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V Crunelli

Publications and source records attributed to V Crunelli.

At least 73 records · Page 4Linked to original sources
PubMed1988

[Spontaneous rhythmic depolarization in the principal cells of the lateral geniculate body in vitro: the role of NMDA receptors].

Intracellular recordings using standard current clamp techniques were performed on projection cells of the rat lateral geniculate nucleus (LGN) in vitro. These cells are generally quiescent in vitro but when magnesium was removed from the perfusion medium they invariably showed rhythmic depolarizations (15-20 mV, 210-320 ms) that occurred at a frequency of 1.5-2 Hz and evoked 1 to 4 action potentials. This activity was completely blocked by micromolar concentrations of magnesium (50-150 microM) while tetrodotoxine (1 microM) abolished the action potentials but left the underlying rhythmic depolarizations unchanged. These results demonstrate that rat LGN projection cells are capable of producing rhythmic depolarizations in vitro and suggest the possibility that NMDA receptors might be involved in these rhythmic oscillations.

Action Potentials↗
PubMed1987

Neuroleptics decrease calcium-activated potassium conductance in hippocampal pyramidal cells.

Intracellular recordings were made from pyramidal CA1-neurones of the hippocampal slice preparation. Bath application of a wide variety of neuroleptics was found to depress the slow afterhyperpolarization, which is mediated in these neurons by a calcium-dependent potassium conductance occurring following a burst of spikes. The depression of this conductance took place in the presence of calcium spikes of normal amplitude and duration, and except in the case of trifluoperazine, without alteration in resting membrane potential or input resistance.

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PubMed1987

An in vitro slice preparation of the cat lateral geniculate nucleus.

A slice preparation of the cat thalamus containing the lateral geniculate nucleus and the terminal portion of the optic tract is described. Ultrastructurally the slices remain relatively normal for only a short time after cutting. Indeed most cellular elements deteriorate quickly with time but patches of relatively intact tissue were still present even 10 h after cutting and maintenance in a storage bath. However, for 4-5 h after cutting long-lasting intracellular recordings of high quality and stability were obtained, and intrasomatic injection of horseradish peroxidase used for the morphological identification of recorded neurones as X or Y cells.

Animals↗
PubMed1987

The ventral and dorsal lateral geniculate nucleus of the rat: intracellular recordings in vitro.

1. The membrane properties and the electrotonic structure of neurones in the ventral and dorsal lateral geniculate nucleus (l.g.n.) of the rat were studied using an in vitro slice preparation. 2. Following electrophysiological characterization, horseradish peroxidase (HRP) was injected intrasomatically and the morphological features of impaled cells were characteristic of principal neurones of the rat ventral and dorsal l.g.n. 3. Neurones in the ventral l.g.n. had a higher input resistance but similar membrane time constants (tau o) and resting potentials than cells in the dorsal l.g.n. 4. Using a simple neuronal model, the electrotonic length (L) and the dendritic to somatic conductance ratio (rho) were calculated and found to be similar for cells in both divisions of the l.g.n. The mean value of L (0.7) and rho (1.5) suggest that both groups of neurones are electrotonically compact. 5. The width and after-hyperpolarization of directly evoked action potentials, but not their threshold or their amplitude, were different between cells of the ventral and dorsal l.g.n. 6. At potentials more negative than -55 mV, a slow rising and falling potential could be evoked in each neurone (n = 310) of the dorsal l.g.n. but only in three cells of the ventral l.g.n. (n = 94). The electrophysiological and pharmacological properties of this potential were identical with those of the low-threshold Ca2+-dependent potential observed in other thalamic nuclei. 7. These results indicate that some of the passive and active membrane properties of ventral and dorsal l.g.n. neurones are different. The implications of these findings for the control of the integrative capability and the response of l.g.n. neurones to visual stimulation are discussed.

Action Potentials↗
PubMed1987

On the excitatory post-synaptic potential evoked by stimulation of the optic tract in the rat lateral geniculate nucleus.

1. The electrophysiological and pharmacological properties of the excitatory post-synaptic potentials (e.p.s.p.) evoked by electrical stimulation of the optic tract were studied in projection neurones of the ventral and dorsal lateral geniculate nucleus (l.g.n.) of the rat in vitro. 2. No difference was found in the rise time of e.p.s.p.s. recorded in the dorsal and ventral l.g.n. and in their threshold for action potentials. At membrane potentials more negative than -60 mV, e.p.s.p.s. in the dorsal l.g.n. were always followed by a Ca2+-dependent potential. Its amplitude could easily reach threshold for generating an action potential and thus evoke firing from an e.p.s.p. that was subthreshold at resting potential. No Ca2+ potential was observed to follow e.p.s.p.s. recorded in the ventral l.g.n. 3. At resting potential the excitability of dorsal and ventral cells was unaffected following an initial shock to the optic tract. However, in dorsal neurones, at potentials more negative than -60 mV, the presence of Ca2+ potentials evoked by the e.p.s.p.s. resulted in a period of decreased excitability. 4. Using intrasomatic injection of Cs+ the reversal potential (E) of the e.p.s.p. and of the depolarization produced by glutamate could be measured in the same l.g.n. neurone. They were: Eepsp, -0.9 mV; and Eglut, -3.9 mV. 5. gamma-D-glutamylglycine (DGG), an excitatory amino acid antagonist, reversibly inhibited the e.p.s.p. and depolarization produced by quisqualate and glutamate by a competitive action. The concentration of DGG that produced 50% inhibition (IC50) was 2.7 mM. 6. D-2-amino-5-phosphonovalerate (APV), the potent and selective N-methyl-D-aspartate (NMDA) antagonist, had no effect on the e.p.s.p. both in the presence and absence of Mg2+. The isomers of 2-amino-4-phosphonobutyrate (APB) were inactive or had a non-specific action on the e.p.s.p. 7. No difference could be detected in either the reversal potential or the action of the antagonists between neurones of the dorsal and the ventral l.g.n. 8. These results suggest that Ca2+-dependent potentials play an important role in modulating synaptic efficacy in principal neurones of the dorsal l.g.n. The quisqualate/kainate nature of the optic nerve receptors and the similarity of Eepsp and Eglut constitute strong support in favour of a glutamate-like substance as the transmitter of the optic nerve.

2-Amino-5-phosphonovalerate↗
PubMed1987

Membrane properties of morphologically identified X and Y cells in the lateral geniculate nucleus of the cat in vitro.

1. The membrane properties and the electrotonic features of cells in lamina A of the cat dorsal lateral geniculate nucleus (l.g.n.) were studied using an in vitro slice preparation. 2. Following intrasomatic injection of horseradish peroxidase (HRP) each neurone was classified as an X (n = 20) or a Y (n = 27) cell on the basis of its morphology. For both classes, the frequency distribution of soma area was similar to that reported in vivo where the identification of X and Y cells in lamina A of the cat l.g.n. was based on physiological criteria. 3. No difference was observed in the mean resting membrane potential between the two classes of cells. However, the input resistance (RN) of X cells was greater (82 M omega) and their membrane time constant (tau 0) longer (22 ms) than of Y cells (RN, 32 M omega; tau 0, 15 ms). 4. Using a simple neuronal model, the calculated electrotonic length (L) and the dendritic to somatic conductance ratio (rho) were similar for the two classes of cells. The mean value of L (0.7) and rho (1.9) suggests that both X and Y cells are electrically compact. 5. The specific membrane resistance (Rm, 28,000 omega cm2) of X cells, calculated using two different approaches, was found to be higher than that of Y cells (17,000 omega cm2). 6. The implication of these results for the integration of synaptic signals in the two classes of l.g.n. cells and the feasibility of differentiating between X and Y cells on the basis of their membrane properties are discussed.

Action Potentials↗
PubMed1986

X- and Y-cells identified in the cat lateral geniculate nucleus in vitro.

Using an in vitro preparation of the cat dorsal lateral geniculate nucleus, we have studied the passive membrane properties and the electrotonic structure of single cells each identified as X or Y on the basis of their morphological features following intrasomatic injection of horseradish peroxidase. The input resistance of X-cells is higher and the membrane time constant longer than of Y-cells. The electrotonic length and the dendritic to somatic conductance ratio are similar for both classes of neurones.

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PubMed1985

An electrophysiological study of neurones in the rat median raphe and their projections to septum and hippocampus.

Extracellular single unit recordings were made in the median raphe nucleus from rats anaesthetized with urethane. Spontaneous firing as well as orthodromic and antidromic responses to stimulation of the fornix and the medial septum were studied. One hundred and twelve units (out of a total of 355) with a regular spontaneous firing rate of 0.2-3 spikes/s were classified as serotonin-containing neurons. Fifty nine of them were antidromically invaded from either the fornix or the medial septum (conduction velocity, 0.8 m/s) and 7 additional neurones from both the fornix and the medial septum. Antidromic action potentials were followed by a period of decreased probability of firing, that was already present below threshold for antidromic invasion, were proportional to the stimulation intensity and had a latency similar to orthodromic inhibition. No preferential topographical distribution within the median raphe nucleus was observed for the serotonin neurones, even those invaded antidromically. Twenty six neurones with a clear-cut anatomical location around the borders of the median raphe nucleus showed a spontaneous rhythmic activity (4-20 spikes/s) characterized by the presence of extremely prolonged silent periods (up to 5 min). Only one of these neurones was invaded antidromically from the medial septum and none from the fornix. Of the remaining non-serotonin neurones, 28 showed a very low firing rate consisting of single action potentials every 10-60 s while 189 had a spontaneous activity of 6-30 spikes/s. Regardless of their firing rate they were all antidromically invaded from the fornix and/or the medial septum and had a conduction velocity of 5 m/s. These experiments demonstrate the electrophysiological heterogeneity of the neuronal population of the median raphe nucleus, the presence of strong projections of both putative serotonin and non-serotonin neurones to the medial septum and, via the fornix, to the hippocampus, and the existence of axonal branching in both types of neurones.

Animals↗
PubMed1984

Mg2+ dependence of membrane resistance increases evoked by NMDA in hippocampal neurones.

The response of granule cells and CA1 pyramidal neurones to NMDA was studied in the presence and absence of Mg2+ using an in vitro slice preparation. In the absence of Mg2+ the depolarizing response of hippocampal neurones to NMDA is accompanied by a decrease in input resistance. In the presence of Mg2+ ions, however, the response to NMDA is always associated with an apparent increase in input resistance. These results indicate that the action of NMDA is by a classical mechanism of conductance increase and are in agreement with the suggestion that the apparent increase in input resistance associated with NMDA depolarizations is the result of voltage-dependent channel block by Mg2+ of the NMDA evoked current.

Animals↗
PubMed1984

Lithium ions increase action potential duration of mammalian neurons.

During Lucifer Yellow staining of mammalian neurons, intracellular recording revealed a prolongation of the action potential that is probably the result of leakage of lithium ions into the intracellular fluid. In experiments on dorsal root ganglion neurons intracellular iontophoresis of lithium ions also broadened the action potential. Cadmium, a calcium channel blocker, shortens the lithium-evoked wide actions potentials. The present experiments do not reveal whether lithium directly enhances inward calcium current, or whether a block of outward rectification allows calcium currents to increase the action potential duration.

Action Potentials↗
PubMed1984

The reversal potential of excitatory amino acid action on granule cells of the rat dentate gyrus.

The responses of granule cells to glutamate, aspartate, N-methyl-D-aspartate (NMDA), quisqualate and kainate applied by ionophoresis on to their dendrites in the middle molecular layer of the dentate gyrus were studied with intracellular electrodes using an in vitro hippocampal slice preparation. On passive depolarization 75% of the granule cells displayed anomalous rectification, which persisted in the presence of TTX and TEA but was eliminated by Co2+ or the intracellular injection of Cs+. Short ionophoretic applications of all the excitatory amino acids evoked dose-dependent depolarizations that were highly localized: movement of the ionophoretic electrode by as little as 10 microns could substantially change the size of the response. The depolarizations evoked by glutamate, asparatate, quisqualate and kainate were unaffected by TTX and Co2+. The depolarization evoked by NMDA was unaffected by TTX but markedly reduced by Co2+. Following intracellular injection of Cs+, neurones could be depolarized to +30 mV and the depolarizations produced by glutamate, quisqualate, NMDA and kainate reversed. The reversal potentials (E) were Eglutamate: -5.6 +/- 0.4 mV; ENMDA: 1.8 +/- 1.9 mV; Equisqualate: -3.9 +/- 1.9 mV; Ekainate: -4.6 +/- 2.0 mV. The excitatory post-synaptic potential (e.p.s.p.) evoked by stimulation of the medial perforant path could also be reversed and Ee.p.s.p. was -5.5 +/- 1.1 mV. The 6 mV difference between ENMDA and the equilibrium potential for the other exogenously applied excitatory amino acids and the statistically significant difference between ENMDA and Ee.p.s.p. (P less than 0.005; d.f.: 7) is consistent with our earlier hypothesis that both the transmitter released by the medial perforant path and exogenously applied glutamate are unlikely to interact with NMDA receptors.

Action Potentials↗
PubMed1983

Passive membrane properties of neurones in the dorsal raphe and periaqueductal grey recorded in vitro.

A slice preparation of the rat mesencephalon containing the dorsal and medial raphe nucleus, the periaqueductal grey, the superior colliculi and the reticular formation is described. Intracellular recordings showed marked differences in the passive membrane properties of neurones of the dorsal raphe. Serotonin-containing neurons were characterized by a high membrane input resistance, a very long time constant and by the presence of membrane rectification only in a very hyperpolarized (less than -120 mV) region of their voltage-current relationship. In most of the neurones in and around the dorsal raphe area a brief pulse of depolarizing current was followed by a pronounced after-hyperpolarization, which appeared to be mediated by the activation of a Ca2+ dependent-K+ conductance.

Action Potentials↗
PubMed1983

Blockade of amino acid-induced depolarizations and inhibition of excitatory post-synaptic potentials in rat dentate gyrus.

Excitatory post-synaptic potentials (e.p.s.p.s) evoked by stimulation of the medial perforant path and depolarizations induced by excitatory amino acids were recorded from granule cells in the preparation of the hippocampal slice from the rat. The effects of (+/-)-2-amino-5-phosphonovalerate (APV), gamma-D-glutamylglycine (gamma DGG) and cis-2,3-piperidinedicarboxylate (PDA), antagonists of excitatory amino acids on these phenomena were compared. gamma DGG was the most effective antagonist of the e.p.s.p. Its action was reversible and not associated with any change in the passive membrane properties of the granule cells or in the apparent reversal potential of the e.p.s.p. Quantal analysis showed that the reduction in the e.p.s.p. paralleled the decrease in quantal size rather than quantal content, confirming a post-synaptic site of the action of gamma DGG. The potency of gamma DGG against the exogenous agonists was N-methyl-D-aspartate greater than kainate greater than or equal to quisqualate. APV had very little effect on the e.p.s.p. but was a selective antagonist of N-methyl-D-aspartate-induced depolarizations. PDA depolarized granule cells and increased their membrane input resistance. Although gamma DGG was a potent antagonist of both glutamate- and aspartate-induced depolarizations, no clear pattern of specificity could be found. The action of glutamate was unaffected by APV. These results indicate that the receptor for the transmitter at the synapses formed by the fibres of the perforant path with the granule cells is of the quisqualate and/or kainate type. The present data are consistent with the biochemical evidence that glutamate may be the endogenous transmitter at his synapse.

2-Amino-5-phosphonovalerate↗
PubMed1981

Action of 5-hydroxytryptamine on granule cells in the rat hippocampal slice.

1. The action of iontophoretic applications of 5HT on granule cells of the dentate gyrus was studied in the rat hippocampal slice with intracellular electrodes. 2. The inhibition produced by 5HT was accompanied by a depolarization of the membrane and a substantial decrease in input resistance. 3. 5HT was only inhibitory when applied close to the soma and had no effect when applied to the dendritic region of the cell. 4. The reversal potential for the 5HT response was estimated to be 15.5 +/- 6 mV depolarizing with respect to resting membrane potential; increasing intracellular Cl- shifted the reversal potential to a more positive value. 5. Equipotent applications of GABA applied from adjacent barrels of the same multibarrel electrode evoked similar responses with an identical equilibrium potential.

Animals↗