[2] The subsequent discovery of genes encoding enzymes that synthesize dopamine, and transporters that incorporate dopamine into synaptic vesicles or reclaim it after synaptic release, enabled scientists to identify dopaminergic neurons by labeling gene or protein expression that is specific to these neurons.
In the mammalian brain, dopaminergic neurons form a semi-continuous population extending from the midbrain through the forebrain, with eleven named collections or clusters among them.
[4] It is for the most part identical with the pars compacta of the substantia nigra as seen from the accumulation of neuromelanin pigment in the midbrain of healthy, adult humans.
[6] Group A13 is distributed in clusters that, in the primate, are ventral and medial to the mammillothalamic tract of the hypothalamus; a few extend into the reuniens nucleus of the thalamus.
It is located in ventral and dorsal components within the preoptic periventricular nucleus and adjacent parts of the anterior hypothalamic region.
[4] This group is a population of cells immunoreactive for dopamine and tyrosine hydroxylase that are broadly distributed in the rostral forebrain, including such structures as: substantia innominata, diagonal band, olfactory tubercle, prepyriform area, striatum (at levels rostral to the anterior commissure), claustrum, and deep cortical layers of all gyri of the frontal lobe rostral to the head of the caudate nucleus; the cells are also numerous in intervening white matter, including the external capsule, extreme capsule and frontal white matter.