Muscarinic M1 and M2 receptors, fasting and seizure development in animals

Muscarinic M-1 and M-2 receptors are widely distributed in the brain and contribute to various physiological and pathological functions. It is well known that enhancement of cholinergic activity produces convulsions in animals. Pilocarpine, the M-1 muscarinic receptor agonist, is commonly used to induce seizures in rodents. On the other hand it has been reported that fasted rats and mice pretreated with the M-1 and M-2 receptor antagonist atropine, scopolamine or biperiden develop convulsions after food intake indicating cholinergic hypoactivity as the underlying mechanism. This review will present pharmacological data for the M-1 and M-2 receptors in the brain and focus on the contrasting findings related to their contribution to convulsions

Contribution of M-1 and M-2 muscarinic receptor subtypes to convulsions in fasted mice treated with scopolamine and given food

Treatment of fasted mice and rats with the nonselective muscarinic antagonist, scopolamine or atropine, causes convulsions after food intake. This study evaluated the effect of fasting on the expression of M-1 and M-2 muscarinic receptors in the brain regions, the relationship between receptor expression and seizure stages, and the muscarinic receptor subtype which plays a role in the occurrence of convulsions. Mice were grouped as allowed to eat ad lib (fed) and deprived of food for 24 h (fasted). Fasted animals developed convulsions after being treated with scopolamine (60%) or the selective M-1 receptor antagonist pirenzepine (10 mg/kg; 20% and 60 mg/kg; 70%) and given food. Fasting increased expression of M-1 receptors in the frontal cortex and M-2 receptors in the hippocampus, but produced no change in the expression of both receptors in the amygdaloid complex. Food intake after fasting decreased M-1 receptor expression in the frontal cortex and M-1 and M-2 receptor expression in the hippocampus. Seizure severity was uncorrelated with muscarinic receptor expression in the brain regions. Taken together, these findings provide evidence for the role of M-1 muscarinic receptor antagonism and fasting-induced increases in M-1 and M-2 expression possible underlying mechanism in the occurrence of convulsions in fasted animals

Contribution of M-1 and M-2 muscarinic receptor subtypes to convulsions in fasted mice treated with scopolamine and given food

Treatment of fasted mice and rats with the nonselective muscarinic antagonist, scopolamine or atropine, causes convulsions after food intake. This study evaluated the effect of fasting on the expression of M-1 and M-2 muscarinic receptors in the brain regions, the relationship between receptor expression and seizure stages, and the muscarinic receptor subtype which plays a role in the occurrence of convulsions. Mice were grouped as allowed to eat ad lib (fed) and deprived of food for 24 h (fasted). Fasted animals developed convulsions after being treated with scopolamine (60%) or the selective M-1 receptor antagonist pirenzepine (10 mg/kg; 20% and 60 mg/kg; 70%) and given food. Fasting increased expression of M-1 receptors in the frontal cortex and M-2 receptors in the hippocampus, but produced no change in the expression of both receptors in the amygdaloid complex. Food intake after fasting decreased M-1 receptor expression in the frontal cortex and M-1 and M-2 receptor expression in the hippocampus. Seizure severity was uncorrelated with muscarinic receptor expression in the brain regions. Taken together, these findings provide evidence for the role of M-1 muscarinic receptor antagonism and fasting-induced increases in M-1 and M-2 expression possible underlying mechanism in the occurrence of convulsions in fasted animals