In the absence of testosterone T exposure, the default pathway organizes as feminine neural patterns, resulting in female-typic adult behaviors. The influence of age-related loss of brain volume could have a greater role in the loss of interhemispheric fibers and, hence, callosal area. Using RIA, we measured the E2 content of six regions of the developing brain immediately post partum. To compare their results with those of previous reports, absolute callosal area and brain volumes were calculated by reversing the dimensions of scaling used for the transformation process, and their ratios were also examined. Of the 25 subjects in our repeatability study, six could not have been studied without reformatting; the rest all differed in their orientation, to a lesser degree. Second, their method of image analysis was not based on a consistently defined midsagittal image of the corpus callosum. It is also not clear whether the expression of HD-like symptoms at the pre-motor stage in this mouse model differs between the two sexes. Men had a larger absolute total callosal area, and women larger callosal-brain volume ratios.
The images were registered into Talairach-like stereotaxic space by using linear transformations to normalize for the effects of brain volume between sexes; the need to use area-volume ratios was thus avoided. The session was concluded with a final block of six consecutive pulse-alone trials as in the first block. On the same day, tail samples were collected for DNA extraction and subsequent PCR assessment of the genotypes as previously described . The wide variation in the shape and size of the corpus callosum in healthy subjects remains largely unexplained. Sex is only one of many possible factors that could influence interhemispheric connectivity. Most sexually dimorphic areas of the brain contain substantial levels of both aromatase cytochrome P CYP19 , the enzyme responsible for the conversion of T to E2, and high densities of estrogen receptors 8 , 13 — Of the 25 subjects in our repeatability study, six could not have been studied without reformatting; the rest all differed in their orientation, to a lesser degree. The use of multiple social essays allowed us to detect potential HD-like deficits in different specific aspects of social behavior: In addition, our stimulus mice were most probably not cycling, given the well-known suppression of the estrous cycle in females housed in unisexual groups in the absence of any contact with males  , . This may explain the lack of a significant sex difference in the absolute callosal area in their data. Tests that relied mainly on observations of spontaneous behavior were conducted first in order to minimize possible undesirable transfer effects; tests that involved stressful stimulation i. Whereas our concept of steroids and their myriad mechanisms of action continue to expand, there remains a relative dearth of data on brain region-specific levels, uptake, and metabolism of gonadal steroids in the developing brain. It is well established that, as a group, men have a greater cerebral volume than women 47 , Finally on day 11 a repeated direct social interaction test, but this time with an adult female, was conducted where social habituation and ultrasonic communication were also evaluated. The IF had the greatest interrater variability of all the landmarks. Lack of reliance on optimal subject orientation within the imaging unit maximizes the use of all acquired data. A total of 33 mice were subjected to behavioral testing: This limitation occurs in almost all quantitative imaging studies involving a method is based on normal anatomy. Each mouse was introduced into an activity cage at 5 p. A metal weight was attached to the roof in order to keep the stimulus cage stable. On day 5, prepulse inhibition of the acoustic startle reactivity PPI was tested followed on day 8 by circadian modulation of locomotor activity. Exploration of each stimulus was assessed by measuring the time spent in each compartment containing the stimulus cage. Possible linear, quadratic, and logarithmic relationships between the absolute callosal area, CC ratio, and cerebral volume were examined. Materials and Methods Animals All animal experimentation was conducted in accord with accepted standards of humane animal care and approved by the University of Maryland, Baltimore Institutional Animal Care and Use Committee. The same authors have also suggested that the relationship between callosal CCA and cerebral volume is better described by a non-isometric relationship. Locomotor activity was evaluated based on the number of breaks of the infrared captors. A community sample of control subjects is more closely matched to patients when comparisons are made between disease states and the normal state.
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