Inhibitory role of the spinal cholinergic system in the control of urethral continence reflex during sneezing in rats

Abstract

The urethral continence reflex during stress conditions such as sneezing or coughing is an important mechanism preventing stress urinary incontinence (SUI). Although the spinal noradrenergic and serotonergic pathways are known to modulate this reflex activity, the role of spinal cholinergic pathways in the control of urethral continence reflex has not been elucidated. We therefore investigated the effect of intrathecal administration of an acetylcholine esterase (AChE) inhibitor, which increases ACh in synaptic terminals, and anti-cholinergic agents on the sneeze-induced urethral reflex in rats. Female SD rats were anesthetized with urethane. Urethral function was evaluated during sneezing induced by insertion of the rat whisker into the nostril. Effects of an AChE inhibitor, neostigmine, and muscarinic or nicotinic receptor antagonists administered at the level of L6-S1 spinal cord were examined. Neostigmine dose-dependently and significantly decreased the amplitude of urethral responses during sneezing (A-URS) with an approximately 70% reduction at 3 nmol, without changing urethral baseline pressure. The neostigmine-induced decrease in A-URS was significantly reversed by pretreatment with atropine (nonselective muscarinic receptor antagonist), methoctramine (M2 receptor antagonist) or 4-DAMP (M3 receptor antagonist), but not with pirenzepine (M1 receptor antagonist), tropicamide (M4 receptor antagonist), or mecamylamine (nicotinic receptor antagonist). These results indicate that an increase in endogenous ACh in the lumbosacral spinal cord inhibits the sneeze-induced urethral continence reflex via activation of M2 and/or M3-muscarinic receptors, implying the inhibitory role of spinal cholinergic pathways in the control of urethral continence reflex under stress conditions such as sneezing.