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Biomedical subjects

D A Redburn

Publications and source records attributed to D A Redburn.

At least 37 records · Page 2Linked to original sources
PubMed1987

Synaptosomal neurotransmitter uptake systems in the retina and brain nuclei of light- and dark-adapted rabbits.

High affinity uptake rate for [14C]aspartate and [3H]dopamine by retinal homogenate (H), Pl (outer plexiform layer, OPL), and P2 (inner plexiform layer, IPL) retinal synaptosomal fractions were not significantly different between light- and dark-adapted rabbits. However, there were significant increases in the dark in [3H]gamma-aminobutyric acid high affinity uptake rate by retinal H and P2 but not that of Pl. There was a significantly higher [3H]choline uptake rate by retinal H, Pl and P2 in the dark-adapted compared to light-adapted rabbits, but there was no significant change in this rate for synaptosomal fractions from the lateral geniculate body, superior colliculus, visual cortex (VA I + II), caudate nucleus (CN) and hippocampus (HP). Data obtained in this study, along with reports of others, indicate that the change in retinal neurotransmission functions may not always be parallel with the change in high affinity uptake rates of neurotransmitters by retinal synaptosomal fractions. Data obtained indicate an increase in retinal cholinergic neuronal activities in the dark and indicate that optic nerves are not cholinergic and cholinergic neurons in brain nuclei, such as VA, CN and HP, are not significantly influenced by optic nerve inputs in light and dark conditions.

Acclimatization↗
PubMed1987

An indoleamine system in photoreceptor cell terminals of the Long-Evans rat retina.

Uptake of 3H-serotonin is localized to the outer plexiform layer in Long-Evans rat retinas. Autoradiographic accumulation is seen only after in vitro incubation in the light, with retinas isolated from the underlying sclera. Potassium stimulates the release of 3H-serotonin. In this species, amacrine cells do not accumulate these compounds; thus the outer plexiform layer appears to be the only site of uptake and release of this indoleamine. The age-related loss of 3H-serotonin accumulation in the outer plexiform layer of retinal dystrophic rats coincides temporally with the spontaneous degeneration of photoreceptor cells that occurs in this species. Electron-microscopic autoradiography of 3H-serotonin accumulation further confirms that uptake is localized to rod and cone terminals in the outer plexiform layer. The specific accumulation of indoleamines into rod and cone terminals that is observed in the light but is absent in darkness suggests that indoles have an important physiological role in photoreceptors.

5,7-Dihydroxytryptamine↗
PubMed1986

Glutamate receptor agonists release [3H]GABA preferentially from horizontal cells.

A total of 5-6 different cell types in vertebrate retinas accumulate [3H]gamma-aminobutyric acid (GABA). In frog retina, specific populations of cells in the horizontal, amacrine and ganglion cell layers are labeled autoradiographically after a 15-min in vitro incubation with [3H]GABA. Cells which may be bipolar or interplexiform cells are also labeled. Similar autoradiographic patterns are observed in chick retina except for the absence of labeled bipolar or interplexiform cells. In rat retinas, [3H]GABA uptake is limited primarily to Muller and amacrine cells. Depolarizing glutamate receptor agonists (glutamate, aspartate and kainic acid) applied in an in vitro perfusion system, stimulated massive release of [3H]GABA from frog and chick retina but not from rat retina. Under these conditions, autoradiographic labeling of horizontal cells was virtually depleted, while labeling of other cell types remained robust. In contrast, potassium caused release of the label from all 3 types of retina, and loss of autoradiographic labeling occurred uniformly in all cell types. We conclude that [3H]GABA-accumulating horizontal cells possess depolarizing glutamate receptors and that activation of these receptors leads to a release of GABA stores. On the other hand, Muller cells and the various subclasses of [3H]GABA-accumulating amacrine, bipolar and/or interplexiform cells, do not release GABA in response to glutamate receptor stimulation and thus appear to be relatively insensitive to excitatory amino acids.

Animals↗
PubMed1986

Postnatal development of 3H-GABA-accumulating cells in rabbit retina.

Light and electron microscopic autoradiography demonstrates that 3H-GABA is accumulated by horizontal cells in neonatal rabbit retina but not in the adult. A specific population of horizontal cells appears to be mature at birth and they avidly accumulate 3H-GABA during a 15-minute incubation period in vitro. Uptake into horizontal cells is not observed after the fifth postnatal day; 3H-GABA-accumulating horizontal cell bodies and their processes are the first identifiable components that clearly mark the future location of the outer plexiform layer at birth and as such, may be considered pioneering elements. Our observations raise the interesting possibility that the pioneering horizontal cell may provide structural and/or chemical factors necessary for the subsequent development of the outer plexiform layer of the retina. Labeling patterns of other retinal cells also show varying degrees of change during development. A population of amacrine cells accumulate 3H-GABA at birth. These cells show little change in their morphological or 3H-GABA uptake properties from birth to adulthood. Müller cells show weak accumulation of 3H-GABA at birth. Subsequent to this time, labeling of Müller cells is significantly more robust, resulting in Müller cell domination of retinal autoradiographic patterns in more mature retinas. Every cell body in the ganglion cell layer accumulates 3H-GABA at birth. The number of labeled cells declines during postnatal development, resulting in a very limited adult population. We conclude that the ability of retinal cells to accumulate 3H-GABA does not remain constant during postnatal development; rather each cell population displays a unique maturation sequence that results in a dramatic developmental shift in the number and types of GABA-accumulating cells present in the retina.

Age Factors↗
PubMed1985

Light evoked release of acetylcholine in response to a single flash: cholinergic amacrine cells receive ON and OFF input.

By pharmacologically blocking the inhibitory inputs to the cholinergic amacrine cells of the rabbit retina, we have been able to detect the light-evoked release of ACh in response to a single flash. Under these conditions ACh is released equally at light ON and light OFF. This implies that: the cholinergic amacrine cells receive ON and OFF input; they respond to light with depolarizing transients; and the inputs to this system have a basic symmetry.

Acetylcholine↗
PubMed1985

Analysis of pre- and postsynaptic factors of the serotonin system in rabbit retina.

[3H]Serotonin is accumulated by a specific set of amacrine cells in the rabbit retina. These cells also accumulate the neurotoxin, 5,7-dihydroxytryptamine, and show signs of necrosis within 4 h of in vivo exposure to the drug. Biochemical analysis of [3H]serotonin uptake reveal a sodium- and temperature-dependent, high affinity uptake system with a Km of 0.94 microM and Vmax of 1.08 pmol/mg protein/min. [3H]Tryptophan is also accumulated in rabbit retinal homogenates by a high affinity process. Accumulated [3H]serotonin is released in response to potassium-induced depolarization of intact, isolated retinas. In vitro binding studies of rabbit retinal homogenate membranes demonstrate specific sets of binding sites with characteristics of the postsynaptic serotonin receptor. These data strongly suggest that rabbit retina contains virtually all of the molecular components required for a functional serotonergic neurotransmitter system. The only significant difference between the serotonin system in rabbit retina and that in the well-established serotonin transmitter systems in nonmammalin retinas and in brains of most species is the relatively low concentration of endogenous serotonin in rabbit retinas, as demonstrated by high-performance liquid chromatography, histofluorescence, or immunocytochemistry.

5,7-Dihydroxytryptamine↗
PubMed1984

Kainic acid-induced denervation supersensitivity of nicotinic, cholinergic receptors in ganglion cells of the rat retina.

The rat retina contains both nicotinic and muscarinic cholinergic receptor sites as demonstrated by specific, high affinity binding of the nicotinic ligand, [3H]-alpha-bungarotoxin, and the muscarinic ligand, [3H]-quinuclidinyl benzylate. Seven days after an intraocular injection of 5 nmol of kainic acid, nicotinic binding was increased three-fold. We suggest that nicotinic sites may be located on ganglion cells because previous studies have shown that many ganglion cells are spared after kainic acid treatment and in fact, have an increased physiological response to ACh under these conditions. The increase in nicotinic sites may reflect a supersensitivity response to the loss of acetylcholine input after the kainic acid lesion. In contrast, muscarinic binding was decreased by 70% after kainic acid treatment. These data suggest that muscarinic sites are located on amacrine cells since these cells are destroyed by kainic acid treatment and some are known to be cholino-receptive. Some of the retinal muscarinic sites may function as inhibitory autoreceptors which regulate acetylcholine release from cholinergic amacrine cells.

Acetylcholine↗
PubMed1984

Serotonin systems in the inner and outer plexiform layers of the vertebrate retina.

In retinas of certain nonmammalian vertebrate species such as frog, pigeon, and chick, serotonin appears to function as the neurotransmitter of a specific population of amacrine cells. Neurochemical and morphological studies have demonstrated high endogenous levels of 5-hydroxytryptamine (5-HT) as well as uptake, release, and receptor-binding activity restricted to the inner plexiform layer. In retinas from most mammalian species, uptake, release, and receptor-binding activity have also been localized to amacrine cell terminals in the inner plexiform layer. However, serotonin content in mammalian retinas is low, and attempts to localize the endogenous store of 5-HT have failed. Thus the status of serotonin as a candidate in mammalian retina is still open to question. Our more recent studies have revealed a light-sensitive serotonin system associated with photoreceptor terminals in retinas of Long-Evans rats. Uptake, synthesis, and release of [3H]serotonin have been demonstrated. Endogenous levels of 5-HT decrease in the dark and increase in the light. Electrophysiological studies are needed to illucidate the functional role(s) of serotonin within retinas of different species.

Animals↗
PubMed1984

Permanent alterations in muscarinic receptors and pupil size produced by chronic atropinization in kittens.

Chronic mydriasis was induced in six kittens (four monocular, two binocular) and two adult cats (both monocular) by the daily topical application of atropine. Both the kittens and the adult cats were atropinized for a 13-week period with the treatment regimen beginning at the time of eye opening for the kittens. Pupil size measurements, obtained 1 year after the atropinization were discontinued, revealed that, although the pupils of the adult cats were normal, the pupils of the kittens' treated eyes were consistently smaller than pupils in control eyes. The status of the muscarinic receptors in the kittens' irides was investigated using 3H-QNB binding assays. In comparison with iris muscle homogenates from the control eyes, those from the treated eyes demonstrated an eightfold increase in the number of receptor binding sites. The results indicate that pupil size can be altered permanently by chronic mydriasis initiated early in the life of a kitten and that the permanent change in pupil size may result, in part, from a type of permanent supersensitivity response in the muscle following chronic blockade of muscarinic transmission by atropine.

Age Factors↗
PubMed1983

GABA as a trophic factor during development.

The process of synaptogenesis has been studied by many investigators to determine the factors which regulate synapse formation. We have used neonatal rabbit retina to investigate the role of the gamma-aminobutyric acid (GABA) neurotransmitter system during development. By utilizing an in vitro incubation treatment of isolated eyecups we found that treatment with nipecotic acid, a GABA uptake blocker, resulted in a 4-fold increase in the amount of specific 3H-muscimol binding. In addition, incubation of the tissue in the presence of the GABA agonists muscimol, 4,5,6,7-tetrahydroisoxazolo [5,4-c]pyridine-3-ol (THIP), or GABA itself led to similar increases in specific 3H-muscimol binding. The findings support the conclusion from previous studies that the induction of GABA receptors observed after in vivo treatment of 1-day-old rabbits with nipecotic acid resulted from an increase in the extracellular concentration of GABA. A possible role for GABA in the regulation of GABAergic synapse formation is presented in this report.

Animals↗
PubMed1983

Autoradiographic analysis of 3H-glutamate, 3H-dopamine, and 3H-GABA accumulation in rabbit retina after kainic acid treatment.

We have previously reported that exposure of isolated rabbit retina to 10(-3) M kainic acid produces profound morphological changes in specific retinal neurons (Hampton et al, 1981). We noted specific swelling of horizontal cell bodies and neurites, necrosis of cell bodies in the amacrine and ganglion cell layers, and swelling of elements in the inner plexiform layer. We now report a differential sensitivity to kainic acid of specific subclasses of amacrine cells autoradiographically labeled with 3H-glutamate, 3H-GABA, or 3H-dopamine. Three different effects were observed: (1) Labeling of neurons after incubation in 3H-glutamate was uniformly reduced while labeling of glia was much less affected. (2) The accumulation of 3H-dopamine was also decreased by kainic acid in two of the three labeled bands of the inner plexiform layer. The outermost labeled band was insensitive to kainic acid at the highest concentration tested (10(-2) M). These findings provide a basis for the subclassification of dopaminergic amacrine cells into at least two subclasses based on their sensitivity to kainic acid. (3) Kainic acid caused a dramatic increase in the labeling of GABAergic amacrine cell bodies and their terminals. This increased intensity may reflect a compensatory increase in uptake activity in response to kainic acid-induced depletion of endogenous GABA stores. These results confirm the highly toxic nature of kainic acid and demonstrate a high degree of specificity and complexity in its action in the retina.

Animals↗
PubMed1983

The effects of 2-amino-4-phosphonobutyric acid (APB) on the ERG and ganglion cell discharge of rabbit retina.

Perfusion of 100 microM 2-amino-4-phosphonobutyric acid (APB) into the in vivo rabbit eye-cup selectively and reversibly blocked the b-wave of the ERG and all On responses from retinal ganglion cells. In contrast, Off responses were occasionally enhanced, sometimes dramatically. The antagonistic surround inputs to Off ganglion cells, identified by their latency to light stimulation and magnesium sensitivity, were unchanged by APB. These observations suggest that APB selectively blocks depolarizing bipolar cells in rabbit retina in close agreement with the results of Slaughter and Miller (1981) from mudpuppy retina. We conclude that APB may be useful as a pharmacological tool to differentiate On and Off pathways in the rabbit visual system.

Action Potentials↗
PubMed1983

The cholinergic amacrine cells of rabbit retina receive on and off input: an analysis of [3H]-ACh release using 2-amino-4-phosphonobutyric acid (APB) and chloride free medium.

Using the in vitro rabbit eye-cup we have examined the light-evoked release of ACh from cholinergic amacrine cells under conditions known to eliminate On responses in the retina. APB (100 microM), which blocks the photoreceptor/depolarizing bipolar cell synapse, reduced the light-evoked release of ACh by 80% but a small light-evoked response remained, which was potentiated by bicuculline. Depolarizing bipolar cells are also Cl- dependent. Cl- free medium caused a tenfold Ca2+-dependent increase in the release of ACh but some small light evoked release remained. These results indicate that the cholinergic amacrine cells receive On and Off input. Our findings are consistent with anatomical and electrophysiological evidence which suggests that the displaced cholinergic amacrine cells are On cells and the conventionally placed cholinergic amacrine cells are Off cells.

Acetylcholine↗
PubMed1983

Synaptic interactions in the GABA system during postnatal development in retina.

Using biochemical analyses, we have demonstrated the presence of a high-affinity, sodium- and temperature-dependent uptake system for GABA in the retinas of newborn rabbits. The activity of this system two days after birth is approximately 70 percent of adult values, slowly increasing to adult level by postnatal day 6-8. An intraocular injection nipecotic acid (final concentration = 10 mM) into one-day-old rabbit pups resulted in a 60 percent inhibition in uptake activity. In order to study the possible role of the GABA uptake system in retinal development, we have determined the consequences of blocking GABA uptake with nipecotic acid on the postnatal development of post-synaptic GABA receptors, as measured by 3H-muscimol binding. Nipecotic acid treatment caused a significant increase in receptor binding in retinas prior to eye opening, with the maximal stimulation being one day after the intraocular injection. Our data indicate that the development of GABA receptor sites is influenced by the activity of the GABA uptake system and suggest that GABA may function as a trophic factor in the developing rabbit retina.

Animals↗
PubMed1983

Intraocular injections of nipecotic acid produce a preferential block of neuronal 3H-GABA accumulation in adult rabbit retina.

A procedure by which the activity of the retinal GABA uptake system can be manipulated in vivo has been developed. Intraocular injections of nipecotic acid, a proported GABA uptake blocker, were administered to adult rabbits every 48 hours for a two-week period. No behavioral or systemic changes were observed. Injections were well-tolerated with less than 10% loss of the tissue caused by physical damage or injection. Biochemical analyses demonstrated a dose-dependent inhibition of 14C-GABA uptake into retinal tissue. No effect on uptake was observed for saline-treated tissue. Autoradiographic analyses showed that in vivo treatment with nipecotic acid preferentially blocked accumulation of 3H-GABA into the amacrine cell bodies and processes in the inner plexiform layer. This treatment may be especially useful in assessing the functional significance of GABA transport in vivo.

Animals↗
PubMed1982

2-amino-4-phosphonobutyric acid and N-methyl-D-aspartate differentiate between "3H]glutamate and [3H] aspartate binding sites in bovine retina.

Three pharmacologically and kinetically distinct binding sites for acidic amino acids were observed in synaptic membranes from bovine retina. One site preferentially binds aspartate with an apparent Kd of 6.3 nM and Bmax of 0.033 pmol/mg protein. [3H] Glutamate binds preferentially to two sites which have KdS of approximately 10 and 800 nM; and BmaxS of 0.148 and 0.417 pmol/mg protein, respectively. Only one of these sites, the 800 nM glutamate site, displayed a pharmacological specificity which was in extensive agreement with that reported for the putative glutamate receptor previously localized to a specific set of retinal neurons, the on-center, depolarizing bipolar cells.

Aminobutyrates↗
PubMed1982

[3H]GABA binding in developing rabbit retina.

We have studied the developmental sequence of the GABA system in the rabbit retina using an in vitro binding assay to monitor developmental changes in the post-synaptic receptor. A variety of tissue treatments including perchlorate and Triton X-100 were employed to optimize binding and remove endogenous factors which inhibit binding. Pre-treatment of the tissue with 0.05% Triton X-100 revealed high affinity binding for [3H]GABA which increased in a sigmoidal fashion with the post-natal age of the animal. A constant level of binding, at about 16% of adult levels, was noted until day 8, at which time a rapid increase occurred. At 16 days post-natal, the amount of specific binding reached a plateau near adult levels. Kinetic analysis of the GABA receptor showed an increase in the number of receptors (Bmax) with little or no change in the apparent affinity (KD). Our results suggest that the onset of post-synaptic receptor activity is delayed approximately 1 to 2 days, relative to the pre-synaptic components, and the period of rapid increase in GABA receptor binding coincides with the period of maximum increase in retinal synaptic density.

Aging↗