Biology subjects

Frechter, S.

Publications and source records attributed to Frechter, S..

4 recordsLinked to original sources

bioRxiv2018

Neurogenetic dissection of the Drosophila innate olfactory processing center

Animals exhibit innate behaviours in response to a variety of sensory stimuli such as olfactory cues. In Drosophila, a higher olfactory centre called the lateral horn (LH) is implicated in innate behaviour. However, our knowledge of the structure and function of the LH is scant, due to the lack of sparse neurogenetic tools for this brain region. Here we generate a collection of split-GAL4 driver lines providing genetic access to 82 LH cell-types. We identify the neurotransmitter and axo-dendritic polarity for each cell-type. Using these lines were create an anatomical map of the LH. We found that [~]30% of LH projections converge with outputs from the mushroom body, the site of olfactory learning and memory. Finally, using optogenetic activation of small groups of LH neurons. We identify cell-types that drive changes in either valence or specific motor programs, such as turning and locomotion. In summary we have generated a resource for manipulating and mapping LH neurons in both light and electron microscopy and generated insights into the anatomy and function of the LH.

neuroscience↗

bioRxiv2018

Neural circuit basis of aversive odour processing in Drosophila from sensory input to descending output.

Evolution has shaped nervous systems to produce stereotyped behavioural responses to ethologically relevant stimuli. For example when laying eggs, female Drosophila avoid geosmin, an odorant produced by toxic moulds. Here we identify second, third, and fourth order neurons required for this innate olfactory aversion. Connectomics data place these neurons in a complete synaptic circuit from sensory input to descending output. We find multiple levels of valence-specific convergence, including a novel form of axo-axonic input onto second order neurons conveying another danger signal, the pheromone of parasitoid wasps. However, we also observe extensive divergence: second order geosmin neurons connect with a diverse array of 80 third order cell types. We find a pattern of convergence of aversive odour channels at this level. Crossing one more synaptic layer, we identified descending neurons critical for egg-laying aversion. Our data suggest a transition from a labelled line organisation in the periphery to a highly distributed central brain representation that is then coupled to distinct descending pathways.

neuroscience↗

bioRxiv2018

Functional and Anatomical Specificity in a Higher Olfactory Centre

Most sensory systems are organized into parallel neuronal pathways that process distinct aspects of incoming stimuli. For example, in insects, second order olfactory projection neurons target both the mushroom body, which is required for learning, and the lateral horn (LH), which has been proposed to mediate innate olfactory behavior. Mushroom body neurons encode odors in a sparse population code, which does not appear stereotyped across animals. In contrast the functional principles of odor coding in the LH remain poorly understood. We have carried out a comprehensive anatomical analysis of the Drosophila LH, counting ~1400 neurons; combining genetic driver lines, anatomical and functional criteria, we identify 165 LHN cell types. We then show that genetically labeled LHNs have stereotyped odor responses across animals for 33 of these cell types. LHN tuning can be ultra-sparse (1/40 odors tested), but on average single LHNs respond to three times more odors than single projection neurons. This difference can be rationalized by our observation that LHNs are better odor categorizers, likely due to pooling of input projection neurons responding to different odors of the same category. Our results reveal some of the principles by which a higher sensory processing area can extract innate behavioral significance from sensory stimuli.

neuroscience↗

bioRxiv2017

Memory retrieval recruits both innate and learned olfactoryprocessing centres in Drosophila

Animals can show either learned or innate behavioral responses to a given stimulus. How these circuits interact to produce an appropriate behavioral response is unknown. In the Drosophila olfactory system, the lateral horn (LH) and the mushroom body (MB) are thought to mediate innate and learned olfactory behavior respectively, although the function of the LH has not been directly tested. Here we identify two LH cell-types (PD2a1/b1) that receive input from an MB output neuron required for recall of aversive olfactory memories. In contrast to the model above we find that PD2a1/b1 are required for aversive memory retrieval. PD2a1/b1 activity is modulated by training, indicating that memory information is passed to the innate olfactory processing centre. We map the connectivity of PD2a1/b1 to other olfactory neurons with connectomic data. This provides a circuit mechanism by which learned and unlearned olfactory information can interact to produce appropriate behavior.

neuroscience↗