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There is a stark disparity in motor vehicle crash deaths and injuries between male and female drivers. Female drivers are 13% more likely to be killed than their male counterparts in similar motor accidents. However, vehicle safety test practices do not account for diverse body proportions when assessing safety outcomes. Vehicle crash testing standards only require testing of two variations of adult-sized crash test dummies: a 50th percentile male and a 5th percentile female. Automotive companies are not required to test safety outcomes in crash test model’s representative of average female proportions or of non-average body sizes and physiological compositions. Current crash test standards are regulated by the National Highway Traffic Safety Administration (NHTSA) under the US Department of Transportation. This memo proposes three actions for the NHTSA and the Department of Transportation to address disparities in vehicle safety outcomes: 1) update safety standard requirements to include a 50th percentile female crash test dummy, 2) implement a federal tax incentive program for companies to include a greater diversity of vehicle occupant models, and 3) allocate funds for research and development of virtual crash testing models. These proposed initiatives seek to raise the minimum safety requirements and prioritize wider representation of vehicle occupants to improve parity in vehicle safety outcomes.

In females, the hippocampus–a critical brain region for coordination of learning, memory, and behavior–displays altered physiology and behavioral output across the estrous or menstrual cycle. However, the molecular effectors and cell types underlying these observed cyclic changes have only been partially characterized to date. Recently, profiling of mice null for the AMPA receptor trafficking geneCnih3have demonstrated estrous-dependent phenotypes in dorsal hippocampal synaptic plasticity, composition, and learning/memory. We therefore profiled dorsal hippocampal transcriptomes from female mice in each estrous cycle stage, and contrasted it with that of males, across wildtype andCnih3mutants. In wildtypes, we identified only subtle differences in gene expression between the sexes, while comparing estrous stages to one another revealed up to >1000 differentially expressed genes. These estrous-responsive genes are especially enriched in gene markers of oligodendrocytes and the dentate gyrus, and in functional gene sets relating to estrogen response, potassium channels, and synaptic gene splicing. Surprisingly,Cnih3knockouts showed far broader transcriptomic differences between estrous cycle stages and males. Moreover,Cnih3knockout drove subtle but extensive expression changes accentuating sex differential expression at diestrus and estrus. Altogether, our profiling highlights cell types and molecular systems potentially impacted by estrous-specific gene expression patterns in the adult dorsal hippocampus, enabling mechanistic hypothesis generation for future studies of sex-differential neuropsychiatric function and dysfunction. Moreover, these findings suggest an unrecognized role ofCnih3in buffering against transcriptional effects of estrous, providing a candidate molecular mechanism to explain estrous-dependent phenotypes observed withCnih3loss.Significance StatementCnih3mutants show estrous-dependent alterations in learning, as well as physiological and anatomical changes in the dorsal hippocampus. However, the transcriptomic consequences of the estrous cycle on gene expression in the dorsal hippocampus of mice, including ofCnih3mutants, have not been characterized. Here, we identify candidate cell types, pathways, and gene regulators putatively involved in estrous-dependent gene expression in wildtype mice. We then contrast these with dorsal hippocampal transcriptomics inCnih3knockout mice. Utilizing our wild-type data as a reference, we demonstrate thatCnih3knockout mice have accentuated transcriptional responses across the estrous cycle.

The hippocampus represents a key structure in the integration of emotional processing, learning and memory, and reward-related behaviors. While the ventral subdivision of the hippocampus (vHPC) is involved in processing emotional values of salient stimuli and goal-directed behaviors, the dorsal hippocampus (dHPC) plays a critical role in episodic, spatial, and associative memory. In addition, it has been shown that the dHPC is necessary for context- and cue-associated reward behaviors, including the expression of reward seeking. The nucleus accumbens (NAc), a central structure in the mesolimbic reward pathway, integrates the salience of aversive and rewarding stimuli and its activity is sufficient to drive aversive and appetitive behaviors. Recent evidence has demonstrated that dHPC→Nucleus Accumbens (NAc) pathway is necessary for the expression of a conditioned place preference. However, despite years of groundbreaking research and identification of direct projections from the dHPC to the NAc, the sufficiency for dHPC→NAC inputs to drive reinforcement and reward-associated behavior remains to be determined. Here using a wide range of complementary and cutting-edge techniques including behavior, in-vivo manipulation using optogenetics, chemogenetics, brain clearing, local field potential, and fiber photometry recordings, we demonstrate that activation of excitatory projections from the CA1 subregion of the dHPC (dCA1) is sufficient to drive reinforcing behaviors. In addition, we provide strong evidence that this reinforcing behavior is driven by 1) a direct projection from the dCA1 to the NAc and 2) enhanced glutamatergic signaling within the NAc. Furthermore, we uncovered that while dCA1 stimulation increases the activity of both enkephalin- and dynorphin-containing medium spiny neurons in the NAc, the selective activity of dynorphin-containing neurons is necessary for the expression of this reinforcing behavior. Our findings shed light on a novel pathway governing reinforcement and further extend the role of the dHPC on reward seeking.

The hippocampus is a critical brain region for coordinating learning, memory, and behavior. In females, the estrous cycle alters these functions through steroid hormone activity, with well-characterized effects on cellular physiology and behavior. However, the molecular basis of these outcomes has not been systematically explored. Therefore, we profiled the transcriptome of dorsal hippocampi from female mice in each estrous cycle stage, and contrasted it with that of males. We identify only subtle sex differences in gene expression between the sexes on average, yet comparing males to individual estrous stages reveals up to thousands of genes deviating from male expression patterns at specific estrous stages. These estrous-responsive genes are especially enriched in gene markers of oligodendrocytes and the dentate gyrus, and in functional gene sets relating to estrogen response, potassium channels, and synaptic gene splicing. Next we profiled Cnih3 knockouts across estrous to provide insight into their previously reported estrous-dependent phenotypes in hippocampal synaptic plasticity, composition, and learning and memory behaviors. Surprisingly, Cnih3 knockouts showed far broader transcriptomic differences between estrous cycle stages and males. Moreover, Cnih3 knockout drove subtle but extensive expression changes accenting sex differential expresssion at diestrus and estrus. Altogether, our profiling constitutes both a resource characterizing estrous-specific gene expression patterns in the adult hippocampus, which can provide insights into mechanisms of sex differential neuropsychiatric functions and dysfunctions, while also highlighting roles of Cnih3 as a buffer against transcriptional effects of estrous and providing insights into the molecular mechanisms that may underlie estrous-dependent phenotypes with its loss.