FAPs Bat avoidance is modulated by a constant stream of sensory input

Escape response and Central pattern generators: Neural circuits that produce self-sustaining patterns of behavior. Spanish shawl Sea slug

Tritonia brain > 1000 neurons

Upon contact with an aversive stimulus, such as the tube feet of the seastar, Tritonia respond with an escape swim consisting of a series of alternating ventral and dorsal whole-body flexions. The Tritonia escape swim and its underlying circuit

The known swim circuit. Solid lines direct connections, broken lines represent indirect connections Synaptic symbols: lines = excitatory, black circles = inhibitory, lines and circles = multiple component The known number of neurons of each type on each side of the brain are: S-cells, 80; Tr1, 1; DRI, 1; DSI, 3; C2, 1; VSI, 2; FNs, 55 The Tritonia escape swim and its underlying circuit

The swim motor program elicited via DRI stimulation. DRI and three CPG interneurons (C2 and two DSIs) were impaled with intracellular electrodes. When DRI was stimulated to fire at 10 Hz for 50 sec, resulting in a 6 cycle swim motor program. The Tritonia escape swim and its underlying circuit

DRI firing is necessary to elicited swim motor program. When DRI activity was blocked it blocks its firing response to the stimulus. This prevented the swim motor program from running. DRI is the “command neuron”

DRI, C2 and 2 DSIs were impaled with intracellular electrodes. The two DSIs were stimulated to fire at 20 Hz for 20 sec (hatched bar) while DRI was hyperpolarized to prevent its spiking. This procedure failed to prevent the swim motor program, consistent with the view that DRI is not part of the cycle generating mechanism, but instead functions as a pre-CPG command neuron. DRI is not a CPG element

The S-cells and Tr1 fire briefly at the onset of the swim motor program. A brief stimulus (10 Hz, 1 sec) applied via suction electrode to Pedal Nerve 3 (arrow) elicited a brief firing train in the S-cell and Tr1 cell, followed by a three cycle swim motor program in CPG neurons DSI and C2. Tr1 necessary to elicit swim response: Trigger command neuron

A. Tr1 neuron injected with Carboxyfluorescein in the live preparation. B. S-cell excitatory synaptic connection to Tr1 in normal saline. C. Tr1 makes an indirect excitatory connection to DSI. A Tr1 train caused the tonically active DSI (DSI-1) to increase its firing rate. Holding a second DSI (DSI-2) hyperpolarized during the train revealed that the DSI excitation resulted from a flurry of EPSPs that did not follow the Tr1 action potentials one-for-one. D. A Tr1 train elicited by intracellular current injection (10 sec, mean = 15.2 Hz) elicited a swim motor program that outlasted the train by 2 full cycles. Identifying characteristics of Tr1.

A. Tr1 connects to DRI produces EPSPs. B. A Tr1 spike train produced several seconds of firing in DRI. C. Hyperpolarizing DRI during a Tr1 train revealed a dual component fast/slow EPSP in DRI. Tr1 “triggers” the initiation of the command neuron

Simple escape response requires ~8 neuron type network