Samuel, A. D. T. | Search bioRxiv

bioRxiv2017

Invariances in a combinatorial olfactory receptor code

Animals can identify an odorant type across a wide range of concentrations, as well as detect changes in concentration for individual odorant type. How olfactory representations are structured to support these functions remains poorly understood. Here, we studied how a full complement of ORNs in the Drosophila larva encodes a broad input space of odorant types and concentrations. We find that dose-response relationships across odorants and ORN types follow the Hill function with shared cooperativity but different activation thresholds. These activation thresholds are drawn from a power law statistical distribution. A fixed activation function and power law distribution of activation thresholds underlie invariances in the encoding of odorant identity and intensity. Moreover, we find similar temporal response filters of ORNs across odorant types and concentrations. Such uniformity in the temporal filter may allow identity invariant coding in fluctuating or turbulent odor environments. Common patterns in ligand-receptor binding and sensory transduction across olfactory receptors may give rise to these observed invariances in the olfactory combinatorial code. Invariant patterns in the activity responses of individual ORNs and the ORN ensemble may simplify decoding by downstream circuits.

neuroscience↗

bioRxiv2017

Integration of plasticity mechanisms within a single sensory neuron of C. elegans actuates a memory

Neural plasticity--the ability of a neuron to change its cellular properties in response to past experiences--underpins the nervous systems capacity to form memories and actuate behaviors. How different plasticity mechanisms act together in vivo and at a cellular level to transform sensory information into behavior is not well understood. Here we show that in the nematode C. elegans two plasticity mechanisms--sensory adaptation and presynaptic plasticity--act within a single cell to encode thermosensory information and actuate a temperature-preference memory. Sensory adaptation enables the primary thermosensory neuron, AFD, to adjust the temperature range of its sensitivity to the local environment, thereby optimizing its ability to detect temperature fluctuations associated with migration. Presynaptic plasticity transforms this thermosensory information into a behavioral preference by gating synaptic communication between sensory neuron AFD and its postsynaptic partner, AIY. The gating of synaptic communication is regulated at AFD presynaptic sites by the conserved kinase nPKC{varepsilon}. Bypassing or altering AFD presynaptic plasticity predictably changes the learned behavioral preferences without affecting sensory responses. Our findings indicate that two distinct and modular neuroplasticity mechanisms function together within a single sensory neuron to encode multiple components of information required to enact thermotactic behavior. The integration of these plasticity mechanisms result in a single-cell logic system that can both represent sensory stimuli and guide memory-based behavioral preference.

neuroscience↗