ORIGINAL ARTICLE Neurochemical Properties of Aquaporin 1-Expressing Sensory Neurons from the Ovine Trigeminal Ganglion M. B. Arciszewski* Address of author: Department of Animal Anatomy and Histology, Faculty of Veterinary Medicine, University of Life Sciences, Akademicka 12, 20-033, Lublin, Poland *Correspondence: Tel.: + 48 (81) 445 65 96; fax: + 48 (81) 445 65 96; e-mail: mb.arciszewski@wp.pl With 2 figures Received June 2011; accepted for publication November 2011 doi: 10.1111/j.1439-0264.2011.01122.x Summary Aims of the present study were to investigate the distribution and morphology of aquaporin 1-immunoreactive (AQP1-IR) neurons in the sensory ganglia of the sheep. Double immunohistochemical staining was applied to figure out whether substance P (SP), calcitonin gene-related peptide (CGRP) and galanin are present in AQP1-bearing primary afferent neurons. The expression of AQP1 was present only in trigeminal ganglion, whereas in nodose ganglion, jugular ganglion as well as C 1 –C 7 dorsal root ganglia no presence of AQP1 was found. In trigeminal ganglion, 15.4 ± 2.3% of Hu C/D-IR neurons (pan-neuro- nal marker) showed the presence of AQP1. The vast majority of AQP1-IR tri- geminal sensory neurons (approximately 69.6 ± 3.3%, n = 5) were classified as middle in size, 28.6 ± 3.0% of AQP1-IR neurons were small and only 1.8 ± 0.6% of AQP1-positive neurons were large in size. Amongst the popula- tion of AQP1-IR trigeminal neurons as many as 58.5 ± 3.9% were immuno- positive to SP, 30.7 ± 2.3% showed the presence of CGRP and 10.9 ± 0.2% coexpressed galanin. In trigeminal ganglion, SP-IR as well as CGRP-IR (but not galanin-IR) nerve fibres were found in close neighbourhood of AQP1-IR neurons. It is concluded that AQP1 is present in certain neuronal subsets of the ovine trigeminal ganglion; however, the exact role of this water channel has to be elucidated. Introduction A family of highly conserved channel-forming proteins called aquaporins (AQPs) is known to regulate rapid water movement across cell membranes. So far, nine mammalian AQPs have been characterised and cloned. Based on its permeability properties, the family consist of classic AQPs that selectively pass water (AQP1, AQP2, AQP4, AQP5 and AQP8) as well as aquaglyceroporins (AQP3, AQP7 and AQP9) that pass glycerol and some other small mole- cules (for review see van Os et al., 2000). AQP6 is a spe- cific water channel localised exclusively in intracellular membranes in renal epithelia and not involved in transcel- lular fluid absorption (Yasui et al., 1999). AQPs were localised in many tissues such as kidney’s proximal tubules and descending limb of Henle, collecting renal ducts, lens fibre cells, apical membrane of lacrimal and salivary glands, skin, adipocytes or even hepatocytes (for review see Agre et al., 2002). So far, three AQPs (AQP1, AQP4 and AQP9) were found to be present on apical membrane of neurons of central (Nielsen et al., 1997; Oshio et al., 2004; Sulyok et al., 2004), peripheral (Nandasena et al., 2007; Shields et al., 2007) and enteric nervous system (Nagahama et al., 2006; Arciszewski et al., 2011). Recent studies indicated that in central and peripheral nervous system, the expres- sion of AQPs may be region-specific, especially that the presence of AQP4 and AQP9 was noted in astroglial cells in brain and spinal cord but not in glial cells at the periph- ery (Gao et al., 2006). Although it has been shown that AQP1 is present in rodents peripheral sensory ganglia colocalisation studies defining chemical coding of AQP1-bearing neurons are scarce and fragmentary. Moreover, no studies showing the presence of AQP1 in primary afferent neurons of higher mammalian species have been conducted. There- fore, the aim of this study was to immunohistochemically © 2011 Blackwell Verlag GmbH Anat. Histol. Embryol. 41 (2012) 184–189 184