P266 Two distinct bursting mechanisms in cold-sensitive neurons of Drosophila Larva
Akira Sakurai, Natalia V. Maksymchuk, Sergiy M. Korogod, Daniel N. Cox,Gennady S. Cymbalyuk*
Neuroscience Institute, Georgia State University, Atlanta, GA 30302-5030, USA
*Email: gcymbalyuk@gmail.com
Introduction
In Drosophila larvae, noxious low temperatures are detected by CIII primary sensory neurons lining the inside of the body wall [1,2]. About half of these neurons respond to rapid temperature drops with transient bursts, producing a clear spike-rate peak that likely signals the rapid change. Previously, we developed a biophysical model, which captured various extracellularly recorded cold-evoked CIII responses [2]. Here, having overcome the challenge posed by the small size of CIII neurons and obtained intracellular recordings, we used the waveforms of bursting to identify two distinct types of bursting generated by these neurons.
Methods
We used electrophysiological intracellular and extracellular recordings and modeling to investigate the mechanisms underlying pattern generation by CIII neurons. We upgraded the model [2], by including dynamics of concentrations of Cl-, Na+, and K+, since Ca2+-activated Cl-current (ICaCl) was implicated in CIII dynamics [3]. We investigated the patterns caused by injected current, a drop in extracellular Cl-, and drop of temperature. We also considered a simplified model with an effective (e) leak current including Cl-currents lumped together with Na+and K+leak currents. We map oscillatory and silent regimes under variation of EeLeakand geLeakand compare the model activity to the experimental data.
Results
At ambient temperatures, CIII neurons exhibited a stationary state around -40 mV and sporadic spikes at 1.0 ± 1.3 Hz (N = 20). In the activity of 90% of sporadically spiking neurons, elliptic bursts with an intra-burst spike frequency of 6.0 ± 1.7 Hz were detected. With a temperature drop from 24°C to 10°C, CIII neurons depolarized and spiked at 2.9 ± 1.5 Hz. In 45% of neurons, square-wave bursts with the intra-burst spike frequency 38.2 ± 19.5 Hz were observed. Similar square-wave bursting and high-frequency spiking were induced by direct depolarizing injected currents. Low-Cl⁻conditions induced transitions between patterns of activity dominated by spiking, fast bursting, or slow bursting.
The model represents waveform properties of the experimentally recorded bursting under variation of the injected current, extracellular Cl-, and temperature. We found large parameter domains of silent and spiking regimes at low and high EeLeak, respectively, and a domain of square-wave bursting in an intermediate range of geLeakas EeLeak. In a certain range of geLeakas EeLeakgrows the model transitions from silence to elliptic bursting and then to spiking. These transitions qualitatively map transitions observed in experimental data.
Conclusion
We identified two distinct types of bursting patterns—elliptic bursting and square-wave bursting in responses of CIII neurons. These findings enhance our understanding of the temperature sensing in insect peripheral sensory neurons, providing insights into how sensory systems respond to environmental stimuli.
Acknowledgements
NIH grant R01NS115209 to DNC and GSC.
References
·1. Turner, H. N., et al. (2016).Current Biology, 26(23): 3116-3128.https://doi.org/10.1016/j.cub.2016.09.038
·2. Maksymchuk, N., et al. (2022).Frontiers in Cellular Neuroscience,16, 831803.https://doi.org/10.3389/fncel.2022.831803
·3. Himmel, N. J., et al., (2023).eLife, 12, e76863.https://doi.org/10.7554/eLife.76863
