Immunocytochemical localization of tyrosine hydroxylase in the visual cortex of the microbat, Rhinolophus ferrumequinum

In order to enhance our understanding of bat vision, we investigated tyrosine hydroxylase (TH)-immunoreactive (IR) fibers in the visual cortex of the microbat. The study was conducted on 12 freshly-caught adult bats (Rhinolophus ferrumequinum, both sexes, weighing 15-20 g). We used standard immunocytochemistry and confocal microscopy. TH-IR fibers were distributed throughout all layers of the visual cortex, with the highest density in layer I. Two types of TH-IR fibers were observed: small and large varicose fibers. TH-IR cells were not found in the microbat visual cortex. The microbat substantia nigra and ventral tegmental areas, previously identified sources of TH-IR fibers in the mammalian visual cortex, all contained strongly labeled TH-IR cells. The average diameters of TH-IR cells in the substantia nigra and the ventral tegmental areas were 14.39 ± 0.13 μm (mean ± SEM) and 11.85 ± 0.13 μm, respectively. Our results suggest that the microbat has a well-constructed neurochemical organization of THIR fibers. This observation should provide fundamental insights into a better understanding of the nocturnal, echolocating bat visual system.