Inorganic arsenic (iAs) is an important natural pollutant. Millions of individuals worldwide drink water with high levels of iAs. Chronic exposure to iAs has been associated with lower IQ and learning disabilities as well as memory impairment. iAs is methylated in tissues such as the brain generating mono and dimethylated species. iAs methylation requires cellular glutathione (GSH), which is the main antioxidant in the central nervous system. In humans, As species cross the placenta and are found in cord blood. A CD1 mouse model was used to investigate effects of gestational iAs exposure which can lead to oxidative damage, disrupted cysteine/glutamate transport and its putative impact in learning and memory. On postnatal days (PNDs) 1, 15 and 90, the expression of membrane transporters related to GSH synthesis and glutamate transport and toxicity, such as xCT, EAAC1, GLAST and GLT1, as well as LAT1, were analyzed. Also, the expression of the glutamate receptor N-methyl-D-aspartate (NMDAR) subunits NR2A and B as well as the presence of As species in cortex and hippocampus were investigated. On PND 90, an object location task was performed to associate exposure with memory impairment. Gestational exposure to iAs affected the expression of cysteine/glutamate transporters in cortex and hippocampus and induced a negative modulation of NMDAR NR2B subunit in the hippocampus. Behavioral tasks showed significant spatial memory impairment in males while the effect was marginal in females.

Vascular endothelial growth factor (VEGF) delays disease onset and progression in transgenic rodent models of familial amyotrophic lateral sclerosis (ALS). Because most cases of ALS are sporadic, it is important to determine whether VEGF can protect motoneurons in a nontransgenic ALS paradigm. We tested this possibility in a new model of chronic excitotoxic spinal neurodegeneration in the rat. Using osmotic minipumps, we continuously infused the glutamate receptor agonist α-amino-3-hydroxy-5-methyl-4-isoxazole propionate (AMPA) directly in the lumbar spinal cord. The effect of this treatment on motor behavior was assessed with 3 motor performance tests, and neurodegeneration was evaluated by histologic and immunohistochemical analyses. AMPA infusion produced dose-dependent progressive hindlimb motor deficits, reaching complete bilateral paralysis in ∼10 days, which was correlated with the loss of spinal motoneurons. VEGF administered together with AMPA completely prevented the motor deficits, and the motoneuron death was reduced by more than 75%. Thus, we have developed an in vivo model of progressive spinal motoneuron death due to overactivation of AMPA receptors. The finding that VEGF protected motoneurons from this AMPA receptor-mediated excitotoxic death suggests that it may be a therapeutic agent in sporadic ALS.

New neurons are continuously generated and functionally integrated into the dentate gyrus (DG) network during the adult lifespan of most mammals. The hippocampus is a crucial structure for spatial learning and memory, and the addition of new neurons into the DG circuitry of rodents seems to be a key element for these processes to occur. The Morris water maze (MWM) and contextual fear conditioning (CFC) are among the most commonly used hippocampus-dependent behavioral tasks to study episodic-like learning and memory in rodents. While the functional contribution of adult hippocampal neurogenesis (AHN) through these paradigms has been widely addressed, results have generated controversial findings. In this review, we analyze and discuss possible factors in the experimental methods that could explain the inconsistent results among AHN studies; moreover, we provide specific suggestions for the design of more sensitive protocols to assess AHN-mediated learning and memory functions.