Transcript CH5L2

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.
Sea slug
Spanish shawl
Tritonia brain > 1000 neurons
The Tritonia escape swim and its underlying circuit
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.
DRI is the “command neuron”
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 not a CPG element
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.
Tr1 necessary to elicit swim response: Trigger command neuron
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.
Identifying characteristics of Tr1.
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.
Tr1 “triggers” the initiation of the command neuron
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.
Simple escape response requires ~8 neuron type network