Biology subjects

Fletcher, M. L.

Publications and source records attributed to Fletcher, M. L..

6 recordsLinked to original sources

bioRxiv2026

Cellular heterogeneity in the response of Burkholderia thailandensis to antibiotics and phages in synthetic spatial refuges

Understanding the complex interactions between phage, antibiotics and bacteria is vital for the development of rationale phage-antibiotic therapies. These interactions have traditionally been investigated via bulk assays, thus masking eventual cellular heterogeneities and the impact of spatial refuges on phage and antibiotic efficacy. Using microfluidics-based time-lapse microscopy, we reveal large phenotypic heterogeneity in the response of Burkholderia thailandensis to both the bacteriophage {Phi}Bp-AMP1 and sub-inhibitory concentrations of two selected antibiotics ciprofloxacin and trimethoprim. We discover that simultaneous exposure to ciprofloxacin and phage decreases the size of individual B. thailandensis cells, whereas phage and trimethoprim together slow down cell doubling. Exposure to ciprofloxacin also causes extended phage lysis of B. thailandensis which is preceded by a distinguishable pause in cell elongation, whereas exposure to trimethoprim constrains lysis. As a consequence, exposure to ciprofloxacin further hinders the growth of B. thailandensis in the presence of phage, whereas exposure to trimethoprim enhances growth in the presence of phage. These findings help understand the effects of the interactions between antibiotics and phage on bacterial subpopulations in spatial refuges that are notoriously difficult to treat with antibiotics.

microbiology↗

bioRxiv2024

Neural coding in gustatory cortex reflects consumption decisions: Evidence from conditioned taste aversion

Taste-responsive neurons in the gustatory cortex (GC) have been shown to encode multiple properties of stimuli, including whether they are palatable or not. Previous studies have suggested that a form of taste-involved learning, conditioned taste aversion (CTA), may alter the cortical representation of taste stimuli in a number of ways. We used miniscopes to image taste responses from a large population of neurons in the gustatory cortex of mice before and after CTA to NaCl, comparing taste responses in control and conditioned mice. Following conditioning, no significant effects on the number of responsive cells, or the magnitude of response to either NaCl or other taste stimuli were found. However, population-level analyses showed that in mice receiving a CTA, the representation of NaCl diverged from other appetitive stimuli in neural space and moved closer to that of aversive quinine. We also tracked extinction of the CTA in a subset of animals and showed that as NaCl became less aversive, the neural pattern reverted to match the behavior. These data suggest that the predominant function of the taste representation in GC is palatability; the neuronal response pattern to stimuli at the population level reflects the decision of the animal to consume or not consume the stimulus, regardless of quality or chemical identity.

neuroscience↗

bioRxiv2024

Experience and behavior modulate piriform cortex odor representation in freely moving mice

In rodents, activity in the piriform cortex (PC) has been shown to reliably encode the identity of olfactory information within single sessions of odor delivery. However, recent evidence from chronic PC recordings found significant unreliability in this ensemble code over longer periods. The causes of this phenomenon, termed representational drift, are still being investigated across multiple sensory systems, but prior work has suggested a role for animal behavior in this observed unreliability of coding. To explore this possibility in PC, we recorded from the same populations of neurons in freely-moving, awake mice using micro-endoscopic calcium imaging as they gained passive experience with a panel of odorants over 5 consecutive days. As in prior studies, PC odor responses within a single session could be used to accurately decode odor identity. However, responses became less consistent across days of experience as odor-evoked response properties of the neurons shifted with experience. During these recordings, within and across sessions, decreases in olfactory investigative behavior correlated with decreased odor-evoked response from PC neurons. Similarly, decreases in odor investigation correlated with a decrease in representational consistency, and trials with greater odor investigation could be used to decode odor identity from PC neurons more accurately over time. Overall, this data supports recent evidence of long-term shifts in the ensembles of PC neurons encoding odor-identity (drift) but supports a role for behavioral modulation of overall PC activity and ensemble response consistency.

neuroscience↗

bioRxiv2022

The impact of familiarity on cortical taste coding

The role of the gustatory region of the insular cortex in mediating associative taste learning, such as conditioned taste aversion, has been well studied. However, while associative learning plays a role in some taste behaviors, such as avoidance of toxins, taste stimuli are often encountered by animals in their natural environment without explicit consequences. This type of inconsequential experience with sensory stimuli has been studied in other sensory systems, generally with the finding that neuronal responses habituate with repeated sensory exposure. The present study sought to determine the effect of taste familiarity on population taste coding in mouse gustatory cortex (GC). Using microendoscope calcium imaging, we studied the taste responses of visually identifiable neurons over five days of taste experience, during which animals could freely choose to consume taste stimuli. We found that the number of active cells in insular cortex, as well as the number of cells characterized as taste-responsive, significantly decreased as animals became familiar with taste stimuli. Moreover, the magnitude of taste-evoked excited responses increased, and inhibited responses decreased with experience. By tracking individual neurons over time, we focused on taste coding in a subpopulation of "stable" neurons that were present on all days of the taste familiarity paradigm. The population-level response across these stable cells was distinct when taste stimuli were novel but became more intercorrelated among those taste stimuli mice willingly consumed as the stimuli became familiar. Overall, these results highlight the effects of familiarity on taste responses in gustatory cortex.

neuroscience↗

bioRxiv2017

Olfactory fear conditioning non-specifically enhances glomerular odor responses and increases representational overlap of learned and neutral odors

Associative fear learning produces fear toward the conditioned stimulus (CS) and often generalization, the expansion of fear from the CS to similar, unlearned stimuli. However, how fear learning affects early sensory processing of learned and unlearned stimuli in relation to behavioral fear responses to these stimuli remains unclear. We subjected mice to a classical olfactory fear conditioning paradigm and used awake, in vivo calcium imaging to quantify learning-induced changes in glomerular odor responses, which constitutes the first site of olfactory processing in the brain. The results demonstrate that olfactory fear learning non-specifically enhances glomerular odor representations in a learning-dependent manner and increases representational similarity between the CS and non-conditioned odors. This mechanism may prime the system towards generalization of learned fear. Additionally, CS-specific enhancements remain even when associative learning is blocked; suggesting two separate mechanisms lead to enhanced glomerular responses following odor-shock pairings.

neuroscience↗

bioRxiv2017

Overlapping representation of primary tastes in a defined region of the gustatory cortex

Two-photon imaging was used to examine taste responses in neurons in a region of gustatory cortex defined by thalamic input. This area contained an overlapping representation of primary tastes, with neurons that were either narrowly or broadly responsive to taste stimuli. Analysis demonstrates that activity in the neuronal population in this area yields information about both taste quality and hedonics.

neuroscience↗