Histamine H₁ receptors in the brain and spinal cord of the cat

The regional distribution of histamine H₁ receptors in the feline brain and spinal cord was determined in vitro using the radio-actively labeled histamine H₁ antagonist, [³H]pyrilamine. This distribution of H₁ receptors, which was different from that reported for other species, was highest in the hypothalamus and mammillary bodies. Intermediate levels of binding were observed in the cerebral cortical and limbic regions, corpus striatum, colliculi, cerebellum, and medulla. The lowest binding was found in the pons and spinal cord. Binding in the spinal cord was concentrated in the gray matter, but the number of binding sites detected in the dorsal and ventral horns did not differ. The equilibrium dissociation constants for [³H]pyrilamine were similar for the various regions and were in the range of 2-3 nM and the pharmacological characteristics of the feline brain and spinal H₁ receptors were similar to those found in the brains of other mammalian species with the exception of the guinea pig.