The influence of thyroid gland and thyroxine on the acetylcholinesterase activity of rat brain and adenohypophysis.

Acetylcholinesterase (AChE) activity in the cerebral cortex, amygdala, hypothalamus, pons, medulla oblongata and adenohypophysis of intact, thyroidectomized, and thyroxine treated-thyroidectomized adult male rats was determined by a spectrophotometric method. AChE activity was higher in the brain areas than in the adenohypophysis. There was regional variation in the enzyme activity in the brain with the highest and lowest activities occurring in the medulla oblongata and the cerebral cortex, respectively. Thyroidectomy increased AChE activity in the pons, decreased it in the amygdala, but did not alter it in the other brain areas and adenohypophysis. Thyroxine treatment of thyroidectomized rats had no effect on AChE activity in any of the areas studied.