To investigate whether melatonin protects neurons from apoptosis, we used amyloid beta-peptide 25±35 (Ab25-35) to induce apoptosis in cultured hippocampal neurons, and monitored the apoptotic activity of the neurons with or without melatonin treatment. Present study shows that melatonin at concentrations of 1×10－6 and 1×10－5mol/L prevents neuronal morphological changes induced by apoptosis, as characterized by the shrunken and rounded morphology caused by condensed chromatin and fragmented DNA. Melatonin further exhibited the ability to inhibit apoptotic internucleosomal DNA degradation. Moreover, ow cytometric analysis of cell cycle demonstrated that melatonin abolished the Ab25-35-induced apoptotic peak. Our results suggest that melatonin may play an important role to protect neurons from Ab25±35-induced apoptosis.

To investigate the role of melatonin in D-galactose-induced amnesic mice, the avoidance/escape and water maze tests were performed to evaluate their learning and memory function. Spectrophotometry was employed to determine the content of thiobarbituric acid-reactive substances (TBARS) and the activities of antioxidative enzymes in the brain. The present results demonstrate that D-galactose-induced amnesic mice had signir cantly decreased learning and memory function. The reduced activities of superoxide dismutase and glutathione peroxidase and increased levels of TBARS were found in brain tissue of the amnesic mice. Melatonin, administered (ig) at doses of 0.1, 1, or 10mg/kg to the D-galactose-treated mice for 3 months, was su

To investigate the effects of Glucosides of Chaenomeles speciosa (GCS) on rat adjuvant arthritis (AA) and to clarify the role of synoviocytes in this process. METHODS: Complete Freund's adjuvant was used to induce AA in rats. Secondary paw swelling of AA rats was measured with MK-550 volume meter. The pain response and polyarthritis index were scored. Synoviocytes were separated by incubation of collagenase and trypsin, and morphological changes of synoviocytes were observed by transmission electron microscope. Interleukin-1 (IL-1) production was measured by thymocyte proliferation assay. Tumor necrosis factor (TNFα) and prostaglandin E2 (PGE2) production were determined by radioimmunoassay. RESULTS: There were significant secondary inflammatory reactions in AA rats. The morphology of synoviocytes from AA rats was changed, companying the elevation of the level of IL-1,TNFα, and PGE2 produced by synoviocytes from AA rats. GCS (60 and 120 mg/kg, ig, 8d) suppressed secondary inflammatory paw swelling, pain response, and polyarthritis index. It also improved ultrastructural changes of synoviocytes and inhibited IL-1,TNFα, and PGE2 production in AA rats. The inhibitory effect of GCS 120mg/kg was more evident than that of Actarit 60 mg/kg. CONCLUSION: GCS reduced the secondary inflammatory in AA rats, which is associated with prevention of ultrastructural changes of synoviocytes and inhibition of secretion of proimflammatory cytokines.

To investigate improvement of melatonm on leammg and memory impairment induced by amyloid β- peptide 25-35 (Aβ25-35) in elder rats. METHODS: Step-down type passive avoidance test, shuttle-box test, and Morris water maze were used together to determine effects of Aβ25-35 and melatonin on learning and memory. Pathological changes were observed by HE, Congo red, and Ag staining. RESULTS: The elder rats were injected bilaterally Aβ25-35 20 g into the hippocampus to induce learning and memory dysfunction. Melatonin administration (0.1, 1, and 10mg/kg, ig×8 d) to the Aβ25-35-treated rats prolonged the latency, shortened the total stimulating time, and decreased the number of errors in the step-down test. Suttle-box test showed that melatonin improved amnesic rats" performace at the same doses. Melatonin (0.1, 1, and 10mg/kg), giving for 10 d, could enhance the spatial resolution of amnesic rats in Morris water maze test. Also in Aβ25-35-treated group, a decrease in the number of neurons in cortex and hippocampus, a massive glial reaction, and neurophilic phenomenon were detected by HE staining; the positive vascular amyloidosis by Congo red and fibrils by Ag staining were observed. Melatonin (0.1 and 1 mg/kg)could inhibit above pathological changes in Aβ25-35-group. CONCLUSION: Melatonin improved the impaired learning and memory induced by Aβ25-35 in elder rats.

To study the effects and mechanisms of melatonin (MT) on immune responses in mice of different months. METHODS: Thymocyte proliferation and IL-2 activity were assayed by 3-(4,5-dimethylthiazol-2-yl) 2,5-diphenyltetrazolium bromide (MTT) and activated mouse splenocyte proliferation methods, respectively; cAMP and methionine-enkephalin (met-Enk) level was determined by competitive protein binding assay and radioimmunoassay, respectively. RESULTS: The function of lymphocytes, obtained from BALB/c mice aged 6 and 11 months were decreased, which was restored by melatonin at the dose of 5 mg/kg or 30 mg/kg. In vitro, proliferation of lymphocytes in 11-month-old mice was decreased and cAMP level was increased. Melatonin (0.1nmol/L or 1mmol/L) had negative regulation to this. Forskolin (10 mmol/L) enhanced the cAMP level of lymphocytes in 2-and 11-month-old mice (P<0.01), which was antagonized partially by melatonin and this effect of melatonin was also abolished by pertussis toxin (1mg/L) completely. Melatonin (1mmol/L and 0.1nmol/L) increased the content of met-Enk of lymphocytes in 2-and 11-month-old mice, respectively (P<0.01), which was blocked by nifedipine (1 mmol/L). CONCLUSION: Melatonin exerted an effect on immune responses in mice of different months, which might be mediated by G protein-AC-cAMP signal transduction pathway and regulation of met-Enk level.