David G. Tieman

The blood supply of the cat's visual cortex and its postnatal development

We examined the blood supply of the cats visual cortex using alkaline phosphatase histochemistry to demonstrate the capillary endothelial cells. In the adult, layer 4 is marked by a band that is of obviously greater density, extends throughout areas 17 and 18, and ends abruptly at the 18/19 border. We quantified blood vessel density in area 17, observing a 23% greater density in layer 4 than in supragranular and infragranular layers. This difference reflects a laminar difference in metabolic rate. In three animals studied using the metabolic marker 2-deoxyglucose, layer 4 was 25% denser than the other layers. The band of greater density in layer 4 is not present in newborn kittens, but becomes apparent at about 5 weeks of age. Early in development, the endothelial cells form filopodia as the capillaries grow and branch. The density of blood vessels decreases slightly during the first week of postnatal life, but increases between 1 and 6 weeks of age, so that by 6 weeks, the blood supply of the visual cortex resembles that seen in the adult. This pattern resembles that of cortical metabolism seen with 2-deoxyglucose [J. Cereb. Blood Flow Metab. 11 (1991) 35], but the increase in vascular density precedes that in glucose metabolism.

Intracellular injection in fixed slices: obtaining complete dendritic arbors of large cells.

Intracellular injection of Lucifer yellow into fixed brain slices is widely used to demonstrate dendritic morphology. A major limitation of this technique is that large dendritic arbors are usually truncated at the cut surfaces. Here we describe modifications that allowed us to obtain complete dendritic arbors of large spiny stellate cells. Lucifer Yellow cadaverine biotin-X (LY-X) was injected into individual neurons within 300-1000 microm thick aldehyde-fixed slices of kitten visual cortex. Subsequently, the LY-X was histochemically reacted using standard ABC methods to obtain a permanent record of the injected cells. Dendrites, studded with a variety of dendritic spines, were darkly labeled and well defined against virtually no background. Somatic spines, dendritic varicosities and growth cones were common in the younger animals. Computer-assisted reconstructions demonstrated that, in older animals, the dendritic arbors of cells injected in 300 microm slices were truncated, whereas the arbors of cells injected deep within thick slices were complete. The modifications described here remove the most critical limitation of intracellular injection in slices, allowing quantitative analysis of even large dendritic arbors.

A computer-assisted video technique for preparing high resolution pictures and stereograms from thick specimens.

A computer-assisted video technique is presented for rapidly and accurately gathering, storing and depicting three-dimensional anatomical structures in thick specimens. Several optical sections through the specimen are combined to produce high-resolution photographs with essentially infinite depth-of-field. Further, the depth information implicit in the series of optical sections makes the creation of stereoscopic pairs relatively simple. The technique employs a real-time digitizing frame store and a computer. A video camera is attached to a microscope and successive optical sections are stored digitally as the plane of focus is systematically changed. After storage, the image of each optical section is enhanced to emphasize elements that are sharply focussed. The final two-dimensional image is generated by selecting for each point in the final picture the darkest grey value occurring at the corresponding point in any of the pictures in the through-focus series. A picture with essentially infinite depth-of-field is produced when points of correspondence in the series are determined by a ray passing normal to the plane of optical section. Right and left pictures for a stereoscopic pair are produced when points of correspondence are determined by a ray slanting either left or right of normal. This technique is illustrated with cobalt chloride-filled neurons from whole-mounted cricket ganglia, with HRP-filled axons from whole-mounted goldfish tectum, with Golgi-Kopsch-impregnated neurons from cat visual cortex, and with sections of cobalt chloride-filled antennal afferents in cricket.

Effects of exposure to lines of one or two orientations on different cell types in striate cortex of cat.

We raised cats using goggles to control early visual exposure (stripe‐rearing). Four conditions were used: (a), both eyes exposed to 0 degrees lines, (b), both eyes exposed to 90 degree lines, (c), one eye exposed to 45 degree lines, the other to 135 degree lines, (d), one eye exposed to 0 degree lines, the other to 90 degree lines. At the completion of the rearing, we recorded extracellularly from single cells in striate cortex (area 17) of these animals; circular statistics were used to analyse the distribution of the orientation preferences of neurones recorded. Exposure to either one or two stimulus orientations produced a significant bias in the distribution of the orientation preferences of cells recorded. We found no more non‐selective cells in cats exposed to one orientation (15%) than in cats exposed to two orientations (14%). We found about the same mean proportion of binocular cells in cats exposed to one orientation (27%) as in cats exposed to two orientations (24%). Cells were comparable in orientation selectivity in cats exposed to one orientation (mean half‐width at half‐height = 37 degrees) and in cats exposed to two orientations (mean half‐width at half‐height = 34 degrees). The effects of the rearing depended upon the receptive field properties of the cells. For cells with narrow receptive fields and low cut‐off velocities, the rearing produced no bias in the distribution of the orientation preferences; for all other groups of cells the rearing produced a bias toward the exposed orientation. In addition, the cells with narrow receptive fields and low cut‐off velocities were more finely tuned for orientation than the remaining cells. We conclude that there are cell types in the striate cortex of the cat which differ in their susceptibility to the effects of stripe‐rearing; these cell types can be discriminated on the basis of their physiological characteristics. We can compare these cell types with morphologically identified cell types that also differ in their susceptibility to the effects of stripe‐rearing.

N-acetylaspartylglutamate immunoreactivity in human retina

The acidic dipeptide N-acetylaspartylglutamate (NAAG), which satisfies many of the criteria for a neurotransmitter, was identified immunohistochemically within two human retinae. We observed NAAG immunoreactivity in retinal ganglion cells, their dendrites in the inner plexiform layer, and their axons in the optic nerve fiber layer. The vast majority of ganglion cells were stained, including displaced ganglion cells, ganglion cells of different sizes, and those whose dendrites arborized in the inner and outer sublaminae of the inner plexiform layer, that is, presumed On- and Off- cells. The sizes of labeled and unlabeled cells in the ganglion cell layer, as measured in counterstained material, suggest that the unlabeled cells consist primarily or only of displaced amacrine cells. We also saw immunoreactivity in small cells along the inner margin of the inner nuclear layer, presumably amacrine cells, and in small cells with little cytoplasm in the inner plexiform and ganglion cell layers, presumably displaced amacrine cells. These results are consistent with a role for NAAG in the transmission of visual information from the retina to the rest of the brain. Further, they are similar to those reported previously in rat, cat and monkey, thus demonstrating the relevance of previous studies to humans.

Binocular competition affects the pattern and intensity of ocular activation columns in the visual cortex of cats

The effect of binocular competition on the development of ocular activation columns in areas 17 and 18 of cats was studied using the 14C-2-deoxyglucose (14C-2DG) technique to visualize the regions of cortex activated by one eye in cats reared with equal alternating monocular exposure (equal AME), unequal AME, or monocular deprivation (MD). The average size of the ocular activation columns of the eye stimulated during administration of 2DG was positively correlated with the competitive advantage during rearing. In order of increasing percentage of visual cortex activated, the eyes were (1) deprived eye of MD cats, (2) less experienced eye of unequal AME cats, (3) either eye of equal AME cats, (4) more experienced eye of unequal AME cats, and (5) experienced eye of MD cats. In area 17, the shape of the activation columns also was affected by the relative experience of the eye. The columns of the deprived eye of MD cats were widest in layer IV, where they were about the same width as those of the less experienced eye of the unequal AME cats; in other layers they were narrower, sometimes disappearing altogether. In contrast, the activation columns of the less experienced eye of the unequal AME cats were about the same width in all layers. These results suggest that when one eye is placed at a severe disadvantage and receives no patterned input, as in MD, both geniculocortical connections and intracortical connections may be disrupted, but when the disadvantage is less, as in unequal AME, only the geniculocortical connections are disrupted. Binocular competition also affected the intensity of activation within columns in area 17. We used video densitometry to determine ratios of the amount of label in cortical and thalamic structures. Both the ratio of label in area 17 to that in the lateral geniculate nucleus (LGN) and the ratio of label in the binocular segment of area 17 to that in the monocular segment were significantly less for the deprived eye of MD cats than for any other group. These results suggest that even within the smaller activation columns, deprived geniculocortical afferents are relatively ineffective at driving cortical cells. This finding is consistent with earlier reports that the synapses from the deprived pathway are both morphologically abnormal and reduced in number. The cortical labeling for the less experienced eye of the unequal AME cats and the experienced eye of the MD cats were also significantly less than that in equal AME cats.(ABSTRACT TRUNCATED AT 400 WORDS)

Dark-rearing fails to affect the basal dendritic fields of layer 3 pyramidal cells in the kitten's visual cortex

The development of the cats visual cortex is incomplete at birth and is influenced by the cats early visual experience. We have previously demonstrated that the basal dendritic fields of layer 3 pyramidal cells grow substantially during the first 5 weeks after birth and that stripe-rearing affects their orientation. In this paper we determined the effects on these dendritic fields of visual deprivation (dark-rearing) during the first 3 months of life. The visual cortices of both normally reared and dark-reared cats were impregnated by the Golgi method, sectioned in the tangential plane and counterstained. The basal dendritic fields of completely impregnated pyramidal cells from layer 3 were drawn with the aid of a camera lucida, and compared in terms of number and length of primary dendrites, branching, size, elongation, and distribution of dendritic field orientations. Surprisingly, we observed no significant differences in any parameter measured. Thus, although stripe-rearing can specifically alter the orientation of the dendritic fields of the layer 3 pyramidal cells, and dark-rearing has been shown by others to alter the size of layer 4 stellate cells, dark-rearing failed to affect the dendritic fields of layer 3 pyramidal cells.

Behavioral and physiological effects of monocular deprivation: a comparison of rearing with diffusion and occlusion.

To compare the effects of monocular deprivation produced by occlusion and diffusion, 9 cats were reared in the dark from birth to 4 weeks of age, when they were brought out for periods of exposure with one eye covered. For 3 cats, the left eye was covered with a white diffuser while the right eye received 8 h of normal patterned exposure (MD/D-8). For 2 cats, the left eye was covered with a black occluder while the right eye was exposed for 8 h (MD/O-8), and for 4 cats, the right eye was covered with a black occluder while the left eye was exposed for 1 h (MD/O-1). Monocular exposure continued until the cats were 3 months old, when they began receiving binocular exposure. For all cats, the visual field of the exposed eye was normal. For the MD/D cats, the field of the pattern-deprived eye was restricted to the monocular crescent, and resembled the fields of monocularly lid-sutured cats. In contrast, for the MD/O cats, the field of the pattern-deprived eye was much larger, extending nearly to the midline. Thus, monocular diffusion produced more restricted visual fields than did monocular occlusion. Preliminary physiological data from the MD/D-8 and MD/O-8 cats showed that more cortical cells responded to stimulation of the pattern-deprived eye in the MD/O-8 cats than in the MD/D-8 cats. Taken together with our earlier results on cats reared with unequal patterned input to the two eyes, these results further suggest that there is a temporal-to-nasal gradient in sensitivity to the effects of an imbalance in stimulation to the two eyes.

Interocular reversal of up-down mirror images in pigeons

Abstract Both pigeons and chiasm-sectioned monkeys have been reported to show a paradoxical preference for the previously unrewarded stimulus when tested for interocular transfer of discriminations between left-right mirror images. We have induced such paradoxical transfer of up-down mirror images in two pigeons by training one eye fitted with goggles that occluded the upper half of the visual field and testing the other eye fitted with goggles that occluded the lower half. One other bird transferred veridically and six performed near chance. Performance on tests of interocular transfer with control patterns was significantly more veridical than performance with up-down mirror images. These results provide support for an explanation of paradoxical transfer based on asymmetries in the visual field that are reversed for the two eyes, and they argue against anatomical explanations based on commissural inversion of sensory or mnemonic information.

Chronic intraventricular administration of lysergic acid diethylamide (LSD) affects the sensitivity of cortical cells to monocular deprivation

In kittens, but not in adult cats, depriving one eye of pattern vision by suturing the lids shut (monocular deprivation or MD) for one week reduces the proportion of binocular units in the visual cortex. A sensitivity of cortical units in adult cats to MD can be produced by infusing exogenous monoamines into the visual cortex. Since LSD interacts with monoamines, we have examined the effects of chronic administration of LSD on the sensitivity to MD for cortical cells in adult cats. Cats were assigned randomly to one of four conditions: MD/LSD, MD/No-LSD, No-MD/LSD, No-MD/No-LSD. An osmotic minipump delivered either LSD or the vehicle solution alone during a one-week period of MD. The animals showed no obvious anomalies during the administration of the drug. After one week the response properties of single units in area 17 of the visual cortex were studied without knowledge of the contents of the individual minipumps. With the exception of ocular dominance, the response properties of units recorded in all animals did not differ from normal. In the control animals (MD/No-LSD, No-MD/LSD, No-MD/No-LSD) the average proportion of binocular cells was 78%; similar to that observed for normal adult cats. However, in the experimental animals, which received LSD during the period of MD, only 52% of the cells were binocular. Our results suggest that chronic intraventricular administration of LSD affects either directly or indirectly the sensitivity of cortical neurons to MD.