Participation of the opioid- and serotonergic systems of the ventrolateral medullary regions in the control of respiratory activity in early postnatal rats.

Autor: Marchenko, V., Fenik, V., Preobrazhenskii, N., Seredenko, M.
Zdroj: Neurophysiology; Jan1996, Vol. 28 Issue 1, p49-58, 10p
Abstrakt: The effects of blockers of opioid and serotonin receptors (naloxone and methisergide, respectively) on the respiratory activity recorded from the n. phrenicus of semi-isolated medullo-spinal preparations (SIMSP) were studied in newborn (1-day-old) and 4- to 5-day-old rats. The preparations were superfused in situ, and inspiratory discharges (ID) were recorded before and after transverse sections of the ventrolateral medullary regions (VLMR) at different levels. Naloxone evoked an increase in the ID frequency in the n. phrenicus both at the initial configuration of preparations and after successive transections of the VLMR between the M and S chemosensitive zones and between the S and L zones. The relative intensity of this effect was significantly higher in newborn rats than in 4- to 5-day-old ones. In contrast, methisergide made the ID frequency lower at all configurations of the SIMSP, and this effect was more intensive in 4- to 5-day-old animals. In the course of progressive separations of more rostral VLMR zones, the effects of naloxone and methisergide applications on the ID frequency became weaker. This allows us to suppose that in newborn rats the rostral VLMR portions provide more intensive opioidergic inhibitory control influences on the activity of respiratory networks than those in 4- to 5-day-old animals. At the same time, tonic activating influences from serotonergic VLMR neurons on the mechanisms generating respiratory rhythm are more intensive in 4- to 5-day-old animals than those in newborn ones. Thus, it can be supposed that the levels of maturation of the opioid- and serotonergic neurotransmitter systems, which provide tonic control of respiratory activity generated in the VLMR, are different in newborn and 4- to 5-day-old animals. The problems of how the opioid- and serotonergic mechanisms controlling respiratory rhythm generation are formed in the course of early stages of ontogenetic development are discussed. [ABSTRACT FROM AUTHOR]
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