Pontomedullary transection in arterially‐perfused adult rat elicits diverse phrenic burst patterns and alters spectral dynamics

Abstract

It is widely accepted that transection of the brainstem at the pontomedullary (PM) border shifts the eupneic pattern of breathing to gasping in vivo. Recent observations in the decerebrate arterially-perfused adult rat preparation, however, have demonstrated that similar transection may elicit multiple patterns of inspiratory motor output. Here, we examined the temporal and spectral (including time-frequency) characteristics of inspiratory discharge patterns following PM transection as well as transection caudal to the PM border in 6 decerebrate arterially-perfused adult rat preparations. Following PM transection, fractionated, square wave, bell-shaped, augmenting, and decrementing phrenic burst patterns were seen. These modified bursts exhibited increased burst duration (from 0.73±0.08 to 1.17±0.09 s; p=0.037) and reduced burst amplitude. Spectral analysis revealed decreased HFO power with little or no effect on MFO power, resulting in an increase in the MFO/HFO ratio by ~ 3-fold (p=0.009). The frequency of the MFO peak, however, was reduced from 43.8±1.3 to 36.3±2.3 Hz (p=0.047). Spectral activity also exhibited an earlier onset (~10% TI) and prolonged duration (~80% TI) following PM transection. Transection ~1–2 mm caudal to the PM border was ineffective in further altering either burst pattern or spectral content; however, TI was decreased. Subsequent transection at or caudal to the obex abolished all rhythmic output. These results confirm that PM transection elicits multiple patterns of phrenic nerve discharge in the arterially-perfused adult rat preparation, and further demonstrates that these modified burst patterns are associated with alterations in the spectral dynamics underlying the central inspiratory network. Supported by NS045321