Vagal and spinal sensory innervation is responsible for the regulation of neurogenic inflammation in the airways. Neurogenic inflammation is the result of the activation of sensory nerve endings by stimulant and induced through axon reflex to release neuropeptides from sensory nerve endings. These neuropitides are tachykinins, including substance P, neurokinin A and neuronkinin B. Tachykinin-1 (NK-1) receptors are mainly involved in neurogenic inflammation in the airway. It is found that 6-hydroxydopamine (6-OHDA) acts as a stimulant of sensory neurons that produces inflammation in the rat trachea. The magnitude of plasma leakage was expressed by the area density (%) of India ink-labeled blood vessels in tissue whole mounts. The present study found that area density of India ink-labeled blood vessel were 36.5%, 29.5%, 27.7%, 28.2%, 19.2%, 15.5% in the rat larynx, trachea, left bronchus, right bronchus, upper esophagus and distal esophagus after i.v. injection of 6-OHDA (100 mg /Kg), respectively. 6-OHDA could stimulate sensory neurons by free radicals that produced by non-enzymatic oxidation. NK-1 receptor antagonist can inhibit plasma leakage in airways. This study also tested the effect of a free radical scavenger. Rats are pretreated with a full dose (2.25 g/kg, i.v.) or lower doses of dimethylthiourea (DMTU) for a period of 15 min. We found that pretreatment with a full dose of DMTU could inhibit inflammatory plasma leakage induced by 6-OHDA, that was 4.8%, 1.6%, 1.1%, 2.4%, 0.4% and 1.0% in the rat larynx, trachea, left bronchus, right bronchus, upper esophagus and distal esophagus, respectively. It is suggested hydroxyl radicals mediated the inflammatory response in the respiratory tract and esophagus. DMTU dose-dependently decreased 6-OHDA-induced plasma leakage in the rat respiratory tract and esophagus. One sixth dose was effective in inhibition in esophagus. 6-OHDA-induced inflammation in the left and right bronchus could be reduced with 2/3 dose of DMTU. A full dose of DMTU (2.25g/Kg) was needed to inhibit inflammation in the larynx and trachea. It is concluded that sensitivity to 6-OHDA was different in the different part of lower airways and esophagus.

The mechanisms underlying the 6-hydroxydopamine (6-OHDA)-induced inflammatory response in the urinary bladder and prostate in anaesthetized male rats of Long- Evan strain were investigated. The magnitude of inflammatory responses were evaluated by morphometric analysis of the area density of India ink-labeled blood vessels in urinary bladder whole mounts and spectrophotometric analysis of Evans blue dye contents in urinary bladder and prostate. Moreover, scanning electron microscopy was employed to observe the venular endothelium in the urinary bladder wall and glandular epithelium in the prostate gland. Fifteen minutes after local application of 6-OHDA to the urinary bladder, 6-OHDA induced an increase of plasma leakage in a dose-dependent manner. It was revealed that area densities of India ink-labeled blood vessels in the rat urinary bladder whole mount were 5.65¡Ó1.72 % (N=6), 22.63¡Ó3.12 % (N=6), and 35.02¡Ó2.25 % (N=6) respectively, following a local injection of vehicle, 5 mg/kg 6-OHDA, and 10 mg/kg 6-OHDA. Using Evans blue dye as a tracer for spectrophotometric analysis, the results were similar. The Evans blue dye content was 80.53¡Ó60.74 ng/mg in the urinary bladder and 48.81¡Ó2.83 ng/mg in the prostate following injection of 5 mg/kg 6-OHDA (N=6). The Evans blue dye content was 157.73¡Ó4.45 ng/mg in the bladder and 65.52¡Ó4.25 ng/mg in the prostate following injection of 10 mg/kg 6-OHDA (N=6). Evans blue dye contents in the vehicle group (N=6) were much lower, 18.82¡Ó3.74 ng/mg in the urinary bladder and 18.50¡Ó2.47 ng/mg in the prostate, which were significantly smaller than the 6-OHDA treated group. Interestingly, the inflammatory responses were completely abolished by pretreating alone with dimethylthiourea (DMTU), a hydroxyl radical scavenger, and were moderately attenuated by pretreatment with L-732,138, a NK1 receptor antagonist. Under scanning electron microscope observation, 6-OHDA caused endothelial gaps formation in the venules of urinary bladder wall and triggered the release of secretory granules in the prostate gland cells. We concluded that 6-OHDA could induce inflammation in the urinary bladder and prostate gland involving free radical and tachykinin mechanisms.

A theoretical post-translational processing model of the proprotein form of glial cell line-derived neurotrophic factor (GDNF) likely produces three biologically active peptides. The three prospective peptides formed are 5, 11, and 17 amino acid peptides, entitled dopamine neuron stimulating peptide -5 (DNSP-5), -11 (DNSP-11), and -17 (DNSP-17), respectively. The DNSPs were hypothesized to increase dopaminergic neuron function because of their relationship to GDNF: a molecule with established neurotrophic actions on dopaminergic neurons. The DNSPs have the potential to provide a therapeutic molecule similar to GDNF, but with increased ease of delivery and improved bioavailability. Neurochemical effects of DNSPs were examined in the nigrostriatal pathway of normal Fischer 344 rats, and DNSP-11 was found to be the most effective in increasing dopamine neurochemical function. Striatal microdialysis, four weeks after a single intranigral administration of DNSP-11, showed significant increases in the baseline concentrations of dopamine, DOPAC, and HVA. In addition, both, potassium and d-amphetamine-evoked dopamine overflow were significantly increased. DNSP-11 was delivered intranigrally to aged Fischer 344 rats to examine DNSP-11’s ability to improve dopaminergic function in aged dopamine neurons. DNSP-11 affected striatal dopaminergic function 28 days after treatment by decreasing baseline concentrations of dopamine and evoked dopamine release. Investigation of DNSP-11 continued, using two models of neurotoxin-induced dopamine neuron loss that model cell loss associated with Parkinson’s disease. The neuroprotective properties of DNSP-11 were evaluated by delivering DNSP-11 prior to the neurotoxic insult. DNSP-11 treatment was unable to protect dopaminergic neurons, but significantly increased dopamine metabolism. In a model of severe dopamine neuron loss, DNSP-11 treatment significantly improved apomorphine-induced rotation behavior, indicative of alterations in the function of nigrostriatal dopaminergic neurons. Subsequent examination of dopamine content within the SN revealed significant increases in dopamine and DOPAC levels by DNSP-11. Taken together, DNSP-11 treatments modified dopamine neurochemistry in all investigated rodent models. The observed long-term alterations of dopamine neurochemistry by DNSP-11 and subsequent behavioral changes support a potential use for DNSP-11 as a therapeutic for dopaminergic cell loss. Increased dopaminergic function by DNSP-11 is evidence for the novel concept that peptides contained within the prodomain of trophic factors can have neurotrophic actions.

No description available.

A perda de neurônios dopaminérgicos na substância negra é típica na doença de Parkinson (DP) e resulta em hiperexcitabilidade dos neurônios espinais médios advinda de uma neurotransmissão glutamatérgica corticoestriatal anormal, que pode provocar dentre outros danos, déficits motores característicos da doença. Considerando os efeitos neuroprotetores promovidos pelo exercício físico, o objetivo deste estudo foi observar o impacto do exercício realizado a curto e a longo prazo durante a evolução da lesão por 6-OHDA em ratos. As modificações encontradas nesse estudo podem ser relevantes para o circuito corticoestriatal, uma vez que a plasticidade dependente do exercício é capaz de modular a excitabilidade neuronal, reduzindo a hiperexcitabilidade glutamatérgica encontrada na DP. De forma geral, estes resultados suportam os potenciais efeitos do exercício físico em alterar a conectividade sináptica dos circuitos corticoestriatal e nigroestriatal em uma situação de depleção dopaminérgica, e assim, possivelmente modificar a progressão da doença em indivíduos com DP. / The loss of nigral dopaminergic neurons characteristic of Parkinson\'s disease (PD) is responsible for hyperexcitability of medium spinal neurons resulting in abnormal corticostriatal glutamatergic neurotransmission, which can cause, among other alterations, motor deficits typical of that disease. Considering the neuroprotective effects of exercise, the aim of this study was to observe the impact of short and long-term exercise during evolution of the 6-hydroxy-dopamine (6-OHDA) animal model of PD. The modifications found in this study may be relevant for corticostriatal circuits, since the exercise-dependent plasticity can modulate neuronal excitability by reducing glutamatergic hyperexcitability found in PD. Overall, these results reinforce the potential effects of exercise to change synaptic connectivity of corticostriatal and nigrostriatal circuits in a dopaminergic depletion state, and to possibly modify the progression of the disease in patients with PD.

A doença de Parkinson (DP) apresenta declínio da capacidade respiratória. Estudo utilizando um modelo de DP induzido pela injeção de 6-hidroxidopamina (6-OHDA) no estriado mostrou redução no número de neurônios envolvidos no controle da respiração. O objetivo desse estudo foi avaliar alterações gliais no núcleo retrotrapezóide (RTN), núcleo do trato solitário, complexo pré-Bötzinger e grupamento respiratório ventrolateral rostral (rVRG) utilizando o mesmo modelo experimental. Em ratos Wistar que receberam a injeção de 6-OHDA bilateralmente no estriado observou-se redução na imunorreatividade para proteína ácida fibrilar glial em astrócitos no rVRG a partir de 30 dias, no RTN a partir de 40 dias e nas demais regiões a partir de 60 dias. Ainda, observamos o aumento da proteína ligante de actina cruzada em microglias na região do RTN aos 30 e 40 dias. Nossos dados sugerem que a redução astrocitária contribui para as alterações respiratórias observadas neste modelo experimental e a presença de neuroinflamação no RTN pode contribuir para a perda celular nesta região. / Parkinson\'s disease (PD) has a decline in respiratory capacity. A study using a model of PD induced by the injection of 6-hydroxydopamine (6-OHDA) in the striatum showed a reduction in the number of neurons involved in the control of breathing. The aim of this study was to evaluate glial changes in the retrotrapezoid nucleus (RTN), nucleus of the solitary tract, pre-Bötzinger complex and rostral ventral respiratory group (rVRG) using the same experimental model. Wistar rats that received bilateral 6-OHDA injection in the striatum present a reduction in immunoreactivity for glial fibrillary acidic protein in astrocytes in the rVRG from 30 days, in the RTN from 40 days and in the other regions from 60 days. We also observed an increase of the Ionized calcium binding adaptor molecule 1 in microglia in the region of the RTN at 30 and 40 days. Our data suggest that astrocytic reduction contributes to the respiratory changes observed in this experimental model and the presence of neuroinflammation in the RTN may contribute to the cellular loss in this region.

Bien que les mécanismes moléculaires précis à l’origine de la neurodégénérescence dopaminergique ne soient pas encore totalement connus, un ensemble de preuves épidémiologiques, cliniques et expérimentales indiquent que la neuroinflammation peut avoir un rôle important dans la pathogenèse de la MP. L’étude des liens spatio-temporels entre la neuroinflammation et la neurodégénérescence au cours de la MP pourrait améliorer la compréhension du mécanisme physiopathologique et aussi l'accessibilité à un diagnostic précoce et/ou à de nouvelles approches thérapeutiques anti-inflammatoires. Le développement actuel des méthodes non invasives d'imagerie moléculaire permettant la surveillance directe du processus de neuroinflammation devrait être utile à cet effet. La cible moléculaire de choix dans ce domaine est la protéine de 18 kDa translocateur (TSPO), biomarqueur sensible associée à la neuroinflammation, qui est surexprimé dans les microglies activées. Dans le travail présenté ici nous avons réalisé l'évaluation longitudinale des deux mécanismes physiopathologiques en parallèle avec les modifications de la fonction dopaminergique à plusieurs points au cours du temps après lésion à la 6-OHDA chez le rat, modèle qui imite un stade précoce de la MP. Après l'administration unilatérale, intra-striatale de la 6-OHDA, nous avons quantifié l'évolution temporelle de la TSPO, de l’immunoréactivité TH et du DAT dans le striatum et la SNC de 3 à 56 jours post-lésion (jpl). L’augmentation de la liaison des ligands de la TSPO utilisés, c-à-d [3H]-PK11195 et [125I]-CLINDE, a été observée dans le striatum lésé à 3, 7 et 14 jpl, suivie d'un retour progressif à un niveau basal à 56 jpl. Le profil de liaison dans la SNC a montré une augmentation progressive de la fixation qui débute à 3 jpl, avec un pic à 14 jpl, et diminue progressivement jusqu'à ce que 56 jpl. Dans ce modèle de rongeur de la MP, les processus neuroinflammatoire et neurodégénératif surviennent de façon concomitante. La présence transitoire de l'activation microgliale pourrait être impliquée dans l’apparition et l'installation durable de la perte neuronale dopaminergique. Cette étude confirme donc le lien entre la neuroinflammation et de la neurodégénérescence et met aussi l'accent sur l'intérêt du CLINDE comme traceur potentiel de la neuroinflammation in-vivo en fournissant des informations précieuses pour le diagnostic précoce et le suivi longitudinal de la progression de la maladie, avec des applications potentielles chez l'homme. En effet, la détection précoce de la neuroinflammation, de façon antérieure à une perte neuronale cliniquement significative, pourrait devenir un enjeu majeur dans la prise en charge pré-symptomatique de la MP. Dans ce sens, nous mettons en évidence l’existence d'une fenêtre thérapeutique, survenant juste après la lésion, qui peut être proposé pour l'introduction de traitements anti-inflammatoires qui viseraient à ralentir le processus neurodégénératif. La poursuite de l’exploration des relations entre la neuroinflammation et la neurodégénéréscence in-vivo dans le même modèle animal avec la méthode d’imagerie micro-TEP, transposable à l’homme, en utilisant en parallèle le [18F]-DPA714 pour la TSPO et le [18F]-LBT999 pour le DAT est en cours. / Although the precise molecular mechanisms causing the dopaminergic neurodegeneration are still not totally understood, a body of epidemiological, clinical and experimental evidence indicates that neuroinflammation may have an important role in the pathogenesis of PD. Study of spatio-temporal links between neuroinflammation and neurodegeneration during the course of PD would improve understanding of the physiopathological mechanism and also accessibility to early diagnosis and/or new antiinflammatory therapeutic approaches. The current development of non-invasive molecular imaging methods allowing direct monitoring of the neuroinflammation process should be valuable for this purpose. The molecular target of choice in this field is the 18 kDa translocator protein (TSPO), a sensitive biomarker associated with neuroinflammation, which is over-expressed in activated microglia. In the study presented here we achieved the longitudinal evaluation of both physiopayhological mechanisms in parallel with the modifications of dopaminergic function at several time-points after 6-OHDA lesion in the rat that mimics an early stage of PD. After unilateral intra-striatal 6-OHDA administration, we quantified the temporal evolution of the TSPO, TH immunoreactivity and DAT in the striatum and the SNc from 3 to 56 days post-lesion (dpl). Increased binding of TSPO ligands used, i.e. [3H]PK11195 and [125I]CLINDE, was observed in the lesioned striatum at 3, 7 and 14 dpl, followed by a progressive return to the basal level at 56 dpl. The binding profile in the SNc showed progressive binding beginning at 3 dpl, peaking at 14 dpl, and progressively decreasing until 56 dpl. In this rodent model of PD, the neuroinflammatory and neurodegenerative processes occurred concomitantly. The transitory occurrence of microglial activation could be involved in the advent and the lasting installation of dopaminergic neuron loss. This study supports the link between neuroinflammation and neurodegeneration and emphasizes the interest of CLINDE as potent in vivo tracer of neuroinflammation by providing valuable information for early diagnosis and longitudinal follow-up of disease progression, with potential applications to human patients. Indeed, early detection of neuroinflammation, prior to a clinically significant loss of neurons, could become a major issue in the management of pre-symptomatic PD. To support this idea, we demonstrate the existence of a therapeutic window, occurring just after the lesion, which may be proposed for the introduction of anti-inflammatory treatments that aimed to slow the neurodegenerative process. Further exploration of the relationship between neuroinflammation and neurodegeneration in vivo in the same animal model with the method of micro-PET imaging, transposable to humans, using in parallel the [18F]-DPA714 for TSPO and [18F]-LBT999 for DAT is pending.

A doença de Parkinson (DP) apresenta declínio da capacidade respiratória. Estudo utilizando um modelo de DP induzido pela injeção de 6-hidroxidopamina (6-OHDA) no estriado mostrou redução no número de neurônios envolvidos no controle da respiração. O objetivo desse estudo foi avaliar alterações gliais no núcleo retrotrapezóide (RTN), núcleo do trato solitário, complexo pré-Bötzinger e grupamento respiratório ventrolateral rostral (rVRG) utilizando o mesmo modelo experimental. Em ratos Wistar que receberam a injeção de 6-OHDA bilateralmente no estriado observou-se redução na imunorreatividade para proteína ácida fibrilar glial em astrócitos no rVRG a partir de 30 dias, no RTN a partir de 40 dias e nas demais regiões a partir de 60 dias. Ainda, observamos o aumento da proteína ligante de actina cruzada em microglias na região do RTN aos 30 e 40 dias. Nossos dados sugerem que a redução astrocitária contribui para as alterações respiratórias observadas neste modelo experimental e a presença de neuroinflamação no RTN pode contribuir para a perda celular nesta região. / Parkinson\'s disease (PD) has a decline in respiratory capacity. A study using a model of PD induced by the injection of 6-hydroxydopamine (6-OHDA) in the striatum showed a reduction in the number of neurons involved in the control of breathing. The aim of this study was to evaluate glial changes in the retrotrapezoid nucleus (RTN), nucleus of the solitary tract, pre-Bötzinger complex and rostral ventral respiratory group (rVRG) using the same experimental model. Wistar rats that received bilateral 6-OHDA injection in the striatum present a reduction in immunoreactivity for glial fibrillary acidic protein in astrocytes in the rVRG from 30 days, in the RTN from 40 days and in the other regions from 60 days. We also observed an increase of the Ionized calcium binding adaptor molecule 1 in microglia in the region of the RTN at 30 and 40 days. Our data suggest that astrocytic reduction contributes to the respiratory changes observed in this experimental model and the presence of neuroinflammation in the RTN may contribute to the cellular loss in this region.

L’ADHD (Attention-deficit/hyperactivity disorder) est une maladie du développement caractérisée par l’impulsivité, l’hyperactivité, et l’inattention. Les voies neuronales impliquées dans ces déficits indiquent des dysfonctionnements dans les réseaux catécholaminergiques frontal-sous-corticaux, impliquant l'innervation dopaminergique et noradrénergique. Des études récentes ont mis en évidence une hypersensibilité à la douleur chez les patients ADHD et soulignent une possible comorbidité entre l’ADHD et la douleur. Cependant, les mécanismes et les circuits neuraux impliqués dans ces interactions sont inconnus. Afin de décrypter cette relation, nous avons généré un modèle ADHD de souris à P5 par une lésion néonatale des voies dopaminergiques centrales avec la 6-Hydroxydopamine (6-OHDA) et nous avons démontré la validité du modèle pour mimer le syndrome ADHD. Ensuite, nous avons analysé les comportements douloureux dans le modèle de souris 6-OHDA. Ces derniers présentent un abaissement des seuils de la douleur, ce qui suggère que l’ADHD induit une sensibilisation à la douleur (comorbidité ADHD-Douleur). Nous avons confirmé à l’aide d’enregistrements extracellulaires unitaires, que les modifications de la sensibilité à la douleur des souris 6-OHDA sont dues à une augmentation de l’excitabilité des neurones nociceptifs de la moelle épinière. Cette sensibilisation passe donc par une altération de l’intégration sensorielle dans la moelle épinière via la mise en jeu de contrôles descendants. La connectivité "cortex cingulaire antérieur (ACC) – insula postérieur (PI)" est la clé dans cette comorbidité ADHD-douleur, impliquée dans les fonctions exécutives, les émotions et elle envoie aussi des projections vers la corne dorsale de la moelle épinière. En effet, en combinant les analyses électrophysiologiques, optogénétiques et comportementales, nous avons démontré que les effets de l’ADHD sur la sensibilisation douloureuse passent par la mise en jeu de l’ACC et de la voie ACC – PI. En conclusion, nous montrons que les conditions ADHD induisent une hyperactivation des neurones nociceptifs de la moelle épinière et une hypersensibilité à la douleur. Nous suggérons également que le circuit ACC – PI pourrait déclencher un dysfonctionnement des neurones de la moelle épinière sur la douleur dans les conditions ADHD. / Attention deficit hyperactivity disorder (ADHD) is characterized by the core symptoms of inattention, hyperactivity and impulsivity. Neural pathways underlying these deficits point to deficits within frontal-subcortical catecholaminergic networks, involving dopaminergic and noradrenergic innervation. Hence, impairment of the dopaminergic neurotransmission is a frequent target of ADHD medication. Low-dose psychostimulants, including methylphenidate (MpH) and amphetamines (AMP) are the most widely used treatments of ADHD. Recent evidence pointed to pain hypersensitivity in subjects with ADHD history, and suggests possible comorbidity of ADHD with pain. However, the mechanisms and neural circuits involved in these interactions are unknown. In order to understand this comorbidity, the first objective was to create a good animal model of ADHD. We generated a mouse model at P5 by neonatal disruption of central dopaminergic pathways with 6-Hydroxydopamine (6-OHDA) and we demonstrated the validity of the model to mimic ADHD syndrome. Next, we analyzed nociceptive responses in the 6-OHDA mouse model of ADHD. We found that 6-OHDA mice exhibited a marked decrease of withdrawal thresholds, suggesting that ADHD increase nociceptive sensitivity. Interestingly, by using in vivo electrophysiological recordings, we demonstrated that allodynia and hyperalgesia may be caused by neuronal hyperexcitability in the dorsal spinal cord. Moreover, we found that both lowered wihdrawal threshold and increased activity of nociceptive neurons in ADHD-like mice was not normalized by MpH. We tested the hypothesis that descending controls are responsible for pain alterations through the modulation of spinal circuits. The ‘anterior cingulate cortex (ACC) – posterior insular (PI)’ connectivity is at the cross-road of ADHD and pain, being involved in executive functions and emotions, as well as sending projections to the dorsal horn of the spinal cord. By combining electrophysiological, optogenetic and behavioral analyzes, we have shown that the effects of ADHD on painful sensitization involve the implication of ACC and the ACC - PI pathway. In conclusion, we showed that ADHD conditions induce spinal cord nociceptive neurons hyperactivation and pain hypersensitivity. We also suggest that the ACC - PI circuit may trigger dysfunction of spinal cord neurons in ADHD conditions.

Ce travail de thèse porte sur l'étude de la réaction microgliale et des interactions microglie/neurones dans un modèle murin de neurodégénérescence dopaminergique induit par l'injection de 6‐hydroxydopamine (6‐ OHDA). Dans ce modèle, nous décrivons tout d'abord les cinétiques d'activation microgliale, de perte neuronale et d'altérations comportementales en relation avec le déficit dopaminergique. Dans la substance noire lésée ont été observées une perte progressive des neurones dopaminergiques TH+ (Tyrosine Hydroxylase) ainsi qu'une activation microgliale précoce mais transitoire. Le rôle délétère de cette activation microgliale est fortement suggéré par la mise en évidence d'une protection partielle contre la toxicité induite par la 6‐OHDA dans des souris génétiquement modifiées DAP12 Knock‐In, dont la densité microgliale est constitutivement diminuée. Par ailleurs, nous avons identifié différents types de contacts intercellulaires entre les neurones et la microglie de la substance noire lésée. Ces interactions physiques sont matérialisées entre autres sous la forme de contacts intimes entre le corps cellulaire des cellules microgliales et le soma des neurones dopaminergiques. De façon intéressante, ce type d'interaction se met en place quelques jours avant le pic de mort neuronale et dans la grande majorité des cas, concerne des neurones présentant des signes morphologiques d'apoptose. Finalement, nous avons également identifié un nouveau type d'interaction physique entre neurones et microglie sous la forme de ramifications microgliales pénétrant le soma des neurones. Ces interactions s'apparentent aux "tunelling nanotubes" décrits dans la littérature et représentent un type particulier de ramifications microgliales perforantes que nous avons nommées "tunelling ramifications". La présence de vacuoles TH+ dans le cytoplasme de nombreuses cellules microgliales suggère que les ramifications microgliales pénétrantes sont le support d'un processus de microphagocytose ciblant le cytoplasme des neurones dopaminergiques. La fonction précise de ces interactions et les mécanismes moléculaires qui les suscitent restent à définir. Toutefois, ce travail de thèse apporte un ensemble de données originales sur le dialogue microglie/neurones dans un modèle murin de la maladie de Parkinson / This thesis work is aimed to study microglial reaction and microglia/neuron interactions in a murine model of dopaminergic neurodegeneration induced by the injection of 6‐hydroxydopamine (6‐OHDA). In this model, we first describe the kinetics of microglial activation, neuronal cell loss and behavioral alterations in relation with the dopaminergic defect. In the injured substantia nigra, we observed a progressive loss of TH+ (Tyrosine Hydroxylase ‐positive) dopaminergic neurons and an early but transient microglial activation. The deleterious role of microglial activation is strongly suggested by the observation of a partial neuroprotection against 6‐OHDA‐induced toxicity in genetically DAP12 Knock‐In mice, in which microglial cells are defective in regard to their number and function. In addition, we identified various types of cell‐tocell contacts between neurons and microglia in the injured substantia nigra. Such physical interactions were established between microglia and neuronal cell bodies several days before the peak of neuronal death and in the majority of cases in neurons showing morphological signs of apoptosis. Finally, we also identified a new type of physical interactions consisting in microglial ramifications penetrating the soma of TH+ neurons. These interactions present similarities with the so‐called « tunelling nanotubes » previously described in the literature and represent a particular type of penetrating microglial ramifications the we named "tunelling ramifications.". Interestingly, in the injured substantia nigra, the presence of TH+ vacuoles in the cytoplasm of numerous microglial cells strongly suggests that microglial ramifications support microphagocytosis targeted toward the cytoplasm of dopaminergic neurons. The precise function and molecular mechanisms of such unique interactions need to be further assessed. However, our work provides a set of original data that deepens our knowledge on the dialogue between microglia and neurons in a mouse model of Parkinson's disease