Neurocentre Magendie

Cyril DEJEAN





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Cursus:
Ph D - Lab. de Neurophysiologie, U. Bordeaux2 (2006)
Post doc - University of Otago, New Zealand (2007-2009)
Post doc - CNIC, U. Bordeaux1 (2009-2010)
Assoc. Researcher INCIA, U. Bordeaux1 (2010-2013)


Expertise: Electrophysiology, Neuroscience, Behavior, Optogenetics, Addiction, Learning





14 publication(s) depuis Juillet 2004:


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* equal contribution
Les IF indiqués ont été collectés par le Web of Sciences en


21/07/2016 | Nature   IF 38.1
Prefrontal neuronal assemblies temporally control fear behaviour.
Dejean C, Courtin J, Karalis N, Chaudun F, Wurtz H, Bienvenu TC, Herry C

Abstract:
Precise spike timing through the coordination and synchronization of neuronal assemblies is an efficient and flexible coding mechanism for sensory and cognitive processing. In cortical and subcortical areas, the formation of cell assemblies critically depends on neuronal oscillations, which can precisely control the timing of spiking activity. Whereas this form of coding has been described for sensory processing and spatial learning, its role in encoding emotional behaviour remains unknown. Fear behaviour relies on the activation of distributed structures, among which the dorsal medial prefrontal cortex (dmPFC) is known to be critical for fear memory expression. In the dmPFC, the phasic activation of neurons to threat-predicting cues, a spike-rate coding mechanism, correlates with conditioned fear responses and supports the discrimination between aversive and neutral stimuli. However, this mechanism does not account for freezing observed outside stimuli presentations, and the contribution of a general spike-time coding mechanism for freezing in the dmPFC remains to be established. Here we use a combination of single-unit and local field potential recordings along with optogenetic manipulations to show that, in the dmPFC, expression of conditioned fear is causally related to the organization of neurons into functional assemblies. During fear behaviour, the development of 4 Hz oscillations coincides with the activation of assemblies nested in the ascending phase of the oscillation. The selective optogenetic inhibition of dmPFC neurons during the ascending or descending phases of this oscillation blocks and promotes conditioned fear responses, respectively. These results identify a novel phase-specific coding mechanism, which dynamically regulates the development of dmPFC assemblies to control the precise timing of fear responses.




15/02/2016 | Nat Neurosci   IF 16.7
4-Hz oscillations synchronize prefrontal-amygdala circuits during fear behavior.
Karalis N, Dejean C, Chaudun F, Khoder S, Rozeske RR, Wurtz H, Bagur S, Benchenane K, Sirota A, Courtin J, Herry C

Abstract:
Fear expression relies on the coordinated activity of prefrontal and amygdala circuits, yet the mechanisms allowing long-range network synchronization during fear remain unknown. Using a combination of extracellular recordings, pharmacological and optogenetic manipulations, we found that freezing, a behavioral expression of fear, temporally coincided with the development of sustained, internally generated 4-Hz oscillations in prefrontal-amygdala circuits. 4-Hz oscillations predict freezing onset and offset and synchronize prefrontal-amygdala circuits. Optogenetic induction of prefrontal 4-Hz oscillations coordinates prefrontal-amygdala activity and elicits fear behavior. These results unravel a sustained oscillatory mechanism mediating prefrontal-amygdala coupling during fear behavior.




01/09/2015 | Biol Psychiatry   IF 8.9
Neuronal Circuits for Fear Expression and Recovery: Recent Advances and Potential Therapeutic Strategies.
Dejean C, Courtin J, Rozeske RR, Bonnet MC, Dousset V, Michelet T, Herry C

Abstract:
Recent technological developments, such as single unit recordings coupled to optogenetic approaches, have provided unprecedented knowledge about the precise neuronal circuits contributing to the expression and recovery of conditioned fear behavior. These data have provided an understanding of the contributions of distinct brain regions such as the amygdala, prefrontal cortex, hippocampus, and periaqueductal gray matter to the control of conditioned fear behavior. Notably, the precise manipulation and identification of specific cell types by optogenetic techniques have provided novel avenues to establish causal links between changes in neuronal activity that develop in dedicated neuronal structures and the short and long-lasting expression of conditioned fear memories. In this review, we provide an update on the key neuronal circuits and cell types mediating conditioned fear expression and recovery and how these new discoveries might refine therapeutic approaches for psychiatric conditions such as anxiety disorders and posttraumatic stress disorder.




11/2014 | Med Sci (Paris)
[Prefrontal parvalbumin-expressing interneurons control fear behavior].
Courtin J, Dejean C, Herry C

Abstract:





11/2013 | Neurobiol Dis   IF 4.9
Opiate dependence induces network state shifts in the limbic system.
Dejean C , Boraud T , Le Moine C

Abstract:
Among current theories of addiction, hedonic homeostasis dysregulation predicts that the brain reward systems, particularly the mesolimbic dopamine system, switch from a physiological state to a new 'set point.' In opiate addiction, evidence show that the dopamine system principal targets, prefrontal cortex (PFC), nucleus accumbens (NAC) and basolateral amygdala complex (BLA) also adapt to repeated drug stimulation. Here we investigated the impact of chronic morphine on the dynamics of the network of these three interconnected structures. For that purpose we performed simultaneous electrophysiological recordings in freely-moving rats subcutaneously implanted with continuous-release morphine pellets. Chronic morphine produced a shift in the network state underpinned by changes in Delta and Gamma oscillations in the LFP of PFC, NAC and BLA, in correlation to behavioral changes. However despite continuous stimulation by the drug, an apparent normalization of the network activity and state occurred after 2 days indicating large scale adaptations. Blockade of mu opioid receptors was nonetheless sufficient to disrupt this acquired new stability in morphine-dependent animals. In line with the homeostatic dysregulation theory of addiction, our study provides original direct evidence that the PFC-NAC-BLA network of the dependent brain is characterized by a de novo balance for which the drug of abuse becomes the main contributor.




11/2013 | Neurobiol Dis   IF 4.9
Why am I lost without dopamine? Effects of 6-OHDA lesion on the encoding of reward and decision process in CA3.
Retailleau A, Dejean C , Fourneaux B , Leinekugel X , Boraud T

Abstract:
There is growing evidence that Parkinson's disease, generally characterized by motor symptoms, also causes cognitive impairment such as spatial disorientation. The hippocampus is a critical structure for spatial navigation and receives sparse but comprehensive dopamine (DA) innervation. DA loss is known to be the cause of Parkinson's disease and therefore it has been hypothesized that the associated spatial disorientation could result from hippocampal dysfunction. Because DA is involved in the prediction of reward expectation, it is possible to infer that spatial disorientation in DA depleted subjects results from the loss of the ability to detect the rewarding features within the environment. Amongst hippocampal formation subdivisions, CA3 properties such as the high liability of its place fields make it a serious candidate for interfacing DA reward system and spatial information encoding. We addressed this issue using multiple electrode recordings of CA3 in normal and dopamine depleted rats performing a spatial learning in a Y-maze. Our data confirm that DA is essential to spatial learning as its depletion results in spatial impairments. The present work also shows that CA3 involvement in the detection of spatial feature contextual significance is under DA control. Finally, it also shows that CA3 contributes to the decision making processes of navigation tasks. The data also reveal a lateralization effect of DA depletion underlined by neural correlates.




16/10/2013 | J Neurosci   IF 5.9
Optic Flow Stimuli Update Anterodorsal Thalamus Head
Direction Neuronal Activity in Rats

Arleo A, Dejean C, Allegraud P, Khamassi M, Zugaro MB, Wiener SI

Abstract:





05/2012 | Neurobiol Dis   IF 4.9
Evolution of the dynamic properties of the cortex-basal ganglia network after dopaminergic depletion in rats.
Dejean C , Nadjar A , Le Moine C , Bioulac B , Gross CE , Boraud T

Abstract:
It is well established that parkinsonian syndrome is associated with alterations of neuronal activity temporal pattern basal ganglia (BG). An increase in synchronized oscillations has been observed in different BG nuclei in Parkinson's disease patients as well as animal models such as 6-hydroxydopamine treated rats. We recently demonstrated that this increase in oscillatory synchronization is present during high-voltage spindles (HVS) probably underpinned by the disorganization of cortex-BG interactions. Here we investigated the time course of both oscillatory and motor alterations. For that purpose we performed daily simultaneous recordings of neuronal activity in motor cortex, striatum and substantia nigra pars reticulata (SNr), before and after 6-hydroxydopamine lesion in awake rats. After a brief non-dopamine-specific desynchronization, oscillatory activity first increased during HVS followed by progressive motor impairment and the shortening of SNr activation delay. While the oscillatory firing increase reflects dopaminergic depletion, response alteration in SNr neurons is closely related to motor symptom.




Abstract:
Modulation of oscillatory activity through basal ganglia-cortical loops in specific frequency bands is thought to reflect specific functional states of neural networks. A specific negative correlation between beta and gamma sub-bands has been demonstrated in human basal ganglia and may be key for normal basal ganglia function. However, these studies were limited to Parkinson's disease patients. To confirm that this interaction is a feature of normal basal ganglia, we recorded local field potential (LFP) from electrodes in globus pallidus (GP) of intact rats. We found significant negative correlation between specific frequencies within gamma ( approximately 60 Hz) and beta ( approximately 14 Hz) bands. Furthermore, we show that fluctuations in power at these frequencies are differentially nested within slow ( approximately 3 Hz) oscillations in the delta band, showing maximum power at distinct and different phases of delta. These results suggest a hierarchical organization of LFP frequencies in the rat GP, in which a low-frequency signal in the basal ganglia can predict the timing and interaction of power fluctuations across higher frequencies. Finally, we found that dopamine D(1) and D(2) receptor antagonists differentially affected power in gamma and beta bands and also had different effects on correlation between them and the nesting within delta, indicating an important role for endogenous dopamine acting on direct and indirect pathway neurons in the maintenance of the hierarchical organization of frequency bands. Disruption of this hierarchical organization and subsequent disordered beta-gamma balance in basal ganglia disorders such as Parkinson's disease may be important in the pathogenesis of their symptoms.




Abstract:
High-frequency stimulation of around 130 Hz delivered to the subthalamic nucleus (STN-DBS [deep brain stimulation]) is an effective treatment of Parkinson's disease (PD), but the mechanisms of its therapeutic effect remain obscure. Recently, it has been shown in anaesthetized rats that STN-DBS antidromically activates cortical neurons with coincident reduction of the cortical slow wave oscillations that occur in this preparation. Here we extend this work; recording the effect of STN-DBS upon cortical EEG and akinesia, in unanesthetized rats rendered cataleptic by acute dopaminergic blockade. STN-DBS-like stimulation resulted in a short latency, presumed antidromic, evoked potential in the cortex. In cataleptic animals, there was a significant increase in the power of beta oscillations in the electroencephalography which was reversed by stimulation that evoked the cortical response. We also observed a significant rescue of motor function, with the level of akinesia (bar test score) being inversely correlated to the amplitude of the evoked potential (R2 = 0.84). These data confirm that (probably antidromic) short latency cortical responses occur in the awake animal and that these are associated with reductions in abnormal cortical oscillations characteristic of PD and with improvements in akinesia. Our results raise the possibility that STN-DBS reduces PD oscillations and symptoms through antidromic cortical activation.