Morphology of basal optic tract terminals in the turtle,
            <i>Pseudemys scripta elegans</i>

Martin, John R.; Kogo, Naoki; Ariel, Michael

doi:10.1002/(sici)1096-9861(19980413)393:3<267::aid-cne1>3.0.co;2-#

Cited by 5 publications

(11 citation statements)

References 27 publications

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“…The turtle cerebellum can be isolated and maintained in a physiological state as an in vitro preparation allowing stabilized iontophoretic ejections and intraaxonal transport (Martin et al 1998). Thirteen pond turtles (Pseudemys scripta elegans) were used for this study.…”

Section: Methodsmentioning

confidence: 99%

Quantitative analysis of granule cell axons and climbing fiber afferents in the turtle cerebellar cortex

2004

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The turtle cerebellar cortex is a single flat sheet of gray matter that greatly facilitates quantitative analysis of biotylinated dextran amine labeled granule cell and olivocerebellar axons and Nissl-stained granule and Purkinje neurons. On average, ascending granule cell axons are relatively thicker than their parallel fiber branches (mean +/- SD: 0.84 +/- 0.17 vs 0.64 +/- 0.12 microm, respectively). Numerous en passant swellings, the site of presynaptic contact, were present on both ascending and parallel fiber granule cell axons. The swellings on ascending axons (1.82 +/- 0.34 microm, n = 52) were slightly larger than on parallel fibers (1.43 +/- 0.24 microm, n = 430). In addition, per unit length (100 microm) there were more swellings on ascending axons (11.2 +/- 4.2) than on parallel fibers (9.7 +/- 4.2). Each parallel fiber branch from an ascending axon is approximately 1.5 mm long. Olivocerebellar climbing fiber axons followed the highly tortuous dendrites of Purkinje cells in the inner most 15-20% of the molecular layer. Climbing fibers displayed relatively fewer en passant swellings. The spatial perimeter of climbing fiber arbors (area) increased 72% from anteriorly (1797 microm2) to posteriorly (3090 microm2) and 104% from medially (1690 microm2) to laterally (3450 microm2). Differences in the size and spacing of en passant swellings on granule cell axons suggest that ascending axons may have a functionally more significant impact on the excitability of a limited number of radially overlying Purkinje cells than the single contacts by parallel fiber with multiple orthogonally aligned Purkinje cell dendrites. The spatially restricted distribution of climbing fibers to the inner most molecular layer, the paucity of en passant swellings, and different terminal arbor areas are enigmatic. Nevertheless, these finding provide important anatomical information for future optical imaging and electrophysiological experiments.

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Section: Methodsmentioning

confidence: 99%

Quantitative analysis of granule cell axons and climbing fiber afferents in the turtle cerebellar cortex

2004

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“…Also, labeling neurons during whole-cell recordings has dem- Martin et al, 1998) is also shown in its position within a BON. Also, labeling neurons during whole-cell recordings has dem- Martin et al, 1998) is also shown in its position within a BON.…”

Section: Discussionmentioning

confidence: 99%

“…Our previous study revealed that BOT axon terminals spread throughout the rostrocaudal extent of the BON where varicosities and terminal boutons often formed clusters within regions of 150 mm 3 or less and that these sites presumably provide synaptic contact with BON cells (Martin et al, 1998). The turtle BOT is the singular path of direct retinal input.…”

Section: Retinal Inputsmentioning

confidence: 99%

“…The BON is a small isolated collection of large neurons on the ventral surface of the midbrain (Figs. We have shown that the prominent input to the BON comes from basal optic tract (BOT) axons that are direction sensitive and course through the long axis of the nucleus in a rostral to caudal direction (Martin et al, 1998). We have shown that the prominent input to the BON comes from basal optic tract (BOT) axons that are direction sensitive and course through the long axis of the nucleus in a rostral to caudal direction (Martin et al, 1998).…”

Section: Introductionmentioning

confidence: 98%

“…However, a study of the morphology and visual responses of the axon terminals of the BOT in the BON has shown that each retinal input was direction sensitive and ran through the BON across most of the rostrocaudal extent (Martin et al, 1998). However, a study of the morphology and visual responses of the axon terminals of the BOT in the BON has shown that each retinal input was direction sensitive and ran through the BON across most of the rostrocaudal extent (Martin et al, 1998).…”

Section: Introductionmentioning

confidence: 99%

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Morphology of the turtle accessory optic system

et al. 2003

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Neural signals of the moving visual world are detected by a subclass of retinal ganglion cells that project to the accessory optic system in the vertebrate brainstem. We studied the dendritic morphologies and direction tuning of these brainstem neurons in turtle (Pseudemys scripta elegans) to understand their role in visual processing. Full-field checkerboard patterns were drifted on the contralateral retina while whole-cell recordings were made in the basal optic nucleus in an intact brainstem preparation in vitro. Neurobiotin diffused into the neurons during the recording and was subsequently localized in brain sections. Neuronal morphologies were traced using appropriate computer software to analyze their position in the brainstem. Most labeled neurons were fusiform in shape and had numerous varicosities along their processes. The majority of dendritic trees spread out in a transverse plane perpendicular to the rostrocaudal axis of the nucleus. Neurons near the brainstem surface were often oriented tangential to that surface, whereas more cells at the dorsal side of the nucleus were oriented radial to the brainstem surface. Further analysis of Nissl-stained neurons revealed the largest neurons are located in the rostral and medial portions of the nucleus although neurons are most densely packed in the middle of the nucleus. The preferred directions of the visual responses of the neurons in this sample did not correlate with their morphology and position in the nucleus. Therefore, the morphology of the cells in the turtle accessory optic system appears dependent on its position within the nucleus while its visual responses may depend on the synaptic inputs that contact each cell.

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Analysis of direction-tuning curves of neurons in the turtle's accessory optic system

Rosenberg

Ariel

1998

Experimental Brain Research

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Visual-movement sensitivity of neurons in the turtle's accessory optic system was investigated. Neuronal responses to stimulus direction and speed were analyzed to determine whether they reflect processing by a one-dimensional encoder of visual motion or whether they indicate directional integration of presynaptic direction-sensitive responses whose maximal-response directions are distributed. Both of these mechanisms make predictions about the functional relationship between stimulus direction and response. The responses of single units in the basal optic nucleus to visual stimulation in different directions were described by both cosine and wrapped normal fitting functions. The wrapped normal function (a Gaussian curve mapped onto a circle) performed at least as well as the cosine function and described directional tuning curves of varying widths. Unlike cosines, the addition of two wrapped normals could describe multi-lobed directional data. Next, it was demonstrated that these neurons did not encode visual motion projected onto a single, spatial axis. Responses to the projected speed along the maximal-response direction were systematically lower than responses to the actual speed along that direction. Thus, for speeds above 1 degrees/s, neuronal response varies with respect to direction but not speed. Summation of presynaptic direction-sensitive responses with distributed maximal-response directions (referred to as directional integration) is discussed as a means of accounting for these results.

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Morphology of basal optic tract terminals in the turtle, Pseudemys scripta elegans

Cited by 5 publications

References 27 publications

Quantitative analysis of granule cell axons and climbing fiber afferents in the turtle cerebellar cortex

Quantitative analysis of granule cell axons and climbing fiber afferents in the turtle cerebellar cortex

Morphology of the turtle accessory optic system

Analysis of direction-tuning curves of neurons in the turtle's accessory optic system

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