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Lesions of regions for in vitro ventilatory genesis eliminate gasping but not eupnea
1Department of Physiology, Dartmouth Medical School, Dartmouth-Hitchcock Medical Center, Lebanon, NH 03756, USA.
Abstract:
Medullary regions, termed 'pre-inspiratory' and 'pre-Bötzinger', are considered critical for the neurogenesis of rhythmic ventilatory activity of in vitro preparations of the neonatal rat. We examined the influence of destruction of neurons in these regions, by microinjections of kainic acid, upon eupnea and gasping in vivo. Decerebrate, vagotomized, paralyzed and ventilated rats of age 8-15 days were used; the phrenic nerve activity was recorded. Eupnea was not consistently altered following destruction of neurons in any region. However, in the majority of animals, anoxia-induced gasping was not observed following injections of kainic acid into the 'pre-inspiratory' region, 'pre-Bötzinger' complex or lateral tegmental field; the latter region is important for the neurogenesis of gasping in adults. Injections into other regions did not prevent the elicitation of gasping. These results do not support the possibility that neuronal activities which are responsible for respiratory rhythm generation in vitro underlie the neurogenesis of eupnea in vivo.
Insights
Destruction of specific medullary neurons in neonatal rats did not affect normal breathing (eupnea). However, it abolished anoxia-induced gasping, suggesting these neurons are crucial for the gasping reflex, not regular breathing.
Area of Science:
- Neuroscience
- Respiratory Physiology
Background:
- Medullary regions, including the pre-inspiratory and pre-Bötzinger complexes, are implicated in generating rhythmic breathing.
- Understanding the in vivo function of these regions is crucial for respiratory control research.
Purpose of the Study:
- To investigate the role of specific medullary neurons in eupnea and gasping in vivo.
- To determine if in vitro findings on respiratory rhythm generation apply to in vivo respiratory control.
Main Methods:
- Used decerebrate, vagotomized, paralyzed, and ventilated neonatal rats (8-15 days old).
- Recorded phrenic nerve activity to assess respiratory function.
- Destroyed neurons in targeted medullary regions using kainic acid microinjections.
Main Results:
- Eupnea was not consistently altered by neuronal destruction in the studied regions.
- Anoxia-induced gasping was abolished in most rats after kainic acid injections into the 'pre-inspiratory' region, 'pre-Bötzinger' complex, or lateral tegmental field.
- Gasping was still elicited when other medullary regions were injected.
Conclusions:
- Neuronal activities responsible for respiratory rhythm generation in vitro do not appear to underlie eupnea in vivo.
- Specific medullary regions are critical for the neurogenesis of gasping, but not for eupnea, in vivo.