Intravenous Glycine Inhibits the Micturition Reflex in Normal and Spinal Cord Injury Rats

Abstract

We examined the influence of intravenous injection of glycine on the spinobulbospinal and spinal micturition reflexes in rats. Female rats were divided into an intact group and a chronic spinal cord injury (SCI) group with transection of the lower thoracic cord, and studied at 4 weeks after SCI. Under urethane anesthesia, isovolumetric cystometry was performed in each group before and after intravenous injection of glycine (0.01-100 mg/kg). Intravenous injection of glycine (0.1-100 mg/kg) transiently abolished bladder contractions after a delay of several minutes in both groups. In intact rats, intravenous injection of glycine prolonged the interval between bladder contractions, but did not change the amplitude of the contractions. On the other hand, intravenous glycine both prolonged the interval and decreased the amplitude of bladder contractions in SCI rats. However, intrathecal injection of low dose of strychnine (a selective glycine receptor antagonist; 0.001 pg) and following intravenous injection of glycine (0.1 mg/kg) did not affect the bladder contractions in intact rats. These results suggest that systemically administered glycine inhibits the afferent limb of the spinobulbospinal micturition reflex, and inhibits both the afferent and efferent limbs of the spinal micturition reflex at the lumbosacral cord level.