Nuclear parcellation of pontine catecholaminergic and cholinergic neurons in gray parrots and pied crow brains

Employing immunohistochemical procedures with antibodies raised against tyrosine hydroxylase (TH) and choline acetyltransferase we identified and mapped the locus coeruleus complex (LoC) and the pontine laterodorsal tegmental (LDT) and pedunculopontine tegmental (PPN) cholinergic nuclei in the brains of a Congo gray parrot, a timneh gray parrot, and a pied crow. The LoC and LDT/PPN are centrally involved in the regulation and generation of different sleep states, and as all birds studied to date show both REM and non-REM sleep states, like mammals, we investigated whether these noradrenergic and cholinergic nuclei in the avian pons shared anatomical features with those in the mammalian pons. The LoC was parcellated into 3 distinct nuclei, including the locus coeruleus (A6), subcoeruleus (A7), and the fifth arcuate nucleus (A5), while distinct LDT and PPN nuclei were revealed. Several similarities that allow the assumption of homology of these nuclei between birds and mammals were revealed, including their location relative to each other and other structures within the pontine region, as well as a specific degree of topographical overlap of the noradrenergic and cholinergic neurons. Despite this, some differences were noted that may be of interest in understanding the differences in sleep between birds and mammals. Further anatomical and physiological studies are needed to determine whether these pontine nuclei in birds play the same role as in mammals, as while the homology is apparent, the functional analogy needs to be revealed.