Biomedical subjects

U Misgeld

Publications and source records attributed to U Misgeld.

At least 55 records · Page 3Linked to original sources

PubMed1992

Burst activity and synaptic mechanisms in a hypothalamic network grown in culture.

In a cultured network of rat embryonic hypothalamic cells, synaptic interaction is through GABAA-receptors, that mediate inhibition by an increase in Cl- conductance, and AMPA-receptors, that mediate excitation by an increase in monovalent cationic conductance. Changes in the balance of inhibition and excitation towards a predominance of excitation lead to phasic synchronous activity of the cells. Synaptic interaction through these receptors is thus capable of modulating neurosecretion rapidly.

Action Potentials↗

PubMed1991

Cells from embryonic rat striatum cocultured with mesencephalic glia express dopaminergic phenotypes.

To study region-specific transmitter phenotype expression, cells of embryonic day 14 (E14) rat neostriatum (ganglionic eminence plus cortical plate) or of the substantia nigra (ventral mesencephalon) were cultured on glial cells either from substantia nigra or neostriatum (E21). By antityrosine hydroxylase immunocytochemistry, immunoblotting of tyrosine hydroxylase protein and quantitation of dopamine and its metabolites by HPLC, dopaminergic cells were revealed in nigral and neostriatal cultures plated on nigral glial cells. No dopaminergic cells were found among neostriatal neurons plated on neostriatal glial cells. It is concluded that glia from substantia nigra but not glia from neostriatum is capable of inducing development or promoting survival of dopaminergic cells.

Animals↗

PubMed1991

Reduction of GABAA receptor-mediated inhibition by the non-NMDA receptor antagonist 6-cyano-7-nitroquinoxaline-2,3-dione in cultured neurons of rat brain.

The action of the non-N-methyl-D-aspartate (non-NMDA) receptor antagonist 6-cyano-7-nitroquinoxaline-2,3-dione (CNQX) on gamma-aminobutyric acid-A (GABAA) receptor-mediated currents was studied in dissociated rat midbrain and hypothalamic cultures using whole-cell recording. Spontaneous synaptic activity consisted of excitatory (EPSCs) and inhibitory postsynaptic currents (IPSCs). Bicuculline (20 microM) blocked IPSCs and increased the frequency of EPSCs. CNQX (1 microM) reduced both EPSCs and IPSCs. In the presence of 0.3 microM tetrodotoxin (TTX), CNQX (1-20 microM) blocked miniature EPSCs and reduced IPSCs. In TTX, increasing K+ (20 mM) evoked EPSCs and IPSCs in a Ca-dependent manner. CNQX (10 microM) blocked evoked EPSCs and diminished evoked IPSCs similarly as miniature IPSCs. Muscimol-(0.2-5 microM) induced currents were dose-dependently reduced by CNQX (10-50 microM). It is concluded that CNQX reduces GABAA receptor-mediated inhibition primarily by reducing the excitatory drive in the evolving network, but, in addition, has a significant blocking effect on the GABAA receptor-channel complex.

6-Cyano-7-nitroquinoxaline-2,3-dione↗

PubMed1991

Effects of antagonists on quisqualate and nicotinic receptor-mediated currents of midbrain neurones in culture.

1. The action of non-N-methyl-D-aspartate (non-NMDA) and nicotinic antagonists on excitatory postsynaptic currents (e.p.s.cs) and on quisqualate (Quis)- and nicotine-gated currents was studied by use of whole-cell recording in dissociated culture of the rat midbrain. 2. 6-Cyano-7-nitroquinoxaline-2,3-dione (CNQX; 0.1 microM) and kynurenic acid (0.1 mM) attenuated network-generated and miniature e.p.s.cs while mecamylamine (100 microM) and hexamethonium (400 microM) had no effect. Acetylcholine (ACh) enhanced or suppressed e.p.s.cs. The suppressing effect of ACh was blocked by atropine (0.1-10 microM). 3. ACh (50-1000 microM) and quisqualate (Quis, 0.1-20 microM) induced inward currents with the same reversal potential as e.p.s.cs. 4. Application of Quis and alpha-amino-3-hydroxy-5-methylisoxazole-4-propionic acid (AMPA) in a low concentration (0.5 and 5 microM, respectively) evoked a maintained current which was attenuated by CNQX (1 microM) and kynurenic acid (0.5 mM) but not by mecamylamine (100 microM). 5. Higher concentrations of Quis (5-20 microM) and AMPA (50-100 microM) evoked a transient and a maintained current component. Kynurenic acid (1 mM) reduced the transient but not the maintained component. CNQX (5-10 microM) increased the maintained component without reducing the transient one; 20 microM CNQX reduced both components. 6. ACh-induced transient current was mimicked by nicotine and reversibly and dose-dependently blocked by mecamylamine. Atropine (10 microM), hexamethonium (400 microM) as well as CNQX (100 microM) and kynurenic acid (1 mM) did not affect the current. 7. Hexamethonium (50-400 microM) voltage-dependently depressed the maintained current elicited by both Quis and ACh. 8. In conclusion, although the antagonists examined here seem to discriminate between non-NMDA and nicotinic receptor-mediated e.p.s.cs, they vary considerably in respect of their mode of action when tested on Quis, AMPA and ACh-induced currents.

6-Cyano-7-nitroquinoxaline-2,3-dione↗

PubMed1991

Picrotoxin- and 4-aminopyridine-induced activity in hilar neurons in the guinea pig hippocampal slice.

1. Paired extra- and intracellular recording was used to study the activity of neurons in the dentate hilus and their interaction with CA3/CA4 pyramidal neurons and granule cells during picrotoxin- or 4-aminopyridine (4-AP)-induced rhythmical activity in the guinea pig hippocampal slice. 2. Picrotoxin induced synchronous repetitive population spikes in the CA3, CA4, and hilar region, but no extracellular activity in the granule cell layer. 4-AP induced rhythmically occurring positive field-potential waves in the CA3, CA4, and granular layer coincident to negative/positive field potentials in the hilus. 3. Picrotoxin-induced activity originated in the CA3 area and subsequently appeared in the CA4 and hilar region, whereas 4-AP-induced activity appeared simultaneously in all subfields. 4. Blockade of fast glutamatergic excitation by 6-cyano-7-nitroquinoxaline-2,3-dione (CNQX, 10 microM) blocked the picrotoxin-induced activity but not the 4-AP-induced activity. 5. Focal application of tetrodotoxin (TTX) between area CA3 and CA4 blocked picrotoxin-induced activity in the CA4 and hilar region but decoupled 4-AP-induced activity in the CA3 area. 6. Under intracellular recording, picrotoxin induced bursts in CA3, CA4, and hilar neurons but K-dependent slow IPSPs in granule cells. 4-AP induced rhythmically occurring burst in hilar neurons synchronous to Cl- and K-dependent IPSPs in CA3, CA4, and granule cells. 7. Comparison of picrotoxin- and 4-AP-induced rhythmical burst activity reveals that many hilar neurons are excited by CA3/CA4 pyramidal neurons in addition to the well-known excitation by granule cells and perforant path fibers, and that, in turn, many hilar neurons inhibit CA3, CA4, and granule cells.

4-Aminopyridine↗

PubMed1990

Interaction of lithium with postsynaptic inhibition in guinea pig hippocampal neurons.

Intracellular recording techniques were used to study the effects of Li+ on postsynaptic inhibition of CA3 neurons in guinea pig hippocampal slices. Carbachol (0.3 microM) suppressed and phenylephrine (3 microM) enhanced the hyperpolarization induced by baclofen (0.15 microM). Low intracellular concentrations of Li+ (less than 10 microM) suppressed the muscarinic blockade of the K(+)-dependent inhibition, leaving its enhancement by noradrenergic receptor stimulation unchanged. K(+)-dependent inhibition per se was not affected. At high intracellular concentrations Li+ impaired postsynaptic Cl(-)-dependent inhibition by reducing the efficacy of an outward Cl- pump. While the effect of Li+ on the modulation of K(+)-dependent inhibition may be therapeutically relevant, its action on Cl(-)-dependent inhibition may underly some toxic effects.

Animals↗

PubMed1990

Neurons sensitive to pH in slices of the rat ventral medulla oblongata.

The effects of extracellular pH changes on neurons in slices of the rat ventral medulla oblongata were investigated by extracellular recording. Changes in discharge rate were correlated with pH changes in the tissue next to the recorded cell, as measured by H(+)-selective microelectrodes. pH was altered by varying the bicarbonate concentration ([HCO3-]) in the superfusion solution. In 136 out of 316 neurons, the number of spontaneous or electrically evoked discharges per unit time increased with decreasing pH and decreased with increasing pH. Changes of only 0.01-0.04 pH unit were effective in these pH-sensitive neurons. The response was transient; the discharge rate returned to the control value within a few minutes. The pH sensitivity persisted in the presence of 0.5 microM atropine, 20 microM bicuculline and after replacing Ca2+ by Mg2+ in the superfusion solution to reduce synaptic transmission. The response to the same pH decrease was stronger when increasing PCO2 than when reducing [HCO3-]0. The pH-induced response significantly increased during hypoxia. The results show that in the ventral medulla oblongata neurons exist that transiently respond to small decreases and increases of pH. The pH sensitivity is an intrinsic property of these neurons; it is not due to a synaptic mechanism but is modulated by PCO2 and PO2.

Animals↗

PubMed1990

Inhibitory role of dentate hilus neurons in guinea pig hippocampal slice.

1. Current and voltage-clamp recording of CA3/CA4 pyramidal neurons, hilar neurons, and granule cells or pairs of these neurons were used to study the generation of Cl-dependent and K-dependent inhibitory postsynaptic potentials (IPSPs) in the guinea pig hippocampal slice preparation. 2. A sequence of an early Cl-dependent and a late K-dependent IPSP was evoked in CA3 neurons by electrical stimulation from the stratum moleculare of the dentate gyrus, the hilus, and the stratum oriens/alveus. Blockade of glutamatergic excitation by 6-cyano-7-nitroquinoxaline-2,3-dione (CNQX, 10 microM) and D(-)-2-amino-5-phosphonovaleric acid (APV, 30 microM) abolished IPSPs evoked from the stratum moleculare of the dentate gyrus, but IPSPs could still be evoked from the hilus and the stratum oriens/alveus. 3. Repetitive giant IPSPs, which consisted of Cl-dependent and K-dependent components, were evoked by bath application of 4-aminopyridine (4-AP, 10-50 microM) in CA3 neurons and in granule cells. Giant IPSPs were blocked by bath-applied tetrodotoxin (TTX). In addition, 4-AP hyperpolarized CA3 neurons in a Cl-dependent and picrotoxin-sensitive way. 4. Focal application of TTX to the dentate gyrus or the hilus considerably reduced the amplitude of giant IPSPs evoked by 4-AP in CA3 neurons. In hilar neurons, 4-AP evoked repetitive bursts, eventually, but not necessarily intermingled with giant IPSPs. Bursts were observed in hilar neurons in presence as well as absence of CNQX and APV. 5. In paired recordings, bursts in hilar neurons induced by 4-AP occurred simultaneously to giant IPSPs in granule cells and CA3 neurons, and giant IPSPs in granule cells occurred simultaneously to giant IPSPs in CA3 neurons. Blockade of glutamatergic excitation by CNQX and APV did not abolish this synchrony. 6. 4-AP-evoked Cl- and K-dependent IPSPs were, unlike electrically evoked IPSPs, not strictly coupled: some 20% of large IPSPs and up to 90% of small IPSPs were either Cl or K dependent. In granule cells K-dependent components either preceded or followed Cl-dependent components. 7. K-dependent IPSPs only could be evoked in CA3 neurons by focal application of 4-AP (1 mM) to the hilus, the stratum lacunosum moleculare or the stratum pyramidale. Wash out of Ca for 15-20 min blocked the Cl-dependent but not the K-dependent component of giant IPSPs evoked by bath-applied 4-AP.(ABSTRACT TRUNCATED AT 400 WORDS)

4-Aminopyridine↗

PubMed1990

Development and properties of synaptic mechanisms in a network of rat hypothalamic neurons grown in culture.

1. Dissociated neurons from embryonic rat hypothalamus (E14-15) were cultured on a glial background monolayer for up to three months. Dendrites of cells 7-14 days in culture (DIC) intracellularly stained with the fluorescent dye Lucifer yellow were thin and smooth, and multiple growth cones could be observed. The length of the dendrites of older cells did not differ much, but dendrites were thicker and branched more profoundly, forming a complicated network. Growth cones were rare, but few spine-like protrusions could be observed. 2. Randomly occurring depolarizing potentials were recorded in 60% of the cells 7-14 DIC and in 90% of the cells 21 DIC. Activity became phasic when the gamma-aminobutyric acid (GABA) antagonists picrotoxin or bicuculline were applied. After 21 DIC the majority of the cells showed burst discharges, whereas only approximately 10% of the cells 7 DIC exhibited bursting. 3. With low [Cl] in the recording pipette, spontaneous activity consisted of hyperpolarizing and depolarizing potentials at -40-mV membrane potential. Some spontaneous activity persisted with Na channels blocked by tetrodotoxin (TTX, 0.3-1 microM), and when reducing the external [Ca]o from 5 to 0.3 mM. Picrotoxin blocked part of the activity, and the remaining activity was blocked by kynurenic acid. 4. Bursts of action potentials were superimposed on rhythmically occurring clusters of excitatory synaptic potentials (EPSPs), which had a steep rising phase and decayed within hundreds of milliseconds. Bursts of similar appearance could be triggered by brief (10 ms) depolarizing current injections, and a few cells had properties indicative for endogenous pacemakers. 5. From 7 DIC on, all cells responded to GABA and to the GABA agonist muscimol. Under voltage clamp, zero current potential depended on the Cl gradient across the membrane and corresponded to the zero current potential of picrotoxin-sensitive postsynaptic currents. 6. After 21 DIC all cells responded to glutamate and its agonist quisqualate. Under voltage clamp, nanomolar concentrations of quisqualate (100-500 nM) induced long-lasting inward currents, which did not decay substantially during prolonged drug application. Quisqualate concentrations greater than 1 microM induced a diphasic inward-current response consisting of an initial fast current transient followed by a maintained current component. With internal Cs replacing K and Na and external TTX (0.3 microM), both current components reversed sign at approximately 8 mV, as predicted by the Nernst equation for currents through channels that were permeable for monovalent cations. 7. Focal applications of GABA and muscimol elicited larger currents when applied near the soma than when applied to the dendrites.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗

PubMed1989

Activity dependent alkaline and acid transients in guinea pig hippocampal slices.

Changes of extracellular proton concentration ([H+]o) and K+ activity ([K+]o) were simultaneously measured by ion-sensitive microelectrodes in the CA3 region of guinea pig hippocampal slices. Repetitive electrical stimulation and application of glutamate or GABA were associated with prominent alkaline transients of up to 0.2 pH units lasting 2-10 s followed by smaller acid transients lasting up to 4 min. About 10-fold smaller alkaline transients were induced by spontaneous field discharges in the presence of bicuculline. The time to the maximal amplitude of the alkaline transients and the time to maximal increases of [K+]o were in the same range, concurring with the assumption that alkaline transients are due to a proton influx through cationic channels. However, spontaneous field discharges in low-calcium solution in which synaptic transmission is reduced were associated with acid transients of up to 0.02 pH units lasting 2-20 s. An alkaline transient was superimposed on the acid transient only when increases of [K+]o exceeded 1.5 mM. The effects of changing [H+]o on electrically evoked field potentials and spontaneous field discharges were studied in the range from pH 7.00 to 7.80. Electrically evoked field potentials were markedly depressed from pH 7.15 to 7.00 and enhanced from pH 7.60 to 7.80. The frequency of spontaneous field discharges in the presence of bicuculline significantly decreased by reducing pH from 7.40 to 7.30 and continuously increased from pH 7.40 to 7.80. In the same way, the frequency and the amplitude of spontaneous field discharges in low-calcium solution decreased from pH 7.40 to 7.15 and increased from pH 7.40 to 7.80.(ABSTRACT TRUNCATED AT 250 WORDS)

Acid-Base Equilibrium↗

PubMed1989

Carbachol reduces IK,baclofen, but not IK,GABA in guinea pig hippocampal slices.

In the presence of bicuculline and/or picrotoxin (-)-baclofen and gamma-aminobutyric acid (GABA) induced outward currents (IBac and IGABA) at holding potentials of -55 to -75 mV in guinea pig CA3 neurones of hippocampal slices. Zero potentials for these currents were at the K-equilibrium potential indicating that they were carried by K-ions (IK.Bac, IK.GABA). IK.Bac was strongly reduced by carbachol (Cch) in low concentration (0.1 0.3 microM), while IK.GABA was not affected by Cch concentrations even up to 20 microM. The K-dependent late inhibitory postsynaptic potential (IPSP) was reduced significantly by Cch concentrations higher than 1 microM, but with these concentrations the early, Cl-dependent IPSP was reduced as well. The baclofen-derivative phaclofen, considered a selective antagonist of both the postsynaptic action of baclofen and the bicuculline - and picrotoxin - resistant action of GABA, exhibited, in our hands, partial agonistic effects and effects on non-transmitter gated K-currents. Our findings cast some doubt on the assumption that IK.Bac, IK.GABA and the late IPSP are all mediated by the same receptor and generated by the same mechanism.

Animals↗

PubMed1989

Synaptic potentials in the rat neostriatum in dissociated embryonic cell culture.

Neostriatal cells of embryonic days 19-21 were grown in dissociated cell culture. To test whether the cultures contained predominantly neostriatal cells, a glyoxylic acid staining procedure was used which, after dopamine loading, stained neostriatal cells but not neurons of embryonic neocortical tissue. Whole cell current clamp recording was performed in the neurons after 1-2 weeks in cell culture. Although cells could be driven to discharge by direct depolarization, spontaneous activity was low. All cells responded to gamma-aminobutyric acid (GABA) (0.1-0.5 mM), and the majority of them responded to glutamate (Glu) (0.1 mM). Only about 50% were depolarized by acetylcholine (ACh) (0.1-0.5 mM). Atropine (1-10 microM) did not block this depolarization. Barrages of postsynaptic potentials (PSPs) were induced by applications of Glu or ACh, even if the neuron under observation was not depolarized. All PSPs were depressed by bicuculline (50 microM), indicating their mediation by GABAergic receptors. Exclusively GABAergic PSPs were also observed in cultures raised in the presence of nerve growth factor. The study indicates that neostriatal cells form GABAergic, but not excitatory cholinergic synapses when cultured at this embryonic age under our conditions, resembling the pattern of development observed in slices obtained from neonatal rats.

Acetylcholine↗

PubMed1989

Lithium discriminates between muscarinic receptor subtypes on guinea pig hippocampal neurons in vitro.

In CA3 pyramidal neurons of guinea pig hippocampal slices an outward current activated by the GABAB agonist, baclofen (0.3 microM, Ibac) was reduced by low concentrations of carbachol (Cch, 0.1-0.3 microM). The effect of Cch desensitized suggesting that the receptor subtype involved in this muscarinic effect of Cch was of the M1 subtype. The receptor subtype was also characterized by its equilibrium dissociation constant for pirenzepine (10 nM) as an M1 receptor. Li+ applied extracellularly (1 mM) or intracellularly blocked the suppression of Ibac by Cch without affecting the Cch blockade of a current termed IAHP, which is mediated by M2 receptors. While the effect of intracellular Li+ application was immediate, it developed very slowly with extracellular application. Since Li+-salts are used effectively in the treatment of mania and depression, the selective effect of Li+ on M1-mediated muscarinic neurotransmission might be important for the cholinergic hypothesis of affective disorders.

Animals↗

PubMed1989

gamma-Aminobutyric acid-induced ion movements in the guinea pig hippocampal slice.

gamma-Aminobutyric acid (GABA)-induced regional changes of extracellular Cl, K and Na concentration ([Cl]o, [K]o, [Na]o), as well as of the extracellular space were measured with ion-sensitive microelectrodes in guinea pig hippocampal slices. Microdrop application of GABA to the pyramidal cell layer of CA3 or CA1 induced a decrease of [Cl]o, while application to the dendritic layer of CA3 or CA1 induced an increase of [Cl]o in addition. All changes of [Cl]o persisted in the presence of TTX and were blocked by bath-applied bicuculline. The GABA-induced decrease of [Cl]o was reduced by bicuculline application to the pyramidal cell layer. The increase of [Cl]o was blocked by bicuculline application to the dendritic layer. Additionally, GABA induced an increase of [K]o and decreases/increases of [Na]o. Changes of [Cl]o, [K]o and [Na]o together were approximately electroneutral. [Cl]o increases were exaggerated and [Cl]o decreases partly masked by shrinkage of the extracellular space after GABA application. Changing [K] in the superfusate transiently changed GABA-induced [Cl]o movements in a way predicted from a change in driving force due to the effect of [K] on membrane potential. Then a partial recovery followed towards the original [Cl]o change. We conclude that inward and outward Cl transports maintain [Cl]i below equilibrium in CA3 and CA1 pyramidal somata and above equilibrium in CA3 and CA1 dendrites. The significance of this Cl-distribution for hippocampal inhibition is discussed.

Animals↗

PubMed1989

Quisqualate receptor-mediated rhythmic bursting of rat hypothalamic neurons in dissociated cell culture.

Dissociated hypothalamic neurons from embryonic rat brain exhibit a level of spontaneous synaptic activity after 21 days in culture. When GABA-mediated responses are blocked by picrotoxin or bicuculline (20 microM), the neurons burst rhythmically. Rhythmic burst activity is generated in most cells by postsynaptic excitatory currents (EPSCs) through non-specific cationic channels rather than by intrinsic pacemaker currents. We present evidence that EPSCs are mediated by an excitatory amino acid and a quisqualate receptor type.

Action Potentials↗

PubMed1989

Muscarinic slow EPSPs in neostriatal and hippocampal neurons in vitro.

Cholinergic slow excitatory postsynaptic potentials (slow EPSPs) can be elicited by presynaptic tetanic stimulation in brain slices obtained from rat neostriatum or guinea pig hippocampus. Slow EPSPs are generated by a reduction of a K-leak-conductance. In hippocampal neurons slow EPSPs are amplified by the reduction of an outward current termed IAHP through the activation of a second muscarinic receptor subtype. While hippocampal slow EPSPs might be involved in information processing across hippocampal pathways, muscarinic modulation in the neostriatum consists of a presynaptic tuning of nicotinic fast synaptic transmission.

Acetylcholine↗

PubMed1989

Carbachol and pirenzepine discriminate effects mediated by two muscarinic receptor subtypes on hippocampal neurons in vitro.

Measurement of [Cch] in the bath and in slices demonstrated a considerable concentration discrepancy between the bath and the extracellular space. With fast (bolus) application of Cch this discrepancy is due to the speed of diffusion, while equilibration with continuous application is considerably impaired by cellular uptake of Cch (Creese and Taylor, 1967). Low concentrations (less than or equal to 1 microM) of Cch reduce the afterhyperpolarization following a train of action potentials and depolarize the membrane. Analysis of [Cch]0 (t) and the effects of pirenzepine allowed these effects to be assigned to two different muscarinic receptor subtypes.

Acetylcholine↗

PubMed1989

Characterization of input synapses on intracellularly stained neurons in hippocampal slices: an HRP/EM study.

This study describes the fine structure of input synapses on identified neurons in slices of the guinea pig hippocampus. For morphological identification, granule cells of the fascia dentata and pyramidal neurons of regio inferior of the hippocampus were impaled and intracellularly stained with horseradish peroxidase (HRP). Input synapses on the HRP-stained neurons were identified in the electron microscope by the location of the synapses in inner or outer zones of the dentate molecular layer, as in the case of the synaptic contacts on injected granule cells, or by unique fine structural characteristics, as in the case of the giant mossy fiber boutons on CA3 pyramidal cells. As in tissue fixed in situ by transcardial perfusion, a large number of terminals arising from the different afferents in inner and outer zones of the dentate molecular layer were well preserved and formed synaptic contacts with small spines, large complex spines, and dendritic shafts of the HRP-filled granule cells. Mossy fiber synapses on the stained CA3 neurons were densely filled with clear vesicles, contained a few dense-core vesicles, and formed synaptic contacts with large spines or excrescences. Occasionally electrondense degenerating boutons were also found impinging on the stained dendrites and spines. The significance of the present findings for electrophysiological and pharmacological studies on brain slices is discussed.

Animals↗