Magnesium deficiency induces anxiety and HPA axis dysregulation: modulation by therapeutic drug treatment

Abstract

Preclinical and some clinical studies suggest a relationship between perturbation in magnesium (Mg(2+)) homeostasis and pathological anxiety, although the underlying mechanisms remain largely unknown. Since there is evidence that Mg(2+) modulates the hypothalamic-pituitary adrenal (HPA) axis, we tested whether enhanced anxiety-like behaviour can be reliably elicited by dietary Mg(2+) deficiency and whether Mg(2+) deficiency is associated with altered HPA axis function. Compared with controls, Mg(2+) deficient mice did indeed display enhanced anxiety-related behaviour in a battery of established anxiety tests. The enhanced anxiety-related behaviour of Mg(2+) deficient mice was sensitive to chronic desipramine treatment in the hyponeophagia test and to acute diazepam treatment in the open arm exposure test. Mg(2+) deficiency caused an increase in the transcription of the corticotropin releasing hormone in the paraventricular hypothalamic nucleus (PVN), and elevated ACTH plasma levels, pointing to an enhanced set-point of the HPA axis. Chronic treatment with desipramine reversed the identified abnormalities of the stress axis. Functional mapping of neuronal activity using c-Fos revealed hyper-excitability in the PVN of anxious Mg(2+) deficient mice and its normalisation through diazepam treatment. Overall, the present findings demonstrate the robustness and validity of the Mg(2+) deficiency model as a mouse model of enhanced anxiety, showing sensitivity to treatment with anxiolytics and antidepressants. It is further suggested that dysregulations in the HPA axis may contribute to the hyper-emotionality in response to dietary induced hypomagnesaemia. This article is part of a Special Issue entitled 'Anxiety and Depression'.

Fig. 1

Effect of Mg²⁺ deficiency and chronic paroxetine treatment on selected anxiety-related measures in C57Bl/6N mice. A. In mice fed a Mg²⁺ restricted diet (MgD) the time spent in the anxiogenic centre of an open field was decreased compared with mice fed the control diet (control) indicating enhanced anxiety-related behaviour. B. Anxiety-related behaviour was also elevated in the light/dark test as indicated by the increased latency to enter the (anxiogenic) brightly lit compartment. Chronic treatment with paroxetine (MgD + PAR) did not alter anxiety-related behaviour of Mg²⁺ deficient mice in these tests. n = 10 per experimental group. Data represent means ± SEM. *P < 0.05, **P < 0.01 for Mg²⁺ deficient vs. control mice.

Fig. 2

In the hyponeophagia test, the latency to eat a preferred food placed in the centre of the testing arena and the distance travelled is shown for C57Bl/6N mice fed either the control diet (control; n = 19), the Mg²⁺ deficient diet (MgD; n = 16), or the Mg²⁺ deficient diet and additional long-term treatment with either desipramine (MgD + DMI; n = 12) or paroxetine (MgD + PAR; n = 16). Data represent means ± SEM. *P < 0.05, **P < 0.01, ***P < 0.001 for Mg²⁺ deficient vs. control mice, ^###P < 0.001 for drug-treated Mg²⁺ deficient mice vs. Mg²⁺ deficient mice.

Fig. 3

This figure shows (A) representative autoradiograms and (B) quantification of prepro-CRH mRNA expression in the paraventricular hypothalamic nucleus for C57Bl/6N mice fed either the control diet (control; n = 10), the Mg²⁺ deficient diet (MgD; n = 10), or the Mg²⁺ deficient diet after long-term treatment with desipramine (MgD + DMI; n = 10); it also provides quantification of unspecific hybridisation. Data represent mean ± SEM. *P < 0.05, ***P < 0.001 for Mg²⁺ deficient vs. control mice and ^###P < 0.001 for desipramine-treated Mg²⁺ deficient mice vs. Mg²⁺ deficient mice.

Fig. 4

Effect of Mg²⁺ deficiency and diazepam treatment (1 mg/kg, i.p.) on behaviour and c-Fos expression in the paraventricular hypothalamic nucleus (PVN) of BALB/c mice following exposure to the open arm of an elevated plus maze. A. In mice fed a Mg²⁺ restricted diet the anxiety-related behaviour was elevated as indicated by the number of entries into the (anxiogenic) distal compartment of the open arm. Treatment with diazepam normalised this anxious phenotype. B. Compared with vehicle-treated controls, c-Fos induction was increased in the magnocellular portion of the PVN in Mg²⁺ deficient mice and was reversed by diazepam treatment. C. Representative photograph (scale bar = 100 μm) showing delineation of the PVN regions analysed with the help of a mouse brain atlas (Paxinos and Franklin, 2001). D. High magnification photograph showing c-Fos-positive cells in the magnocellular portion of the PVN in all experimental groups. Data represent mean ± SEM. n = 10 per experimental group. *P < 0.05, ***P < 0.001 for Mg²⁺ deficient vs. control mice, ^###P < 0.001 for diazepam vs. vehicle. 3V: third ventricle; DZP: diazepam; magno: magnocellular portion of the PVN; parvo: parvocellular portion of the PVN; V: vehicle.