Low-level N-methyl-D-aspartate receptor activation provides a purinergic inhibitory threshold against further N-methyl-D-aspartate-mediated neurotransmission in the cortex. 1992

C G Craig, and T D White
Department of Pharmacology, Dalhousie University, Halifax, Nova Scotia, Canada.

N-methyl-D-aspartate (NMDA) is 33 times more potent at releasing adenosine than it is at releasing [3H]norepinephrine from slices of rat parietal cortex. Consequently, maximal adenosine release occurs at levels of NMDA receptor activation which release little norepinephrine. The potential modulatory role of the adenosine released during NMDA receptor activation on NMDA-evoked [3H]norepinephrine release was investigated. The A1-selective agonist R-(-)N6-(2-phenylisopropyl)adenosine (10 microM) decreased 100 microM NMDA-evoked [3H]norepinephrine release by 27%; this was reversed by the P1 antagonist 8-phenyltheophylline (8-PT, 10 microM), indicating that NMDA-evoked norepinephrine release from cortical slices is susceptible to purinergic modulation. On the other hand, 8-PT had no effect on [3H]norepinephrine release evoked by 100 microM NMDA, suggesting that endogenous adenosine, released during NMDA receptor activation, does not modulate [3H]norepinephrine release. However, [3H]norepinephrine release precedes adenosine release, so that the released adenosine may not be temporally available to modulate [3H]norepinephrine release. Pretreatment with a concentration of NMDA (10 microM) which releases substantial endogenous adenosine, but very little [3H]norepinephrine decreased subsequent 100 microM NMDA-evoked [3H]norepinephrine release by 52%. 8-PT partially reversed this inhibition, indicating that prereleased adenosine, acting at P1 purinoceptors, modulated subsequent NMDA-evoked [3H]norepinephrine release. These results suggest that adenosine, released during submaximal NMDA receptor activation, may provide an inhibitory threshold which must be overcome in order for other NMDA-mediated processes to proceed maximally.

UI MeSH Term Description Entries
D008297 Male Males
D009435 Synaptic Transmission The communication from a NEURON to a target (neuron, muscle, or secretory cell) across a SYNAPSE. In chemical synaptic transmission, the presynaptic neuron releases a NEUROTRANSMITTER that diffuses across the synaptic cleft and binds to specific synaptic receptors, activating them. The activated receptors modulate specific ion channels and/or second-messenger systems in the postsynaptic cell. In electrical synaptic transmission, electrical signals are communicated as an ionic current flow across ELECTRICAL SYNAPSES. Neural Transmission,Neurotransmission,Transmission, Neural,Transmission, Synaptic
D009638 Norepinephrine Precursor of epinephrine that is secreted by the ADRENAL MEDULLA and is a widespread central and autonomic neurotransmitter. Norepinephrine is the principal transmitter of most postganglionic sympathetic fibers, and of the diffuse projection system in the brain that arises from the LOCUS CERULEUS. It is also found in plants and is used pharmacologically as a sympathomimetic. Levarterenol,Levonorepinephrine,Noradrenaline,Arterenol,Levonor,Levophed,Levophed Bitartrate,Noradrenaline Bitartrate,Noradrénaline tartrate renaudin,Norepinephrin d-Tartrate (1:1),Norepinephrine Bitartrate,Norepinephrine Hydrochloride,Norepinephrine Hydrochloride, (+)-Isomer,Norepinephrine Hydrochloride, (+,-)-Isomer,Norepinephrine d-Tartrate (1:1),Norepinephrine l-Tartrate (1:1),Norepinephrine l-Tartrate (1:1), (+,-)-Isomer,Norepinephrine l-Tartrate (1:1), Monohydrate,Norepinephrine l-Tartrate (1:1), Monohydrate, (+)-Isomer,Norepinephrine l-Tartrate (1:2),Norepinephrine l-Tartrate, (+)-Isomer,Norepinephrine, (+)-Isomer,Norepinephrine, (+,-)-Isomer
D010660 Phenylisopropyladenosine N-Isopropyl-N-phenyl-adenosine. Antilipemic agent. Synonym: TH 162. Isopropylphenyladenosine,L-Phenylisopropyladenosine,N(6)-Phenylisopropyl-Adenosine,L Phenylisopropyladenosine
D011919 Rats, Inbred Strains Genetically identical individuals developed from brother and sister matings which have been carried out for twenty or more generations or by parent x offspring matings carried out with certain restrictions. This also includes animals with a long history of closed colony breeding. August Rats,Inbred Rat Strains,Inbred Strain of Rat,Inbred Strain of Rats,Inbred Strains of Rats,Rat, Inbred Strain,August Rat,Inbred Rat Strain,Inbred Strain Rat,Inbred Strain Rats,Inbred Strains Rat,Inbred Strains Rats,Rat Inbred Strain,Rat Inbred Strains,Rat Strain, Inbred,Rat Strains, Inbred,Rat, August,Rat, Inbred Strains,Rats Inbred Strain,Rats Inbred Strains,Rats, August,Rats, Inbred Strain,Strain Rat, Inbred,Strain Rats, Inbred,Strain, Inbred Rat,Strains, Inbred Rat
D002540 Cerebral Cortex The thin layer of GRAY MATTER on the surface of the CEREBRAL HEMISPHERES that develops from the TELENCEPHALON and folds into gyri and sulci. It reaches its highest development in humans and is responsible for intellectual faculties and higher mental functions. Allocortex,Archipallium,Cortex Cerebri,Cortical Plate,Paleocortex,Periallocortex,Allocortices,Archipalliums,Cerebral Cortices,Cortex Cerebrus,Cortex, Cerebral,Cortical Plates,Paleocortices,Periallocortices,Plate, Cortical
D000241 Adenosine A nucleoside that is composed of ADENINE and D-RIBOSE. Adenosine or adenosine derivatives play many important biological roles in addition to being components of DNA and RNA. Adenosine itself is a neurotransmitter. Adenocard,Adenoscan
D000818 Animals Unicellular or multicellular, heterotrophic organisms, that have sensation and the power of voluntary movement. Under the older five kingdom paradigm, Animalia was one of the kingdoms. Under the modern three domain model, Animalia represents one of the many groups in the domain EUKARYOTA. Animal,Metazoa,Animalia
D016194 Receptors, N-Methyl-D-Aspartate A class of ionotropic glutamate receptors characterized by affinity for N-methyl-D-aspartate. NMDA receptors have an allosteric binding site for glycine which must be occupied for the channel to open efficiently and a site within the channel itself to which magnesium ions bind in a voltage-dependent manner. The positive voltage dependence of channel conductance and the high permeability of the conducting channel to calcium ions (as well as to monovalent cations) are important in excitotoxicity and neuronal plasticity. N-Methyl-D-Aspartate Receptor,N-Methyl-D-Aspartate Receptors,NMDA Receptor,NMDA Receptor-Ionophore Complex,NMDA Receptors,Receptors, NMDA,N-Methylaspartate Receptors,Receptors, N-Methylaspartate,N Methyl D Aspartate Receptor,N Methyl D Aspartate Receptors,N Methylaspartate Receptors,NMDA Receptor Ionophore Complex,Receptor, N-Methyl-D-Aspartate,Receptor, NMDA,Receptors, N Methyl D Aspartate,Receptors, N Methylaspartate
D016202 N-Methylaspartate An amino acid that, as the D-isomer, is the defining agonist for the NMDA receptor subtype of glutamate receptors (RECEPTORS, NMDA). N-Methyl-D-aspartate,NMDA,N-Methyl-D-aspartic Acid,Acid, N-Methyl-D-aspartic,N Methyl D aspartate,N Methyl D aspartic Acid,N Methylaspartate

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