To answer whether the mammalian retinotectal pathway is modifiable in the adult, an attempt was made to induce long-term potentiation (LTP) in retinal synapes in the superior colliculus (SC) of the adult rat, in vivo. Extracellular field potentials were recorded in the primary retinotectal afferent zone of the rat superior colliculus while electrically stimulating the optic chiasm. Induction of LTP in this primary visual pathway was attempted using a wide range of stimulus parameters. However, LTP was not observed. Iontophoretic application of bicuculline methiodide, before and during trains of stimuli, did not facilitate LTP in the rat SC. The broad spectrum glutamatergic antagonist, kynurenic acid, greatly reduced the size of the field potentials. This supports suggestions that retinotectal neurotransmission may be mediated by excitatory amino acids. An N-methyl-D-aspartate (NMDA) glutamate receptor mediated contribution to synaptic transmission in the evoked field potential was not evident. Iontophoretic application of the NMDA receptor selective antagonist 2-amino-5-phosphonovaleric acid (APV) had no effect on the field potentials. Even in the presence of bicuculline, there was no evidence for an NMDA component in the field potential response. The non-NMDA glutamate receptor antagonist, 6-cyano-7-nitroquinoxa-line-2,3-dione (CNQX), did not affect the evoked potentials. These data suggest that LTP was not observed in the retinotectal pathway due to several factors that may include: a loss of visual plasticity in the adult rat following the critical period, absence of necessary modulation factors and insufficient NMDA receptor mediated synaptic transmission. / Medicine, Faculty of / Graduate

It has been hypothesized that head-unrestrained gaze shifts are controlled by an error signal produced by a feedback loop. It has also been hypothesized that the superior colliculus (SC) is within this feedback loop. If the feedback-to-SC hypothesis is valid, an unexpected mid-flight perturbation in gaze trajectory should be quickly followed by a concurrent change in the discharges of collicular saccade-related neurons. To verify this prediction experimentally, primate head movements were unexpectedly and briefly halted during head-unrestrained gaze shifts in the dark. Perturbed gaze shifts were composed of first a gaze saccade made when the head was immobilized by the head-brake, followed by a period where gaze was immobile, called a gaze plateau. The latter was composed of an initial period when the eyes and head were immobile, followed by a period wherein the head was released and the eyes counter-rotated to stabilize gaze. The plateau ended with a corrective gaze saccade to the goal location. In perturbed gaze shifts, there was widely distributed activity on the SC map during gaze plateaus, and there was no evidence that the initial motor program was aborted; the corrective gaze saccades were not "fresh" small stand-alone movements. Cells on the SC map responded at short latencies to head accelerations and associated gaze shift perturbations and carried a gaze position error (GPE = final - instantaneous gaze position) signal. As a large gaze shift progressed there was a caudo-rostral moving hill of activity on the SC map that encoded, not instantaneous veridical GPE, but a filtered version of it (time constant 100ms). Recordings from both the motor map and the so-called "fixation zone" in the rostral SC during perturbed head-unrestrained gaze shifts reveal gaze feedback control and a gaze feedback signal to the SC. However, these results do not prove that the SC is within the online gaze feedback loop, only that such a loop exists and that the collicular map is informed about its calculations.

No description available.

O Colículo Superior (SC) é conhecido por apresentar diversas funções que modulam a caça predatória. Neste estudo, investigamos as funções do SC em ratos expostos a caça de insetos. Primeiramente, verificamos que o comportamento predatório induz uma distinta ativação da porção lateral do SC (SCl). Para entender as potenciais funções dessa região colicular, foi analisado o comportamento predatório antes e após lesões bilaterais iontoforéticas por NMDA do SCl. Animais com SCl lesados ficaram menos motivados a perseguirem as baratas, falharam para se orientarem na direção do movimento das presas e quando tentaram capturar as presas, eles apresentaram sérios déficits para capturá-las e segurá-las eficientemente. Por outro lado, animais com lesões da porção medial do SC (SCm) apresentaram apenas um aumento da latência para iniciar a caça, enquanto os outros parâmetros não diferiram significantemente dos animais intactos. Posteriormente, examinamos as conexões eferentes do SCl e do SCm usando como traçador anterógrado a leucoaglutinina do Phaseolus vulgaris. Notamos projeções densas do SCl para a região rostral da coluna lateral da matéria cinzenta periaquedutal (PAGl), um setor criticamente envolvido no controle dos aspectos motivacionais relacionados aos comportamentos de caça predatória e forrageamento. Além disso, o SCl se projeta densamente para o tálamo dorsal, especificamente para os núcleos ventral lateral, central medial e paracentral do tálamo, os quais sabemos que se projetam para setores estriatais ou para áreas motoras corticais, que provavelmente estão envolvidas no ajuste da ação motora durante a captura das presas. O SCm, por sua vez, aferenta densamente a coluna dorsolateral da PAG, núcleo cuneiforme, e núcleos reticulares mesencefálico e pontino, que são setores envolvidos na elaboração de respostas defensivas, além disso, o SCm se projeta esparsamente para os núcleos posterior lateral e suprageniculado do complexo geniculado medial / The superior colliculus is classically known to present a number of functions that fit hunting behavior. In the present study, we investigate the potential roles of the superior colliculus in rats displaying insect hunting. First, we have found that predatory hunting induces a distinct activation of the lateral region of the intermediate layer of the superior colliculus (SCl). To understand the potential roles of this collicular region, we analyzed the hunting performance before and after iontophoretic NMDA lesions bilaterally placed into the SCl. Animals with SCl lesions were clearly less motivated to pursue the roaches, failed to orient themselves toward the moving prey, and whenever the SCl-lesioned rats tried to catch the roaches, they presented serious deficits to capture and hold them efficiently. Next, we examined the SCl efferents connections using Phaseolus vulgaris leucoagglutinin as an anterograde tracer. Of particular relevance, we noted that the SCl projects to the rostral lateral periaqueductal gray, a site critically involved in controlling motivational drive to chase prey and forage. In addition, the SCl also present particularly strong projections to the dorsal thalamus, aimed at the ventral lateral, ventral medial, central medial and paracentral nuclei of thalamus, all of which known to project either to striatal sites or to cortical motor areas, likely to be involved in adjusting the motor action during prey capture. Therefore, the SCl, which seems to present cells responding to prey displacement in the temporal field, presents important arms to the periaqueductal gray and dorsal thalamic sites, influencing, respectively, the motivational drive and the motor skills to hunt

O Colículo Superior (SC) é conhecido por apresentar diversas funções que modulam a caça predatória. Neste estudo, investigamos as funções do SC em ratos expostos a caça de insetos. Primeiramente, verificamos que o comportamento predatório induz uma distinta ativação da porção lateral do SC (SCl). Para entender as potenciais funções dessa região colicular, foi analisado o comportamento predatório antes e após lesões bilaterais iontoforéticas por NMDA do SCl. Animais com SCl lesados ficaram menos motivados a perseguirem as baratas, falharam para se orientarem na direção do movimento das presas e quando tentaram capturar as presas, eles apresentaram sérios déficits para capturá-las e segurá-las eficientemente. Por outro lado, animais com lesões da porção medial do SC (SCm) apresentaram apenas um aumento da latência para iniciar a caça, enquanto os outros parâmetros não diferiram significantemente dos animais intactos. Posteriormente, examinamos as conexões eferentes do SCl e do SCm usando como traçador anterógrado a leucoaglutinina do Phaseolus vulgaris. Notamos projeções densas do SCl para a região rostral da coluna lateral da matéria cinzenta periaquedutal (PAGl), um setor criticamente envolvido no controle dos aspectos motivacionais relacionados aos comportamentos de caça predatória e forrageamento. Além disso, o SCl se projeta densamente para o tálamo dorsal, especificamente para os núcleos ventral lateral, central medial e paracentral do tálamo, os quais sabemos que se projetam para setores estriatais ou para áreas motoras corticais, que provavelmente estão envolvidas no ajuste da ação motora durante a captura das presas. O SCm, por sua vez, aferenta densamente a coluna dorsolateral da PAG, núcleo cuneiforme, e núcleos reticulares mesencefálico e pontino, que são setores envolvidos na elaboração de respostas defensivas, além disso, o SCm se projeta esparsamente para os núcleos posterior lateral e suprageniculado do complexo geniculado medial / The superior colliculus is classically known to present a number of functions that fit hunting behavior. In the present study, we investigate the potential roles of the superior colliculus in rats displaying insect hunting. First, we have found that predatory hunting induces a distinct activation of the lateral region of the intermediate layer of the superior colliculus (SCl). To understand the potential roles of this collicular region, we analyzed the hunting performance before and after iontophoretic NMDA lesions bilaterally placed into the SCl. Animals with SCl lesions were clearly less motivated to pursue the roaches, failed to orient themselves toward the moving prey, and whenever the SCl-lesioned rats tried to catch the roaches, they presented serious deficits to capture and hold them efficiently. Next, we examined the SCl efferents connections using Phaseolus vulgaris leucoagglutinin as an anterograde tracer. Of particular relevance, we noted that the SCl projects to the rostral lateral periaqueductal gray, a site critically involved in controlling motivational drive to chase prey and forage. In addition, the SCl also present particularly strong projections to the dorsal thalamus, aimed at the ventral lateral, ventral medial, central medial and paracentral nuclei of thalamus, all of which known to project either to striatal sites or to cortical motor areas, likely to be involved in adjusting the motor action during prey capture. Therefore, the SCl, which seems to present cells responding to prey displacement in the temporal field, presents important arms to the periaqueductal gray and dorsal thalamic sites, influencing, respectively, the motivational drive and the motor skills to hunt