PubMed Health⌕ Search

Biomedical subjects

U Misgeld

Publications and source records attributed to U Misgeld.

85 records · Page 5Linked to original sources
PubMed1982

Depolarizing IPSPs and Depolarization by GABA of rat neostriatum cells in vitro.

In neostriatal slices pretreated with sodium pentobarbital (100 microM) and 4-aminopyridine (50 microM), intrastriatal stimulation elicited EPSPs followed by a slowly decaying depolarization which lasted about 200 ms and was associated with a membrane conductance increase and a suppression of spike potentials. This depolarizing inhibitory synaptic action could be blocked by picrotoxin (50 microM) or bicuculline (50 microM). The reversal potential for the slowly decaying depolarization was -57 to -62 mV, i.e. it was positive with respect to the resting membrane potential (mean = -67 mV). GABA, injected into the tissue in the vicinity of the recording electrode by pressure application, or added to the perfusate (10 microM -1 mM), depolarized the cells and reduced both the membrane resistance and the amplitude of EPSPs. The reversal potential of GABA depolarization was found in a potential range approximating that of the slowing decaying depolarization. These results are compatible with the assumption that GABA is the transmitter of an intrinsic inhibition in rat neostriatum, but indicate that GABA-mediated IPSPs of neostriatal cells in vitro are depolarizing at the resting membrane potential. The possible reasons for this are discussed.

Animals↗
PubMed1982

Dependence of the viability of neurons in hippocampal slices on oxygen supply.

Hippocampal slices were tested for their viability by recording monosynaptic responses in granule cell and CA3 pyramidal cell layer. Subsequently, they were studied by light and electron microscopy. Cross sections through the slices contained intact cells clustered in the central part, while the rims consisted of swollen neurons. Electrophysiological and morphological findings indicated that a greater number of granule cells than of CA3 neurons was preserved. This difference was not due to different sensitivity of the neurons to hypoxia, since synaptic responses disappeared within 3-5 min in both cell layers, when the slices were incubated in N2/CO2 instead of O2/CO2. The block of synaptic transmission during hypoxia was caused by hyperpolarization, decrease of EPSP/IPSP amplitudes and increase of membrane conductance as revealed by intracellular recording. Synaptic potentials recorded extracellularly recovered even after 20 min of hypoxia. Morphologically these slices were not different from control slices. After 1 hr of hypoxia no recovery of electrical potentials was seen. In cross sections of these slices, swollen neurons outnumbered intact cells.

Aerobiosis↗
PubMed1981

Ultrastructure of mossy fiber endings in in vitro hippocampal slices.

0.2 to 0.4 mm thick slices of guinea pig hippocampus were studied morphologically after varying periods of incubation at 36 degrees C in Krebs-Ringer solution. Prior to fixation, the slices were tested for the presence of synaptically driven discharges of CA 3 neurons following mossy fiber (mf) stimulation because tissue preservation was satisfactory only in slices in which electrical responses were obtained. The fine structure of the MF layer in slices was compared with the ultrastructure of this region in hippocampal tissue fixed by transcardial perfusion or immersion of the tissue in the fixative. In the central part of the slices many intact neuronal structures of the mf layer could be seen even after 4 h of incubation. In the outer parts of the slices, neurons were swollen and vacuolated. These alterations were not observed in hippocampal tissue fixed by transcardial perfusion or by immersion. In all parts of the slices dark neurons and processes were found. Since dark neurons were also numerous in tissue blocks immersed in the fixative but were rare in perfused material, these changes were obviously caused by damage to unfixed tissue and fixation by immersion.

Animals↗
PubMed1980

The preservation of nerve cells in rat neostriatal slices maintained in vitro: a morphological study.

The in vitro preservation of neurons in 300 micron thin neostriatal slices, which are routinely used for electrophysiological studies, was examined by light and electron microscopy and was compared to 700 micron thick neostriatal slices. The thin slices displayed well-preserved cells after up to 5 h of incubation. This finding correlated well with whether electrical activity could be recorded. In cross-section, the thin slices consisted of three layers: the inner layer contained many intact cells (80%) and was sandwiched between the outer layers where deteriorating cells predominated. In contrast to the thin slices, the thick slices (700 micron) displayed no layering of intact cells in cross-section. Instead, the majority of cells throughout these thick slices was swollen (98%), with only small patches of intact cells. Two types of deteriorating cells were apparent: swollen cells and dark (pycnotic) cells. The proportion of swollen cells increased with incubation time. In the thin slices this swelling occurred in the outer layers with the middle layer of intact cells remaining relatively unchanged over long incubation periods, whereas all cells in the thick slices were swollen after 2 h of incubation. Dark cells were localized to the outer portion of both slices and the number of such dark cells did not change with incubation time.

Animals↗
PubMed1980

Intrinsic cholinergic excitation in the rat neostriatum: nicotinic and muscarinic receptors.

An in vitro slice technique was employed to study the receptors involved in intrinsic cholinergic excitation in the rat neostriatum. The locally evoked synaptic potentials were suppressed by antinicotinic agents, mecamylamine (10 muM), d-tubocurarine (3 muM) or hexamethonium (100 muM), but not by the antimuscarinic agent atropine (100 muM). If the slices were exposed to an acetylcholinesterase (AChE)-inhibitor (paraoxon 1--20 muM, physostigmine 0.1--0.5 muM), the synaptic potentials were potentiated. The amplitude of the orthodromic population spike increased, and it was further facilitated when the stimulus frequencies were raised from 1--3 Hz to 10--30 Hz. The frequency facilitation following exposure to an AChE-inhibitor was blocked by atropine (1--100 muM). Intracellular recording indicated that a slow depolarizing potential caused the frequency potentiation of the orthodromic discharges. Apparently rat neostriatum is similar to cholinergic systems in sympathetic ganglia and spinal Renshaw cells, in that nicotinic receptors mediate fast excitation and muscarinic receptors mediate slow excitation.

Acetylcholinesterase↗
PubMed1979

Locally evoked potentials in slices of rat neostriatum: a tool for the investigation of intrinsic excitatory processes.

Field potentials, extracellular unitary discharges and intracellular potentials evoked by intrastriatal stimulation were recorded from slices (thickness 200-400 micron) of rat neostriatum maintained in an artificial medium. The field potentials consisted of two negative waves appearing at latencies of 0.5-1.5 ms (N-1) and 2-4 ms (N-2). Extracellular unitary records showed two typed of discharges, one with short but constant latencies at threshold level stimulation and the other with longer and variable latencies. In intracellular recordings the late discharge was seen to arise from EPSPs. Based on the intra- and extracellular unitary records, N-1 was identified as the population spike of antidromically or directly activated unitary discharges and N-2 as that of orthodromically activated discharges. This interpretation was substantiated by the fact that the N-2 potential was blocked in a perfusion medium containing a lower Ca++ or a higher Mg++ concentration than the standard solution. Neither interruption of ascending neostriatal inputs nor decortication 14 days prior to recording altered the configuration of the locally evoked potentials or the probability of synaptically driven discharge occurrence. Thus by intrastriatal stimulation, neostriatal neurons are activated antidromically or directly and/or orthodromically through intrinsic excitatroy synapses. Since the intracellular recordings showed that neostriatal neurons can be well preserved, this preparation can be regarded as a useful tool for electrophysiological and neuropharmacological investigations on intrinsic excitatory processes in the neostriatum.

Afferent Pathways↗
PubMed1979

Heterosynaptic postactivation potentiation in hippocampal CA 3 neurons: long-term changes of the postsynaptic potentials.

CA 3 neurons were excited synaptically by stimulation in the dentate hilus and the stratum radiatum of CA 1 in guinea pig hippocampal slices. Following repetitive stimulation (10--20 c/s, 10 s) of either stimulation site, the amplitudes of orthodromic population spikes or the probability of unitary discharges increased. Changes of the intracellularly recorded potentials were either (a) increased EPSP amplitudes associated with decreased IPSP amplitudes, or (b) increased IPSP amplitudes. A cell showing enhanced IPSPs after repetitive activation could respond with increased EPSP amplitudes and decreased IPSP amplitudes upon further repetitive activation. The potentiation, which was always preceded by a 5--10 min depression, lasted up to 3 h. This potentiation was heterosynaptic, since the responses to the non-stimulated input also changed and since the inputs were found to excite the pyramidal cells through separate synapses in double shock experiments. The heterosynaptic mode of the potentiation as well as the changes of the IPSPs indicate that not only the excitatory pathway but also the inhibitory pathway must be considered in explaining postactivation potentiation in this hippocampal field.

Animals↗
PubMed1979

Intrinsic excitation in the rat neostriatum mediated by acetylcholine.

Synaptic excitation elicited by local stimulation in neostriatal slices was found to be mediated by acetylcholine (ACh). The synapses generating this excitation belong to intrinsic neurons. Thus, for the first time, direct evidence for the existence of intrinsic excitatory cholinergic neurons in the neostriatum is provided.

Acetylcholine↗
PubMedDate not supplied

(-)-Baclofen-induced and constitutively active inwardly rectifying potassium conductances in cultured rat midbrain neurons.

Biophysical and pharmacological properties, and development of the (-)-baclofen-induced potassium (KBac) conductance and the constitutively active inwardly rectifying potassium (KIR) conductance were characterised using the patch-clamp technique in cultured embryonic rat midbrain neurons. KBac conductance was induced by (-)-baclofen acting on gamma-aminobutyric acid B (GABAB) receptors, and displayed a high degree of selectivity for potassium ions, an approximate square-root dependence of conductance on extracellular potassium concentration and strongly voltage-dependent activation. Ba2+ blocked the conductance in a voltage-independent manner, whereas Cs+ produced a voltage-dependent block. In the same preparation, the KIR conductance displayed biophysical properties indistinguishable from those of the KBac conductance. Block of KIR currents by Ba2+ was voltage independent (KI, 4 microM), whereas Cs+ produced a voltage-dependent block (KI, 370 microM at -100 mV, equivalent valence, z', 1.67). The KBac and KIR conductances additionally displayed a strikingly similar pattern of development in culture; the specific conductance (nS/pF) of both conductances increased two- to three-fold between the first and second week in vitro, and remained constant thereafter.

Animals↗