Kazuo Wakakuwa

Quantitative analysis of a cross-sectional area of the optic nerve: A comparison between albino and pigmented rats

SummaryComparative studies were made on albino and gray rats by measuring several morphological characteristics seen in cross-sections of the optic nerve. The total cross-sectional area of the optic nerve was about 30% smaller in the albino than in the gray rat, while the fiber density was 1.4 times higher in the albino than in the gray rat. The estimated total fiber count was about the same in the two strains: around 100,000 to 110,000 fibers. Except for a few unmyelinated fibers (less than 1%) all fibers were myelinated. Axon diameters of the optic nerve fibers were distributed in smaller values for the albino than for the gray rat, though the overall diameter range was similar (0.2–3.0 μm). The myelin sheath was also thinner in the albino than in the gray rat.

Retinotopic organizations of the expanded ipsilateral projection to the rat's superior colliculus; variations along its rostrocaudal axis.

The retinotopic organization of the expanded projection to the ipsilateral colliculus was studied electrophysiologically in 12 adult albino rats with one eye removed at birth. For comparison, the contralateral projection was rather variable in the representation of the nasotemporal axis of the retina along the rostrocaudal dimension of the colliculus; on the other hand, the representation of dorsal-to-ventral retinal axis onto the mediolateral dimension of the colliculus was relatively stable.

Intraretinal axons of ganglion cells in the Japanese monkey (Macaca fuscata): conduction velocity and diameter distribution

In anesthetized and immobilized Japanese monkeys (Macaca fuscata), intraretinal conduction velocities of the ganglion cell axons were measured. The field potentials elicited by optic chiasm shocks consisted of fast and slow components with estimated conduction velocities of 1.19 and 0.72 m/s in recordings from the optic nerve fiber layer, and 1.65 and 1.00 m/s in recordings from the ganglion cell layer. Single cell recordings verified that the time course of the fast component corresponded to the antidromic spike latencies of Y-like cells, whereas that of the slow component covered the latency range of both X-like and W-like cells. In an electron microscopic study of the cross-sections of the intraretinal optic nerve fiber bundles, the axon diameter histograms of large samples (n = 3000-6000) all showed a unimodal distribution with a sharp peak at 0.3-0.6 micron and a long tail extending to 2-3 micron. The mean diameter was largest in the ventral and nasal bundles, smallest in the papillomacular bundle and intermediate in the dorsal, upper arcuate and lower arcuate bundles. However, diameter histograms of a small number of regional axons (n = 255-300) showed a broad tail distinct from the peak at 0.3-0.6 micron, enabling us to segregate a group of larger axons from the medium-sized to small axons. From such regional axon diameter histograms we estimated the mean relative occurrences of the larger axons (7.1-11.3%) and their mean diameters (0.9-1.3 micron). We further applied this relative frequency to the unimodal distribution of the histograms with larger samples in the upper and lower arcuate bundles and estimated the mean axon diameter of the large axons (1.1 micron) and that of the medium-sized to small axons (slightly below 0.5 micron). Finally, in studying the relation between axon diameter and conduction velocity in the two arcuate fiber bundles, we found it to be somewhat different from that previously reported for the cat retina.

Axonal projections of X-cells to the superior colliculus and to the nucleus of the optic tract in cats

Axonal projections of ganglion cells to the superior colliculus (SC) and to the nucleus of the optic tract (NOT) were re-examined physiologically in the cats retina. Taking care to minimize current spreads around the stimulating electrodes placed in the NOT or the SC, we reached a conclusion that a substantial proportion of X-cells project to the NOT while a small but definite proportion of them project to the SC.

Retinal inputs and laminar distributions of the dorsal lateral geniculate nucleus relay cells in the eastern chipmunk (Tamias sibiricus asiaticus)

SummaryRetinal inputs and their laminar distributions in the dorsal lateral geniculate nucleus (LGNd) of the eastern chipmunk (Tamias sibiricus asiaticus) were studied using histological and microelectrode recording techniques. A previous anatomical study (Fukuda et al. 1986a) indicated that the chipmunk LGNd had five laminae: contralaterally (contra) innervated lamina 1 and ipsilaterally (ipsi) innervated lamina 2 in its ventromedial part; laminae 3a (contra), 3b (ipsi) and 3c (contra) in its dorsolateral part. We have confirmed this finding in our present anatomical study and have also noted another ipsilaterally innervated thin lamina 0, medial to lamina 1. In our electrophysiological study, however, we were unable to record units from lamina 0 and to investigate it functionally. We recorded 232 units from laminae 1, 2 and the 3 complex, of which 95 were identified as Y-like, 46 as W-like, 15 as X-like, and 8 as mixed Y/W-like cells; the rest were either unclassified or visually unresponsive. In laminae 1 and 2, only Y-like and X-like cells were recorded, whereas in the laminae 3 complex W-like cells were recorded as well. The results suggest that the chipmunk laminae 1,2 and 3 complex correspond relatively well to the cat laminae A, A1 and C complex, respectively. In the chipmunk LGNd, however, there were more Y-like cells in laminae 1 and 2, and a few X-like cells of which some were color sensitive. Also, lamina 3a had a concentration of mixed-type cells with Y-like receptive field properties and W-like OX latencies. As for retinotopy, the dorsoventral transition of the contralateral visual field (laminae 1, 3a, 3c) is represented along the dorsoventral dimension of the chipmunk LGNd, whereas the temporonasal transition is represented in the rostrocaudal direction. Receptive field positions of the ipsilaterally innervated relay cells are limited to the central overlapping field of the contralateral visual fields of both eyes. Relay cells with visual fields having elevations of below -20° had relatively fast latency range and Ylike properties.

Distribution and soma size of ganglion cells in the retina of the eastern chipmunk (Tamias sibiricus asiaticus)

Topographic distribution and soma size of ganglion cells were studied in Nissl-stained, whole-mounted retinas of the eastern chipmunk. High density areas in the central retina were elongated horizontally, making up the visual streak. The total count of ganglion cells was estimated as 410,000. Throughout the retina soma size of ganglion cells showed a uimodal distribution, although a distinct population of large cells was found in the dorso-temporal periphery.

An electron microscopic analysis of the optic nerve of the eastern chipmunk (Tamias sibiricus asiaticus): total fiber count and retinotopic organisation

On the basis of light and electron microscopic observations of the cross-section, the total count of optic nerve fibers in the eastern chipmunk (Tamias sibiricus asiaticus) was estimated to be 5.65 x 10(5). Almost all the fibers were myelinated and only 0.9% were unmyelinated. Axon diameters of myelinated fibers showed a skewed unimodal distribution ranging from 0.2 to 3.6 microns (mean, 0.83) with the peak at 0.6-0.7 microns. Myelin sheath thickness positively correlated with the axon diameter. In the cross-section fiber density was highest in the naso-dorsal to the central part and lowest in the temporo-ventral part. Large axons are concentrated in the temporo-ventral part of the optic nerve, corresponding to the localisation of large ganglion cells in temporal crescent of the retina. A gross retinotopic organisation was verified among the optic nerve fibers in the cross-section after localised lesions by laser beam in the nasal and temporal periphery. However, when the retinal lesion was made in or around the central high density area, a non-retinotopic arrangement of the optic nerve fibers was suggested.

Ipsilateral retinal projections and laminations of the dorsal lateral geniculate nucleus in the eastern chipmunk (Tamias sibiricus asiaticus)

The ipsilateral retinal projections and laminations of the dorsal geniculate nucleus (LGNd) were studied in the eastern chipmunk (Tamias sibiricus asiaticus). From cyto-, myelo- and chemoarchitectures the LGNd was divided into the ventromedial and dorsolateral parts. Anterograde axonal transport of wheat germ agglutinated horseradish peroxidase (WGA-HRP) and Fink-Heimer staining after unilateral eye removal both indicated that the ipsilateral projection terminates in lamina 2 of the ventromedial part and in lamina 3b of the dorsalateral part. The remaining laminas, lamina 1 of the ventromedial part and laminas 3a and 3c of the dorsolateral part, receive afferents from the contralateral retina. It was suggested that laminas 1 and 2 of the chipmunks LGNd correspond to laminas A and A1 of the cats LGNd, and the lamina 3 complex to its lamina C complex.

Ipsilaterally projecting retinal ganglion cells in the eastern chipmunk (Tamias sibiricus asiaticus).

Ipsilaterally projecting ganglion cells were studied in whole-mounted retinas of the eastern chipmunk (Tamias sibiricus asiaticus) by labelling these cells with horseradish peroxidase (HRP) injected into the optic tract. The HRP-labelled cells were distributed exclusively in the temporal crescent which occupied about a quarter of the whole retinal area. The temporal crescent contained contralaterally projecting cells as well as ipsilaterally projecting cells. The soma size of ipsilaterally projecting cells, especially of those in the dorso-temporal crescent, was significantly larger than that of contralaterally projecting cells.

Retinal inputs to the geniculate relay cells in the eastern chipmunk (Tamias sibiricus asiaticus): a comparison between color and non-color sensitive cells

Single unit recordings were made from the relay cells of the lateral geniculate nucleus in the eastern chipmunk. Of 362 relay cells, 47 cells (13%) were classified as color sensitive and the rest as non-color sensitive cells. Non-color sensitive cells were further classified into 5 subclasses: off-phasic, on-phasic, on-off-phasic, on-tonic and uncommon types. Within the color sensitive cells there were 3 subclasses; blue excited and green inhibited (+B-G), blue inhibited and green excited (-B+G), and blue excited (+B) cells. Retinal afferents to color sensitive relay cells had the following characteristics: ganglion cells of their origin were distributed in the central high density areas of the retina and axonal conduction velocities were in the intermediate range, though they were somewhat slow in +B cells.