Neuroscience
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Modulation of endogenous adenosine levels by inhibition of adenosine metabolism produces a peripheral antinociceptive effect in a neuropathic pain model. The present study used microdialysis to investigate the neuronal mechanisms modulating extracellular adenosine levels in the rat hind paw following tight ligation of the L5 and L6 spinal nerves. Subcutaneous injection of 50 microl saline into the nerve-injured paw induced a rapid and short-lasting increase in extracellular adenosine levels in the subcutaneous tissues of the rat hind paw ipsilateral to the nerve injury. ⋯ These results suggest that following nerve injury, peripheral capsaicin-sensitive primary sensory afferent nerve terminals are hypersensitive, and are able to release adenosine following a stimulus that does not normally evoke release in sham-operated or intact rats. Sympathetic postganglionic afferents do not appear to be involved in such release. The lack of effect on such release by the inhibitors of adenosine metabolism suggests an altered peripheral adenosine system following spinal nerve ligation.
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The identification of leptin and a range of novel anorectic and orexigenic peptides has focussed attention on the neural circuitry involved in the genesis of food intake and the reflex control of thermogenesis. Here, the neurotropic virus pseudorabies has been utilised in conjunction with the immunocytochemical localisation of a variety of neuroactive peptides and receptors to better define the pathways in the rat hypothalamus directed polysynaptically to the major thermogenic endpoint, brown adipose tissue. Infected neurones were detected initially in the stellate ganglion, then in the spinal cord followed by the appearance of third-order premotor neurones in the brainstem and hypothalamus. ⋯ Neurones in the retrochiasmatic nucleus and in the adjacent lateral arcuate nucleus which project to the brown adipose tissue express cocaine- and amphetamine-regulated transcript, pro-opiomelanocortin and leptin receptors. Neurones in the lateral hypothalamus, a site traditionally associated with the promotion of feeding, project to brown adipose tissue and large numbers of these contained melanin-concentrating hormone and orexin A and B. These data provide part of an anatomical framework which subserves the regulation of energy expenditure.
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beta-Endorphin is a non-selective opioid peptide which binds mu-, delta- and putative epsilon (beta-endorphin-sensitive non-mu-, non-delta- and non-kappa(1)-)-opioid receptors. We have previously reported that beta-endorphin-produced G-protein activation is mediated by the stimulation of both mu- and putative epsilon-opioid receptors. The present study was designed to further characterize this putative epsilon-opioid receptor-mediated G-protein activation in the pons/medulla membrane obtained from mice lacking mu-opioid receptor, using a guanosine-5'-O-(3-[(35)S]thio)triphosphate ([(35)S]GTPgammaS)-binding assay. beta-Endorphin and the mu-opioid receptor agonist [D-Ala(2),N-MePhe(4),Gly-ol(5)]enkephalin (DAMGO) increased the [(35)S]GTPgammaS binding in a concentration-dependent manner (0.001-10 microM), and at 10 microM beta-endorphin and DAMGO produced approximately 250 and 120% increases of [(35)S]GTPgammaS binding in the pons/medulla membrane obtained from wild-type mice, respectively. ⋯ The residual increase in [(35)S]GTPgammaS binding by 10 microM beta-endorphin in mu-opioid receptor knockout mice was partially but significantly attenuated by the putative epsilon-opioid receptor partial agonist beta-endorphin (1-27), but not by the delta-opioid receptor antagonist naltrindole or the kappa(1)-receptor antagonist norbinaltorphimine. Furthermore, buprenorphine significantly attenuated the residual increase in [(35)S]GTPgammaS binding by 10 microM beta-endorphin in mu-opioid receptor knockout mice. The present results indicate that beta-endorphin activates G-protein by stimulation of putative epsilon-opioid receptors in the condition lacking the mu-opioid receptor, and buprenorphine acts as an antagonist for putative epsilon-opioid receptors in this condition.
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Immobilization stress rapidly modulates BDNF mRNA expression in the hypothalamus of adult male rats.
We demonstrated that short times (15 min) of immobilization stress application induced a very rapid increase in brain-derived neurotrophic factor (BDNF) mRNA expression in rat hypothalamus followed by a BDNF protein increase. The early change in total BDNF mRNA level seems to reflect increased expression of the BDNF transcript containing exon III, which was also rapidly (15 min) modified. The paraventricular and supraoptic nuclei, two hypothalamic nuclei closely related to the stress response and known to express BDNF mRNA, were analyzed by in situ hybridization following immobilization stress. ⋯ In contrast, in the two other regions examined, the lateral and ventral magnocellular regions of the paraventricular nucleus, as well as in the supraoptic nucleus, signals above control were increased later, at 60 min. After stress application, plasma adrenocorticotropic hormone and corticosterone levels were strongly and significantly increased at 15 min. These studies demonstrated that immobilization stress challenge very rapidly enhanced BDNF mRNA levels as well as the protein, suggesting that BDNF may play a role in plasticity processes related to the stress response.
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As visualized by light and electron microscopic immunocytochemistry, the distribution of the neuronal serotonin-2A (5-HT(2A)) receptor is mainly intracellular throughout adult rat brain. This localization is particularly striking in the pyramidal cells of cerebral cortex, the dendrites of which are intensely immunoreactive, but without any labeling of their spines. In view of recent yeast two-hybrid and biochemical results suggesting an association of 5-HT(2A) receptors with the cytoskeletal microtubule-associated protein MAP1A, the respective subcellular distributions of the receptors and of MAP1A were compared by quantitative electron microscopic immunocytochemistry in dendrites of adult rat frontoparietal cortex. ⋯ The co-localization of 5-HT(2A) receptors and MAP1A protein in the same dendrites could be demonstrated in double immunolabeling experiments. These results confirmed the predominantly somato-dendritic, intracellular localization of 5-HT(2A) receptors in cerebral cortex, showed their higher concentration in distal as opposed to proximal dendrites, and suggested their potential association to the cytoskeleton in cortical neurons in vivo. Such a distribution of 5-HT(2A) receptors reinforces our earlier hypothesis that 5-HT(2A) receptors participate in intraneuronal signaling processes involving the cytoskeleton, and raises the possibility that their activation could be dependent upon that of another co-localized, plasma membrane-bound, 5-HT receptor.