The cytoarchitectonic and TH-immunohistochemical characterization of the dopamine cell groups in the substantia nigra, ventral tegmental area and retrorubral field in a bat (Artibeus planirostris)

- The SNC shows an unusual subdivision not reported previously in bats.
- The VTA is divided into seven neuronal clusters in A. Planirostris.
- SN neurons have a significantly higher cellular area than the VTA, and RRF.

The dopamine (DA) neurons of the retrorubral field (RRF - A8), the substantia nigra (SN - A9), and the ventral tegmental area (VTA - A10) have been implicated in motor regulation, reward, aversion, cognition, and several neuropsychiatric disorders. A series of studies have identified subdivisions of these cell groups in rodents, but these cell groups have not been well described in bats. An understanding of the motor system organization in bats would provide a context for comparing motor systems across rodent, primate, and bat phylogenies. The aim of this work was to determine whether typical subdivisions of RRF, SN, and VTA are present in Artibeus planirostris, a common frugivorous bat species found throughout South America. Coronal and sagittal sections of bat brain were subjected to Nissl staining and TH immunohistochemistry. The organizational pattern of the nuclei in A. planirostris showed a conspicuous tail in the SN, which has been not described in bats to date, and also contained a well-defined substantia nigra reticulata (SNR) not previously reported in microbats. This work provides for the first time a morphometric analysis of DA neurons in a microchiropteran species, enabling a comparative investigation of vertebrates. Our analysis revealed an apparent phylogenetic stability in these structures, although the SN tail might represent a functional specialization in this species.