Parallel feedback pathways in visual cortex of cats revealed through a modified rabies virus

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For studies of visual cortex organization, mouse is becoming an increasingly more often used model. In addition to its genetic tractability, the relatively small area of cortical surface devoted to visual processing simplifies efforts in relating the structure of visual cortex to visual function. However, the nature of this compact organization can make some comparisons to the much larger non-human primate visual cortex difficult. The squirrel, as a highly visual rodent offers a useful means for better understanding how mouse and monkey cortical organization compares. More in line with primates than their nocturnal rodent cousin, squirrels rely much more on sight and have evolved a larger expanse of cortex devoted to visual processing. To reveal the detailed organization of visual cortex in squirrels, we injected a highly sensitive monosynaptic retrograde tracer (glycoprotein deleted rabies virus) into several locations of primary visual cortex (V1) in California ground squirrels. The resulting pattern of connectivity revealed an organizational scheme in the squirrel that retains some of the basic features of the mouse visual cortex along the medial and posterior borders of V1, but unlike mouse has an elaborate and extensive pattern laterally that is more similar to the early visual cortex organization found in monkeys. In this way, we show that the squirrel can serve as a useful model for comparison to both mouse and primate visual systems, and may help facilitate comparisons between these two very different yet widely used animal models of visual processing.

Section: Viral Tracer Injectionsmentioning

confidence: 99%

V1 connections reveal a series of elongated higher visual areas in the California ground squirrel, Otospermophilus beecheyi

Negwer

Liu

Schubert³

et al. 2017

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“…In conclusion, our results suggest that inputs to V4 are less direct than they are to neighboring extrastriate area MT. V4 and MT are considered important early areas in the ventral and dorsal streams of visual processing, respectively (Livingstone and Hubel, 1988;Merigan and Maunsell, 1993;Sincich and Horton, 2005;Nassi and Callaway, 2009;Connolly et al, 2012), streams that involve many higher order areas important for object perception and visuospatial actions (Milner and Goodale, 2008;Ungerleider and Mishkin, 1982). Therefore, the more hierarchical pathway to V4 and the more direct route to MT likely contribute to functional differences not just between the two areas but to their respective streams as well.…”

Section: Lack Of Disynaptic Inputs To V4mentioning

confidence: 99%

Lack of robust LGN label following transneuronal rabies virus injections into macaque area V4

Lyon

Rabideau

2012

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In primates, retinal inputs are relayed through the magno- and parvocells of the lateral geniculate nucleus (LGN) indirectly to extrastriate visual cortex. The most direct pathway identified to the extrastriate cortex is a disynaptic one that provides robust magno- and parvocellular inputs to the middle temporal area (MT). The inclusion of parvocells in this projection is somewhat surprising because of their importance for color and form vision, whereas MT is more strictly tuned to velocity. This raises the question of whether areas more involved in color and form processing, such as V4, receive similar projections. We report here on experiments that use rabies virus injections into V4 to retrogradely label mono- and disynaptic inputs. We find only a small number of labeled neurons in the LGN in a pattern consistent with monosynaptic labeling of koniocells, rather than disynaptic labeling of magno- and parvocells. The lack of robust magno- and parvocellular label was not due to ineffective viral transport because in the same cases we find hundreds of neurons labeled in the thalamic reticular nucleus, a structure that can only be labeled disynaptically from the cortex. We also find a complete absence of neurons labeled in V1, but thousands in adjacent areas V2 and V3. This result helps explain the absence of labeled magno- and parvocells in the LGN because disynaptic transport from an extrastriate visual area should require a relay through V1. Taken together, these results suggest that ascending magno/parvocellular inputs to V4 are more hierarchically organized than the relatively direct inputs to MT.

“…Prior to using the cell type specific helper viruses to target EnvA‐ΔG‐RV, we first made injections of ΔG‐RV. The ΔG‐RV version of rabies virus acts as a monosynaptic retrograde tracer and does not require a helper virus (Wickersham et al, ; Connolly, Hashemi‐Nezhad, & Lyon, ). While this virus cannot distinguish between inputs to inhibitory and excitatory neurons, the goal of these injections was to determine the ability and degree to which rabies virus infects basal forebrain neurons targeting V1 by comparing to the number of infected neurons in the LGN.…”

Section: Resultsmentioning

confidence: 99%

Cell type specific tracing of the subcortical input to primary visual cortex from the basal forebrain

Lean

Liu

Lyon

2018

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The basal forebrain provides cholinergic inputs to primary visual cortex (V1) that play a key modulatory role on visual function. While basal forebrain afferents terminate in the infragranular layers of V1, acetylcholine is delivered to more superficial layers through volume transmission. Nevertheless, direct synaptic contact in deep layers 5 and 6 may provide a more immediate effect on V1 modulation. Using helper viruses with cell type specific promoters to target retrograde infection of pseudotyped and genetically modified rabies virus evidence was found for direct synaptic input onto V1 inhibitory neurons. These inputs were similar in number to geniculocortical inputs and, therefore, considered robust. In contrast, while clear evidence for dorsal lateral geniculate nucleus input to V1 excitatory neurons was found, there was no evidence of direct synaptic input from the basal forebrain. These results suggest a direct and more immediate influence of the basal forebrain on local V1 inhibition.