Biomedical subjects

B R Payne

Publications and source records attributed to B R Payne.

13 recordsLinked to original sources

PubMed1991

Visual-field map in the transcallosal sending zone of area 17 in the cat.

The representation of the visual field in the part of area 17 containing neurons that project axons across the corpus callosum to the contralateral hemisphere was defined in the cat. Of 1424 sites sampled along 77 electrode tracks, 768 proved to be in the callosal sending zone, which was identified by retrograde transport of horseradish peroxidase that had been deposited in the opposite hemisphere. The results show that the callosal sending zone has a fairly constant width of between 3 and 4 mm at most levels in area 17. However, the representation of the contralateral field at the different elevations of the visual field is not equal in this zone. The zone represents positions within 4 deg of the midline at the 0-deg horizontal meridian, and positions out to 15-deg azimuths in the upper hemifield and out to positions of 25-deg azimuth in the lower hemifield. The shape of the representation is approximately mirror-symmetric about the horizontal meridian, although there is a greater extent in the lower hemifield, which can be accounted for by the greater range of elevations (greater than 60 deg) represented there compared with the upper hemifield (approximately 40 deg). The representation in the sending zone of one hemisphere matches that present in the area 17/18 transition zone, which receives the bulk of transcallosal projections, in the opposite hemisphere. The observations on the sending zone show that callosal connections of area 17 are concerned with a vertical hour-glass-shaped region of the visual field centered on the midline. The observations suggest that in addition to interactions between neurons concerned with positions immediately adjacent to the midline, there are positions, especially high and low in the visual field, where interactions can occur between neurons that have receptive fields displaced some distance from the midline.

Animals↗

PubMed1991

Visual-field map in the callosal recipient zone at the border between areas 17 and 18 in the cat.

The representation of the visual field in the callosal fiber recipient zone of area 17 and the adjacent area 17/18 transition zone was determined in the cat. The callosal fiber recipient zone was identified by anterograde transport of tritiated amino acids that had been injected into transcallosal sending zone of the opposite hemisphere. Application of autoradiographic procedures revealed that transcallosal projections are densest in the area 17/18 transition zone, and that their density in area 17 diminishes within 1-2 mm of the transition zone. Of 980 sites sampled in the visual-field mapping part of the study, 507 proved to be in the zone demarcated by transcallosally transported label. In this zone, both ipsilateral- and contralateral-field positions are represented, and the representation of the visual field at the different elevations is not equal. When ipsilateral-field positions are considered, the representation extends to about 4 deg close to the visual axis, and to 15-20 deg at elevations greater than +/- 30 deg, the representation is approximately mirror-symmetric about the horizontal meridian, and the representation is concordant with that of the representation in the area 17 transcallosal sending zone of the opposite hemisphere.

Animals↗

PubMed1991

Complex transcallosal interactions in visual cortex.

Reversible inactivation by cooling of the transcallosal projecting neurons in areas 17 and 18 of one hemisphere bring about complex changes in the spontaneous and evoked activity of neurons in the callosal receiving zone of the opposite hemisphere. These changes include increases and decreases in evoked and spontaneous activities. Overall, 90% of neurons in layers II and III, 50% in layer IV, and 100% in layers V and VI were affected by the block of transcallosal input. The complexity of the changes was greatest in layers II and III, which are the major callosal recipient layers. The results indicate that many excitatory and inhibitory circuits are under the direct control of transcallosal fibers in the normally functioning brain.

Action Potentials↗

PubMed1990

Transcallosal non-pyramidal cell projections from visual cortex in the cat.

Non-pyramidal cells with transcallosal projections were identified in the area 17/18 border region of the cat by retrograde transport of horseradish peroxidase injected into border region of the opposite hemisphere. From several hundred neurons filled with a Golgi-like diaminobenzidine (DAB) reaction product, seven cells were identified by their radially oriented smooth dendrites as possible non-pyramidal cells. Following thin-sectioning and examination with the electron microscope, four of the neurons proved to be layer IV spiny stellate cells with incompletely filled dendritic spines, and two proved to be layer III pyramidal cells with an incompletely labelled apical dendrite and dendritic spines. The remaining neuron was a non-pyramidal cell whose essentially smooth dendrites were covered with synapses, and whose cell body formed both symmetric and asymmetric synapses with presynaptic terminals. To better assess how many non-pyramidal cells might be labelled, thin sections of the area 17/18 border were surveyed using material processed with tetramethylbenzidine (TMB), and another five labelled non-pyramidal cells with transcallosal projections were identified by the needle-like crystals of TMB reaction product they contained. During the study it became evident that both the DAB and TMB reaction products in the lightly labelled neurons tended to be associated with granules that are 0.5 microns or larger in diameter and that had the characteristics of lysosomes. These granules are also visible in the light microscope as dark puncta. The numbers of puncta in profiles of pyramidal and of non-pyramidal cells in layers II/III and IVa of the area 17/18 border region and in the control acallosal region of area 17 were counted and compared. These comparisons revealed that labelled transcallosally projecting non-pyramidal cells may constitute 10-32% of the non-pyramidal cell population at the area 17/18 border region. Similar values were also obtained for pyramidal cells in this region. Consequently, it is concluded that significant numbers of non-pyramidal cells have axons that project through the corpus callosum to the contralateral hemisphere.

Animals↗

PubMed1990

Function of the corpus callosum in the representation of the visual field in cat visual cortex.

Interposed between areas 17 and 18 of cat cerebral cortex is an architectonically distinct zone that represents a substantial portion of the ipsilateral visual field. The extent of this representation was assessed following severance of the corpus callosum by recording the activities of neurons and plotting their receptive fields. The results show that, even after the hemispheres are disconnected, the transition zone still contains a representation of part of the ipsilateral visual hemifield, albeit a reduced one. The extent of this representation is contracted towards the midline so that just one-half to one-third of the azimuths mapped in intact cats can be plotted. As in the intact cat, the width of the region represented is not equal at all elevations, for it extends to only -1.4 deg near the visual axis whereas it extends to -6.6 deg at an elevation of -20 deg. The retention of this representation after the transition zone neurons have been disconnected from the opposite hemisphere indicates that other pathways make a functional contribution to the representation of the ipsilateral field in this region of cortex.

Animals↗

PubMed1990

Representation of the ipsilateral visual field in the transition zone between areas 17 and 18 of the cat's cerebral cortex.

The representation of the visual field in the architectonically defined transition zone between areas 17 and 18 of cat cerebral cortex was assessed by recording the activities and plotting the receptive fields of neurons at 2327 sites along 148 electrode penetrations made in 19 cats. The results show that the transition zone contains a significant representation of the ipsilateral visual hemifield although not all elevations in the visual field are represented to the same extent. The shape of the field region represented resembles an hour glass, for the region represented is narrowest on the 0-deg horizontal meridian and increasingly wider at progressively more positive and negative elevations. When receptive-field centers are considered, the extent of the representation reaches to -2.5 deg on the 0-deg horizontal meridian and to 10 or more degrees towards the field periphery. When receptive-field areas are considered, the representation at the 0-deg horizontal meridian extends to -3.6 deg and to beyond 20 deg at other elevations. In contrast, the visual-field representations in flanking areas 17 and 18 are essentially limited to the contralateral hemifield. The presence of a distinct representation of part of the ipsilateral hemifield in the transition zone suggests that the zone may have connections distinctly different from those of the adjacent areas. The observations bear on the problems of understanding the visual pathways in hypopigmented cats and binocular disparity mechanisms about the midline.

Animals↗

PubMed1990

Receptive fields of neurons at the confluence of cerebral cortical areas 17, 18, 20a, and 20b in the cat.

The activity of neurons was recorded extracellularly at the junction of visual cortical areas 17, 18, 20a, and 20b in the cat. The receptive fields of these neurons were striking for their size, which ranged from a diameter of more than 40 deg of visual angle to the complete visual field of the contralateral eye. It is speculated that these large receptive fields may be generated by perturbations in the individual maps as the four areas merge together.

Animals↗

PubMed1989

Consequences of visual deprivation in the absence of binocular competitive mechanisms in Siamese cat area 17.

The Siamese cat is a mutant with abnormally crossed visual pathways, which provides a model for studying the effects of visual deprivation in the absence of binocular competitive interactions. Siamese cats are known to be resistant to the effects of monocular eyelid suture. To further explore the nature of this resistance, the receptive field properties of neurons in area 17 of monocularly (MD) and binocularly (BD) deprived Siamese cats were studied. Neither condition produced a loss of cortical responsiveness, which is a characteristic result of binocular deprivation in normally pigmented cats. Somewhat more units in the deprived hemisphere of MD Siamese cats were orientation-selective, and many more units were direction-selective than in BD Siamese cats. This difference may be due to an effect of visual attentional mechanisms, which can function in MD but not BD Siamese cats. To test whether the resistance to the effects of visual deprivation in Siamese cats might be a more general phenomenon. Siamese and normally pigmented cats were raised in an 8-Hz stroboscopically illuminated environment. Both groups showed a severe loss of direction selectivity. Some of the normally pigmented cats also showed a loss of binocularity, which appeared to be secondary to strabismus.

Animals↗

PubMed1989

Pyruvate carboxylase as a model for oligosubstituted enzyme-ligand conjugates in homogeneous enzyme immunoassays.

Theoretical models suggest that the detection capabilities of homogeneous enzyme immunoassays can be improved by the use of oligosubstituted enzyme-ligand conjugates rather than the traditionally used multisubstituted ones. The natural form of pyruvate carboxylase contains four covalently bound biotins (one per subunit) and it can be considered as an oligosubstituted enzyme-biotin conjugate. The enzyme is nearly completely inhibited in the presence of the natural binder for biotin, avidin. When the enzyme is incubated with avidin and free biotin, a competition occurs between the free biotin and the prosthetic group of the enzyme for the avidin. Steep dose-response curves are obtained by relating the observed inhibition to the free biotin concentration. By variation of the amount of avidin or enzyme in the assay, the detection limits of the system can be altered allowing for sensitive determinations over a wide range of biotin concentrations. Such data from real sample analysis of several vitamin supplements are reported.

Avidin↗

PubMed1989

Cytochrome oxidase patches and Meynert cells in monkey visual cortex.

In area 17 of Macaca mulatta large Meynert cells have their cell bodies located in the vicinity of the border between layers V and VI. When the distribution of these cell bodies is plotted in the tangential plane they are found not to be randomly distributed, but arranged in a sheet such that they outline holes or gaps. In sections of area 17 reacted for cytochrome oxidase, which indicates the relative level of metabolic activity in neurons and neuropil. Meynert cell bodies are clearly visible as large highly reactive neurons against a background of much lower reactivity. In reconstructions it is apparent that the holes or gaps in their distribution pattern lie beneath the high cytochrome oxidase reactive patches or blobs in layer II/III. In other words, the Meynert cell bodies lie predominantly beneath the low cytochrome oxidase reactive interpatch regions of layer II/III. On the basis of what is known about the functional connections of neurons in area 17 it is suggested that this arrangement of Meynert cells indicates that they are involved in the detection of movement in the visual field, a suggestion that is supported by the known projections of the Meynert cells to the superior colliculus and cortical area V5.

Animals↗

PubMed1989

Modular organization of ON and OFF responses in the cat lateral geniculate nucleus.

Multiunit mapping techniques were used to investigate whether or not units with ON- and OFF-center receptive fields occur in an orderly arrangement in the cat lateral geniculate nucleus. In the A layers, ON- and OFF-center sites were partially segregated in the dimension parallel to the laminae, with ON-center sites predominant at the dorsal surface of each layer and OFF-center sites relatively more numerous at the ventral surface of the layer. Microelectrode tracks were placed to traverse the visual field map in the nucleus parallel to projection lines, parallel to isoelevation lines and parallel to isoazimuth lines. The tracks placed parallel to projection lines contained long sequences of units of the same center sign, providing evidence that ON and OFF zones are organized in vertical modules which span much or all of the thickness of a layer. The tracks placed parallel to isoelevation and isoazimuth lines contained alternating clusters of ON- and OFF-center sites. These clusters were larger in the dimension representing isoelevation than in the dimension representing isoazimuth. Taken together, these results indicate that the cat lateral geniculate nucleus contains ON and OFF modules oriented perpendicular to the layers.

Action Potentials↗

PubMedDate not supplied

The visual map in the corpus callosum of the cat.

The corpus callosum conveys all the fibers that connect areas 17 and 18 in the 2 cerebral hemispheres of the cat. The purpose of the present study was to ascertain the organization of the visual field map described by these fibers in the corpus callosum. This was achieved by injecting anterograde and retrograde pathway tracers at known locations in the callosally connected zones of areas 17 and 18. The positions of the injection sites were varied systematically to include all visual field elevations represented along the marginal and posterolateral gyri. Overall, the results show (1) that callosal fibers projecting between the 2 marginal gyri, where the lower visual fields are represented, pass through the body of the corpus callosum; (2) that fibers connecting the junction of the marginal and posterolateral gyri in the 2 hemispheres, where central fields are represented, pass through the dorsal splenium of the corpus callosum; and (3) that fibers passing between the ventral portions of the 2 posterolateral gyri, where upper fields are represented, pass through posterior and ventral splenium. In addition, the density of visual fibers in the splenium is greater than in the body of the corpus callosum. Within the overall pattern, a finer arrangement exists, and it was possible, by comparison with the cortical visual field maps, to describe a map of visual field elevations in the corpus callosum. In this map, the representations of the different visual field elevations are not a simple reflection of the map in the cortex. The map of the lower fields contained in the body is spread out, whereas the map of the central and upper fields in the splenium is highly compressed. The high degree with which observations can be reproduced in different cats indicates that the map is stereotyped from one animal to another.

Animals↗

PubMedDate not supplied

Survival and death of neurons in cortical area PMLS after removal of areas 17, 18, and 19 from cats and kittens.

The long-term morphological consequences on laminar thickness and neuron survival were assessed in cerebral cortical area PMLS following excision of visual cortical areas 17, 18, and 19 from adult and adolescent cats and from neonatal kittens. Following excisions from kittens, layers III, V, and VI in area PMLS were reduced in thickness and there was a significant loss of neurons from layers III and VI. Following excisions from adolescent cats, layers V and VI were thinner than normal, whereas excisions from adult cats resulted in a detectable thinning only of layer V and no neuron loss from any layer. In a parallel study, the configuration of projections between area PMLS and areas 17, 18, and 19 in adult cats and newborn kittens was analyzed and related to the patterns of neuron survival and death in area PMLS following the excisions. In adult cats, projections from areas 17, 18, and 19 terminate in all layers, but they are heaviest into layer III in area PMLS. Layers III and VI contain the largest number of neurons that form the origin of the reciprocal projections back to areas 17, 18, and 19. In area PMLS of the newborn kitten, the laminar distribution of cells projecting to areas 17, 18, and 19 resembles the pattern in the adult cat, although the laminar pattern of the terminations is poorly differentiated. The pattern of cell death following the excisions from the kittens can be most easily explained on the basis of the mature configuration of the reciprocal pathways and on the neurons' maturational status at the time areas 17, 18, and 19 were removed. Thus, immature cortical neurons that are deprived of their targets and inputs undergo degenerative changes. These changes are most severe in infancy, and they can be predicted on the basis of the final patterns of projections the neurons would have developed with the damaged region. This loss of neurons in early-lesioned animals in regions of cortex anatomically connected to the damaged tissue implies that there may be cognitive deficits associated with the secondary degeneration in addition to the deficits caused by the primary lesion.

Aging↗