| The water channel aquaporin I (AQPI) is expressed in a variety of tissues that are known to contribute to fluid balance in the body, including kidney, choroid plexus, and vascular endothelium. However, we have also discovered that AQPI is expressed in the nervous system, in a remarkably limited distribution that includes primary afferent sensory neurons that transduce noxious stimuli and also includes the olfactory bulb. The work presented in this dissertation describes these findings in detail.;AQPI immunoreactivity was detected in a subset of neurons of the dorsal root and trigeminal ganglia that express markers of nociceptive neurons, including substance P, IB4, and the capsaicin receptor, TRPVI. Ultrastructural studies showed that the protein is present on the plasma membrane of these neurons. AQPI expression begins at embryonic day 15.5, similar to the time when these neurons begin to form connections within the spinal cord. The very restricted expression of AQP I in nociceptors led us to hypothesize that it may contribute to nociceptive function. However, neither electrophysiological assessment of responsivity to noxious thermal stimulation nor behavioral testing using a comprehensive battery of assays for acute and persistent nociception illuminated differences between normal mice and mice with a null mutation for AQPI. Thus, our studies demonstrate that despite the abundant and restricted expression of AQPI in nociceptive primary afferent neurons, this water channel is not required for normal pain processing, and the physiological function of neuronal AQPI for the moment remains unresolved.;In addition to primary sensory neurons, AQPI is also present in a dense meshwork of fine fibers that cover the superficial surface of the olfactory bulb. We have found evidence that the olfactory bulb AQPI immunoreactivity does not derive from olfactory receptor neurons, olfactory ensheathing glia, astrocytes, periglomerular cells, or trigeminal axons. Instead, we propose that AQPI may be a marker of a unique, previously unrecognized fiber tract in the mouse olfactory bulb. |
