Strain and sex dependent effects of isolation housing relative to environmental enrichment on operant sensation seeking in mice

Sensation seeking is a multidimensional phenotype that predicts the development of drug addiction in humans and addiction-like drug seeking in rodents. Several lines of evidence suggest that chronic stress increases sensation seeking and addiction-like drug seeking through common genetic mechanisms. Discovery and characterization of these mechanisms would reveal how chronic stress interacts with the genome to influence sensation seeking and how drugs of abuse hijack these fundamental reward mechanisms to drive addiction. To this end, we tested the hypothesis that chronic isolation housing stress (relative to environmental enrichment) influences operant sensation seeking as a function of strain, sex, or their interaction. To determine if the BXD recombinant inbred panel could be used to identify genetic and epigenetic mechanisms underlying any identified gene-by-environment interactions, we used mice from the two BXD founder strains. Following 10 weeks of differential housing, we assessed operant sensation seeking using several reinforcement schedules. The primary finding from this study was that DBA/2J but not C57BL/6J mice were significantly vulnerable to an isolation-induced increase (relative to environmental enrichment) in sensation seeking during extinction when the sensory reward was no longer available; this effect was significantly more robust in females. These data reveal a previously unknown isolation-induced effect on extinction of operant sensation seeking that is sex-dependent, addiction-relevant, and that can be dissected using the BXD recombinant inbred panel.

Nfkbid is required for immunity and antibody responses to Toxoplasma gondii

ABSTRACTNo fully protective vaccine has yet been developed for any human parasite. We previously reported that South American strains of Toxoplasma gondii are adept at immune evasion and cause lethal secondary infections in chronically infected mice. Here we report that unlike susceptible C57BL/6J mice, A/J mice were highly resistant to secondary infection. Mapping immunity loci that segregated within a recombinant inbred panel of mice we identified Nfkbid, a nuclear regulator of NF-κB that is required for B-1 cell development. Nfkbid-null mice (bumble) were susceptible to secondary, but not primary infections and failed to generate parasite-specific IgM and lacked robust parasite-specific IgG. In resistant mice, B-1 cells bore evidence for Nfkbid-dependent responses, including Ighg expression, and were partially responsible for the immunity defect in bumble mice. We propose a model where adaptive immunity to T. gondii must be ‘layered’ with B-1 responses to promote protection to virulent challenge.