Neurotransmitters are defined by four essential characteristics. These are: Neurotransmitters are synthesized within presynaptic neurons. Depolarization of a neuron results in the release of a neurotransmitter, which exerts a multitude of actions on the postsynaptic neuron. Their action on postsynaptic neurons can be replicated by administering a drug that mimics the activity of the endogenous neurotransmitter. Their action in the synaptic cleft is terminated by a specific action. A, C, and D only

The correct answer is A, C, and D only.

Explanation:

A neurotransmitter is a biomolecule, generally synthesized by neurons, which is poured from vesicles in the presynaptic neuron into the synaptic gap and produces a change in the action potential of the postsynaptic neuron. Depending on the nature of the neurotransmitter, this can be synthesized in the neuronal soma or in the nerve endings. Some neurotransmitters are synthesized directly in nerve endings thanks to enzymes that have been synthesized in the soma and transported to these endings. Through the interior of the axon flows a current of substances free or enclosed in vesicles, which can be precursors of both neurotransmitters or their enzymes, called axonal flow.Another characteristic of the transmitter function in each of the substances commonly accepted as neurotransmitters is that when administered exogenously as a drug that in reasonable concentrations perfectly mimics the effects of the endogenously released transmitter.