AJP - Cell Physiology, Vol 260, Issue 2 C213-C218, Copyright © 1991 by American Physiological Society
Dual effect of glycine on isolated rat suprachiasmatic neurons
C. Ito, M. Wakamori and N. Akaike
Department of Neurophysiology, Tohoku University School of Medicine, Sendai, Japan.
Pharmacological properties of strychnine-sensitive and -insensitive glycine
receptors have been investigated in rat suprachiasmatic nucleus (SCN)
neurons. Because the SCN neurons were too small for stable intracellular
recordings by the glass-microelectrode technique, a conventional whole cell
mode patch-clamp technique was employed on the acutely dissociated SCN
neurons. Dissociated SCN neurons were morphologically heterogeneous and
could be distinguished into several types. All cells responded to glycine
in a concentration-dependent manner. The glycine-induced current was
primarily Cl- sensitive and competitively blocked by strychnine. The SCN
neurons also responded to excitatory amino acids: glutamate, quisqualate,
kainate, and N-methyl-D-aspartate (NMDA). Responses to glutamate and
aspartate, which are endogenous neurotransmitter candidates, were enhanced
by adding glycine. Glycine especially augmented the maximum response to
NMDA in a full concentration range. 6-Cyano-7-nitroquinoxaline-2,3-dione
(CNQX) did not suppress the strychnine-sensitive glycine response but did
suppress the strychnine-insensitive NMDA response in a competitive manner
for glycine. The results suggest that glycine influences neural activity in
the SCN as a classical inhibitory neurotransmitter and an excitatory
neuromodulator.
