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Results for “Optical mapping”

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At least 55 records · Page 3Linked to original sources
PubMed1977

[Responses of neurons in the nucleus isthmi region of the frog to optic nerve stimulation].

Neuronal responses were studied in the nucleus isthmi area of Rana temporaria. The animals were immobilized by diplacine, a curare-like drug. Single neurons in this area had no background activity. After single-pulse electric stimulation of the contralateral optic nerve these neurons discharged as a rule with one action potential only, its minimal latency being 20-110 msc. The latencies decrease significantly when the stimulus intensities were increased from threshold to maximal, indicating development of summation process in the corresponding afferent pathway. Only 14 per cent (7 of 57) of neurons responded to stimuli exciting myelinated optic fibres and not exciting the ummyelinated ones. All the nucleus isthmi neurons discharged with unstable latency; this means that these neurons were excitated not antidromically. The functional role of nucleus isthmi in Anurans is discussed.

Animals↗
PubMedDate not supplied

[Visual projections in to the brain of the sturgeon Acipenser güldenstädti].

Visual projections have been studied after unilateral lesion of the optic nerve. Degenerated fibers and terminals, as well as fibers labelled by horseradish peroxidase were found contralaterally in the lateral geniculate thalamic nucleus, the second (stratum opticum) and the third (stratum fibrosum et griseum superficiale) layers of the midbrain tectum. In other brain structures (lateral ventrothalamic nucleus, in the pretectal area--cortical nucleus, pretectal nucleus, posterior comissure nucleus) the density of degeneration of optic fibers was significantly lower. Separate fragments of degeneration were found in the fourth layer of the tectum. Ipsilaterally, thalamic, pretectal and tectal visual projections of the same localization were found, although they were less massive than at the opposite side.

Animals↗
PubMed2025

New insights into genetic comorbidity mechanisms: type 2 diabetes and primary open-angle glaucoma.

AIMS: To investigate the shared genetic mechanisms between type 2 diabetes (T2D) and primary open-angle glaucoma (POAG). Using large-scale genome-wide association study (GWAS) data, we performed single nucleotide polymorphism (SNP) level analysis to detect pleiotropic variants and loci, paired eQTL mapping analysis and gene-level analysis to identify candidate pleiotropic genes. In addition, Mendelian randomisation (MR) analysis was performed to assess causal associations. MATERIALS AND METHODS: We used POAG GWAS data from Finngen (9565 cases and 430 250 controls) and T2D GWAS data from 55 555 European ancestry samples. We used Linkage Disequilibrium SCore (LDSC) regression to assess the genetic association between T2D and POAG and further used PLeiotropic Analysis under the COmposite null hypothesis (PLACO) to identify shared genetic variants between paired traits. Finally, we further used MR analysis to explore the causal association between T2D and POAG at the genetic level. RESULTS: The LDSC results and MR analysis revealed that the T2D effect was significantly higher than that of the POAG (OR=1.09, 95% CI 1.03 to 1.14, p=1.50×10-3). The PLACO property analysis determined that the T2D sum POAG shared 178 individual SNPs, separate localisation of 79 individual causes. The five most popular choices are based on the effectiveness of CCND2, SVEP1, ST6GAL1, TCF7L2 and HMGA2. expression quantitative trait loci mapping further revealed 36 genes with regulatory roles in optic nerve-related brain tissues. Functional enrichment analyses indicated that these pleiotropic genes are involved in neurodevelopmental, neuroprotective and metabolic pathways, with tissue-specific enrichment observed in neural, pancreatic, adipose and retinal tissues. It is possible to present the main comorbid mechanisms of T2D and POAG. CONCLUSIONS: Our study provides new insights into the aetiology and pathogenesis of T2D and POAG at the genetic level.

Humans↗
PubMed1978

Anatomical mapping of retino-tectal connections in developing and metamorphosed Xenopus: evidence for changing connections.

Neural connections between the eye and optic tectum in Xenopus laevis were anatomically traced by observing the tectal location of Wallerian degeneration after discrete retinal lesion. These retinotectal connections were mapped in postmetamorphic frogs and tadpoles at stage 51, the stage at which retinal axons have grown into about the rostral one-half of the tectum. The course of the experimental degeneration was the same in frogs and tadpoles, but degeneration proceeded faster in the younger animals. In the frogs, connections were ordered, with nasal retina mapping to the caudal part of the tectum and temporal retina mapping to the rostral tectum. In the tadpoles, within the innervated area at the rostral tectum, the retino-tectal connections were generally organized as in the adults, with the temporal retina mapping to the rostral part of the innervated tectum and nasal retina mapping primarily to the caudal part. But a portion of the nasal fibers consistently mapped to the far rostral tectum as well. Electron microscopic observations showed degenerating synaptic terminals at both rostral and caudal portions of the innervated tectum after lesion of just the nasal retina. Degeneration was not seen in control animals. These results indicate that some fibers (particularly from nasal retina) may shift their terminals caudally on the tectum to match tectal growth and produce the adult pattern of connections. If there is such connection readjustment, the 'aberrant' connections from nasal retina in tadpoles may be an indication of this process.

Animals↗
PubMed1978

"Thermal stability" maps for several double-stranded DNA fragments of known sequence.

The origin of cooperatively melting regions in DNA, which appear as fine structures in the optical melting profile, has been examined for DNA fragments of known base sequences from bacteriophages phiX174 and fd. Thermal stability maps, which indicate the states of base pairs along these DNA strands, were constructed within the established theoretical framework using the parameters which best reproduce the melting profiles obtained by high temperature resolution experiments. By comparing these stability maps with genetic maps, it was found that several cooperatively melting regions which span several hundred bases have some correlation with the gene locations.

Base Sequence↗
PubMed1975

Histological evidence for direct connections between the optic lobes of the cockroach Leucophaea maderae.

Heretofore, descriptions of direct interconnections between insect optic lobes have been based on histological examinations of normal brains or on inference from electrophysiological or behavioral data. We present here what we believe to be the first demonstration of such monosynaptic connections by techniques of experimental neuroanatomy. Twenty-four to 39 h after extirpation of the left optic lobe, degenerating axons and axon terminals, as silvered by a modified Nauta technique, were abundant in the central portion of the medulla of the right optic lobe. The periphery of the medulla was free of argyrophilic debris as were the lobula and lamina. The distribution of neuronal somata with processes terminating in the the left optic lobe was established by retrograde axonal transport of horseradish peroxidase injected into the left lobe and by the development of distinctive perinuclear rings of RNA (a 'chromatolytic' reaction) by some cells within 1-2 weeks following amputation of the left lobe. Both techniques revealed distinct clusters of cells in the anteroventral and posterior regions of the right optic lobe, and in the medial portion of the right protocerebrum. The cells which interconnect the two optic lobes may be involved not only in the bilateral representation of visual information, but also in the coordination of optic lobe pacemakers which control a circadian rhythm of locomotory activity.

Animals↗
PubMedDate not supplied

[Visual projections into the telencephalon and diencephalon of the teleost fish Serranus scriba (electrophysiologic study)].

In acute experiments on Serranus scriba, two discrete foci of visual activity in the telencephalon were shown--in the dorsal pallium and in the central telencephalic area. The latency of focal potentials evoked by optic tectum stimulation was at least 2 msec shorter than that of the responses elicited by optic nerve stimulation. In the region of nucleus rotundus and some other thalamo-pretectal structures, focal potentials and single unit reactions to both types of stimulation were registered. Responses to optic tectum stimulation in nucleus pretectalis exhibited the shortest latency. It is suggested that visual impulses to the central telencephalic area are relayed consequently in the optic tectum and probably in more than one thalamo-pretectal nucleus.

Animals↗
PubMed1978

The tectum opticum of Pantodactylus schreiberii Wiegmann (Teiidae, Lacertilia, Reptilia).

We study the histology of the optic lobe of Pantodactylus schreiberii Wiegmann. It has 14 layers with characteristic cells in each of them. We study with emphasis the elements of the superficial layers, discussing some physiologic implications. We described four strata of optic terminals. To the strata 1 and 3 reach fibres from layer 14. To the stratum 4, from the layer 12 and to the stratum 2, fibres from both layers 14 and 12. Some optic fibres from layer 12 send collaterals which reach the stratum 4 of optic terminals.

Animals↗
PubMed1976

Central mechanisms of vision: parallel processing.

Despite repeated attempts by several laboratories to discover increasingly complex "feature detector" neurons in higher visual centers of mammals, there has been little convincing evidence for the existence of such neurons. What had been reported instead is that many neurons in higher centers show less rather than more specificity when compared with cells in areas 17, 18 and 19. Studies in mammalian retina have revealed multiple processing systems apparently operating in parallel at the level of the ganglion cells. Striate cortex receives at least two different kinds of visual input from the lateral geniculate, and sends at least two different parallel outputs to other brain regions. Within striate cortex there is some segregation of different functional cell types in separate layers. The accumulated evidence suggests the existence of parallel visual processing mechanisms beginning in mammalian retina and extending through striate cortex to higher cortical centers. The notion of separate processing systems for the detection of different features in the visual world recalls earlier work by Lettvin, Maturana, McCulloch and Pitts concerning visual processing in the frog retina and optic tectum.

Animals↗
PubMed1979

Conduction velocity distribution of the retinal input to the hamster's superior colliculus and a correlation with receptive field characteristics.

Cells driven reliably by shocks delivered to the optic nerve or optic chiasm were encountered throughout the depth of the colliculus. The incidence of such cells, however, decreased markedly in the laminae ventral to the stratum opticum. The distribution of conduction velocities for the retinal afferents to the tectum was quite broad (range: 1.7-25.5 m/sec) and clearly biomodal with peaks at about 6 and 12 m/sec. A small number of cells were innervated by rapidly (greater than 15 m/sec) conducting axons. No evidence of an indirect-fast pathway from the retina to the colliculus via the lateral geniculate nucleus and visual cortex was obtained. Afferent conduction velocity was not correlated with retinal eccentricity, collicular depth or speed selectivity. It was, however, clearly related to directional selectivity. Ninety percent of the tectal neurons receiving inputs from axons having conduction velocities of less than 5 m/sec were directionally selective while only 41% of those neurons innervated by more rapidly conducting fibers (greater than 5 m/sec) exhibited selectivity. One hundred and sixteen cells in the anterior portion of the colliculus were tested with shocks delivered to the ipsilateral optic nerve and photic stimulation of the ipsilateral eye. Of these, 11% exhibited some degree of binocularity and only 6% were responsive to optic nerve shocks. These electrophysiological findings were correalted with the limited nature of the retinal input to the ipsilateral superior colliculus.

Animals↗