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.