An anomaly in the communication from a neuron to a target across a synapse. This is a four step process, comprising (i) synthesis and storage of neurotransmitters; (ii) neurotransmitter release; (iii) activation of postsynaptic receptors by the neurotransmitter; and (iv) inactivation of the neurotransmitter. Thus, this term is defined as an anomaly of neurotransmitter metabolic process. [from
HPO]