Fructose ingestion modifies NMDA receptors and exacerbates the seizures induced by kainic acid.

Fructose ingestion elicits a diversity of brain alterations, but it is unknown how it affects N-methyl-D-Aspartate receptors (NMDAr). Here, we analyzed the expression of NMDAr subunits and protein kinases after the long-term dietary fructose intake. Since NMDAr are related to epileptogenesis, we also examined whether fructose increases the susceptibility to seizures after the microinjection of kainic acid (KA) in the rat hippocampus. Wistar rats were randomly divided into water (control) and fructose groups. For twelve weeks, groups had ad libitum access to water or fructose solution (10% w/v). After treatment, hippocampal protein expression of NMDAr subunits and protein kinases involved in NMDAr regulation were analyzed. Additionally, electroencephalographic and behavioral changes related to seizures were evaluated after the microinjection of a sub-convulsive dose of KA in the hippocampus. Fructose induced the decrease of NR1 and, conversely, the increase of NR2A subunits expression in the hippocampus. Also, the phosphorylation of protein kinase C alpha (PKCα) and c-Src increased significantly. No electroencephalographic or behavioral patterns related to convulsive motor seizures were observed in the control group. However, all the rats that ingested fructose showed stage 3 seizures (forelimb clonus) and a significant increase in the number of wet-dog shakes. Moreover, electroencephalographic recordings revealed pronounced epileptiform activity and increased total spectral power at 30 and 60 min after the microinjection of KA. This study shows for the first time that fructose intake exacerbates the seizures induced by KA. Therefore, we propose that this proconvulsant effect could be mediated by changes in NMDAr subunits expression and increased activation of kinases modulating NMDAr function.

Whole-brain irradiation differentially modifies neurotransmitters levels and receptors in the hypothalamus and the prefrontal cortex.

BACKGROUND: Whole-brain radiotherapy is a primary treatment for brain tumors and brain metastasis, but it also induces long-term undesired effects. Since cognitive impairment can occur, research on the etiology of secondary effects has focused on the hippocampus. Often overlooked, the hypothalamus controls critical homeostatic functions, some of which are also susceptible after whole-brain radiotherapy. Therefore, using whole-brain irradiation (WBI) in a rat model, we measured neurotransmitters and receptors in the hypothalamus. The prefrontal cortex and brainstem were also analyzed since they are highly connected to the hypothalamus and its regulatory processes. METHODS: Male Wistar rats were exposed to WBI with 11 Gy (Biologically Effective Dose = 72 Gy). After 1 month, we evaluated changes in gamma-aminobutyric acid (GABA), glycine, taurine, aspartate, glutamate, and glutamine in the hypothalamus, prefrontal cortex, and brainstem according to an HPLC method. Ratios of Glutamate/GABA and Glutamine/Glutamate were calculated. Through Western Blott analysis, we measured the expression of GABAa and GABAb receptors, and NR1 and NR2A subunits of NMDA receptors. Changes were analyzed comparing results with sham controls using the non-parametric Mann-Whitney U test (p < 0.05). RESULTS: WBI with 11 Gy induced significantly lower levels of GABA, glycine, taurine, aspartate, and GABAa receptor in the hypothalamus. Also, in the hypothalamus, a higher Glutamate/GABA ratio was found after irradiation. In the prefrontal cortex, WBI induced significant increases of glutamine and glutamate, Glutamine/Glutamate ratio, and increased expression of both GABAa receptor and NMDA receptor NR1 subunit. The brainstem showed no statistically significant changes after irradiation. CONCLUSION: Our findings confirm that WBI can affect rat brain regions differently and opens new avenues for study. After 1 month, WBI decreases inhibitory neurotransmitters and receptors in the hypothalamus and, conversely, increases excitatory neurotransmitters and receptors in the prefrontal cortex. Increments in Glutamate/GABA in the hypothalamus and Glutamine/Glutamate in the frontal cortex indicate a neurochemical imbalance. Found changes could be related to several reported radiotherapy secondary effects, suggesting new prospects for therapeutic targets.