Melatonin attenuates cerebral hypoperfusion-induced hippocampal damage and memory deficits in rats by suppressing TRPM7 channels

Melatonin Modulates Cell Cycle Dynamics and Promotes Hippocampal Cell Proliferation After Ischemic Injury in Neonatal Rats

Promoting neural cell proliferation may represent an important strategy for enhancing brain repair after developmental brain injury. The present study aimed to assess the effects of melatonin on cell proliferation after an ischemic injury in the developing hippocampus, focusing on cell cycle dynamics. After in vivo neonatal hypoxia-ischemia (HI), hippocampal cell cycle dynamics were assessed by flow cytometry, together with histological evaluation of dentate gyrus cellularity and proliferation. Melatonin significantly increased the number of proliferating cells in the G2/M phase as well as the proliferating cell nuclear antigen (PCNA) and doublecortin (DCX) labeling reduced by HI. In vivo BrdU labeling revealed a higher BrdU-positivity in the dentate gyrus of ischemic rats treated with melatonin, an effect followed by increased cellularity and preserved hippocampal tissue integrity. These results indicate that the protective effect of melatonin after ischemic injury in neonatal rats may rely on the modulation of cell cycle dynamics of newborn hippocampal cells and increased cell proliferation.

Involvement of TRPM7 Channel on the Induction of Diabetic Neuropathic Pain in Mice: Protective Role of Selenium and Curcumin

Excessive levels of the mitochondrial reactive oxygen radical (mitSOX) and Ca²⁺ influx were found to cause neuropathic pain in patients with diabetes mellitus (DM). Naltriben (NLT) and mitSOX activate the transient receptor (TRP) melastatin 7 (TRPM7) channel, but antioxidants and carvacrol inhibit it. Selenium (Se) and curcumin (CRC) have been thoroughly studied for their modulator effects on streptozotocin (STZ)-induced neuropathic pain, apoptosis, and oxidative stress through the blockage of TRP channels in dorsal root ganglion (DRG) neurons. It has not yet been fully understood how Se and CRC protect against STZ-induced neuropathic pain by modulating TRPM7. Here, we assessed how Se and CRC affected the Ca²⁺ influx, mitSOX-mediated oxidative damage, and apoptosis in the DRGs of mice through modifying TRPM7 activity. Seven groups (control, Se, CRC, STZ, STZ + Se, STZ + CRC, and STZ + Se + CRC) were induced from the 56 male mice. We observed that the STZ-induced stimulation of TRPM7 increased mechanical neuropathic pain (von Frey), thermal neuropathic pain (hot plate), cytosolic Ca²⁺, TRPM7 current density, TRPM7 expression, lipid peroxidation, mitSOX, cytosolic ROS, apoptosis, caspase-3, caspase-8, and caspase-9 concentrations, whereas Se and CRC therapies diminished the alterations. The STZ-mediated decreases of DRG viability, brain glutathione, glutathione peroxidase, vitamin A, and vitamin E concentrations were also upregulated in the treatment groups by the therapies. These findings collectively imply that an imbalance of neuropathic pain, oxidative neurotoxicity, and apoptosis in the mice is caused by the STZ-mediated activation of TRPM7. However, the downregulation of TRPM7 activity caused by the injections of Se and CRC reduced the neurotoxicity and apoptosis.

Protective effect of melatonin on learning and memory impairment and hippocampal dysfunction in rats induced by high-fructose corn syrup

Objectives

We investigated the harmful effects of high fructose corn syrup (HFCS) on learning and memory in the hippocampus and the ameliorative effects of melatonin (Mel).

Materials and Methods

Thirty-six adult male Sprague Dawley rats were divided into three groups: Group I, control; Group II, HFCS; and Group III, HFCS+Mel. HFCS form F55 was prepared as a 20% fructose syrup solution. Rats in HFCS and HFCS+Mel groups were given drinking water for 10 weeks. Rats in the HFCS+Mel group have been given 10 mg/kg/day melatonin orally for the 6 weeks, in addition to HFCS 55. The Morris water maze (MWM) test was applied to all animals for 5 days to determine their learning and memory levels. After decapitation, one-half of the hippocampus samples were collected for western blot analysis, and another half of the tissues were collected for histopathological and immunohistochemical analyses.

Results

In the HFCS group, there was a significant difference between the time to find the platform in the MWM test and time spent in the quadrant between days 1 and 5 (P=0.037 and P=0.001, respectively). In addition, a decreased level of MT1A receptor, TNF-α, iNOS, osteopontin (OPN), and interleukin-6 (IL-6) expressions were significantly increased in the HFCS group. Melatonin treatment reversed MT1A receptor levels and TNF-α, iNOS, OPN, and IL-6 expressions. During the histopathological examination, increased neuronal degenerations were observed in the HFCS group. Melatonin ameliorated these changes.

Conclusion

Consumption of HFCS caused deterioration of learning and memory in adult rats. We suggest that melatonin is effective against learning and memory disorders.