Generation of an Iba1-EGFP Transgenic Rat for the Study of Microglia in an Outbred Rodent Strain.

Neuroscience has been transformed by the ability to genetically modify inbred mice, including the ability to express fluorescent markers specific to cell types or activation states. This approach has been put to particularly good effect in the study of the innate immune cells of the brain, microglia. These specialized macrophages are exceedingly small and complex, but also highly motile and mobile. To date, there have been no tools similar to those in mice available for studying these fundamental cells in the rat brain, and we seek to fill that gap with the generation of the genetically modified Sprague Dawley rat line: SD-Tg(Iba1-EGFP)Mmmc Using CRISPR-Cas/9 technology, we knocked in EGFP to the promoter of the gene Iba1 With four male and three female founders confirmed by quantitative PCR analysis to have appropriate and specific insertion, we established a breeding colony with at least three generations of backcrosses to obtain stable and reliable Iba1-EGFP expression. The specificity of EGFP expression to microglia was established by flow cytometry for CD45low/CD11b+ cells and by immunohistochemistry. Microglial EGFP expression was detected in neonates and persisted into adulthood. Blood macrophages and monocytes were found to express low levels of EGFP, as expected. Last, we show that EGFP expression is suitable for live imaging of microglia processes in acute brain slices and via intravital two-photon microscopy.

Mast Cells in the Developing Brain Determine Adult Sexual Behavior.

Many sex differences in brain and behavior are programmed during development by gonadal hormones, but the cellular mechanisms are incompletely understood. We found that immune-system-derived mast cells are a primary target for the masculinizing hormone estradiol and that mast cells are in turn primary mediators of brain sexual differentiation. Newborn male rats had greater numbers and more activated mast cells in the preoptic area (POA), a brain region essential for male copulatory behavior, than female littermates during the critical period for sexual differentiation. Inhibiting mast cells with a stabilizing agent blunted the masculinization of both POA neuronal and microglial morphology and adult sex behavior, whereas activating mast cells in females, even though fewer in number, induced masculinization. Treatment of newborn females with a masculinizing dose of estradiol increased mast cell number and induced mast cells to release histamine, which then stimulated microglia to release prostaglandins and thereby induced male-typical synaptic patterning. These findings identify a novel non-neuronal origin of brain sex differences and resulting motivated behaviors.SIGNIFICANCE STATEMENT We found that immune-system-derived mast cells are a primary target for the masculinizing hormone estradiol and that mast cells are in turn primary mediators of brain sexual differentiation. These findings identify a novel non-neuronal origin of brain sex differences and resulting motivated behaviors.

The Creative Benefits Scale: Connecting Generativity to Life Satisfaction.

Long-term participation in creative activities has benefits for middle-aged and older people that may improve their adaptation to later life. We first investigated the factor structure of the Creative Benefits Scale and then used it to construct a model to help explain the connection between generativity and life satisfaction in adults who participated in creative hobbies. Participants included 546 adults between the ages of 40 and 88 (Mean = 58.30 years) who completed measures of life satisfaction, generativity, and the Creative Benefits Scale with its factors of Identity, Calming, Spirituality, and Recognition. Structural equation modeling was used to examine the connection of age with life satisfaction in older adults and to explore the effects of creativity on this relation. The proposed model of life satisfaction, incorporating age, creativity, and generativity, fit the data well, indicating that creativity may help explain the link between the generativity and life satisfaction.