Nuclear organization of cholinergic, putative catecholaminergic and serotonergic systems in the brains of two megachiropteran species

Abstract

The nuclear organization of the cholinergic, putative catecholaminergic and serotonergic systems within the brains of the megachiropteran straw-coloured fruit bat ( Eidolon helvum) and Wahlberg's epauletted fruit bat ( Epomophorus wahlbergi) were identified following immunohistochemistry for cholineacetyltransferase, tyrosine hydroxylase and serotonin. The aim of the present study was to investigate possible differences in the nuclear complement of the neuromodulatory systems of these species in comparison to previous studies on megachiropterans, microchiropterans and other mammals. The nuclear organization of these systems is identical to that described previously for megachiropterans and shows many similarities to other mammalian species, especially primates; for example, the putative catecholaminergic system in both species presented a very compact nucleus within the locus coeruleus (A6c) which is found only in megachiropterans and primates. A cladistic analysis of 38 mammalian species and 82 characters from these systems show that megachiropterans form a sister group with primates to the exclusion of other mammals, including microchiropterans. Moreover, the results indicate that megachiropterans and microchiropterans have no clear phylogenetic relationship to each other, as the microchiropteran systems are most closely associated with insectivores. Thus a diphyletic origin of Chiroptera is supported by the present neural findings.