Biomedical subjects

S W Bolden

Publications and source records attributed to S W Bolden.

5 recordsLinked to original sources

PubMed1993

Organisation of the thalamofugal visual projections in chick embryos, and a sex difference in light-stimulated development.

The organisation of the thalamofugal visual projections to the forebrain has been determined in chick embryos by injecting retrograde tracers (true blue and either fluorogold or diamidino yellow) into the left or right hyperstriatum. The embryos were injected on day 19 of incubation and allowed to survive for a further 4 days. Unlike chicks posthatching, the embryos were found to have no asymmetry of the thalamofugal visual projections, irrespective of whether they had received 24 h of light exposure prior to injecting the tracer dyes or had been kept in darkness. The light exposure did, however, lead to a significant increase in the ratio of the number of cell bodies in the thalamus labelled contralaterally to the injection site to the number labelled ipsilaterally (CI ratio) in male embryos. The elevation of the CI ratio appeared to be due to an increase in the number of contralateral projections from each side of the thalamus to the hyperstriatum on the other side of the forebrain. Thus, growth of these visual projections is promoted by light experience during the later stages of embryonic development. Most likely, light stimulation promotes increased arborisation of end-terminals in the hyperstriatum. Development of the thalamofugal visual projections in female embryos was not influenced by exposure to light, a finding consistent with earlier studies demonstrating that circulating oestrogen either inhibits or over-rides the sensitivity of these developing neurones to light stimulation.

Animals↗

PubMed1993

Visual dysfunction in the spontaneously hypertensive rat.

We report two forms of visual defect in the spontaneously hypertensive rat (SHR) compared to its normotensive control strain (WKY). Ten-month-old male SHR and WKY were tested for intensity discrimination ability using a Y-maze and food reward. The SHR took more trials in the acquisition phase of the task using white light. In the test phase, in which the white light intensity difference was reduced, there was no significant difference in performance between SHR and WKY. Also, there was no significant difference between the strains when red light was used. The defect in SHR occurred in the blue range of the spectrum. Using blue light, the performance of SHR declined significantly at an intensity difference of 1.15 lux, whereas the performance of WKY did not decline significantly until the difference reached 0.01 lux. The defect in SHR for intensity discrimination was not related to cataract formation, but we detected a strain difference in the nuclei of the photoreceptor cells. Thus, this visual dysfunction may involve the rod photoreceptors. Further testing revealed a deficit in visual acuity in SHR aged 40-66 days, prior to the development of hypertension. Thus, the visual dysfunction of SHR is not secondary to their development of hypertension, but rather a discrete characteristic of the strain.

Animals↗

PubMed1992

Structural asymmetry in the thalamofugal visual projections in 2-day-old chick is correlated with a hemispheric difference in synaptic density in the hyperstriatum accessorium.

Differences in visual discrimination ability between the left and right eyes of chicks, which are most prominent in young males, may result from a structural asymmetry in the organization of the visual projections from the thalamus to the visual Wulst. This asymmetry in projections is no longer present by 21 days in males when the contralateral projections from the right thalamus to the left hyperstriatum have developed. Since the asymmetry of the thalamo-hyperstriatal system results in a differential input of fibres to regions of the hyperstriatum which in turn project to the hyperstriatum accessorium (HA), one of the major differences expected within this region would be an asymmetry in the numerical density of synapses (Nv.syn/microns3). When this was examined in the hyperstriatum accessorium of 2-day-old male chicks, the density of synapses in the right HA was found to be significantly higher (22%, P less than 0.05) than in the left HA. The consequences of this asymmetry in synaptic density in the HA could be widespread and influential within the chick visual system.

Animals↗

PubMed1991

Light-dependent development and asymmetry of visual projections.

The projections from thalamus to visual Wulst in chicks are asymmetrical and their development is determined by exposure to light just before and after hatching. The asymmetry results from the orientation of the embryo in the egg, the left eye being occluded and not the right. We have shown that this asymmetry can be eliminated by incubating the embryos in darkness or light so that both eyes receive the same stimulation.

Animals↗

PubMed1990

Neonatal stress and long-term modulation of GABA receptors in rat brain.

Neonatal handling, known to have long-term effects on behaviour and neuroendocrine responses to acute stress, has been found to produce a long-term change in gamma-aminobutyric acid (GABA) receptor binding (Bmax) in whole-brain membranes of spontaneously hypertensive (SHR) and Wistar-Kyoto (WKY) rats. A significant 10% increase in the binding of [3H] GABA to receptors was evident more than 100 days after handling. There were no differential effects of handling between these two strains, but there was a whole-brain deficit in GABA receptor binding in SHR as compared to WKY animals. Adult corticosterone levels did not correlate with GABA receptor binding.

Analysis of Variance↗