Does Nocturnality Drive Binocular Vision? Octodontine Rodents as a Case Study

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A defining feature of the amniote tecto‐fugal visual pathway is a massive bilateral projection to the thalamus originating from a distinct neuronal population, tectal ganglion cells (TGCs), of the optic tectum/superior colliculus (TeO/SC). In sauropsids, the thalamic target of the tecto‐fugal pathway is the nucleus rotundus thalami (Rt). TGCs axons collateralize en route to Rt to target the nucleus pretectalis principalis (PT), which in turn gives rise to bilateral projection to the TeO. In rodents, the thalamic target of these TGCs afferents is the caudal division of the pulvinar complex (PulC). No pretectal structures in receipt of TGC collaterals have been described in this group. However, Baldwin et al. (Journal of Comparative Neurology, 2011;519(6):1071–1094) reported in the squirrel a feedback projection from the PulC to the SC. Pulvino‐tectal (Pul‐T) cells lie at the caudal pole of the PulC, intermingled with the axonal terminals of TGCs. Here, by performing a combination of neuronal tracing, immunohistochemistry, immunofluorescence, and in situ hybridization, we characterized the pattern of projections, neurochemical profile, and genoarchitecture of Pul‐T cells in the diurnal Chilean rodent Octodon degus. We found that Pul‐T neurons exhibit pretectal, but not thalamic, genoarchitectonical markers, as well as hodological and neurochemical properties that match specifically those of the avian nucleus PT. Thus, we propose that Pul‐T cells constitute a pretectal cell population hidden within the dorsal thalamus of mammals. Our results solve the oddity entailed by the apparent existence of a noncanonic descending sensory thalamic projection and further stress the conservative character of the tectofugal pathway.

Section: Discussionmentioning

confidence: 99%

Section: Tecto-pulvinar Pathwaysmentioning

confidence: 99%

The nucleus pretectalis principalis: A pretectal structure hidden in the mammalian thalamus

Deichler

Carrasco

González-Cabrera

et al. 2018

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“…In Photoshop CS5 (Adobe Systems, San Jose, CA), isodensity contours were drawn to visualize the cell distribution of the GCL across the retina. Furthermore, the total cell number in the GCL was estimated by assuming mean cell densities for the isodensity areas and multiplying those values by the respective areas in mm 2 , according to the following model (Vega‐Zuniga et al, ):

{normalN}_{t o t a l} = {true \sum}_{i = 1}^{n} A_{i} {\bar{d}}_{i} true{\begin{array}{l} {\bar{d}}_{i} = true(\frac{d_{i n n e r} + d_{o u t e r}}{2} true), i \geq 2 \\ {\bar{d}}_{i} = d, i = 1 \end{array}

where A i are the isodensity areas,

{\bar{d}}_{i}

the respective mean densities, and d inner , d outer the cell densities for the isodensity contours confining each area, respectively.…”

Section: Methodsmentioning

confidence: 99%

Section: The Visual System Of a Palaeognathous Birdmentioning

confidence: 99%

The visual system of a Palaeognathous bird: Visual field, retinal topography and retino‐central connections in the Chilean Tinamou (Nothoprocta perdicaria)

Krabichler

Vega‐Zuniga

Morales

et al. 2014

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Most systematic studies of the avian visual system have focused on Neognathous species, leaving virtually unexplored the Palaeognathae, comprised of the flightless ratites and the South American tinamous. We investigated the visual field, the retinal topography, and the pattern of retinal and centrifugal projections in the Chilean tinamou, a small Palaeognath of the family Tinamidae. The tinamou has a panoramic visual field with a small frontal binocular overlap of 20°. The retina possesses three distinct topographic specializations: a horizontal visual streak, a dorsotemporal area, and an area centralis with a shallow fovea. The maximum ganglion cell density is 61,900/ mm(2) , comparable to Falconiformes. This would provide a maximal visual acuity of 14.0 cycles/degree, in spite of relatively small eyes. The central retinal projections generally conform to the characteristic arrangement observed in Neognathae, with well-differentiated contralateral targets and very few ipsilateral fibers. The centrifugal visual system is composed of a considerable number of multipolar centrifugal neurons, resembling the "ectopic" neurons described in Neognathae. They form a diffuse nuclear structure, which may correspond to the ancestral condition shared with other sauropsids. A notable feature is the presence of terminals in deep tectal layers 11-13. These fibers may represent either a novel retinotectal pathway or collateral branches from centrifugal neurons projecting to the retina. Both types of connections have been described in chicken embryos. Our results widen the basis for comparative studies of the vertebrate visual system, stressing the conserved character of the visual projections' pattern within the avian clade.

“…In birds and mammals, the ventrothalamic and pretectal nuclei receive a significant retinal input (Gamlin and Cohen, ; Major et al, ; Vega‐Zuniga et al, ; Krabichler et al, ). Also, these structures show a projection pattern that is very similar in both groups.…”

Section: Discussionmentioning

confidence: 99%

Microconnectomics of the pretectum and ventral thalamus in the chicken (Gallus gallus)

Vega‐Zuniga

Marı́n

González-Cabrera

et al. 2015

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The avian pretectal and ventrothalamic nuclei, encompassing the griseum tectale (GT), n. lentiformis mesencephali (LM), and n. geniculatus lateralis pars ventralis (GLv), are prominent retinorecipient structures related to optic flow operations and visuomotor control. Hence, a close coordination of these neural circuits is to be expected. Yet the connectivity among these nuclei is poorly known. Here, using intracellular labeling and in situ hybridization, we investigated the detailed morphology, connectivity, and neurochemical identity of neurons in these nuclei. Two different cell types exist in the GT: one that generates an axonal projection to the optic tectum (TeO), LM, GLv, and n. intercalatus thalami (ICT), and a second population that only projects to the LM and GLv. In situ hybridization revealed that most neurons in the GT express the vesicular glutamate transporter (VGluT2) mRNA, indicating a glutamatergic identity. In the LM, three morphological cell types were defined, two of which project axons towards dorsal targets. The LM neurons showed strong VGluT2 expression. Finally, the cells located in the GLv project to the TeO, LM, GT, n. principalis precommisuralis (PPC), and ICT. All neurons in the GLv showed strong expression of the vesicular inhibitory amino acid transporter (VIAAT) mRNA, suggesting a GABAergic identity. Our results show that the pretectal and ventrothalamic nuclei are highly interconnected, especially by glutamatergic and GABAergic neurons from the GT and GLv, respectively. This complex morphology and connectivity might be required to organize orienting visuomotor behaviors and coordinate the specific optic flow patterns that they induce. J. Comp. Neurol. 524:2208-2229, 2016. © 2015 Wiley Periodicals, Inc.