Acetylcholine release in the rat hippocampus as measured by the microdialysis method correlates with motor activity and exhibits a diurnal variation.
Extracellular levels of acetylcholine were measured by the microdialysis method coupled to high performance liquid chromatography in the dorsal hippocampus of freely moving rats over a period of 24 h to examine whether the acetylcholine release in the hippocampus exhibited a diurnal variation. Spontaneous motor activity was simultaneously measured with an automatic animal activity monitor. The amount of acetylcholine collected per 20-min sample varied markedly, in a range from about 5 to 90 pmol. There appeared to be variations in the amount with a 2-4 h periodicity as well as an apparent diurnal periodicity. In all five rats studied, the overall mean value for the dark cycle (11.1-34.5, average 20.9 pmol/20 min) was significantly greater than that for the light cycle (5.1-21.3, average 12.3 pmol/20 min), showing a 70% average increase. Cross-correlation analysis performed between the amount of acetylcholine and the motor activity count for the animal during the sampling revealed a significant positive correlation coefficient in four rats studied. The present study demonstrates for the first time that the acetylcholine release shows a diurnal variation.
Mizuno
T
T
Department of Physiology, Yokohama City University School of Medicine, Japan.
Endo
Y
Y
Arita
J
J
Kimura
F
F
D000109:Acetylcholine / Q000378:metabolism*; D000818:Animals; D002940:Circadian Rhythm; D003956:Dialysis; D006624:Hippocampus / Q000378:metabolism*; D008297:Male; D009043:Motor Activity; D051381:Rats; D011919:Rats, Inbred Strains; D012636:Secretory Rate
D000109:Acetylcholine