Neurons in the primary visual cortex (V1) receive feedforward input from the thalamus, which shapes receptive-field properties. They additionally receive recurrent inputs via horizontal connections within V1 and feedback from higher visual areas that are thought to be important for conscious visual perception. Here, we investigated what roles different glutamate receptors play in conveying feedforward and recurrent inputs in macaque V1. As a measure of recurrent processing, we used figure-ground modulation (FGM), the increased activity of neurons representing figures compared with background, which depends on feedback from higher areas. We found that feedforward-driven activity was strongly reduced by the AMPA receptor antagonist 6-cyano-7-nitroquinoxaline-2,3-dione (CNQX), whereas this drug had no effect on FGM. In contrast, blockers of the NMDA receptor reduced FGM, whereas their effect on visually driven activity varied with the subunit specificity of the drug. The NMDA receptor blocker 2-amino-5-phosphonovalerate (APV) caused a slight reduction of the visual response, whereas ifenprodil, which targets NMDA receptors containing the NMDA receptor NR2B subunit, increased the visual response. These findings demonstrate that glutamate receptors contribute differently to feedforward and recurrent processing in V1 and suggest ways to selectively disrupt recurrent processing so that its role in visual perception can be elucidated.T he areas of the primate visual cortex are arranged in a hierarchy, with feedforward connections propagating information from lower to higher areas and feedback connections carrying information in the opposite direction, back to the lower areas (1). Feedforward and recurrent processing differ greatly in function. Feedforward connections drive neurons in the visual cortex. They shape the receptive field of neurons, causing the rapid formation of tuning properties such as orientation and direction selectivity (2) and even sensitivity to complex objects such as faces. In contrast, recurrent input, carried by feedback connections from higher areas and by horizontal connections within a visual area, is thought not to drive neurons but to mediate modulatory, contextual effects (3, 4). Recurrent connections have been suggested to be involved in attention (5-7), figure-ground segregation (8-11), and conscious visual perception (12, 13), although their precise function is not well understood. One problem in studying the role of recurrent connections has been the lack of a tool to selectively inhibit them without disrupting feedforward processing. Some studies blocked the source of recurrent processing by suppressing activity in higher-level visual areas using cooling or injections of GABA while recording in lower-level areas (9,14,15). The results of these studies vary because some showed strong effects on V1 activity (15) and a decrease in contextual modulation (9), whereas others showed no effect (14). The exact effect of recurrent input into V1, therefore, remains to be elucidated.Why might feed...
The mouse is a useful and popular model for studying of visual cortical function. To facilitate the translation of results from mice to primates, it is important to establish the extent of cortical organization equivalence between species and to identify possible differences. We focused on the different types of interneurons as defined by calcium binding protein (CBP) expression in the layers of primary visual cortex (V1) in mouse and rhesus macaque. CBPs parvalbumin (PV), calbindin (CB), and calretinin (CR) provide a standard, largely non-overlapping, labelling scheme in macaque, with preserved corresponding morphologies in mouse, despite a slightly higher overlap. Other protein markers, that are relevant in mouse, are not preserved in macaque. We fluorescently tagged CBPs in V1 of both species, using antibodies raised against preserved aminoacid sequences. Our data demonstrate important similarities between the expression patterns of interneuron classes in the different layers between rodents and primates. However, in macaque, expression of parvalbumin and calbindin is more abundant, calretinin expression is lower, and the laminar distribution of interneuron populations is more differentiated. Our results reveal an integrated view of interneuron types that provides a basis for translating results from rodents to primates, and suggest a reconciliation of previous results.
Fragments of mature tRNAs have long been considered as mere degradation products without physiological function. However, recent reports show that tRNA-derived small RNAs (tsRNAs) play prominent roles in diverse cellular processes across a wide spectrum of species. Contrasting the situation in other small RNA pathways the mechanisms behind these effects appear more diverse, more complex and are generally less well understood. In addition, surprisingly little is known about the expression profiles of tsRNAs across different tissues and species. Here, we provide an initial overview of tsRNA expression in different species and tissues, revealing very high levels of 5' tRNA halves (5' tRHs) particularly in the primate hippocampus. We further modulated the regulation capacity of selected 5' tRHs in human cells by transfecting synthetic tsRNA mimics ("overexpression") or antisense-RNAs ("inhibition") and identified differentially expressed transcripts based on RNAseq. We then used a novel k-mer mapping approach to dissect the underlying targeting rules, suggesting
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