Involvement of endogenous carbon monoxide in regulation of respiratory rhythm in vitro / 生理学报

The aim of the present study was to investigate the effect of endogenous carbon monoxide (CO) on respiratory rhythm. The experiments were carried out on the medullary slices of newborn Sprague-Dawley rats. The rhythmic discharge frequency (DF) of hypoglossal rootlets was taken as an index of rhythmic respiratory activity. The slices of medulla oblongata were superfused with ZnPP-9 (inhibitor of heme oxygenase), CO and hemin (substrate of heme oxygenase), respectively, to observe their effects on respiratory rhythm. The preparations were divided into 5 groups: control group of artificial cerebrospinal fluid (ACSF), group of ZnPP-9, group of exogenous CO, group of hemin and group of ZnPP-9 + hemin. The results obtained were as follows. In ZnPP-9 group, the rhythmic DF of the hypoglossal rootlets was increased (P<0.05); while in exogenous CO group, it was decreased (P<0.05). In the groups of hemin and ZnPP-9 + hemin, the rhythmic DF of the hypoglossal rootlets was increased (P<0.05). It is suggested that endogenous CO may play an important role in the regulation of respiratory rhythm.

Effect of tetramethylpyrazine on the responses of respiration and expression of nNOS in brainstem to hypoxia in rats / 生理学报

The aim of the present study was to investigate the effect of tetramethylpyrazine (TMP) on the changes of respiration and expression of neuronal nitric oxide synthase (nNOS) in brainstem induced by hypoxia in the rats. Hypoxia was induced by inhalation of 8% O2-balanced N2.The electromyogram (EMG) of diaphragm was monitored to evaluate the respiratory response of the rats to hypoxia. The immunohistochemical staining technique was used to study the change of the expression of nNOS in the brainstem during hypoxia. In the rats of hypoxia group, a successive process of response, excitatory followed by inhibitory, was produced. Twenty min after hypoxia, a significant inhibition of respiration occurred, which was characterized with a marked decrease in the inspiratory duration, the respiratory frequency, and the amplitude of inspiration and a prolongation of expiratory duration (P<0.05). In the rats of pretreated with TMP, the respiratory activity was not obviously depressed (P>0.05). In the rats of hypoxia group, the level of nNOS immunoreactivity was enhanced remarkably in the lateral reticular nucleus, nucleus of trapezoid, hypoglossal nucleus and the facial nucleus compared with the control group (P<0.05). In the rats of pretreated with TMP, the nNOS level increased further in the nuclei mentioned above (P<0.05). The results obtained indicate that TMP can reverse the inhibitory effect of hypoxia on respiration in the rats and that nNOS may be involved in the respiratory protective action of TMP.