Análise morfo-quantitativa e neuroquímica do núcleo geniculado lateral dorsal e colículo superior do sagui (Callithix jacchus) no envelhecimento

Abstract

The Dorsal Lateral Geniculate Nucleus (DLG) and the Superior Colliculus (SC) are subcortical structures that comprise image-forming system. Functionally, DLG is considered a first-order thalamic nucleus in the processing of visual information, with relay properties and modulating the retinal inputs to the visual cortex. The CS participates in transferring incoming retinal inputs to other subcortical visual structures and sensorimotor transformations to drive movements of orientation and attention of the eyes and head. These two subcortical nuclei constitute the two primary visual pathways in mammals, contributing to the interpretation and subsequent formulation of adequate visual responses by the visual cortex. However, this visual processing is changed by aging, leading progressive functional deficits. Despite these, few studies discuss possible morphological and neuropeptidergic changes that might be directly related to the decline in visual function during aging. In this context, the present study aims to describe quantitatively morphological and neurochemical parameters in the DLG and CS in response to the aging process. Female and male marmosets (Callithrix jacchus) were divided into two age groups: adults (36-50 months old; n = 3 per histological procedure) and aged (119-140 months old; n= 3 3 per histological procedure) and perfused with formalin (10%). Then, the brains were sectioned (30µm) and submitted to Nissl method and immunohistochemistry for neuronal nuclear protein (NeuN) and protein glial fibrillary acidic protein (GFAP). Through the morphometric cell counting, optical density (OD) and design-based stereological probes, such as Cavalieri estimator, the neuronal number and immunoexpression of astrocytic GFAP, as well as the total and layers volume of DLG and SC were assessed, respectively. Based on these techniques, our results evidence a total and layers volumetric increase of the GLD, in addition to an overall stability in the volume and neuronal number of the superficial layers of SC with aging. A age-related decrease of GFAP immunoexpression was found in the DLG and SCv. Our findings suggest a region-dependent variation in volumetric aspect during aging, perhaps due structural plastic events in response to inflammation and compensatory mechanisms in the cellular and subcellular componentes of this visual structures. Moreover, the SCv appears to be less vulnerable to aging effects regarding of volume and neuronal number. Neuropeptidergic data suggest that declined GFAP expression may reflects a astrocytic atrophy. Hence, we provide an update the current state of knowledge of aging effects in the visual system and an important foundation for future works in terms of visual perception over course of aging, particularly in its morphological-quantitative and neurochemical parameters.