Neuroscience
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Besides corticotropin releasing factor, central stress regulatory pathways utilize various neurotransmitters/neuropeptides, such as urocortin and cocaine and amphetamine-regulated transcript, which play an important role in modifying the efferent components of endocrine, immune and behavioral responses to stress. Urocortin's distribution in the rat's brain has been demonstrated, with the most abundant urocortin-ir perikarya present in Edinger-Westphal nucleus. Cocaine and amphetamine-regulated transcript is widely expressed in the rat brain, with a dominant seat of cellular expression also in the Edinger-Westphal nucleus. ⋯ Our experiments revealed that urocortin and cocaine and amphetamine-regulated transcript immunoreactivities colocalize in the Edinger-Westphal nucleus. In addition, our studies using the inducible immediate early gene c-fos as a marker of activated neurons demonstrated a significant stress-induced activation in perikarya colocalizing urocortin- and cocaine and amphetamine-regulated transcript-ir in the Edinger-Westphal nucleus. In view of these data it can be postulated that neurons colocalizing cocaine and amphetamine-regulated transcript and urocortin immunoreactivities respond to acute stress, and may play a role in modulating various physiological functions, such as feeding behaviors.
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Comparative Study
Intrathecal substance p-saporin attenuates operant escape from nociceptive thermal stimuli.
Destruction of neurons in the superficial dorsal horn that express substance P receptor (NK-1R) has been reported to block development of behavioral hypersensitivity following peripheral sensitization of nociceptors. Baseline sensitivity was not altered in these rat models that assessed innate reflex responses (i.e. hind-paw withdrawal to thermal or mechanical stimulation). In the present study, we evaluated effects of intrathecal substance P-saporin (SP-sap), a toxin selective for cells expressing NK-1R, on operant escape responses of rats to thermal stimulation. ⋯ Lick/guard responses were enhanced by mustard oil for both SP-sap and control animals. Administration of morphine (1.0 mg/kg, s.c.) before testing decreased escape responding at 47 degrees C for both controls and SP-sap rats. Thus, partial loss of NK-1R-expressing neurons in the superficial dorsal horn attenuated thermal nociceptive sensitivity and prevented secondary hyperalgesia when studied with an operant algesia assay, in contrast to innate reflexes which were less sensitive to modification by intrathecal SP-sap.
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Comparative Study
Dehydroepiandrosterone 7-hydroxylase CYP7B: predominant expression in primate hippocampus and reduced expression in Alzheimer's disease.
Neurosteroids such as dehydroepiandrosterone (DHEA), pregnenolone and 17beta-estradiol are synthesized by cytochrome P450s from endogenous cholesterol. We previously reported a new cytochrome P450 enzyme, CYP7B, highly expressed in rat and mouse brain that metabolizes DHEA and related steroids by hydroxylation at the 7alpha position. Such 7-hydroxylation can enhance DHEA bioactivity in vivo. ⋯ We also measured CYP7B expression in Alzheimer's disease (AD). CYP7B mRNA was significantly decreased (approximately 50% decline; P<0.05) in dentate neurons from AD subjects compared with controls. A decline in CYP7B activity may contribute the loss of effects of DHEA with ageing and perhaps to the pathophysiology of AD.
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Comparative Study
Temporal pattern of hippocampal high-frequency oscillations during sleep after stimulant-evoked waking.
Hippocampal ripple oscillations (140-200 Hz) are believed to be critically involved in the consolidation of memory traces during slow-wave sleep (SWS). We investigated the temporal pattern of ripple occurrence in relation to sleep phases following different types of waking. Amphetamine, the atypical wakening drug modafinil or non-pharmacological sleep deprivation lead to an increased ripple occurrence ("rebound") during the subsequent SWS episode. ⋯ At the end of the recovery period paradoxical sleep (PS) acted like waking, elevating ripple occurrence during subsequent SWS episodes. On the other hand, PS decreased ripple occurrence if recovery from the rebound was not yet complete. Thus occurrence and structure of ripple oscillations are regulated by the timing and duration of previous SWS, PS and waking episodes.
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Immunohistochemistry and confocal microscopy were used to investigate endocytosis and recycling of the native mu opioid receptor (muOR) in enteric neurons. Isolated segments of the guinea-pig ileum were exposed to increasing concentrations of muOR agonists at 4 degrees C to allow ligand binding and warming to 37 degrees C for 0 min (baseline) to 6 h in ligand-free medium to allow receptor internalization and recycling. The endogenous ligand, [Met]enkephalin, and [D-Ala(2),MePhe(4),Gly-ol(5)] enkephalin (DAMGO), an opioid analog, and the alkaloids, etorphine and fentanyl, induced rapid internalization of muOR immunoreactivity in enteric neurons, whereas morphine did not. muOR internalization was prevented by muOR antagonists. ⋯ A second exposure to DAMGO (100 nM) following recovery of internalized muOR immunoreactivity at the cell surface induced a translocation of muOR immunoreactivity in the cytoplasm comparable to the one observed following the first exposure (46.89+/-3.11% versus 43.31+/-3.80%). muOR internalization was prevented by hyperosmolar sucrose, phenylarsine oxide or potassium depletion, which inhibit clathrin-mediated endocytosis. muOR recycling was prevented by pre-treatment with bafilomycin A1, an acidotropic agent that inhibits endosomal acidification, but not by the protein synthesis inhibitor, cycloheximide. This study shows that native muOR in enteric neurons undergoes ligand-selective endocytosis, which is primarily clathrin-mediated, and recycles following endosomal acidification. Following recycling, muOR is activated and internalized by DAMGO indicating that recycled receptors are functional.