Adrenaline (Ad) strengthens contextual fear memory by increasing blood glucose, possibly enhancing hippocampus acetylcholine synthesis. Nevertheless, it is unclear if peripheral Ad influences the cholinergic system, contributing to contextual fear memory strengthening. We aimed to evaluate whether peripheral Ad alters muscarinic receptor expression and if the cholinergic system is involved in peripheral Ad contextual fear memory strengthening effect. Wild-type (WT) and Ad-deficient male mice (129x1/SvJ) underwent a fear conditioning procedure followed by intraperitoneal pre-training and pre-context administration of Ad (0.1 mg/kg), atropine (10 mg/kg), methylatropine (0.5 mg/kg), Ad (0.1 mg/kg) plus atropine (10 mg/kg) or vehicle (NaCl, 0.9%). Shock responsiveness and freezing behaviour were accessed. Hippocampal M