Investigation Of Involvement Of Endogenous Carbon Monoxide In Central Respiratory Control In Vitro

The purpose of our present study is to investigate whether endogenouscarbon monoxide (CO) is involved in central respiratory regulation. Theexperiments were carried out on medullary slices of neonatalSprague-Dawley rats. Electrophysiological technique was used to reveal theeffects of endogenous CO in central respiratory control.The rhythmic burst activity of hypoglossal rootlets of medullary sliceswas taken as the index of rhythmic respiratory activity. The slices wereperfused with ZnPP-9 (a potent inhibitor of heme oxygenase), CO andhemin (substrate of heme oxygenase), respectively, to observe their effectson rhythmic burst activity of hypoglossal rootlets of medullary slices.The slices were divided into 5 groups (8 for each group), control group,group of ZnPP-9, group of exogenous CO, group of Hemin and group of ZnPP-9+Hemin. The burst duration (BD), burst interval (BI), burstfrequency (BF) and integrated amplitude (IA) of the rhythmic burst activityof hypoglossal rootlets of medullary slices were observed. The resultsobtained were as follows. Comparing to the pre-control, ZnPP-9 produced adecrease in BD and BI, an increase in BF and a decrease in IA (P＜0.05).Comparing to the pre-control, exogenous CO caused a decrease in BD, anincrease in BI, a decrease in BF and an increase in IA (P＜0.05). In responseto hemin, BI decreased, BF increased and IA decreased (P＜0.05), and BDdidn't change significantly (P＞0.05), comparing to the pre-control.Administration of both ZnPP-9 and hemin produced a decrease in BI and anincrease in BF (P＜0.05), and didn't affect the BD and IA significantly(P＞0.05), comparing to the pre-control. Besides, there is no significantdifference in BD, BI, BF and IA between group of ZnPP-9 and group ofZnPP-9+Hemin or between group of Hemin and group ofZnPP-9+Hemin(P＞0.05).It is concluded from the results above that endogenous CO may play animportant role in central respiratory regulation.After the application of hemin, its effects didn't disappear even if theslices were perfused by artificial cerebrospinal fluid (ACSF) for washing.The reason accounting for this phenomenon may be that the hemin was notwashed out. To verify this presumption, relative absorbance was taken as anindex of hemin level of the medullary slices, which could determinewhether hemin can be washed out.The slices were divided into 4 groups (6 for each group), blank group, ACSF group, group of hemin with washing (hemin group-l) and group ofhemin without washing (hemin group-2). The results obtained were asfollows. The hemin level didn't show any significant difference betweenblank group and ACSF group (P＞0.05). The hemin level of hemin group-1and hemin group-2 was significantly higher than that of blank group andACSF group (P＜0.01). There is no significant difference of heroin levelbetween hemin group-1 and hemin group-2.It is concluded from the results above that hemin was not washed out,which caused irreversible changes in burst activity of hypoglossal rootletsof medullary slices.