Docosahexaenoic acid (DHA), an omega-3 polyunsaturated fatty acid (n-3 PUFAs), is an essential polyunsaturated fatty acid in the central nervous system, and possesses many physiological functions in neurodegenerative diseases. Previously, there are some reports that n-3 PUFAs contribute to pain relief. As the antinociceptive effect of DHA alone has not been reported, this study examined the antinociceptive effect of DHA on various pain stimuli. To evaluate the antinociceptive effect of DHA on thermal and chemical nociception, we employed the tail flick test, acetic acid writhing test and formalin test in mice. DHA was orally administrated at 5, 15 and 25 mmol/kg at 30 min before measurement. DHA administration dose-dependently exerted an antinociceptive effect against thermal and chemical stimulation in comparison to the control olive oil administration. These effects of DHA were abolished when mice were pretreated with naloxone, an opioid receptor antagonist. These findings suggest that DHA has opiod receptor-mediated pain control activities, and may provide valuable information towards an advanced therapeutic approach for pain control.
Abstract. Orexin-A is a newly identified neuropeptide expressed in the lateral areas of the hypothalamus that plays a role in various physiological functions, including regulation of glucose metabolism. We have previously reported that the development of post-ischemic glucose intolerance is one of the triggers of ischemic neuronal damage. Therefore, the aim of this study was to determine the effects of orexin-A on the development of post-ischemic glucose intolerance and ischemic neuronal damage. Male ddY mice were subjected to middle cerebral artery occlusion (MCAO) for 2 h. Neuronal damage was estimated by histological and behavioral analysis after MCAO. Intracerebroventricular administration of orexin-A (2.5, 25, or 250 pmol/mouse) significantly and dose-dependently suppressed the development of post-ischemic glucose intolerance on day 1 after MCAO and neuronal damage on day 3 after MCAO. In the liver and skeletal muscle, the expression levels of insulin receptor were decreased, whereas those of gluconeogenic enzymes were increased on day 1 after MCAO. Furthermore, these expressions were completely recovered to normal levels by orexin-A and were reversed by the administration of SB334867, a specific orexin-1 receptor antagonist. These results suggest that regulation of post-ischemic glucose intolerance by orexin-A suppressed cerebral ischemic neuronal damage.
Neural cell adhesion molecule (NCAM) is a membrane protein abundantly expressed in the central nervous system. Recently, it has been reported that dysfunction of NCAM is linked to human brain disorders. Furthermore, NCAM is one of the proteolysis targets of matrix metalloproteinase (MMP), whose activation is implicated in neuronal damage. The aim of this study was to elucidate the involvement of MMP-mediated proteolysis of NCAM in the development of ischemic neuronal damage. Male ddY and MMP-9 knockout (KO) C57BL/6J mice were subjected to 2 h of middle cerebral artery occlusion (MCAO). In MCAO model mice, development of infarction and behavioral abnormality were clearly observed on days 1 and 3 after MCAO. Protein levels of MMP-2 and MMP-9 were significantly increased on days 1 and 3 after MCAO. In addition, full-length NCAM (180 kDa) was significantly decreased, but its metabolite levels increased on day 1 by ischemic stress per se. NCAM small interfering RNA significantly increased the neuronal damage induced by MCAO. MMP inhibition or MMP-9 gene KO attenuated the infarction, behavioral abnormalities, and decrease of NCAM (180 kDa) observed after MCAO in mice. The present findings clearly suggest that MMP-2/MMP-9-mediated NCAM proteolysis is implicated in the exacerbation of ischemic neuronal damage.
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