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The properties of composite systems can normally be explained in terms of the sum of the properties of their constituents, with small corrections for how they combine (binding energy, relative angular momentum etc.), but not so the nucleon. The constituent quarks account for less than 15% of the nucleon mass and less than half of its spin. In order to understand these "building blocks" of our universe we are unable to take them apart, due to confinement, and have to resort to probing their bulk properties and behaviour as a system. In the A2 Collaboration of the Institut fuer Kernphysik at Johannes Gutenberg University Mainz, we investigate the nucleon using a photon beam derived from the Mainzer Mikrotron (MAMI) electron beam in combination with the Glasgow Photon Tagger. This quasi-monoenerghetic photon beam is then directed onto a variety of targets, including polarised 3He, protons & deuterons, with the resulting particles being detected in a combined Crystal Ball - TAPS 4pi detector array. Reactions studied include single and multiple meson photoproduction, Compton Scattering and rare meson decays. The high flux photon beam combined with the large acceptance detector system and polarised target capability allow for world leading, and often unique measurements. We will provide an overview of the detector system and physics program with a focus on the determination of the nucleon polarisabilities through Compton Scattering.

It is clear that much of the masculinization of the brain in rats and mice is mediated by aromatized metabolites of testicular androgens acting upon estrogen receptors (ERs). For example, exogenous estrogens, which presumably exert little effect on androgen receptors (ARs), can reverse the loss of masculine behavior and neural morphology in males that have been castrated, both in development and adulthood. However, we find that rats and mice carrying a dysfunctional AR gene, so-called testicular feminization mutation (Tfm) males, are partly or completely demasculinized in terms of at least one non-reproductive behavior and each of the numerous brain regions we have examined so far. These findings indicate that in fact AR normally plays a role in the masculinization of at least some behaviors, and potentially every brain region, in rodents.

For example, the medial amygdala (MeA) is about 150% larger in volume in wildtype (wt) male rats than in wt females. Tfm males display an intermediate volume, significantly greater than wt females yet significantly less than wt males. Astrocytes in the posterodorsal portion of the MeA (MePD) of rats are also sexually dimorphic, both in number and arbor complexity, and Tfm males are wholly feminine in these features. Likewise, in our measurements of sexually dimorphic characters in the ventromedial hypothalamus (VMH), the suprachiasmatic nucleus (SCN), and the paraventricular nucleus (PVN), Tfm males are wholly feminine. Even in the sexually dimorphic nucleus of the preoptic area (SDNPOA), where the volume is masculine in Tfm males, the size of the neurons is nevertheless reduced in Tfm males compared to wt males.

It is difficult to assess masculine reproductive behavior in Tfm males because they have an entirely feminine exterior phenotype, with a clitoris, vagina, etc. Nevertheless, they have been reported to show many masculine reproductive behaviors, as would be expected if those were mediated by ERs. However, we find that anxiety-related behaviors, such as measured in an open field with a novel object, the elevated plus maze, and the light/dark box, are greater in Tfm males than in wt males in both rats and mice. Tfm animals also show a heightened corticosterone response to mild stress. These results suggest that masculinization of anxiety-related behavior is heavily reliant on stimulation of AR, presumably in the brain. We are exploring the sites of AR action by use of Cre- lox technology to delete AR in selective tissues.

We are using the same technology to explore the site(s) of androgen action on the spinal nucleus of the bulbocavernosus (SNB), a group of motoneurons that innervate two striated muscles, the bulbocavernosus and levator ani (BC/LA), which are attached to the base of the penis. By selectively deleting AR in either motoneurons alone, or in muscle fibers alone, we hope to understand how androgen spares this system from apoptosis in development, and regulates neural plasticity of the motoneurons in adulthood.