Chapter 12 - Ontogeny of Neurotransmitters: Monoamines

Abstract

The monoaminergic neurotransmitter systems that innervate the mammalian central nervous system (CNS) include the catecholamine neurotransmitters dopamine and norepinephrine, and the indoleamine serotonin. The perikarya of the monoaminergic neurotransmitter systems undergo histogenesis very early in CNS development. Neurons expressing dopamine, norepinephrine, or serotonin can be visualized by immunohistochemical or fluorescence histochemical methods by embryonic day (ED) 12–13 in the brainstem of the rat. Neurons that synthesize norepinephrine are found only in the pontine and medullary tegmental regions of the brainstem. The primary aggregation of noradrenergic neurons is the locus coeruleus. Serotonin synthesizing neurons are found in the mesencephalon, pons, and medulla oblongata. These neurons are distributed mainly within the raphe nuclei. The raphe nuclei that provide the majority of the serotonergic innervation to the forebrain are the dorsal raphe, the median raphe, and the caudal linear raphe nucleus. The neurochemical processes that take place at the synapse may be characterized as being presynaptic or postsynaptic in nature. It is found that the high affinity uptake of monoaminergic neurotransmitters is primarily a function of the presynaptic monoaminergic terminal.