Diurnal effects on motor control are evident in the human disease of Restless 
Leg Syndrome (RLS), which is purported to be linked to brain iron deficiency as 
well as alterations in dopaminergic systems. Thus, we explored the relationship 
between daily rhythms, the onset of motor dysregulation and brain iron 
deficiency in an animal model of iron deficiency. Male and female weanling 
Sprague-Dawley rats consuming control (CN) or iron-deficient (ID) diets were 
examined weekly for acoustic startle response (ASR) and prepulse inhibition 
(PPI) for a 5-week period. Iron deficiency reduced the magnitude, but not 
timing, of the ASR at specific time points. ASR was elevated 60% at the onset of 
the dark cycle relative to the median of the light cycle in male CN and ID rats. 
The respective elevation was 400% and 150% in female CN and ID rats during the 
first 2 weeks of testing. The diurnal cycle of ASR response was attenuated by 3 
weeks of testing in both dietary treatment groups. PPI was not affected by iron 
deficiency, sex, diurnal cycle or the interaction between these factors. These 
results thus demonstrate that iron deficiency moderately alters ASR signaling 
although the inhibitory pathways of ASR do not appear to be affected.