Brain Iron Deficiency Changes the Stoichiometry of Adenosine Receptor Subtypes in Cortico-Striatal Terminals: Implications for Restless Legs Syndrome

Brain iron deficiency (BID) constitutes a primary pathophysiological mechanism in restless legs syndrome (RLS). BID in rodents has been widely used as an animal model of RLS, since it recapitulates key neurochemical changes reported in RLS patients and shows an RLS-like behavioral phenotype. Previous studies with the BID-rodent model of RLS demonstrated increased sensitivity of cortical pyramidal cells to release glutamate from their striatal nerve terminals driving striatal circuits, a correlative finding of the cortical motor hyperexcitability of RLS patients. It was also found that BID in rodents leads to changes in the adenosinergic system, a downregulation of the inhibitory adenosine A(1) receptors (A(1)Rs) and upregulation of the excitatory adenosine A(2A) receptors (A(2A)Rs). It was then hypothesized, but not proven, that the BID-induced increased sensitivity of cortico-striatal glutamatergic terminals could be induced by a change in A(1)R/A(2A)R stoichiometry in favor of A(2A)Rs. Here, we used a newly developed FACS-based synaptometric analysis to compare the relative abundance on A(1)Rs and A(2A)Rs in cortico-striatal and thalamo-striatal glutamatergic terminals (labeled with vesicular glutamate transporters VGLUT1 and VGLUT2, respectively) of control and BID rats. It could be demonstrated that BID (determined by measuring transferrin receptor density in the brain) is associated with a selective decrease in the A(1)R/A(2A)R ratio in VGLUT1 positive-striatal terminals.

Automated summary

Brain iron deficiency (BID) is a primary mechanism in restless legs syndrome (RLS), and BID in rodents has been used as an animal model for RLS. Previous studies have shown that BID leads to increased sensitivity of cortical pyramidal cells to glutamate release, which is correlated with the motor hyperexcitability observed in RLS patients. It has also been found that BID in rodents causes changes in the adenosinergic system, specifically a downregulation of inhibitory adenosine A(1) receptors (A(1)Rs) and an upregulation of excitatory adenosine A(2A) receptors (A(2A)Rs). This study aimed to investigate the relationship between A(1)Rs and A(2A)Rs in cortico-striatal and thalamo-striatal glutamatergic terminals of control and BID rats using a FACS-based synaptometric analysis. The results showed a selective decrease in the A(1)R/A(2A)R ratio in VGLUT1 positive-striatal terminals in BID rats.