| Abstract: | Acetylcholinesterase and butyrylcholinesterase activities in sensori-motor cortex, hypothalamus, cerebellum, and brain stem were compared in normally developing Long-Evans rats and after neonatal whole-body exposure to 450 r X-radiation. Enzyme activities were measured on three postnatal days: day 10, when brain is still immature; day 24, when it has reached functional and morphological maturity; and day 64, after sexual maturation. In controls, acetylcholinesterase and butyrycholinesterase activities increased with age in all areas, especially between 10 and 24 days; e.g., in sensori-motor cortex acetylcholinesterase activity increased 60 per cent from 10 to 24 days and 12 per cent from 24 to 64 days. At all ages acetylcholinesterase activity was highest in the brain stern, followed in decreasing order by the hypothalamus, cerebellum, and sensori-motor cortex. Butyrylcholinesterase activity was higher in subcortical than in cortical areas. In neonatally irradiated rats, acetylcholinesterase activity was significantly decreased in the ontogenetically newer structures at 10, but not at 64, days; in the hypothalamus, it remained normal at 10 days but was significantly decreased at 24 and 64 days. Butyrylcholinesterase activity was significantly decreased in some areas 1 week after radiation but returned to normal at 24 days. Total esterase activity in whole blood was signtficantly decreased at 10 days in irradiated rats but returned to control levels by the end of the experiment. The greatest post-radiation decline in acetylcholinesterase activity (60 per cent below controls) did not result in spontaneous gross behaviour alterations, but may be related to disturbances in functional brain maturation evidenced by specific tests. If the role of acetycholine as a central neurotransmitter is accepted, these data suggest that radiation alters acetycholine/acetylcholinesterase ratios and thereby cholinergie synaptic transmission. |
