SHOUKFEH, Omar M.; AHMED, Nafisa; CARR, James A.; Texas Tech Univ., Lubbock; Texas Tech Univ., Lubbock; Texas Tech Univ., Lubbock: Neurochemical Coding of a Behavioral Circuit Breaker

The Texas toad Bufo speciosus responds to a moving but otherwise artificial prey-item (worm) by orienting toward the worm in precisely the same manner that it would approach a natural prey. Reorienting the worm 90 degrees perpendicular (antiworm) results in the toad becoming motionless and in some cases eliciting a crouching defensive behavior. Interestingly, presenting both stimuli (worm, antiworm) simultaneously completely inhibits prey-oriented movement. This suggests that triggering predator-detecting neuronal circuits may trip a neuronal “circuit breaker” that overrides prey-catching, allowing the toad to rapidly redirect behavior when faced with a potential threat. At present, the neurochemical coding of the predator-detecting pathways are unknown, but may involve pretectal-tectal inhibitory pathways that produce neuropeptide Y (NPY) or the inhibitory neurotransmitter GABA. Here we investigate NPY and GABAergic innervation of the tectum in B. speciosus. There was extensive innervation of all tectal layers by NPY-immunoreactive (ir) fibers, and NPY-ir cells were identified in regions of the thalamus known to respond to predatory stimuli. GABAergic projections were identified using antisera raised against GABA and glutamate decarboxylases 65 and 67 (GAD 65/67). Both GABA- and GAD-ir terminals and fibers were observed in the tectum, although GABAergic innervation appeared to be more restricted than found for NPY, with GABAergic punctuate processes found principally in deeper layers of the tectum. Our findings suggest that NPY and GABAergic projections may play a role in inhibiting prey-oriented turning in the presence of a threat. Supported by a Howard Hughes Medical Institute grant through the Undergraduate Biological Sciences Education Program to Texas Tech University