Long-term changes in noradrenaline (NA) and dopamine (DA) contents of rat cerebellum following neonatal X-irradiation

Abstract

The effects of neonatal X-irradiation on cerebellar cathecholamine levels in rats were studied at different postnatal intervals. Since synaptogenesis in the cerebellar cortex is basically a postnatal phenomenon, changes in noradrenaline (NA) and dopamine (DA) levels induced by X-rays on the cerebella (CE) of adult rats (60 days old) were also studied. With 200 rad at birth there was an increase in both NA (+ 75%) and DA (+ 40%) levels at day 30, with a return to control values by day 90. CE weight did not change with this dose. Both 500 and 700 rad given at birth induced a persistent increase in NA levels, even when studied at day 390 (+ 127%) and a long-term decrease in DA levels. A marked atrophy of CE was found, even at day 390 (a 61% decrease in weight). Histologic analysis showed that the cerebellar cortex lacked its interneurons (agranular cerebellar cortex) and that Purkinje cells were randomly arranged. Rats showed dystonia, fine tremor, posterior train ataxia and microcephalia. On the other hand, X-irradiation of adult rats did not change cerebellar catecholamine levels or produced cerebellar atrophy. These animals did not show motor deficits or microcephalia. Taken together, these results suggest that the long-term changes in cerebellar catecholamine levels induced by neonatal X-irradiation may be somehow related to the loss of cerebellar interneurons which develop early in the postnatal period, although a primary change(s) in the activity of noradrenergic neurons can not be excluded.