Rapid decrease and restoration of acetylcholinesterase activity in the hypothalamus of the rat in response to suckling stimulus.

Abstract

The effect of the suckling stimulus on the acetylcholinesterase (AchE) activity was determined in the whole hypothalamus, the anterior and posterior parts of the hypothalamus in lactating rats. On the morning of the 7th or the 8th day of lactation, the mother was isolated from her young for 8hr. Then, eight pups were placed with the mother and allowed to suckle. The time when the mother was reunited with her pups was designated as zero time of suckling. The animals were guillotined at 2, 5 and 15min of suckling. The AchE activity was measured colorimetrically. Suckling for 2min induced a significant decrease in the AchE activity in the anterior part of the hypothalamus. Thereafter, the activity was restored gradually and returned to the pre-suckling level at the end of the 15min-suckling period. A similar trend was found in the changes of the activity both in the posterior part of the hypothalamus and in the whole hypothalamus, although the changes were not significant. These results suggest that a cholinergic mechanism in the anterior part of the hypothalamus relates with the release of oxytocin in response to the suckling stimulus.