Involvement of central muscarinic receptors in social and nonsocial learning in sheep

Within 12 h following parturition, ewes develop visual and auditory recognition of their lamb. To investigate whether central cholinergic muscarinic transmission plays a specific role in this social learning, we studied the effects of a muscarinic antagonist on neonate recognition via visual/auditory cues and acquisition of a nonsocial visual discrimination. Injections of scopolamine (100 microg/kg; a muscarinic antagonist crossing the blood-brain barrier) after birth did not affect maternal behavior but impaired visual/auditory recognition of the offspring. Recognition impairment did not occur in mothers treated with methylscopolamine (100 microg/kg; a peripheral muscarinic antagonist), indicating that central muscarinic transmission is specifically involved in this social learning. Similar doses of scopolamine strongly delayed learning of a nonsocial, visual discrimination task in comparison to either control or methylscopolamine-treated ewes. Performance on this task was not affected when scopolamine treatment was applied after learning, demonstrating that central muscarinic receptors are necessary for acquisition but not for retrieval. These results suggest that the central muscarinic transmission participates in the establishment of visual/auditory recognition of conspecifics. Moreover, activation of central muscarinic receptors is critical for learning regardless of the social properties of the stimulus.