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Biomedical subjects

A E Stuart

Publications and source records attributed to A E Stuart.

At least 37 records · Page 2Linked to original sources
PubMed1989

Biochemical and physiological evidence that histamine is the transmitter of barnacle photoreceptors.

We tested the hypothesis that histamine is the transmitter released by barnacle photoreceptors. Median and lateral ocelli were incubated with 3H-histidine and found to synthesize 3H-histamine, identified by high-voltage electrophoresis. Synthesis could be blocked by the histidine decarboxylase inhibitor (S)-alpha-fluoromethylhistidine. Histamine was applied to I-cells either by superfusion or by pressure ejection from a pipette (100 microM or 1 mM histamine) positioned close to the I-cell's soma. When bath-applied at concentrations ranging from 5-100 microM, histamine hyperpolarized the I-cell in a dose-dependent fashion and increased its conductance. At 100 microM, histamine abolished the I-cell's response to light. The response to a pulse of pressure-applied histamine was a hyperpolarization whose amplitude was graded with dose (determined by the duration of the pulse). This response persisted in concentrations of Co2+ and Cd2+ that blocked synaptic transmission from the photoreceptors. Cimetidine, an antagonist of mammalian H2 receptors, markedly decreased the cell's responses both to HA and to light at 100 microM and blocked both responses at 1 mM. Pyrilamine and triprolidine, H1 antagonists, had a complex effect on the I-cell's responses to histamine and to light. Neither H1 nor H2 antagonists, nor histamine itself, affected the voltage or light responses recorded in the presynaptic terminal region, or any phase of calcium-dependent action potentials induced in the terminal in the presence of tetraethylammonium ion. Thus, biochemical, immunocytochemical, and physiological evidence suggests that HA is the transmitter from these photoreceptors to the I-cells. Although gamma-aminobutyric acid (GABA) is also present in the photoreceptors, it did not affect the I-cell's responses to light or to histamine when bath-applied at 100 microM. Thus, GABA does not appear to modulate transmission from the photoreceptor to the I-cell.

Animals↗
PubMed1988

A persistent, TTX-sensitive sodium current in an invertebrate neuron with neurosecretory ultrastructure.

In the CNS of the giant barnacle (Balanus nubilus) a single pair of large neuronal somata (cross-commissural, or CC, cells), located near the entry of the median ocellar nerve, occasionally displays a prominent whitish luster. These somata have ultrastructure typical of neurosecretory cells: numerous Golgi complexes and abundant, large dense-cored vesicles (DCVs; size range, 75-275 nm). Injection of a CC cell with cobalt tracer shows that it arborizes over a 7 mm length of the contralateral peripheral nerve out of which it projects. The processes of the arbor are profuse and varicose; the varicosities are packed with DCVs similar to those in the soma. Stimulation of a single CC cell causes a substantial decrease in the number of DCVs and increases the incidence of clusters of small electron-lucent vesicles, as well as the occurrence of large electron-lucent vesicles and membrane-bound cisternae. We studied ionic currents flowing across this cell's somatic membrane with a single-electrode voltage clamp. Unusual among these currents is an inward current that is blocked by TTX but is essentially noninactivating. In current clamp, this "persistent" current causes the action potential to be prolonged (seconds) if opposing outward current is blocked with 4-aminopyridine. The inward current is carried by Na. Its amplitude depends on the external Na concentration, it is blockable by TTX, and it persists when the cell is bathed in Ca-free saline and/or Co. Other currents present in this cell include an outward current similar to molluscan A-current and a Ca current that contributes to the action potential (Stockbridge and Ross, 1986). The persistent Na current is partially activated at the cell's resting potential and, thus, may participate in determining the frequency of its impulse activity.

Action Potentials↗
PubMed1987

Voltage spread in an identified interneuron of the barnacle's visual system.

1. The interneuron that is postsynaptic to barnacle photoreceptors (the inverting, or I-cell) receives similar synaptic input from the receptors onto its two distinct and separate arbors. We compared the spread of light-evoked synaptic potentials from the proximal and distal arbors with the cell's soma in order to ascertain how well voltages spread in this cell. 2. The proximal and distal arbors are connected by a commissural process approximately 200 microns in length and 2 microns in diameter. Voltages spreading from the distal arbor along this process were 20-60% of their original value, and delayed 15-20 ms, when recorded at the cell's soma. 3. The reversal potential of the receptor's input to the distal arbor, determined by injecting current into the soma, appeared substantially negative (-150 mV) to that of the identical input to the proximal arbor (-80 mV). Assuming identical reversal potentials in the two arbors, this difference indicates that more current must be injected into the I-cell's soma to change the voltage of the distal arbor to a given potential than to change that of the proximal arbor to the same potential. 4. Comparison of input from a lateral eye to the ipsilateral arbor with that from the median eye to the same arbor indicates that these two inputs are at an electrically equivalent distance from the soma. 5. Uneven illumination of the eyes may, through local conductance changes, cause the arbors to function independently, even to the point where one arbor may depolarize when the other is hyperpolarized.

Animals↗
PubMed1986

Pattern of convergence of the receptors of the barnacle's three ocelli onto second-order cells.

The giant barnacle, Balanus nubilus, has three simple eyes, two lateral and one median. We have studied the convergence of the receptors of these ocelli by recording from the second-order cell (I-cell) and from the receptors' terminals. The I-cell's responses to illumination of the median and lateral eyes are similar in shape, dynamic range, and reversal potential, but the response to lateral input has a longer latency, a slower rise time, and a smaller amplitude. These differences primarily reflect the different voltage changes in the terminals of the decrementally conducting median and lateral receptors. Simultaneous recordings from the terminals of median and lateral receptors showed that the responses to light recorded in lateral terminals had a longer latency, a slower rise time, and smaller amplitude than signals in median terminals. The differences in the I-cell's responses to median and lateral input were essentially eliminated by stimulating the median and lateral ocellar nerves with extracellular suction electrodes positioned at equal distances from the receptors' terminals. The similarity of the I-cell's responses to median and lateral input suggests that lateral photoreceptors, like median receptors, contact the I-cell directly. No evidence was found for interaction between median and lateral receptors. Simultaneous fills of median and lateral receptors with cobalt showed minimal overlap between their terminal arbors. No voltage change was detected in the second receptor when the voltage in the first was changed with current pulses or when action potentials were elicited in the presence of tetraethylammonium ions. The absence of a detectable response in the terminals of one eye's receptors when the receptors of the other eye were stimulated with current or light suggests that there is no feedback from the I-cell to the receptors. Simultaneous illumination of the median and lateral eyes produced responses in the I-cell expected from two independent inputs. The first synaptic stage of the visual pathway in the barnacle is thus unusually simple, consisting of a small number of electrically isolated photoreceptors converging upon the same pair of second-order cells with no feedback interaction.

Animals↗
PubMed1985

Adaptation in the input-output relation of the synapse made by the barnacle's photoreceptor.

A study was made of synaptic transmission between the four median photoreceptors of the giant barnacle (Balanus nubilus) and their post-synaptic cells (I-cells). Simultaneous intracellular recordings were made from the presynaptic terminal region of a photoreceptor and from the soma of an I-cell. The photoreceptor's membrane potential provided feed-back to bath electrodes that passed current into the receptors' axons, permitting the voltage to be controlled at the point of arborization of their presynaptic terminals. Simultaneous recordings from a second photoreceptor showed that its voltage tracked the first. Step depolarizations of the receptors from their dark resting potential (about -60 mV) caused hyperpolarizations of the I-cell that reached a peak, then decayed to a plateau value. The amplitude of the I-cell's response grew with presynaptic depolarizations, saturating at presynaptic values 10-20 mV depolarized from dark rest. Step hyperpolarizations of the receptors from dark rest evoked depolarizations of the I-cell consisting of an initial peak, which varied greatly in amplitude and wave form from preparation to preparation, followed by a plateau. The presence of this post-synaptic response indicates that transmitter is released continuously from the receptors at their dark resting potential. An input-output relation of the synapse was obtained by presenting step depolarizations from a holding potential of -80 mV, where steady-state transmitter release is shut off. The relation is sigmoidal; in the exponentially rising phase of the curve, a 5-11 mV presynaptic change produces a 10-fold change in post-synaptic response. When the presynaptic holding potential was set at values ranging from -80 to -40 mV, the relation between the I-cell's response and the absolute potential to which the receptor was stepped shifted along the presynaptic voltage axis. The slopes of the input-output relations were roughly parallel or increased as the photoreceptors were held more depolarized. This observation limits the possible mechanisms of the shift.

Action Potentials↗
PubMed1984

Is gamma-aminobutyric acid the neurotransmitter of barnacle photoreceptors?

The hypothesis that gamma-aminobutyric acid (GABA) is the neurotransmitter of barnacle photoreceptors was tested by studying the effect of GABA on the membrane of the cell directly postsynaptic to the photoreceptor, by testing the ability of GABA antagonists to block transmission at this synapse, and by estimating the free GABA content of the photoreceptor. The results of these experiments suggest that GABA is not the photoreceptor's neurotransmitter.

Animals↗
PubMed1984

Coupling between horizontal cells in the carp retina revealed by diffusion of Lucifer yellow.

Electrical coupling among 4 different types of horizontal cells in Cyprinus carpio was examined from the diffusion of the intracellularly injected Lucifer yellow. The type of horizontal cells was identified by a spectral response and by a distinct morphology when the retina was viewed in flat mounts under a fluorescence microscope. Lucifer yellow diffused from the injected cell into surrounding cells, and in all of these preparations, diffusion was limited to horizontal cells of the same morphological type. Axons of horizontal cells were found to be coupled, and also at axons the coupling is likely to be limited to the same cell type.

Animals↗
PubMed1984

Reed-Sternberg/lymphocyte rosette: lymphocyte subpopulations as defined by monoclonal antibodies.

The Reed-Sternberg cell/lymphocyte rosette characteristic of Hodgkin's disease tissue and cell suspensions was investigated with monoclonal antibodies on fresh viable cell suspensions prepared from nine cases of Hodgkin's disease. The biopsy material comprised six spleens and three lymph nodes. The majority of the rosetting lymphocytes were T cells, primarily of the helper subset. Some of the attached lymphocytes were suppressor T cells. In addition, a few of the rosetting lymphocytes around Reed-Sternberg cells were B cells.

Antibodies, Monoclonal↗
PubMed1983

The lectin binding affinity of Reed-Sternberg cells.

Reed-Sternberg cells from ten cases of Hodgkin's disease were examined by the direct immunofluorescence technique, for their affinity for nine lectins. The surrounding lymphocytes and monocytes of HD tissue were also assessed for their ability to bind lectins. RS cells showed considerable heterogeneity of reaction. Overall, there was a marked decrease in the binding of most of the lectins studied in HD cases as compared to normal peripheral blood mononuclear cells. This was particularly evident for RCA, PHA and PNA binding. It is suggested that there is a defect in carbohydrate metabolism, with fewer lectin-binding sites on both RS cells and on the mononuclear cell populations in Hodgkin's disease. Further quantitative work is required to verify this.

Blood Cells↗
PubMed1983

The reactivity of Reed-Sternberg cells with monoclonal antisera at thin section and ultrastructural levels.

In an attempt to improve the morphology of Reed-Sternberg cells after immunochemical procedures, the biotin-avidin technique has been used. Satisfactory morphology was obtained at the level of both light and electron microscopy. Reed-Sternberg cells failed to react with a monoclonal antimonocyte serum but gave positive results with anti-1a and FMC7, a monoclonal anti-B cell serum. Positive results were also obtained with FMC1 and B1 both of which are monoclonal B cell antisera.

Antibodies, Monoclonal↗
PubMed1983

Staining of human splenic sinusoids and demonstration of unusual banded structures by monoclonal antisera.

The monoclonal antiserum OKT8 is useful as a marker of splenic sinusoids. Banded and fibrillary structures are also delineated by this antiserum; these appear to be different from the ring fibres of the spleen and the tentative suggestion is made that these represent basal plates or endothelial striations. The reactivity of sinus lining cells with a number of antisera is noted and the conclusion is drawn that splenic sinal endothelium differs substantially from the endothelium of blood vessels.

Antibodies, Monoclonal↗
PubMed1983

Lateral visual pathway of giant barnacle.

1. We have studied the responses to light, conduction down the axons, and anatomical projections of the photoreceptors of the lateral eye in the giant barnacle, Balanus nubilus. By recording intracellularly from ganglion cells that respond to visual input, we have described convergence of the lateral and median visual pathways. 2. Each lateral eye contains three photoreceptor cells, two large and one small. Cobalt filling of single large lateral receptor axons demonstrated that they end in a restricted ovoid bush on the ipsilateral side of the ganglion in approximately the same region in which the median receptors arborize. 3. The lateral receptors have dark resting potentials and responses to light similar to those previously described for the receptors of the median eye. Like the median receptors, the lateral receptors conduct visual signals decrementally, although their axons may be twice as long (14-25 mm). 4. Passing current of either polarity into either of the large receptors produced no detectable voltage change in the other cell. Action potentials elicited in either cell by stimulating it in the presence of tetraethylammonium ion were not detected in the other cell. Light-induced membrane noise in one cell did not correlate with noise in the other. Thus, like the receptors of the median eye, the large receptors of the lateral eye are not electrically coupled. 5. By shadowing each ocellus individually, we have shown that the signals from the median and lateral photoreceptors converge at the level of the second-order cells described for the median pathway. Shadowing the median or a lateral eye gave rise to synergistic responses in second-, third-, and all higher order ganglion cells studied. No cells were found that were driven solely by the lateral eyes. Thus, the lateral and median visual pathways are highly convergent.

Animals↗
PubMed1983

Synaptic contacts between physiologically identified neurons in the visual system of the barnacle.

Neurons in the median visual system of the barnacle were injected with horseradish peroxidase (HRP) and their processes traced in serial thick (3 micrometers) and thin (100 nm) sections with light and electron microscopy. The anatomy confirms that the I-cells identified by Oertel and Stuart (Oertel, D., and A. E. Stuart (1981) J. Physiol. (Lond.) 311: 127-146) are second-order neurons in the median visual pathway. The terminal branches of the photoreceptor axons are associated in each half of the supraesophageal ganglion with a region of neuropil that extends for 30 to 40 micrometers along the commissure; this photoreceptor-associated neuropil is continuous with but much simpler than the main mass of neuropil in the core of each hemiganglion. The photoreceptor-associated neuropil consists of a small number of different neuronal elements, each with distinctive cytological features. The photoreceptor terminal processes dominate the neuropil; in addition, one finds there the most medial processes of the arborizations of the ipsilateral and contralateral I-cells and the processes of an axon or class of axons of unknown origin referred to as the "RL" fibers. These RL processes associate and branch with the receptor axons and constitute the only major neuronal element in this region of neuropil besides the median photoreceptors and the I-cells. In preparations with an HRP-filled I-cell, the photoreceptors were shown to be presynaptic to I-cell processes at synapses which are characterized by a pair of closely apposed postsynaptic profiles referred to as a dyad. The filled I-cell constituted only one element of the dyad. Receptor endings were also presynaptic to dyads where both postsynaptic elements were unfilled. The RL processes were presynaptic to the photoreceptor terminals at nondyadic synapses, and the receptor endings made specialized junctions, possibly synaptic, with the RL processes. Lateral to the region occupied by the photoreceptor arborization, varicosities of the I-cell are juxtaposed to processes of the A-cell; thus, these sites of the I-cell, where it is most likely to be presynaptic to the A-cell, are segregated from the sites at which it is postsynaptic to the photoreceptors. The I-cell is postsynaptic to photoreceptors and has varicosities juxtaposed to A-cell processes in both hemiganglia.

Animals↗
PubMed1982

The reaction of xenogeneic and monoclonal antisera with Reed-Sternberg cells.

Xenogeneic antisera have been prepared against human monocytes, B lymphocytes and T lymphocytes. The reactivity of these antisera against a variety of normal and neoplastic cells is described. Reed-Sternberg cells from three cases of Hodgkin's disease failed to react with xenogeneic anti-T and anti-monocyte sera, but reacted with an anti-B serum. A further three cases were examined with monoclonal antibodies. Negative results were obtained with monoclonal anti-T and positive results were given by monoclonal antibodies directed against DR and HLA antigens.

Antibodies, Monoclonal↗
PubMed1981

Properties of tetraethylammonium ion-resistant K+ channels in the photoreceptor membrane of the giant barnacle.

After the offset of illumination, barnacle photoreceptors undergo a large hyperpolarization that lasts seconds or minutes. We studied the mechanisms that generate this afterpotential by recording afterpotentials intracellularly from the medial photoreceptors of the giant barnacle Balanus nubilus. The afterpotential has two components with different time-courses: (a) an earlier component due to an increase in conductance to K+ that is not blocked by extracellular tetraethylammonium ion (TEA+) or 3-aminopyridine (3-AP) and (b) a later component that is sensitive to cardiac glycosides and that requires extracellular K+, suggesting that it is due to an electrogenic Na+ pump. The K+ conductance component increases in amplitude with increasing CA++ concentration and is inhibited by extracellular Co++; the Co++ inhibition can be overcome by increasing the Ca++ concentration. Thus, the K+ conductance component is Ca++ dependent. An afterpotential similar to that evoked by a brief flash of light is generated by depolarization with current in the dark and by eliciting Ca++ action potentials in the presence of TEA+ in the soma, axon, or terminal regions of the photoreceptor. The action potential undershoot is generated by an increase in conductance to K+ that is resistant to TEA+ and 3-AP and inhibited by Co++. The similarity in time-course and pharmacology of the hyperpolarization afterpotentials elicited by (a) a brief flash of light, (b) depolarization with current, and (c) an action potential indicates that Ca++-dependent K+ channels throughout the photoreceptor membrane are responsible for all three hyperpolarizing events.

Aminopyridines↗
PubMed1981

Transformation of signals by interneurones in the barnacle's visual pathway.

1. The photoreceptors of the median eye of the giant barnacle drive decrementally-conducting neurones in the supraoesophageal ganglion termed ;inverting cells' (I-cells) which in turn drive impulse-producing neurones termed ;amplifying cells' (A-cells). Using intracellular recording techniques we have studied the role of I-cells in visual processing.2. Horseradish peroxidase injections show that I-cells are interneurones whose processes are confined to the regions of the photoreceptor terminals on both sides of the bilaterally symmetrical ganglion.3. In the dark, I-cell membrane potentials (-45 mV) are considerably less negative than those of other ganglion cells (-60 to -70 mV). At the onset of a maintained light, I-cells undergo a transient peak hyperpolarization which declines to a steady-state response. Both response components are graded with light intensity.4. The reversal potential of the peak of the I-cell light response depends on the external K(+) concentration more strongly than does the dark resting potential (3-30 mm-K(+)). This evidence indicates that the hyperpolarization results from an increase in the cell's permeability to K(+) ions.5. At the offset of light an I-cell undergoes a transient depolarization that overshoots the dark membrane potential. Dimming of a background light can also cause the I-cell membrane potential to overshoot its dark resting value. This overshoot is associated with a large depolarizing synaptic potential in A-cells.6. An overshoot of the dark resting potential can also be elicited by the break of a hyperpolarizing pulse of current injected into an I-cell. The amplitude of this overshoot increases with pulse duration over a time course of seconds.7. In the presence of external tetraethylammonium ion (TEA) and tetrodotoxin, (TTX), the break of a hyperpolarizing pulse or the onset of a depolarizing pulse can evoke in an I-cell an action potential whose rate of rise and amplitude depend on the external Ca concentration. This action potential can be maintained by replacement of external Ca with Ba, or blocked by addition of 15 mm-Co to the saline. These observation's indicate that depolarizing potential changes in this cell activate a voltage-sensitive Ca conductance.8. When hyperpolarizing current pulses are injected into an I-cell, the voltage during the pulse sags back slowly towards the dark resting potential. Thus, during hyperpolarization with light or current an I-cell's membrane properties change over a time course of seconds.9. The onset of a depolarizing pulse or the offset of a hyperpolarizing pulse of current injected into an I-cell leads to a transient depolarization of a simultaneously impaled A-cell. Synaptic transmission occurs when the I-cell is depolarized to the vicinity of the dark resting potential. The amplitude of the response in an A-cell depends on the rate of change of the I-cell voltage.

Animals↗