Neuroscience
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We have conducted the first study of sleep in the platypus Ornithorhynchus anatinus. Periods of quiet sleep, characterized by raised arousal thresholds, elevated electroencephalogram amplitude and motor and autonomic quiescence, occupied 6-8 h/day. The platypus also had rapid eye movement sleep as defined by atonia with rapid eye movements, twitching and the electrocardiogram pattern of rapid eye movement. ⋯ This suggests that the low-voltage electroencephalogram is a more recently evolved feature of mammalian rapid eye movement sleep. Rapid eye movement sleep occupied 5.8-8 h/day in the platypus, more than in any other animal. Our findings indicate that rapid eye movement sleep may have been present in large amounts in the first mammals and suggest that it may have evolved in pre-mammalian reptiles.
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Inflammation and hyperalgesia induce a dramatic up-regulation of opioid messenger RNA and peptide levels in nociceptive neurons of the spinal dorsal horn. Descending axons modulate nociceptive transmission at the spinal level during inflammatory pain, and may play a role in the development of persistent pain. The role of descending bulbospinal pathways in opioid-containing nociceptive neurons was examined. ⋯ These data suggest that increased dynorphin messenger RNA ipsilateral to inflammation, in rats without descending axons, was due to increased expression within the same cells and not to recruitment of additional dynorphin-expressing cells. This reflects a greater dynamic response of nociceptive neurons to noxious stimuli in the absence of descending modulation. Therefore, the net effect of descending afferents on spinal nociceptive circuits may be to reduce the response of opioid-containing neurons to noxious stimulation from the periphery.
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The amygdala is a complex forebrain structure proposed to play a pivotal role in fear conditioning circuitry. In this study, c-Fos immunomapping was applied to investigate the functional activation of particular amygdalar nuclei following a 50-trial training session of two-way active avoidance reaction. To dissect distinctive responses displayed by the animals and to cluster them into groups of correlated behaviors, factor analysis was employed. ⋯ The expression in the cortical nucleus correlated negatively with grooming behavior, whereas c-Fos immunolabeling of the other three subdivisions of the amygdala could be associated with the number of intertrial responses. No correlation was observed between c-Fos expression and avoidance reactions performed or the amount of shock received by the animal. The results obtained with c-Fos mapping of various regions of rat amygdala, combined with a fine dissection of behavioral repertoire, imply that there are specific functional links between particular parts of the structure and distinctive behaviors that reflect various emotional states of the animal.
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In previous studies we have shown that electrical stimulation of the nucleus submedius inhibits the rat radiant heat-induced tail flick reflex, and that this antinociceptive effect is mediated by the ventrolateral orbital cortex and periaqueductal gray. The aim of the present study was to examine whether electrical stimulation of the nucleus submedius could inhibit the rat jaw-opening reflex, and to determine whether electrolytic lesions of the ventrolateral orbital cortex or the periaqueductal gray could attenuate the nucleus submedius-evoked inhibition. Experiments were performed on pentobarbital-anesthetized rats. ⋯ The onset of inhibition occured 60 ms after the beginning of nucleus submedius stimulation and lasted about 100 ms, as determined by varying the conditioning-test time interval. Furthermore, ipsilateral lesions of the ventrolateral orbital cortex or bilateral lesions of the lateral or ventrolateral parts of periaqueductal gray eliminated the nucleus submedius-evoked inhibition of the jaw-opening reflex. These data suggest that the nucleus submedius plays an important role in modulation of orofacial nociception, and provide further support for a hypothesis that the antinociceptive effect of nucleus submedius stimulation is mediated by ventrolateral orbital cortex and activation of a descending inhibitory system in the periaqueductal gray.
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The activity and/or expression of the mitogen-activated protein kinases c-Jun N-terminal kinase 1, p38 and extracellular signal-regulated kinases 1/2, as well as their substrates, the transcription factors c-Jun and activating transcription factor-2, were examined following systemic application of kainate in the cortex and hippocampus of the adult rat brain. The protein expression levels of all three mitogen-activated protein kinases remained constant during the observation period. Unexpectedly, c-Jun N-terminal kinase 1 was the only mitogen-activated protein kinase activated in this model of excitotoxicity, its activity raised from between 1 and 3 h moderate basal to maximal levels between 6 and 12 h. ⋯ A second set of supershift experiments demonstrated that c-Jun, but not activating transcription factor 2, bound to activator protein-1 sites in the promoter of substance P and collagenase genes, but not of the cyclo-oxygenase-2 gene. Our results demonstrate that activation of c-Jun N-terminal kinase 1, phosphorylation of c-Jun and selective occupation of the c-jun promoter by activating transcription factor-2 or c-Jun are part of the neuronal response following excitotoxicity that is considered as the mechanism for neuronal apoptosis in vivo. Some of these findings differ substantially from in vitro experiments and underline the necessity to analyse the neuronal stress pathways in the adult brain.