Chronic Pelvic Pain Develops in Sensory Neuron Conditional Asic3 Null Mice Subjected to Chemical Injury

Abstract

Sensitization of primary afferents is an important underlying mechanism for visceral hypersensitivity and pain. We investigated the contribution of acid-sensing ion channels (ASICs) in sensory neurons to the development of pain in a model of chemical-induced cystitis. ASICs are assembled as heterotrimers in bladder sensory neurons; however, the deletion of the ASIC3 subunit results in a loss-of-function phenotype with sensory neurons unable to discharge action potentials in response to acidification. In this study, conditional sensory neuron Asic3 knockout (KO) mice ( Asic3 fl/fl ;Avil-Cre +/- ) and control littermates ( Asic3 fl/fl ;Avil-Cre -/- ) received cyclophosphamide (CYP) (IP 80 mg/kg), or saline, every other day for five days. Experimental observations were made after one day (acute) or 14 days (chronic) after the last dose of CYP. In the acute setting, both control and conditional Asic3 KO mice treated with CYP exhibited an irritated bladder phenotype with a high number of voiding events of small volume. However, voiding activity normalized in both groups within two weeks of receiving CYP. In contrast, conditional Asic3 KO mice treated with CYP developed pelvic allodynia that persisted for at least two weeks, whereas control mice had no pain phenotype. In the chronic setting, no apparent edema or inflammatory cells were observed in bladders of control or conditional Asic3 KO mice, indicating that the pelvic allodynia seen in conditional Asic3 KO mice treated with CYP is likely driven by abnormal functioning of the nervous system and not by inflammation. To assess whether, in the chronic setting, the referred pelvic allodynia seen in conditional Asic3 KO mice treated with CYP is caused by sensitized primary afferents, we examined the firing evoked by sustained suprathreshold electrical stimulation of acutely isolated bladder sensory neurons. Sensory neurons were classified based of the sensitivity of the action potential to tetrodotoxin (TTX), as TTX-resistant (TTX-R) or TTX-sensitive (TTX-S). Strikingly, ~ 40% (11/17) of the bladder sensory neurons with TTX-R action potentials from conditional Asic3 KO mice treated with CYP exhibited aberrant firing (i.e., sensitization) in response to suprathreshold stimulation, compared to 3% (1/33) in control mice. These findings indicate that the pelvic allodynia seen in conditional Asic3 KO mice is driven in part by sensitized bladder afferents. Taken together, our studies support the notion that ASICs operate at the nerve terminals to modulate nociceptor excitability and sensitization. This is the full abstract presented at the American Physiology Summit 2023 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.