FIGURE 2.

Expression of somatostatin (SOM), calbindin (CAL), and neurokinin-1 receptor (NK1R) in L6-S1 preganglionic neurons. Representative horizontal sections of spinal cord immunolabeled for pairs of neural markers are shown in (A–C); higher magnification images from different sections are provided in the corresponding lower panels. Preganglionic neurons were identified by ChAT-immunoreactivity, here colorized blue. Images are oriented with rostral at the top and lateral on the right. SOM-, CAL-, and NK1R-immunoreactivity were each identified in subpopulations of preganglionic neurons. Immunoreactivity for SOM and CAL was cytoplasmic, NK1R-immunoreactivity was primarily in the plasma membrane and CAL-immunoreactive preganglionic neurons showed cytoplasmic or nuclear labeling, or both. SOM- and NK1R-immunoreactive dendrites extended toward the midline, and also labeled many neuronal somata near the midline. CAL-immunoreactive somata, presumed interneurons, were found between the intermediolateral column and the midline; these consistently showed cytoplasmic labeling. (D–F) Analysis of expression patterns in preganglionic neurons. (D) Subpopulations of neurons expressed either SOM or CAL, but very few expressed both SOM and CAL (SOM/CAL) (n = 6 rats). (E) Subpopulations of neurons expressed either NK1R or CAL, with few expressing both NK1R and CAL (NK1R/CAL). In total, 45.0 ± 2.4% of sacral preganglionic neurons expressed NK1R and 24.9 ± 1.5% expressed CAL (n = 5 rats). (F) Subpopulations of neurons expressed either NK1R or SOM, with some neurons expressing both NK1R and SOM (NK1R/SOM). In total, 33.1 ± 1.3% of preganglionic neurons expressed NK1R and 33.0 ± 1.3% expressed SOM (n = 6 rats). Calibration bars represent 100 μm.