We report a novel method to generate morphologically, antigenically and transcriptionally dependable microglia-like cells in vivo.

In most animal species, the vomeronasal organ ensures the individual recognition of conspecifics, a prerequisite for a successful reproduction. The vomeronasal organ expresses several receptors for pheromone detection. Mouse vomeronasal type-2 receptors (V2Rs) are restricted to the basal neurons of this organ and organized in four families. Family-A, B and D (family ABD) V2Rs are expressed monogenically (one receptor per neuron) and coexpress with either Vmn2r1 or Vmn2r2, two members of family-C V2Rs. Thus, basal neurons are characterized by specific combinations of two V2Rs. To investigate this issue, we raised antibodies against all family-C V2Rs and analyzed their expression pattern. We found that six out of seven family-C V2Rs (Vmn2r2-7) largely coexpressed and that none of the anti-Vmn2r2-7 antibodies significantly stained Vmn2r1 positive neurons. Thus, basal neurons are divided into two complementary subsets. The first subset (Vmn2r1-positive) preferentially coexpresses a distinct group of family-ABD V2Rs, whereas the second subset (Vmn2r2-7-positive) coexpresses the remaining group of V2Rs. Phylogenetic reconstruction and the analysis of genetic loci in various species reveal that receptors expressed by this second neuronal subset are recent branches of the V2R tree exclusively present in mouse and rat. Conversely, V2Rs expressed in Vmn2r1 positive neurons, are phylogenetically ancient and found in most vertebrates including rodents. Noticeably, the more recent neuronal subset expresses a type of Major Histocompatibility Complex genes only found in murine species. These results indicate that the expansion of the V2R repertoire in a murine ancestor occurred with the establishment of a new population of vomeronasal neurons in which coexists the polygenic expression of a recent group of family-C V2Rs (Vmn2r2-7) and the monogenic expression of a recent group of family-ABD V2Rs. This evolutionary innovation could provide a molecular rationale for the exquisite ability in individual recognition and mate choice of murine species.

BACKGROUND Epidemiological evidence suggests that peer influence plays a significant role in a variety of adolescent risk-taking behaviors, including tobacco use. We attempted to establish this relationship in a controlled laboratory setting. METHOD We modified the Balloon Analogue Risk Task (BART) task to include a peer component to investigate whether peer influences alter risk-taking behaviors. Thirty-nine adolescents (22 smokers, 17 non-smokers) completed one experimental session during which the standard and peer BART were presented in counterbalanced order, with the dependent measures being adjusted pumps and explosions. We also examined the relationship of changes in the BART (standard-peer) to personality measures of impulsivity (BIS-11) and resistance to peer influence (RPI). RESULTS A significant interaction of BART type and smoking status was present (p = .05); specifically smokers had a greater increase in the number of explosions by 2.27 (SD = 3.12) compared to an increase of .29 (SD = 2.87) by non-smokers. BIS-11 scores were related to peer-influenced BART changes: those who were more impulsive experienced greater changes in risk-taking, but no similar relationships were observed for the RPI. CONCLUSIONS These results suggest that peer influences enhance risk-taking among adolescents, and that smokers may be more susceptible to these influences.