Dopaminergic Innervation of the Nidopallium Caudolaterale in the Japanese Quail

Convergent evolution illustrates how distantly related lineages develop comparable traits and abilities in response to similar ecological pressures. In birds, the nidopallium caudolaterale (NCL) is an executive function hub analogous to the mammalian prefrontal cortex, despite their distant roots and major differences in gross structure. While the NCL has been studied in pigeons, songbirds, and chickens, its organization in other Galliformes remains unclear. Here, we investigated the NCL in the Japanese quail (Coturnix japonica), a Galliform species commonly used in studies of reproductive behavior and appetitive conditioning. Using immunohistochemistry for tyrosine hydroxylase, we mapped dopaminergic projections from the ventral tegmental area and substantia nigra, quantified fiber density relative to surrounding pallial regions, and characterized axonal arborizations. We identified postsynaptic targets of tyrosine hydroxylase-positive fibers and examined their neurochemical profiles, including putative glutamatergic neurons expressing CaMKIIa and interneuron subpopulations expressing parvalbumin, calbindin, calretinin, or secretagogin. The NCL of the Japanese quail exhibited dense dopaminergic innervation primarily targeting principal neurons, with only sparse en passant contacts on interneuron populations, following the pattern observed in other Galliformes. These findings indicate that dopaminergic modulation of the NCL is conserved across Galliformes and support the use of the Japanese quail as a model for studying executive circuits and cognitive neurobiology in birds.