Effects Of TFG On The Late Slow Excitatory Postsynaptic Potential Of The Neurons In Inferior Mesenteric Ganglion Of Guinea-pig In Vitro

With the intracellular bioelectric recording technique, we have investigate and analyze the effect of the total flavonoids of ginkgo (TFG) on the late slow excitatory postsynaptic potential (ls-EPSP) of inferior mesenteric ganglion (IMG) neurons of guinea pig in vitro. With the receptor antagonists, low Ca2+/high Mg2+ solution, and low Na~+ Krebs solution etc, we have explored the possible mechanism of TFG effects on the IMG synaptic transmission.1. The electricity character of IMG cell membraneThe mean value of resting potential(RP) of IMG neurons in guinea pig was (-53.1±6.5)mV (n=192) respectively,the mean value of membrane resistance(Rm) and conductance (G) were (42.6±3.3) M? and (23.6±1.8) nS (n=110),respectively;and the mean values of membrane capacity (Cm) and time constant (τ) were (71.2±26.5) pF and (4.8±0.8) ms (n=110),respectively. The action potentials amplitude (APA) and duration (APD) were (60.1±4.6) mV and (2.5±0.4) ms,respectively, The amplitude (AHPA) and duration (AHPD) of the prolonged afterspike hyperpolarization were (-13.1±2.0) mV and (42.1±8.4) ms (n = 100),respectively. The amplitude and duration of f-EPSP induced by stimulating hypogastric nerve were (13.8±2.3) mV and (37.6±10.1) ms,respectively (n = 46),The APA and APD induced by stimulating hypogastric nerve were (65.3±4.5) mV and (2.5±0.3) ms,respectively and the AHPA and AHPD were (-10.6±1.4) mV and (29.3±2.5) ms, respectively(n = 56).2. the effect of the TFG on the ls-EPSP of the neurons of IMG2.1 the ls-EPSP of the neurons of IMGRepetitive stimulation(10V,1ms,20Hz,4s)of hypogastric nerves (HN) elicited a burst of action potentials which was followed by ls-EPSP in 61.1% (33/54) of the IMG neurons. The amplitude and duration of ls-EPSP were (7.7±1.8)mV and (97.4±17.4)s(n=33),respectively. The ls-EPSP was not blocked by cholinoceptor and adrenoceptor antagonists, but was eliminated by a low Ca2+/high Mg2+ Krebs solution,Thus,the ls-EPSP is a nonadrenergic and noncholinergic postsynaptic potential.2.2 The effect of TFG on the ls-EPSP of IMG neuronsSuperfusion of IMG with TFG (100,300,500mg/L) evoked a concentration-dep- endent depression on the amplitude and duration of ls-EPSP in 69.7% and had no response to TFG. in 21.2%of the neurons3 The mechanism of the depressive effect of the TFG on the ls-EPSP3.1 The ion mechanismThe depression induced by TFG could be enhanced a by low Na~+(58mmol/L) or a high K~+(20mmol/L) Krebs solution. It was also enhanced by TTX (10μmmol/L) and weaken by tetraethylammonium(TEA)(1mmol/L). The results show that the depressive effect of TFG on the ls-EPSP probably was associated with the decreasing influx of Na~+ and increasing outflow of K~+.3.2 The synaptic transmission mechanismThe depressive effect induced by TFG was not blocked by cholinoceptor and adrenoceptor antagonists, but was eliminated by a low Ca2+/high Mg2+ Krebs solution. It shows that The depressive effect induced by TFG on the ls-EPSP was associated with the decreasing the putative transmitters delivery or the partly blocking the combination between the putative transmitters and their receptors. We will investigate the possible mechanism of the depressive effect of TFG on the ls-EPSP on the following.3.2.1 5-HT-induced depolarizationSuperfusion of IMG with 5-HT(100μmol/L,30s) evoked a depolarization on the the neurons,72.7% of which has a ls-EPSP induced by repetitive stimulation(10V,1ms,20Hz,4s)of hypogastric nerves (HN) and 27.3% of which has no response in 5-HT sensitive neurons. 5-HT-induced depolarization was not blocked by cholinoceptor and adrenoceptor antagonists or a low Ca2+/high Mg2+ Krebs solution. It shows there have 5-HT receptors in IMG neurons. 3.2.2 The relationship between the depolarization induced by 5-HT and the ls-EPSPThere is no significant difference between the depolarization induced by 5-HT and the ls-EPSP induced by repetitive stimulation of HN. The ls-EPSP induced by repetitive stimulation of HN can be enhanced by superfusion of IMG with 5-HT(100μmol/L,30s)and weaken by continuous superfusion of IMG with 5-HT(100μmol/L,10min) or cyproheptadine(10μmol/L,3min). It shows 5-HT is a putative transmitter of ls-EPSP in IMG neurons of guinea pig.3.2.3 The effect of the TFG on the depolarization induced by 5-HTSuperfusion of IMG with TFG evoked a concentration-dependent depression on the depolarization amplitude and duration induced by 5-HT. The mechanism of this depression may be associated with antagonisting 5-HT receptors. And this depression was similar to the depression of the ls-EPSP affected by TFG. Thus it shows that the mechanism of these two depressions may though the same pathway.3.2.4 5-HT can partly remove the depression effect of TFG on ls-EPSPSuperfusion of IMG with 5-HT(100μmol/L,30s) could weaken the depression effect of TFG on ls-EPSP induced by repetitive stimulation(10V,1ms,20Hz,4s)of HN.3.2.5 The effect of the 5-HT receptor desensitization on the depressive effect of TFGContinuous superfusion of 5-HT(100μmol/L,10min)could enhance the the depressive effect of TFG on ls-EPSP induced by repetitive stimulation(10V,1ms,20Hz,4s)of HN. It shows TFG may partly block the 5-HT receptor and though this way inhibit the ls-EPSP.3.2.6 The effect of the 5-HT receptor antagonist on the depressive effect of TFGBoth the depolarizations induced by 5-HT and the ls-EPSP induced by repetitive stimulation(10V,1ms,20Hz,4s)of HN could be eliminated by superfusion of cyproheptadine ( 10μmol/L ) ,BRL24924 ( 10μmol/L ) and TFG(100mg/L), respectively.Combinidg Superfusion of cyproheptadine ( 10μmol/L ) and TFG(100mg/L) or BRL24924(10μmol/L)and TFG(100mg/L) could enhance the depressive effect than induced by single superfusion of cyproheptadine (10μmol/L),BRL24924(10μmol/L)and TFG(100mg/L) respectively. The depressive effect of TFG on ls-EPSP may be through 5-HT receptors.3.2.7 the depolarization induced by BOM and substance PSuperfusion of IMG with BOM(100μmol/L,30s) or substance P evoked a depolarization on IMG neurons,66.7% and 62.5% of which have ls-EPSPs induced by repetitive stimulation(10V,1ms,20Hz,4s)of hypogastric nerves (HN),respectively. And these depolarizations were not blocked by cholinoceptor and adrenoceptor antagonists or a low Ca2+/high Mg2+ solution. It shows that there are BOM and substance P receptors in IMG neurons of guinea pig.3.2.8 The effect of the TFG on the depolarization induced by BOM and substance PTFG(100,300,500mg/L) had no response to all the depolarization induced by BOM and substance P. It shows that the depressive effect of TFG on ls-EPSP had no relationship with BOM and substance P receptors.Above all, those results the depressive effect of TFG on ls-EPSP could be observed on most IMG neurons of guinea pig, the ion mechanism probably was associated with the decreasing influx of Na~+ and increasing outflow of K~+, and the synaptic transmission mechanism probably was associated with inhibit the delivery of 5-HT and the combination with its receptor.