The entorhinal cortex of Megachiroptera: a comparative study of Wahlberg's epauletted fruit bat and the straw-coloured fruit bat

This study describes the organisation of the entorhinal cortex of the Megachiroptera, Strawcoloured fruit bat and Wahlberg’s epauletted fruit bat. Using Nissl and Timm stains, parvalbumin and SMI-32 immunohistochemistry, we identified 5 fields within the medial(MEA) and lateral (LEA) entorhinal areas. MEA fields ECL and EC are characterised by a poor differentiation between layers II and III, a distinct layer IV and broad, stratified layers V and VI. LEA fields EI, ER and EL are distinguished by cell clusters in layer II, a clear differentiation between layers II and III, a wide columnar layer III, and a broad sublayer Va. Clustering in LEA layer II was more typical of the Straw-coloured fruit bat. Timm-staining was most intense in layers Ib and II across all fields, and layer III of field ER. Parvalbuminlike staining varied along a medio-lateral gradient with highest immunoreactivity in layers II and III of MEA and more lateral fields of LEA. Sparse SMI-32-like immunoreactivity was seen only in Wahlberg’s epauletted fruit bat. Of the neurons in MEA layer II, ovoid stellate cells account for ~38%, polygonal stellate cells for ~8%, pyramidal cells for ~18%, oblique pyramidal cells for ~6%, and other neurons of variable morphology for ~29%. Differences between bats and other species in cellular make-up and cytoarchitecture of layer II may relate to their 3-dimensional habitat. Cytoarchitecture of layer V in conjunction with high encephalisation and structural changes in the hippocampus suggest similarities in efferent hippocampal-entorhinal-cortical interactions between fruit bats and primates