Large - scale identification of proteins involved in the 6 development of a sexually dimorphic behavior 7 8 Günther

25 Sexually dimorphic behaviors develop under the influence of sex steroids, which induce 26 reversible changes in the underlying neural network of the brain. However, little is known about 27 the proteins that mediate these activational effects of sex steroids. Here, we used a proteomics 28 approach for large-scale identification of proteins involved in the development of a sexually 29 dimorphic behavior — the electric organ discharge of brown ghost knifefish, Apteronotus 30 leptorhynchus. In this weakly electric fish, the discharge frequency is controlled by the 31 medullary pacemaker nucleus, and is higher in males than in females. After lowering the 32 discharge frequency by chronic administration of β-estradiol, two-dimensional difference gel 33 electrophoresis revealed 62 proteins spots in tissue samples from the pacemaker nucleus that 34 exhibited significant changes in abundance of more than 1.5-fold. The 20 identified protein spots 35 indicated, among others, a potential involvement of astrocytes in the establishment of the 36 behavioral dimorphism. Indeed, immunohistochemical analysis demonstrated higher expression 37 of the astrocytic marker protein GFAP and increased gap-junction coupling between astrocytes 38 in females, compared to males. We hypothesize that changes in the size of the glial syncytium, 39 glial coupling and/or number of glia-specific potassium channels lead to alterations in the firing 40 frequency of the pacemaker nucleus via a mechanism mediating uptake of extracellular 41 potassium ions from the extracellular space. 42 43