The distribution and morphological characteristics of cholinergic cells in the brain of monotremes as revealed by ChAT immunohistochemistry.

TitleThe distribution and morphological characteristics of cholinergic cells in the brain of monotremes as revealed by ChAT immunohistochemistry.
Publication TypeJournal Article
Year of Publication2002
AuthorsManger, PR, Fahringer HM, Pettigrew JD, Siegel JM
JournalBrain, behavior and evolution
Volume60
Issue5
Pagination275-97
Date Published2002
ISSN0006-8977
KeywordsAnimals, Biological Evolution, Brain, Brain Mapping, Choline O-Acetyltransferase, Cholinergic Fibers, Echidna, hypothalamus, Immunoenzyme Techniques, Neurons, Phylogeny, Platypus, sleep
Abstract

The present study employs choline acetyltransferase (ChAT) immunohistochemistry to identify the cholinergic neuronal population in the central nervous system of the monotremes. Two of the three extant species of monotreme were studied: the platypus (Ornithorhynchus anatinus) and the short-beaked echidna (Tachyglossus aculeatus). The distribution of cholinergic cells in the brain of these two species was virtually identical. Distinct groups of cholinergic cells were observed in the striatum, basal forebrain, habenula, pontomesencephalon, cranial nerve motor nuclei, and spinal cord. In contrast to other tetrapods studied with this technique, we failed to find evidence for cholinergic cells in the hypothalamus, the parabigeminal nucleus (or nucleus isthmus), or the cerebral cortex. The lack of hypothalamic cholinergic neurons creates a hiatus in the continuous antero-posterior aggregation of cholinergic neurons seen in other tetrapods. This hiatus might be functionally related to the phenomenology of monotreme sleep and to the ontogeny of sleep in mammals, as juvenile placental mammals exhibit a similar combination of sleep elements to that found in adult monotremes.

Alternate JournalBrain Behav. Evol.