In the present study we investigated the effects of
NMDA and non-
NMDA glutamate receptor antagonists on the
ischemia-evoked release of [3H]
noradrenaline from rat spinal cord slices. An in vitro
ischemia model (
oxygen and
glucose deprivation) was used to simulate the ischemic conditions known to cause neuronal injury. Spinal cord slices were loaded with [3H]
noradrenaline and superfused with
Krebs solution in a micro-organ bath. Both axonal stimulation and
ischemia increased the release of [3H]
noradrenaline, but the release in response to
glucose and
oxygen deprivation was [Ca2+]o independent.
Dizocilpine (MK-801), an
NMDA receptor antagonist, suppressed the release of [3H]
noradrenaline produced by
ischemia, while it enhanced the release of [3H]
noradrenaline evoked by electrical field stimulation. In contrast, LY300168 (GYKI-53655) [(+/-)-3-N-methylcarbamyde-1-(4-aminophenyl)-4-methyl-1.8-methylen e-dioxy-5H-2.3-
benzodiazepine] and its (-)isomer
LY303070 (GYKI-53784) [(-)-3-N-methylcarbamyde-1-(4-aminophenyl)-4-methyl-1.8-methylene- dioxy-5H-2.3-
benzodiazepine]
AMPA receptor antagonists, had no effect on the release of [3H]
noradrenaline evoked by either electrical stimulation or
ischemia.
Desipramine, a
noradrenaline uptake inhibitor, potentiated the release of [3H]
noradrenaline evoked by
ischemia, while in the absence of [Ca2+]o but under conditions when [3H]
noradrenaline release was further increased, it reduced the release.
Dizocilpine also decreased
glutamate and
aspartate release, measured by high performance liquid chromatography, during
ischemia. It is concluded that
glutamate release and
NMDA receptors, but not
AMPA receptors, are involved in the acute effect of
oxygen and
glucose deprivation on the excessive release of
noradrenaline and that this release is not related to physiological axonal conduction.