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. 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 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. 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. Inate responses to environmental threats like a natural predator is characterized by behavioral responses like freezind and escape followed by analgesia and autonomic responses coordenated by specific sites of medial hypothalamus. SC is involved with defensive behavior in rats and recognition of threatening expression in humans; and medial sites (SCm) express fos protein during exposition to a natural predator. McHaffie et. al. proposed that phylogenetic old closed-loop connections exist between the basal ganglia and brain stem sensory related structures like superior colliculus, however the full extent to which they actually represent functionally segregated parallel closed-loop remains to be determined. So, in attempt to better understand the role of superior colliculus, we intend to verify functional aspects of connections between superior colliculus and basal ganglia during adverse affective situation like predatory and defensive behavior. Manipulations effects of different components of collicular loops over behavioral reactions might provide important information about functional organization of those loops. We suggest that thalamus is an element through which the superior colliculus exert this effect, once thalamus provide the main excitatory imputs to striatum, and is active during cockroaches predation. To this investigation animals prepared with chronic guide-cannulae providing access to the SC will be exposed to the natural predador and to cockroaches. Innactivation of medial or lateral sites of SC by injecting mucimol in this behavioral situation would have a corresponding greater effect over Fos expression in thalamus and basal ganglia over behavioral choice. In order to understand the anatomo-functional loops we will inject PHA-L in the SCl and find out whether anterograde fibers merge cells expressing Fos in thalamus during this situation. We believe the innactivation of SCl in the presence of preys and predador would result in great effects over behavioral choice, though we would be testing the hypothesis that phasic desinhibition mediated by a sub-cortical closed-loop of basal ganglia exert a significant role over behaviors evoked by stimulation of superior colliculus in the presence of preys and predator.
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