Attention-deficit/hyper-activity disorder (ADHD) is more often diagnosed as both neuropsychiatric and neurodevelopmental disorders in children with an evidential prevalence of 3-5% at the universal level. The three key symptoms are inattention, hyperactivity and impulsivity. This neurodevelopmental disorder was detected and diagnosed more often in boys than girls.
Children with ADHD appear to have more than twice the level of glutamate, which is an excitatory neurotransmitter. Along with hypersecretion of excitatory neurotransmitter – glutamate, there are also a few observations of low level of gamma-aminobutyric acid (GABA), which acts as a principal inhibitory molecule to inhibit stimulated neuronal cells.
GABA concentration was reduced in ADHD children compared to typically developing groups with normal functioning. A study was done in Cincinnati Children’s Hospital Medical Center and in Kennedy Krieger Institute that evidenced that there were significantly lower concentrations of GABA in the cerebral cortex of ADHD children. It also has been suggested that the GABAergic system is particularly susceptible to damage during abnormal development because GABAergic neurons arise from a different region of the neural tube than glutamatergic neurons, with which they must later integrate.
Magnetic reasonance spectroscopy (MRS) studies investigating GABA and glutamate in ADHD showed decreased prefrontal GABA levels in children, whereas in another study increased glutamatergic levels were found in comparable prefrontal brain areas.
On the other hand, one of the study found reduced short intercortical inhibition (SICI) in school-age children with ADHD using transcranial magnetic stimulation. SICI is known to be modulated by GABA-A agonists and is thought to be mediated by GABA-A cortical interneurons. Reduced SICI correlated with ADHD symptom severity and motor skills.
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Isaacs, K.M., Augusta, M. & Macneil, L.K., 2011. Motor cortex inhibition A marker of ADHD behavior and motor development in children. Neurology, pp.615–621.
Naaijen, J. et al., 2017. Glutamatergic and GABAergic gene sets in attention-de fi cit / hyperactivity disorder : association to overlapping traits in ADHD and autism. Translational Psychiatry, 7(1), pp.e999-7.
Purkayastha, P. et al., 2015. A review on GABA / glutamate pathway for therapeutic intervention of ASD and ADHD. Current Medicinal Chemistry, 22, pp.1850–1859.