This lecture explores the mechanisms that ensure neurotransmitter signals have an “off switch”:
Three Termination Mechanisms:
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Diffusion:
- Neurotransmitter molecules naturally spread out from the release site.
- Only molecules within reach of the postsynaptic cell’s receptors can be detected.
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Reuptake:
- Presynaptic neurons have transporters that “recycle” released neurotransmitters.
- This is crucial for maintaining neurotransmitter economy and preventing excessive stimulation.
- Drugs like cocaine target reuptake transporters, influencing neurotransmitter levels and potentially leading to addiction.
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Enzymatic Degradation:
- Specific enzymes in the synaptic cleft break down certain neurotransmitters.
- Acetylcholinesterase (AChE) is an example that rapidly degrades acetylcholine.
- Blocking AChE with drugs like physostigmine can be used to treat conditions like myasthenia gravis where acetylcholine signaling is weak.
- Conversely, organophosphate pesticides act as AChE inhibitors, leading to excessive muscle contraction and potentially fatal respiratory failure.
Key Points:
- Termination mechanisms ensure controlled and transient neurotransmitter signaling.
- Reuptake and degradation play a vital role in regulating neurotransmitter levels and their effects.
- Understanding these mechanisms is crucial for developing drugs that target specific neurotransmitter systems. Receptors