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L M Chalupa

Publications and source records attributed to L M Chalupa.

At least 73 records · Page 4Linked to original sources
PubMed1984

Organization of the cat's lateral geniculate nucleus following interruption of prenatal binocular competition.

In adult cats which had an eye removed at least two weeks before birth the remaining retina projects to the entire ipsilateral and contralateral lateral geniculate nucleus. In these prenatally enucleated animals, all lateral geniculate neurons responded apparently normally to visual stimuli and retinotopy also appeared to be normal. These findings demonstrate that termination of in utero binocular competition induces marked morphological changes in the visual system, but the functional organization of the major retino-recipient structure develops normally.

Animals↗
PubMed1983

Development of the retinal pathway to the pretectum of the cat.

The development of retinal projections to the pretectal complex of prenatal and early postnatal cats has been examined using the anterograde transport of horseradish peroxidase and tritiated amino acids. As early as embryonic day 38, the entire dorsal pretectum is penetrated by retinal ganglion cell axons. At this stage the bilateral complement of retinal efferents appears to be dispersed uniformly within the pretectal anlage. A week later, on embryonic day 46, indistinct foci of peroxidase reaction product can be discerned within 2 of the primordial nuclei: the nucleus of the optic tract and the olivary nucleus. By embryonic day 56, five distinct bilateral fields of retinal fiber termination are apparent within the following regions: (i) the nucleus of the optic tract; (ii) the pretectal olivary nucleus; (iii) the posterior pretectal nucleus; (iv) the anterior pretectal nucleus; and (v) the medial pretectal nucleus. Four days before birth, on embryonic day 61, crossed and uncrossed retinal arbors are partially segregated within the nucleus of the optic tract and the pretectal olivary nucleus. The early postnatal retinal connection to the pretectum has an overall pattern virtually indistinguishable from that of the mature cat. The ontogeny of the retinal influx to the pretectum is similar to that of the retinocollicular projection. However, the development of retinal projections to the pretectum and superior colliculus appears to lag behind those to the dorsal lateral geniculate nucleus. These differences may reflect temporal and spatial gradients in the maturation of three major classes of retinal ganglion cells.

Animals↗
PubMed1983

Visual response properties in the tectorecipient zone of the cat's lateral posterior-pulvinar complex: a comparison with the superior colliculus.

The medial portion of the cat's lateral posterior-pulvinar complex (LPm) receives a prominent ascending projection from the superficial layers of the superior colliculus. This region of the thalamus has been suggested to serve as a relay by which visual information from the midbrain could be conveyed to extrastriate cortex. In order to determine how the functional organization within the LPm compares with that of the superior colliculus, visual response properties of LPm and superior collicular neurons were examined under identical experimental conditions. The majority of neurons in the LPm, as in the superior colliculus, respond vigorously to moving stimuli, and a substantial proportion of these cells also exhibit a preference for movements in a particular direction. Furthermore, most cells in the LPm, in common with those of the tectum, respond only in a phasic manner to flashed stimuli, have homogeneous receptive field organization, and show response suppression to stimuli larger than the activating region of the receptive field. As in the colliculus, the ipsilateral visual field is represented in the LPm. In spite of these similarities, there are also some striking differences between the visual responses of LPm and collicular neurons. First, the average size of receptive fields of neurons within the LPm is at least twice that of units in the superficial gray layers of the tectum. Second, more cells in the colliculus are directionally selective than those in the LPm, and the distribution of preferred directions is different in the two regions. Third, an appreciable proportion (27%) of the cells in the LPm are orientation selective, whereas this response property is only rarely encountered in the cat's tectum. Fourth, many LPm neurons can only be activated by binocular stimulation, whereas most collicular units respond equally well to stimulation of either eye. Collectively, these findings indicate that there is a substantial transformation in the lateral posterior-pulvinar complex of the ascending visual influx provided by the superior colliculus.

Acetylcholinesterase↗
PubMed1983

Loss of axons in the cat optic nerve following fetal unilateral enucleation: an electron microscopic analysis.

Between the 48th day of gestation (E-48) and maturity, the number of axons in the cat optic nerve is reduced by approximately 50%. On the basis of an electron microscopic assay, the axon population of the E-48 nerve was estimated to be 328,000. In contrast, estimates from two normal adults were 159,000 and 158,000. In utero unilateral enucleation (at E-45 and E-46) attenuated the severity of this loss since the optic nerves of the experimental animals contained 200,000 and 198,000 fibers. These results indicate that prenatal binocular competition is involved in the elimination of ganglion cell axons during the normal development of the cat's visual system. The increased number of axons in the optic nerve of the prenatally enucleated animals could be due to reduced ganglion cell death or a failure to retract supernumerary axon collaterals. It is suggested that the former explanation is more consistent with what is currently known about the development of retinofugal projections.

Animals↗
PubMed1983

An analysis of axon caliber within the optic nerve of the cat: evidence of size groupings and regional organization.

Axon size in the optic nerves of three adult cats was measured using an accurate planimetric method. A sample of the axon complement was obtained from sets of more than 125 electron micrographs taken at each nerve. In contrast to previous reports, the distribution of axon diameter, as estimated from measurements of axonal cross-sectional area was clearly bimodal. The group of finest axons had a mode at approximately 1 micrometer, and the mode of the group of intermediate size axons was approximately 2 micrometers. Fibers with diameters larger than 3.5 micrometers formed the extensive tail of the distribution. The proportions of large, intermediate, and small axons were estimated to be 5%, 45%, and 50%. These groups probably correspond to the alpha, beta, and gamma classes of retinal ganglion cells. Regional distributions of axon caliber were also bimodal and, in a few instances, even trimodal. A peripheral crescent of each nerve contained a large number of fine fibers. Mean fiber diameter within discrete regions of the optic nerve varied inversely with the density of axon packing. The thickness of the myelin sheath was highly correlated with the inner fiber diameter, hence, myelin sheath width was also distributed in a bimodal manner. These results furnish the first clear evidence that the distribution of fiber caliber within the cat's optic nerve mirrors the principal classes of retinal ganglion cells.

Animals↗
PubMed1982

Behavioural, physiological, and anatomical consequences of monocular deprivation in the golden hamster (Mesocricetus auratus).

The effects of long-term monocular deprivation (MD) on the visual acuity, cortical physiology and dLGN anatomy of the golden hamster were assessed in adult animals which had undergone unilateral eyelid suture at the time of natural eyelid opening. Acuity was measured in a two-alternative forced-choice task in a Y-maze, using a modified method of constant stimuli to vary the spatial frequency of a high-contrast square-wave grating which had the same mean luminance (5 cd/m2) as a uniform grey card. The acuity of the normal (non-deprived) eye of each of two early-MD hamsters was within the normal range (about 0.5 cycles per degree of visual angle), but the acuity of the deprived eyes was reduced by about 0.6 octaves at the 70%-correct criterion. A second reversal of eyelid suture and retesting through the "normal" eye demonstrated that this acuity difference was not attributable to surgical artifacts. Another hamster undergoing prolonged MD beginning in adulthood had normal acuity in both eyes, indicating a "sensitive period" in the development of the hamster's visual system. Single-unit recording from area V1 of the cortex of four early-MD hamsters revealed a shift in ocular dominance favouring the normal eye. The deprived eye's loss of excitatory influence was greater in the ipsilateral hemisphere, but even here 57% of cells were binocularly driven. Only small differences were observed in other receptive field properties. In the dLGN, cell areas in the deprived "lamina" were about 4% smaller than in the non-deprived areas after 5-7.5 months of MD, a difference which was statistically non-significant. However, this difference increased to 19.5% in one hamster in which MD lasted 17 months (p less than 0.025). The relatively small MD effect observed in the hamster is interpreted as being consistent with the absence of a sensitive "detail-analysing" mechanism in the hamster's visual system.

Animals↗
PubMed1982

Prenatal development of retinocollicular projections in the cat: an anterograde tracer transport study.

The retinal projection to the superior colliculus of the cat was examined at four gestational ages, embryonic days 38, 46, 56, and 61, using the antegrade transport of horseradish peroxidase and tritiated leucine. Gestation in the cat averages 65 days. By the 38th day of gestation (E38), the anlage of the entire superior colliculus, both ipsilateral and contralateral to an injection, was labeled intensely. The peroxidase label had an extremely coarse grained texture. As late as E46, the ipsilateral retinal projection extended to the presumed caudal border of the colliculus, while by E56, as in the mature cat, the ipsilateral terminal field was largely excluded from the rostral and caudal tectal poles. The contralateral terminal field at E56, as in younger fetal material, extended across the entire tectal mantle. By E61, clear gaps of label were observed in the contralateral stratum griseum superficiale. At this age, patches or bands of label were accentuated on the ipsilateral side. In double labeled tissue, it could be demonstrated that the ipsilateral patches corresponded quite closely to the gaps in the contralaterally derived label. Thus, a few days before birth, the retinal projection to the superior colliculus has a pattern which resembles that of the adult.

Afferent Pathways↗
PubMed1982

Monocular deprivation in humans: a study of identical twins.

Ultrasonic axial length measurements and psychophysical vernier acuity thresholds were determined for a pair of identical human twins, one of whom had been monocularly deprived since birth with a congenital lens opacity. Axial lengths of both eyes in the normal twin and the nondeprived eye in the other twin differed by less than 0.2 mm, whereas the axial measurement of the deprived eye was approximately 2.0 mm longer. Monocular vernier acuity thresholds in the nondeprived eye of the one twin were not significantly different from those obtained in the normal twin. Our findings are consistent with previous reports of increased axial length after monocular deprivation deprivation but do not support the concept of enhanced vernier acuity in the nondeprived eye of monocularly deprived humans.

Adult↗
PubMed1981

Some observations on the functional organization of the golden hamster's visual system.

A selective review is provided of recent studies dealing with the functional organization of the golden hamster's visual system. Three main topics are considered: (a) the normal organization of the superior colliculus and visual cortex: (b) functional correlates of neonatal damage to the visual system; and (c) the influence of environmental manipulations upon collicular and cortical physiology.

Animals↗
PubMed1980

Retinal ganglion cell projections to the superior colliculus of the hamster demonstrated by the horseradish peroxidase technique.

After a localized injection of horseradish peroxidase into the superior colliculus of the golden hamster, retinal cells of all sizes, except the very smallest, were labeled. Since the smallest cells were probably glia or interneurons, these results indicate that in the hamster all retinal ganglion cell types project directly to the contralateral superior colliculus. This finding is in agreement with recent physiological studies dealing with the conduction velocities of retinocollicular axons in the hamster.

Animals↗
PubMed1980

Effects of neonatal enucleation on receptive-field properties of visual neurons in superior colliculus of the golden hamster.

1. Monocular enucleation in infant hamsters results in a marked expansion of the normally very limited ipsilateral retinotectal projection (13). In 34 hamsters subjected to removal of one eye within 12 h of birth, the receptive-field characteristics of superior collicular neurons ipsilateral and contralateral to the remaining eye were investigated quantitatively and compared to those of normal animals. In six additional neonatal enucleates, the density of the expanded retinotectal projection was studied with the autoradiographic method and an attempt was made to relate the anatomical reorganization with the electrophysiological findings, 2. The response characteristics of visual cells in the colliculus contralateral to the remaining eye were not significantly different from those observed in normal animals. In the ipsilateral tectum, however, numerous changes were observed. Visual receptive fields were abnormally large. The incidence of directional selectivity was markedly reduced, as were the magnitudes of the discharges elicited by either flashed or moving stimuli. Fewer cells were activated by small flashed spots and most of the units that were responsive to such stimulation failed to exhibit the surround suppression typical for the majority of tectal neurons in normal hamsters. Most cells in the ipsilateral colliculus responded only to relatively low (less than 50 degrees/s) stimulus velocities and response decrements resulting from repeated stimulation also occurred much more readily for the neurons tested on this side. 3. The results of additional experiments in neonatal enucleates (n = 8), which were also subjected to acute bilateral removal of the visual cortex, demonstrated that such damage resulted in a marked reduction in the incidence of directional selectivity in the colliculus contralateral to the remaining eye but had no effect on the responses of cells innervated by the aberrant ipsilateral pathway. 4. A correlation between the relative density of the ipsilateral retinal projection at different points in the colliculus, as demonstrated by the autroradiography and the nature of the visual responses obtained in different portions of the structure, indicated that receptive-field size was negatively correlated with the density of the aberrant retinotectal projection and that absolute responsivity (number of impulses elicited by an optimal stimulus) was positively correlated with autoradiographic grain density. 5. These findings demonstrate that while the aberrant retinocollicular projection can, along with the other visual inputs to the tectum, result in the organization of normal response properties for a small number of tectal neurons, the majority of the visual cells innervated by this pathway have responses that are appreciably different from normal.

Animals↗
PubMed1979

An autoradiographic study of the retinotectal projection in the golden hamster.

Intraocular injections of tritiated leucine and proline were used to examine the retinotectal projection of the golden hamster. In the contralateral superior colliculus intense and complete label was seen in the stratum zonale, stratum griseum superficiale and the upper portion of the stratum opticum, with relatively less dense label in the lower part of the optic layer. On the ipsilateral side no label was found in the most rostral portion of the tectum. This area comprised about 10% of the rostro-caudal extent of the colliculus, and most likely, it receives a crossed input from the temporal retina (as demonstrated in the cat by Harting and Guillery, '76). Very sparse label was observed in an anterior segment of the ipsilateral colliculus. In coronal sections it appeared as discrete clumps or patches which were confined to the stratum opticum. Within this layer there was a tendency for the clumps to be located more dorsally with increasing laterality. There was considerable variability between and within animals in the size of the clumps as well as the distance between clumps. Reconstruction of coronal sections showed that the ipsilateral label forms discontinuous ribbons which extend up to 180 microns in the rostro-caudal dimension. No label was seen on the ipsilateral side in the remaining tectum (caudal 60%).

Animals↗
PubMed1979

Functional properties of pulvinar-lateral posterior neurons which receive input from the superior colliculus.

Focal electrical stimulation of the superior colliculus induced short latency responses and/or a long duration suppression of spontaneous activity in single cells isolated in the pulvinar and lateral posterior (LP) nuclei of the cat. Cells which responded with one or more spikes at short latencies were relatively few in number, and these tended to be encountered in or near the principal tectorecipient zone of LP. In contrast, a suppression response was observed in many more cells which were widely distributed throughout the pulvinar-LP complex. Stimulation of the superficial layers of the colliculus was more effective in driving or suppressing pulvinar-LP cells than that of intermediate and deep layers. There was also an indication of a coarse topography in this projection. On the basis of their sensory response properties the cells responsive to tectal stimulation, at short latency or with a suppression, could not be differentiated from the overall sample of pulvinar-LP neurons.

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↗