IS ADHD A THALAMOCORTICAL DYSRHYTHMIA? CHANGES IN ELECTRICAL ACTIVITY OF TRN NEURONS IN A 6-OHDA RODENT MODEL

The thalamic reticular nucleus (TRn) modulates information between the thalamocortical (TC) and corticothalamic (CT) circuits. It plays an important role in cognitive processes such as attention, consciousness and sleep (Brain Res. Rev. 46(1):1-31, 2004). Alterations in the TC and CT pathways are known as thalamocortical dysrhythmias. Studies show that TC/CT dysrhythmias are linked to a wide range of neuropsychiatric disorders including attention deficit and hyperactivity (ADHD) (Front. Hum. Neurosci. 29;5:69, 2011). In ADHD, TRn dysregulation contributes to the thalamus sending unfiltered information to the cortex. TRn neurons are characterized by two firing patterns: 1) Tonic, which occurs when neurons are depolarized, allowing a constant flow of information, and 2) Bursting, which occurs when neurons are hyperpolarized, promoting slow-wave and inhibitory activity (Brain Research Reviews 46 (2004) 1 – 31). Changes in TRn neurons between tonic and bursting patterns are strongly modulated by dopamine, through D1 and D4 receptors. Dopamine deficiency, present in ADHD, modifies these patterns, affecting its ability to filter information, contributing to clinical manifestations (Appl. Neuropsychol. Child Rev. 2015;4(2):89-96, 2015). Thus, we studied whether in an animal model of ADHD-like dysrrythmia with 6-OHDA, there is a TRn dysregulation. We found alterations in the rhythm and firing type of reticular thalamic neurons in the 6-OHDA lesioned rat as compared to the non-lesioned rat. Although the changes were heterogeneous, an increase in the frequency predominates, as well as a reduction in the burst pattern (busrst index).