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Biomedical subjects

J C Horton

Publications and source records attributed to J C Horton.

65 records · Page 4Linked to original sources
PubMed1984

Receptive field properties in the cat's area 17 in the absence of on-center geniculate input.

Most neurons of area 17 in the cat respond to both light and dark stimuli, and it is often assumed that these responses originate from the on-center and off-center cells, respectively, of the lateral geniculate nucleus. This has not been demonstrated experimentally, however. Whether the on and off pathways make unique contributions to some of the response properties characteristic of visual cortex, such as orientation selectivity, is also unknown. The aim of these experiments was to investigate these questions by inactivating the retinogeniculate on pathway. In cats in which D,L-2-amino-4-phosphonobutyric acid (APB) had been injected into one eye, we found that, in the geniculate layers driven by that eye, there were no cells with on-center responses (Horton, J. C., and H. Sherk (1984) J. Neurosci. 4: 374-380). The on pathway appeared to have been inactivated. To see how cortical receptive fields were affected, we examined 184 binocular cells in area 17 contralateral to the injected eye. Each cell still had a normal receptive field in the ipsilateral eye, and we compared the cell's response properties in that eye with those in the eye injected with APB to assess the drug's effects. Overall responsiveness in the injected eye was severely reduced, and responses to the onset of stationary light stimuli were almost entirely abolished. Responses to moving light edges were weak or absent in most cells but still strong in a few; simple cells tended to have more vigorous light edge responses than complex cells. The general reduction in responsiveness, and the specific reduction in light edge responses, indicated that the on and off pathways both contribute (directly or indirectly) to the responses of most cells in area 17. The remaining responses to light edges we think originated mainly from the on-surrounds of off-center geniculate cells. Responses to moving dark edges were somewhat depressed compared to those in the normal eye. There was, however, no systematic change in direction selectivity and no reduction in specificity for orientation or length. In general, receptive field properties remained surprisingly normal despite the conspicuous reduction in responsiveness.

Animals↗
PubMed1979

Non-retinotopic arrangement of fibres in cat optic nerve.

Fibres in the mammalian optic nerve are generally thought to be organised retinotopically. Recording electrophysiologically from the cat optic nerve, we found little evidence to support this notion, which led us to investigate the problem by anatomical methods. We made a localised injection of horseradish peroxidase into the lateral geniculate body of the cat, labelling a small clump of retinal ganglion cells and their axons in the optic nerve. These fibres, emanating from neighbouring cells in the retina, became widely scattered through the optic nerve, indicating that retinotopic order is essentially lacking.

Animals↗
PubMedDate not supplied

Warning on inaccurate Rosenbaum cards for testing near vision.

The Rosenbaum card is the most widely used handheld card for measuring near visual acuity. It was developed by Dr. J. George Rosenbaum of Cleveland, Ohio, for testing vision at the bedside of patients after cataract surgery. Millions of copies of the Rosenbaum card have been distributed free by drug companies or sold by medical supply firms. Most versions of the Rosenbaum card are inaccurate because the numbers are not scaled properly to the Snellen system. This article reviews the history of the Rosenbaum card, briefly summarizes issues raised by near vision testing, and provides standards for the manufacture of Rosenbaum near cards.

Equipment Design↗
PubMedDate not supplied

Pattern of ocular dominance columns in human striate cortex in strabismic amblyopia.

Previous experiments in animals have shown that early unilateral eyelid suture, a model of amblyopia induced by cataract, causes shrinkage of ocular dominance columns serving the deprived eye in the striate cortex. It is unknown whether the ocular dominance columns are affected in amblyopia produced by strabismus. We examined specimens of striate cortex obtained postmortem from a 79-year-old woman with a history of amblyopia in her left eye (20/800) since age 2 from accommodative esotropia. Four years prior to her death, she suffered an ischemic infarct of the left optic disc. This injury to the left optic disc made it possible to label the ocular dominance columns using cytochrome oxidase histochemistry. The pattern of ocular dominance columns was reconstructed throughout most of the right striate cortex. No shrinkage of columns was found. In the left cortex only half the column mosaic was labelled, because the patient had some residual vision in the temporal retina of her left eye. The columns within the labelled portion of the overall mosaic appeared normal. These findings indicate that shrinkage of ocular dominance columns does not occur in humans with amblyopia caused by accommodative esotropia. The ocular dominance columns are probably no longer susceptible to shrinkage at the age when most children with this condition begin to develop amblyopia.

Aged↗
PubMedDate not supplied

Pattern of ocular dominance columns and cytochrome oxidase activity in a macaque monkey with naturally occurring anisometropic amblyopia.

Unilateral eyelid suture, a model for amblyopia induced by congenital cataract, produces shrinkage of the deprived eye's ocular dominance columns in the striate cortex. Loss of geniculocortical projections are thought to account for the poor vision in the amblyopic eye. It is uncertain whether ocular dominance columns become shrunken in other forms of amblyopia. We examined the striate cortex in a pigtailed macaque with natural anisometropia discovered at age 5 months. Amblyopia in the left eye was documented at 1 year by behavioral testing. At age 6 years, the left eye was injected with [3H]proline and the striate cortex was processed for autoradiography and cytochrome oxidase (CO). The ocular dominance columns in layer IVc labelled with [3H]proline were normal. CO staining showed a novel pattern of thin dark bands in layer IV. These bands occupied the core zones at the center of the ocular dominance columns. Their appearance resulted from relative loss of CO activity along the borders of the ocular dominance columns, regions specialized for binocular processing. These findings indicate that not all forms of amblyopia are accompanied by shrinkage of ocular dominance columns. The unusual pattern of CO staining in layer IVc reflected a subtle alteration in metabolic activity which may have resulted from impairment of binocular function in anisometropic amblyopia.

Amblyopia↗
PubMedDate not supplied

Rapid identification of ocular dominance columns in macaques using cytochrome oxidase, Zif268, and dark-field microscopy.

Strabismus induces an abnormal pattern of alternating light and dark columns of cytochrome oxidase (CO) activity in macaque striate cortex. This pattern may arise because visual perception is suppressed in one eye to avoid diplopia. To test whether CO activity is reduced in the ocular dominance columns of the suppressed eye, we performed monocular enucleation to co-label the ocular dominance columns with Zif268 immunohistochemistry in seven exotropic adult Macaca fascicularis. This approach was unsuccessful, for two reasons. First, Zif268 yielded inconsistent labelling, that was usually greater in the enucleated eye's ocular dominance columns, but was sometimes greater in the intact eye's columns. Therefore, Zif268 was not a reliable method for identifying the ocular dominance columns serving each eye. Second, in three control animals we found that a brief survival period following monocular enucleation (needed for Zif268 levels to change) was long enough to alter CO staining. For example, a survival time of only 3 h was sufficient to induce CO columns, indicating that the activity of this enzyme fluctuates more rapidly than realized previously. Independent of these findings, we have also discovered that acute monocular enucleation produces a vivid pattern of ocular dominance columns visible in unstained or CO-stained sections under dark-field illumination. The ocular dominance columns of the acutely enucleated eye appear dark. This was verified by labelling the ocular dominance columns with [3H]proline. Dark-field illumination of the cortex after acute monocular enucleation offers a new, easy method for identifying the ocular dominance columns in macaques.

Animals↗
PubMedDate not supplied

Effect of early monocular enucleation upon ocular dominance columns and cytochrome oxidase activity in monkey and human visual cortex.

We examined cytochrome oxidase (CO) activity in striate cortex of four macaque monkeys after monocular enucleation at ages 1, 1, 5, and 12 weeks. These animal experiments were performed to guide our interpretation of CO patterns in occipital lobe specimens obtained from two children who died several years after monocular enucleation during infancy for tumor. In the macaques, the ocular dominance columns were labelled by injecting [3H]proline into the remaining eye. After enucleation at age 1 week, ocular dominance columns were eliminated in layer IVc(beta), resulting in a uniform pattern of autoradiographic label and CO staining. However, columns could still be seen in wet, unstained sections and with the Liesegang silver stain. Autoradiographs through layers IVc(alpha) and IVa showed residual, shrunken columns belonging to the missing eye, indicating that enucleation has less drastic effects in these layers. In the two human cases, enucleation at age 1 week also resulted in uniform CO staining in layer IVc. In the macaque after enucleation at age 5 weeks, ocular dominance columns belonging to the missing eye were severely narrowed, but still occupied 20% of layer IVc(beta). CO revealed wide, dark columns alternating with thin, pale columns in layer IVc(beta). The CO pattern and the columns labelled by autoradiography matched perfectly. After enucleation at age 12 weeks, only mild shrinkage of ocular dominance columns occurred. Enucleation at ages 1, 5, and 12 weeks did not alter the pattern of thin-pale-thick-pale stripes in V2. The main findings from this study were that (1) CO histochemistry accurately labels the boundaries of columns in layer IVc(beta) of macaque striate cortex after early monocular enucleation, making it a suitable technique for defining the critical period for plasticity of ocular dominance columns in human striate cortex; (2) enucleation causes more severe shrinkage of ocular dominance columns than eyelid suture; (3) early monocular enucleation obliterates ocular dominance columns in layer IVcbeta, but their pattern remains visible in wet sections and with the Liesegang stain; and (4) enucleation does not affect CO staining in V2.

Animals↗