Neurogenetic Heterochrony in Chick, Lizard, and Rat Mapped with Wholemount Acetylcholinesterase and the Prosomeric Model.

In the developing brain, the phenomenon of neurogenesis is manifested heterotopically, that is, much the same neurogenetic steps occur at different places with a different timetable. This is due apparently to early molecular regionalization of the neural tube wall in the anteroposterior and dorsoventral dimensions, in a checkerboard pattern of more or less deformed quadrangular histogenetic areas. Their respective fate is apparently specified by a locally specific combination of active/repressed genes known as "molecular profile." This leads to position-dependent differential control of proliferation, neurogenesis, differentiation, and other aspects, eventually in a heterochronic manner across adjacent areal units with sufficiently different molecular profiles. It is not known how fixed these heterochronic patterns are. We reexamined here comparatively early patterns of forebrain and hindbrain neurogenesis in a lizard (Lacerta gallotia galloti), a bird (the chick), and a mammal (the rat), as demonstrated by activation of acetylcholinesterase (AChE). This is an early marker of postmitotic neurons, which leaves unlabeled the neuroepithelial ventricular cells, so that we can examine cleared wholemounts of the reacted brains to have a birds-eye view of the emergent neuronal pattern at each stage. There is overall heterochrony between the basal and alar plates of the brain, a known fact, but, remarkably, heterochrony occurs even within the precocious basal plate among its final anteroposterior neuromeric subdivisions and their internal microzonal subdivisions. Some neuromeric units or microzones are precocious, while others follow suit without any specific spatial order or gradient; other similar neuromeric units remain retarded in the midst of quite advanced neighbors, though they do produce similar neurogenetic patterns at later stages. It was found that some details of such neuromeric heterochrony are species-specific, possibly related to differential morphogenetic properties. Given the molecular causal underpinning of the updated prosomeric model used here for interpretation, we comment on the close correlation between some genetic patterns and the observed AChE differentiation patterns.

Does negative affectivity predict differential response to an SSRI versus a non-SSRI antidepressant?

OBJECTIVE: This work tested the hypothesis that patients with high negative affectivity (NA) would have a better response to a serotonergic agent (escitalopram) than to one not thought to act directly on serotonin (bupropion). METHOD: Data from a study conducted between August 2007 and July 2011 were reanalyzed retrospectively. Patients (N = 245) meeting criteria for major depressive disorder (MDD), diagnosed with DSM-IV-TR, were randomly assigned to double-blind treatment with bupropion extended-release, escitalopram, or the combination. Negative affectivity score was estimated using the guilt, hostility/irritability, and fear/anxiety items of the Hamilton Depression Rating Scale, the Montgomery-Asberg Depression Rating Scale, the Quick Inventory of Depressive Symptoms, and the Social Adjustment Scale. We felt that these items captured published descriptions of the NA construct. A Clinical Global Impressions-Severity of Illness (CGI-S) score ≤ 2 defined response. Because combined treatment addressed both serotonin and non-serotonin systems, patients treated with both medications did not test the hypothesis and so were excluded from the analyses. RESULTS: Analysis of covariance with treatment as a grouping variable, NA as covariate, and CGI-S as dependent variable showed a significant 2-way interaction between treatment and NA (F1,156 = 4.82, P < .03). In the low-NA group, response rates were similar between treatments (escitalopram: 28/42 [67%]; bupropion: 23/40 [58%]; NS), while there was a significant advantage for escitalopram in patients with high NA (escitalopram: 24/40 [60%]; bupropion = 14/41 [34%]; P = .017). CONCLUSIONS: These data suggest that patients with high negative affectivity respond preferentially to antidepressants that selectively enhance serotonin neurotransmission. Although patients with low NA appear to benefit from serotonin enhancement as well, they also improved with bupropion, an antidepressant not thought to directly affect serotonin neurotransmission. These findings come from retrospective analyses using unproven approximation of NA, so no clinical inferences should be made before independent replication utilizing accepted NA measurement. TRIAL REGISTRATION: ClinicalTrials.gov identifier: NCT00519428.

Correlates of intellectual ability with morphology of the hippocampus and amygdala in healthy adults.

Several prior imaging studies of healthy adults have correlated volumes of the hippocampus and amygdala with measures of general intelligence (IQ), with variable results. In this study, we assessed correlations between volumes of the hippocampus and amygdala and full-scale IQ scores (FSIQ) using a method of image analysis that permits detailed regional mapping of this correlation throughout the surface contour of these brain structures. We delineated the hippocampus and amygdala in high-resolution magnetic resonance images of the brain from 34 healthy individuals. We then correlated FSIQ with overall volumes and with the surface morphologies of each of these structures. Hippocampus volumes correlated significantly and inversely with FSIQ independently of gender, age, socioeconomic status, and whole brain volume. Left and right hippocampus volumes correlated respectively with verbal and performance IQ subscales. Higher IQs were significantly associated with large inward deformations of the surface of the anterior hippocampus bilaterally. These findings suggest that a smaller anterior hippocampus contributes to an increased efficiency of neural processing that subserves overall intelligence.

Morphologic features of the amygdala and hippocampus in children and adults with Tourette syndrome.

CONTEXT: Limbic portions of cortical-subcortical circuits are likely involved in the pathogenesis of Tourette syndrome (TS). They are anatomically, developmentally, neurochemically, and functionally related to the basal ganglia, and the basal ganglia are thought to produce the symptoms of tics, obsessive-compulsive disorder, and attention-deficit/hyperactivity disorder that commonly affect persons with TS. OBJECTIVE: To study the morphologic features of the hippocampus and amygdala in children and adults with TS. DESIGN: A cross-sectional, case-control study using anatomical magnetic resonance imaging. SETTING: University research center. PARTICIPANTS: A total of 282 individuals (154 patients with TS and 128 controls) aged 6 to 63 years. MAIN OUTCOME MEASURES: Volumes and measures of surface morphologic features of the hippocampus and amygdala. RESULTS: The overall volumes of the hippocampus and amygdala were significantly larger in the TS group. Surface analyses suggested that the increased volumes in the TS group derived primarily from the head and medial surface of the hippocampus (over the length of the dentate gyrus) and the dorsal and ventral surfaces of the amygdala (over its basolateral and central nuclei). Volumes of these subregions declined with age in the TS group but not in controls, so the subregions were significantly larger in children with TS but significantly smaller in adults with TS than in their control counterparts. In children and adults, volumes in these subregions correlated inversely with the severity of tic, obsessive-compulsive disorder, and attention-deficit/hyperactivity disorder symptoms, suggesting that enlargement of the subregions may have a compensatory and neuromodulatory effect on tic-related symptoms. CONCLUSION: These findings are consistent with the known plasticity of the dentate gyrus and with findings from previous imaging studies suggesting the presence of failed compensatory plasticity in adults with TS who have not experienced the usual decline in symptoms during adolescence.

Increased number of subcortical hyperintensities on MRI in children and adolescents with Tourette's syndrome, obsessive-compulsive disorder, and attention deficit hyperactivity disorder.

OBJECTIVE: To investigate whether cerebral hyperintensities on T2-weighted magnetic resonance images (MRI) are associated with childhood neuropsychiatric disorders. METHOD: The authors compared the frequency of cortical and subcortical cerebral hyperintensities in 100 children and adolescents with Tourette's syndrome, obsessive-compulsive disorder (OCD), or attention deficit hyperactivity disorder (ADHD) and 32 healthy comparison subjects. RESULTS: The frequency of cerebral hyperintensities was significantly higher in subjects with Tourette's syndrome, OCD, or ADHD than in healthy comparison subjects; each diagnostic group seemed to contribute to this effect. Among the patient groups, the likelihood of detecting cerebral hyperintensities in the subcortex (primarily the basal ganglia and thalamus) was significantly greater than in the cortex. CONCLUSIONS: A childhood diagnosis of Tourette's syndrome, OCD, or ADHD significantly increased the likelihood of detecting cerebral hyperintensities, particularly in the subcortex, supporting the notion that subcortical injury may play a role in the pathophysiology of these conditions.