Aspectos neuroquímicos do estriado e arquitetura axonal das conexões tálamo estriatais do Sagui (Callithrix jacchus)

Abstract

The basal ganglia are subcortical structures involved in motor control and learning and in executive functions, integrating cortical, thalamic and brainstem information. The striatum is the main gateway to this information, being organized into 2 compartments: matrix and striosome, structures with different neurochemical patterns and input-output projections. It is known that the caudal intralaminar nuclei (centromedian and parafascicular) promoves strong input to the striatum in primates. However, studies of projections from other nuclei are poorly documented. Therefore, we aim to describe and characterize quantitatively and qualitatively the thalamus-striatal projections in the commom marmoset (Callithrix jacchus). We used iontophoretic microinjections of BDA, an anterograde tracer, in the mediodorsal (MD), rostral intralaminar (IL) and medial pulvinar (MP) nuclei to study the axonal arborizations types of the thalamo-striatal neurons. We performed different histological staining procedures to delineate and identify structures (to delineate the nuclei, to identify the striatal compartments and to localize the deposits and the axons/varicosities). The two striatal compartments were clearly distinguished, exhibiting a mosaic appearance. The matrix is strongly reactive for calbindin, parvalbumin and acetylcholinesterase histochemistry, while the striosome has low reactivity for all three markers. Type 1 arborization contains axons with varying length and thickness and varicosities of different sizes in passant, while type 2 has variable thickness, with many ramifications and display many short radiating dendrites studded with protrusions and grapelike appendages. The MP presented scarce and sparse projections in a large rostrocauldal extension of the striatum, with an important input to the tail of the caudate nucleus and type 1 arborization. The MD projects more focally and denser than the MP, and shows both types of afforestation. The projection from the IL was dense, with both types of arborization, mainly in the dorsolateral putamen, in a restrict rostrocaudal extension. All nuclei exhibited projections that preferentially reach the matrix. The varicosities of IL are significantly larger than those of MD and MP, and there are no differences in the sizes of the varicosities present in the matrix and the striosome.