Dominique Engel | University of Liege (original) (raw)

Papers by Dominique Engel

ABSTRACTAlthough several ionic mechanisms are known to control rate and regularity of the pacemak... more ABSTRACTAlthough several ionic mechanisms are known to control rate and regularity of the pacemaker in dopamine (DA) neurons from the substantia nigra pars compacta (SNc), a conductance essential for pacing has yet to be defined. Here we provide pharmacological evidence that pacemaking of SNc DA neurons is enabled by an unconventional conductance. We found that 1-(2,4-xylyl)guanidine (XG), an established blocker of gating pore currents in mutant voltage gated sodium channels, selectively stops pacemaking of DA SNc neurons and is without effect on the main pore of their voltage-gated channels. We isolated a voltage-dependent, non-inactivating XG-sensitive current of 20-25 pA which operates in the relevant subthreshold range and is carried by both Na+ and Cl- ions. While the molecular identity of this conductance remains to be determined, we show that this XG-sensitive current is crucial to sustain pacemaking in these neurons.

European Journal of Neuroscience

The Journal of Neuroscience

In many neuronal types, axon initial segment (AIS) geometry critically influences neuronal excita... more In many neuronal types, axon initial segment (AIS) geometry critically influences neuronal excitability. Interestingly, the axon of rat SNc dopaminergic (DA) neurons displays a highly variable location and most often arises from an axon-bearing dendrite (ABD). We combined current-clamp somatic and dendritic recordings, outside-out recordings of dendritic sodium and potassium currents, morphological reconstructions and multicompartment modeling on male and female rat SNc DA neurons to determine cell-to-cell variations in AIS and ABD geometry, and their influence on neuronal output (spontaneous pacemaking frequency, action potential [AP] shape). Both AIS and ABD geometries were found to be highly variable from neuron to neuron. Surprisingly, we found that AP shape and pacemaking frequency were independent of AIS geometry. Modeling realistic morphological and biophysical variations helped us clarify this result: in SNc DA neurons, the complexity of the ABD combined with its excitability predominantly define pacemaking frequency and AP shape, such that large variations in AIS geometry negligibly affect neuronal output and are tolerated.

Frontiers in molecular neuroscience, 2018

The building of the brain is a multistep process that requires the coordinate expression of thous... more The building of the brain is a multistep process that requires the coordinate expression of thousands of genes and an intense nucleocytoplasmic transport of RNA and proteins. This transport is mediated by karyopherins that comprise importins and exportins. Here, we investigated the role of the ß-importin, importin-8 (IPO8) during mouse cerebral corticogenesis as several of its cargoes have been shown to be essential during this process. First, we showed that mRNA is expressed in mouse brain at various embryonic ages with a clear signal in the sub-ventricular/ventricular zone (SVZ/VZ), the cerebral cortical plate (CP) and the ganglionic eminences. We found that acute knockdown of IPO8 in cortical progenitors reduced both their proliferation and cell cycle exit leading to the increase in apical progenitor pool without influencing the number of basal progenitors (BPs). Projection neurons ultimately reached their appropriate cerebral cortical layer, but their dendritogenesis was specifi...

Encyclopedia of Computational Neuroscience, 2013

Journal of Visualized Experiments

Dendrites of dopaminergic neurons receive and convey synaptic input, support action potential bac... more Dendrites of dopaminergic neurons receive and convey synaptic input, support action potential back-propagation and neurotransmitter release. Understanding these fundamental functions will shed light on the information transfer in these neurons. Dendritic patch-clamp recordings provide the possibility to directly examine the electrical properties of dendrites and underlying voltage-gated ion channels. However, these fine structures are not easily accessible to patch pipettes because of their small diameter. This report describes a step-by-step procedure to collect stable and reliable recordings from the dendrites of dopaminergic neurons in acute slices. Electrophysiological measurements are combined with post hoc recovery of cell morphology. Successful experiments rely on improved preparation of slices, solutions and pipettes, adequate adjustment of the optics and stability of the pipette in contact with the recorded structure. Standard principles of somatic patch-clamp recording are applied to dendrites but with a gentler approach of the pipette. These versatile techniques can be implemented to address various questions concerning the excitable properties of dendrites. Video Link The video component of this article can be found at http://www.jove.com/video/54601/ 3 , the optics 4 and refinement of methods for slice preparation 5 during the last decades have enabled recordings from very thin (0.7-3 µm Ø) dendrites 6,7. These methods were, and are, still largely used to examine the excitability of dendrites in a variety of neurons 8. Direct dendritic recordings are essential to determine the distribution 9-19 and differences in the functional properties 20-22 of ion channels in distinct neuronal compartments. These data are the necessary complement of ion channel distributions detected with immunohistochemistry combined to light and electron microscopy 23,24. Dual somatodendritic recordings have been implemented to explore the propagation of action potentials 9,13-15,21,22,25-27 and spreading of synaptic potentials 13,16,18 along the somatodendritic domain of neurons, obtain detailed passive cable models 28-30 and investigate the temporal resolution of neuronal integration 31. The substantia nigra (SN) is a region located in the midbrain involved in several functions such as the control of movement, the coding of reward and habitual behaviors. The decrease of dopamine due to the specific loss of dopaminergic (DA) neurons in the SN is associated with the motor disturbances observed in patients suffering from Parkinson's disease 32. The nigral circuit is composed of two main cell types: dopaminergic and GABAergic neurons. Interestingly, these neurons have several specific features that distinguish them from other neurons. The axon of a large proportion of DA neurons and some GABA neurons originates from a dendritic site indicating that the dendritic arbor is heterogeneous (axonbearing and axon-lacking dendrites) 25,26,33. The morphology of these neurons contrasts therefore with the typical organization of neurons in which the information transfer follows the law of dynamic polarization emitted by Cajal: starting from dendrites, to soma and finally to axon 34. DA neurons are also known to release dopamine from their dendrites 35 , generate bursting activity 36 and NMDA-receptor plasticity 37. The dissection of these phenomena is elusive without direct recordings from the site where they are initiated. To gain insights into the relationship between the precise location and functional properties of ion channels and their role in the dendritic excitability and information transfer in nigral neurons, direct dendritic recordings are the method of choice. This report describes a detailed procedure that can be used to obtain single and dual patch-clamp recordings from dendrites of nigral neurons and the corresponding post hoc biocytin labeling. The basic principles for patching the somatic and the dendritic membrane are very similar. Practically however, recordings from dendritic sites require specific optimization in comparison to somatic recordings. Successful dendritic recordings rely on the quality of the slices, optimal adjustment of the optics, gentle approach of the patch pipette and stability of the recordings.

Journal of Neurophysiology, Mar 1, 2010

Seutin V, Engel D. Differences in Na ϩ conductance density and Na ϩ channel functional properties... more Seutin V, Engel D. Differences in Na ϩ conductance density and Na ϩ channel functional properties between dopamine and GABA neurons of the rat substantia nigra. mine (DA) neurons and GABA neurons of the substantia nigra (SN) promote distinct functions in the control of movement and have different firing properties and action potential (AP) waveforms. APs recorded from DA and GABA neurons differed in amplitude, maximal rate of rise, and duration. In addition, the threshold potential for APs was higher in DA neurons than in GABA neurons. The activation of voltage-gated Na ϩ channels accounts largely for these differences as the application of a low concentration of the voltage-gated Na ϩ channel blocker TTX had an effect on all of these parameters. We have examined functional properties of somatic Na ϩ channels in nucleated patches isolated from DA and GABA neurons. Peak amplitudes of macroscopic Na ϩ currents were smaller in DA neurons in comparison to those in GABA neurons. The mean peak Na ϩ conductance density was 24.5 pS m Ϫ2 in DA neurons and almost twice as large, 41.6 pS m Ϫ2 , in GABA neurons. The voltage dependence of Na ϩ channel activation was not different between the two types of SN neurons. Na ϩ channels in DA and GABA neurons, however, differed in the voltage dependence of inactivation, the mean mid-point potential of steady-state inactivation curve being more positive in DA neurons than in GABA neurons. The results suggest that specific Na ϩ channel gating properties and Na ϩ conductance densities in the somatic membrane of SN neurons may have consequences on synaptic signal integration in the soma of both types of neurons and on somatodendritic release of dopamine by DA neurons.

The Journal of Physiology, 2015

Dendrites of most neurons express voltage-gated ion channels in their membrane. In combination wi... more Dendrites of most neurons express voltage-gated ion channels in their membrane. In combination with passive properties, active currents confer to dendrites a high computational potential. The hyperpolarization-activated cation current Ih present in the dendrites of some pyramidal neurons affects their membrane and integration properties, synaptic plasticity and higher functions such as memory. A gradient of increasing h-channel density towards distal dendrites has been found to be responsible for the location independence of EPSP waveform and temporal summation in cortical and hippocampal pyramidal cells. However, reports on other cell types revealed that smoother gradients or even linear distributions of Ih can achieve homogeneous temporal summation. Although the existence of a robust, slowly activating Ih current has been repeatedly demonstrated in nigral dopamine neurons, its subcellular distribution and precise role in synaptic integration is unknown. Using cell-attached patch-clamp recordings, we find a higher Ih current density in the axon-bearing dendrite than in the soma or in dendrites without axon in nigral dopamine neurons. Ih is mainly concentrated in the dendritic membrane area surrounding the axon origin and decreases with increasing distances from this site. Single EPSPs and temporal summation are similarly affected by blockade of Ih in axon- and nonaxon bearing dendrites. The presence of Ih close to the axon is pivotal to control the integrative functions and the output signal of dopamine neurons and may consequently influence the downstream coding of movement. This article is protected by copyright. All rights reserved.

Neurocomputing, 2001

First we found that applying substances that change intracellular presynaptic GABA concentration ... more First we found that applying substances that change intracellular presynaptic GABA concentration alter the synaptic e$cacy of hippocampal GABAergic neurons. The amplitude as well as the frequency of occurrence of spontaneous postsynaptic currents (mIPSCs) are a!ected. Then, we developed a model of presynaptic vesicle dynamics to better understand the causal relationship between cytosolic GABA concentration and mIPSC amplitude and frequency. One way to explain our experimental "ndings is to postulate that the "lling of vesicles as well as their transition into the readily releasable pool depends on vesicular GABA content.

Neuron, 2005

Is the absence of Na + channels from presynaptic terminals a general phenomenon that also extends... more Is the absence of Na + channels from presynaptic terminals a general phenomenon that also extends to cor-Physiologisches Institut der Universität Freiburg Hermann-Herder-Strasse 7 tical boutons? Unlike peripheral axons, central axons often show extensive branching, and the majority of D-79104 Freiburg Germany synaptic boutons emerge from these axons in an en passant manner. Both axonal branches and en passant boutons may generate a substantial electrical load to Summary the invading AP (Goldstein and Rall, 1974; Lüscher and Shiner, 1990a, 1990b). Although the reliability of con-Action potentials in central neurons are initiated near duction of APs in cortical axons remains controversial the axon initial segment, propagate into the axon, and (Koester and Sakmann, 2000; Cox et al., 2000; Debanne finally invade the presynaptic terminals, where they et al., 1997; reviewed by Debanne, 2004), computatrigger transmitter release. Voltage-gated Na + channels

Journal of Neurophysiology, 2010

European journal of pharmacology, Jan 5, 2016

Although small-conductance Ca(2+)-activated K(+) (SK) channels and various types of voltage-gated... more Although small-conductance Ca(2+)-activated K(+) (SK) channels and various types of voltage-gated Ca(2+) (Cav) channels have been described in midbrain dopaminergic neurons, the nature of their interactions is unclear. More particularly, the role of various Cav channel types in either promoting irregularity of firing (by generating an inward current during SK channel blockade) or promoting regularity of firing (by providing the source of Ca(2+) for the activation of SK channels) has not been systematically explored. We addressed this question using intracellular and extracellular recordings from substantia nigra, pars compacta (SNc), dopaminergic neurons in rat midbrain slices. Neurons were pharmacologically isolated from their differences. When examining the ability of various Cav channel blockers to inhibit the SK-mediated afterhyperpolarization (AHP), we found that only the N-type Cav channel blocker ω-conotoxin-GVIA was able to reduce the apamin-sensitive AHP, but only partially...

The Journal of neuroscience : the official journal of the Society for Neuroscience, Jan 6, 2016

Dopaminergic (DA) neurons located in the ventral midbrain continuously generate a slow endogenous... more Dopaminergic (DA) neurons located in the ventral midbrain continuously generate a slow endogenous pacemaker activity, the mechanism of which is still debated. It has been suggested that, in the substantia nigra pars compacta (SNc), the pacemaking relies more on Ca(2+) channels and that the density of L-type Ca(2+) channels is higher in these DA neurons than in those located in the ventral tegmental area (VTA). This might lead to a higher Ca(2+) load in SNc DA neurons and explain their higher susceptibility to degeneration. However, direct evidence for this hypothesis is lacking. We found that the L-type current and channel density are indeed higher in the somata of rat SNc DA neurons and that this current undergoes less inactivation in this region. Nonstationary fluctuation analysis measurements showed a much higher number of L-type channels in the soma of SNc DA neurons, as well as a smaller single-channel conductance, pointing to a possible different molecular identity of L-type c...

Epilepsy Res, 2000

Vigabatrin (γ-vinyl-GABA, VGB) is a γ-aminobutyric acid (GABA) derivative designed to boost synap... more Vigabatrin (γ-vinyl-GABA, VGB) is a γ-aminobutyric acid (GABA) derivative designed to boost synaptic inhibition by inhibiting the degradation of GABA in brain tissue. Indeed, VGB shows potent anti-convulsant activity in animal models of epilepsy and in humans with complex partial seizures. However, details of the mechanism of action of VGB are not well understood and the systemic effects include possible pro-convulsant actions. We therefore analysed the effects of VGB in rat brain slices in the low-Mg2+ model in vitro. VGB at 100 μM–5 mM showed a concentration- and time-dependent reduction of interictal-like events in the hippocampal CA1 region. Likewise, VGB suppressed epileptiform discharges in the medial entorhinal cortex (mEC), which are known to resist conventional anti-convulsants. In contrast, evoked population spikes in CA1 (which became repetitive after washout Mg2+) were not altered by VGB. Our data show that VGB is efficient against epileptiform discharges in temporal structures including pharmacoresistant patterns of activity. The waveform of evoked population spikes in this in vitro model is no indicator for the anti-convulsant properties of drugs.

Inhibitory synaptic transmission in the human CNS is largely accomplished by GABAergic synapses w... more Inhibitory synaptic transmission in the human CNS is largely accomplished by GABAergic synapses which use ?-aminobutyric acid as the transmitter. Several classical anticonvulsants boost the inhibitory action of GABA by modulating postsynaptic GABA A receptors. However, there are additional functional elements at GABAergic synapses which regulate their efficacy, namely transporters for GABA-uptake and the key enzymes of GABA-metabolism. Some new

Presented at Ucl Neuroscience Symposium Institute of Education London Uk, Jul 1, 2011

The Journal of Physiology, Nov 1, 1998