Neurochemical Properties of Aquaporin 1-Expressing Sensory Neurons from the Ovine Trigeminal Ganglion

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 C1C7 dorsal root ganglia no presence of AQP1 was found. In trigeminal ganglion, 15.4 similar to +/-similar to 2.3% of Hu C/D-IR neurons (pan-neuronal marker) showed the presence of AQP1. The vast majority of AQP1-IR trigeminal sensory neurons (approximately 69.6 similar to +/-similar to 3.3%, n similar to=similar to 5) were classified as middle in size, 28.6 similar to +/-similar to 3.0% of AQP1-IR neurons were small and only 1.8 similar to +/-similar to 0.6% of AQP1-positive neurons were large in size. Amongst the population of AQP1-IR trigeminal neurons as many as 58.5 similar to +/-similar to 3.9% were immunopositive to SP, 30.7 similar to +/-similar to 2.3% showed the presence of CGRP and 10.9 similar to +/-similar to 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.