ABSTRACT
Memantine hydrochloride is an uncompetitive N-methyl-D-aspartate (NMDA) antagonist for treatment of moderate-to-severe Alzheimer's disease. Several studies have shown that memantine can significantly correct the binge-like eating behavior in human and animal models. People with overeating behavior are more likely to be obese. Therefore, we suppose that memantine would be a good candidate for the treatment of obesity. In this study, memantine was shown to increase weight loss in obese mice induced by high fat diet. Memantine was shown to decrease food intake without inducing abdominal discomfort and anxiety, suggesting that this compound would be a good candidate drug for obesity control.
ABSTRACT
Objective To investigate the effects of autophagy on N-methy-D-aspartate (NMDA) receptor and its subunit NR2B and behavioral test in a rat model of neuropathic pain (NP). Methods Male Sprague-Dawley (SD) rats were divided into sham group, NP group, autophagy inhibitor 3-methyladenine (3-MA) pretreatment group (3-MA+NP group) and autophagy inducer rapamyein (Rap) group (Rap+NP group) by random number table with 22 rats in each group. NP animal model was reproduced by ligating sciatic nerve, while sciatic nerve of the rats in the sham group were only exposed but not ligated. The rats in two pretreatment groups were intraperitoneally challenged with 3-MA 15 mg/kg or Rap 10 mg/kg injection 1 hour before operation. Mechanical paw withdrawal threshold (MWT) and thermal paw withdrawal latency (TWL) were measured before and 1, 3, 7, 14 days after operation in each group. Spinal cord tissues were harvested at 1 day and 7 days after operation for autophagosome observation by electron microscope. The expressions of autophagy protein microtubule-associated protein 1 light chain 3 -Ⅱ (LC3 -Ⅱ), Beclin1, and NMDA, NR2B were determined by Western Blot. The positive expression of LC3 was detected by immunofluorescence. Results Compared with sham group, the MWT and TWL of rats in NP group were decreased gradually with the prolongation of operation time, the number of autophagosome, the expressions of LC3 -Ⅱ, Beclin1, NMDA, NR2B, and the positive expression of LC3 in spinal cord were significantly increased at 1 day after operation and till 7 days, which indicated that NP led to hyperpathia and autophagy activation. Compared with NP group, MWT was significantly further decreased, TWL was further shortened, the number of autophagosome was decreased, the expressions of LC3 -Ⅱ and Beclin1 in spinal cord were decreased, and NMDA and NR2B expressions were further increased after 3-MA pretreatment, with significant differences at 1 day after operation [MWT (g): 29.4±2.4 vs. 42.5±6.6, TWL (s): 7.2±1.0 vs. 8.8±1.1, LC3 -Ⅱ/β-actin: 0.38±0.03 vs. 0.52±0.07, Beclin1/β-actin: 0.29±0.06 vs. 0.59±0.05, NMDA/β-actin: 0.62±0.06 vs. 0.50±0.06, NR2B/β-actin: 0.57±0.03 vs. 0.46±0.03, all P < 0.05]. Immunofluorescence staining confirmed that the positive expression of LC3 was significantly decreased. Rap pretreatment could increase MWT, TWL and the number of autophagosome, increase LC3 -Ⅱ and Beclin1 expressions in spinal cord, and decrease NMDA and NR2B expressions in NP rats, and significant differences at 1 day after operation were found as compared with those in NP group [MWT (g): 49.4±4.4 vs. 42.5±6.6, TWL (s): 10.5±1.2 vs. 8.8±1.1, LC3 -Ⅱ/β-actin: 0.67±0.09 vs. 0.52±0.07, Beclin1/β-actin: 0.71±0.08 vs. 0.59±0.05, NMDA/β-actin: 0.40±0.05 vs. 0.50±0.06, NR2B/β-actin: 0.34±0.04 vs. 0.46±0.03, all P < 0.05], and immunofluorescence showed that the positive expression of LC3 was increased and lasted for 7 days. It indicated that Rap could increase the activity of autophagy, alleviate the occurrence of hyperalgesia, and reduce the expressions of NMDA receptor and its NR2B subunit. Conclusion NP could regulate the variety of NMDA/NR2B and hyperalgesia via increasing autophagy.
ABSTRACT
Fragile X syndrome (FXS) is the most common form of inherited intellectual disability. It is caused by the overexpansion of cytosine-guanine-guanine (CGG) trinucleotide in Fmr1 gene, resulting in complete loss of the fragile X mental retardation protein (FMRP). Previous studies using Fmr1 knockout (Fmr1 KO) mice have suggested that a N-methyl-D-aspartate receptors (NMDAR) hypofunction in the hippocampal dentate gyrus may partly contribute to cognitive impairments in FXS. Since activation of NMDAR plays an important role in dendritic arborization during neuronal development, we examined whether deficits in NMDAR function are associated with alterations in dendritic complexity in the hippocampal dentate region. The dentate granule cell layer (GCL) presents active postnatal neurogenesis, and consists of a heterogenous neuronal population with gradient ages from the superficial to its deep layer. Here, we show that neurons with multiple primary dendrites that reside in the outer GCL of Fmr1 KO mice display significantly smaller NMDAR excitatory post-synaptic currents (EPSCs) and a higher α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) to NMDA ratio in comparison to their wild-type counterparts. These deficits were associated with a significant decrease in dendritic complexity, with both dendritic length and number of intersections being significantly reduced. In contrast, although neurons with a single primary dendrite resided in the inner GCL of Fmr1 KO mice had a trend toward a reduction in NMDAR EPSCs and a higher AMPA/NMDA ratio, no alterations were found in dendritic complexity at this developmental stage. Our data indicate that the loss of FMRP causes NMDAR deficits and reduced dendritic complexity in granule neurons with multiple primary dendrites which are thought to be more mature in the GCL.
