Another chapter in the adenosine story.
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Adenosine↗
Biomedical subjects
Radhika Basheer
Publications and source records attributed to Radhika Basheer.
REM sleep changes in rats induced by siRNA-mediated orexin knockdown.
Short interfering RNAs (siRNA) targeting prepro-orexin mRNA were microinjected into the rat perifornical hypothalamus. Prepro-orexin siRNA-treated rats had a significant (59%) reduction in prepro-orexin mRNA compared to scrambled siRNA-treated rats 2 days postinjection, whereas prodynorphin mRNA was unaffected. The number of orexin-A-positive neurons on the siRNA-treated side decreased significantly (23%) as compared to the contralateral control (scrambled siRNA-treated) side. Neither the colocalized dynorphin nor the neighbouring melanin-concentrating hormone neurons were affected. The number of orexin-A-positive neurons on the siRNA-treated side did not differ from the number on the control side 4 or 6 days postinjection. Behaviourally, there was a persistent (approximately 60%) increase in the amount of time spent in rapid eye movement (REM) sleep during the dark (active) period for 4 nights postinjection, in rats treated with prepro-orexin siRNA bilaterally. This increase occurred mainly because of an increased number of REM episodes and decrease in REM-to-REM interval. Cataplexy-like episodes were also observed in some of these animals. Wakefulness and NREM sleep were unaffected. The siRNA-induced increase in REM sleep during the dark cycle reverted to control values on the 5th day postinjection. In contrast, the scrambled siRNA-treated animals only had a transient increase in REM sleep for the first postinjection night. Our results indicate that siRNA can be usefully employed in behavioural studies to complement other loss-of-function approaches. Moreover, these data suggest that the orexin system plays a role in the diurnal gating of REM sleep.
Animals↗
Sleep deprivation-induced protein changes in basal forebrain: implications for synaptic plasticity.
The need to sleep is universal and lack of sleep often results in decreases in alertness and cognitive function. Data suggest that sleep-related mechanisms and deficits resulting from loss of sleep are associated anatomically with the basal forebrain. Long-term effects of sleep deprivation, those lasting a day or more, likely require transcriptional changes leading to changes in protein synthesis, whereas short-term effects may be mediated by rapid changes in the functional status of proteins. To understand sleep deprivation-induced changes in proteins in the wake-promoting area of the basal forebrain in rat, proteomic analysis was carried out by a combination of 2D gel electrophoresis to separate and visualize proteins and matrix-assisted laser desorption/ionization time-of flight mass spectrometry for protein identification. Among 969 protein spots that were compared, 89 spots showed more than a twofold difference between 6-hr sleep-deprived rats and undisturbed sleeping controls. We have identified 11 of these proteins to be either cytoskeletal or associated with synapses. The changes in four of these proteins were analyzed further by Western blots of 1D and 2D. Two proteins associated with the cytoskeleton, tubulin and GAP43, show posttranslational modifications. Increased tyrosination of alpha tubulin isoforms and increased phosphorylation of GAP43 was observed after 6-hr sleep deprivation when compared to that in sleeping controls. The synaptic protein synaptosomal-associated protein-25 (SNAP25) is decreased whereas amphiphysin is phosphorylated after sleep deprivation. These changes in proteins in the basal forebrain during short-term sleep deprivation are suggestive of changes in the substrate for neuronal transmission and plasticity.
Animals↗
Wakefulness-inducing effects of histamine in the basal forebrain of freely moving rats.
Histamine-containing neurons of the tuberomammillary nucleus (TMN) are implicated in facilitating wakefulness. They project to many brain areas, including the cholinergic basal forebrain (BF). The cholinergic magnocellular regions of the BF are important in the regulation of cortical arousal and wakefulness, and a role for histamine in this activity is suggested by in vitro data indicating histamine excites BF cholinergic and non-cholinergic neurons. To test the hypothesis that histamine induces wakefulness via actions in the BF, we performed microdialysis perfusion of different concentrations of histamine (100, 500 and 1000 microM) in the BF of Sprague-Dawley rats. A MANOVA analysis showed that histamine produced a highly statistically significant and dose-dependent increase in wakefulness and decrease in non-rapid eye movement (NREM) sleep compared with artificial cerebrospinal fluid perfusion. From a wakefulness baseline percentage time of about 12% with artificial cerebrospinal fluid, histamine perfusion increased this value to 26% (100 microM), 36% (500 microM), or 47% (1000 microM). There was no statistically significant change in rapid eye movement (REM) sleep. Histamine perfusion (500 microM) in a control site, the centromedian thalamic nucleus, did not produce any change in behavioral state. The results indicate a prominent role of histamine in wakefulness regulation via the BF and further support the hypothesis that the BF has an important role in EEG activation and wakefulness.
Animals↗
Adenosine and sleep-wake regulation.
This review addresses three principal questions about adenosine and sleep-wake regulation: (1) Is adenosine an endogenous sleep factor? (2) Are there specific brain regions/neuroanatomical targets and receptor subtypes through which adenosine mediates sleepiness? (3) What are the molecular mechanisms by which adenosine may mediate the long-term effects of sleep loss? Data suggest that adenosine is indeed an important endogenous, homeostatic sleep factor, likely mediating the sleepiness that follows prolonged wakefulness. The cholinergic basal forebrain is reviewed in detail as an essential area for mediating the sleep-inducing effects of adenosine by inhibition of wake-promoting neurons via the A1 receptor. The A2A receptor in the subarachnoid space below the rostral forebrain may play a role in the prostaglandin D2-mediated somnogenic effects of adenosine. Recent evidence indicates that a cascade of signal transduction induced by basal forebrain adenosine A1 receptor activation in cholinergic neurons leads to increased transcription of the A1 receptor; this may play a role in mediating the longer-term effects of sleep deprivation, often called sleep debt.
Adenosine↗
Adenosine induces inositol 1,4,5-trisphosphate receptor-mediated mobilization of intracellular calcium stores in basal forebrain cholinergic neurons.
In the cholinergic basal forebrain, we found previously that the extracellular adenosine concentration increase that accompanies sleep deprivation, acting via the A1 receptor, led to activation of the transcription factor nuclear factor-kappaB and to the upregulation of A1 adenosine receptor mRNA. We thus began to examine intracellular signaling mechanisms. We report here that adenosine, acting in a dose-dependent manner and predominantly via A1 receptors, stimulated IP3 receptor-regulated calcium release from intracellular stores. To the best of our knowledge, this calcium signaling pathway effect is a novel action of the G(i)-coupled A1 adenosine receptor in neurons. Moreover, this calcium mobilization was not seen at all in noncholinergic neurons but was present in a large proportion of cholinergic neurons. These data suggest a potential role for a calcium-signaling pathway in adenosine-induced long-term effects of sleep deprivation and a key role for cholinergic neurons in this process.
Adenosine↗