Respiratory rhythm and pattern after ibotenic acid (A) injections into the pontine respiratory group (PRG) of awake goats

Abstract

We tested the hypothesis that IA injections into the PRG would disrupt eupneic respiratory rhythm and pattern. Cannula were bilaterally implanted in adult goats into either the lateral (LPBN, n = 4) or medial (MPBN, n = 4) parabrachial nuclei, or the Kölliker‐Fuse nucleus (KFN, n = 4). After recovery from surgery, 1 or 10μl injections of IA were made bilaterally through the implanted cannula during the awake state. Over the first 5 hours after the 10 μl injections, pulmonary ventilation was increased (P<0.05) in LPBN goats, there were no effects (P > 0.05) in MPBN goats, and there was a biphasic response (P < 0.05) in KFN goats. This biphasic response consisted of a tachypneic hyperpnea for 30 minutes followed by a prolonged hypopnea and hypoventilation with marked apneas and apneusis‐like breathing patterns. While awake and during NREM sleep 10–15 hours after the 1 μl and 10 μl injections respectively, there were above control number of apneas and augmented breaths in all groups. However, there were no incidences of terminal apneas. Breathing rhythm and pattern were normal 22 hours after the injections. Subsequent histological analysis showed <10%, 27%, and 62% reduction in number of neurons in the LPBN, MPBN and KFN goats, respectively. The data do not provide evidence that any of the lesioned sites are obligatory for respiratory rhythm generation, but suggest that the KFN contributes to eupneic pattern generation.