Distribution of parvalbumin, calbindin and calretinin containing neurons and terminal networks in relation to sleep associated nuclei in the brain of the giant Zambian mole-rat (Fukomys mechowii)

To broaden the understanding of the neural control and evolution of the sleep-wake cycle in mammals, the distribution and interrelations of sleep associated nuclei with neurons and terminal networks expressing the calcium-binding proteins parvalbumin, calbindin and calretinin were explored in a rodent that lacks a significant visual system. The sleep-associated nuclei explored include the cholinergic basal forebrain and pontine nuclei, the catecholaminergic locus coeruleus complex, the serotonergic dorsal raphe nuclear complex, the hypothalamic orexinergic nuclei, and the thalamic reticular nucleus. Zambian mole-rat brains were sectioned and stained in a one in nine series for Nissl, myelin, choline acetyltransferase (ChAT), tyrosine hydroxylase (TH), serotonin (5HT), orexin (OrxA), calbindin (CB), calretinin (CR) and parvalbumin (PV). We observed that while the density of immunopositive calbindin (CB+) neurons and terminal networks varied in the different sleep related nuclei, they were found in all nuclei apart from the compact and diffuse subdivisions of the subcoeruleus, which lacked CB+ neurons but evinced a CB+ terminal network. The density of calretinin immunopositive (CR+) neurons and terminal networks varied between the sleep related nuclei, but was present in all nuclei examined. Neurons and terminal networks associated with PV immunoreactivity were the most sparsely distributed in these nuclei, but were present in the majority of nuclei. The thalamic reticular nucleus had the highest density of PV+ neurons and terminal networks, while PV+ neurons were absent in the cholinergic pontine nuclei, and PV+ neurons and terminal networks were absent in the orexinergic nuclei. The increased presence of neurons and terminal networks expressing the calcium binding proteins in comparison to that seen in the laboratory rat, specifically in the brainstem, may account for the prominent muscle twitches during REM sleep previously observed in this subterranean African rodent.