Iron deficiency (ID) is the most prevalent micronutrient deficiency in the world and it affects neurobehavioral outcome. It is unclear whether the effect of dietary ID on the brain is due to the lack of neuronal iron or from other processes occurring in conjunction with ID (e.g. hypoxia due to anemia). We delineated the role of murine Slc11a2 [divalent metal ion transporter-1 (DMT-1)] in hippocampal neuronal iron uptake during development and memory formation. Camk2a gene promoter-driven cre recombinase (Cre) transgene (Camk2a-Cre) mice were mated with Slc11a2 flox/flox mice to obtain nonanemic Slc11a2(hipp/hipp) (double mutant, hippocampal neuron-specific knockout of Slc11a2(hipp/hipp)) mice, the first conditionally targeted model of iron uptake in the brain. Slc11a2(hipp/hipp) mice had lower hippocampal iron content; altered developmental expression of genes involved in iron homeostasis, energy metabolism, and dendrite morphogenesis; reductions in markers for energy metabolism and glutamatergic neurotransmission on magnetic resonance spectroscopy; and altered pyramidal neuron dendrite morphology in area 1 of Ammon's Horn in the hippocampus. Slc11a2(hipp/hipp) mice did not reach the criterion on a difficult spatial navigation test but were able to learn a spatial navigation task on an easier version of the Morris water maze (MWM). Learning of the visual cued task did not differ between the Slc11a2(WT/WT) and Slc11a2(hipp/hipp) mice. Slc11a2(WT/WT) mice had upregulation of genes involved in iron uptake and metabolism in response to MWM training, and Slc11a2(hipp/hipp) mice had differential expression of these genes compared with Slc11a2(WT/WT) mice. Neuronal iron uptake by DMT-1 is essential for normal hippocampal neuronal development and Slc11a2 expression is induced by spatial memory training. Deletion of Slc11a2 disrupts hippocampal neuronal development and spatial memory behavior.

Depression is the most common psychiatric comorbidity in epilepsy. To better understand the contribution of seizures versus environment to depression in epilepsy, we investigated differential gene expression using microarray and quantitative RT-PCR, and depressive behavior, in the Porsolt forced swim test in juvenile rats reared in different environments after kainic acid (KA)-induced seizures. We selected for genes significantly down-regulated by KA seizures and upregulated by environmental enrichment. This common gene selection process yielded one known gene involved in mood and affect: serotonin receptor 5B. The changes in serotonin receptor gene expression were paralleled by decreased mobility in the forced swim tests; depressive behavior exhibited after seizures was no longer evident in rats reared in environmental enrichment. Our results suggest that seizures lead to increased susceptibility to depression through transcriptional regulation while environment, in turn, can interact with gene expression to influence the behavioral outcome of epilepsy.

Neonatal brain iron deficiency occurs after insufficient maternal dietary iron intake, maternal hypertension, and maternal diabetes mellitus and results in short and long-term neurologic and behavioral deficits. Early iron deficiency affects the genomic profile of the developing hippocampus that persists despite iron repletion. The purpose of the present study was threefold: 1) quantitative PCR confirmation of our previous microarray results, demonstrating upregulation of a network of genes leading to beta amyloid production and implicated in Alzheimer disease etiology in iron deficient anemic rat pups at the time of hippocampal differentiation; 2) investigation of the potential contributions of iron deficiency anemia and iron treatment to this differential gene expression in the hippocampus; and 3) investigation of these genes over a developmental time course in a mouse model where iron deficiency is limited to hippocampus, is not accompanied by anemia and is not repletable. Quantitative PCR confirmed altered regulation in 6 of 7 Alzheimer-related genes (Apbb1, C1qa, Clu, App, Cst3, Fn1, Htatip) in iron deficient rats relative to iron sufficient controls at P15. Comparison of untreated to treated iron deficient animals at this age suggested the strong role of iron deficiency, not treatment, in the upregulation of this gene network. The non-anemic hippocampal iron deficient mouse demonstrated upregulation of all 7 genes in this pathway from P5 to P25. Our results suggest a role for neonatal iron deficiency in dysregulation of genes that may set the stage for long-term neurodegenerative disease and that this may occur through a histone modification mechanism.