Effects of sleep modulation on stroke recovery in rats

The general aim of the present thesis was to investigate the role of sleep in the recovery process of the brain after ischemic stroke in rats, and in particular to understand whether sleep promotion could improve post-stroke recovery. Sleep-wake disturbances have been described in patients suffering from stroke and appear to have a negative impact on rehabilitation and long-term outcomes. In the experimental stroke model, sleep disruption has detrimental effects on infarct size, expression of plasticity-related genes, and functional recovery, while sleep stimulant gamma-hydroxybutyrate (GHB) accelerates stroke recovery in mice. Yet, the role of sleep and its underlying mechanisms in modulating the injured brain and clinical outcomes are poorly known. Promotion of neuroplasticity during recovery may represent an effective therapeutic strategy and, since sleep has been implicated in facilitation of neuroplasticity, approaches targeting sleep may lead to development of treatment able to improve long- term functional outcome after stroke. The first goal was to evaluate whether two pharmacological agents, baclofen (Bac) and GHB would induce a physiological sleep in rats. Recently, a lot of effort have been put to create drugs acting through GABA receptors in order to promote physiological sleep for therapeutic purposes. Both drugs, which act through GABAB receptors, have been shown to promote sleep in humans, but their effects in rodents remain unclear. The results of this study demonstrated that Bac and GHB induced a non-physiological state characterised by atypical behaviour and abnormal electroencephalogram (EEG) pattern, and affected vigilance in rats. However, the principal finding was that Bac, but not GHB, had sleep- promoting properties (facilitated and consolidated sleep). Therefore, as the next step we decided to use Bac as a sleep-promoting drug and evaluate effects on functional recovery after stroke. The second study aimed at investigating stroke outcome following repeated treatment with Bac in a rat model of focal cerebral ischemia. The first injections of Bac or saline were given 24 h after initiation of ischemia and then twice daily for 10 consecutive days. The data demonstrated that repeated Bac treatment after stroke affected sleep, neuroplasticity and motor function but not the size of the brain damage. Thus, Bac administration increased non-rapid eye movement (NREM) sleep amount and improved motor function recovery concomitantly with enhanced axonal sprouting and neurogenesis. Furthermore, although Bac had no effect on the size of the lesion volume, it reduced atrophy of the corpus callosum. These results indicate that delayed repeated Bac treatment promotes neuronal plasticity after stroke and thereby benefits motor function recovery. We suggest that observed effects might be mediated by sleep, emphasizing the importance of sleep in recovery processes. In summary, the results of this work contribute to the understanding of the sleep- modulating effects on stroke recovery processes, indicating that pharmacological sleep promotion could mediate and enhance endogenous recovery mechanisms in a rat model of focal cerebral ischemia. Furthermore, these studies not only advance our knowledge in basic principles of sleep function in the injured brain but may also offer a rationale for a novel strategy to promote recovery after stroke, and possibly other brain injuries, by developing sleep-modulating treatments

Baclofen and gamma-hydroxybutyrate differentially altered behavior, EEG activity and sleep in rats.

OBJECTIVES Animal and human studies have shown that sleep may have an impact on functional recovery after brain damage. Baclofen (Bac) and gamma-hydroxybutyrate (GHB) have been shown to induce physiological sleep in humans, however, their effects in rodents are unclear. The aim of this study is to characterize sleep and electroencelphalogram (EEG) after Bac and GHB administration in rats. We hypothesized that both drugs would induce physiological sleep. METHODS Adult male Sprague-Dawley rats were implanted with EEG/electromyogram (EMG) electrodes for sleep recordings. Bac (10 or 20 mg/kg), GHB (150 or 300 mg/kg) or saline were injected 1 h after light and dark onset to evaluate time of day effect of the drugs. Vigilance states and EEG spectra were quantified. RESULTS Bac and GHB induced a non-physiological state characterized by atypical behavior and an abnormal EEG pattern. After termination of this state, Bac was found to increase the duration of non-rapid eye movement (NREM) and rapid eye movement (REM) sleep (∼90 and 10 min, respectively), reduce sleep fragmentation and affect NREM sleep episode frequency and duration (p<0.05). GHB had no major effect on vigilance states. Bac drastically increased EEG power density in NREM sleep in the frequencies 1.5-6.5 and 9.5-21.5 Hz compared to saline (p<0.05), while GHB enhanced power in the 1-5-Hz frequency band and reduced it in the 7-9-Hz band. Slow-wave activity in NREM sleep was enhanced 1.5-3-fold during the first 1-2 h following termination of the non-physiological state. The magnitude of drug effects was stronger during the dark phase. CONCLUSION While both Bac and GHB induced a non-physiological resting state, only Bac facilitated and consolidated sleep, and promoted EEG delta oscillations thereafter. Hence, Bac can be considered a sleep-promoting drug and its effects on functional recovery after stroke can be evaluated both in humans and rats

Baclofen facilitates sleep, neuroplasticity, and recovery after stroke in rats.

OBJECTIVE Sleep disruption in the acute phase after stroke has detrimental effects on recovery in both humans and animals. Conversely, the effect of sleep promotion remains unclear. Baclofen (Bac) is a known non-rapid eye movement (NREM) sleep-promoting drug in both humans and animals. The aim of this study was to investigate the effect of Bac on stroke recovery in a rat model of focal cerebral ischemia (isch). METHODS Rats, assigned to three experimental groups (Bac/isch, saline/isch, or Bac/sham), were injected twice daily for 10 consecutive days with Bac or saline, starting 24 h after induction of stroke. The sleep-wake cycle was assessed by EEG recordings and functional motor recovery by single pellet reaching test (SPR). In order to identify potential neuroplasticity mechanisms, axonal sprouting and neurogenesis were evaluated. Brain damage was assessed by Nissl staining. RESULTS Repeated Bac treatment after ischemia affected sleep, motor function, and neuroplasticity, but not the size of brain damage. NREM sleep amount was increased significantly during the dark phase in Bac/isch compared to the saline/isch group. SPR performance dropped to 0 immediately after stroke and was recovered slowly thereafter in both ischemic groups. However, Bac-treated ischemic rats performed significantly better than saline-treated animals. Axonal sprouting in the ipsilesional motor cortex and striatum, and neurogenesis in the peri-infarct region were significantly increased in Bac/isch group. CONCLUSION Delayed repeated Bac treatment after stroke increased NREM sleep and promoted both neuroplasticity and functional outcome. These data support the hypothesis of the role of sleep as a modulator of poststroke recovery