Retinal projections in the caecilian Ichthyophis kohtaoensis (Amphibia, Gymnophiona)

Retinal projections in a sturgeon were studied by injecting biocytin or HRP into the optic nerve. The target areas are the preoptic area, thalamus, area pretectalis, nucleus of posterior commissure, optic tectum, and nuclei of the accessory optic tract. Furthermore, a few labeled fibers and terminals were found in a ventrolateral area of the caudal telencephalon. All retinal projections are bilateral, although contralateral projections were more heavily labeled. Retrogradely labeled neurons were found in the ventral thalamus bilaterally. Retinal projections in sturgeons are similar to those of other non-teleost actinopterygians and chondrichthyans (sharks), in terms of the targets and extent of bilateral projections. Distribution patterns of ganglion cells in the retina were examined in Nissl-stained retinal whole mount preparations. The highest density areas were found in the temporal and nasal retinas, and a dense band of ganglion cells was observed along the horizontal axis between the nasal and temporal areas of highest density. The density of ganglion cells in the dorsal retina is the lowest. The total number of ganglion cells was estimated to be about 5 × 10⁴ in a retina. The existence of a low density area in the dorsal retina suggests reduced visual acuity in the ventral visual field.

Section: Discussionsupporting

confidence: 64%

Section: Discussionmentioning

confidence: 85%

Retinal Projections and Retinal Ganglion Cell Distribution Patterns in a Sturgeon (Acipenser transmontanus), a Non-Teleost Actinopterygian Fish

Ito

Yoshimoto²,

Albert³

et al. 1999

“…The first one refers to the rich nitrergic innervation of the retinocipient neuropils in the ventral thalamus. Tracing studies are very scarce in gymnophionans, but the identification of the thalamic neuropil in the region with dense nitrergic innervation has been experimentally confirmed [Himstedt and Manteuffel, 1985]. The second was observed in the pretectal region where nitrergic cell groups were present in all species studied.…”

Section: Diencephalonmentioning

confidence: 94%

“…However, if the situation in Dermophis is similar to that of Ichthyophis [Himstedt and Manteuffel, 1985] the retinal axons in the tectum would be restricted to the medial and superficial zone and, therefore, an overlap with the nitrergic fibers might occur. This evidence is in line with the previously mentioned nitrergic innervation of retinocipient regions in the diencephalon of Dermophis.…”

Section: Mesencephalonmentioning

confidence: 99%

Distribution of NADPH-Diaphorase/Nitric Oxide Synthase in the Brain of the Caecilian Dermophis mexicanus (Amphibia: Gymnophiona): Comparative Aspects in Amphibians

González¹,

Moreno²,

López³

2002

The organization of nitrergic systems in the brains of anuran and urodele amphibians was recently studied and significant differences were noted between both amphibian orders. However, comparable data are not available for the third order of amphibians, the gymnophionans (caecilians). In the present study we have investigated the distribution of neuronal elements that express nitric oxide synthase (NOS) in the brain of the gymnophionan amphibian Dermophis mexicanus by means of immunohistochemistry with specific antibodies against NOS and enzyme histochemistry for NADPH-diaphorase. Both techniques yielded identical results and were equally suitable to demonstrate the nitrergic system. In addition, they were useful tools in the identification of cell groups and brain structures, otherwise indistinct in the brains of caecilians. The distribution of nitrergic structures observed in Dermophis conforms to the overall amphibian pattern but numerous distinct peculiarities were also noted. These included a dense innervation of the olfactory bulbs but a lack of reactivity in olfactory and vomeronasal fibers and glomeruli. A large population of nitrergic cells in the striatum and the presence of thalamic neurons, as well as the specific distribution of nitrergic cells in the isthmic region, are some of the differential features in the gymnophionan brain. Given the variability among species in the same class of vertebrates any discussion including amphibians should also include evidence for gymnophionans.

“…During prey capture, the forelimbs are extended and used to capture prey and move it to the mouth. In a third amphibian group, the limbless caecilian Ichthyophis kohtaoensis displays contralateral retinal projections as well as IRP [Himstedt and Manteuffel, 1985].…”

Section: Vp: In the Agamid Uromastix Acanthinurusmentioning

confidence: 99%

Binocular Vision and Ipsilateral Retinal Projections in Relation to Eye and Forelimb Coordination

Larsson

2011

It is commonly proposed that the number of fibers that do not cross in the optic chiasm (OC) is proportional to the size of the binocular visual field, and that the major advantage of binocular vision is acute depth perception. I present an alternative, an ‘eye-forelimb’ (EF) hypothesis, suggesting that alterations in the OC influence the length of neural pathways that transmit visual information to motor nuclei and somatosensory areas involved in forelimb coordination. Evolutionary processes resulting in increased ipsilateral retinal projections (IRP) are of adaptive value in animals that regularly use the forelimbs in a frontal position, while evolutionary change towards reduced IRP is of value for animals that mainly use the forelimbs in lateral positions. Primates and cats, to a large extent, use visually guided forelimb maneuvers, and both groups have high proportions of IRP. The fact that vertebrates’ IRP arise exclusively from the temporal retina supports the hypothesis, since IRP from the nasal retina would increase the length of neural pathways involved in forelimb coordination. The EF hypothesis offers new perspectives on why a high proportion of IRP among early limbless vertebrates became reduced during the evolution of laterally situated limbs, and why reptiles that lost their limbs (snakes) evolved more IRP. Anatomical, neurophysiological, phylogenetic, ontogenetic and ecological data suggest that mutations changing the proportions of ipsilateral visual connections in the OC may have selective value for EF coordination.