The raphe nuclear organization and serotonergic system in the bat ( <i>Artibeus planirostris</i> )

5-Hydroxytryptamine (5-HT), widely recognized as serotonin, is a multifunctional substance present across various body tissues, performing as a neurotransmitter within the nervous framework. Serotonergic neurons are predominantly localized within the raphe nuclei of the brainstem, rendering neuronal 5-HT a definitive marker for these nuclei. Research has substantiated serotonin's role in the modulation of thermoregulation, appetite, reproductive drive, circadian patterns, slumber, motoric activity, and cognitive processing. While the anatomical structure of serotonergic systems has undergone extensive review in mammalian species, such as rodents, rabbits, felines, and non-human primates, it remains unexplored in South American bat species. This investigation sought to delineate the serotonergic architecture in the cerebrum of Artibeus planirostris through the application of serotonin immunohistochemistry. The study used six adult males Artibeus planirostris (family Phyllostomidae, class Mammalia). Following anesthesia and perfusion, their brains were sectioned. Coronal brain sections were acquired using a sliding microtome and processed with an immunohistochemical assay specific to 5-HT. Caudal linear (CLi), dorsal (DR), median (MnR), paramedian (PMnR), pontine (PnR), magnus (RMg), pallidus (RPa), and obscurus (ROb) raphe nuclei, as well as the B9 and rostral and caudal ventrolateral (rVL/cVL) groups, were marked. Contrary to the serotonergic structures commonly observed in bats, A. planirostris dorsal raphe showed a distinct nuclear subdivision, while the median raphe exhibited bilateral representation. The morphometric analysis in this study does not show significant differences in the size of the neuronal area among raphe nuclei. Fresh insights into the field of neuroanatomy are offered by these results, which emphasize potential variations in brain structure among echolocating species in South America as opposed to the more commonly researched models in bats, rodents, and non-human primates.