| Research Abstract |
We analyzed intrinsic burst generating property of respiratory neurons in the medulla of the rat fetus. In the E17-20 preparations that showed the fetal type-C4 inspiratory burst pattern, about 60% of inspiratory neurons exhibited voltage-dependent burst activity. In E19 preparations, the input resistance of the bursting neurons was significantly higher than that of non-bursting cells. Membrane capacitance tended to be lower (but not significant) in the bursting neurons than in the non-bursting cells. Since the bursting neurons still kept the bursting activity in the low Ca2+/high Mg2+ solution, we concluded that they possess intrinsic burst generating properties.
Using optical recordings, we analyzed respiratory neuron network activity in the ventral medulla of fetus stained with voltage-sensitive dye. In E20/21 preparations, respiratory neuron activity appeared in the limited area of the rostral ventrolateral medulla (para-facial respiratory group, pFRG), and propagated mainly caudall
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y. Then, during the inspiratory phase, the peak of activity was detected, caudally, in the caudal ventrolateral medulla (CVLM) and, rostrally, in the mainly lateral and medial region of the facial nucleus. Such pattern was basically identical to that of neonatal rat preparations. In contrast, in all of El7 and most of El8 preparations, respiratory activity first appeared in the CVLM region, coincidently with the start of inspiratory burst, and then propagated rostrally. Successively, strong activity appeared in the whole region of the facial nucleus and continued 1-3 sec after termination of C4 inspiratory activity. In half of E19 preparations, respiratory activity started from the pFRG (neonatal type), whereas it started from the CVLM in
others (fetal type). However, even in the preparations that showed the neonatal type-network activity pattern, C4 inspiratory activity was the fetal type showing short burst duration. We suggest that the primary rhythm generating network and the spatio-temporal pattern develops to the neonatal type before the neuron network generating inspiratory activity does. Less
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