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G H Henry

Publications and source records attributed to G H Henry.

At least 19 recordsLinked to original sources
PubMed1995

Neural and behavioral effects of early eye rotation on the optokinetic system in the wallaby, Macropus eugenii.

1. Total optokinetic responses measured by electro-oculography and single unit recordings from the nucleus of the optic tract and dorsal terminal nucleus (NOT-DTN) of the accessory optic system were taken from young adult wallabies, whose one eye had been rotated about the optic axis at birth, and were compared with those from normal controls. 2. The velocities of the horizontal component of the slow phases of optokinetic nystagmus were measured in the horizontal plane as a function of the direction of stimulus motion. In normal animals the overall gain during monocular stimulation was greatest for horizontal temporonasal movement, with a lesser response to movement in the opposite, nasotemporal, direction. Upward or downward vertical stimulus motion did not elicit horizontal responses. In animals where one eye was removed at birth and the other eye was normal, the characteristic bidirectional response was retained; the response was identical with that elicited from one eye of a normal animal. 3. After surgical rotation (extorsion) of the left eye by approximately 90 degrees on or within a few days of birth, the animals were grown to adulthood. The visual streak of the retina of the operated eye was then found, in individual cases, to be between 30-100 degrees from horizontal with the head held in the standard resting position. This angle was taken as the definitive degree of cyclotorsion resulting from the operation in each animal. The extraocular muscles connected with regions of the eye adjacent to the location of their outgrowth in the orbit and not with the normal point of attachment on the globe.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1994

Visual corticogeniculate projections in the cat.

The anterograde axonal tracer Biocytin was injected into areas 17-19 of the cat visual cortex to determine the nature of the corticofugal projection from each area to the dorsal lateral geniculate nucleus (LGNd). Each projection had extremely fine terminal branches with even finer twigs that ended in single synaptic boutons. The terminal contacts of the projections from areas 17 and 18 extended throughout the LGNd while those from area 19 were found only in the A1 and CMAG laminae. Unlike earlier experiments, where injections were made into the optic radiations, no beaded axons were found, which adds support to the proposal that such fibres originate from the perigeniculate nucleus rather than the visual cortex. Within the LGNd, fibres of large calibre appeared only to arise from retrogradely labelled cells. All fibres of cortical origin were fine in diameter although there was a higher density of boutons contacting LGNd cell bodies for the area 17 terminals. The recurring fineness of the corticofugal projections indicates that corticofugal signals travel much more slowly than their geniculo-cortical counterparts while the greater bouton density of the area 17 projections points to a more independent effect from this cortical area.

Animals↗
PubMed1993

Projections from the lateral division of the lateral posterior-pulvinar complex to area 21a and the striate cortex in the cat.

The axonal tracer HRP-WGA, injected into area 21a of the cat, was used in conjunction with AChE histochemistry to demonstrate that a reciprocal pathway links area 21a with the LPl (striate recipient zone) in the lateral posterior-pulvinar complex. Separate injections of the fluorescent tracers, Fast blue (FB) and Diamidino yellow (DY), were then placed simultaneously in the striate cortex and area 21a, respectively, to identify the relative position of cells projecting to both cortical areas and to pinpoint the location of efferent terminals in the LPl. Both FB and DY labelled cells and terminals are located together in the LPl but none of the neurons projecting to the striate cortex and area 21a was double labelled which would have indicated the presence of cells with axons projecting to both areas. Nonetheless, the intermingling of cells projecting to the striate cortex and area 21a, and the reciprocal character of both pathways, is consistent with a model in which the two cortical areas exchange signals via the LPl.

Acetylcholinesterase↗
PubMed1992

Cytoarchitecture and visual field representation in area 17 of the tammar wallaby (Macropus eugenii).

Tritiated proline was injected into one eye in the tammar wallaby and transported label was studied in the cortex after transneuronal passage through the lateral geniculate nucleus. The autoradiographic label and cytoarchitecture were used to anatomically demarcate the borders of area 17. Electrophysiological recordings from single units were done to obtain a retinotopic map of area 17. Single units in area 17 were found to have orientation sensitivity comparable to those seen in placental mammals such as cat and monkey. They could also be classified as simple, complex, and hypercomplex cells. Changes in the cortical areal magnification factor with eccentricity were found to match the drop off in retinal ganglion cell density only along the vertical meridian representation. Along the horizontal meridian, the cortical magnification falls off significantly with eccentricity, whereas the ganglion cell density shows only a mild reduction. Thus central vision, especially the binocular segment, is heavily represented at the cost of the periphery.

Animals↗
PubMed1992

Area 21a in the cat and the detection of binocular orientation disparity.

Visual response properties were examined in 115 cells, recorded in area 21a of the cerebral cortex of anaesthetized and paralysed adult cats. Cells were binocular and had receptive fields consisting of a single uniform discharge region which fired with composite ON/OFF responses to stationary flashing stimuli. Most cells were sharply tuned for orientation, but this was unaffected by changes in stimulus length. This result is consistent with a model in which the cells of area 21a receive their input from C cells of the striate cortex. Evidence for this was obtained by studying the decline in the responsiveness in area 21a that accompanied the cooling of areas 17 and 18. There was little indication that the cells of area 21a were effective detectors of spatial disparity, but their sharp monocular orientation tuning and differences in the preferred orientation of ipsilateral and contralateral eyes hinted at a role in the detection of binocular orientation disparity. Our results, however, showed that the recorded binocular disparity curves could be accounted for by summing the two monocular contributions and there was no apparent novel binocular component.

Animals↗
PubMed1992

Response characteristics of the cells of cortical area 21a of the cat with special reference to orientation specificity.

1. Extracellular recording using tungsten-in-glass microelectrodes was conducted on 115 neurons in area 21a of fifteen anaesthetized cats. Quantitative analysis using computer-controlled display and collecting routines were used to investigate the excitatory and inhibitory regions of the receptive field and to see if interaction, within and between these regions, contributed to the response properties of the cells. 2. The responses of the cells in the sample appeared to arise from a single, homogeneous class. All cells had single discharge regions which responded with composite ON/OFF firing to a stationary flashing bar. The same region also responded to moving light and dark bars and edges. There was little evidence of inhibition as measured by the suppression of spontaneous or induced firing. Most cells had relatively small receptive fields (primary width: mean = 2.1 +/- 0.9 deg (S.D.); n = 108), all were binocular and were located within 15.0 deg of the visual axes. 3. All cells responded well to slowly moving stimuli but generally failed to respond to stimuli moving faster than 10.0 deg s-1. All responses were bi-directional and, although many showed evidence of length summation, there was no sign of linear summation. 4. Despite the absence of significant sideband inhibition many cells were acutely tuned for orientation (half-width at half-height: mean = 15.6 +/- 5.3 deg; n = 48). To investigate this property further, cells were analysed to assess the effect of changing the length of a moving bar stimulus on the acuteness of the orientation tuning curve. Short bars, of similar length to the width of the receptive field, had orientation tuning curves of equivalent sharpness to those obtained with longer bars. 5. The equivalence of orientation tuning for long and short bars stands in contrast to the results obtained for both simple (S) and complex (C) cells of the striate cortex where tuning for the longer bar is sharper than that for the shorter. The result from area 21a cells is consistent with the absence of sideband inhibition and can be related to an input from the striate cortex that passes through a threshold barrier. 6. The orientation tuning of cells of area 21a can be explained if it is assumed that they receive their major input from C or complex cells of the striate cortex in which firing must reach a threshold frequency to activate the recipient cell.

Animals↗
PubMed1992

Partition of function in the morphological subdivisions of the lateral geniculate nucleus of the tammar wallaby (Macropus eugenii).

Extra-cellular recordings from single cells in the dorsal lateral geniculate nucleus (dLGN) of the tammar wallaby, Macropus eugenii, were made to find out whether the stratification of the nucleus could be correlated with the receptive field properties of units. Retinofugal fibres terminate in the lateral geniculate nucleus of the wallaby in nine interleaved eye-specific layers. These may be grouped into a lateral alpha segment of six laminae and a medial beta segment of three, in which the cells are less densely packed. Ninety percent of the geniculate neurons recorded from in the alpha segment gave brisk responses to stimulation of their receptive fields. Cells with sluggish responses predominated in the beta segment, but there was also a sizable minority of cells with brisk responses that were indistinguishable from those recorded in the alpha segment. In contrast, other response properties were rarely differentiated in individual layers. Thus, in most layers, the numbers of cells with transient or sustained responses were not significantly different, and this was also true for cells with ON- or OFF- responses. For each of these response pairings, however, the numbers of one type (ON- and transient) predominated in every layer. The accumulation of this laminar distinction lead to significant differences in the alpha and beta segments and in the nucleus as a whole. We conclude that cells in the individual layers of the dLGN of the tammar wallaby show no evidence of having receptive field properties in common that might correlate with separate functional streams. There is a functional segregation of receptive field properties between the alpha and beta segments. The organization of these two segments resembles that of the A and the C layers of the dLGN in cats and, possibly, the magnocellular and koniocellular components of the dLGN in primates. These broad similarities in functional partition of the dLGN of different species suggests that this aspect of the organization of the nucleus is independent of lifestyle.

Animals↗
PubMed1990

Properties of area 17/18 border neurons contributing to the visual transcallosal pathway in the cat.

In a series of physiological experiments, a total of 203 neurons at the Area 17/18 border were recorded with a callosal link either demonstrated by antidromic or transsynaptic activation from stimulating electrodes located in the homotopic contralateral hemisphere (CH), or in the splenial segment of the corpus callosum (CC). Forty-four percent of the transcallosal cells could also be driven from stimulating electrodes in or just above the lateral geniculate nucleus (OR1). The majority (69%) of transcallosal neurons were classifiable as belonging to the complex family (B and C cells) and most of these were found in the supragranular laminae and in lamina 4A. The ocular dominance distribution of transcallosal cells was trimodal, consisting of roughly equal numbers of monocularly dominated and binocularly balanced neurons. Estimates of conduction time and synaptic delay were obtained for neurons driven from CH, CC, and from OR1, and in most instances the response latency was short enough to suggest a monosynaptic input from either the ipsi- or contra-lateral hemisphere. The distribution of transcallosal conduction times showed that S cells, as a class, had significantly faster conduction than cells of the complex family but otherwise there was no obvious signs of multimodality in the distribution curve. An analysis of the synaptic delays in transcallosal activation produced a mean of 0.6 to 0.7 ms but some were too short to be consistent with a transsynaptic drive, suggesting that some cells with an antidromic drive may have been included in the transsynaptic category. Results are interpreted in terms of the contribution made by the corpus callosum to stereoscopic vision.

Animals↗
PubMed1990

Relationship between preferred orientation and ordinal position in neurones of cat striate cortex.

Striate cortical cells were classified according to whether or not their preferred orientation was close to one of the "primary" orientations (horizontal, vertical or radial, i.e. directed to the area centralis) and according to their ordinal position on the afferent pathway from the dorsal lateral geniculate nucleus (dLGN). Among the neurones that could be driven monosynaptically from the dLGN, there was a high representation of those with a preference for the primary orientations. This was particularly evident in the case of C (complex) cells. There was no such preponderance of primary orientations among the polysynaptically activated cells. It is proposed that the asymmetry of distribution seen among the first-order cells reflects the asymmetry seen subcortically in neurones that show orientation biases. It may be that the cortex elaborates a more uniform representation of orientations only at the higher ordinal levels.

Afferent Pathways↗
PubMed1989

Neurons of the striate cortex driven trans-synaptically by electrical stimulation of the superior colliculus.

The latencies of trans-synaptic responses in cells of the striate cortex, following electrical stimulation in the superior colliculus, were evaluated to assess the possible path taken by the neural signal. Most of the recorded striate neurons were judged to be driven by the signal passing back along the axons and then into the collaterals of cortico-tectal cells in lamina 5. The present results indicate that striate neurons, in communicating with the superior colliculus, at the same time, send signals via their collaterals to neighbouring cells in lamina 5 which appear to have similar C or complex receptive fields.

Animals↗
PubMed1988

Physiological studies on the feedback connection to the striate cortex from cortical areas 18 and 19 of the cat.

The functional characteristics of the feedback connections from areas 18 and 19 to area 17 in the cat have been examined with electrophysiological techniques. The experiments involved single unit recording in laminae 2 and 3 of area 17 while stimulating electrically a small region of area 18 or 19. It was found that a precise retinotopic correspondence between the sites of recording and stimulation was necessary before neurons of area 17 could be activated by electrical stimulation in extrastriate areas. Latencies were long compared to those obtained after stimulation of the optic radiation. The mean latency for orthodromic drive from area 19 was 10.4 ms and 6.1 ms from area 18, suggesting that the conduction velocities in these pathways are of the order of 1 m/s. The jitter of the latency after repeated orthodromic stimulation was often shorter than 0.3 ms, indicating that a large number of the sampled neurons received a direct drive from area 18 or from area 19. The functional properties of neurons driven from area 19 were different from those of cells driven from area 18. Thus, most striate neurons orthodromically driven from area 19 were of the SH and S type whereas the cells activated by area 18 stimulation belonged to the C and B categories.

Animals↗
PubMed1987

The duplex character of the corticofugal pathway from the striate cortex to the lateral geniculate complex of the cat.

From studies on signal conduction times in the corticofugal pathway from the striate cortex of the cat it has been proposed that S cells project to the LGN and C cells to the PGN. This concept has not received support from the histological examination of axons projecting to the two nuclei. The physiological experiments pointed to a clear segregation not apparent in the distribution of axonal diameters. A larger sample of signal conduction times, collected in the present study, is more consistent with the findings on the morphology of the pathway.

Animals↗
PubMed1986

Morphology and distribution of neurons in the retinal ganglion cell layer of the adult tammar wallaby--Macropus eugenii.

The morphology of the ganglion cell layer of the adult tammar wallaby has been examined from Nissl-stained retinal flatmounts. From this material, neurons have been classed as ganglion cells or displaced amacrine cells according to the disposition of Nissl substance. A further subdivision of ganglion cells into a separate group of alphalike cells was assisted by determining the range of soma sizes in neurofibrillar-stained flatmounts, a method which, in the cat, has revealed the presence of alpha cells. Isodensity contour maps prepared from the Nissl-stained flatmounts show a well-developed visual streak and an area centralis in the total neuronal population. A similar pattern was also found in the ganglion cells, thus confirming Tancred's (J. Comp. Neurol. 196:585-603, '81) finding, and, as well, in the alphalike ganglion cells and the displaced amacrine cells. The relative proportions of ganglion cells to displaced amacrines (GC:DA) were evaluated from isodensity profiles drawn along and vertical to the visual streak for the two cell types and also from maps showing the variation in the GC:DA ratio throughout the retina. A comparison with results published for other species shows that the visual streak development in the tammar wallaby is consistent with the expectations of the "terrain" theory and that, in its relative proportion of displaced amacrines, the tammar closely resembles the rabbit but contrasts sharply with the cat, which has half as many ganglion cells and three times as many displaced amacrines as the other two species.

Animals↗
PubMed1986

Layering in lamina 6 of cat striate cortex.

Retrograde transport after the injection of the tracer, wheatgerm agglutinin-horseradish peroxidase, into different neural sites revealed a layering of labelled cells in lamina 6 of the striate cortex of the cat. Depending on their destination, efferent cells were clustered at different levels in lamina 6 so that cells projecting to the claustrum congregated in the lower half of the lamina while those projecting to other parts of the visual cortex, in either ipsi- or contralateral hemispheres, were found principally in the upper half and the cells with axons passing to the lateral geniculate nucleus occupied the central expanse (middle three-fifths) of the lamina.

Animals↗
PubMed1986

Bistratified amacrine cells in the retina of the tammar wallaby--Macropus eugenii.

Cajal (1911) noted that bistratified amacrine cells were common in non mammalian species and extremely rare in the mammalian retina. An examination of the marsupial retina of the tammar wallaby, stained with a modified Golgi procedure, revealed that a particular type of bistratified amacrine was frequently impregnated with the silver stain. Flat mount and transverse sections showed that the morphology of this cell did not correspond with any of the species-dependent bistratified amacrines reproduced in Cajal's drawings. Instead, the cell appeared to be almost identical to the AII or rod amacrine that has been observed in a number of mammalian retinas. The relative frequency with which the cell appears in our material, and its confirmed rod input in other species, are both consistent with the grazing habits of the tammar wallaby which is a crepuscular animal that does most of its feeding at dusk and after dark.

Animals↗
PubMed1985

The character and influence of the claustral pathway to the striate cortex of the cat.

In paralyzed and anaesthetized cats, the pathway running from the claustrum to the striate cortex was characterized from the trans-synaptic latencies of responses that were initiated by electrical stimulation in the claustrum (CL) and recorded extra-cellularly in single striate neurons. A second stimulating electrode (OR1) in the primary visual pathway provided information on the input coming to the recorded cell from the lateral geniculate nucleus. An analysis of the classified striate neurons receiving a claustral drive revealed that 68% were C cells and 26% were S cells. For the C cells, 81% had CL latencies of less than 2.5 ms (mean = 1.8 ms) and the potential to receive a direct drive from a fast conducting input; the remaining 19% had latencies around 3.0 ms (mean = 3.0 ms), a value consistent with a disynaptic input from the same type of input. From their CL latencies, the S cells also could be subdivided into two subgroups; one, made up of 36% of the sample had CL latencies of less than 2.5 ms (mean = 1.9 ms) and the capacity, like the majority of C cells, to receive a direct, fast-conducting input; the second subgroup, consisting of 74% of the S cells, had CL latencies longer than 3.0 ms (mean = 5.4 ms). The majority of cells with a claustral-drive (85%) were encountered either in laminae 4 or 6. Claustral-driven cells belonging to both S and C categories were found in the two laminae (4 and 6) and there was no observed predisposition for a particular cell type to cluster in either of these lamina. From a comparison of CL and OR1 latencies, justified on the grounds of independent stimulation, a strict correlation was found for signal conduction properties in the claustral and LGN pathways running to a given striate neuron. From a quantitative evaluation of receptive field properties the claustral-driven striate neurons were found to resemble cells in the general population. As a group, however, they were distinctive in that both end-zone inhibition and direction selectivity were either weak or absent from the cell's response. This finding held for cells in both the C and the S categories. It is concluded from the high incidence of claustral-driven C cells, that the claustral loop from the striate cortex is involved in an aspect of motion detection.

Afferent Pathways↗
PubMed1983

Different geniculate inputs to B and C cells of cat striate cortex.

Cells with uniform receptive fields were selected for extra cellular recording in the striate cortex of anaesthetised cats. From their responses to electrical stimulation at three sites in the primary visual pathway the cells were grouped according to their ordinal position and whether their afferent drive came from the brisk sustained or brisk transient type of LGN neuron. From differences in laminar distribution and afferent stream the population was divided into 4 subgroups. Within these 4 subgroups there were two basic visual response patterns, which had been identified previously, and attributed to B and C cells. The B cells, which have a smaller receptive field, a lower spontaneous activity and cut-off velocity than C cells, were found to receive their input from slowly conducting afferents while the afferents to C cells arose from the fast stream. A high proportion of both B and C cells received a monosynaptic or direct drive from the optic radiations and responded with multiple spiking to a single electrical shock. Multiple spiking was viewed as evidence of secondary pathways travelling via intermediate cortical neurons to contribute to the cell's input. An examination of the visual properties of all subclasses showed that the more obvious differences in receptive field properties were associated with the type of afferent coming from the LGN rather than with the ordinal or the laminar position of the cell. In this respect the cells in the C/B family resemble S cells, whose receptive field properties also show a dependence on the type of LGN input.

Animals↗