engleski

Microinjection of methysergide into the raphe nucleus attenuated phrenic long term facilitation in rats

Exposure to acute intermittent hypoxia (AIH) evokes persistent increase in respiratory activity that lasts up to 60 minutes after hypoxic episodes have ceased. This long lasting increase in the phrenic nerve activity is known as phrenic long- term facilitation (LTF). AIH induced phrenic LTF in anesthetized rats is serotonin dependant but the underlying mechanism remains unknown. The present study was performed to determine whether microinjection of broad spectrum 5-HT receptor antagonist, methysergide (4 mM, 20± 5 nl), into the caudal raphe nuclei influences phrenic LTF. Peak integrated phrenic nerve activity (PNA) and respiratory frequency were monitored at 15, 30, and 60 min after five 3-min episodes of normocapnic hypoxia in urethane-anesthetized, vagotomized, paralyzed and ventilated male Sprague-Dawley rats. In control animals, phrenic nerve amplitude was elevated to 66.7± 8.6% one hour after episodic hypoxia, indicating phrenic LTF. Conversely, central microinjections of methysergide prior to AIH exposure attenuated phrenic LTF (2.62± 2.9%). We conclude that methysergide microinjections into the caudal raphe region attenuate phrenic LTF induced by acute intermittent hypoxia, indicating involvement of 5- HT receptor activation at supraspinal level.

hypoxia ; phrenic nerve ; long-term facilitation ; raphe nucleus ; serotonin ; methysergide

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