Abstract
Previous studies reported that a subpopulation of mouse and rat trigeminal neurons express water channel aquaporin-1 (AQP1). In this study we make a comparative investigation of AQP1 localization in the human and mouse trigeminal systems. Immunohistochemistry and immunofluorescence results showed that AQP1 was localized to the cytoplasm and cell membrane of some medium and small-sized trigeminal neurons. Additionally, AQP1 was found in numerous peripheral trigeminal axons of humans and mice. In the central trigeminal root and brain stem, AQP1 was specifically expressed in astrocytes of humans, but was restricted to nerve fibers within the central trigeminal root and spinal trigeminal tract and nucleus in mice. Furthermore, AQP1 positive nerve fibers were present in the mucosal and submucosal layers of human and mouse oral tissues, but not in the muscular and subcutaneous layers. Fluorogold retrograde tracing demonstrated that AQP1 positive trigeminal neurons innervate the mucosa but not skin of cheek. These results reveal there are similarities and differences in the cellular localization of AQP1 between the human and mouse trigeminal systems. Selective expression of AQP1 in the trigeminal neurons innervating the oral mucosa indicates an involvement of AQP1 in oral sensory transduction.
Highlights
Aquaporins (AQPs) function as water selective channels providing a major route for osmotically driven water transport through cell membranes [1]
Immunoreactivity for AQP1 was localized to the cytoplasm and cell membrane of medium and small-sized trigeminal neurons in humans and mice, as demonstrated by the immunohistochemistry (Figure 1A–B and Figure S1) and double immunofluorescence with b-tubulin III, a neuronal maker (Figure 1C–H)
The large-sized AQP1 positive trigeminal neurons were not observed in humans or mice
Summary
Aquaporins (AQPs) function as water selective channels providing a major route for osmotically driven water transport through cell membranes [1]. AQP1 is a 28 kD pore-forming membrane protein first discovered in human red blood cells [3]. AQP1 is expressed in the mammalian nervous system [5]. AQP1 mRNA or immunoreactivity has been observed in trigeminal ganglion neurons in rodents [13,17,18,19,20]. These results indicate that AQP1 could play a relevant role in trigeminal neurotransmission. The localization of AQP1 in the human trigeminal system and more detailed localization of this water channel in the rodent trigeminal system have not been investigated
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