Role of spinal serotonergic pathways in sneeze-induced urethral continence reflex in rats

Abstract

To clarify the role of spinal serotonergic mechanisms in preventing stress urinary incontinence (SUI) during sneezing, we investigated the effect of intrathecal (it) application of 8-OH-DPAT (a 5-HT1A agonist), mCPP (a 5-HT2B/2C agonist), and fluoxetine (a serotonin reuptake inhibitor) using a rat model that can examine the neurally evoked continence reflex during sneezing. Amplitudes of urethral pressure responses during sneezing (A-URS), urethral baseline pressure (UBP) at the midurethra, and sneeze-induced leak point pressure (S-LPP) were measured in normal female adult rats and rats with SUI induced by vaginal distention (VD). In normal rats, 8-OH-DPAT decreased A-URS by 48.9%, whereas mCPP increased A-URS by 33.6%. However, A-URS was not changed after fluoxetine. 8-OH-DPAT, mCPP, or fluoxetine did not alter UBP. The effect of 8-OH-DPAT and mCPP was antagonized by WAY-100635 (it), a selective 5-HT1A antagonist, and RS-102221 (it), a selective 5-HT2C antagonist, respectively. Fluoxetine in the presence of WAY-100635 did not change either A-URS or UBP, but fluoxetine in the presence of RS-102221 decreased A-URS. In VD rats, S-LPP was decreased by 14.6 cmH2O after 8-OH-DPAT, whereas it was increased by 12.8 cmH2O after mCPP. However, S-LPP was not changed after fluoxetine. These results indicate that activation of 5-HT2C receptors enhances the active urethral closure reflex during sneezing at the spinal level, whereas 5-HT1A inhibits it and that no apparent changes in the sneeze-induced continence reflex after fluoxetine treatment are due to coactivation of excitatory 5-HT2C receptors and inhibitory 5-HT receptors other than the 5-HT1A subtype. Thus, activation of excitatory 5-HT receptor subtypes such as 5-HT2C could be effective for the treatment of SUI.