Modification of the tail flip escape response in crayfish by neuromodulation and behavioral state with and without descending CNS input

The neural circuitry used during the tail flip behavior of crayfish continues to serve as a model for investigating sensory integration and the actions of neuromodulators. Systemic injections of 5-HT produce an increase in responsiveness to sensory stimuli and decrease the rate of sensory habituation of the tail flip. In behaving animals the loss of the chelipeds also promotes a greater responsiveness to tail flipping on sensory stimulation of the telson. By transecting the Ventral Nerve Cord (VNC) it was demonstrated that the animals were less responsive to the tail flip reflex, implying that the sensory-VNC-motor circuit for the tail flip can be modulated in the animals by higher command neurons. However, the CNS isolated neuronal circuitry of the tail was still responsive to 5-HT. The results imply that there is direct CNS regulation as well possible hormonal action in intact behaving animals and that factors which alter one or the other could impinge on the tail flip escape behavior.