Meeting Abstract

62.5  Thursday, Jan. 6  Characterization of Brain Neurons Involved in Spontaneously Initiated Walking in Crayfish KAGAYA, Katsushi*; TAKAHATA, Masakazu; Hokkaido University, Sapporo 060-0810, Japan; Hokkaido University, Sapporo 060-0810, Japan kagaya@sci.hokudai.ac.jp

Animals initiate behavior not only reflexively in response to external stimuli but also spontaneously depending on their internal state. How are the brain neurons recruited for the spontaneous walking and what morphological characters do they have? To clarify the neural mechanisms underlying spontaneously initiated walking in crayfish, Procambarus clarkii, we analyzed spike and synaptic activities of brain neurons as well as their morphological features using intracellular recording and staining techniques. In the previous study, using multi-unit recordings from the circumesophageal commissure, we found descending spike activities whose spike rate increased preceding to behavioral onset, during walking and at the termination of walking. Here we report the descending neurons that correspond to those functional units. The dendrites of those neurons were found to project mainly to the medial protocerebral neuropil. Experimental alteration of membrane potential by current injection revealed that the descending neurons were chemically driven. In one type of neuron, current injection to increase spike discharge rates caused walking behavior. We also found local spiking and nonspiking neurons involved in the walking. These results suggest that spontaneously initiated walking is controlled by parallel descending neurons and a variety of local neurons which might control descending neurons although it remains open whether the local neurons are presynaptic to the descending interneurons. However, it is clear that descending neurons increase their spike discharge rate by excitatory synaptic input rather than by endogenous excitability changes. The synaptic activation is most likely to take place in the medial protocerebrum.