Highly H+-sensitive neurons in the caudal ventrolateral medulla of the rat
The ventral surface of the caudal ventrolateral medulla (cVLM) has been shown to generate intense respiratory responses after surface acid-base stimulation. With respect to their chemosensitive characteristics, cVLM neurons have been less studied than other rostral-most regions of the brainstem. The...
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Published in | The Journal of physiology Vol. 549; no. 1; pp. 181 - 194 |
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Main Authors | , , , , |
Format | Journal Article |
Language | English |
Published |
Oxford, UK
The Physiological Society
15.05.2003
Blackwell Publishing Ltd Blackwell Science Inc |
Subjects | |
Online Access | Get full text |
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Summary: | The ventral surface of the caudal ventrolateral medulla (cVLM) has been shown to generate intense respiratory responses after
surface acid-base stimulation. With respect to their chemosensitive characteristics, cVLM neurons have been less studied than
other rostral-most regions of the brainstem. The purpose of these experiments was to determine the bioelectric responses of
cVLM neurons to acidic stimuli and to determine their chemosensitive properties. Using extracellular and microiontophoretic
techniques, we recorded electrical activities from 117 neurons in an area close to the ventral surface of the cVLM in anaesthetised
rats. All neurons were tested for their sensitivity to H + . The fluorescent probe BCECF was used to measure extracellular pH changes produced by the microiontophoretic injection of
H + in brainstem slices. This procedure provided an estimation of the local changes in pH produced by microiontophoretic H + application in the anaesthetised rat. Neurons coupled to the respiratory cycle, R ( n = 51), were not responsive to direct stimulation with H + . Sixty-six neurons that did respond to H + stimulation were uncoupled from respiration, and identified as NR neurons. These neurons presented distinct ranges of H + sensitivity. The neuronal sensitivity to H + was mainly assessed by the slope of the stimulus-response curve, where the steeper the slope, the higher the H + sensitivity. On this basis, NR neurons were classed as being either weakly or highly sensitive to H + . NR neurons with a high H + sensitivity ( n = 12) showed an average value of 34.17 ± 7.44 spikes s â1 (100 nC) â1 (mean ± s.d. ) for maximal slope and an EC 50 of 126.76 ± 33 nC. Suprathreshold H + stimulation of highly sensitive NR neurons elicited bursting pattern responses coupled to the respiratory cycle. The bursting
responses, which were synchronised with the inspiratory phase and the early expiratory phase of the respiratory cycle, lasted
for several seconds before returning to the steady state firing pattern characteristic of the pre-stimulus condition. These
NR neurons, which possess the capacity to detect distinct H + concentrations in the extracellular microenvironment, are excellent candidates to serve in a chemoreceptor capacity in the
caudal medulla. |
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Bibliography: | ObjectType-Article-1 SourceType-Scholarly Journals-1 ObjectType-Feature-2 content type line 23 |
ISSN: | 0022-3751 1469-7793 |
DOI: | 10.1113/jphysiol.2002.036624 |