Critical postnatal period for the induction of a long-term increase in the noradrenaline content of rat cerebellum by X-irradiation

Abstract

Abstract Littermate Wistar rats were X-irradiated according to different schemes, and noradrenaline (NA) levels were determined in adult cerebella (CE) (90 days old). When animals were exposed to a 200 rad (2.0 Gy) single dose immediately after birth, and two doses (150 rad/dose) 24 and 48 h postnatally, there was a significant increase in NA content (+56.7%), without a marked cerebellar atrophy. Purkinje cells failed to arrange in their characteristic monolayer, and their apical pole was randomly oriented. After applying doses of 150 rad on days 4, 5, 7, 9, 11, 13 and 15, there was also a net increase in NA content (+74%), with a marked decrease in the weight of CE (34% of controls). Disarrangement and disorientation of Purkinje cells were also found. In another group, doses of 150 rad on days 8, 9, 11, 13, 15 and 17 postnatally, failed to induce a significant change in NA content, but atrophy of CE (50% of controls) resulted in an increase of NA concentration (−133%). Purkinje cells were lined up in a monolayer. On the other hand, rats exposed to doses of 150 rad on days 12, 13, 15, 17 and 19 postnatally did not show either changes of NA levels in cerebellum or marked histological abnormalities in the cerebellar cortex. This lack of changes in the variables measured was also found in rats X-irradiated with a single dose of 150 rad on postnatal day 7. These results suggest that X-rays applied within a critical period of cerebellar development (days 0–6 postnatally) produce a long-term increase in NA content, time-related to the disarrangement of Purkinje cells (the main target for NA terminals in CE), induced by the ionizing treatment.