Dietary magnesium deficiency impairs hippocampus-dependent memories without changes in the spine density and morphology of hippocampal neurons in mice

•Effects of Mg2+ deficiency (MgD) on memory and neuron morphology were examined.•Mice fed MgD diet show deficits in hippocampus-dependent memories.•MgD did not affect amygdala-dependent memory, locomotion, or emotional behaviors.•Mice fed MgD diet show normal spine density and morphology of hippocampal neurons.•Dietary Mg2+ is important for memory function of the hippocampus. Magnesium (Mg2+) is an essential mineral for maintaining biological functions. One major action of Mg2+ in the brain is modulating the voltage-dependent blockade of N-methyl-d-aspartate type glutamate receptors, thereby controlling their opening, which is crucial for synaptic plasticity. Therefore, Mg2+ has been shown to play critical roles in learning and memory, and synaptic plasticity. However, the effects of dietary Mg2+ deficiency (MgD) on learning and memory and the morphology of neurons contributing to memory performance have not been examined in depth. Here, we show that MgD impairs hippocampus-dependent memories in mice. Mice fed an MgD diet showed deficits in hippocampus-dependent contextual fear, spatial and social recognition memories, although they showed normal amygdala- and insular cortex-dependent conditioned taste aversion memory, locomotor activity, and emotional behaviors such as anxiety-related and social behaviors. However, MgD mice showed normal spine density and morphology of hippocampal neurons. These findings suggest that MgD impairs hippocampus-dependent memory without affecting the morphology of hippocampal neurons.