AJP - Regulatory, Integrative and Comparative Physiology, Vol 273, Issue 1 359-R363, Copyright © 1997 by American Physiological Society
Vitamin B12 enhances GABA content but reduces glutamate content in the rat suprachiasmatic nucleus
M. Ikeda, S. Azuma and S. Inoue
Institute for Medical and Dental Engineering, Tokyo Medical and Dental University, Japan.
The present study attempted to elucidate effects of vitamin B12 (VB12) on
the rat suprachiasmatic nucleus (SCN), which is the locus of the circadian
clock in mammals, by evaluating the contents of its major
neurotransmitters, gamma-aminobutyric acid (GABA) and glutamate (Glu).
First, contents of these amino acids were analyzed from tissue samples
prepared at three different circadian times (CTs) in free-running rats
under constant dim illumination. The content of GABA was highest in the
middle of the resting phase (CT 6), intermediate early in the active phase
(CT 14), and lowest late in the active phase (CT 20), whereas Glu content
indicated inverse circadian variations. Subsequently, effects of
intracerebroventricularly infused VB12 were assayed at CT 20. Compared with
the saline-infused control, the infusion of VB12 (30 nmol/30 microliters)
at CT 12-15 significantly increased GABA content but decreased Glu content.
The quantitative balance of these amino acids after VB12 infusion was
similar to that at CT 6 in noninfused rats. These results suggest that
infusion of VB12 to active rats shifts the ratio of SCN neurotransmitters
toward that observed in resting rats.
