Department of Psychiatry, Iwaki Kyoritsu General Hospital, Iwaki, Japan
Received Date: July 12, 2016; Accepted Date: August 05, 2016; Published Date: August 10, 2016
Citation: Ikemoto K (2016) So Called - D-Neuron. J Cytol Histol 7:421. doi:10.4172/2157-7099.1000421
Copyright: © 2016 Ikemoto K. This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.
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The D-neuron in the rat central nervous system (CNS) was described by Jaegeret al. in 1983. Initially, they defined as “the nonmonoaminergic aromatic L-amino acid decarboxylase (AADC)- containing cell”, and called the “D-cell”. AADC is an equivalent enzyme to dopa decarboxylase (DDC). The D-cell contains AADC but not dopaminergic nor serotonergic. Then, it is natural that the D-cell is thought to produce the trace amine (TA), such as β-phenylethylamine (PEA), tyramine, tryptamine and octopamine. AADC is the ratelimiting enzyme for TA synthesis. However, it is confusing that these TAs are also “monoamines”, as each TA has one amino residue. D-cells which Jaeger et al. reported were proved to be neurons by electromicroscopic observation, and they are also called D-neurons. The latter is much more accurate nomenclature.
The localizations of D-neurons were specified into 14 groups, from D1 (the spinal cord) to D14 (the bed nucleus of stria terminalis) in caudo-rostral orders of the rat central nervous system using AADC immunohistochemistry. In this usage, the classification term “D” means decarboxylation. In rodents, a small number of D-neurons in the striatum were rostrally described. The author reported in 1997,“dopa-decarboxylating neurons specific to the human striatum”, that is, “D-neurons” in the human striatum (classified to be D15) and the nucleus accumbens (Acc, D16) (Figure 1), though monkey striatum did not contain D-neurons in these areas. By using human post-mortem brain materials, D-neurons have been also described in the basal forebrain (D17) and the cerebral cortex (D18). In humans, D-neuron system is far developed in the forebrain. Corresponding to anatomical nomenclature of amine neurons, that is, A group for catecholamine neurons (A1-A16), B group for serotonergic neurons (B1-B14), and C group for epinephrine (adrenergic) neurons (C1-C3), D group is used as the classification term for TA neurons (D1-D18) .
In 2003, by using pathological and legal autopsy brains of patients with schizophrenia, reduction of D-neurons in the striatum (D15) and Acc (D16) of patients with schizophrenia was also shown. This finding lead to establish D-cell hypothesis of schizophrenia, that links dopamine hypothesis to neural stem cell (NSC) dysfunction hypothesis, explaining molecular mechanisms of mesolimbic dopamine hyperactivity (Figure 1).