Defining the neuroanatomic basis of motor coordination in children and its relationship with symptoms of attention-deficit/hyperactivity disorder

BACKGROUND

When children have marked problems with motor coordination, they often have problems with attention and impulse control. Here, we map the neuroanatomic substrate of motor coordination in childhood and ask whether this substrate differs in the presence of concurrent symptoms of attention-deficit/hyperactivity disorder (ADHD).

METHOD

Participants were 226 children. All completed Diagnostic and Statistical Manual of Mental Disorders, fifth edition (DSM-5)-based assessment of ADHD symptoms and standardized tests of motor coordination skills assessing aiming/catching, manual dexterity and balance. Symptoms of developmental coordination disorder (DCD) were determined using parental questionnaires. Using 3 Tesla magnetic resonance data, four latent neuroanatomic variables (for the cerebral cortex, cerebellum, basal ganglia and thalamus) were extracted and mapped onto each motor coordination skill using partial least squares pathway modeling.

RESULTS

The motor coordination skill of aiming/catching was significantly linked to latent variables for both the cerebral cortex (t = 4.31, p < 0.0001) and the cerebellum (t = 2.31, p = 0.02). This effect was driven by the premotor/motor cortical regions and the superior cerebellar lobules. These links were not moderated by the severity of symptoms of inattention, hyperactivity and impulsivity. In categorical analyses, the DCD group showed atypical reduction in the volumes of these regions. However, the group with DCD alone did not differ significantly from those with DCD and co-morbid ADHD.

CONCLUSIONS

The superior cerebellar lobules and the premotor/motor cortex emerged as pivotal neural substrates of motor coordination in children. The dimensions of these motor coordination regions did not differ significantly between those who had DCD, with or without co-morbid ADHD.

Immunomodulation by cannabinoids is absent in mice deficient for the cannabinoid CB(2) receptor

Cannabinoids have immunomodulatory as well as psychoactive effects. Because the central cannabinoid receptor (cannabinoid CB(1) receptor) is highly expressed in many neuronal tissues and the peripheral cannabinoid receptor (cannabinoid CB(2) receptor) is highly expressed in immune cells, it has been suggested that the central nervous system effects of cannabinoids are mediated by cannabinoid CB(1) receptors and that the immune effects are mediated by cannabinoid CB(2) receptors. To test this hypothesis, we have generated the first mouse strain with a targeted mutation in the cannabinoid CB(2) receptor gene. Binding studies using the highly specific synthetic cannabinoid receptor agonist (-)-cis-3-¿2-Hydroxy-4-(1, 1-dimethylheptyl)phenyl-trans-4-(3-hydroxypropyl)cyclohexanol (¿3HCP 55,940) revealed no residual cannabinoid binding sites in the spleen of the cannabinoid CB(2) receptor knockout mice, while binding in the central nervous system was unchanged. Cannabinoid CB(2) receptor knockout mice, which appear healthy, are fertile and care for their offspring. Fluorescence activated cell sorting (FACS) analysis showed no differences in immune cell populations between cannabinoid CB(2) receptor knockout and wildtype mice. We investigated the immunomodulatory effects of cannabinoids in cannabinoid CB(2) receptor deficient mice using a T cell co-stimulation assay. Delta(9)Tetrahydrocannabinol inhibits helper T cell activation through macrophages derived from wild type, but not from knockout mice, thus indicating that this effect is mediated by the cannabinoid CB(2) receptor. In contrast, central nervous system effects of cannabinoids were not altered in these mice. Our results suggest that cannabinoid CB(2) receptor-specific ligands may be clinically useful in the modulation of macrophage immune function while exhibiting no central nervous system activity. Furthermore, we conclude that the cannabinoid CB(2) receptor knockout mouse is a useful animal model in which to study the role of the cannabinoid system in immunoregulation.

Dioxin Precursors: NQR Studies of Group 1 and Related 2,6-Dichlorophenolate and 2,4,6-Trichlorophenolate Salts

The 81Br and 35Cl NQR spectra of anhydrous Group 1, tetraalkylammonium, and thallium(I) 2,6-dichlorophenolates, 2,4,6-trichlorophenolates, and 4-bromo-2,6-dichlorophenolates were searched for evidence of solid-state cation-organochlorine interactions that might, for example, be (in part) responsible for the difference in the thermal decomposition reactions of these salts (to give the supertoxic environmental pollutants, the polychlorinated dibenzodioxins) versus those of the corresponding Group 11 chlorophenolate complexes, which do not decompose to dioxins.

For cations ranging in size from tetraethylammonium to potassium, the total range of 35Cl NQR frequencies in 2,6-dichlorophenolate and 2,4,6-trichlorophenolate salts is only 1.401 MHz, which, although larger than the 0.7 MHz range likely in molecular chlorocarbons, is smaller than in individual chlorophenolates of copper(I) and silver(I) (up to 2.0 MHz). In sodium and thallium(I) 2,4,6-trichlorophenolates substantially large frequency shifts (ca. 2.0 MHz) occur, to higher frequencies for the para-chlorines and lower frequencies for the ortho-chlorines (Na only). These disappear even in closely related compounds and show a pattern that seems unrelated to the decomposition products of the chlorophenolates.

Characterization of murine A-raf, a new oncogene related to the v-raf oncogene

A 1.6-kilobase cDNA (A-raf) has been isolated from a murine spleen cDNA library which encodes part of a protein related to the raf oncogene. Its amino acid sequence has 85% homology to raf in a central portion of 100 amino acids. In contrast to raf, A-raf shows a highly restricted tissue distribution of expression, with highest levels observed in epididymis, followed by intestine. When incorporated into a retrovirus, the resulting gag-A-raf fusion gene causes transformation in vitro and induces tumors in newborn mice. Thus, A-raf represents a new proto-oncogene. Transformation by A-raf is independent of ras gene function, as is the case for raf and mos but not other oncogenes.

The human homologs of the raf (mil) oncogene are located on human chromosomes 3 and 4

Two human genes that are homologous to both the murine transforming gene (oncogene) v-raf and the chicken transforming gene v-mil have been mapped by means of human-rodent somatic cell hybrids to human chromosomes previously devoid of known oncogenes. One gene, c-raf-2, which appears to be a processed pseudogene, is located on chromosome 4. The other gene, c-raf-1, which appears to be the active gene, is located on chromosome 3 and has been regionally mapped by chromosomal in situ hybridization to 3p25. This assignment correlates with specific chromosomal abnormalities associated with certain human malignancies.