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NMDA-receptor-independent effects of low magnesium: involvement of adenosine
T W Stone1, J H Connick, J T Bartrup
1Department of Pharmacology, University of Glasgow, Scotland, U.K.
Abstract:
Perfusion of hippocampal slices with magnesium-free media elicits epileptiform activity attributable partly to the activity of N-methyl-D-aspartate (NMDA) receptors, but recent reports have documented an NMDA-independent enhancement of orthodromic potentials by moderate reductions in magnesium concentration. The present experiments indicate that this enhancement is comparable with that produced by perfusion with an adenosine antagonist, 8-phenyltheophylline, and that superfusion with this compound or adenosine deaminase precludes any enhancement of potential size in low magnesium solutions. The low magnesium enhancement is probably attributable to the recently described magnesium dependency of presynaptic inhibition by adenosine.
Insights
Reduced magnesium enhances brain activity by blocking adenosine, a key factor in presynaptic inhibition. This finding sheds light on N-methyl-D-aspartate (NMDA) receptor-independent mechanisms in neural potentiation.
Area of Science:
- Neuroscience
- Neurophysiology
- Molecular Biology
Background:
- N-methyl-D-aspartate (NMDA) receptors are implicated in epileptiform activity.
- Previous studies noted NMDA-independent potentiation of neural activity by reduced magnesium.
- Adenosine plays a role in modulating synaptic transmission.
Purpose of the Study:
- To investigate the mechanism behind NMDA-independent potentiation of orthodromic potentials in low magnesium.
- To explore the role of adenosine in magnesium-dependent synaptic enhancement.
- To determine if adenosine antagonism mimics or occludes the effects of low magnesium.
Main Methods:
- Perfusion of hippocampal slices with magnesium-free and low magnesium solutions.
- Application of adenosine antagonist (8-phenyltheophylline) and adenosine deaminase.
- Measurement of orthodromic potentials to assess synaptic transmission.
Main Results:
- Moderate reduction in magnesium concentration enhanced orthodromic potentials independently of NMDA receptors.
- This enhancement was comparable to perfusion with 8-phenyltheophylline.
- Superfusion with 8-phenyltheophylline or adenosine deaminase blocked the low magnesium-induced enhancement.
- The findings suggest magnesium-dependent presynaptic inhibition by adenosine.
Conclusions:
- Low magnesium enhances synaptic transmission by inhibiting adenosine's presynaptic inhibitory effects.
- Adenosine signaling is a critical component of magnesium-dependent modulation of neuronal excitability.
- This mechanism contributes to understanding epileptiform activity and synaptic plasticity.