Subcortical connections of area V4 in the macaque

Abstract

Astroglial cells are involved in directional movements of neurons such as migration of the neuronal cell body and growth of neurites. In the mammalian midbrain, medial (M) and lateral (L) radial glia and derived astrocytes differ in their ability to support neuritic growth. In previous work, we have demonstrated that the growthpermissive ability of L astrocytes and non-permissive properties of M astrocytes correlate with the respective composition of the cell surface-associated and secreted glycosaminoglycans (GAGs). Recent work also shows that the GAG-degrading enzyme heparitinase I increases the neurite growth-promoting ability of M midbrain astrocytes (Garcia-Abreu J et al. 2000 Glia 29: 260). In agreement with previous AFM studies of living glial cell lines and cells in primary culture, imaging of living L and M cells at similar load forces showed structures identified as F-actin fibers. Moreover, no systematic differences were observed between L and M pictures. By contrast, the surfaces of formaldehyde-fixed lateral (L) and medial (M) astrocytes differ by the presence of conspicuous 250 nm protrusions in the former, and of a fibrillar network in the extracellular matrix of the latter. Furthermore, we show that treatment with heparitinase I leads to disappearance of the fibrils from M cells and, consequently, to the assumption of an L-like appearance. Our results suggest that the formation of fibrils may follow from an ability to form large aggregates by association of HS carbohydrate units as has been unexpectedly detected by AFM for oligomers of polysialic acid or polysialic acid-containing carbohydrate units of N-CAM, with formation of filament bundles (Toikka J et al. 1998. J Biol Chem 273: 28557). Taken together with the functional effects of heparitinase I treatment, our present results demonstrate an important role of the extracellular matrix on the functional properties of astrocytes. They also emphasize the power and potentialities of AFM in the study of the extracellular matrix on the surface of fixed cells. - ( June 27, 2000 ) . * Supported by PRONEX/ MCT, CNPq, FAPERJ, CEPG/UFRJ. E-mail: gweissmuller@hotmail.com Aggregation of amyloid β peptide (Aβ) into fibrils and deposition as senile plaques are primarily related to neurotoxicity in Alzheimer's Disease (AD). Thus, agents interfering with aggregation may be potentially useful in preventing or decreasing Aβ toxicity. We first studied the effects of guanidine hydrochloride and temperature on the stability of fibrillar Aβ using peptides truncated at different positions. These experiments suggested that hydrophobic interactions mediated by the C-terminal portion of Aβ are important for fibril stability. Based on these results, we found two compounds capable of disaggregating amyloid fibrils at micromolar concentrations, as indicated by light scattering measurements and transmission electron microscopy. When applied to primary cultures of E18 rat hippocampal neurons, both drugs significantly reduced Aβ-induced cell death (as assayed by trypan blue ...

Microstimulation of the superior colliculus focuses attention without moving the eyes

“…The most parsimonious explanation for our data is that microstimulation improved performance by focusing attention on a specific region of visual space, consistent with the hypothesis that SC activity contributes to the control of covert visuo-spatial attention in the absence of eye movements. Thus, our data provide important causal evidence of a role for the SC in the control of attention to complement the correlative evidence provided by electrophysiological recording studies (7,8,16).…”

“…Following the original observation by Goldberg and Wurtz (6) of attention-related neural activity in the superior colliculus (SC) (7,8), single-unit recordings have detected attentional effects in other eye movementrelated areas of the brain, including the inferior parietal cortex (9)(10)(11) and the frontal eye fields (FEF) (12)(13)(14). Recent studies by Bisley and Goldberg (15) in the lateral intraparietal area and by Ignashchenkova et al (16) in the SC were particularly incisive because the neural effects correlated parametrically with variations in the strength and timing of attentional effects in the behavioral data.…”

Cross-Modality Dysfunction between the Visual and Olfactory Systems in Parkinson’s Disease

“…A recent study has shown that a pleasant odor is associated with bilateral or left AMG activation, and an unpleasant odor is associated with activation of the right AMG [27]. The left/right difference for smell-evoked emotion may be linked to AMG processing, because these regions are strongly connected at a fiber level [44].…”

Very Early Responses to Colour Stimuli Detected in Prestriate Visual Cortex by Magnetoencephalography (MEG)

“…It has long been known that the lateral geniculate nucleus (LGN), a thalamic station in the classical visual pathway from retina to cortex, projects not only to the primary visual cortex (striate cortex or area V1) but also to the visual areas of the prestriate cortex (Benevento & Yoshida, 1981;Fries, 1981;Yukie & Iwai, 1981;Gattass et al, 2014) and that visual signals are detected in the LGN in the 20-30 ms time window after stimulus onset (Maunsell & Gibson, 1992;Nowak et al, 1995;Givre et al, 1995).…”