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Biomedical subjects

D Ehrlich

Publications and source records attributed to D Ehrlich.

At least 55 records · Page 3Linked to original sources
PubMed1988

Development of the supraoptic decussation in the chick (Gallus gallus).

The developing supraoptic decussation (SOD), a major interhemispheric tract in birds, has been implicated in both transfer of visual information and in the modulation of brain asymmetry. Moreover little is known of its morphology during development. We have examined the development of the chick SOD, which consists of three subregions; dorsal, ventral and subventral SOD. In the dorsal SOD the total number of fibres reach 968,000 on the 19th day of incubation (E-19), falling to 570,000 by the 8th day after hatching (P-8). In the ventral SOD, the number of fibres at E-19 reach 660,000, followed by a gradual reduction in their number to about 490,000 at P-22. In the subventral SOD the number of fibres estimated was 87,000 at E-15 falling to about 36,000 P-1. Compared with adult levels, there is, respectively, a drop in the number of fibres of 44%, 25% and 69% in the dorsal, ventral and subventral SOD during development. At E-19 in both the dorsal and ventral SOD there is qualitative evidence of axonal loss; disrupted axonal profiles, increased extracellular space and cells containing lysosomal cytoplasmic inclusions indicative of macrophages. Differences were also observed in the pattern of myelination, the dorsal, ventral and subventral SOD were shown to myelinate at different rates. Thus, in a single named tract, the SOD, there are major differences in the onset, rate and extent of fibre loss and myelogenesis within its three subregions. The functional implications of these differences are considered.

Animals↗
PubMed1988

Neurotoxic effects of kainic acid on developing chick retina.

The neurotoxic effects of kainic acid (KA) on developing neurons in the chick retina was investigated in an in vitro preparation. Eyecups from chick embroyos at 6 (E-6), 8, 10, 12, 14, 16, and 20 days of incubation and from chicks on day 1 posthatch (D-1) were exposed to different doses of KA for 30 min and then processed for light microscopy. Neurotoxic damage was evaluated by the presence of swollen cell bodies, containing pale cytoplasm and pyknotic nuclei. At E-8, amacrine cells first became sensitive to KA and displayed neurotoxic damage at a threshold concentration of 20 microM. Their sensitivity to KA increased over the following 4 days, so that by E-12 they attained a threshold sensitivity of 5.0 microM KA. At E-14, one third of the retinae showed amacrine cell damage at 0.5-2.0 microM KA, less than the threshold dose of 5.0 microM KA required at D-1. Bipolar cells first become sensitive to KA at E-12, at a threshold concentration of 5.0 microM. The threshold concentration decreased over the following 10 days: 2.0 microM at E-16, 1.0 microM at E-20, and 0.5 microM at D-1. At E-8 and E-10, horizontal cells were susceptible to a relatively high concentration of 80 microM KA. The sensitivity to KA is evident prior to the formation of photoreceptor input. These results indicate that amacrine and horizontal cells are susceptible to KA at an earlier age than bipolar cells. Both amacrine and bipolar cells exhibit an age-dependent relationship with the threshold concentration of KA required to cause neurotoxicity; in general, the older the embryo, the lower the dose of KA. However, the increased susceptibility of amacrine cells at E-14 suggests a transient hypersensitivity to KA during this period which may reflect an overproduction of the receptor-ionic channel complex necessary for KA to exert its effect.

Animals↗
PubMed1987

Distribution of substance P-like immunoreactive retinal ganglion cells and their pattern of termination in the optic tectum of chick (Gallus gallus).

Substance P-like immunoreactive (SP-LI) neurons were identified within the inner nuclear layer and ganglion cell layer of the chick retina. The SP-LI cells in the inner nuclear layer consisted of several subtypes of neurons, differing in soma size and dendritic arborization. In the ganglion cell layer a population of moderately labelled SP-LI neurons was also present. About 6-9 microns in diameter and spaced 50-80 microns apart, they formed a regular array across the entire retina, with a density of about 400 cells/mm2 in the superior temporal retina, declining to less than 100 cells/mm2 in the peripheral retina. The total number of SP-LI cells in the ganglion cell layer was approximately 75,000. Individual axons could be followed toward the optic nerve head. Lesions near the optic nerve head resulted in axotomy of ganglion cells within a limited portion of the retina. Two days of postaxotomy there were numerous SP-LI swellings in the proximal segments of axotomized axons. SP-LI neurons in the axotomized zone were larger, more numerous, and showed increased staining of their processes. Fourteen days following a retinal lesion, there was depletion of all SP-LI cells in the ganglion cell layer within the axotomized zone, but the SP-LI neurons in the inner nuclear layer were not noticeably affected. Following a localized injection of rhodamine-coupled latex beads into the optic tectum, a population of retinal ganglion cells (RGCs) in the contralateral retina was retrogradely labelled. Many of these cells also exhibited SP-like immunoreactivity. Examination of the optic tectum indicated the presence of SP-LI fibres in laminae 2-13 (nomenclature of Cajal: Histologie du Systeme Nerveux. Vol. 2. Paris: Maloine, '11), with immunoreactive terminal regions present mainly in laminae 2-4, 7, and 9-13. SP-LI cell bodies were found predominantly in laminae 10-12 and 13. Fourteen days following a retinal lesion, SP-LI processes and terminals were depleted from laminae 2 and 3. Immunoreactive cells and processes in the remaining laminae of the optic tectum were not noticeably altered. The present report confirms the existence of SP-LI retinal ganglion cells in the chick retina and demonstrates their contribution to lamina specific SP-LI arborization in the optic tectum.

Animals↗
PubMed1987

Intravitreal kainic acid severely reduces the size of the developing optic tectum in newly hatched chickens.

Following a single intravitreal injection of 200 nmol of kainic acid (KA) to newly hatched chickens, there are acute and long-term effects on retinal ganglion cells in the chicken retina. Thirty min after injection, most ganglion cells showed cytoplasmic vacuolization. However, 14 days later, most ganglion cell soma appeared normal. Almost 60% of the cells in the ganglion cell layer (GCL) were lost, suggesting that displaced amacrine cells and not more than 40% of the ganglion cells had been eliminated. Following intravitreal injection of wheat germ agglutinin conjugated to horseradish peroxidase 14 days after the KA lesion, the amount of HRP reaction product was reduced in all retinorecipient layers, especially layers IIc and IId, of the tectum contralateral to the KA-treated eye. Fourteen days after the injection of kainic acid, during which the control tecta grow appreciably, all the superficial layers of the tectum contralateral to the kainic acid-lesioned eye, especially layers IIc and IId, were smaller than in controls, and did not differ in size from those seen in tecta contralateral to cut optic nerves. It is not clear whether this is a result of a developmental failure, or a shrinkage, or a combination of these factors. These results suggest that subtypes of ganglion cells may have a disproportionate influence in the maintenance of the cytoarchitectural integrity in the optic tectum. Alternatively the removal of the OFF-bipolar cells and amacrine cells presynaptic to ganglion cells may decrease their metabolism, and restrict the supply of trophic influences to the developing tectal cells.

Aging↗
PubMed1987

Sequence analysis, cellular localization, and expression of a neuroretina adhesion and cell survival molecule.

A cDNA for purpurin, a secreted 20,000 dalton neural retina cell adhesion and survival protein, has been sequenced and expressed in mammalian cells. Purpurin mRNA is found in both embryonic and adult retina, but not the brain, heart, or liver. The protein is highly concentrated in the neural retina between the pigmented epithelium and the outer segments of the photoreceptor cells; it is synthesized by photoreceptor cells. The predicted purpurin sequence contains 196 residues, has approximately 50% sequence homology with serum retinol binding protein, and is a member of the alpha-2 mu-globulin superfamily. Purpurin binds retinol and may play a major role in retinol transport across the interphotoreceptor cell matrix.

Amino Acid Sequence↗
PubMed1987

Specific ganglion cell death induced by intravitreal kainic acid in the chicken retina.

In young chickens, intravitreal kainic acid (60 nmol) causes axonal and terminal degeneration in some retinorecipient areas of the chicken brain. The accessory optic nuclei are markedly affected, suggesting that the large displaced ganglion cells are destroyed by kainic acid, and a specific pattern of degeneration is caused in the optic tectum, which suggests that other minor ganglion cell groups may also be sensitive to intravitreal kainic acid.

Animals↗
PubMed1987

The avian pecten provides a potent substrate for growth and development of dissociated embryonic neural implants.

A cell suspension of the optic tecta of 3-day-old chick embryos was injected into the vitreal chamber of 2-day-old posthatch chicks. After a 14-21-day survival period, examination of eyeballs showed that all implants survived and, in 50% of cases, were attached to the pecten. The implants had proliferated and showed a laminated pattern of organization, with small cells in the superficial regions and large cells in the deep regions of the implant. The implants also contained a well-developed neuropil with mature synapses. The host retina was not affected by the presence of the implant. We suggest that the avian pecten represents a highly amenable structure for studies involving the response(s) by damaged retinae to neural implants.

Animals↗
PubMed1987

Folic acid protects chick retinal neurons against the neurotoxic action of excitatory amino acids.

In this study we have examined the neurotoxic effects of folic acid (FA), alone or in combination with selected excitotoxins using in vitro preparations of chick retina. Folic acid alone at concentrations of up to 10 mM had no effect. Co-incubation of 10 mM FA with 2 microM kainic acid (KA) protected all cell types susceptible to KA toxicity, namely amacrine and bipolar cells. At lower concentrations the protective effect of FA to susceptible cell types was found to be dose-dependent. The rank order of cells which are protected by FA, in order of the lowest concentration of FA required, was amacrine, inner bipolar and outer bipolar cells. The effect of FA against KA is a very weak one, as a 130-400-fold concentration of FA is required to protect amacrine cells from KA and a 1000-5000-fold dose of FA required to protect bipolar cells. However, FA (2 mM) also protects susceptible retinal neurons from the neurotoxic effects of 40 microM N-methyl-DL-aspartic acid (NMDLA) and 60 microM quinolinic acid (QUIN); only requiring respectively 50 and 33 times the concentration of FA. Interestingly 10 mM FA had little effect against 40 microM quisqualic acid (QUIS). Thus FA antagonizes the effects of KA, NMDLA, QUIN and to a small extent QUIS. Although its action may be mediated through several receptor types, FA appears to be a more potent antagonist of the N-methyl-D-aspartic acid (NMDA)-preferring than the KA-preferring or QUIS-preferring receptor.

Animals↗
PubMed1987

Retinal afferent and efferent connections in congenitally monophthalmic chicks.

The visual projections of the remaining eye of posthatch congenitally monophthalmic chicks were examined using wheat germ agglutinin-horseradish peroxidase. The morphology of the primary visual centres and their retinal projections contralateral to the injected eye were similar to those of normal chicks. The ipsilateral primary visual centres were smaller and less organized, yet all received retinal input. These ipsilateral retinal projections differ from those found in normal posthatch chicks [O'Leary et al.: Devl. Brain Res. 10: 93-109, 1983] in that they are more extensive and occupy some centres not previously reported to receive input. In the case of the ipsilateral isthmo-optic projection to the retina there was a substantial increase in the number of cells compared with normal chicks [O'Leary and Cowan: Devl. Brain Res. 12: 293-310, 1984]. A comparison of the extent of ipsilateral retinal afferents with that of normal chicks suggests that following loss of an eye two responses occur within the visual centres: in some centres there is a massive increase in the amount of ipsilateral terminals, whereas in others there is only a small increase. We propose that these responses are related to the intrinsic retinotopy within the visual centres. That is, highly retinotopic visual centres do not normally contain ipsilateral fibres, but following eye removal fibres from the ipsilateral eye are able to substantially innervate these regions. Presumably this effect is due to loss of the overriding influence of contralateral input, which would normally recognize and eliminate inappropriate ipsilateral fibres. In poorly retinotopic regions ipsilateral fibres are able to persist in both normal and monophthalmic chicks, as recognition cues may not be as precise as in highly retinotopic regions. Thus, the greater the retinotopic precision the finer the cues able to recognize ipsilateral fibres.

Animals↗
PubMed1987

Morphology of quisqualate-induced neurotoxicity in the chicken retina.

In this study, the acute neurotoxic effects of quisqualic acid on the chick retina were examined 2 hr or 2 days following intravitreal injections of either 100 or 200 nmol quisqualic acid (QUIS). Both doses resulted in marked nuclear pyknosis and cytoplasmic swelling of a large population of cells located in the inner aspect of the inner nuclear layer, consistent with amacrine cells. The associated swelling of the inner plexiform layer was primarily due to swollen processes of amacrine cells. Also affected was a row of cells located in the outer margin of the inner nuclear layer, consistent with horizontal cells. Ganglion cells developed hyperchromic, vacuolated cytoplasm. Bipolar cells appeared to be spared from damage at these doses. Electron microscopy of photoreceptor synapses revealed that QUIS was associated with a decrease in the relative frequency of long synaptic ribbons and an increase in the frequency of short ribbons, granular ribbons, "synaptic stalks," and paranuclear granules. After 2 days survival, most ganglion cells and some amacrine cells appeared normal, while degeneration was observed in a small number of photoreceptors. Remaining photoreceptor terminals appeared normal. QUIS may provide a useful tool in understanding the dynamics of normal photoreceptor ribbon turnover. The results are also discussed in relation to other known classes of excitatory amino acids.

Animals↗
PubMed1987

A comparative study in the use of closed-circuit television reading machines and optical aids by patients with retinitis pigmentosa and maculopathy.

Patients with retinitis pigmentosa (RP) who have insufficient vision to benefit from optical low vision aids are frequently helped by the closed-circuit television (CCTV) reading machines. RP patients' use of the CCTV is compared with that of patients with maculopathy (i.e. a group with a central scotoma only, is compared to a group which also has additional peripheral field loss), and with that of a "normal" control group. The performance of people with RP is improved by using white print on a black background, while macular degeneration subjects have no significant preference. Speed limits appear to be a function of restrictions imposed by the machine. Both groups frequently read faster with "optical aids".

Adolescent↗
PubMed1986

The influence of testosterone on the sex-dependent structural asymmetry of the medial habenular nucleus in the chicken.

The volume of the left and right medial habenular nuclei of male and female chicks was analysed for evidence of structural asymmetry. The influence of exogenous testosterone on habenular asymmetry was also examined. Male and female chickens were injected intramuscularly with either testosterone enanthate or an oil vehicle on day 2 (15 animals per group) and were perfused at days 5, 12, and 19 respectively. Paraffin sections (8 microns) containing the medial habenular nucleus were stained with cresyl violet and both left and right medial habenular nuclei were measured by planimetry. In control chicks, males had structural asymmetry at day 12, whereas females did not show any structural asymmetry. Testosterone did not appear to influence asymmetry in the male chick but induced structural asymmetry at all three ages in the female to favour the right hemisphere. This study demonstrates a role for testosterone in influencing structural asymmetry of a nucleus in the vertebrate brain.

Animals↗
PubMed1986

A note on the projection from the rostral thalamus to the visual hyperstriatum of the chicken (Gallus gallus).

The rostral thalamo-hyperstriatal projection in young chicks was examined following large injections of wheat germ agglutin labelled with horseradish peroxidase (HRP-WGA) into the hyperstriatum. Retrograde labelling of thalamic neurons was present in the dorsolateral thalamus, rostrolateral part (DLAlr) and dorsolateral thalamus, lateral part (DLL). There was no evidence of a contralateral projection from the lateral anterior thalamic nucleus (LA) to the posterior aspect of the visual hyperstriatum as reported recently by Boxer and Stanford (1985). Furthermore, a comparison of labelled neurons in the contralateral rostral thalamus following injections into either the left or right hyperstriatum revealed no difference in the number of neurons. The study could therefore not confirm the presence of an asymmetrical LA-hyperstriatal projection, as reported by the above authors.

Animals↗
PubMed1986

Role of the supraoptic decussation in the development of asymmetry of brain function in the chicken.

The supraoptic decussation plays an important role in the development of asymmetry of brain function for visual discrimination learning in the chicken. Lesioning the decussation on day 2 has no effect on the asymmetry normally revealed by unilaterally treating either the left or right forebrain hemisphere with cycloheximide on day 4 of life. However, the lesion removes the asymmetry revealed by cycloheximide treatment on day 8 and reverses that revealed by treatment on day 10, albeit to a lesser extent. The asymmetry of learning performance between the left and right eyes present in untreated chickens tested monocularly in the second week of life is also removed by lesioning the supraoptic decussation. Thus, in the first week of life functional asymmetry is present but not dependent on left-to-right side coupling via the supraoptic decussation. The difference between lesioning during the first and second week of life may relate to the relative degree of maturation in the supraoptic decussation.

Age Factors↗
PubMed1985

The effect of eye enucleation on the number of fibres in the supraoptic decussation of posthatch chicks (Gallus gallus).

In this study of the young chick we examine the effects of unilateral or bilateral eye enucleation on the number of axons in the supraoptic decussation, a major interhemispheric tract subserving visual function. On posthatch day 25, chicks underwent removal of either one or both eyes. After a survival period of 32 days, electron microscopic examination of the supraoptic decussation revealed a substantial loss of fibres. In the bilaterally enucleated group, a significant decrease in the number of axons occurred in both the dorsal and ventral aspects of the supraoptic decussation. The effect of unilateral enucleation was not as severe. The results indicate that enucleation of the precocial and functioning visual system of the chick leads to a transneuronal loss of axons. The degree of loss may reflect the amount of fibres in the crossed visual projection within the supraoptic decussation.

Animals↗
PubMed1985

Visual deficits following intraocular treatment of chicks with glutamate or kainic acid.

After intraocular treatment with kainate or glutamate, chicks were tested for visual discrimination performance, pecking aim, bead detection, optokinetic response and pupillary response. Kainate at an amount of 6 nmol per eye impaired performance in all of the tests except pupillary response. No effects were seen after 0.6 nmol of kainic acid. Glutamate at 6000 nmol impaired performance on all tests but the optokinetic and pupillary response. Although glutamate caused less severe deficits in visual behaviour than the high dose of kainate, cellular organization of the retina, at least in some regions, was more disrupted in these animals. Glutamate at 600 nmol caused a late onset defect in visual discrimination performance but no effects on optokinetic response.

Animals↗
PubMed1985

Sequential treatment with low doses of kainic acid alters sensitivity of retinal cell types.

Examination of chick retinae soon after treatment with a single intraocular injection of 5 nmol kainic acid revealed degenerative changes in a small population of neurons located in the outer aspect of the inner nuclear layer, consistent with either bipolar and/or horizontal cells. Damage to the outer plexiform layer was also present. After one week, affected retinae were clear of neuronal debris. Following a second, identical injection, one week after the first, there was degeneration of a different population of neurons confined to the inner aspect of the inner nuclear layer indicative of amacrine cells. As amacrine cells were the only cell type affected by the second injection, our results suggest that they are directly affected by the second dose of kainic acid. The pattern of neuronal damage following successive doses of kainic acid appears to be potentially useful technique in elucidating retinal circuitry.

Animals↗