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F F Weight

Publications and source records attributed to F F Weight.

At least 91 records · Page 5Linked to original sources
PubMed1987

Patch-clamp study of the calcium-dependent chloride current in AtT-20 pituitary cells.

1. Voltage-clamp recordings were made from cultured AtT-20 pituitary cells using the whole-cell patch-clamp technique. Cells were perfused internally with Cs+ to block K+ currents and bathed externally with either 1 microM tetrodotoxin or with tetraethylammonium (TEA) as a Na+ substitute to block voltage-activated Na+ currents. 2. Depolarizing voltage steps from a holding potential of -80 mV to potentials positive to -30 mV evoked two currents: a fast inward current that activated between -30 and +70 mV and a slowly activating current (designated "slow step current") that was inward between -30 and near 0 mV (the Cl- equilibrium potential) and outward positive to about 0 mV. Repolarization to -80 mV revealed a slowly decaying, inward tail current, whose magnitude with respect to step potential closely matched the current-voltage relationship of the voltage-activated Ca2+ current. 3. Activation of the fast inward current, slow step current, and tail current, was prevented by extracellular application of Cd2+ or removal of extracellular Ca2+. Replacement of extracellular Ca2+ with Ba2+ potentiated the fast inward current but blocked the slow step and tail currents. Intracellular perfusion with greater than 1 mM of the Ca2+ chelators ethyleneglycol-bis(beta-aminoethylether)-N,N'-tetraacetic acid (EGTA) or [1,2-bis(2)aminophenoxy]ethane N,N,N',N'-tetraacetic acid (BAPTA) prevented activation of the slow step and tail currents, but not the fast inward current. 4. The reversal potential of the slow inward current was sensitive to changes in the Cl- equilibrium potential but not to substitution of TEA for Na+. The slow step current, but not the fast inward current, was partially blocked by the Cl- channel blocker, 4-acetamido-4'-isothiocyanostilbene-2,2'-disulfonic acid. 5. These data indicate that both the slow inward tail current and the slowly activating, reversible step current were a Ca2+-dependent Cl- current, similar to that described in other neuronal and nonneuronal cell types. The fast inward current was a voltage-activated Ca2+ current, described previously in these and other cells. 6. In the absence of intracellular EGTA, the tail current decayed with complex kinetics, its time course apparently dependent on the magnitude of the voltage-activated Ca2+ current. In the presence of 200 microM intracellular EGTA, the tail current decayed significantly faster and often decayed exponentially.

Animals↗
PubMed1987

Muscarine-stimulated neurotransmitter release from PC12 cells.

The effect of muscarine on neurosecretion was studied in the rat pheochromocytoma cell line, PC12. When PC12 cells were exposed to muscarine the cells responded rapidly with elevation of cellular inositol trisphosphate levels, elevation of intracellular free Ca++ and release of stored transmitter. These three phenomena were totally inhibited by the muscarinic antagonist, atropine, but were unaffected by the nicotinic antagonist, d-tubocurarine. Muscarine did not stimulate the production of cyclic GMP in these cells. The muscarine-stimulated increases in inositol trisphosphate, intracellular free Ca++ and neurotransmitter release displayed similar time courses and concentration dependencies suggesting that the secretion observed may be associated with the formation of inositol trisphosphate and elevation of intracellular free Ca++. The increase in intracellular free Ca++ appeared to be due to a mobilization of Ca++ from intracellular stores inasmuch as the increase in intracellular free Ca++ was not inhibited by the voltage-dependent Ca++ channel antagonist, nifedipine, at concentrations demonstrated to block K+-induced Ca++ influx into the cells, and little or no uptake of 45Ca++ was noted when cells were stimulated with muscarine. Elevation of inositol trisphosphate, intercellular free Ca++ and stimulation of transmitter release were, however, inhibited by the absence of extracellular Ca++. The results suggest that muscarine-stimulated release of neurotransmitter may be associated with an inositol trisphosphate-induced mobilization of intracellular Ca++.

Animals↗
PubMed1986

MPTP causes a non-reversible depression of synaptic transmission in mouse neostriatal brain slice.

MPTP (1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine) causes a Parkinson's disease-like syndrome. The mechanism of MPTP's neurotoxicity is unknown; however, one hypothesis is that MPP+ (1-methyl-4-phenylpyridinium), a product of MPTP's oxidation, is the neurotoxic agent. Using a mouse brain slice preparation we studied the effects of MPTP and MPP+ on synaptic transmission. We found MPTP caused a decrease in amplitude of an excitatory synaptic response not reversed by washing. This non-reversible action of MPTP was prevented by GBR-32 and pargyline. MPP+s caused a decrease in synaptic transmission, but this decrease was reversed by washing. The results suggest that the toxic effect of MPTP on synaptic transmission is not accounted for by the action of MPP+.

1-Methyl-4-phenyl-1,2,3,6-tetrahydropyridine↗
PubMed1986

Cerebral 2-deoxyglucose uptake in rats during ethanol withdrawal and postwithdrawal.

The overt ethanol withdrawal syndrome is associated with a generalized increase in cerebral uptake of 2-deoxyglucose. Relatively high elevations of 2-deoxyglucose were observed in many structures associated with motor function, the mamillary body-anterior thalamus-cingulate cortex pathway, many thalamic nuclei, and the raphe. Overtly withdrawing rats had higher levels of 2-deoxyglucose than postwithdrawing animals that had been abstinent for 1-5 weeks in 96% of the gray areas evaluated. Postwithdrawal was associated with increased amounts of 2-deoxyglucose in comparison to controls in 80% of the gray areas evaluated. Postwithdrawal and control rats did not differ in some areas involved with motor function and some limbic structures, such as the mamillary body-anterior thalamus-cingulate cortex pathway. It is concluded that the ethanol-withdrawal syndrome results in alterations in cerebral physiology, some of which persist for at least 5 weeks postwithdrawal.

Animals↗
PubMed1986

Effects of ethanol administration on parameters of immunocompetency in rats.

Ethanol administered to rats intragastrically in doses sufficient to cause dependency resulted in a rapid cell loss from the thymus and spleen. Cell loss from the peripheral blood was due primarily to a loss of lymphocytes, but a concomitant granulocytosis resulted in only small changes in the total leukocyte count. Lymphocyte proliferation to both T- and B-cell mitogens was severely compromised by ethanol treatment. The cell loss and functional lymphocyte impairment also occurred at half the ethanol dose required to induce dependency. Although cell numbers recovered relatively quickly after ethanol withdrawal, lymphocyte function, as measured by proliferation, recovered more slowly. Ethanol administration before or during immunization with sheep erythrocytes resulted in an impairment in the ability of animals to respond with a primary immune response to this antigen. These data suggest that ethanol given in quantities sufficient to produce dependence impairs in vitro and in vivo parameters of immunocompetency.

Animals↗
PubMed1986

A guanine nucleotide-binding protein mediates the inhibition of voltage-dependent calcium current by somatostatin in a pituitary cell line.

Somatostatin reduces voltage-dependent Ca2+ current (ICa) and intracellular free Ca2+ concentration in the AtT-20/D16-16 pituitary cell line. We tested whether guanine nucleotide-binding proteins (G or N proteins) are involved in the signal transduction mechanism between the somatostatin receptor and voltage-dependent Ca2+ channels. Treatment of the cells with pertussis toxin, which selectively ADP ribosylates the GTP binding proteins Gi and Go and suppresses the ability of Gi to couple inhibitory receptors to adenylate cyclase, abolished the action of somatostatin on both ICa and intracellular free Ca2+. Intracellular application of the nonhydrolyzable guanine nucleotide analog guanosine 5'-[gamma-thio]triphosphate (GTP[gamma S]), which irreversibly activates G proteins, changed the somatostatin effect on ICa from a reversible to an irreversible inhibition. Intracellular GTP[gamma S] alone caused a very slowly developing inhibition of ICa. When ICa was inhibited by GTP[gamma S] (alone or with somatostatin), it failed to respond to subsequent applications of somatostatin. The effect of GTP[gamma S] on the inhibition of ICa by somatostatin was not altered by the intracellular application of cAMP and 3-isobutyl-1-methylxanthine. The results suggest that a GTP-binding protein is directly involved in the cAMP-independent receptor-mediated inhibition of voltage-dependent Ca2+ channels.

Adenylate Cyclase Toxin↗
PubMed1986

Non-cholinergic synaptic excitation in neostriatum: pharmacological evidence for mediation by a glutamate-like transmitter.

We studied the synaptic pharmacology of an excitatory pathway in the neostriatum using electrophysiological techniques in tissue slices from rats. In response to single electrical stimuli, two negative, extracellular potentials (N-1 and N-2) were recorded through micropipette electrodes within 150-450 micron of the stimulating cathode. N-2 was reversibly reduced or abolished by reducing the concentration of calcium in the bathing medium, while N-1 was unaffected. Both N-1 and N-2 were reversibly abolished by the local anaesthetic procaine. Single-unit, extracellular action potentials were, at times, associated with either N-1 or N-2. Intracellular recordings showed action potentials at N-2 latency arising from graded, monophasic, depolarizing potentials. Bath-applied cholinoceptor and dopamine receptor antagonists failed to reduce N-2. By contrast, antagonists of excitatory amino acid transmitters reversibly reduced or abolished N-2. gamma-D-Glutamylglycine (GG), (+/-)-cis-2,3-piperidine dicarboxylic acid (PDA) and DL-2-amino-4-phosphonobutyric acid (APB) blocked N-2 with ED50S of 0.79 mM, 1.0 mM and 1.1 mM, respectively. (-)-Baclofen reversibly blocked N-2 with an ED50 of 0.79 microM; (+)-baclofen was 330 times less potent. The results suggest that N-1 results from direct activation of fibre tracts or cell bodies, while N-2 is a population spike mediated by excitatory synapses whose natural transmitter pharmacologically resembles glutamate.

Animals↗
PubMed1986

Na+ and Ca2+ currents of acutely isolated adult rat nodose ganglion cells.

The electrical properties of nodose ganglion cells acutely isolated from adult rats were studied using the whole-cell patch-clamp recording method. Current-clamp recordings revealed a mean resting membrane potential of -54.3 mV and an input resistance of 527 M omega. Depolarizing current steps evoked action potentials with the following properties (mean): amplitude 111 mV, threshold -36 mV, and rate of rise 117 V/s. Two types of action potentials were observed, short and long duration. These properties, with the exception of input resistance (527 M omega cf. 50 M omega), are similar to those reported previously using intracellular recording methods in intact nodose ganglia (11, 20, 28). Brief application of 10 microM 5-hydroxytryptamine resulted in a rapid depolarization and burst of action potentials in the majority of cells. With voltage-clamp recording, step depolarizations to potentials positive to -10 mV elicited a transient inward current that was followed by a sustained outward current. Inward Na+ current was isolated by ion substitution and pharmacological agents. Two types of Na+ current were observed. One current was completely abolished by 3-15 microM tetrodotoxin (TTX), had a rapid time course, activated over the potential range -60 to -10 mV, and attained half-maximal conductance at -30 mV. The other current persisted in the presence of 15 microM TTX, had a slower time course, activated over the potential range -30 to 0 mV, and attained half-maximal conductance at -15 mV. In addition, 500 microM Cd2+ and 5.0 mM Co2+ reduced the TTX-insensitive current to 53 and 42% of control, respectively. Inward Ca2+ current was isolated by ion substitution and pharmacological agents and was identified by a dependence on external Ca2+. Cd2+ (500 microM) and Co2+ (5 mM) reduced the maximal inward current to 5 and 20% of control, respectively. When Ba2+ was substituted for Ca2+ as the charge carrier, the maximal inward current increased to 175% of control. Some cells had two Ca2+ current components, an inactivating component that activated near -60 mV and a large sustained current that activated near -40 mV. The initial inactivating current appeared as a "hump" on the current-voltage (I-V) curve over the potential range of -60 to -30 mV. The results indicate that, following isolation of these adult mammalian neurons, the membrane surfaces are sufficiently clean to allow patch-clamp recording.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed1986

The pathway for the slow inhibitory postsynaptic potential in bullfrog sympathetic ganglia.

Intracellular and sucrose gap recording techniques were used to examine synaptically evoked potentials and the response of neurons in bullfrog paravertebral sympathetic ganglia to muscarinic agonists. These neurons were defined as either B or C cells on the basis of the conduction velocity of antidromically evoked action potentials. Following stimulation of preganglionic C-fibers in the rostral portion of the VIIIth spinal nerve, a fast nicotinic excitatory postsynaptic potential (EPSP) and a slow atropine-sensitive inhibitory postsynaptic potential (IPSP) could be recorded intracellularly in C cells of the IXth and Xth paravertebral ganglia treated with 70 microM d-tubocurarine chloride (dTC). Under these conditions, local iontophoretic application of acetylcholine (ACh) could produce a slow hyperpolarization of C cell membrane potential. ACh hyperpolarizations or slow IPSPs were not detected in ganglionic B cells. Stimulation of the preganglionic B-fibers in the sympathetic chain produced a fast nicotinic EPSP and a slow muscarinic EPSP in ganglionic B cells. A small population of C cells also received cholinergic B-fiber innervation from the sympathetic chain and exhibited a slow IPSP upon tetanic stimulation of this pathway. When curarized ganglia were examined by means of sucrose gap recording, superfusion of the muscarinic agonist, methacholine (MCh), produced an initial hyperpolarization (MChH) followed by a depolarization (MChD). Both responses were blocked by atropine and therefore presumably reflect the activation of muscarinic receptors involved in the generation of the slow IPSP and the slow EPSP, respectively. Although synaptic transmission was blocked by Ringer solution containing 4 mM Co2+, neither this solution nor 10 microM tetrodotoxin reduced the amplitude of the MChH. The MChH was slightly reduced by Ringer solution containing 0.1 mM Ca2+, however, the response could be restored by the addition of 6 mM Mg2+. These results indicate that the MChH in curarized bullfrog sympathetic ganglia results from a direct muscarinic action on ganglionic cells. This suggests that the slow IPSP is mediated by ACh released from cholinergic preganglionic fibers that make synaptic contact with ganglionic C cells.

Acetylcholine↗
PubMed1985

Single acetylcholine channel currents in sympathetic neurons.

Single acetylcholine (ACh) channel currents were studied by the gigaohm patch-clamp technique in cultured sympathetic neurons of the bullfrog, Rana catesbeiana. Recordings were made at 22 degrees C on cell-attached and excised membrane patches. When ACh (0.5-1 microM) was present in the pipette, a single class of inward currents was observed with a chord conductance of 30 pS and a reversal potential of -2 mV. The mean channel open time was 11.6 ms at -65 mV and showed little or no voltage-dependence over the range -85 to -45 mV. These channels appear to mediate the fast nicotinic excitatory postsynaptic current.

Acetylcholine↗
PubMed1985

Dopaminergic mechanisms in subthalamic nucleus of rat: analysis using horseradish peroxidase and microiontophoresis.

Afferent connections to the subthalamic nucleus (STN) were studied by microiontophoretically injecting horseradish peroxidase (HRP) into the STN and studying its retrograde transport. Remotely labelled neurons were frequently observed in both the globus pallidus and the pars compacta region of substantia nigra. In addition, individually labelled neurons were occasionally found in other brain regions. The sensitivity of neurons in the STN to dopamine (DA) was studied by applying DA to neurons in the STN by microiontophoresis. Three patterns of response to DA were observed. The most frequent response, observed in 46% of the STN neurons studied, was a decrease in the discharge frequency. In 15% of the neurons there was an increased frequency of firing. Eleven percent of the neurons exhibited a mixed response consisting of an initial depression of discharge rate followed by a delayed increase. The responses of STN neurons to DA were not antagonized by iontophoretically applied haloperidol. In neurons whose firing frequency was decreased by DA, the iontophoretic application of apomorphine and norepinephrine also decreased discharge rate. The observations of HRP-labelled neurons in the pars compacta region of substantia nigra following injection of HRP into the STN together with the DA responsiveness of STN neurons suggest the possibility of a dopaminergic nigro-subthalamic pathway.

Animals↗
PubMed1985

Perforant pathway-evoked long-term potentiation of CA1 neurons in the hippocampal slice preparation.

Previously, we have presented electrophysiological evidence reaffirming the existence of a controversial hippocampal pathway. These fibers are part of the perforant pathway and terminate directly on the CA1 cells. We now report that, in the hippocampal slice preparation, tetanic stimulation of the perforant pathway produces long-term potentiation (LTP) of CA1 cell responses. LTP of population spikes varied from 150% to 500%. The results were of interest because these axons synapse at distal sites on the apical dendrite. This location is usually thought to be a difficult site to evoke action potentials.

Animals↗
PubMed1985

Transient voltage and calcium-dependent outward currents in hippocampal CA3 pyramidal neurons.

Membrane currents activated by step changes in membrane potential were studied in hippocampal pyramidal neurons of region CA3 using the single microelectrode voltage-clamp technique. The transient outward current activated by depolarizing steps appeared to be composed of two transient currents that could be distinguished by differences in voltage sensitivity, time course, and pharmacological sensitivity. The more slowly decaying current was activated by voltage steps positive to -60 mV and declined exponentially with a time constant between 200 and 400 ms. This current inactivated as the holding potential was made more positive over the range of -75 to -45 mV and was 50% inactivated near -60 mV. The more slowly decaying transient current was selectively blocked by 0.5 mM 4-aminopyridine (4-AP) but not by 5-10 mM tetraethylammonium (TEA) or 2-5 mM Mn2+. The second transient current had a much faster time course than the 4-AP-sensitive current, having a duration of 5-20 ms. This very fast transient current was observed during potential steps positive to -45 mV. The fast transient current was inactivated when the holding potential was made positive to -45 mV. The amplitude of the fast transient current was greatly reduced by the application of 4 mM Mn2+ or Ca2+-free artificial cerebrospinal fluid (CSF). The fast transient current appeared to be unaffected by 0.5 mM 4-AP but was greatly reduced by 10 mM TEA. These results suggest that the transient outward current observed during depolarizing steps is composed of at least two distinct transient currents. The more slowly decaying current resembles the A-current originally described in molluscan neurons (9, 32, 42) in voltage sensitivity, time course, and pharmacological sensitivity. The faster transient current resembles a fast, Ca2+-dependent transient current previously observed in bull-frog sympathetic neurons (5, 27).

4-Aminopyridine↗
PubMed1983

Action potentials and membrane ion channels in clonal anterior pituitary cells.

The electrophysiological properties of the mouse anterior pituitary cell line AtT-20/D16-16 were investigated with intracellular and patch-clamp techniques. Clonal AtT-20/D16-16 cells were found to be electrically excitable, with most cells exhibiting spontaneous bursting action potentials. The mean burst rates varied from 1.4 Hz at -55mV to 8.2 Hz at -25mV, showing an approximately linear frequency-current relationship in the low current range. The bursts consisted of one to several fast Na+ spikes superimposed on a slow pacemaker potential, followed by a Ca2+ spike and a Ca2+-sensitive afterhyperpolarization. Removal of either Na+ or Ca2+ from the bathing medium led to cessation of spontaneous activity and the appearance of arrhythmic firing patterns. Single channel recordings revealed the presence of Ca2+-dependent K+ channels with unitary conductances of approximately equal to 130 pS in physiological medium. These channels were activated by both intracellular Ca2+ and membrane depolarization. Addition of norepinephrine (10 microM) led to increases in burst frequency and beta-endorphin secretion mediated by activation of beta-adrenergic receptors. Our results, in conjunction with previous work, suggest that the Ca2+ that enters the cell during the burst may be involved in hormone secretion.

Action Potentials↗
PubMed1982

Action potential repolarization may involve a transient, Ca2+-sensitive outward current in a vertebrate neurone.

Repolarization of the action potential in squid axon1 and several types of neurones2-4 involves a voltage-activated potassium (K+) current. Voltage clamp analysis has demonstrated that this current has rapid activation kinetics1,3-5. In several neuronal types, the same technique has also revealed a slowly activated K+ current that is calcium (Ca2+)-sensitive3,5-10. This slow Ca2+-activated K+ current is the major current underlying the late, slower portion of the after-hyperpolarization following an action potential11-14. In several muscle types, fast, transient Ca2+-dependent K+ currents have been described15-17 which may contribute to repolarization of the action potential. Rapidly activating, Ca2+-dependent K+ currents have been observed in sympathetic neurones of the bullfrog and it has been suggested that they contribute to action potential repolarization of those neurones8,9,18. We have studied the membrane currents in bullfrog sympathetic neurones using voltage clamp methods and report here a transient outward current that appears to be composed of two separate currents. One of those currents is a transient, Ca2+-sensitive outward current as indicated by a significant reduction of the current by treatments that reduce or block Ca2+ entry (Mn2+, Cd2+, Co2+, Mg2+ or Ca2+-free Ringer). Such treatments also decreased the rate of action potential repolarization. The results suggest that this current is involved in repolarization of the action potential and consequently may regulate Ca2+ entry into the neurone during spike activity.

Action Potentials↗
PubMed1982

Ethanol-withdrawal syndrome associated with both general and localized increases in glucose uptake in rat brain.

Glucose uptake was studied in the brains of rats undergoing an overt ethanol-withdrawal syndrome by 2-deoxy-D-[14C]glucose autoradiography. In addition to a general increase in glucose uptake, localized alterations were observed in sensorimotor cortex, globus pallidus, thalamus and cerebellum. The results suggest that the ethanol-withdrawal syndrome is associated with a general increase in glucose metabolism as well as localized increases in functionally distinct regions of sensory and motor brain regions.

Alcoholism↗
PubMed1982

Perforant pathway activation of hippocampal CA1 stratum pyramidale neurons: electrophysiological evidence for a direct pathway.

Electrophysiological techniques were used to investigate the effect of stimulating the perforant pathway (PP) on pyramidal neurons in the CA1 region of the hippocampal slice. Stimulation of the PP evoked both field potentials and single unit discharges in the pyramidal cell layer of the CA1 region. Several lines of experimental evidence suggest that the CA1 response does not involve granule or CA3 neurons: (i) movement of the recording electrode in the CA1 region away from the site of stimulation in the PP and closer to the CA3 region increased the latency of the evoked potential; (ii) the sum of latencies of the individual pathways in a trisynaptic circuit - from the PP to granule cells to CA3 neurons to CA1 neurons - was 2-3 times longer than the latency of the PP evoked response recorded in the CA1 region: (iii) lesioning the mossy fiber pathway or excising the CA3 region did not inhibit the CA1 response to PP stimulation. Other experimental results suggest that the PP activation of CA1 pyramidal neurons involves a direct synaptic pathway: (i) PP stimulation evoked potentials with similar latencies in the dentate gyrus and the CA1 region; (ii) the CA1 response was abolished in a Krebs' solution containing low calcium/high magnesium; (iii) excising a portion of the CA1 region between the stimulating electrode in the PP and the CA1 recording electrode, but sparing the PP, did not abolish the CA1 response; (iv) electrolytic lesions of the PP abolished the CA1 response to PP stimulation, but did not affect the CA1 response to stimulation of the CA3 region. The data suggest that fibers in the PP make direct synaptic connection with pyramidal neurons in the CA1 region of the hippocampus.

Animals↗