The Effects Of Bombesin On Synaptic Transmission Of The Guinea-piginferior Mesenteric Gangliain Vitro

Among the cells in guinea-pig inferior mesenteric ganglia (1MG) in vitro, the work was carried out to investigate the effects of bombesin on the synaptic transmission of 1MG by means of intracelluar recording technique. The main experimental results are as follows: I. In addition to cholinergic postsynaptic potential, repetitive stimuli applied to the presynaptic nerves elicited a non-cholinergic late slow excitatory postsynaptic potential (ls-EPSP) in about 60%(69/1 15) of the neurons sampled. 2. The amplitude/duration of ls-EPSP elicited by different nerves linked to 1MG had no significant variance. Changing the stimulation parameters in a certain field, such as increasing the frequency, intensity or duration, could increase the amplitude/duration of ls-EPSP in responding. Combined stimuli of these nerves could evoke a ls-EPSP or increase the amplitude and/or duration of ls-EPSP previously existed.It suggested that 1MG had a role of integration. 3. BOM (106?05M) applied by superfusion, induced a depolarization in a large number of cells sampled (66.5%,109/164), which had dose- dependence, with mean amplitude and average duration of6.2監.2mV, 166.O?.2s respectively; in a part of cells sampled (7.9%,13/164), 4. BQM evoked a biphasic response which consisted of an initial hyperpolarization phase followed by a slow depolarization phase. The remainder (25.6%,42/164) cells showed no reaction to BOM. 4. The effects of BOM persisted during nicotinic and muscarinic synaptic blockade being applied. The effects of BOM also persisted in a low 24- Ca , high Mg24- solution. Thus, by a non-cholinergic and non- adrenergic way, the site of action of BOM was on the receptor in postsynaptic membrane. 5. Membrane depolarization caused by BOM enhanced the excitability of postganglionic neurons and converted subthreshold synaptic potentials to action potentials, suggesting that BOM may facilitate f-EPSP. 6. Applied by superfusion, BOM(106-.105M) or SP(106M) caused a slow depolarization that closely minicked ls-EPSP. In BOM-sensitive neurons, ls-EPSP was markedly suppressed by BOM exogenously applied. Similarly, superfusion of the ganglia with SP attenuated the Is- EPSP of SP-sensitive neurons, but there was no cross-desensitization between SP and BOM. It indicated that BOM as well as SP coij~monly participated in the formation of ls-EPSP in guinea pig 1MG neurons via postsynaptic membrane receptors respectively. 7. Both ls-EPSP and BOM depolarization elicited on BOM-sensitive neurons were reversibly suppressed by a BOM antagonist, Tyr4,[D- phe?]BOM (106M). In contrast, ls-IEPSP elicited on BOM-insensitive neurons was not appreciably affected. It also suggested that BQM may mediate the ls-EPSP of guinea pig 1MG neurons. 8. In 27.4% (23/84) of the BOM-sensitive cells, the membrane depolarization was accompanied by a decrease in membrane input resistance (Rm), in 13.1% (11/84) of the cells, there was an increase in Rm, in the rest 59.5%(50/84) of cells had no changes in Rm. Among the neurons that exhibited ls-EPSP, 80.0% of them were sensitive to BOM. During BQM-depolarization, the changes in Rm were very similar to wh...