Tyrosine hydroxylase-immunoreactive neurons in the human cerebral cortex: a novel catecholaminergic group?

Neurochemical characterization of tyrosine hydroxylase-immunoreactive interneurons in the developing rat cerebral cortex

“…No catecholamine-synthesizing enzymes subsequent to TH, including AADC, have been observed in TH-IR neurons in the developing or adult rodent or primate cortex, calling into question the catecholaminergic status of these cells (Berger et al, 1985;Gaspar et al, 1987;Satoh and Suzuki, 1990;Ikemoto et al, 1999;Weihe et al, 2006). Additionally, in the developing rat, labeling of the cortical TH-IR neurons was insensitive to 6-hydroxydopamine toxicity, and no endogenous catecholamines were detected in cortical somata (Berger et al, 1985).…”

“…These TH cells, however, remain enigmatic because of their species-specific laminar distribution, lack of additional catecholaminergic traits, and developmental characteristics. In the rat cortex, TH-IR neurons were observed mainly in layer II/III (Berger et al, 1985;Kosaka et al, 1987a;1987b), whereas in the mouse (Satoh and Suzuki, 1990) and human (Gaspar et al, 1987;Hornung et al, 1989;Kuljis et al, 1989;Trottier et al, 1989;Ikemoto et al, 1999;Benavides-Piccione and DeFelipe, 2003;Marui et al, 2003;Benavides-Piccione and DeFelipe, 2007), TH-IR neurons were seen predominantly in layers V and VI. Not only are these TH neurons outside the classically-defined catecholaminergic cell groups (Hokfelt et al, 1984), but their final transmitter phenotype is also uncertain.…”

“…Not only are these TH neurons outside the classically-defined catecholaminergic cell groups (Hokfelt et al, 1984), but their final transmitter phenotype is also uncertain. In all species examined, cortical TH-IR cells failed to express any catecholaminergic enzymes subsequent to TH, including aromatic amino acid decarboxylase (AADC), which synthesizes dopamine (Berger et al, 1985;Gaspar et al, 1987;Ikemoto et al, 1999;Weihe et al, 2006). Although very few TH-IR cells were noted in the adult rat cortex in classical TH distribution studies (Hokfelt et al, 1984), later reports described a population of cortical TH-IR cells that were observed transiently during postnatal development in the rat (Berger et al, 1985) and mouse (Satoh and Suzuki, 1990).…”

“…A subset of cortical neurons also expresses TH in the rodent (Berger et al, 1985;Kosaka et al, 1987a;1987b;Satoh and Suzuki, 1990), non-human primate (Weihe et al, 2006), and human (Gaspar et al, 1987;Hornung et al, 1989;Kuljis et al, 1989;Trottier et al, 1989;Fukuda et al, 1999;Ikemoto et al, 1999;Benavides-Piccione and DeFelipe, 2003;Marui et al, 2003;Benavides-Piccione and DeFelipe, 2007). Based on their size, morphology, and partial colocalization with GABA, cortical TH-IR cells were hypothesized to be interneurons.…”

Molecular signaling of 5-HT<sub>1A</sub> and presence of serotonergic cells in the fetal cerebral cortex

“…In conclusion it seems possible that as it happens with serotonergic fibers that augment significantly during certain periods of corticogénesis and after some time they decrease to normal, the serotonergic cells here described in the fetal neopallium in culture or in situ, could transiently express the serotonergic phenotype that would possibly allow them to participate directly in the structuration processes of the cerebral cortex, to disappear afterwards, as it happens with the mentioned TH positive cells [18,31].…”