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E F Stanley

Publications and source records attributed to E F Stanley.

At least 37 records · Page 2Linked to original sources
PubMed1992

Stabilization of acetylcholine receptors at the neuromuscular synapse: the role of the nerve.

The majority of acetylcholine receptors (AChRs) at innervated neuromuscular junctions (NMJs) are stable, with half-lives averaging about 11 days in rodent muscles. In addition to the stable AChRs, approximately 18% of AChRs at these innervated junctions are rapidly turned over (RTOs), with half lives of less than 24 h. We have postulated that RTOs may be precursors of stable AChRs, and that the motor nerve may influence their stabilization. This hypothesis was tested by: (i) labeling AChRs in mouse sternomastoid (SM) muscles with 125I-alpha-BuTx; (ii) denervating one SM muscle in each mouse, and (iii) following the fate of the labeled AChRs through a 5-day period when RTOs were either stabilized or degraded. The hypothesis predicts that denervation should preclude stabilization of RTOs, resulting in a deficit of stable AChRs in denervated muscles. The results showed a highly significant (P less than 0.002) deficit of stable AChRs in denervated as compared with innervated muscles. Control experiments excluded the possibility that this deficit could be attributed to independent accelerated degradation of either RTOs or pre-existing stable AChRs. The observed deficit was quantitatively consistent with the deficit predicted by a mathematical model based on interruption of stabilization following denervation. We conclude that: (i) the observed deficit after denervation of NMJs is due to failure of stabilization of pre-existing RTOs; (ii) RTOs at normally innervated NMJs are precursors of stable AChRs; (iii) stabilization occurs after the insertion of AChRs at NMJs, and (iv) motor nerves play a key role in stabilization of RTOs. The concept of receptor stabilization has important implications for understanding the biology of the neuromuscular junction and post-synaptic plasticity.

Animals↗
PubMed1992

FMRFamide-related peptides potentiate transmission at the squid giant synapse.

The stellate ganglion of the squid Loligo pealli contains the neuropeptides Phe-Met-Arg-Phe-NH2 (FMRFamide), Phe-Leu-Arg-Phe-NH2 (FLRFamide) and at least one N-terminally extended FMRFamide-related peptide that is yet to be fully characterized. Both local application and arterial perfusion of FLRFamide potentiate transmission at the giant synapse. The N-terminally related peptide Ser-Asp-Pro-Phe-Leu-Arg-Phe-NH2 (SDPFLRFamide) produced a similar effect. The threshold for both the tetra- and the hepta-peptides was less than 10 microM. Potentiation could be detected as an increase in rate of rise of the EPSPs, as an increase in amplitude of the EPSP in the absence of spikes, or under voltage clamp as an increase in the EPSC. The effect was most pronounced when the synapse was fatigued by high frequency stimulation. Another molluscan peptide, eledoisin and also leucine enkephalin were without effect. In the absence of any detectable effects of FLRFamide on the resting membrane potential of either pre- or postsynaptic terminals or on the presynaptic spike, it is suggested that the peptide influences transmitter mobilization. However, the peptide could also exert small changes in preterminal calcium currents, which so far we have been unable to detect.

Animals↗
PubMed1992

The calyx-type synapse of the chick ciliary ganglion as a model of fast cholinergic transmission.

The calyx-type synapse of the embryonic chick ciliary ganglion is reviewed as a model of transmitter release from a vertebrate presynaptic nerve terminal. This nerve terminal is extensive in area, enabling the penetration with microelectrodes and the application of patch-clamp techniques. In other respects the calyx synapse is a typical fast-transmitting cholinergic nerve terminal. This synapse has been used to obtain the first recordings of action potentials and calcium currents in a vertebrate presynaptic nerve terminal and is the only preparation in which it has proved possible to record single calcium channels directly from the transmitter release sites. The calyx remains a powerful experimental preparation for the further analysis of the mechanism and control of neurotransmitter release in fast-transmitting nerve terminals.

Animals↗
PubMed1991

Single calcium channels on a cholinergic presynaptic nerve terminal.

The calyx-type synapse of the chick ciliary ganglion was used to examine single calcium channels in a vertebrate cholinergic presynaptic nerve terminal by means of the cell-attached, patch-clamp technique. Calcium channels were recorded on the internal, transmitter-release face of the nerve terminal, but were not detected on the external face. These channels were recruited at -30 mV, with maximum activation at about +30 mV, and were sometimes clustered at high densities. Single-channel conductance estimates with voltage-pulse or -ramp techniques gave values of 11-14 pS with 110 mM barium, which is in the intermediate, N-type range for calcium channels on a control neuron. This nerve terminal calcium channel, termed the NPT-type, may link action potentials to transmitter release at many vertebrate fast-transmitting synapses.

Animals↗
PubMed1991

Characterization of a calcium current in a vertebrate cholinergic presynaptic nerve terminal.

Calcium currents were recorded from a cholinergic presynaptic nerve terminal in the chick ciliary ganglion using the whole-cell voltage-clamp technique. The presynaptic element of this synapse is in the form of a calyx that envelops the postsynaptic ciliary neuron. A method was developed to isolate the ciliary neuron, expose the calyx, and apply patch-clamp electrodes under visual control. The presynaptic Ca current activated at +30 mV with a fast time constant of about 1.5 msec and deactivated at -80 mV with a time constant of about 0.5 msec, values that are consistent with a role in action-potential-dependent transmitter release. The calyx Ca current was blocked by 0.1 mM Cd or 2 microM omega-conotoxin and was resistant to voltage-dependent inactivation. The presynaptic Ca channel exhibits similarities to the N-type group but differs from these by the minimal voltage-dependent inactivation. This type of channel, designated CaN-PT (N-like, presynaptic terminal), may play a key role in transmitter release at many vertebrate fast-transmitting synapses.

Animals↗
PubMed1990

Calcium currents recorded from a vertebrate presynaptic nerve terminal are resistant to the dihydropyridine nifedipine.

The influx of Ca ions into the presynaptic nerve terminal through ion channels is a key link between the action potential and the release of chemical transmitters. It is not clear, however, which types of Ca channel are involved in neurosecretion at vertebrate synapses. In particular, there is disagreement as to whether these channels are sensitive to dihydropyridine blockers, characteristic of L-type Ca channels. We have used the chicken ciliary ganglion calyx synapse to test the effect of the dihydropyridine nifedipine on Ca current recorded directly from a cholinergic presynaptic nerve terminal. We used a control neuron to define the experimental conditions under which L-type Ca channels are blocked by 10 microM nifedipine. We then tested the effect of the dihydropyridine on Ca currents recorded from the presynaptic terminal using the same conditions. Nifedipine did not reduce the calyx Ca current nor did it block chemical transmission through the ganglion. The lack of effect of the dihydropyridine was not due to restricted access since omega-conotoxin GVIA, a peptide toxin that blocks transmission at this synapse, rapidly blocked the calyx Ca current. Thus, the predominant Ca channel in this presynaptic nerve terminal is not dihydropyridine sensitive and, hence, cannot be characterized as L-type.

Animals↗
PubMed1989

Calcium currents in a vertebrate presynaptic nerve terminal: the chick ciliary ganglion calyx.

Ca currents (ICa) were recorded from presynaptic nerve terminals in the chick ciliary ganglion. Ciliary neurons are innervated by a single nerve terminal that extends over a wide area of the neuron surface to form a 'calyx'. The neurons were dissociated enzymatically with the calyx intact and the patch clamp technique was used in the whole cell mode to record ion currents. A small inward ICa (peak current 20-80 pA) was recorded that was blocked by external Cd. Only one component of ICa was detected. This was recruited at positive membrane potentials, exhibited no evidence of inactivation during a 25-ms depolarizing pulse, and deactivated rapidly. Thus, the ICa recorded in this vertebrate presynaptic nerve terminal was similar to the high-voltage activated, fast deactivating, current reported in other neurons.

Animals↗
PubMed1988

Inactivation of calcium channels in rat pituitary intermediate lobe cells.

The voltage-dependent inactivation of Ca currents was explored in dissociated intermediate lobe (IL) cells from the rat pituitary. On the basis of current-voltage relations two main inward currents could be identified in this cell, a transient current, (I-t), and a sustained current, (I-s). Inactivation was explored either by changing the holding potential and testing the change in the inward currents during a brief test pulse, or, by depolarizing the membrane and following the decay of the evoked inward current. Three current decay rates were identified, each with a characteristic dependence on membrane potential. The fastest decay rate (tau 1), was attributed to the inactivation of the I-t current and had a value of 57 ms at -40 mV, decreasing to 10 ms at -10 mV (extrapolated value of 6 ms at 0 mV). The other two decay rates, tau 2 and tau 3, decreased monotonically with depolarization of the membrane potential and reflected the inactivation of the I-s current with values of 1.8 and 20 s at 0 mV. I-s inactivation and reactivation was found to occur even in the normal resting potential range of this cell. These properties of the calcium channels can explain the voltage-dependent inactivation of secretion that has been observed previously in this and other secretory cells. In addition, they suggest that calcium currents, and hence secretion, may be modulated by external factors that cause small, but sustained, changes in the resting potential of the IL cell.

Adenosine Triphosphate↗
PubMed1988

Evidence for anion channels in secretory vesicles.

Secretory vesicles from bovine neurohypophysis were reconstituted into lipid bilayers. Electrical measurements on the lipid bilayers under voltage clamp demonstrated the presence of channels that are permeable to chloride ions, are blocked by 4,4'-diisothiocyanostilbene-2,2'-disulfonate, and are slightly voltage dependent. When several different membrane fractions were used for the reconstitution, the probability of finding channels correlated with the fraction of secretory vesicle membrane in the membrane fraction, indicating that the secretory vesicles are the source of the channels. The observed anion channel can provide a pathway for the anion transport that has previously been described for secretory vesicles. The secretory vesicle anion channel may play a role in calcium-induced secretion.

Animals↗
PubMed1987

Light microscopic visualisation of the presynaptic nerve terminal calyx in dissociated chick ciliary ganglion neurons.

The pre- and postsynaptic elements of the calyx-type synapse in the chick ciliary ganglion were stained with Lucifer yellow in situ, and the structure of this synapse was examined after enzymatic dissociation of the ganglion. Back-staining of the ciliary nerve resulted in darkly stained neuronal cell bodies. Foreward-staining of the presynaptic oculomotor nerve did not stain the neurons, but instead resulted in a 'halo' of fluorescence around the cell bodies, corresponding to the large presynaptic calyxes. This study demonstrates the feasability of staining the presynaptic terminals in dissociated ciliary neurons and demonstrates the range of calyx structure at this physiologically interesting synapse.

Animals↗
PubMed1986

The effects of nerve section on the non-quantal release of ACh from the motor nerve terminal.

The spontaneous release of acetylcholine (ACh) from motor nerve terminals is now thought to occur by two mechanisms: (a) quantal release, giving rise to miniature endplate potentials; and (b) non-quantal release. In this study we have examined the effect of nerve section on spontaneous non-quantal ACh release, and have compared the time-course of cessation of non-quantal and quantal ACh release. Non-quantal ACh release, measured by an electrophysiological technique, declined 4 h after nerve section to approximately 50% of the control value. At 8-10 h it briefly rose again, then gradually declined to undetectable levels. Spontaneous quantal release (frequency of miniature endplate potentials) in the same muscle fibers remained close to control levels for 8 h after nerve section, and also increased prior to failure. Decline of non-quantal ACh release appears to be the earliest change in the nerve terminal following nerve transection; it may therefore be relevant in understanding the effects of denervation on the consequent changes in muscle properties.

Acetylcholine↗
PubMed1986

Botulinum toxin prevents stimulus-induced backfiring produced by neostigmine in the mouse phrenic nerve-diaphragm.

The origin of motor nerve antidromic activity (backfiring) induced by anticholinesterase treatment was examined in the mouse phrenic nerve-hemidiaphragm preparation. Botulinum toxin was used to determine whether backfiring is due to (a) a direct effect of the cholinesterase inhibitor on the nerve terminal, or (b) an indirect effect via the prolongation of the action of acetylcholine. In previously untreated control preparations, neostigmine produced spontaneous and stimulus-induced antidromic activity in the phrenic nerve when rapidly introduced into the diaphragm via its vasculature. This activity could be reversibly blocked by d-tubocurarine and decamethonium, but not by atropine. Neostigmine-induced backfiring did not occur in preparations in which transmitter release was blocked with botulinum toxin. Infusion of a small bolus of a high concentration of acetylcholine following neostigmine treatment resulted in a short-term increase in the incidence of antidromic activity, followed by block, in both controls and botulinum toxin-treated preparations. It is concluded that transmitter release is necessary for the production of backfiring following cholinesterase inhibition since neostigmine alone does not elicit antidromic activity in botulinum toxin-treated preparations at concentrations which are effective in controls. Our results support the hypothesis that the effects of neostigmine on the motoneurone terminal are mediated by the prolonged action of acetylcholine that occurs with inhibition of acetylcholinesterase.

Acetylcholine↗
PubMed1986

Decline in calcium cooperativity as the basis of facilitation at the squid giant synapse.

The role of Ca in transmitter release and facilitation has been examined at the squid giant synapse by evaluating the effect of changes in the external concentration of Ca on the excitatory postsynaptic potential (EPSP). Changes in Ca were achieved by means of an arterial perfusion technique, circumventing the diffusion barrier that exists between the synapse and the bathing medium. Transmitter release was found to follow a high power (n) of the external Ca at low nonsaturating Ca concentrations and low stimulus frequencies: 4.0 +/- 0.1 (mean +/- SE) in 22 experiments. The value of n was not fixed, however, but declined at stimulus frequencies above 0.3 Hz to 2.9 at Hz, 2.3 at 10 Hz, 1.7 at 50 Hz, and 1.1 at 80 Hz. This decline in n was due to a greater proportional facilitation of the EPSP at lower Ca levels. In a separate experiment, facilitation was determined at a fixed low Ca level over a wide range of stimulus frequencies. A plot of the maximum percentage increase in the EPSP against the stimulus frequency described three "steps," with plateaus occurring at 0.3-10 Hz, 10-50 Hz, and over 80 Hz. The timing of these steps corresponds to the stimulus frequencies at which the cooperativity declines. The results of this study indicate that the cooperative action of four Ca ions are required to trigger the transmitter release mechanism, and that the phenomenon of facilitation involves a reduction in Ca cooperativity. It is proposed that Ca ions can bind up to four receptors on the release site and that binding results in the opening of "gates." The opening of all four gates triggers transmitter release.(ABSTRACT TRUNCATED AT 250 WORDS)

Action Potentials↗
PubMed1985

A model for exocytosis based on the opening of calcium-activated potassium channels in vesicles.

It is proposed that the role of calcium in calcium-induced exocytosis is to open Ca-activated K channels present in vesicle membranes. The opening of these channels coupled with anion transport across the vesicle membranes would result in an influx of K and anions, increasing the osmotic pressure of the vesicles. For those vesicles situated very close to the cell plasma membrane, this would lead to fusion with the membrane and exocytosis of the vesicle contents. This model can account for facilitation and other key properties of transmitter release. In addition, the model predicts that vesicles with a higher transmitter content, and hence higher initial osmotic pressure, would be preferentially discharged. The model also predicts that a faster response can be obtained for small vesicles than for large vesicles, providing a rationale as to why neurotransmitters, which must be released quickly, are packaged in small vesicles.

Action Potentials↗
PubMed1985

Structure and function of urodele myelin lacking alpha-hydroxy fatty acid-containing galactosphingolipids: slow nerve conduction and unusual myelin thickness.

Myelin of several Caudata (Urodela) species appears to be unique in the fact that it lacks hydroxycerebrosides and hydroxysulfatides although it contains their non-hydroxy counterparts. Comparison of the nerve conduction velocities in the Urodeles Necturus (salamander) and Notophthalmus (newt) with that in a reptile, Anolis (chameleon) which contains hydroxycerebrosides and -sulfatides indicated that the values were significantly reduced in the urodeles. Furthermore, urodele myelin thickness remained uniformly the same regardless of the size of the nerve fiber. Despite these differences the myelins appeared structurally similar. Electron microscopic and X-ray diffraction studies did not disclose any structural difference between the two orders. A teased fiber technique established that the ratio of internodal distance and fiber diameter in urodele nerves was essentially similar to that in Anolis. These findings suggest that the absence of hydroxycerebroside and -sulfatide may be related to the reduction in nerve conduction velocity and unusual myelin thickness in the urodele nervous system.

Animals↗