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 μm 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.