TrkB is necessary for male copulatory behavior in the Syrian Hamster (Mesocricetus auratus).

The magnocellular medial preoptic nucleus (MPN mag), a subdivision of the medial preoptic area (MPOA), plays a critical role in the regulation of copulation in the male Syrian hamster; in part by mediating the effects of gonadal steroids. For example, ablation of the MPN mag eliminates mating and testosterone placed in the MPN mag restores mating in castrated males. Furthermore, testosterone treatment enhances synaptic density and dendritic spines in the MPN mag. Thus, copulatory behaviors are correlated with increases in synaptic morphology in the MPN mag. As brain derived neurotrophic factor (BDNF) and its receptor, tyrosine receptor kinase-B (TrkB), effect neuronal growth and synaptic plasticity, this study explored the role of TrkB and BDNF in mediating testosterone's effects on the MPN mag and behavior. Testosterone treatment increased BDNF expression and conversely lowered TrkB expression in the MPOA. siRNA-mediated TrkB knockdown in the MPN mag eliminated copulation two-days post injection and the behavior was restored one week later. These data indicate that testosterone influences the expression of BDNF and TrkB in the MPOA and that expression of copulation is dependent on the presence of TrkB. Taken together our findings support a role for TrkB and BDNF in mediating the effects of testosterone on copulatory behavior in the Syrian hamster.

BDNF infusion into the MPN mag is sufficient to restore copulatory behavior in the castrated Syrian hamster.

Testosterone plays a key role in the expression of male sex behavior by influencing cellular activity and synapses within the magnocellular medial preoptic nucleus (MPN mag), a sub-nucleus of the medial preoptic area (MPOA) in the Syrian hamster. Although the mechanisms underlying hormonally-induced synaptic plasticity in this region remain elusive, the data suggests that an increase in synaptic density may mediate testosterone's effects on copulation. As brain derived neurotrophic factor (BDNF) plays an integral role in regulating synaptic plasticity and gonadal steroids regulate the levels of BDNF, we hypothesize that BDNF may mediate the effects of gonadal hormones on copulatory behavior. To test this hypothesis, we infused BDNF or controls into the MPN mag of long-term castrates. Our results indicate that BDNF, but not the controls, restored copulatory behavior in castrated male Syrian hamsters. Furthermore, the rise of BDNF expression in the MPOA preceded the rise of synaptophysin following testosterone replacement in castrated males. These data are consistent with our hypothesis, implicating a role for BDNF in mediating testosterone's action on copulation and suggest that the delay in testosterone's restoration of copulation is, in part, due to the delay in the increase of BDNF and synaptophysin.

Exposure to female pheromones stimulates a specific type of neuronal population in the male but not female magnocellular division of the medial preoptic nucleus (MPN mag) of the Syrian hamster.

The magnocellular division of the medial preoptic area (MPN mag) integrates pheromonal and hormonal signals to play a critical role in the expression of male typical sex behavior. The MPN mag contains two morphologically distinct neuronal populations; the percentage of each type within the nucleus is sex specific. Males have more neurons with a single nucleolus whereas females have more with multiple nucleoli. To determine which neuronal subtype mediates pheromonal induction of copulation, tissue from male and female hamsters exposed to female pheromones was immunolabeled for the immediate early protein (EGR-1). Subsequently the tissue was counterstained and the number of ERG-1 neurons with one or two nuclei was determined. The results indicate that pheromones stimulate neurons with single nucleoli in males but fail to stimulate either neuronal subtype in females suggesting that synaptic input to the MPN mag is sexually differentiated.

Academic bullying and diversity: challenges and solutions.

The academy remains disproportionally white despite decades of efforts to diversify the professoriate. Recruitment of faculty from underrepresented populations continues to challenge and little attention has been placed on retention. Bullying threatens all workplaces and is particularly insidious in higher education where the practice of tenure grants bad actors immunity from many corrective measures. Strategies and approaches summarized here have been proposed and should be adopted to provide a better workplace for all.

Hamster sperm-associated alpha-L-fucosidase functions during fertilization.

Sperm-associated alpha-L-fucosidases have been identified in diverse organisms. Their wide phylogenetic distribution and known properties support the likelihood that L-fucose and alpha-L-fucosidase have fundamental function(s) during gamete interaction. This is consistent with the substantial evidence in the literature documenting the importance of carbohydrate moieties during fertilization. Direct enzyme assays were employed to evaluate the functional distribution of alpha-L-fucosidase in preparations of hamster sperm. In vitro fertilization was performed using Syrian hamster sperm and eggs to identify the functional role of hamster sperm-associated alpha-L-fucosidase during zona pellucida binding/penetration, sperm-egg membrane fusion, and postfusion events. Results reported here document the presence of hamster sperm-associated alpha-L-fucosidase and demonstrate that it functions during fertilization at the stage of sperm-oocyte membrane interaction and/or postfusion events within the zygote. Understanding the role of alpha-L-fucosidase during human fertilization could lead to development of improved infertility treatments.

Sexual dimorphic expression of TrkB, TrkB-T1, and BDNF in the medial preoptic area of the Syrian hamster.

Neurotrophins regulate many aspects of neuronal function and activity. Specifically, the binding of Brain-derived neurotrophic factor (BDNF) to Tyrosine receptor kinase-B (TrkB) or its truncated version, TrkB-T1, can cause growth and differentiation or dominant inhibition of receptor signaling, respectively. There is evidence that these neurotropic effects on nervous tissue, in both the central and peripheral nervous system, behave differently between the sexes. This study used western blots to examine the expression of these neurotrophins in the medial preoptic area (MPOA), a sexually dimorphic region of the hamster brain that controls male sex behavior. We report that TrkB-FL and BDNF show greater expression in male MPOA tissue, when compared to female. On the contrary, TrkB-T1 is expressed in greater abundance in the female MPOA. Our results indicate a clear sexual dimorphism of neurotrophins in the MPOA of the Syrian hamster. Furthermore, the greater expression of TrkB-FL and BDNF in the male MPOA suggests that these neurotrophins could be promoting synaptic growth to facilitate male-typical copulation. In contrast, the greater TrkB-T1 expression in the female MPOA suggests a possible inhibition of synaptic growth, and may contribute to the lack of male-typical copulation. Altogether, our data suggests that neurotrophins may play a larger role sexual differentiation than previously thought.

The MPN mag: introducing a critical area mediating pheromonal and hormonal regulation of male sexual behavior.

Mating behavior in male hamsters is regulated by a chemosensory pathway that converges on the bed nucleus of the stria terminalis (BST) and the medial nucleus of the amygdala (Me). Both the BST and the Me project to the lateral part of the medial preoptic area. Lesion studies have identified a small group of large cells referred to as the magnocellular medial preoptic nucleus (MPN mag) whose integrity is required for normal mating behavior. Our data, summarized within, indicate that the MPN mag is a sexually differentiated nucleus in a large steroid-responsive network that relays pheromonal signals from the sensory systems to the motor areas to affect behavior.

Neuronal composition of the magnocellular division of the medial preoptic nucleus (MPN mag) is sex specific in the Syrian hamster (Mesocricetus auratus).

The magnocellular division of the medial Preoptic nucleus (MPN mag) plays a critical role in the regulation of male sexual behavior in the hamster. Results from previous studies indicated that the number of neurons in the MPN mag is greater in males than females but failed to find significant differences in the volume of the nucleus suggesting that other elements in the nucleus may be greater in the female. The results of the present study, using NeuN to identify neurons, are in line with this hypothesis. The data show that (1) neurons in the MPN mag display two distinct phenotypes, those with a single nucleolus and those with multiple nucleoli; (2) the percentage of each phenotype is sex specific, differing over the course of development and (3) there is no sex difference in the number of glial cells at any age. Sex differences in the numbers of each type are correlated with developmental milestones and suggest that morphological changes are influenced by changes in circulating gonadal steroids during development.

Temperature, peroxide concentration, and immunohistochemical staining method affects staining intensity, distribution, and background.

The techniques used to label neural tissue for specific antigens can vary significantly. Some immunostaining methods use free-floating tissue sections, whereas others use tissue sections mounted on slides. Mounting sections on glass slides before labeling the tissue with antigens is preferred method for neonatal tissue; processing young tissue by free-floating methods often destroy it. Surprisingly optimal temperature for storing tissue can vary with age. This study describes parameters developed to obtain robust staining of both young and old tissue. Our results show the most robust staining was found in tissue that was (1) stored at very low temperatures (-20 degrees C and -80 degrees C), (2) pretreated with 0.01% peroxide, and (3) entirely immersed in the staining solutions during immunohistochemistry.