A recent study, examining the expression of Fos protein, suggest the key neural systems mobilized during predatory behavior of rats hunting cockroaches. Of particular interest, it was found that predatory hunting induce a distinct activation of the lateral region of the intermediate layer of the superior colliculus (SCl), which does not appear to be particularly mobilized in other behavioral situations, such as after nocturnal peak of food ingestion, defensive responses in a confront with the natural predator, forced swimming and so far. Several literature data support the idea that deep layers of superior colliculus are related to motor control and sensory guided behavior. In order to understand the potential roles of this collicular region in the context of predatory hunting, it was analyzed the hunting performance of the animals before and after iontophoretic NMDA (N-METHIL-D-ASPARTIC ACID) lesions bilaterally placed into SCl. Notably, collicular lesions did not interfere with the motivation to pursue the roaches, however, they did induce severe deficits related to motor praxia, i.e, lesioned animals handled the preys very awkwardly and were unable to capture and hold them efficiently. In addition, lesioned animals could not properly orient themselves toward fast moving roaches, which is a very immediate and accurate reflex in rats not surgically manipulated nor lesioned at SCl. Next the conncetions of SCl was examined. The efferent projections of the SCl which were analyzed by using the Phaseolus vulgaris leucoagglutinin method, suggest that SCl appear to influence the motor output via two main pathways: a descending putative involved in coordenating eyes, orofacial and forelimb orienting movements toward the moving preys; and ascending pathways, which is in a position to modulate motor responses by influencing thalamic regions also targeted by the basal ganglia and cerebellum. Experiments with the retrograde tracer Fluoro-Gold showed that the SCl, likewise structures related to motor control, receives information related to somatosensory sensibility from the whiskers and orofacial region. Interestingly SCl integrates sensory information from orofacial region and whiskers as well as information related to motor control. Experiments in our proposal will contribute to better understand the neural basis of predatory hunting in rats, especially SCl. We believe the preys movements and their contact with rats whiskers are fundamental stimulli to trigger predation and they might, as well, be involved to the increasement of Fos protein expression in SCl while rats hunt roaches. We aim to evaluate how effectively sensory information from whiskers can mediate predatory hunting in the context of collicular circuitry and also its influence in other circuits involved in the predatory behavior, especially striatal regions of basal ganglia. We will carry out behavioral experiments using normal rats and rats with their whiskers removed, in association to protein Fos dettection.
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