1. Brittany N. Dugger 1, John A. Morris 1, Cynthia L. Jordan 1,2, S. Marc Breedlove 1,2 1 Neuroscience Program; 2 Department of Psychology Michigan State University, East Lansing, MI 48825 Introduction Methods Literature Cited ResultsConclusions Acknowledgments Androgens Maintain Soma Size in the Sexually Dimorphic Nucleus of the PreOptic Area of Adult Male Rats Figure 5. Mean unilateral SDN-POA volume for male rats subjected to either castration or sham surgery. Figure 1. (A) Nissl stain of a 40µm coronal section of an adult male sacrificed 28 days after sham surgery taken with a 4X objective. Abbreviations: SDN-POA, Sexually Dimorphic Nucleus of the PreOptic Area; AC, Anterior Commissure; OC, Optic Chiasm; 3V, Third Ventricle. (B) Higher magnification view of somas (arrows) within the SDN-POA taken with a 100X oil objective. Volume- The PreOptic Area (POA) is involved in sexual and maternal behaviors. Volume of the Sexually Dimorphic Nucleus of the POA (SDN-POA) is larger in wildtype males than in females (Gorski et al. 1978). In male rats with a dysfunctional androgen receptor (AR) (rendering them androgen insensitive) the volume is similar to that of wildtype males. Suggesting that AR plays no role in determining this sex difference. Data suggests that the volume of the SDN-POA is controlled by the hormonal environment during the perinatal period (Dohler et al., 1982). Soma Size- Surprisingly, soma size in the SDN-POA of androgen insensitive genetic male rats is significantly reduced compared to their wildtype male littermates, and is not significantly different from that of their normal female littermates (Morris et al. 2005). Question- Do androgens in adulthood affect soma size in the SDN- POA? Male Soma Size - The reduced soma size of adult males 28 days after castration suggests that androgens are needed to maintain soma size in adult male rats. Unlike SDN-POA volume, testosterone acts both in adulthood and perinatally to masculinize the SDN-POA soma size. Female Soma Size – Testosterone treatment can masculinize female SDN-POA soma size in adulthood. This result suggests that the female SDN-POA soma size retains a sensitivity to testosterone in adulthood. Male SDN-POA Volume- Castration in adulthood does not affect SDN-POA volume in adult male rats. This further supports the idea that SDN-POA volume is determined perinatally. Female SDN-POA Volume- Surprisingly, testosterone may affect SDN-POA volume in adult females. This result suggests that SDN-POA volume of female rats may retain a capacity to respond to androgens after the perinatal period. Thanks to all members of the Breedlove/Jordan lab for their support and assistance. Supported by NIH grant MH58703. Figure 4. Average SDN-POA soma size for male rats subjected to either castration or sham surgery. Figure 3. Mean unilateral SDN-POA volume for ovariectomized female rats given either testosterone (T) filled or blank Silastic capsules. Figure 2. Average SDN-POA soma size for ovariectomized female rats given either testosterone filled or blank Silastic capsules. Gorski RA et al. 1978. Evidence for a morphological sex difference within the medial preoptic area of the rat brain. Brain Res 148:333- 346. Dohler KD, et al. 1982 Differentiation of the sexually dimorphic nucleus in the preoptic area of the rat brain is determined by the perinatal hormone environment. Neurosci Lett. 33(3):295-8. Morris JA, et al. 2005. Partial demasculinization of several brain regions in adult male (XY) rats with a dysfunctional androgen receptor gene. J Comp Neurol. 487(2):217-26. Females Testosterone masculinizes female SDN-POA somas in adulthood. Males Soma size is decreased in adult males 28 days after castration. SDN-POA Soma Size Males Castration does not affect SDN-POA volume in adult males. Table 1. Male and female Long Evans rats 60 days of age were sacrificed at 14 or 28 days after the noted treatment or surgery. All females were ovariectomized at 60 days of age. SDN-POA volume was measured using a 5X objective every 80µm in Nissl stained material using Stereoinvestigator Software (Microbrightfield). 6-8 somas were sampled per section throughout the rostal caudal extent of the nucleus with a 63X objective using the optical fractionator probe (range of 11-66 somas per animal ). SDN-POA Volume Females Testosterone may affect SDN-POA volume in adult females. Contact Information: duggerbr@msu.edu