tetrodotoxin and Cystitis

Visceral pain is very common and represents a major unmet clinical need for which current pharmacological treatments are often insufficient. Tetrodotoxin (TTX) is a potent neurotoxin that exerts analgesic actions in both humans and rodents under different somatic pain conditions, but its effect has been unexplored in visceral pain. Therefore, we tested the effects of systemic TTX in viscero-specific mouse models of chemical stimulation of the colon (intracolonic instillation of capsaicin and mustard oil) and intraperitoneal cyclophosphamide-induced cystitis. The subcutaneous administration of TTX dose-dependently inhibited the number of pain-related behaviors in all evaluated pain models and reversed the referred mechanical hyperalgesia (examined by stimulation of the abdomen with von Frey filaments) induced by capsaicin and cyclophosphamide, but not that induced by mustard oil. Morphine inhibited both pain responses and the referred mechanical hyperalgesia in all tests. Conditional nociceptor‑specific Na

Topics: Analgesics; Animals; Capsaicin; Colon; Cystitis; Disease Models, Animal; Female; Hyperalgesia; Male; Mice; Mice, Knockout; Morphine; Mustard Plant; Nociceptors; Pain Measurement; Plant Oils; Sodium Channels; Tetrodotoxin; Visceral Pain

Tetrodotoxin (TTX)-resistant sodium channels are found in small diameter primary sensory neurons and are thought to be important in the maintenance of inflammatory pain. Here we examined bladder urodynamics of Nav1.9 voltage-gated sodium channel knock out (KO) mice, and the contribution of Nav1.9 to the development of inflammation-based bladder dysfunction. Basal urodynamics were not different between wildtype (WT) mice and those lacking Nav1.9. Peripheral nerve recordings from pelvic afferents in Nav1.9 KO mice revealed a lack of sensitization to intravesicularly applied prostaglandin E2 (PGE2). Consistent with this, cyclophosphamide treatment in vivo, which is associated with an enhancement of PGE2 production, evoked a reduction in bladder capacity of WT, but not Nav1.9 KO mice. We conclude that the Nav1.9 sodium channel provides an important link between inflammatory processes and changes in urodynamic properties that occur during urinary bladder inflammation.

Topics: Acetic Acid; Animals; Antirheumatic Agents; Cyclophosphamide; Cystitis; Dinoprostone; Disease Models, Animal; Female; In Vitro Techniques; Male; Mice; Mice, Knockout; NAV1.9 Voltage-Gated Sodium Channel; Nerve Fibers, Unmyelinated; Neuropeptides; Sodium Channel Blockers; Sodium Channels; Tetrodotoxin; Urinary Bladder; Urination; Urodynamics

The properties of bladder afferent neurons in L6 and S1 dorsal root ganglia of adult rats were evaluated after chronic bladder inflammation induced by 2 week treatment with cyclophosphamide (CYP; 75 mg/kg). Whole-cell patch-clamp recordings revealed that most (70%) of the dissociated bladder afferent neurons from control rats were capsaicin sensitive, with high-threshold long-duration action potentials that were not blocked by tetrodotoxin (TTX; 1 microM). These neurons exhibited membrane potential relaxations during voltage responses elicited by depolarizing current pulses and phasic firing during sustained membrane depolarization. After CYP treatment, a similar proportion (71%) of bladder afferent neurons were capsaicin sensitive with TTX-resistant spikes. However, the neurons were significantly larger in size (diameter 29.6 +/- 1.0 micrometer vs 23.6 +/- 0.8 micrometer in controls). TTX-resistant bladder afferent neurons from CYP-treated rats exhibited lower thresholds for spike activation (-25.4 +/- 0.5 mV) than those from control rats (-21.4 +/- 0.9 mV) and did not exhibit membrane potential relaxation during depolarization. Seventy percent of TTX-resistant bladder afferent neurons from CYP-treated rats exhibited tonic firing (average 12.3 +/- 1.4 spikes during a 500 msec depolarizing pulse) versus phasic firing (1.2 +/- 0.2 spikes) in normal bladder afferent neurons. Application of 4-aminopyridine (1 mM) to normal TTX-resistant bladder afferent neurons mimicked the changes in firing properties after CYP treatment. The peak density of an A-type K+ current (IA) during depolarizations to 0 mV in TTX-resistant bladder afferent neurons from CYP-treated rats was significantly smaller (42.9 pA/pF) than that from control rats (109.4 pA/pF), and the inactivation curve of the IA current was displaced to more hyperpolarized levels by approximately 15 mV after CYP treatment. These data suggest that chronic inflammation induces somal hypertrophy and increases the excitability of C-fiber bladder afferent neurons by suppressing IA channels. Similar electrical changes in sensory pathways may contribute to cystitis-induced pain and hyperactivity of the bladder.

Topics: 4-Aminopyridine; Action Potentials; Animals; Chronic Disease; Cyclophosphamide; Cystitis; Female; Ganglia, Spinal; Membrane Potentials; Nerve Fibers; Neurons, Afferent; Patch-Clamp Techniques; Rats; Rats, Sprague-Dawley; Tetrodotoxin; Urinary Bladder