GABAergic mechanisms underlying episodic breathing in rat brainstem‐spinal cord preparations

Abstract

Using neonatal rat brainstem‐spinal cord preparations, we examined respiratory activity to characterize the production of episodic breathing patterns with the pons intact and the pons removed; and in the presence of GABA receptor agonists and antagonists. Neonatal rats (P0‐P4) were anesthetized and brainstem spinal cords removed. Respiratory‐like activity from C1 and C4 ventral roots were recorded (21–23C) and raw recordings were integrated and analyzed for respiratory burst duration, peak height, peak area, frequency and breathing pattern (episodic vs. continuous) before and after GABA receptor activation or blockade. Episodic patterns were expressed in a high percentage of young preparations at room temperature. With the pons intact, the GABAA antagonist, bicuculline, increased burst frequency and burst duration. The increase in duration appeared to be due to the combination of two or three distinct bursts with no expiratory pauses, suggesting the appearance of episodic pattern formation. With the pons removed, bicuculline increased burst frequency but had no effect on duration. GABAA receptor agonists (muscimol and chlorpromazine) decreased frequency and turned episodic patterns to continuous patterns. Phaclofen, a GABAB receptor antagonist, had no effect on respiratory pattern or frequency. These results show that GABAA but not GABAB receptors play a role in episodic respiratory pattern generation and that pontine mechanisms are involved in this pathway.