Glycinergic nerve endings in hippocampus and spinal cord release glycine by different mechanisms in response to identical depolarizing stimuli

Abstract

Studies on hippocampal glycine release are extremely rare. We here investigated release from mouse hippocampus glycinergic terminals selectively pre‐labelled with [3H]glycine through transporters of the GLYT2 type. Purified synaptosomes were incubated with [3H]glycine in the presence of the GLYT1 blocker NFPS to abolish uptake (∼ 30%) through GLYT1. The non‐GLYT1‐mediated uptake was entirely sensitive to the GLYT2 blocker Org25543. Depolarization during superfusion with high‐K+ (15–50 mmol/L) provoked overflows totally dependent on external Ca2+, whereas in the spinal cord the 35 or 50 mmol/L KCl‐evoked overflow (higher than that in hippocampus) was only partly dependent on extraterminal Ca2+. In the hippocampus, the Ca2+‐dependent 4‐aminopyridine (1 mmol/L)‐evoked overflow was five‐fold lower than that in spinal cord. The component of the 10 μmol/L veratridine‐induced overflow dependent on external Ca2+ was higher in the hippocampus than that in spinal cord, although the total overflow in the hippocampus was only half of that in the spinal cord. Part of the veratridine‐evoked hippocampal overflow occurred by GLYT2 reversal and part by bafilomycin A1‐sensitive exocytosis dependent on cytosolic Ca2+ generated through the mitochondrial Na+/Ca2+ exchanger. As glycine sites on NMDA receptors are normally not saturated, understanding mechanisms of glycine release should facilitate pharmacological modulation of NMDA receptor function.

Glycine transporters type 1 inhibitor promotes brain preconditioning against NMDA-induced excitotoxicity

“…The mechanisms of expression, regulation and internalization of glycine transporters have not been fully elucidated yet, but the inhibition of GlyT1 by NFPS could be triggering a compensatory mechanism of exchange of GlyT1 to GlyT2 (Luccini et al, 2008;Jim enez et al, 2011). In accordance to this hypothesis, NFPS Fig.…”

“…Nevertheless, at some conditions, the glycine transporters (GlyT1 and GlyT2) show opposite actions (Luccini et al, 2008;Jim enez et al, 2011). For instance, the stimulation of purinergic receptors (PY2R) led to a functional inhibition of GlyT2 and stimulation of GlyT1 through the same signal transduction pathways, whereas lithium exposition inhibits GlyT1 and stimulate GlyT2 (Jim enez et al, 2011;P erez-Siles et al, 2011).…”

High-affinity GABA uptake by neuronal GAT1 transporters provokes release of [3H]GABA by homoexchange and through GAT1-independent Ca2+-mediated mechanisms

“…Evidence was provided for vesicular exocytotic release independent of external Ca 2þ but triggered by Ca 2þ ions mobilized from intraterminal stores (for a review, see Berridge, 1998). Internal Ca 2þ can be mobilized from different pools, depending on the stimulus applied to nerve endings and it can mediate transmitter release by different modes (Luccini et al, 2008;Romei et al, 2011). Cytosolic Na þ increases can lead to transmitter release by mobilizing internal Ca 2þ through mitochondrial Na þ /Ca 2þ exchangers (Rizzuto and Pozzan, 2006;Palty et al, 2012).…”

Beta Amyloid Differently Modulate Nicotinic and Muscarinic Receptor Subtypes which Stimulate in vitro and in vivo the Release of Glycine in the Rat Hippocampus

“…Being aware that several neurotransmitters that play important roles in cognitive functions could be affected either directly or indirectly by Aβ, we focused our attention on GLY. Indeed increasing evidence demonstrate that GLY is an important aminoacid at hippocampal level which has a dual role (a) acting as an inhibitory neurotransmitter when interacting with the strychnine-sensitive receptors and (b) playing a fundamental stimulatory role when co-activating excitatory N -Methyl- d -aspartic acid receptors together with glutamate (Johnson and Ascher, 1987; Hirai et al, 1996; Luccini et al, 2008; Kubota et al, 2010; Zappettini et al, 2011). The changes in the GLY release may therefore directly interfere with glutamate neurotransmission, which plays an important role in the processes of learning and memory in this brain area.…”

“…Increasing evidence demonstrate that glycine (GLY) is an important aminoacid at hippocampal level which may have a dual role acting as an inhibitory neurotransmitter, when interacting with the strychnine-sensitive receptors, and playing a stimulatory role, when co-activating excitatory N -Methyl- d -aspartic acid receptors together with glutamate (Johnson and Ascher, 1987; Luccini et al, 2008; Romei et al, 2009, 2011; Zappettini et al, 2011). No data are available so far on the possible effects of Aβ on the cholinergic receptors which modulate GLY release at the hippocampal level.…”