Subclass-specific expression patterns of MET receptor tyrosine kinase during development in medial prefrontal and visual cortices.

Met encodes a receptor tyrosine kinase (MET) that is expressed during development and regulates cortical synapse maturation. Conditional deletion of Met in the nervous system during embryonic development leads to deficits in adult contextual fear learning, a medial prefrontal cortex (mPFC)-dependent cognitive task. MET also regulates the timing of critical period plasticity for ocular dominance in primary visual cortex (V1). However, the underlying circuitry responsible remains unknown. Therefore, this study determines the broad expression patterns of MET throughout postnatal development in mPFC and V1 projection neurons (PNs), providing insight into similarities and differences in the neuronal subtypes and temporal patterns of MET expression between cortical areas. Using a transgenic mouse line that expresses green fluorescent protein (GFP) in Met+ neurons, immunofluorescence and confocal microscopy were performed to visualize MET-GFP+ cell bodies and PN subclass-specific protein markers. Analyses reveal that the MET expression is highly enriched in infragranular layers of mPFC, but in supragranular layers of V1. Interestingly, temporal regulation of the percentage of MET+ neurons across development not only differs between cortical regions but also is distinct between lamina within a cortical region. Further, MET is expressed predominantly in the subcerebral PN subclass in mPFC, but the intratelencephalic PN subclass in V1. The data suggest that MET signaling influences the development of distinct circuits in mPFC and V1 that underlie subcerebral and intracortical functional deficits following Met deletion, respectively.

Inter- and intra-mouse variability in odor preferences revealed in an olfactory multiple-choice test.

Animals choose between sensory stimuli, a highly complex behavior which includes detection, discrimination, preference, and memory processes. Rodents are reported to display robust preferences for some odors, for instance, in the context of choosing among possible mates or food items. In contrast to the apparent robustness of responses toward these and other "ethologically relevant" odors, little is known about the robustness of behaviors toward odors which have no overt role in the rodent ecological niche, so-called "nonethologically relevant" odors. We developed an apparatus for monitoring the nose-poking behavior of mice and used this apparatus to explore the prevalence and stability of choices among different odors both across mice, and within mice over successive days. Mice were tested with a panel of either ethologically relevant or nonethologically relevant odors in an olfactory multiple-choice test. Significant preferences to nonethologically relevant odors were observed across the population of mice, with longer investigation durations to some odors more than to others. However, we found substantial inter-mouse variability in these responses, and that responses to these odors even varied within mice across days of testing. Tests with ethologically relevant odors revealed that responses toward these odors were also variable across mice, but within individual mice, responses were somewhat stable. This work establishes an olfactory multiple-choice test for monitoring odor investigation, choice, and preference behaviors and the application of this apparatus to assess across- and within-mouse odor-preference choice stability. These results highlight that odor preferences, as assayed by measuring choice behaviors, are variable. (PsycINFO Database Record