The long-term objectives of this research are to describe the neural mechanisms in crayfish for the initiation of backward walking in response to abdominal illumination, and to describe the role of neural inhibiton in suppressing competing behavioral responses. This research can serve as a model for the study of normal and pathological mechanisms of behavioral initiation and coordination in humans. Intracellular microelectrode recording techniques will be used to identify and describe neurons in the crayfish brain that are excited by a pair sensory neurons, the caudal photoreceptors (CPRs) that project to the brain from the abdomen. These brain neurons provide the link between the CPR terminals in the brain and pattern initiating neurons (PIs) in the abdomen that excite the abdominal motor pattern associated with backward walking. Responses of the brain neurons to CPR input should account for the probabalistic nature of the backward walking response and the long and variable latency between CPR stimulation and the PI and motor responses. Since many non-phasic behaviors of animals are activated probabalistically with a long and variable latency following stimulation, this investigation may identify underlying neural mechanisms common to all these behaviors. The initiation of behavior requires the suppression of competing behaviors along with the selection of a preferred behavior. Behavioral evidence in crayfish and gastropod molluscs indicates that reciprocal inhibition between command systems for competing behaviors is a mechanism for this suppression. This research will investigate the inhibition of the neural circuitry for backward walking generated by the tailflip command neuron, and compare it to the inhibition of the tailflip command neuron produced by the PI neurons for backward walking. These reciprocal neural inhibitions are likely to be asymmetric in a way that reflects the asymmetry between the two behaviors: tailflip completely interrupts backward walking while backward walking merely raises the threshold for tailflip. The asymmetry of inhibition can then be seen to help establish behavioral priorities for the crayfish, such that escape tailflip is a high threshold, high priority withdrawal response, whereas backward walking is a lower threshold, easily overridden withdrawal response.
| Edwards, D H (1991) Mutual inhibition among neural command systems as a possible mechanism for behavioral choice in crayfish. J Neurosci 11:1210-23 |
| Beall, S P; Langley, D J; Edwards, D H (1990) Inhibition of escape tailflip in crayfish during backward walking and the defense posture. J Exp Biol 152:577-82 |
| Edwards Jr, D H; Mulloney, B (1987) Synaptic integration in excitatory and inhibitory crayfish motoneurons. J Neurophysiol 57:1425-45 |
