Influence of Neonatal Hypothyroidism and of Thyroxine on the Acetylcholinesterase and Cholinesterase Activities in the Developing Central Nervous System of the Rat

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Abstract
The activities of the enzymes acetylcholinesterase (AChE) and cholinesterase (ChE) were determined in the brain of weanling female rats following a hypothyroid condition induced by radiodestruction of the thyroid gland at 1 day of age and after thyroid hormone therapy initiated from the 6th day of age. Enzyme activities were expressed as mean rates in [mu] imoles substrate hydrolyzed per unit wet tissue and per unit deoxyribonucleic acid (DNA) concentration. Neonatal hypothyroidism resulted in a significant reduction in AChE and ChE in the cerebral cortex and AChE in the hypothalamus compared with controls. The administration of physiological levels of thyroxine (10 [mu]g/100 g body weight) restored brain growth and enzyme activity to normal. The present results show that thyroid hormone deficiency alters enzyme activity in the developing brain of the rat. These alterations may be related to the structural and neuro-physiological changes which occur under the same experimental conditions.