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W K Stell

Publications and source records attributed to W K Stell.

At least 55 records · Page 3Linked to original sources
PubMed1986

Gonadotropin-releasing hormone (GnRF), molluscan cardioexcitatory peptide (FMRFamide), enkephalin and related neuropeptides affect goldfish retinal ganglion cell activity.

Recently gonadotropin-releasing hormone (GnRF)-like and molluscan cardioexcitatory peptide (FMRFamide)-like compounds have been colocalized immunocytochemically to the terminal nerve, a presumed olfactoretinal efferent system in goldfish. In the present study these and related neuropeptides were shown to affect ganglion cell activity, recorded extracellularly, when applied to the isolated superfused goldfish retina. GnRF was usually excitatory. Salmon GnRF (sGnRF) was 10-30x more potent than chicken or mammalian GnRF. FMRFamide and enkephalin also were often excitatory but caused more varied responses than sGnRF. Met5-enkephalin-Arg6-Phe7-NH2 (YGGFMRFamide), which contains both enkephalin and FMRFamide sequences, tended to act like both of these peptides but with mainly enkephalin-like properties. Neuropeptide Y and the C-terminal hexapeptide of pancreatic polypeptides, whose C-terminus (-Arg-Tyr-NH2) is closely related to that of FMRFamide (-Arg-Phe-NH2), gave no consistent responses. Threshold doses were equivalent to: 0.1 microM for sGnRF; 0.5 microM for YGGFMRFamide; 1.5 microM for FMRFamide and enkephalin. Rapid, complete and irreversible desensitization was induced by single, 10-20x threshold doses of sGnRF; but desensitization was infrequent and limited with the other peptides. In general, all peptides tested affected the spatially and chromatically antagonistic receptive field components similarly, but selective actions were seen in a few cases with FMRFamide and with the opioid antagonist, naloxone. Responses, especially to sGnRF and FMRFamide, tended to be most frequently obtained and pronounced in winter and spring, suggesting a correlation with seasonally regulated sexual and reproductive activity. Our observations provide further evidence for transmitter-like roles of neuropeptides related to sGnRF and FMRFamide in the teleostean terminal nerve. The actions of agonists and antagonists, singly and in combination, imply strongly that there are distinctive postsynaptic receptors and/or neural pathways for GnRF-, FMRFamide- and enkephalin-like peptides in the goldfish retina.

Animals↗
PubMed1986

Putative cholinergic interneurons in the optic tectum of goldfish.

We have demonstrated that a significant fraction of cells in layer 1 of goldfish optic tectum are immunoreactive for choline acetyltransferase. These cells constitute 4-7% of type XIV cells, which are thought to be intrinsic neurons and represent 95% of all tectal cells. The number of immunoreactive type XIV cells is unchanged following short-term enucleation. The possible integrative role of these putative cholinergic neurons is discussed in relation to sensory functions of the optic tectum.

Animals↗
PubMed1986

Choline acetyltransferase immunoreactivity suggests that ganglion cells in the goldfish retina are not cholinergic.

Published evidence that ganglion cells in the retinae of nonmammalian species are cholinergic is strong but indirect. In this paper we report results of attempts to demonstrate choline acetyltransferase immunoreactivity in ganglion cells of goldfish retina using two different antisera against choline acetyltransferase (ChAT), the acetylcholine-synthesizing enzyme. We obtained ChAT-immunoreactive staining of amacrine and displaced amacrine cells in the retina and type XIV cells in the tectum, but we obtained no direct immunocytochemical evidence that ganglion cells in the goldfish retina are cholinergic. Thus, ganglion cells identified by retrograde transport of propidium iodide were never ChAT-immunoreactive. Intraocular injections of colchicine did not result in the appearance of a population of ChAT-immunoreactive neurons in the ganglion cell layer. ChAT-immunoreactive axons were not observed in intact, ligated, or transected optic nerves. And finally, the ChAT immunoreactivity of cells and fibers in the optic tectum was unaffected by deafferentation. These experiments provide no positive evidence that any ganglion cells in goldfish retina contain the acetylcholine-synthesizing enzyme, ChAT. While it is possible that our method is too insensitive to detect the enzyme in ganglion cell somata or too specific to recognize the form of ChAT present in these cells, the fact that we can stain putatively cholinergic retinal amacrine cells and tectal neurons makes these alternative explanations improbable. We conclude that it is unlikely that any of the ganglion cells in the retina are cholinergic and that alternative explanations should be sought for previously published results that suggest that they are.

Acetylcholine↗
PubMed1985

Formation of new rod photoreceptor synapses onto differentiated bipolar cells in goldfish retina.

In goldfish new rods are continuously added to the entire retina at a rate that assures stable rod density, while the densities of other neurons decrease. The b1 bipolar, known to contact every rod within its dendritic domain, was used to determine the fate of these newly formed rods. Golgi-stained b1 bipolars were sectioned serially at 0.5 micron in the plane of the receptor terminals and reconstructions of their rod and cone contacts were prepared from camera lucida drawings. The newly formed rods are accommodated within the dendritic trees of already-formed b1 bipolars at a rate of about one new rod synapse/bipolar/month. During growth from about 6 months to 5 years of age the number of synapses onto each b1 bipolar increases by 50%. Concomitantly the dendritic tree area increases by about 50%, and the density of rod-b1 synapses remains constant at about one synapse/11 micron 2. Assuming a dendritic coverage factor of 1, the b1 bipolars will contact every retinal rod. The numbers of cones contacted and not contacted do not significantly change. The overall dimensions of b1 bipolars increase with retinal growth and new branches are added to their dendritic trees. These observations show that new rods added to adult goldfish retina form synapses with old bipolars. Some functional inferences are also made.

Animals↗
PubMed1985

Peptidergic modulation of patterned motor activity in identified neurons of Helisoma.

The neuroactive peptides SCP(B) (small cardioactive peptide B) and FMRFamide (Phe-Met-Arg-Phe-NH(2)), both originally isolated from molluscs, have potent modulatory effects upon the production of patterned motor activity in identified neurons (e.g., B5 and B19) in the buccal ganglia of the snail Helisoma. Such patterned motor activity has previously been shown to underlie feeding behavior. Micromolar concentrations of SCP(B) initiate patterned motor activity in quiescent ganglia and increase the rate of activity in ganglia that are spontaneously active. Micromolar concentrations of FMRFamide inhibit patterned motor activity in Helisoma buccal ganglia, and 10 muM FMRFamide completely suppresses such activity. In addition, there are both anti-SCP(B)-and anti-FMRFamide-immunoreactive neurons in Helisoma buccal ganglia. Our results suggest that peptides may play a prominent role in the regulation of feeding behavior in Helisoma.

Journal Article↗
PubMed1984

Tetrodotoxin does not block the axonal transmission of S-potentials in goldfish retina.

Light-evoked responses (S-potentials) have been recorded from the somata and the axon terminals of horizontal cells of goldfish retinas. Data obtained in the controlled states of retinas and following tetrodotoxin (TTX) application show that TTX does not affect the quantitative relationships of the two sets of response potential. It is concluded that TTX does not influence the axonal transmission of S-potentials.

Animals↗
PubMed1984

Immunocytochemical localization of putative cholinergic neurons in the goldfish retina.

The presence of putative cholinergic neurons in goldfish retina was demonstrated by immunocytochemical localization of choline acetyltransferase (ChAT), the synthesizing enzyme for acetylcholine. Four populations of ChAT-immunoreactive neurons were localized: two with cell bodies in the inner nuclear layer and two with cell bodies in the ganglion cell layer. The processes of these neurons ramified in lamina 2 and/or 4 (of 5) in the inner plexiform layer. These cell populations are comparable to populations of putative cholinergic neurons that have been identified by [3H]choline uptake [3, 10].

Acetylcholine↗
PubMed1984

Synaptic contacts of somatostatin-immunoreactive amacrine cells in goldfish retina.

Retinal amacrine cells containing somatostatinlike immunoreactivity (SLI) were labeled by the peroxidase-antiperoxidase technique and their connections were analyzed by light and electron microscopy. The labeled processes were found in two distinct plexuses--one near the most proximal border of the inner plexiform layer and the other near the most distal border. They received most (89%) of their input from amacrine cells and the remainder from bipolar cells. A majority (56%) of their output synapses go to processes of amacrine cells, a substantial proportion (38%) go to ganglion cell dendrites, and the remainder go to bipolar cell axon terminals. The relative frequencies of each of the types of contacts were nearly identical in the distal and proximal plexuses. The cells containing SLI are different in their morphology and synaptic connections from any goldfish amacrine cells containing conventional neurotransmitters, but one type of amacrine cell containing SLI resembles certain other peptidergic amacrine cells in the goldfish retina.

Animals↗
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↗
PubMed1984

Evidence for FMRF-amide as a neurotransmitter in the gill of Aplysia californica.

In Aplysia californica, multiple regulatory mechanisms are involved in the actions of neurotransmitters on the gill. Neurotransmitter receptors and adenylate cyclase were examined in a particulate fraction of gill homogenates. The neuropeptide FMRF-amide stimulated enzyme activity 7- to 8-fold (EC50, 1 microM) via receptors that were pharmacologically distinct from those for dopamine and serotonin. FMRF-amide augmented cyclic AMP levels in slices of gill tissue with a time course similar to that for adenylate cyclase activation. Increases in cyclic AMP levels produced by the neuropeptide were potentiated by the phosphodiesterase inhibitor theophylline. Physiological responses to neuropeptides and cyclic AMP analogues were examined in a perfused, isolated gill preparation. Phasic contractions evoked by FMRF-amide (EC50, 0.1 microM) were mimicked by membrane-permeable analogues of cyclic AMP. Comparison of FMRF-amide effects on adenylate cyclase and gill behavior suggests an association between cyclic AMP and phasic contractions. In addition, FMRF-amide-like immunoreactivity, detected by antisera raised against the neuropeptide, was found in nerve fibers innervating the gill. These findings indicate that in Aplysia, FMRF-amide or a closely related peptide neurotransmitter may be involved in the physiological regulation of gill behavior.

Adenylyl Cyclases↗
PubMed1982

Ratfish retina--intracellular recordings and HRP injections in an isolated, superfused all-rod retina.

Hyperpolarizing responses to light were studied by intracellular recording in the isolated, superfused retina of the ratfish (Hydrolagus colliei). Two of these hyperpolarizing units were identified as horizontal cells by iontophoretic injection of horseradish peroxidase (HRP). These cells had rather large cell bodies (15 x 30 micrometer), elliptical dendritic arborizations measuring 150 x 300 micrometers and no axons. Since their physiological receptive fields were found to be at least 2.15 mm in diameter, it appears likely that either the photoreceptors or the horizontal cells are electrically coupled. Electron microscopy of HRP-injected horizontal cells showed their dendrites to end laterally in ribbon synapses of rods only and revealed dendro-dendritic contacts resembling gap junctions between injected and uninjected horizontal cells. The spectral sensitivity function of a dark-adapted horizontal cell can be described by a Dartnall nomogram based on a retinene pigment with lambda max = 473 nm. These findings are consistent with the histological observation that the ratfish retina appears to contain only rod photoreceptors.

Animals↗
PubMed1981

An opiate system in the goldfish retina.

Recently, in addition to conventional neurotransmitters such as acetylcholine, dopamine, glycine and gamma-aminobutyric acid (GABA), putative neuroactive peptide transmitters have been localized to specific retinal amacrine cells. In particular, opiate receptors 2,3, assayable enkephalin immunoreactivity and enkephalin-immunoreactive neurones 1,5 have been described in avian and mammalian retinae. However, little physiological evidence has been obtained for the involvement of neuropeptides in retinal function. Here we report that exogenous opiates affect both the release of GABA from GABAergic amacrine cells and the firing patterns of ganglion cells in the goldfish retina. Our results show that the output of the retina is modulated by an opiate system whose neural organization and pharmacological properties resemble those described elsewhere in the vertebrate central nervous system.

Action Potentials↗
PubMed1980

Rod and cone inputs to bipolar cells in goldfish retina.

Five morphological types of bipolar cells which make synaptic contact with rods and cones are distinguished in the retina of adult goldfish (Carassius auratus) by characteristics readily observable in the light microscope. Cells were designated type a or type b according to whether their axons terminate in the distal part (sublamina a) or proximal part (sublamina b) of the inner plexoform layer, respectively. Analysis of serial semi-thin sections of Golgi-impregnated cells demonstrates that each subtype of bipolar contacts rods and a characteristic set of chromatic subtypes of cones: types a1 and b1 cells contact rods and red-sensitive cones, while types a2, b2 and b3 contact rods and red- and green-sensitive cones. Comparison with published descriptions of cells stained with Procion Yellow after intracellular recordings had been made suggests that type a cells should be off-center types and type b on-center. Furthermore, it is suggested that the receptive fields of cell types a1 and b1 should be non-color-coded, and those of a2, b2, and b3 color-coded.

Animals↗
PubMed1978

GABA-ergic pathways in the goldfish retina.

A high-affinity uptake mechanism for [3H]-gamma-aminobutyric acid (GABA) has been localized to type H1 cone horizontal cells and type Ab pyriform amacrine cells in the retina of the goldfish by light and electron microscopy autoradiography. By stimulating isolated retinas with colored lights during incubation we have been able to use [3H]-GABA uptake as a probe of light-evoked changes in membrane potential. All colors of lights increase and darkness decreases [3H]-GABA uptake by H1 cone horizontal cells. Our model of voltage dependence of GABA uptake predicts that all colors of light should hyperpolarize H1 cone horizontal cells and other investigators have shown by intracellular recording and dye-marking that type H1 cone horizontal cells hyperpolarize to all wavelengths of light. We have also obtained evidence that dark-induced depolarization of cone horizontal cells leads to release of GABA. Type Ab pyriform amacrine cells show maximal [3H]-GABA uptake in darkness and when exposed to green or blue lights, but red lights dramatically suppress uptake. We predict these neurons to be red-depolarizing, and recent intracellular recordings and dye-marking by Famiglietti et al. ('77) support our conclusions. Synaptic relations of apparently GABA-ergic neurons were investigated in the electron microscope. We propose type H1 cone horizontal cells to be both pre- and post-synaptic to red-sensitive cones and type Ab pyriform amacrine cells to be both pre- and post-synaptic to red-sensitive center-depolarizing bipolar cells.

Animals↗
PubMed1978

Inputs to bipolar cell dendrites in goldfish retina.

Goldfish mixed bipolar cells, which contact both rods and cones, comprise two types; Ma, with axon terminals in the distal sublamina(a) and Mb, with axon terminals in the proximal sublamina(b) of the inner synaptic layer. Type Ma cells make only wide-cleft junctions (WCJ), whereas type Mb cells make only narrow-cleft junctions (NCJ) with rods and cores. It follows that WCJs mediate sign-conserving synaptic transmission to the center hyperpolarizing Ma cells, whereas NCJs mediate sign-inverting transmission to the center depolarizing Mb cells. Bipolar cell (BC) surrounds may be mediated largely through horizontal cell (HC) pathways. Type Ma BCs appear to be influenced primarily through HC feedback at cones and both feedback and nonribbon feedforward contacts at rods; in contrast most Mb BCs may be influenced by both HC feedback and ribbon-associated feedforward contacts at rods and cones, accounting for the greater complexity of Mb BC surrounds. BC subtypes Mal and Mbl, which contact only red-sensitive cones (+ rods), are likely to have red-opponent (non-color-coded) surrounds mediated by H1 (L-type) cone HCs; while subtypes Ma2 and Mb2 and 3, which contact also green-sensitive cones, are likely to have red + green-opponent (color-coded) surrounds mediated by H1 and H2 (R/G C-type) cone HCs.

Animals↗
PubMed1977

Structural basis for on-and off-center responses in retinal bipolar cells.

Electron microscopy of Golgi preparations of goldfish retina shows that dendrites of type a (hyperpolarizing, off-center) bipolar cells make wide cleft junctions unassociated with synaptic ribbons, while those of type b (depolarizing, on-center) bioplar cells make narrow cleft junctions and synaptic ribbon contacts, with rods and cones. This suggests that wide cleft junctions are the site of sign-conserving, and narrow cleft junctions or ribbon contacts (or both) are the site of sign-inverting synaptic transmission from photoreceptors to bipolars.

Animals↗