SYNAPTIC AND SUB-SYNAPTIC LEVELS OF EQUILIBRATIVE NUCLEOSIDE TRANSPORTER TYPE 1 (ENT1) IN THREE BRAIN REGIONS OF AN ANIMAL MODEL OF ADHD

Background: Attention Deficit Hyperactivity Disorder (ADHD) is a neurodevelopmental condition caused by dopaminergic imbalance in critical brain regions, which can be normalized by adenosinergic signaling. Extracellular adenosine levels are regulated by enzymes and nucleoside transporters such as ENT1. Our study aim to investigate ENT1 levels in the frontocortical, striatal, and hippocampal regions of a validated animal model of ADHD and explore how they impact this model.

Methods: All procedures were approved by an Ethics Committee on Animal Use (#7023070523). The brain frontal cortex, striatum, and hippocampus from 75-days-old male and female Wistar Kyoto (WKY) and Spontaneously Hypertensive Rats (SHR) were collected and processed for synaptosomal and total membrane fractions. After western blotting, membranes were incubated with an anti-ENT1 primary antibody or anti-α-tubulin primary antibody as a loading protein control.

Results: In synaptosomes (n=4-5), there was no significant difference in cortical ENT1 levels when comparing strain (p=0.669), sex (p=0.595) or their interaction (p=0.570), as well as in striatal ENT1 levels (strain, p=0.354; sex, p=0.963; interaction, p=0.824). Hippocampal ENT1 levels, however, were higher in female SHR (p=0.004) in comparison with sex (p=0.004) but not strain (p=0.112) or interaction (p=0.350). In total membranes (n=4-5), cortical ENT1 levels showed no difference between strain (p= 0.555), sex (p= 0.994) or interaction (p= 0.451), as well as in hippocampal levels (strain, p=0.866; sex, p=0.177; interaction p=0.335). Lastly, striatal levels were also higher in females (p=0.043) but not strain (p=0.090) or interaction (p=0.149).

Conclusions: Based on our study, higher levels of ENT1 in striatal synaptosomes and hippocampal total membranes, especially in females, may contribute to ADHD symptoms. Further research is necessary to determine whether ENT1 levels might play a significant role in the behavioral variations seen in ADHD.