats progressively recovered their usual ethanol intake. When NC, 500 or 1000 ng/rat, was tested versus the effect of ethanol in the place conditioning paradigm, NC significantly reduced the increase in time spent in the ethanol-paired compartment after conditioning. This finding suggests that NC reduces the rewarding properties of ethanol in msP rats; thus, they may respond to the acute NC administration by increasing their ethanol intake in an attempt to achieve the usual reinforcing effect of ethanol, whereas subchronic NC treatment may result in extinction of ethanol drinking. The results of the present study suggest that the brain NC mechanisms may represent an interesting target of pharmacological interventions for the treatment of alcoholism. Received: 11 August 1998/Final version: 15 October 1998     

Characterization of endothelin-1 receptor subtypes in isolated human cardiomyocytes.

On cardiac membranes and isolated cardiomyocytes from the human heart, cell-type distribution and functional activities of endothelin-1 (ET-1) receptor subtypes were investigated by using binding methods and messenger RNA (mRNA) in situ hybridization. The ET-receptor antagonist BMS-182874 selectively and competitively inhibits ET(A) receptors both on isolated myocytes and ventricular membranes with approximately 1,300 times greater affinity for ET(A) than ET(B) subtypes. The [125I]-ET-1 specific binding revealed 42.851+/-2,546 receptors/myocyte with a prevalent proportion of ET(A)-receptor subtypes on both myocytes (84+/-2%) and ventricular membranes (66+/-3%). In situ hybridization studies revealed that mRNA for ET(A) receptors was expressed on both myocytes and nonmyocyte cells, whereas mRNA for ET(B) receptors was almost exclusively expressed on fibroblasts and endothelial cells. Specific binding of [125I]-ET-1 to both myocytes and ventricular membranes in the presence of specific ET(A) (BMS-182874) and ET(B) (BQ-788)-receptor antagonists showed a displacement of [125I]-ET-1 by unlabeled ET-1, which were significantly faster from ET(B) than from ET(A). This suggests a clearance function of ventricular ET(B) receptors.