Serotonergic modulation of cat bladder function before and after spinal transection

Micturition was evoked in conscious cats by infusing saline into the bladder at a physiological rate. Drugs were administered intrathecally. Micturition volume threshold was increased by 5-hydroxytryptamine (5-HT, serotonin) and decreased by zatosetron, a 5-HT₃ receptor antagonist, in spinally intact cats. Thus 5-HT₃ receptors inhibit micturition. After complete spinal transection, serotonin reduced volume threshold in 3 of 4 cats, indicating an alteration in serotonergic control. However, 2-methyl-5-HT, a 5-HT₃ receptor agonist, increased volume threshold. Thus 5-HT₃ receptor-mediated inhibition of bladder function remains after spinal transection. We conclude that some, but not all, serotonergic modulation of bladder function is altered after spinal transection.