Noradrenergic influences on blocking: interactions with development.

Two experiments assessed the effects of various noradrenergic agents on selective attention. Selective attention was operationally defined as blocking of a conditioned odor aversion by prior conditioning to spatial cues. In Experiment 1, there was a trend for such blocking to increase developmentally. In addition, the administration of isoproterenol prior to training tended to facilitate the demonstration of blocking in adolescent rats and reduced it in adult subjects. In Experiment 2, administration of yohimbine or propranolol prior to training also reduced blocking in adult subjects; however, the concomitant administration of these two drugs restored blocking in adult rats. These results were interpreted to support a model relating an optimal level of noradrenergic activity in the dorsal bundle and selective attention.