Distribution of histaminergic, muscarinic and serotonergic binding sites in cat spinal cord with emphasis on the region surrounding the central canal.

[3H]Quinuclidinyl benzilate (QNB), [3H]lysergic acid diethylamide (LSD) and [3H]pyrilamine were used with radiohistochemistry to determine the distribution of muscarinic, serotonergic and histaminergic binding sites, respectively, in cat spinal cord. Each ligand displayed a unique pattern of binding sites in the superficial laminae of the dorsal horn [3H]Pyrilamine binding sites were localized most superficially, while [3H]LSD binding sites were densest in the region of the laminae II/III border. The distribution of [3H]QNB binding sites partially overlapped those of LSD and pyrilamine. In the region surrounding the central canal, pyrilamine binding sites were concentrated within a zone 100 microns lateral to the canal while [3H]QNB and [3H]LSD binding sites were localized outside of this zone. The distribution of binding sites in the region surrounding the central canal may provide an important neurochemical correlate for lamina X in the cat as defined by Rexed.