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Integration of the olfactory code across dendritic claws of single mushroom body neurons

Nature Neuroscience volume 16, pages 1821–1829 (2013) Cite this article

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Abstract

In the olfactory system, sensory inputs are arranged in different glomerular channels, which respond in combinatorial ensembles to the various chemical features of an odor. We investigated where and how this combinatorial code is read out deeper in the brain. We exploited the unique morphology of neurons in the Drosophila mushroom body, which receive input on large dendritic claws. Imaging odor responses of these dendritic claws revealed that input channels with distinct odor tuning converge on individual mushroom body neurons. We determined how these inputs interact to drive the cell to spike threshold using intracellular recordings to examine mushroom body responses to optogenetically controlled input. Our results provide an elegant explanation for the characteristic selectivity of mushroom body neurons: these cells receive different types of input and require those inputs to be coactive to spike. These results establish the mushroom body as an important site of integration in the fly olfactory system.

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Figure 1: Imaging dendritic claws of Kenyon cells reveals distinct odor responses.
Figure 2: Kenyon cell dendrites collect inputs with diverse odor response profiles.
Figure 3: Detecting functional and anatomical connectivity between projection neurons and Kenyon cells using ChR2-based stimulation.
Figure 4: Additivity of synaptic input in Kenyon cells.
Figure 5: Kenyon cells require activation of multiple dendritic claws to spike.

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Acknowledgements

We thank D. Tracey (Duke University), T. Clandinin (Stanford University) and the Bloomington Drosophila Stock Center for fly strains, G. Jefferis for advice on MARCM experiments, T. Hige for support with whole-cell recordings, and T. Clandinin, V. Jayaraman, G. Jefferis, S. Ranade, Y. Zhong and members of the Turner laboratory for comments on the manuscript. E.G. is supported by the Elisabeth Sloan Livingston fellowship from the Watson School of Biological Sciences. This work was funded by US National Institutes of Health grant R01 DC010403-01A1.

Author information

Author notes

  1. Eyal Gruntman

    Present address: Present address: Janelia Farm Research Campus, Howard Hughes Medical Institute, Ashburn, Virginia, USA.,

Authors and Affiliations

  1. Cold Spring Harbor Laboratory, Cold Spring Harbor, New York, USA

    Eyal Gruntman & Glenn C Turner

  2. Watson School of Biological Sciences, Cold Spring Harbor Laboratory, Cold Spring Harbor, New York, USA

    Eyal Gruntman & Glenn C Turner

Authors
  1. Eyal Gruntman
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  2. Glenn C Turner
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Contributions

E.G. and G.C.T. designed the experiments. E.G. performed the experiments and analyzed the data. E.G. and G.C.T. wrote the manuscript.

Corresponding author

Correspondence to Glenn C Turner.

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The authors declare no competing financial interests.

Integrated supplementary information

Supplementary Figure 1 KC responses rely on spike-dependent synaptic transmission through nicotinic acetylcholine receptors.

(a) KC membrane potential in response to PN photostimulation before and after application of 1μM tetrodotoxin (TTX) (black: single trials, magenta: mean response). (b) Single trial and mean responses before and after the application of 100 μM Mecamylamine (Mec). Colors as in the left panels. Blockers were administered by addition to the bath saline.

Supplementary Figure 2 Complex KC claws that contact more than one PN bouton.

(a) Complex claw wrapping around a small bouton and the base of a bigger bouton. (b) Complex claw wrapping around the base of a big bouton, while having room (arrowhead) for a potential connection with an unlabeled bouton from a different PN type. This type of connection suggests that some integration of PN channels could take place within a complex claw. Scale bar 2 μm.

Supplementary Figure 3 Total number of claws per KC.

Claws counted for synaptically connected KCs (n=39) whose responses are summarized in Fig. 5a.

Supplementary Figure 4 Depolarization rate increases with the number of connected claws.

Top: Rate of change of membrane potential in response to different photostimulus durations for each cell (n=39 KCs). Cells grouped according to number of connected claws. Bottom: Mean change in membrane potential for KCs with the same number of connected claws. Colors as in top panel. Slope was calculated by fitting a 2nd or 3rd degree polynomial to the rising phase of the depolarization, finding the midpoint in the response and analytically calculating the derivative.

Supplementary Figure 5 KCs show no evidence of voltage-dependent boosting of synaptic input.

(a) Average membrane potential responses of a KC to a series of prolonged current injections (750 ms; black bar), with a bout of photostimulation in its midst (250 ms; red bar). (b) Summary of light-evoked response amplitudes at different holding potentials (n=4 KCs). Response magnitude tended to decrease at more depolarized holding potentials, as expected of a passive (i.e. non-voltage-dependent) membrane potential response. (c) Example timecourses of KC membrane potential in response to increasing current injections (shown in inset). (d) I-V relationship of n=5 KCs. Trials in which current injection evoked a spike were excluded from this analysis.

Supplementary Figure 6 Different KCs exhibit a range of synaptic strengths.

Left: Distribution of EPSP sizes for KCs (n=16) connected via only one claw. Measurements are from the first EPSP in response to 25 ms photostimulation. Asterisk above cell 14 represents an outlier beyond the axis limit (6.7 mV). Mean number of EPSPs measured per cell: 17 ± 8. Right: Histogram of EPSP amplitudes from all 16 KCs (n=270 EPSPs).

Supplementary information

Supplementary Text and Figures (download PDF )

Supplementary Figures 1–6 and Supplementary Movies 1,2 (PDF 4438 kb)

Supplementary Movie 1 (download AVI )

Movie of calcium responses in two adjacent claws belonging to the same KC (different cell from that presented in Figure 1). Response on the left is for methyl benzoate; response on the right is for apple cider vinegar. Red square at the bottom right corner denotes odor presentation. (AVI 80890 kb)

Supplementary Movie 2 (download MOV )

Movie of a confocal z-stack showing a dye-filled KC (magenta) with five claws that contact ChR2-YFP-expressing PNs (green). Five different claw-bouton contacts are circled at the appropriate frames in the movie. (MOV 8800 kb)

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Gruntman, E., Turner, G. Integration of the olfactory code across dendritic claws of single mushroom body neurons. Nat Neurosci 16, 1821–1829 (2013). https://doi.org/10.1038/nn.3547

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