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1.  Effects of Bax Gene Deletion on Social Behaviors and Neural Response to Olfactory Cues in Mice 
The European journal of neuroscience  2011;34(9):1492-1499.
Bax is a pro-death protein that plays a crucial role in developmental neuronal cell death. Bax−/− mice exhibit increased neuron number and the elimination of several neural sex differences. Here we examined the effects of Bax gene deletion on social behaviors (olfactory preference, social recognition, social approach, and aggression) and the neural processing of olfactory cues. Bax deletion eliminated the normal sex difference in olfactory preference behavior. In the social recognition test, both genotypes discriminated a novel conspecific, but wildtype males and Bax−/− animals of both sexes spent much more time than wildtype females investigating stimulus animals. Similarly, Bax−/− mice were more sociable than wildtype mice in a social approach test. Bax deletion had no effect on aggression in a resident/intruder paradigm where males, regardless of genotype, exhibited a shorter latency to attack. Thus, the prevention of neuronal cell death by Bax gene deletion results in greater sociability as well as the elimination of sex differences in some social behaviors. To examine olfactory processing of socially relevant cues, we counted c-Fos immunoreactive (Fos-ir) cells in several nodes of the accessory olfactory pathway after exposure to male-soiled or control bedding. In both genotypes, exposure to male-soiled bedding increased Fos-ir cells in the posterodorsal medial amygdala, principal nucleus of the bed nucleus of the stria terminalis, and medial preoptic nucleus (MPN), and the response in the MPN was greater in females than in males. However, a reduction in Fos-ir cells was seen in the anteroventral periventricular nucleus of Bax−/− mice.
doi:10.1111/j.1460-9568.2011.07881.x
PMCID: PMC3205466  PMID: 22034980
cell death; c-Fos; olfactory preference; sex difference
2.  Social Status and Sex Effects on Neural Morphology in Damaraland Mole-Rats, Fukomys damarensis 
Brain, Behavior and Evolution  2011;77(4):291-298.
We previously reported that in a eusocial rodent, the naked mole-rat (Heterocephalus glaber), traditional neural sex differences were absent; instead, neural dimorphisms were associated with breeding status. Here we examined the same neural regions previously studied in naked mole-rats in a second eusocial species, the Damaraland mole-rat (Fukomys damarensis). Damaraland mole-rats live in social groups with breeding restricted to a small number of animals. However, colony sizes are much smaller in Damaraland mole-rats than in naked mole-rats and there is consequently less reproductive skew. In this sense, Damaraland mole-rats may be considered intermediate in social organization between naked mole-rats and more traditional laboratory rodents. We report that, as in naked mole-rats, breeding Damaraland mole-rats have larger volumes of the principal nucleus of the bed nucleus of the stria terminalis and paraventricular nucleus of the hypothalamus than do subordinates, with no effect of sex on these measures. Thus, these structures may play special roles in breeders of eusocial species. However, in contrast to what was seen in naked mole-rats, we also found sex differences in Damaraland mole-rats: volume of the medial amygdala and motoneuron number in Onuf's nucleus were both greater in males than in females, with no significant effect of breeding status. Thus, both sex and breeding status influence neural morphology in Damaraland mole-rats. These findings are in accord with the observed sex differences in body weight and genitalia in Damaraland but not naked mole-rats. We hypothesize that the increased sexual dimorphism in Damaraland mole-rats relative to naked mole-rats is related to reduced reproductive skew.
doi:10.1159/000328640
PMCID: PMC3182041  PMID: 21701152
Bed nucleus of the stria terminalis; Damaraland mole-rat; Medial amygdala; Naked mole-rat; Onuf's nucleus; Paraventricular nucleus; Sex difference; Social status

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