Autoradiography of [³H)α,β-methylene-ATP binding sites in medulla oblongata and spinal cord of the rat

Excitatory purinoceptors of P(2x)-type have long been known to exist on smooth muscle cells, but recently it has been shown that they are also involved in synaptic transmission in the CNS. We have used a P(2x)-specific agonist, α,β-methylene-ATP, as a ³H-labelled radioligand, to study the distribution and characteristics of P(2x) receptor-binding sites in the spinal cord and medulla oblongata. Using autoradiographic techniques, [³H]α,β-methylene-ATP binding was found throughout the grey matter of the spinal cord with small areas of above-average density of binding sites in the marginal zone acid substantia gelatinosa at all spinal levels and in the central grey matter of the thoracic spinal cord. In the medulla, [³H]α,β-methylene-ATP binding was found to be strong in all cranial nerve nuclei, particularly those known to receive primary sensory fibres. We have found that the binding of [³H]α,β-methylene-ATP in the spinal cord and medulla was inhibited by a broad-spectrum P₂-receptor antagonist suramin (IC₅₀, ≃ 27 μM). This is in accordance with the data obtained previously in the forebrain and cerebellum. There was, however, no inhibition of [³H]α,β-methylene-ATP binding by another close analogue of α,β-methylene-ATP and P(2x) ligand β,γ-methylene-ATP (10 μM). The latter result is discussed in terms of possible involvement of Ca²⁺in the binding of [³H]α,β-methylene-ATP to P(2x) receptors in the CNS.