Severe postnatal iron deficiency alters emotional behavior and dopamine levels in the prefrontal cortex of young male rats

Abstract

Iron deficiency in early human life is associated with abnormal neurological development. The objective of this study was to evaluate the effect of postnatal iron deficiency on emotional behavior and dopaminergic metabolism in the prefrontal cortex in a young male rodent model. Weanling, male, Sprague-Dawley rats were fed standard nonpurified diet (220 mg/kg iron) or an iron-deficient diet (2-6 mg/kg iron). After 1 mo, hematocrits were 0.42 ± 0.0043 and 0.16 ± 0.0068 (mean ± SEM; P < 0.05; n = 8), liver nonheme iron concentrations were 2.3 ± 0.24 and 0.21 ± 0.010 μmol/g liver (P < 0.05; n = 8), and serum iron concentrations were 47 ± 5.4 and 23 ± 7.1 μmol/L (P < 0.05; n = 8), respectively. An elevated plus maze was used to study emotional behavior. Iron-deficient rats displayed anxious behavior with fewer entries and less time spent in open arms compared to control rats (0.25 ± 0.25 vs. 1.8 ± 0.62 entries; 0.88 ± 0.88 vs. 13 ± 4.6 s; P < 0.05; n = 8). Iron-deficient rats also traveled with a lower velocity in the elevated plus maze (1.2 ± 0.15 vs. 1.7 ± 0.12 cm/s; P < 0.05; n = 8), behavior that reflected reduced motor function as measured on a standard accelerating rotarod device. Both the time on the rotarod bar before falling and the peak speed attained on rotarod by iron-deficient rats were lower than control rats (156 ± 12 vs. 194 ± 12 s; 23 ± 1.5 vs. 28 ± 1.6 rpm; P < 0.05; n = 7-8). Microdialysis experiments showed that these behavioral effects were associated with reduced concentrations of extracellular dopamine in the prefrontal cortex of the iron-deficient rats (79 ± 7.0 vs. 110 ± 14 ng/L; P < 0.05; n = 4). Altered dopaminergic signaling in the prefrontal cortex most likely contributes to the anxious behavior observed in young male rats with severe iron deficiency.

FIGURE 1

Elevated plus maze (A) and standard accelerating rotarod (B) tests of behavior and motor coordination of rats fed a control or iron-deficient diet for 4 wk on postnatal d 45 and 52, respectively. Data are mean ± SEM, n = 8. *Different from control, P < 0.05 (Wilcoxon’s Rank Sum test).

FIGURE 2

Microdialysis measurements of extracellular resting and stimulated dopamine (A) and Western-blot analysis of DAT and D2R (B) in prefrontal cortex of rats fed a control iron-deficient diet for 4 wk. Data are mean ± SEM, n = 4. *Different from control, P < 0.05 (Wilcoxon’s Rank Sum test). Western blot shows 3 representative samples with similar results observed for 7–8 different rats in each group. D2R, dopamine D2 receptor; DAT, dopamine transporter.