Final answer:
Increasing extracellular magnesium concentrations generally leads to a decrease in neurotransmitter release due to its blocking effect on NMDA receptors. However, the overall impact on neurotransmitter release can depend on whether the neurotransmitter in question utilizes pathways that involve these receptors.
Step-by-step explanation:
The question What will happen to neurotransmitter release when magnesium is added to the extracellular solution? can be addressed by looking at the physiology of neurotransmitter release at synapses. Magnesium ions (Mg2+) have a known effect on NMDA (N-methyl-D-aspartate) receptors, which are involved in synaptic transmission. These receptors are cation channels that play a role in the depolarization of the postsynaptic membrane through the influx of positively charged ions such as Na+ and Ca2+ when activated.
Magnesium ions naturally block NMDA receptors at resting membrane potentials but are expelled from the channel upon depolarization. Therefore, increasing extracellular magnesium concentration could enhance this blocking effect, leading to a decreased probability of the receptor's channel opening, which in turn would lead to a decrease in neurotransmitter-induced depolarization events.
However, it is worth noting that the effect of magnesium on neurotransmitter release may not be uniform across all types of receptors or neurotransmitters. The option D) It depends on the neurotransmitter acknowledges the diversity of neurotransmitter systems and their differing responses to extracellular magnesium. For example, neurotransmitters that do not rely on NMDA receptor-mediated pathways might not be as affected by changes in extracellular magnesium levels.