High-affinity substance P binding sites in rat sympathetic ganglia

Substance P binding sites were characterized and quantitated in single rat sympathetic ganglia by incubation of tissue sections with 125I-Bolton-Hunter substance P, autoradiography, image analysis coupled with computer-assisted microdensitometry, and comparison with 125I standards. The prevertebral celiac-superior mesenteric sympathetic ganglia contained clusters of high-density, high-affinity substance P binding sites [maximum binding (Bmax) 7.12 +/- 0.20 pmol/mg protein; affinity constant (Ka) 2.08 +/- 0.02 X 10(9) M-1]. In the paravertebral superior cervical sympathetic ganglia, the number of high-affinity substance P binding sites was substantially lower (Bmax 1.38 +/- 0.04 pmol/mg protein; Ka 1.71 +/- 0.03 X 10(9) M-1). Future studies should address the issue of whether the substance P binding sites identified in prevertebral ganglia of the rat serve as receptors for the peptide presumed to be released by terminals of sensory neurons.