Catecholamines and cyclic nucleotides in the modulation of superior cervical ganglia

Four hypotheses have been advanced to explain the relationships between the cholinergic presynaptic afferents, principal ganglionic neurons, and small, intensely fluorescent (SIF) cells in synaptic transmission in the mammalian superior cervical ganglion (SCG). The first hypothesis involves the role of the dopaminergic SIF cell and cyclic AMP in the modulation of ganglionic transmission through the generation of a slow inhibitory postsynaptic potential (s-IPSP). The second concerns the generation of a slow excitatory postsynaptic potential (s-EPSP), and the role of dopamine and cyclic AMP in potentiating it. The third postulates that a presynaptic α-adrenergic receptor is responsible for inhibiting f-EPSP generation. A fourth hypothesis concerns the localization of the β-adrenergic receptor—adenylate cyclase complex in SCG. This paper discusses the evidence for each hypothesis, with special emphasis on species variations in the modulation of ganglionic transmission by catecholamines, adrenergic receptors, and cyclic AMP.