Neuro-ethological study of superior colliculus in sensory and motor integration during predatory behavior in rats.

Abstract

A recent study, examining the expression of Fos protein, suggest the key neural systems mobilized during predation of rats hunting roaches. 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, 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 predation in the context of collicular circuitry and also its influence in other circuits involved in the predation, especially striatal regions of basal ganglia. We will carry out behavioral experiments using T-maze where animals will choose between an environment with alive roaches and another with dead ones, associated to Fos dettection. In order to evaluate how sensory information can influence choosing environment a group of animals will have their whiskers removed. In addition animals with intact whiskers will have access to an environment which provides restrict contact to alive roches, in a way that the rat will not be allowed to hunt and consume them, however they will have free access to auditory, olfactory, visual and whiskers information once they will be separated from roaches by perforated walls. These experiments will be associated with Fos protein dettection. In order to understand the anatomo-functional role of SC we will inject PHA-L in the SCl of animals that will be exposed to T-Maze or to the environment with restrict contact and find out whether anterograde fibers merge cells expressing Fos in the motor thalamic nuclei that are target by basal ganglia and cerebellum towards motor cortex. We believe this project will provide a better comprehention of the importance of sensory and motor integration at the level of SC and other circuits involved in motor response in predation.