Acetylcholinesterase in the hypothalamo-hypophyseal axis of the white-crowned sparrow, zonotrichia leucophrys gambelii

Abstract

Considerable acetylcholinesterase (AChE) activity was found in the median eminence (1.2 × 10⁻⁵ mmoles/minute/mg tissue) and adenohypophysis (4 × 10⁻⁵ mmoles/minute/mg tissue) of the white-crowned sparrow whereas low activity was found in the neurohypophysis (0.3 × 10' mmoles/minute/mg tissue).

Acetylcholinesterase activity in the adenohypophysis of photosensitive birds was 50 times greater than activity in the adenohypophysis of photorefractory birds. Also, photosensitive birds held on 8-hour daily photoperiods (8L 16D), then placed in continuous light, showed a striking periodicity in AChE activity in the adenohypophysis with the peak of activity corresponding to the time of maximal testicular response to light. Acetylcholinesterase activity in the cephalic lobe of the adenohypophysis was significantly higher than in the caudal lobe.

There was a consistent daily cycle of AChE activity in the median eminence of photosensitive birds held on 8L 16D, with a gradual decrease in AChE activity during the course of the subjective day (low of 0.8 × 10⁻⁵ mmoles/minute/mg tissue to high of 1.6 × 10⁻⁵ mmoles/minute/mg tissue). Also, there was a trend toward a. decreasing mean activity of AChE with increasing photosensitivity in birds held on 8L 16D. No consistent daily cycle of AChE activity could be demonstrated in photosensitive birds on 20L 4D.

Cholinesterase activity was low (0.049–0.122 × 10⁻⁵ mmoles/minute/mg tissue) in all tissues examined except the adenohypophysis in which moderate activity (0.27–1.20 × 10⁻⁵ mmoles/minute/mg tissue) was found.