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Magnesium sulfate treatment decreases N-methyl-D-aspartate receptor binding in the rat brain: an autoradiographic
M Hallak1, R F Berman, S M Irtenkauf
1Department of Obstetrics and Gynecology, Wayne State University, Hutzel Hospital, Detroit, MI 48201, USA.
Objective:
We determined the effect of peripherally administered magnesium sulfate on N-methyl-D-aspartate (NMDA) receptor binding capacity in various regions of the rat brain.
Methods:
Three separate experiments were performed. 1) Six rats were injected intraperitoneally with 270 mg/kg of magnesium sulfate, followed by 27 mg/kg every 20 minutes for 4 hours; controls (n = 6) received saline. 2) Six rats received intraperitoneal injections of magnesium sulfate (270 mg/kg) every 4 hours for 24 hours, while six received saline. 3) Six rats received intraperitoneal magnesium sulfate (270 mg/kg) every 12 hours for a total of 2 weeks, and six received saline. Rats were subsequently perfused and sacrificed, and their brains were dissected, rinsed, and frozen. Cryostat sections were taken, labeled by in vitro [3H]-CGP 39653, assayed autoradiographically, and mounted on Ultrofilm for 4 weeks. Optical density measurements of binding on each section were performed using an image analyzing system. Eleven brain regions were sampled: 1, 2) frontal and occipital cortex; 3-7) hippocampus--CA-1, CA-3, stratum radiatum, stratum oriens, dentate gyrus; 8) thalamus; 9) hypothalamus; 10) caudate nucleus; and 11) cerebellum.
Results:
The NMDA receptor binding density in the hippocampus was significantly higher than in all other brain regions in all three experiments. In experiment 1, there was no significant effect on NMDA receptor binding. However, prolonged systemic administration of magnesium sulfate for 24 hours resulted in significantly reduced [3H]-CGP binding in all brain regions sampled. After chronic magnesium sulfate administration (2 weeks), the [3H]-CGP binding was still reduced in the cortex and some regions of the hippocampus; however, there was no significant change in other regions.
Conclusions:
Peripheral treatment with magnesium sulfate results in a significant reduction in the NMDA receptor binding capacity in the rat brain. These results support the hypothesis that magnesium central activity is mediated, at least in part, via the NMDA receptor.
Insights
Peripheral magnesium sulfate administration significantly reduces N-methyl-D-aspartate (NMDA) receptor binding capacity in the rat brain, particularly with prolonged exposure. These findings suggest magnesium
Area of Science:
- Neuroscience
- Pharmacology
- Neurochemistry
Background:
- The N-methyl-D-aspartate (NMDA) receptor is a crucial ionotropic glutamate receptor involved in synaptic plasticity and memory.
- Magnesium ions play a vital role in modulating NMDA receptor activity, acting as a channel blocker.
- Understanding the central effects of peripherally administered magnesium sulfate is essential for its therapeutic applications.
Purpose of the Study:
- To investigate the impact of peripherally administered magnesium sulfate on NMDA receptor binding capacity in distinct regions of the rat brain.
- To determine the dose- and time-dependent effects of magnesium sulfate on NMDA receptor density.
- To explore the potential mechanism of magnesium's central action through NMDA receptor modulation.
Main Methods:
- Three experimental groups of rats received varying durations and frequencies of intraperitoneal magnesium sulfate injections or saline controls.
- Brain tissue was collected, dissected into eleven specific regions, and frozen for cryostat sectioning.
- NMDA receptor binding capacity was quantified using in vitro [3H]-CGP 39653 labeling and autoradiography, followed by optical density measurements.
Main Results:
- The hippocampus exhibited the highest NMDA receptor binding density across all experimental groups.
- Short-term magnesium sulfate administration showed no significant effect on NMDA receptor binding.
- Prolonged administration (24 hours and 2 weeks) of magnesium sulfate led to a significant reduction in [3H]-CGP binding across most sampled brain regions, including the cortex and hippocampus.
Conclusions:
- Peripheral administration of magnesium sulfate effectively reduces NMDA receptor binding capacity in the rat brain, particularly with sustained exposure.
- These findings support the hypothesis that the central effects of magnesium are, at least partly, mediated through interaction with the NMDA receptor system.
- The study highlights the potential for magnesium sulfate to modulate glutamatergic neurotransmission centrally.
