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C E Rocha-Miranda

Publications and source records attributed to C E Rocha-Miranda.

At least 37 records · Page 2Linked to original sources
PubMed1986

Effects of monocular enucleation at different stages of development on the uncrossed retinocollicular projection in the opossum.

Pouch young opossums aged from 5 to 34 days underwent unilateral eye enucleation and the projection from the remaining eye to the superior colliculus (SC) was explored at maturity by anatomical and physiological methods. The results were compared to data from normal or adult enucleated animals. Analysis of the experimental group showed that early enucleation resulted in an increased ipsilateral pathway which varied in terminal distribution with the timing of the lesion. When performed in the very young (first and second postnatal week) the uncrossed retinocollicular projection covered the entire area of the superficial layers of the superior colliculus but formed mediolateral bands of high and low label density at the rostral aspects of the SC. In the remainder of the early enucleated group the labeling also covered the entire area of the optic layers but the density of labeling was relatively homogeneous throughout the rostrocaudal extension of the SC. The distribution pattern of the uncrossed projection in adult enucleated opossums was similar to that described previously in normal animals. The electrophysiological results showed that, at all ages examined, early enucleation resulted in an orderly but expanded map in the SC restricted to the sector of the visual field seen by the temporal retina. The different anatomical patterns found in animals enucleated at these two early stages of development could not be distinguished by multiunit recordings.

Age Factors↗
PubMed1985

Visuotopic information conveyed by each eye to the opossum's superior colliculus.

The uniocular visual field representations on the superior colliculus (SC), as estimated from multiunit response field centres about the horizontal meridian, were compared in midpontine pretrigeminal opossums (Didelphis marsupialis aurita Wied 1826). Recordings from the rostral pole (RP) and its caudal neighbour, the direct binocular region (DBR), as defined by Rocha-Miranda et al. (1978), were distinguished by the histological control. The results showed that while the hemifield contralateral to the recording site was well represented on the DBR by both eyes, the ipsilateral hemifield was generously represented at the RP only by the contralateral eye. At the RP the ipsilateral eye usually conveyed information about the vertical meridian, bringing about an expanded representation of the central visual space. Distinct patterns of representation were also recognized on graphs which relate recording sites along the AP axis of the SC with the azimuths of response field centres. The representation of the vertical reference meridian upon this axis on an oculocentric system was estimated from the DBR data and localized in the RP, at about 500 microns from the rostral end, for the ipsilateral eye (Vo') and in the DBR, at about 800 microns for the other eye (Vo). Similarly, plots of the magnification factor against the AP collicular axis indicated different strategies of representation for each eye. At the segment between 500 and 800 microns on this axis the magnification factors of the ipsilateral eye were usually much higher than those of the other eye. Furthermore, horizontal disparities between field centres were shown to have distinct distributions along the AP axis within the RP and DBR regions.(ABSTRACT TRUNCATED AT 250 WORDS)

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PubMed1985

Growth and restriction of the ipsilateral retinocollicular projection in the opossum.

The distribution of optic nerve fibers and terminals in the superior colliculus (SC) was followed throughout its development in pouch young opossums in order to establish the normal sequence of events leading to the formation of mature patterns. Up to 7 days of life in the pouch, labeled fibers can be followed only as far as the rostral aspect of the optic tract. The earliest evidence for crossed retinal projections in the SC is found at 10 days of age. In parasagittal sections, the label extends along the rostrocaudal tectal axis from the rostral border to the presumptive caudal pole of the SC. Unequivocal evidence for ipsilateral retinocollicular projection is found at 15 days extending to all but the caudal 5th of the rostrocaudal extent of the SC. The projections from both eyes overlap extensively in the SC at 22 days and after this age significant changes occur, mostly at the ipsilateral side: a sub-pial tier of fine label develops excluding both rostral and caudal collicular poles; a deeper tier of coarse label extends from the rostral to the caudal pole and a third, patchy tier of label is found at the prospective strata griseum superficiale and griseum intermediate. By 47 and 60 days the tangential distribution of the projections is virtually indistinguishable from the adult pattern although laminar segregation does not seem as sharp as in the adult. Comparisons of the changeable patterns of ipsilateral retinocollicular projections from 22 to 34 days with the invariant, aberrant pattern in adult animals submitted to uniocular enucleation at either age suggests that the preservation of a juvenile pattern does not provide a comprehensive explanation for the formation of aberrant projections.

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PubMed1984

Observations on postnatal neurogenesis in the superior colliculus and the pretectum in the opossum.

Postnatal neurogenesis has been detected in the superior colliculus (CS) and caudal pretectum of the opossum in the period ranging from 2 to 13 days ( PND2 to PND13 ) of life in the pouch. Examination of the pattern of labeling in specimens exposed to a pulse of tritiated thymidine ( [3H]T) in PND4 or PND7 and allowed 1.5 h survival reveals that postnatal cell proliferation for the CS is virtually confined to the ventricular zone with no evidence for in situ[3H]T uptake in the collicular plate. Semi-quantitative analysis in long survival animals shows that postnatal neurogenesis peaks later in the CS ( PND7 ) than in the caudal pretectum ( PND4 ) and also persists longer in the former than in the latter. Comparisons of the numerical density of heavily labeled neurons suggest the occurrence of ventro-dorsal and rostro-caudal gradients of neurogenesis in the CS. Separate analysis of superficial, intermediate and deep layers shows, in addition, a combined rostrolateral-to-caudomedial gradient of neurogenesis in the superficial layers. Comparisons of the time schedules of neurogenesis for the superficial layers and of the deployment of optic fibers suggest that migration of neurons to their eventual destination is completed at or after the arrival of afferents.

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PubMed1983

Visual perception fields in the superficial layers of the opossum's superior colliculus: representation of the ipsi and contralateral hemifields by each eye.

Visual receptive fields of single units in the superior colliculus of the opossums were analysed in regions representing the ipsilateral (rostral pole - RP) and the contralateral hemifields (direct binocular region - DBR) close to and including the representation of the horizontal meridian. Of 242 units half had receptive field centres of the contralateral eye at the ipsilateral hemifield and the other half at the contralateral hemifield. The proportion of units driven by the ipsilateral eye was considerably smaller at the RP than at the DBR and the frequency of unit response to this eye diminished within the ipsilateral hemifield with progressively more rostral penetrations in the RP. The midline was unequally represented by the two eyes in RP units: while 24 out of 26 receptive fields of the ipsilateral eye straddled the vertical meridian, only 50 out of 120 of the contralateral eye did so. Furthermore, at the RP receptive fields of units responsive to the contralateral eye extended up to 46.8 degrees into the ipsilateral visual field while those mapped for the ipsilateral eye extended only up to 26 degrees. As a result of this tendency for the receptive fields of the ipsilateral, but not the contralateral eye, to overlap the vertical meridian, progressively more rostral recordings yielded an increase in the binocular convergent disparity as a function of the eccentricity for the receptive field of the contralateral eye. Since the disparity didn't vary with the eccentricity in the DBR units, we suggest that stimuli at the midline and close to the animal might be the natural ones to drive large disparity units present in the RP.(ABSTRACT TRUNCATED AT 250 WORDS)

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PubMed1983

Organization of the visual thalamus: corticothalamic projections from the primary visual area in the opossum.

The projections from the visual cortex to thalamic nuclei in the opossum were investigated by degeneration and radioautographic methods. Efferent axons from the striate cortex course from the internal capsule to the thalamus in two bundles, one of which innervates the reticular and dorsal lateral geniculate nuclei, while the other bundle innervates the external layer of the ventral lateral geniculate nucleus. Both bundles course along and through terminal fields found in the lateral posterior nucleus. The visuotopic organization inferred from the corticofugal pathway shows that projection lines in the dorsal lateral geniculate nucleus (DLGN) run along medio-lateral strips including both the beta and alpha segments, across the quasi-laminae of retino-geniculate projection, and that naso-temporal axes in the visual field run in a dorso-ventral direction through the DLGN. The external layer of the ventral lateral geniculate nucleus receives a projection from the striate cortex and bilateral projections from the retina, and naso-temporal axes in the visual field are represented along a dorso-ventral direction in this layer. The striate cortical projections cover approximately the lateral two-thirds of the lateral posterior nucleus, overlapping a small retinal terminal field, and naso-temporal axes in the visual field are represented onto the cortico-recipient zone in a mirror-symmetric direction to that of the adjoining DLGN. In all these three cortico-recipient zones, dorso-ventral axes in the visual field are represented in a rostro-caudal direction.

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PubMed1982

Visuotopic organization of the superior colliculus of the opossum.

The representation of the visual field in the upper layers of the opossum's superior colliculus was studied by recording the response of multi-units to visual stimulation. Overall, the visual topography is similar to that of other non-primate mammals. Along the horizontal meridian and magnification factor decreases assymetrically about the vertical meridian, falling more abruptly in the region of the representation of the ipsilateral hemifield. The colliculus may be divided into three parts on the basis of the projections from the retina: a rostral region that does not receive any ipsilateral retinal afferents, a region that receives binocular retinal projections and a monocular region that receives only contralateral retinal input. Electrophysiological recording revealed that the rostral region contains a representation of 40 degrees of the ipsilateral field. The representation of the vertical meridian forms the border between the rostral region and the binocular region and the representation of the 40-45 degrees longitude meridian forms the border between the binocular and monocular regions.

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PubMed1981

The pretectal complex in the opossum: projections from the striate cortex and correlation with retinal terminal fields.

Two terminal fields were revealed in the pretectal complex of the opossum by the Fink-Heimer method after striate cortical lesions. A rostral field is located within a rostrolateral strip of the compact part of the anterior pretectal nucleus, where a partial topographic arrangement of this projection is present. A caudal field is located within the sub-brachial nucleus of the optic tract, located between the brachium of the superior colliculus and the posterior pretectal nucleus. The corticotopic projection to this field is mirror-symmetric to that found in the superior colliculus and overlaps a bilateral projection from the retina. Based on neural pathway evidence, it is concluded that the nucleus of the optic tract in the opossum can be subdivided in (a) an intrabrachial nucleus receiving a direct projection from the contralateral retina and (b) a sub-brachial nucleus receiving projections from both retinae and from the striate cortex. The pretectal complex, as the superior colliculus, can be anatomically subdivided in a superficial region receiving visual input (the optic pretectum) and a deep region only remotely connected to the visual system. The optic pretectum, however, differs from the superior colliculus in displaying a multiple-map arrangement within its constituent nuclei, instead of a single continuous representation of the visual field.

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PubMed1978

Postnatal development of retinogeniculate, retinopretectal and retinotectal projections in the opossum.

The postnatal development of retinogeniculate, retinopretectal and retinotectal projections has been studied by the anterograde transport of proline-labeled proteins in 20 pouch young opossums aged from 10 to 60 days. Radioautographical findings suggest delayed development of uncrossed as compared to crossed projections. There is a phase of overlapping projections from both eyes in thalamic and tectal target sites. Partial segregation of projections to the dorsal lateral geniculate nucleus (GLD) is preceded by differential distribution of crossed and uncrossed terminal fields along its dorsoventral axis (at age 23 days). The quasilaminar pattern of projections in the dorsocaudal region of GLD pars alpha is incipient by 42 days and is fully established at 60 days of age, as eye opening starts. The mature pattern of projections to the ventral lateral geniculate nucleus (GLV) is established much earlier, at 23 days of age. The development of retinopretectal projections is assessed mostly from the analysis of the olivary pretectal nucleus (PO). Distribution of silver grains into discrete areas coextensive with PO is relatively delayed (by 23 days of age) as compared to the nuclei of the lateral geniculate body. Soon after, however, the mature pattern of projections to PO is established (at 33 days of age). The early development of retinotectal projections (from 10 to 23 days) is compatible with an initial tangential course of crossed optic fibers in the superior colliculus (CS) but other alternatives remain open, such as a sequential outside-in arrangement of terminal fields of deeply coursing fibers. Arborization of uncrossed fibers is delayed at extreme rostromedial and caudolateral portion of the territory of the main uncrossed retinotectal projection. Segregation of uncrossed projections at different depths of CS is nearly complete by 42 days. Differences in the development of terminal fields in different target nuclei or in regions of a given target site are discussed in relation to retinal and local factors.

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PubMed1976

Receptive field properties of single units in the opossum striate cortex.

On the basis of their trigger-features, 98 units out of 127 recorded in striate cortex of immobilized opossums, under forced breathing of a nitrous oxide/oxygen mixture, were classified into 5 receptive field groups. Group 1 units (20/127) responding to small stationary spots were shown to be made up of regions of opposite response type and mutual antagonism, separate by linear boundaries. The optimal discharge was elicited by a stimulus configuration consisting of rectilinear regions of opposite contrast positioned and oriented in the visual field so as not to elicit antagonism while maximizing the overlap with regions responsive to that contrast. To edges in motion these units were shown to be made up of light and dark discharge centers, the locations of which could not be predicted from the map to stationary spots. In addition to position and orientation, direction was another important stimulus parameter. Group 2 units (34/127) had uniform requirements of stimulus orientation, direction of motion or both, througout the receptive field. Width was rarely a significant variable. Three subgroups were detected: orientation selective, directional selective and orientation-direction sensitive. Group 3 units (18/127) required stopped stimuli. In most instances (14/18) this property was attributed to a suppressive surround with relatively non-specific stimulus requirements. Oriented and non-oriented responsive receptive fields were observed. Group 3 units with no surround (4/18) responded best to properly positioned and oriented wedges, usually of 90 degrees. Group 4 units (24/127) had uniform fields with little stimulus specificity and were often responsive to diffuse light. Although not sensitive to stimulus orientation and direction, motion was frequently a requisite for optimal responses. Group 5 receptive fields (2/127) had concentrically arranged regions of distinct response type which displayed mutual antagonism. No sensitivity to orientation or direction was detected. Twenty-nine units remained unclassified. Other group distinctions were the relatively higher spontaneous activity of group 4 units and the large field sizes encountered among groups 1 and 4 when compared to group 2. Based on their properties and receptive field type distribution, we propose that striate receptive fields in the opossum have a similar organization to those of other mammals.

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PubMed1975

Visual activation of neurons in inferotemporal cortex depends on striate cortex and forebrain commissures.

Neurons in inferotemporal cortex respond only to visual stimuli and a majority have receptive fields that extend well into both visual half-fields. After bilateral removal of striate cortex, no inferotemporal neurons responded to visual stimuli. After unilateral removal of striate cortex, inferotemporal neurons in both hemispheres responded only to stimuli in the hemifield contralateral to the intact striate cortex. After section of the corpus callosum and anterior commissure, inferotemporal neurons in both hemispheres responded only to stimuli in the hemifield contralateral to the recording site. These results indicate that inferotemporal cortex visual information from striate cortex and that the pathway from striate cortex to the contralateral inferotemporal cortex includes the forebrain commissures. This same striate-temporal pathway is also necessary for normal discrimination learning. We suggest that the converging input onto single inferotemporal neurons from widely separated retinal areas may provide a mechanism for stimulus equivalence over different parts of the visual field, and it may be the absence of such a mechanism that contributes to the visual discrimination deficit that follows inferotemporal lesions.

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