Site of adrenaline blockade in the superior cervical ganglion of the rabbit

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Abstract
1. The blocking action of adrenaline on the superior cervical ganglion of the rabbit was investigated with intracellular recording techniques.2. Adrenaline (10(-5)M) blocked initiation of post-synaptic action potentials and decreased the amplitude of excitatory post-synaptic potentials (e.p.s.p.s), but did not hyperpolarize the post-synaptic membrane.3. The depressant action of adrenaline was antagonized by phenoxy-benzamine and dihydroergotamine.4. Acetylcholine depolarizations from iontophoretic ACh were not affected by adrenaline.5. Adrenaline decreased the frequency of miniature excitatory post-synaptic potentials (m.e.p.s.p.s) and decreased the quantal content of e.p.s.p.s in a low [Ca(2+)]: [Mg(2+)] media.6. It was concluded that adrenaline blocks ganglionic transmission by acting at an alpha-adrenoceptive site in the presynaptic nerve terminals.