Further evidence for peptidergic transmission in sympathetic ganglia

We previously proposed that, in sympathetic ganglia of the bullfrog, a peptide which resembles luteinizing hormone-releasing factor (LH-RF, luliberin) functions as the transmitter for the late slow excitatory postsynaptic potential (epsp), a signal that may last 5-10 min. To test this hypothesis further, we have compared the physiological andpharmacological effects of LH-RF with those of the natural transmitter and have found a close parallel. (i) LH-RF, when ejected with a brief pulse of pressure through a micropipette near a ganglion cell, produces a depolarizing response lasting for minutes. (ii) The LH-RF-induced response is associated with changes in input resistance similar to thoe during a late slow epsp. (iii) 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. (iv) Both responses increase the excitability of ganglion cells. (v) The two responses interact with the cholinergic epsps in a parallel manner: they cause diminution of the slow epsp but not of the fast epsp. (vi) Both responses are blocked by an analog of LH-RF that antagonizes the effects of LH-RF in the rat.