Final answer:
A presynaptic neuron can regulate neurotransmitter release through auto receptors, which provide feedback based on neurotransmitter levels, and through presynaptic inhibition or facilitation where another neuron influences neurotransmitter release.
Step-by-step explanation:
A presynaptic neuron can regulate neurotransmitter release through two main mechanisms:
- Auto receptors: These are receptors located on the presynaptic neuron's membrane that bind to the neurotransmitters it releases. When activated by high levels of the neurotransmitter, these autoreceptors can signal the neuron to reduce neurotransmitter release, effectively serving as a feedback mechanism to downregulate transmission.
- Presynaptic Inhibition or Facilitation: Another neuron can also affect the amount of neurotransmitter the presynaptic neuron releases through axoaxonic synapses. For example, if a neurotransmitter released by neuron A binds to neuron B's axon terminal (presynaptic to neuron C), it can inhibit or enhance the release of neurotransmitter from neuron B onto neuron C, thus upregulating or downregulating neurotransmitter release.
These mechanisms ensure the balance and proper function of neural communication, preventing excessive or insufficient neurotransmitter activity in the synaptic cleft.