Sex matters during adolescence: Testosterone-related cortical thickness maturation differs between boys and girls

Age-related changes in cortical thickness have been observed during adolescence, including thinning in frontal and parietal cortices, and thickening in the lateral temporal lobes. Studies have shown sex differences in hormone-related brain maturation when boys and girls are age-matched, however, because girls mature 1-2 years earlier than boys, these sex differences could be confounded by pubertal maturation. To address puberty effects directly, this study assessed sex differences in testosterone-related cortical maturation by studying 85 boys and girls in a narrow age range and matched on sexual maturity. We expected that testosterone-by-sex interactions on cortical thickness would be observed in brain regions known from the animal literature to be high in androgen receptors. We found sex differences in associations between circulating testosterone and thickness in left inferior parietal lobule, middle temporal gyrus, calcarine sulcus, and right lingual gyrus, all regions known to be high in androgen receptors. Visual areas increased with testosterone in boys, but decreased in girls. All other regions were more impacted by testosterone levels in girls than boys. The regional pattern of sex-by-testosterone interactions may have implications for understanding sex differences in behavior and adolescent-onset neuropsychiatric disorders. © 2012 Bramen et al

Patterns of inter- and intralaminar GABAergic connections distinguish striate (V1) and extrastriate (V2, V4) visual cortices and their functionally specialized subdivisions in the rhesus monkey.

Local GABAergic connections are undoubtedly important for the operation of cerebral cortex, including the tuning of receptive field properties of visual cortical neurons. In order to begin to correlate specific configurations of GABAergic networks with particular receptive field properties, we examined the arrangement of GABAergic neurons projecting to foci in compartments of known functional specialization in striate (area V1) and extrastriate (areas V2, V4) cortices of rhesus monkeys. GABAergic cells were detected autoradiographically following microinjections into supragranular, granular, or infragranular layers of 5, 10, or 50 nl of 3H-nipecotic acid, which selectively exploits the GABA reuptake mechanism. These injections produced complex inter- and intralaminar distributions of retrograde perikaryal labeling that was selective for GABA-immunopositive neurons and glia. The pattern of retrograde labeling depended on both the laminar and cytoarchitectonic location of injection sites. In all cases, a high density of labeled neurons was present in the immediate vicinity of injection sites, with the density of labeled neurons decreasing for the most part uniformly with horizontal distance. Injections in supragranular layers produced relatively widespread labeling (up to 1.5-1.7 mm from the center of injections) in upper layers, whereas in granular and infragranular layers, labeling was confined to a radius of 0.25-0.5 mm. Conversely, injections in infragranular layers produced labeling that was widest (up to 1 mm) in lower layers, but more laterally restricted in supragranular layers. Injections in granular layers, on the other hand, produced an even distribution of labeling, 0.6-1.0 mm in diameter, throughout all layers. Comparably placed injections in V1, V2, and V4 resulted in patterns of labeling that were distinguished by features including stepwise increases in the lateral extent of labeling from striate to extrastriate areas, and the circular versus markedly elongated intralaminar distribution of labeled neurons in V1 and V4 versus V2. Further, for superficial injections, labeling was present in all layers in V1 and V2, but did not extent below the top layer V in area V4. These findings offer clear examples of organizational differences in the intrinsic inhibitory connections of visual cortices. The results also demonstrate that the number of GABAergic neurons projecting to any spot in cortex decreases systematically with horizontal distance from the spot, and that radiolabeled cells do not coalesce to form slabs, columns, or clusters. This relatively even distribution of retrogradely labeled cells in the tangential plane is consistent with recent computer simulations (Worgotter and Koch, 1991) that suggest that inhibitory neurons broadly tuned as a population can produce the specific response properties of cortical neurons.(ABSTRACT TRUNCATED AT 400 WORDS

Different effects of scopolamine on learning, memory, and nitric oxide metabolite levels in hippocampal tissues of ovariectomized and Sham-operated rats

Different effects of scopolamine on learning, memory, and nitric oxide (NO) metabolites in hippocampal tissues of ovariectomized (OVX) and sham-operated rats were investigated. The animals in the Sham-Scopolamine (Sham-Sco) and OVX-Scopolamine (OVX-Sco) Groups were treated with 2 mg/kg scopolamine before undergoing the Morris water maze, while the animals in the Sham and OVX Groups received saline. The time latency and path length were significantly higher in both the Sham-Sco and the OVX-Sco Groups, in comparison with the Sham and OVX Groups, respectively (p<0.001). Significantly lower NO metabolite levels in the hippocampi of the Sham-Sco Group were observed, compared with the Sham Group (p<0.001), while there was no significant difference between the OVX-Sco and OVX Groups. The decreased NO level in the hippocampus may play a role in the learning and memory deficits induced by scopolamine. However, it seems that the effect of scopolamine on hippocampal NO differs between situations of presence and absence of ovarian hormones