SCOPOLAMINE IMPAIRS THE ABILITY OF PARTURIENT EWES TO LEARN TO RECOGNIZE THEIR LAMBS

Within a 4-h period after parturition, the ewe learns the odor of her lamb that will later allow recognition of her offspring from an alien lamb. This study investigated the involvement of the cholinergic syste m in this olfactory learning. At parturition and 2 h later, ewes recei ved IM injections of saline (C group, n = 21), scopolamine methylbromi de (METSCOP group, 100 mu g/kg, n = 14) a peripherally acting muscarin ic antagonist, a low dose of scopolamine hydrobromide (SCOP32 group, 3 2 mu g/kg, n = 15) or a higher dose of scopolamine hydrobromide (SCOP1 00 group, 100 mu g/kg, n = 18). Maternal behavior was observed at part urition and selective behavior was tested after 4 h of mother-young co ntact. No differences in maternal behavior at parturition were found b etween groups. By contrast, the proportion of ewes showing selectivity was significantly lower in the SCOP100 group (7/18) than in the METSC OP group (12/14, P = 0.01), SCOP32 group (12/15, P = 0.03), or C group (17/21, P = 0.01). In addition, saline-treated ewes, after having est ablished their selective bond, received 100 mu g/kg scopolamine and we re again tested for selectivity 20 min later. Only one out of the 17 t ested ewes failed to recognize their lambs after this treatment. These results indicate that intact central muscarinic transmission of the b rain is required for the learning of individual lamb odor at parturiti on but not for the recall of this information.