Biomedical subjects

A K Ball

Publications and source records attributed to A K Ball.

27 records · Page 2Linked to original sources

PubMed1986

Localization of 3H-GABA, -muscimol, and -glycine in goldfish retinas stained for glutamate decarboxylase.

Glutamic acid decarboxylase (GAD), the synthesizing enzyme for the neurotransmitter GABA, has been localized in goldfish retina using a new antiserum. We observed at least six types of GAD-immunoreactive amacrine cells, one of which was large and pyriform (Ab type). In addition, immunoreactive synaptic terminals were located throughout the inner plexiform layer (IPL). Amacrine cells that were GAD-immunoreactive also had high-affinity uptake mechanisms for both 3H-GABA and 3H-muscimol that were detectable autoradiographically. Type Ab pyriform amacrine cells were heavily labeled because of 3H-GABA uptake and were GAD-immunoreactive. Other types of GAD-immunoreactive amacrine cells, including a subpopulation of Ab amacrines, were lightly labeled because of 3H-GABA uptake. Because the same neurons that were GAD-immunoreactive also accumulated 3H-GABA and 3H-muscimol, these three are appropriate markers for GABAergic cells in the goldfish retina. However, the uptake of 3H-muscimol by many non-GAD-immunoreactive cells, detectable at longer autoradiographic exposure times, indicates that this label must be used with caution. Thirty percent of goldfish retinal amacrine cells are GABAergic, and their processes are distributed throughout all levels of the IPL. Few GAD-immunoreactive amacrine cells accumulated 3H-glycine, so the goldfish retina contains distinct populations of glycinergic and GABAergic amacrine cells.

Animals↗

PubMed1985

The development of auditory temporal acuity in children.

The development of auditory temporal acuity was studied in 56 children aged 6-12 years and compared with that of 8 adults. Acuity was measured by determining the minimum detectable duration of a brief cessation in a noise band with the 2-alternative forced-choice method. For detection of gaps in a broadband noise, acuity improved significantly with age and reached adult values by 11 years. The minimum detectable duration was significantly shorter at higher levels of the noise. For narrow-band noises, acuity also improved significantly with age and depended on the center frequency of the band. The improvement in temporal acuity with age was attributed to the development of sensory processes and not to age-related changes in nonsensory factors.

Adult↗

PubMed1984

The goldfish nervus terminalis: a luteinizing hormone-releasing hormone and molluscan cardioexcitatory peptide immunoreactive olfactoretinal pathway.

Antisera to two putative neurotransmitters, luteinizing hormone-releasing hormone (LHRH) and molluscan cardioexcitatory tetrapeptide (H-Phe-Met-Arg-Phe-NH2; FMRF-amide), bind specifically to neurites in the inner nuclear and inner plexiform layers of the goldfish retina. Retrograde labeling showed that intraocular axon terminals originate from the nervus terminalis, whose cell bodies are located in the olfactory nerves. Double immunocytochemical and retrograde labeling showed that some terminalis neurons project to the retina; others may project only within the brain. All terminalis neurons having proven retinal projections were both LHRH- and FMRF-amide-immunoreactive. The activity of retinal ganglion cells was recorded with microelectrodes in isolated superfused goldfish retinas. In ON- and OFF-center double-color-opponent cells, micromolar FMRF-amide and salmon brain gonadotropin-releasing factor ( [Trp7, Leu8] LHRH) caused increased spontaneous activity in the dark, loss of light-induced inhibition, and increased incidence of light-entrained pulsatile response. The nervus terminalis is therefore a putatively peptidergic retinopetal projection. Sex-related olfactory stimuli may act through it, thereby modulating the output of ganglion cells responsive to color contrast.

Animals↗

PubMed1983

Diurnal variations in the photoreceptor synaptic terminals of the newt retina.

Newt photoreceptor synaptic terminals undergo a variety of morphological changes over a 24-hr (LD 12:12) cycle. During the day, dense-cored synaptic vesicles were found to increase in number and accumulate near the synaptic lamellae; during the dark phase, the dense-cored vesicles decreased in number, while large clear vesicles and profiles of smooth endoplasmic reticulum increased in frequency. The most marked change in photoreceptor synaptic terminal morphology occurred after 10 hr of darkness, at 0730 hr. At this time, photoreceptor synaptic terminal cross-sectional area was found to increase dramatically. Morphometric analysis showed that the number of synaptic vesicles in these terminals remained constant throughout the day, as did the perimeter of photoreceptor terminal profiles. The observed increase in area of synaptic terminals at 0730 hr was found to be due to a decrease in the folding of the terminal plasma membrane. Qualitative observations showed endocytosis to be occurring at a rapid rate at this time as well; and since the number of synaptic vesicles and terminal perimeter did not change, exocytosis of synaptic vesicles was assumed to be occurring at an equally rapid rate. These findings support an extension to the hypothesis of Monaghan and Osborne (1975), suggesting that photoreceptor synaptic vesicles become "supercharged" with transmitter substance in the light.

Animals↗

PubMed1983

Displaced amacrine and ganglion cells in the newt retina.

The inner nuclear layer and ganglion cell layer of the newt retina contain taurine- and GABA-accumulating cells which are located immediately adjacent to the inner plexiform layer. Transport studies with horseradish peroxidase (HRP) indicate the presence of displaced ganglion cells within the inner nuclear layer of the retina. These are more numerous at the periphery of the retina and constitute about 2.5% of the retinal ganglion cells. Autoradiography, combined with HRP-transport studies, indicate that the taurine-accumulating cells in the ganglion cell layer of the newt retina are not 'true' ganglion cells, but may be displaced amacrine cells. Counts of axons in the optic nerve compared with cell bodies in the ganglion cell layer, demonstrate that only 50-60% of the cells in the ganglion cell layer of the newt retina are truly ganglion cells.

Animals↗

PubMed1983

Identification of sulfur groups in the outer plexiform layer of the newt retina.

The staining of newt photoreceptor synaptic vesicles with the zinc iodide-osmium (ZIO) method can be abolished by prior incubation in amphibian Ringer's containing 0.1 M-N-ethyl maleimide which specifically blocks -SH groups. The existence of high concentrations of sulfur groups in the outer plexiform layer of the newt retina has been further demonstrated with mercury orange and a newly synthesized fluorescent thiol probe, DACM. The reason why such high concentrations of -SH groups are present within photoreceptor synaptic vesicles is unclear, however, it is possible that ZIO stains the photoreceptor neurotransmitter itself.

Animals↗

PubMed1981

An alternative to the flat substrate method of preparing electron microscope autoradiographs.

Difficulty with flat substrate methods of preparing electron microscope autoradiographs has prompted reconsideration and refinement of a technique in which an electron microscope grid is placed beneath the specimen prior to dipping. This technique avoids the problems commonly associated with the direct application of emulsions to specimen grids, and should be considered as an alternative to flat substrate techniques when difficulty with these methods is encountered.

Animals↗

PubMedDate not supplied

Neuromodulation of pigment movement in the RPE of normal and 6-OHDA-lesioned goldfish retinas.

The role of dopamine as the endogenous signal-initiating light-dependent changes in the distribution of pigment granules in goldfish retinal pigment epithelium was investigated. In normal retinas, light adaptation resulted in the dispersion of pigment granules. This effect of light was mimicked by the intraocular injection of dopamine or serotonin, which is thought to increase endogenous dopamine release, into dark-adapted eyes. The effect of light, dopamine, or serotonin on dark-adapted retinas was blocked by the dopamine receptor antagonists haloperidol and sulpiride. However, lesioning the endogenous source of retinal dopamine, by prior intraocular injection of 6-hydroxydopamine (6-OHDA), did not block the dispersion of pigment granules in light-adapted retinas. No significant differences in pigment dispersion were noted between unlesioned and lesioned light- or dark-adapted retinas. However, the effect of light on pigment dispersion was no longer blocked by haloperidol or sulpiride in 6-OHDA lesioned animals. Dopamine and serotonin mimicked the effect of light when injected into lesioned dark-adapted eyes, but their effects were also not blocked by haloperidol or sulpiride. These results suggest that dopamine, acting on D2 receptors, is sufficient to induce pigment migration in unlesioned animals. In 6-OHDA-lesioned animals, however, pigment migration is mediated by a receptor mechanism other than D2.

Animals↗

PubMedDate not supplied

Co-localization of neurotensin-like immunoreactivity and 3H-glycine uptake system in sustained amacrine cells of turtle retina.

Amacrine cells are axonless intrinsic neurones of the vertebrate retina which have cell bodies in the proximal inner nuclear layer and processes contributing to the synaptic network of the inner plexiform layer. They receive input from bipolar, interplexiform and other amacrine cells, and synapse onto these and ganglion cells. Amino acid and monoamine transmitters are found in most retinal neurones, but peptide transmitters are exclusively located in amacrine cells. Only one neuropeptide, amino acid or monoamine transmitter exists in any single amacrine cell population. Coexistence of neuropeptides with classical transmitters has been demonstrated histologically in many neurones of the central nervous system, but the physiological relevance of these findings is unknown. We report here evidence of such coexistence in retinal amacrine cells of the turtle, Pseudemys scripta elegans. Using combined immunocytochemistry and autoradiography, we have localized both neurotensin-like immunoreactivity and a high affinity uptake system for 3H-glycine to the same amacrine cell, implying that this cell type may use both substances as neurotransmitters. We also present electrophysiological evidence that this type of amacrine cell responds to photic stimulation with a sustained and graded membrane depolarization.

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