“…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.…”