Precise Temperature Compensation of Phase in a Rhythmic Motor Pattern

Computational modeling and experimentation in a model system for network dynamics reveal how network phase relationships are temperature-compensated in terms of their underlying synaptic and intrinsic membrane currents

Neuropilar projections of the anterior gastric receptor neuron in the stomatogastric ganglion of the Jonah crab, Cancer borealis.

Sensory neurons provide important feedback to pattern-generating motor systems. In the crustacean stomatogastric nervous system (STNS), feedback from the anterior gastric receptor (AGR), a muscle receptor neuron, shapes the activity of motor circuits in the stomatogastric ganglion (STG) via polysynaptic pathways involving anterior ganglia. The AGR soma is located in the dorsal ventricular nerve posterior to the STG and it has been thought that its axon passes through the STG without making contacts. Using high-resolution confocal microscopy with dye-filled neurons, we show here that AGR from the crab Cancer borealis also has local projections within the STG and that these projections form candidate contact sites with STG motor neurons or with descending input fibers from other ganglia. We develop and exploit a new masking method that allows us to potentially separate presynaptic and postsynaptic staining of synaptic markers. The AGR processes in the STG show diversity in shape, number of branches and branching structure. The number of AGR projections in the STG ranges from one to three simple to multiply branched processes. The projections come in close contact with gastric motor neurons and descending neurons and may also be electrically coupled to other neurons of the STNS. Thus, in addition to well described long-loop pathways, it is possible that AGR is involved in integration and pattern regulation directly in the STG

Segment specificity of load signal processing depends on walking direction in the stick insect leg muscle control system

Akay T, Ludwar BC, Goeritz ML, Schmitz J, Bueschges A. Segment specificity of load signal processing depends on walking direction in the stick insect leg muscle control system. JOURNAL OF NEUROSCIENCE. 2007;27(12):3285-3294

Clustered sites of putative chemical synapses are found in the AGR projections, but typically not in the AGR axon.

<p><b>A1</b>. Double labeling with an antibody against synapsin reveals patches of immuno-labeling on the LY dye-filled AGR projections. The image was processed to only show synapsin labeling in the AGR (see methods). Scale bar is 30µm. <b>A2</b>. Putative pre- and postsynaptic sites in the AGR projections in the same preparation. Different masking methods allow distinguishing between potentially presynaptic and postsynaptic sites in the AGR neuron (see methods). Synapsin labeling that mostly overlapped with the volume of the reconstructed AGR surface was classified as putative pre-synaptic (blue), and is found predominantly in the distal parts of the AGR process. Synapsin labeling that mostly overlapped with a thin shell around the AGR neuron was interpreted to be located in the processes of adjacent cells, marking putative post-synaptic sites in the AGR neuron (yellow). Scale bar is 30µm. <b>A3</b>. Overlay of the putative pre-and postsynaptic sites with the AGR projection (magenta). The close-up in the inserts reveals the distinct clustering in putative pre- and postsynaptic sites of the AGR projection and axon. Putative pre-synaptic sites in the AGR neuron are blue and putative post-synaptic sites are yellow. A1-A3 are blend mode projections of the same data set of 8 merged confocal image stacks, each consisting of 84 optical slices (acquired at resolution of 0.067µm x 0.067µm x 0.378µm).</p

The AGR axon typically runs along the ventral surface of the STG and projects dorsally into the neuropil.

<p><b>A1</b>. Volume-rendered dorsal view of LY dye-filled AGR (green), projected along the dorso-ventral axis. <b>A2</b>. Lateral, maximum intensity projection of the same ganglion. <b>B1</b>. Double labeling with anti-synapsin antibody (purple) reveals the synaptic neuropil in the STG. <b>B2</b>. Lateral projection of the anti-synapsin labeled ganglion shows the ventrally located AGR axon and its dorsal projections into the synaptic neuropil. Blend mode (A1, B1 and B2) and maximum intensity (A2) projections of 10 merged confocal image stacks, each consisting of 264 optical slices (acquired at resolution of 0.179µm x 0.179µm x 0.38µm). Scale bar is 50µm. </p

Schematic overview of the STNS, showing the location of the AGR neuron (yellow) in the <i>dvn</i>, its projections through the <i>dgn</i>, and its anterior projections through the <i>stn</i> into the commissural ganglia (CoG).

<p>Schematic overview of the STNS, showing the location of the AGR neuron (yellow) in the <i>dvn</i>, its projections through the <i>dgn</i>, and its anterior projections through the <i>stn</i> into the commissural ganglia (CoG).</p

Quantification of pyloric network output at different temperatures.

<p>(A) Example extracellular nerve recordings of the pyloric rhythm at cold temperature (T = 7°C). The onset and offset delay of each neuron relative to the onset of PD neuron burst are indicated. Horizontal scale bar, 1 s, for both (A) and (B). (B) Example extracellular nerve recordings from the same preparation as in (A) but at warm temperature (T = 19°C). The same delay measurements are indicated as in (A). (C) The frequency of the pyloric rhythm plotted as a function of temperature from T = 7°C to T = 23°C (<i>n</i> = 7). (D) The mean phase (delay divided by cycle period) values of the pyloric rhythm plotted as a function of temperature from T = 7°C to T = 23°C (<i>n</i> = 7).</p