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

Abstract

The present study describes the organization of the cholinergic, catecholaminergic, serotonergic and orexinergic (hypocretinergic) neurons in the brains of the giant otter shrew, the Hottentot golden mole and the four-toed sengi, three members of the mammalian super order Afrotheria. The aim of the present study was to investigate the possible differences in the nuclear complement of these neural systems in comparison to previous studies on other Afrotheria species and other mammalian species. Brains of the golden mole, sengi and giant otter shrew were coronally sectioned and immunohistochemically stained with antibodies against cholineacetyl-transferase, tyrosine hydroxylase, serotonin and orexin-A. The majority of nuclei revealed in the current study were similar between the species investigated, to other Afrotherian species investigated, and to other mammals, but certain differences in the nuclear complement highlighted phylogenetic interrelationships. The golden mole was seen to have cholinergic interneurons in the cerebral cortex, hippocampus, olfactory bulb and amygdala. The four-toed sengi had cholinergic neurons in both colliculi and in the cochlear nucleus, but lacked the catecholaminergic A15d group in the hypothalamus. In both the golden mole and the four-toed sengi, the locus coeruleus (A6d group) was made up of few neurons. The golden mole also exhibited an unusual foreshortening of the brain, such that a major kink in the brainstem was evident. The results of this study, framed in a phylogenetic context, appear to indicate that the golden mole and four-toed sengi share a more recent common ancestor that diverged from the tenrec lineage early in the phylogenetic history of the Afrotherians.