Bilateral coordination of inspiratory neurones in the rat.
Inspiratory activity on the left and right sides must be coordinated to be effective. We used cross-correlation to examine the hypothesis that the coordination of left and right medullary inspiratory neurones is produced by excitation from common sources and by midline-crossing excitatory connections among these neurones. In adult rats, a total of 185 contralateral pairs of inspiratory neurones ( n=370) were recorded extracellularly, and classified, according to their firing pattern, as augmenting ( n=262), constant ( n=82) or decrementing ( n=26). Of the 262 augmenting inspiratory neurones, 98 were classified as phrenic premotor neurones by cross-correlation with phrenic nerve discharge. The 185 cross-correlograms showed little evidence of common activation, or midline-crossing excitatory connections. Of the 45 cross-correlograms for pairs of augmenting neurones, only 4 (approximately equal to 9%) indicated a common activation, and only one a monosynaptic connection. Of the 45 for pairs of augmenting and phrenic premotor neurones, only 9 (20%) showed a common activation, and only 2 a monosynaptic excitatory connection. Of the 19 pairs of phrenic premotor neurones, 5 from the same rat showed high-frequency oscillations, and 1 a monosynaptic excitatory connection. Cross-correlograms for pair combinations of other types of neurones also exhibited few features. We suggest that, in the adult rat, although both common activation and excitatory cross-connections exist as a means for coordinating left and right ventral group inspiratory neurones to the same respiratory rhythm, they are insufficient to account for it.
Shen
Linlin
L
Department of Physiology, University of Toronto, Toronto, Ontario, M5S 1A8, Canada.
Peever
John H
JH
Duffin
James
J
D000818:Animals; D003655:Decerebrate State; D004594:Electrophysiology; D007839:Functional Laterality / Q000502:physiology*; D008297:Male; D008526:Medulla Oblongata / Q000166:cytology / Q000502:physiology; D009046:Motor Neurons / Q000502:physiology*; D010507:Periodicity; D010791:Phrenic Nerve / Q000166:cytology / Q000502:physiology; D051381:Rats; D017207:Rats, Sprague-Dawley; D012132:Respiratory Muscles / Q000294:innervation*