Further evidence for peptidergic transmission in sympathetic ganglia.

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Abstract
In sympathetic ganglia of the bullfrog, a peptide which resembles luteinizing hormone-releasing factor (LH-RF, luliberin) may function as the transmitter for the late slow excitatory postsynaptic potential (epsp), a signal that may last 5-10 min. To test this hypothesis further, the physiological and pharmacological effects of LH-RF were compared with those of the natural transmitter and a close parallel found. LH-RF, when ejected with a brief pulse of pressure through a micropipette near a ganglion cell, produces a depolarizing response lasting for minutes. The LH-RF-induced response is associated with changes in input resistance similar to those during a late slow epsp. The amplitudes of the LH-RF-induced response and the late slow epsp vary in parallel as the membrane potential is shifted over a wide range. Both responses increase the excitability of ganglion cells. The 2 responses interact with the cholinergic epsp in a parallel manner: they cause diminution of the slow epsp but not of the fast epsp. Both responses are blocked by an analog of LH-RF [[D-pGlu1, D-Phe2, D-Trp3,6]LH-RF] that antagonizes the effects of LH-RF in the rat.