Mechanisms of Glycine Release in Mouse Brain Stem Slices

Abstract

In the brain stem glycine is associated with multiple sensory and visceral regulations, being involved in, for instance, cardiovascular, respiratory and auditory functions. We here studied the mechanisms of the release of preloaded [(3)H]glycine from mouse brain stem slices in a superfusion system. A depolarizing concentration of K(+) ions (50 mM) evoked glycine release, but in the absence of Ca(2+) the effect was attenuated, indicating that a part of the evoked release represents Ca(2+)-dependent exocytosis. The Ca(2+)-independent release was enhanced by omission of Na(+) and Cl(-). The stimulatory effect of extracellular glycine confirmed the involvement of transporters functioning in a reverse direction. A part of the release is mediated by Na(+) and Cl(-) channels, since it was inhibited by the inhibitors of these, riluzole and 4-acetamido-4'-isothiocyanostilbene-2,2'-disulphonate, respectively. Glycine release was potentiated by the activation of protein kinase C and diminished by increasing cyclic guanosine monophosphate levels with a phosphodiesterase inhibitor, zaprinast. The release was also modulated by the phospholipase inhibitor quinacrine and the tyrosine kinase inhibitor genistein. Adenosine A(1) receptors likewise regulate glycine release, since it was enhanced by their agonist R(-)N(6)-(2-phenylisopropyl)adenosine, which effect was blocked by the antagonist 8-cyclopentyl-1,3-dipropylxanthine. The ionotropic glutamate receptor agonists N-methyl-D: -aspartate, kainate and 2-amino-3-hydroxy-5-methyl-4-isoxazolepropionate failed to have any effects contrary to their effects in higher brain regions, e.g., in the hippocampus. The group I and III metabotropic glutamate receptor agonists (S)-3,5-dihydroxyphenylglycine and O-phospho-L: -serine, respectively, increased the release in a receptor-mediated manner. Glycine release in the brain stem was also markedly enhanced by cell-damaging conditions, including hypoxia, hypoglycemia and ischemia.

Release of Endogenous Amino Acids from the Hippocampus and Brain Stem from Developing and Adult Mice in Ischemia

“…stimulation was greater in the hippocampus. The present results on the release of endogenous glycine are in keeping with our earlier finding that preloaded labeled glycine is released in appreciable amounts from both immature and mature mouse hippocampus [20] and brain stem [31]. Glutamate and aspartate are known to be released from brain tissue by depolarizing concentrations of K ?…”

GAD65/GAD67 double knockout mice exhibit intermediate severity in both cleft palate and omphalocele compared with GAD67 knockout and VGAT knockout mice

“…Here, it is necessary to consider the presence of glycinergic transmission that is not mediated by VGAT. Glycine can be released in a Ca 2+ -independent manner through glycine transporters localized on plasma membrane (Arago´n and Lo´pez-Corcuera, 2003;Saransaari and Oja, 2009). Furthermore, radial glial cells release glycine via volume-sensitive chloride channels in the fetal mouse spinal cord (Scain et al, 2010).…”

Direct in vivo measurement of glycine and the neurochemical profile in the rat medulla oblongata

“…In addition to its roles in neurotransmission and neuromodulation, Gly is the precursor of metabolites such as purines, creatine (Cr) and glutathione (GSH), and may be incorporated in lipids and proteins 2. The enhancement of Gly release in the brainstem has been proposed to be a neuroprotective mechanism against metabolic noxious stimuli, such as hypoxia, hypoglycaemia and ischaemia 3. In addition, lesions of MO are involved in several pathologies, such as hypertension 4 and multiple sclerosis 5.…”