Immunohistochemical Detection of the Putative Mechanoproteins ASIC2 and TRPV4 in Avian Herbst Sensory Corpuscles

The avian Herbst corpuscles are the equivalent of the Pacinian corpuscles in mammals, and detect vibration and the movement of joints and feathers. Therefore, they can be regarded as rapidly adapting low-threshold mechanoreceptors. In recent years, it has been establish that some ion channels are involved in mechanosensation and are present in both mechanosensory neurons and mechanoreceptors. Here we have used immunohistochemistry to localize some putative mechanoproteins in the Herbst corpuscles from the rictus of Columba livia. The proteins investigated were the subunits of the epithelial Na(+) channel (ENaC), the transient-receptor potential vanilloid 4 (TRPV4), and the acid-sensing ion channel 2 (ASIC2). Immunoreactivity for ENaC subunits was never found in Herbst corpuscles, while the axon expressed ASIC2 and TRPV4 immunoreactivity. Moreover, TRPV4 was also detected in the cell forming the inner core. The present results demonstrate for the first time the occurrence of mechanoproteins in avian low-threshold mechanoreceptors and provide further evidence for a possible role of the ion channels in mechanosensation.