FOS protein in the lumbosacral spinal cord of the rat was detected to study neuronal activation induced by noxious stimulation of the urethra. In rats receiving infusion of 100 μl of 2% formalin into the urethra, a large number of FOS-positive neurons were seen in the lumbosacral cord segments (L6 and S1), and they were primarily distributed in the medial dorsal horn and dorsal commissural nucleus. Nearly all of FOS expression was blocked by bilateral transection of the pudendal nerve, whereas bilateral transection of the pelvic nerve seemed to have no obvious effect on FOS expression.Behavioral changes were also observed in the nerve-transected rats. Bilateral pelvic nerve-transected rats showed frequently licking of the external urethral orifice after application of the irritant to the urethra, which was quite similar to that of the nerve-intact rats. Such behavior completely disappeared in the rats receiving bilateral pudendal nerve transection. The results suggest that the medial dorsal horn and dorsal commissural nucleus in the L6 and S1 segments are involved in processing nociceptive inputs from the urethra, which is carried by the pudendal nerve.

To develop a sensitive analytical method for the determination of the genotoxic impurity mono ethyl ester of ecabet (Imp-I),an HPLC-MS/MS technique was employed. Imp-I was synthesized according to the previ-ous literatures. MS/MS and NMR were used to confirm the structure of Imp-I. A Thermo C18column was used for chromatographic separations. The mobile phase consisting of A:5 mmol/L ammonium acetate (pH adjusted to 3. 0 with formic acid)and B:acetonitrile,with a gradient program:0 min 50%B,4 min 50%B,12 min 80%B,16 min 80%B,16. 1 min 50%B and 20 min 50%B. The column was maintained at 40 °C throughout the analysis.All measurements were carried out with the mass spectrometer operated under the negative ESI mode. The selective reaction monitor (SRM)transition was used. Good linearity was obtained for Imp-I over the concentration range of 4 150 ng/mL with the coefficient of determination (r)of 0. 999. And the LOQ was 4 ng/mL. A rapid and sensi-tive HPLC-ESI-MS/MS method was developed for quantitative analysis of Imp-I in ecabet sodium APIs. This method can be of used for quality assurance of ecabet sodium in bulk commercial drugs.