Abstract
In the isolated CNS from neonatal opossum Monodelphis domestica, low pH superfusion increases both respiratory rate and amplitude. One unusual control mechanism in the isolated Monodelphis CNS is that the frequency of respiration depends primarily on changes in the duration of the expiratory rather than the inspiratory phase [1]. To reveal whether this is a characteristic common to other species, we analyzed in isolated hamster and mouse CNS the respiratory responses to pH in terms of variables for amplitude and for timing. Newborn Golden hamsters and CF1 mice (0-5 days old) were anesthetized with ether and cooled on ice. Their CNS were removed and decerebrated by pontobulbar transections. A vaseline seal at the level of the spinal cord segment C1 allowed selective superfusion of the brainstem. Basal conditions were obtained during brainstem superfusion with a continuos flow of 0.8 ml · min-1 artificial cerebrospinal fluid (aCSF) gassed with 95% O2 and 5% CO2, at 20-24°C (pH7.35-7.40). Fictive respiration was recorded from C3-C5 ventral roots with suction electrodes. Acidification (pH7.3 or lower) of the brainstem superfusion was attained by reducing the aCSF's bicarbonate final concentration. Acidification of the brainstem superfusion (from pH7.4-7.3) increased the frequency and decreased the amplitude of respiration in both hamster and mouse (P < 0.01, Wilcoxon test). A common feature of these results is that changes in rate are brought about solely by changes in the duration of the expiratory phase. The inspiratory phase remains constant in duration. Thus, cycle duration can be represented by a linear function exclusively depending on the expiratory duration. The slope of the straight line is very close to 1. These results indicate that the timing of the respiratory cycle in the neonatal hamster and mouse, as well as in the opossum, are controlled by an expiratory instead of an inspiratory off-switch. Increase in respiratory amplitude in response to chemical stimulation is a distinctive feature of the isolated CNS preparation obtained from newborn opossum.
Highlights
To be effective, inspiratory muscles on the left and right sides must contract together
We have found that a prominent gap in the column of ventral respiratory group (VRG) The nucleus tractus solitarii (NTS) relays information from primary related parvalbumin cells [2] likely corresponds to the pBc since visceral receptors to the central nervous system and is critically parvalbumin cells are rare in this zone and never co-localize with involved in the reflex control of autonomic functions
The specific protein(s) necessary for longterm facilitation (LTF) is unknown, we recently found that episodic hypoxia and LTF are associated with elevations in ventral spinal concentrations of brain derived neurotrophic factor (BDNF)
Summary
Inspiratory muscles on the left and right sides must contract together. The left and right halves of the diaphragm are synchronised because a bilateral population of medullary premotor neurones [1] simultaneously excites left and right phrenic motoneurones. Transection studies demonstrate that each side of the brainstem is capable of generating respiratory rhythm independently [2], so that left and right medullary inspiratory neurones must themselves be synchronised. The interconnections and common excitation that accomplish such synchronisation are unknown in rats. The respiratory rhythm of hypoglossal (XII) nerve discharge in transverse medullary slice preparations from neonatal rats is thought to originate in the region of the ventral respiratory group (VRG); generated there by a combination of “pacemaker” neurones [1] and their interactions with other respiratory neurones. Our goal was to discover interconnections between left and right VRG neurones as well as their connections to XII motoneurones
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