Anatomic and functional study of superior colliculus in the integration of whiskers sensory information during predatory behavior in rats.

• Grant number: 07/05807-9
• Support Opportunities: Scholarships in Brazil - Master
• Start date: March 01, 2008
• End date: August 31, 2009
• Field of knowledge: Biological Sciences - Physiology - Physiology of Organs and Systems
• Principal Investigator: Eliane Comoli
• Grantee: Thiago Santos Gouvêa
• Host Institution: Faculdade de Medicina de Ribeirão Preto (FMRP). Universidade de São Paulo (USP). Ribeirão Preto , SP, Brazil
• Associated research grant: 06/03655-4 - Anatomic and functional study of the closed-loop connection between basal ganglia and superior colliculus during predatory behavior in rats, AP.JP

Abstract

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 predation 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 SC are related to motor control and sensory guided behavior. In order to understand the potential roles of this collicular region in the context of predation, it was analyzed the hunting performance of the animals before and after iontophoretic NMDA 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 an immediate and accurate reflex in rats not surgically manipulated nor lesioned at SCl. 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, like 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 the SCl role. We believe the preys movements and their contact with rats whiskers are fundamental stimulli to trigger predatory behavior 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 behavior in the context of collicular circuitry and also its influence in other circuits involved in predatory behavior, especially striatal regions of basal ganglia, thalamus, and in the brainstem areas that are involved in coordenating eyes, orofacial movements, tongue retraction and protrusion, and forelimb orienting movements toward the moving preys. So animals with their whiskers removed will be exposed and allowed to hunt cockroaches. Also, we will have animals with re-grown whiskes (to normal size) hunting cockroaches. Brains will be detected for Fos protein. In order to understand the anatomic and functional role of SC we will inject PHA-L in the SCl of animals that will be exposed to cockroaches and find out whether anterograde fibers merge cells expressing Fos in the brainstem, especially in supraoculomotor area and parvicelular reticular nucleus of brainstem. We believe this project will provide a better comprehention of the importance of sensory integration at the level of SC and other circuits involved in motor response during predatory behavior.