Dopaminergic neurons play a vital regulatory role in the brain. Their loss is associated with Parkinson’s disease. In this video, we show how to generate primary cultures of central dopaminergic neurons from embryonic mouse mesencephalon. Such cultures are useful to study the extreme vulnerability of these neurons to various stresses.
Dopaminergic neurons represent less than 1% of the total number of neurons in the brain. This low amount of neurons regulates important brain functions such as motor control, motivation, and working memory. Nigrostriatal dopaminergic neurons selectively degenerate in Parkinson's disease (PD). This progressive neuronal loss is unequivocally associated with the motors symptoms of the pathology (bradykinesia, resting tremor, and muscular rigidity). The main agent responsible of dopaminergic neuron degeneration is still unknown. However, these neurons appear to be extremely vulnerable in diverse conditions. Primary cultures constitute one of the most relevant models to investigate properties and characteristics of dopaminergic neurons. These cultures can be submitted to various stress agents that mimic PD pathology and to neuroprotective compounds in order to stop or slow down neuronal degeneration. The numerous transgenic mouse models of PD that have been generated during the last decade further increased the interest of researchers for dopaminergic neuron cultures. Here, the video protocol focuses on the delicate dissection of embryonic mouse brains. Precise excision of ventral mesencephalon is crucial to obtain neuronal cultures sufficiently rich in dopaminergic cells to allow subsequent studies. This protocol can be realized with embryonic transgenic mice and is suitable for immunofluorescence staining, quantitative PCR, second messenger quantification, or neuronal death/survival assessment.
Dopamine, one of the essential brain neurotransmitters1,2, is mainly released by midbrain dopaminergic (DA) neurons. The majority of DA neurons reside in the ventral part of the mesencephalon2-6. Schematically, midbrain DA neurons can be divided in three anatomically and functionally distinct projection systems: mesostriatal, mesolimbic, and mesocortical pathways2,5. The nigrostriatal pathway is involved in motor behavior, the mesolimbic pathways play an important role in reinforcement, motivation, and learning, whereas the dopaminergic pathways projecting to the prefrontal cortex are implicated in cognition2.
DA neurons are involved in several human neurological disorders such as schizophrenia, attention deficit, hyper activity disorder, and Parkinson’s disease (PD)2,4. PD is characterized by a progressive and selective degeneration of DA neurons connecting substantia nigra pars compacta (SNc) to the striatum. The loss of nigro-striatal DA neurons results in severe dopamine depletion in the striatum that is responsible of the motor symptoms of PD (bradykinesia, resting tremor, and rigidity)7. The initial cause of the idiopathic PD has not been established and the current treatments are only symptomatic, aiming at restoring dopamine level in the striatum. The most prescribed drug is L-Dopa (Levodopa), the natural precursor of dopamine. Though administration of Levodopa compensates for the loss of dopamine for a certain time, motor complications occur after long-term treatments (dyskinesia and on/off states)8,9.
Research on dopaminergic neurons and PD is in constant progression and intense efforts are being made to develop treatments based on cell transplantation, gene therapy, or neuroprotective agents10,11. However, a major issue remains non-elucidated: what is the cause of the extreme vulnerability of DA neurons? Part of the answer can be found in the activity of DA neurons. A reduction in the electrical activity and of the excitability of DA neurons seems to augment their propensity to degenerate12. Nevertheless, the complexity of PD pathogenesis requires further studies to identify the mechanisms involved in DA neurons degeneration13-15.
Primary cultures are especially relevant to study DA neuron properties16-19 and to challenge these neurons to various stresses for evaluation of neuroprotective agents20-24. Rat culture models are most often used, as the dissection of rat embryo mesencephalon is easier, compared with the mouse, and higher amounts of neurons can be obtained in the rat. However, generation of transgenic mouse models of the disease25 has considerably increased the interest of the neuroscientist community for primary cultures from the mouse26-29. Although cultures prepared from newborn animals can be used, it is better to prepare them from embryos at the post-mitotic stage (E13.5 for mesencephalon neurons), when neurons have retained their capacity to differentiate. The following protocol presents isolated mesencephalon neurons in primary culture from mouse embryos (E13.5), which are the most difficult to prepare. Notably, we provide a protocol using serum-free culture medium for a better reproducibility. The two most critical steps in culture preparation (dissection and mechanical dissociation) will be carefully detailed in the associated video.
The mice used in this work were cared for and handled in accordance with the guidelines of the European Union Council (86/609/EU) for the use of laboratory animals.
1. Preparation of Required Solutions
2. Preparation of Culture Plates and Instruments
3. Dissection of Mouse Mesencephalon
4. Cell Dissociation
5. Cell Plating
6. Immunofluorescence Protocol
An illustrated flow chart of the mesencephalon culture steps is shown in Figure 1. Briefly, after collecting E13.5 embryos from a pregnant Swiss mouse, ventral mesencephalon is dissected from the entire embryo. The isolated brain fragments are successively submitted to enzymatic digestion and mechanical dissociation. Dissociated cells are pelleted by centrifugation, resuspended in culture medium and plated in pre-coated 12- or 24-well plates. Cells are maintained up to 15 days without medium replacement.
A detailed flow chart of the ventral mesencephalon dissection, corresponding to step 3.2, is shown in Figure 2. Dashed red lines indicate the 3 main cutting lines on a schematic representation of E13.5 mouse brain (adapted from Prestoz et al.30) and cutting steps are illustrated.
Phase contrast images of the culture after 1, 4, and 7 days in vitro (DIV) are shown in Figure 3. Neurons quickly develop extensions and sprouting (Figure 3A). Branching and ramifications are more extended at DIV4 and DIV7 (Figures 3B-3C).
Dopaminergic neurons are detected by immunocytochemistry using an anti-TH antibody (Figure 4A). The number of TH+ cells is expressed per 2.5 cm2 coverslip (Figure 4B). We do not express the number of TH+ cells per well as the density of cells is much higher on the borders of the coated plastic well than on the coated glass coverslip, that is on the center on the well. DA neurons (TH+ cells) represent 2-4% of the whole cell population on the coverslip. TH-positive (TH+) cells appear as early as DIV1 and their number increases rapidly to reach a maximum at DIV6.
The relative proportion of cells is assessed by immunofluorescence labeling of DA cells with an anti-DAT antibody (Figure 5A) or an anti-TH antibody (Figure 5B) and concomitant staining of neuronal cells with anti-MAP2 antibody. Representative immunostaining of several neuronal populations present in the culture is also shown in Figure 5. GABAergic neurons are stained using an anti-GAD67 antibody (Figure 5C) and represent around 50% of the cells. Serotonergic neurons are detected with an anti-serotonin antibody (Figure 5D) and represent less than 1% of the cells in the culture. The mesencephalon cell culture also contains glutamatergic neurons (40% of the culture), cholinergic neurons, and rare glial cells (around 2-3%). Proportion of of glial cells is determined using glial fibrillary acidic protein (GFAP) staining (Figure 5E). Unambiguous identification of mesencephalon dopaminergic neurons can also be achieved using specific markers such as Pitx3 or Foxa231,32.
Higher magnification immunostaining of several neuronal populations present in the culture is shown in Figure 6. Dopaminergic neurons are detected using an anti-DAT antibody (Figure 6A). DAT staining reflects DA neuron maturation state. DAT expression begins at DIV3-4. GABAergic neurons and serotonergic neurons are stained using an anti-GAD67 antibody (Figure 6B) or an anti-serotonin antibody (Figure 6C), respectively.
Figure 1. Illustrated flow chart of the mesencephalon culture. Main culture steps are indicated. (A) Sacrifice a pregnant Swiss mouse, collect E13.5 embryos in Petri dishes and wash them by successive PBS baths. (B-C) Under dissection microscope, dissect ventral mesencephalon from the entire embryos and place them in a tube. (D) Add Trypsin-EDTA to the dissected brain fragments and digest at 37 °C for 15 min. (E) Remove trypsin, add serum containing-culture medium and perform mechanical cell dissociation (10 trituration movements, repeated twice). (F) Pellet the cell, resuspend them in serum-free medium supplemented with hormones and plate them in precoated 12- or 24-well plates. Please click here to view a larger version of this figure.
Figure 2. Detailed flow chart of the mesencephalon dissection. Main dissection steps are indicated. (A) Mouse embryo at E13.5 after removal from the uterine horns. (B) Without beheading the embryo, excise the brain. (C) Schematic representation of embryonic mouse brain at E13.5. Red dashed lines indicate where the brain should be cut to isolate ventral mesencephalon (R, rostral cut; C, caudal cut; D, dorsal cut). The cephalic vesicles telencephalon, diencephalon, mesencephalon, and rhombencephalon are delimited in blue, purple, pink, and gray, respectively. Aq, aqueduct; Hypoth, hypothalamus; LGE, lateral ganglionic eminence; LV, lateral ventricle; MFB, medial forebrain bundle; MGE, medial ganglionic eminence; sc, superior colliculus; Thal, thalamus; VM, ventral mesencephalon; 4V, fourth ventricle (adapted from30). (D) Cutting lines are indicated by red dashed lines on an E13.5 mouse brain. (E) Mouse brain after removal of the fore- and hindbrain regions (i.e. after cut R). (F) Mouse brain after removal of the superior colliculus (i.e. after cuts R and D). (G) Ventral view of an isolated mesencephalon (i.e. after cuts R, C, D). Please click here to view a larger version of this figure.
Figure 3. Phase contrast images of the culture at different stages of development. (A) DIV1, (B) DIV4, and (C) DIV7 images of the same culture are shown. Images were acquired on live cells with an inverted microscope. Please click here to view a larger version of this figure.
Figure 4. Tyrosine hydroxylase staining of dopaminergic neurons. (A) At DIV8, DA neurons were detected using anti-TH antibody. Revelation was performed using a 3,3'-Diaminobenzidine (DAB) kit. The image was acquired with an inverted microscope. (B) Number of TH+ neurons in mesencephalon cultures as a function of the age of the culture. Please click here to view a larger version of this figure.
Figure 5. Representative proportion of neurons and astrocytes in the culture. At DIV4, DA neurons (in magenta) were detected using anti-DAT (A) or anti-TH antibody (B) and GABAergic neurons, serotonergic neurons and astrocytes (in magenta) were detected using anti-GAD67 (C), anti-serotonin (D), and anti-GFAP (E) antibodies, respectively. Neuronal cells (in cyan) were stained with an anti-MAP2 antibody (A-E). Images were acquired with an inverted microscope. Please click here to view a larger version of this figure.
Figure 6. Representative staining of several cell populations of the mesencephalon culture. (A) Dopaminergic neuron detected by DAT staining at DIV9 (in red). (B) GABAergic neurons visualized by GAD-67 staining at DIV9 (in green). (C) Serotonergic neuron stained with an anti-serotonin antibody at DIV9 (in green). Neurons are identified by MAP2 staining (in blue, A-C). Images were acquired with a UV confocal microscope. Please click here to view a larger version of this figure.
This protocol presents the procedures and reagents necessary to prepare a primary culture of mesencephalic neurons from the embryonic mouse and the immunofluorescence procedure to detect dopaminergic neurons. Critical steps of the procedure are the dissection of the embryos and the mechanical dissociation of the collected brain fragments. High quality dissection instruments helps to master the dissection technique. DA neurons constitute a small proportion of mesencephalon. Accordingly, collecting the right part of the ventral mesencephalon is essential to obtain a culture that contains 2-4% of DA neurons. Mechanical dissociation should be performed carefully and gently. If the culture contains clusters of non-dissociated neurons, add one or two more trituration steps.
This protocol uses serum-free medium for neuron culture. However, coating with serum is necessary to enhance attachment of the cells. Hormone mix, which replaces the serum, is defined to allow neuron growth and to minimize glial cells survival and proliferation. Consequently, non-neuronal cells represent around 2-3% of the culture (quantification using GFAP-staining). Alternatively, the cultures can be grown in the presence of serum with the addition, two-days after seeding, of cytosine-β-D-arabinofuranoside (ara-C, 5-8 μM) to suppress the proliferation of glial cells26. Another alternative to the hormone mix is the use of defined media and supplements29.
This technique is suitable to perform immunofluorescence staining, quantitative PCR, second messenger quantification and various types of toxicology/survival screens. It should also be possible to conduct electrophysiological studies on these preparations33,34. These cultures can identify pre-candidate neuroprotective molecules and help to characterize DA neurons properties, while minimizing the number of animals used. However, final confirmation using in vivo models is requested, as cultured neurons do not receive inputs from other brain regions, which might strongly influence their maturation.
This technique is not widely used, compared with rat culture models, despite its first descriptions in the early eighties16,17. The lack of images presenting the delicate dissection may restrain researchers to develop this mouse culture model. However, due to the generation of numerous transgenic mouse models of neurodegenerative disorders25 with specific gene invalidation or labeling of specific neuron types, DA neuron cultures from mouse are now of great interest.
Mastering this technique allows the study of DA neurons isolated from any type of transgenic mouse and to explore the perturbation induced by gene modification. Moreover, these cultures can be used as reference models to be compared with DA neurons derived from mouse stem cells35 or from induced pluripotent stem cells36.
The authors have nothing to disclose.
Supported by grants from CNRS and INSERM. PM acknowledges support from the Fondation pour la Recherche Médicale en France (Equipe FRM 2009). SC acknowledges support from the Fondation de France.
Fetal Bovine Serum | Lonza | 14-801F | |
DMEM 4.5g/L Glucose with L-Glutamine | Lonza | BE12-604F | |
0.05% Trypsin-EDTA (1X), Phenol Red | Life Technologies | 25300-054 | |
Penicillin-Streptomycin (10,000 U/mL) | Life Technologies | 15140122 | |
L-glutamine, 200 mM Solution | Life Technologies | 25030123 | |
Dulbecco’s Phosphate Buffered Saline | Sigma-Aldrich | D8537 | |
Dulbecco’s Modified Eagle’s Medium/Nutrient Mixture F-12 Ham | Sigma-Aldrich | D0547 | Powder |
Laminin – 1 mg/mL in Tris buffered NaCl | Sigma-Aldrich | L2020 | |
Poly-L-Ornithine hydrobromide | Sigma-Aldrich | P3655 | |
Insulin from porcine pancreas | Sigma-Aldrich | I5523 | |
apo-Transferrin human | Sigma-Aldrich | T1147 | |
Putrescine dihydrochloride | Sigma-Aldrich | P5780 | |
Progesterone | Sigma-Aldrich | P8783 | |
Sodium selenite | Sigma-Aldrich | S5261 | |
HEPES | Sigma-Aldrich | H4034 | |
Glycine | Sigma-Aldrich | G7126 | Stock solution 1M in water |
Gelatin | Sigma-Aldrich | G9391 | Stock solution 2% (w/v) in water |
Triton X-100 | Sigma-Aldrich | T8532 | |
Paraformaldehyde 16% in water | Electron Microscopy Sciences | RT 15710-S | |
Sodium hydrogen carbonate (NaHCO3) | Merck Millipore | 106329 | |
D(+)-Glucose, Monohydrate | Merck Millipore | 4074-2 | |
Hydrochloric acid – c(HCl) = 1 mol/l (1 N) Titripur | Merck Millipore | 109057 | |
Sterile water – Aqua B. Braun | Braun | ||
Ethanol absolute NORMAPUR analytical reagent | VWR | 20821.321 | |
Sterile Petri Dishes | VWR | 82050-566 | |
Pasteur pipettes plain glass – Wilhem Ulbrich GdbR. | VWR | 612-2297 | |
Counting chamber Malassez | VWR | 631-0975 | |
Serum Acrodisc Syringe Filter with Supor Membrane, Sterile, GF/0.2 µm, 37 mm | PALL Life science | 4525 | |
Surgical Scissors – Straight, sharp-sharp, 14.5 cm long | Fine Science Tools | 14002-14 | To open the abdominal wall |
Scissors – Straight, pointed, delicate, 10 cm long | MORIA | 4877A | To open the uterine wall |
Forceps – Curved, usual, serrated jaws 1 mm | MORIA | 2183 | To manipulate embryos |
Vannas Scissors – Curved, pointed, 7 mm blades | MORIA | MC50 | To take out the mesencephalon |
Ultra Fine Forceps – Curved, delicate, 13 cm long | MORIA | 9987 | To remove meninges |
BD BioCoat Poly-D-Lysine 24-well Multiwell Plates | BD Bioscience | 356414 | |
BD Falcon 12-well Cell Culture Plate, flat-bottom with lid | BD Bioscience | 353043 | |
SuperFrost Microscope Slides, Ground edges 90º | MENZEL-GLÄSER | AG00008032E | |
Precision cover glasses thickness No. 1.5H circular 18 mm Ø | MARIENFELD | 117580 | |
Polyclonal Rabbit Anti-Microtubule-Associated Protein 2 (MAP2) Antibody | Chemicon Millipore | AB5622 | 1/200 |
Monoclonal Mouse Anti-Glutamate Decarboxylase (GAD67) Antibody, clone 1G10.2 | Chemicon Millipore | MAB5406 | 1/400 |
Monoclonal Rat Anti-Dopamine Transporter (DAT) Antibody, clone DAT-Nt | Chemicon Millipore | MAB369 | 1/500 |
Monoclonal Mouse Anti-5-HT Antibody | 1/8,000 – Generous gift from Yves Charnay (Swizerland, Yves.Charnay@hcuge.ch) | ||
Goat Serum, New Zealand Origin | Life Technologies | 16210-064 | |
Alexa Fluor 405 Goat Anti-Rabbit IgG (H+L) Antibody | Life Technologies | A-31556 | 1/200 |
Alexa Fluor 488 Goat Anti-Mouse IgG (H+L) Antibody | Life Technologies | A-11001 | 1/1000 |
Alexa Fluor 594 Goat Anti-Rat IgG (H+L) Antibody | Life Technologies | A-11007 | 1/1000 |
VECTASHIELD HardSet Mounting Medium | Vector Laboratories | H-1400 | |
Stereomicroscope | Carl Zeiss microscopy | Stemi-2000C | |
Bunsen Burner FIREBOY | VWR | 451-0136 |