Gonzalo Ugarte

Attention deficit-hyperactivity disorder (ADHD) is a neurodevelopmental disorder with high incidence in children and adolescents characterized by motor hyperactivity, impulsivity, and inattention. Magnetic resonance imaging (MRI) has revealed that neuroanatomical abnormalities such as the volume reduction in the neocortex and hippocampus are shared by several neuropsychiatric diseases such as schizophrenia, autism spectrum disorder and ADHD. Furthermore, the abnormal development and postnatal pruning of dendritic spines of neocortical neurons in schizophrenia, autism spectrum disorder and intellectual disability are well documented. Dendritic spines are dynamic structures exhibiting Hebbian and homeostatic plasticity that triggers intracellular cascades involving glutamate receptors, calcium influx and remodeling of the F-actin network. The long-term potentiation (LTP)-induced insertion of postsynaptic glutamate receptors is associated with the enlargement of spine heads and long-term depression (LTD) with spine shrinkage. Using a murine model of ADHD, a delay in dendritic spines’ maturation in CA1 hippocampal neurons correlated with impaired working memory and hippocampal LTP has recently reported. The aim of this review is to summarize recent evidence that has emerged from studies focused on the neuroanatomical and genetic features found in ADHD patients as well as reports from animal models describing the molecular structure and remodeling of dendritic spines.

Attention Deficit-Hyperactivity Disorder (ADHD) is a neurodevelopmental disorder with high incidence in children and adolescents characterized by motor hyperactivity, impulsivity, and inattention. MRI-based evidences support that neuroanatomical abnormalities as the volume reduction of neocortex and hippocampus are shared by several neuropsychiatric diseases as schizophrenia, autism spectrum disorder and ADHD. In addition, it is well documented the abnormal development and postnatal pruning of dendritic spines of neocortical neurons in schizophrenia, autism spectrum disorder and intellectual disability. A recent report using the prenatal nicotine exposure murine model of ADHD support a delay in spine maturation in CA1 neurons correlated with impaired working memory and hippocampal long-term potentiation (LTP). In vivo spine imaging show that dendritic spines are dynamic structures exhibiting Hebbian and homeostatic plasticity triggering intracellular cascades involving glutamate receptors, calcium influx and remodeling of F-actin network. The LTP-induced insertion of postsynaptic glutamate receptors is associated to the enlargement of spine head and long-term depression (LTD) to the spine shrinkage. In this review, we summarize recent evidence emerged from meta-analysis of brain imaging data from ADHD patients, risk loci from global genome-wide analysis and new reports focused on spine molecular structure and dynamics using in vivo imaging in neocortex and hippocampus.

In ADHD treatment, methylphenidate (MPH) is the most frequently used medication. The present work provides evidence that MPH restored behavioral impairments and neuroplasticity due to changes in AMPAR subunit composition and distribution, as well as maturation of dendritic spines, in a prenatal nicotine exposure (PNE) ADHD mouse model. PNE animals and controls were given a single oral dose of MPH (1 mg/kg), and their behavior was tested for attention, hyperactivity, and working memory. Long-term potentiation (LTP) was induced and analyzed at the CA3/CA1 synapse in hippocampal slices taken from the same animals tested behaviorally, measuring fEPSPs and whole-cell patch-clamp EPSCs. By applying crosslinking and Western blots, we estimated the LTP effects on AMPAR subunit composition and distribution. The density and types of dendritic spines were quantified by using the Golgi staining method. MPH completely restored the behavioral impairments of PNE mice. Reduced LTP and AMPA-receptor-mediated EPSCs were also restored. EPSC amplitudes were tightly correlated with numbers of GluA1/GluA1 AMPA receptors at the cell surface. Finally, we found a lower density of dendritic spines in hippocampal pyramidal neurons in PNE mice, with a higher fraction of thin-type immature spines and a lower fraction of mushroom mature spines; the latter effect was also reversed by MPH.