| BackgroundBreathing is one of the basic physiological processes necessary to maintain the metabolism and other functional activities of the body.A normal and stable rhythmic breathing is a necessary condition for the survival of the body.It originates from the medulla oblongata respiratory center,which plays an important role in all respiratory centers.There are progesterone and progesterone receptors in the central nervous system.It has a significant central neuroprotective effect on traumatic craniocerebral injury and cerebrovascular accident.However,it is not known whether progesterone and its receptors also have certain regulation and effect mechanism on central nervous system electrophysiological activity.Therefore,study the regulatory effect and mechanism of progesterone and progesterone receptors on respiratory basic rhythmic discharge activity(RRDA)in neonatal rat medulla oblongata slices in vitro,may be helpful to study the development of mammalian medulla oblongata respiratory center and achieve the prevention and treatment of central respiratory diseases.ObjectivesThis study is designed to explore whether progesterone receptor is involved in regulating the discharge of RRDA and inspiratory neurons in isolated medulla oblongata slices,and to clarify the mechanism of progesterone receptor mediating this action.MethodsWe selected the newborn Sprague-Dawley rats,male and female,who were born for 2 days.The brain slices of neonatal rats were prepared in vitro.The RRDA and inspiratory neuron discharges in m NRF region was recorded at 25-27 ℃ incubating with volume fraction 95% O2 + volume fraction 5% CO2.Three indexes of RRDA were recorded by BL-420 F biological signal acquisition system: inspiratory time(TI),inspiratory amplitude(IA),and respiratory frequency(RF),and three indexes of inspiratory neuron: bursting time(BT),bursting amplitude(BA),bursting frequency(BF).1 To study the effects of progesterone receptor at different concentrations on RRDA in isolated medulla oblongata of neonatal rats and whether progesterone receptor is involved in the regulation of progesterone on RRDA.This experiment was divided into four groups: control group,progesterone group(receptor agonist),mifepristone group(receptor inhibitor),mixed group of progesterone and progesterone+mifepristone.Each group of 6 brain slices,inciuded perfused with blank ACSF,ACSF containing different concentration progesterone of 5,10,20,40 μmol/L,ACSF containing different concentration mifepristone of 5,10,20,40 μmol/L,optimum concentration of progesterone and optimum concentration of progesterone + optimum concentration of mifepristone.The changes of TI,IA and RF,these three indexes of RRDA in isolated medulla oblongata in each group were recorded and compared.To determine the optimal concentration of progesterone receptor agonist progesterone and progesterone antagonist mifepristone on RRDA in neonatal rat medulla oblongata tablets in vitro,and whether progesterone and mifepristone affect RRDA through progesterone receptor pathway.2 The effects of progesterone receptor on the medial area of nucleus retrograde discharges(m NRF)in the medial area of the posterior facial nucleus of the medulla oblongata in neonatal rats were recorded by extracellular recording using glass microelectrode that on isolated medulla oblongata slices in which RRDA discharges were recorded.The brain slices were perfused with 20μmol/L progesterone,blank ACSF,and 20μmol/L mifepristone respectively.According to the changes of firing activity of inspiratory neurons,the relationship between progesterone concentration and progesterone receptor and RRDA was analyzed.Results1 There was no significant difference in the RRDA of brain slices of neonatal rats in the control group(p>0.05),which indicated that there was no debilitating phenomenon of RRDA in the brain slices perfused within 50 minutes,and the model had reliable stability.2 Compared with different concentrations of progesterone and control group were treated with blank ACSF perfusion 10 min and before administration,there was significant statistical differences(p<0.01),progesterone could excite RRDA in the range of 5 μmol/L-20 μmol/L,and 20 μmol/L progesterone was the most suitable concentration for exciting RRDA.3 Compared with different concentrations of mifepristone and control group were treated with blank ACSF perfusion 10 min and before administration,there was significant statistical differences(p<0.01),mifepristone could inhibit RRDA in the range of 5 μmol/L-20 μmol/L,and 20 μmol/L mifepristone was the most suitable concentration for inhibiting RRDA.4 In the mixed group,20 μ mol/L progesterone and 20 μ mol/L progesterone + 20 μ mol/L mifepristone were compared with the control group in 10 min perfusion with blank ACSF and before administration,there was significant difference in TI,IA and RF(P < 0.01),which had the effect of stimulating RRDA;there was no statistical difference in TI,IA and RF between the combination of progesterone and mifepristone(P > 0.05),and there was no effect on RRDA.This indicating that the excitatory effect of progesterone on RRDA was achieved by receptor pathway.5 Progesterone could enhance the excitability of the inspiratory neurons in the m NRF area of the rat medulla oblongata in vitro,prolong the BT,increase the BA and increase the BF;The progesterone receptor antagonist mifepristone could inhibit the excitability of the inspiratory neurons in the m NRF region,shorten BT,decrease the BA and decrease the BF.Conclusions1 Progesterone receptor was found in the m NRF area of the isolated medulla oblongata of neonatal rats,which had a positive regulatory effect on RRDA.2 Progesterone receptor is present on the membrane of inspiratory neurons,which are involved in regulating the discharge of inspiratory neurons in the m NRF region.3 Progesterone receptor regulates the respiratory function and neural development of the medulla oblongata respiratory center. |
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