Cholinergic neurons of the basal forebrain supply the neocortex with ACh and play a major role in regulating behavioral arousal and cortical electroencephalographic activation. Cortical ACh release is greatest during waking and rapid eye movement (REM) sleep and reduced during non-REM (NREM) sleep. Loss of basal forebrain cholinergic neurons contributes to sleep disruption and to the cognitive deficits of many neurological disorders. ACh release within the basal forebrain previously has not been quantified during sleep. This study used in vivo microdialysis to test the hypothesis that basal forebrain ACh release varies as a function of sleep and waking. Cats were trained to sleep in a head-stable position, and dialysis samples were collected during polygraphically defined states of waking, NREM sleep, and REM sleep. Results from 22 experiments in four animals demonstrated that means +/- SE ACh release (pmol/10 min) was greatest during REM sleep (0.77 +/- 0.07), intermediate during waking (0.58 +/- 0.03), and lowest during NREM sleep (0.34 +/- 0.01). The finding that, during REM sleep, basal forebrain ACh release is significantly elevated over waking levels suggests a differential role for basal forebrain ACh during REM sleep and waking.
The present study examined the hypothesis that cholinergic neurons in the pedunculopontine tegmental nucleus (PPT) can cause the release of acetylcholine (ACh) in the pontine reticular formation and contribute to respiratory depression. In vivo microdialysis of the gigantocellular tegmental field (FTG) was performed in 10 adult male cats while respiration was being measured. In four intact, unanesthetized cats these measurements were obtained during states of quiet wakefulness and during the rapid eye movement (REM) sleeplike state caused by FTG microinjections of carbachol. The results demonstrate a simultaneous time course of enhanced ACh release in the FTG and respiratory rate depression. In six barbiturate-anesthetized cats similar measurements were obtained while PPT regions containing NADPH-positive neurons were electrically stimulated. PPT stimulation caused increased ACh release in the FTG and caused respiratory rate depression. Together, these findings are consistent with the hypothesis of a causal relationship between ACh release in the FTG and respiratory depression.
This study was performed to test the hypothesis that cholinoceptive basal forebrain systems can significantly influence cholinoceptive pontine mechanisms known to be important for generating rapid eye movement (REM) sleep. This hypothesis was examined by microinjecting the cholinergic agonist carbachol or saline (vehicle control) into the pons, the basal forebrain, or simultaneously into the pons and basal forebrain, while quantifying the effects on sleep and wakefulness in unanesthetized, chronically instrumented cats. All microinjections were made during wakefulness and were followed by 2 or 4 hr of recording. Polygraphic records were scored for wakefulness, non-REM sleep, REM sleep, and the REM sleep-like state evoked by pontine administration of carbachol (DCarb). Dependent variables quantified following each microinjection included the percentage of recording time spent in each state, the latency to onset of non-REM, REM, and DCarb, the number of episodes per hour of each state, and the duration of the longest episode of each state. A total of 149 microinjections were made into 15 forebrain and 11 pontine sites in eight cats. Basal forebrain administration of carbachol significantly increased wakefulness. Pontine microinjection of carbachol produced a state that polygraphically and behaviorally resembled REM sleep. This REM sleep-like state occurred in amounts significantly greater than natural REM sleep. Pontine carbachol also significantly decreased wakefulness and non-REM sleep. Simultaneous injection of carbachol into the pons and basal forebrain enhanced REM sleep, but the magnitude of this enhancement was significantly less than the increase in REM sleep evoked by carbachol injection into the pons alone. The results show that cholinoceptive regions of the basal forebrain can increase wakefulness and reduce the ability of pontine carbachol to evoke the REM sleep-like state. These findings suggest that basal forebrain administration of carbachol activates an arousal-generating system that can successfully compete with the powerful cholinergic REM sleep-generating system of the pons.
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