Lesioning of the pedunculopontine nucleus reduces rapid eye movement sleep, but does not alter cardiorespiratory activities during sleep, under hypoxic conditions in rats

Abstract

To determine how partial lesioning of the pedunculopontine nucleus (PPT) affects sleep, breathing, and blood pressure in rats, ibotenic acid (IBO) was injected bilaterally into the PPT. Sham-injected (saline) and IBO-lesioned rats were first studied under normoxic conditions (40 recordings were obtained from 15 rats, with each recording lasting for 6 daytime hours). Rats were then exposed to intermittent hypoxia for 4 ± 2 days (51 recordings from 12 rats, each lasting 6 daytime hours). The intermittent hypoxia protocol involved an oxygen decline lasting 35 s (to a nadir of 10 %) followed by a 50 s increase to normoxia. The IBO caused an estimated 53 % reduction in PPT neurons. When normoxic, IBO-lesioned rats had remarkedly normal sleep architecture, respiratory rates, and mean arterial pressure. The exposure to intermittent hypoxia evoked tachypnea in both the IBO-lesioned and sham-injected rats. When intermittently hypoxic, IBO-lesioned rats demonstrated a significant reduction in the duration of rapid eye movement (REM) sleep. We conclude that partial lesions of the PPT do not disrupt cardiorespiratory activities, but a reduction in PPT neurons impairs the ability to sustain REM sleep under hypoxic conditions.

Keywords: Blood pressure; Breathing; Hypoxia; Lesion; Pedunculopontine nucleus; Rapid eye movement sleep.