The Distribution and Morphological Characteristics of Cholinergic Cells in the Brain of Monotremes as Revealed by ChAT Immunohistochemistry

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.

Nuclear organisation of some immunohistochemically identifiable neural systems in five species of insectivore —Crocidura cyanea, Crocidura olivieri, Sylvisorex ollula, Paraechinus aethiopicus and Atelerix frontalis

“…Choline acetyltransferase immunoreactive neurons (ChAT+) were identified in all these subdivisions, except the cortical interneurons, which were absent in all five species of insectivore studied. The nuclei forming the cholinergic system in these species were similar to that observed in previously studied mammals (Woolf, 1991;Manger et al, 2002a;Dell et al, 2010;Kruger et al, 2010a), but there were a few minor differences. The neurons forming the parabigeminal nucleus (PBg) were either not ChAT immunoreactive or absent in all three shrew species, but were present in the two hedgehog species.…”

“…The following cranial nerve motor nuclei and other associated nuclei with ChAT immunopositive neurons were found in positions typical of all mammals in all five species (Woolf, 1991;Manger et al, 2002a;Dell et al, 2010;Kruger et al, 2010a): the oculomotor nucleus (III), trochlear nucleus (IV), motor division of trigeminal nerve nucleus (Vmot) (Fig. 4A, 4B), adbucens nucleus (VI), dorsal and ventral subdivisions of the facial nerve nucleus (VIId and VIIv), nucleus ambiguus, dorsal motor vagus nucleus (X), hypoglossal nucleus (XII), the preganglionic motor neurons of the superior salivatory nucleus or facial nerve (pVII), the preganglionic motor neurons of the inferior salivatory nucleus (pIX) and the ventral horn of the spinal cord (vh) (Figs.…”

The Distribution and Morphological Characteristics of Catecholaminergic Cells in the Brain of Monotremes as Revealed by Tyrosine Hydroxylase Immunohistochemistry

“…In the two companion papers to this, regarding cholinergic and serotonergic cells of monotremes [see Manger et al, 2002a, b], we found no such relationship. Woolf [1991] proposed a relationship between cholinergic cell size and brain width, but our comparison [Manger et al, 2002a] does not support this hypothesis. Unfortunately, the data on somatal areas of CA neurons from different species is limited.…”

Nuclear organisation of some immunohistochemically identifiable neural systems in three Afrotherian species—Potomogale velox, Amblysomus hottentotus and Petrodromus tetradactylus

“…These nuclei were found in positions typical of all mammals (Woolf, 1991;Manger et al, 2002a;Maseko et al, 2007;Dell et al, 2010;Kruger et al, 2010). The ChAT+ nucleiidentified in the three Afrotherian species studied include: the oculomotor (III), trochlear (IV), motor division of thetrigeminal (Vmot), adbucens (VI), dorsal and ventral subdivisionsof the facial (VIId and VIIv), nucleus ambiguus, dorsal motor vagus(X), hypoglossal (XII), Edinger-Westphal (EW), medullary tegmentalfield (mtf) andthe preganglionic motor neurons of thesalivatory (pVII) and the glossopharyngeal (pIX) nerves (Figs.…”