Exogenous monoamines affect the segregation of retinogeniculate fibers in developing rats

The development of retinogeniculate projections was examined in rats which had norepinephrine levels altered by subcutaneous administration of 6-hydroxydopamine (6-OHDA) or exogenous norepinephrine (NE) during early postnatal life. NE, but not 6-OHDA, treatment resulted in an abnormal segregation of crossed and uncrossed axons at postnatal day 10, such that projections from the two eyes occupied extensively overlapping territory. This effect is at least partially reversible since in animals examined 30 days after cessation of NE treatment the retinogeniculate projections ultimately became segregated.