Ca2+ imaging of cricket protocerebrum responses to air current stimulation

Abstract

Crickets (Gryllus bimaculatus) use the cercal sensory system at the rear of the abdomen to detect air currents and direct predator avoidance behavior. Sensory information regarding the direction and dynamic properties of air currents is processed within the terminal abdominal ganglion, and conveyed by ascending giant interneurons (GIs) to higher centers including the brain. However, the brain region responsible for decoding cercal sensory information has not yet been identified, nor the response properties within the brain characterized. In this study, we performed in vivo Ca 2+ imaging to investigate wind-evoked neural activities within the cricket protocerebrum. Ca 2+ responses to air current stimuli were observed at peripheral regions of the ventrolateral neuropile (VLNP) where projection of GIs' axon terminals has been observed in larvae. The wind-evoked Ca 2+ response had temporal dynamics and directional sensitivity that varied with different recorded regions displaying transient or sustained Ca 2+ increases. Individual cells showed Ca 2+ elevation in response to air currents from a specific angle, while stimuli from a different angle evoked decreased signals. Removing the antennae reduced the air-current-evoked responses in VLNP, suggesting contribution of sensory inputs from antennae in addition to the cercal inputs. The VLNP is presumably an integrative center for mechanosensory processing from antennae and cerci where directional information is primarily decoded by protocerebral 3 neurons.

Electrophoresis of polar fluorescent tracers through the nerve sheath labels neuronal populations for anatomical and functional imaging

“…Next we aimed to adapt this labelling technique to allow optical imaging of neural activity through the delivery of calcium indicators. Current methods for the introduction of such indicators are mainly based on microelectrode electrophoresis13, bath application, or pressure-injection of cell membrane permeant indicators1415. All these methods have limited ability to label large populations of neurons reliably.…”