Selective lesioning of forebrain noradrenaline neurons at birth abolishes the improved maze learning performance induced by rearing in complex environment

The effect of selective destruction of forebrain noradrenaline (NA) neurons induced by 6-hydroxydopamine (6-OHDA) at Day 1 after birth on Hebb-Williams maze performance was investigated in adult rats housed after weaning in a complex environment (EC) or an isolated (IC) environment for 35 days. Saline treated control rats raised in the EC made fewer errors than those raised in the IC. This effect of EC was completely abolished in 6-OHDA treated rats; for these animals no improved performance due to the housing condition was obtained. Protection of the NA neurons against 6-OHDA neurotoxicity by pretreatment with desipramine (DMI) resulted in an effect of EC identical to that seen in saline-treated controls. Postweaning housing in the IC led to an increased locomotion as compared to housing in EC, but this effect was not affected by neonatal 6-OHDA and/or DMI treatment. Neurochemical analysis confirmed cortical NA and metabolite depletion as well as a good protection by the DMI pretreatment. The present results indicate that central NA neurons are involved critically in mediating mainly the cognitive components of behavioral alterations induced by EC.