engleski

Different experimental protocols and phrenic long-term facilitation

Introduction: Long term facilitation (LTF) represents form of neural plasticity that persists long after exposures to episodic hypoxia have ceased. LTF stimulation protocol employs wide variety of hypoxic episodes at different O2 levels that could affect the elicitation, magnitude and duration of phrenic LTF in anesthetized rats. Therefore, the present study examined the effects of two different experimental protocols consisting of different hypoxic episode number and duration. Materials and methods: The phrenic nerve activity (PNA) was recorded in 10 adult, male, Sprague-Dawley rats, urethane anesthetized, bilaterally vagotomized, paralyzed and mechanically ventilated. Femoral arteries and veins were cannulated for blood pressure monitoring, obtaining blood samples, and intravenous drugs administrations and infusions. The phrenic nerve recordings monitored central respiratory activity. Phrenic nerve was dissected using dorsal approach at the level of C5 nerve rootlet, mounted on bipolar silver wire electrodes. The rats were placed in a prone position in a stereotaxic instrument. The animals were divided in 2 groups. One group (n=5) was exposed to five hypoxias that lasted for 3 minutes each (FiO2=0.09), separated by 3 minutes of hyperoxia (FiO2=0.5). Another group was exposed to three hypoxias that lasted for 5 minutes each (FiO2=0.09), separated by 5 minutes of hyperoxia (FiO2=0.5). Peak phrenic nerve amplitude (PNA), burst frequency (f), inspiratory time duration (Ti), expiratory time duration (Te) and total respiratory cycle duration (Ttot) were analyzed during the first hypoxia and 15, 30 and 60 minutes after the final hypoxic episode, and compared to the baseline values prior to the first hypoxic episode. Results: Isocapnia was successfully maintained throughout the protocol. There was a significant increase of peak phrenic nerve amplitude (66.7 ± 8.6%, p<0.05) in group of animals that underwent 5 times 3 minutes hypoxic exposures 60 minute after the last hypoxic episode compared to the baseline values. On contrary, in the second gropu of animals that underwent 3 times 5 minutes hypoxic exposure no significant changes of PNA were recorded in any time point after the last hypoxic episode. AIH did not elicit significant changes in phrenic burst frequency, as well as in breathing rhythm parameters (Ti, Te, Ttot) in both groups at all 3 time points after the last hypoxic episode. Conclusion: This study demonstrates that protocols with different number of hypoxic episodes and duration affect the elicitation of the phrenic LTF in urethane anesthetizded rats differently. Protocol of 5 times 3 minutes intermittent hypoxic exposure evokes phrenic LTF while another protocol (3 times, 5 min) failed to elicit phrenic LTF

hypoxia; long term facilitation; phrenic nerve; rats

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