Microdissection of the Rodent Eye
Summary
This paper presents a protocol for ocular micro-dissection in rodents. The process involves the enucleation of the eyeball along with the nictitating membrane (i.e., the third eyelid). This is then followed by the separation of the posterior and anterior eye cups.
Abstract
The ocular micro-dissection of the rodent eye involves the segmentation of the enucleated eyeball with the attached nictitating membrane, or third eyelid, to obtain the anterior and posterior eyecups. With this technique, the sub-parts of the eye, including the corneal tissue, neural tissue, retinal pigment epithelial (RPE) tissue, and lens, can be obtained for wholemounts, cryo-sectioning, and/or single-cell suspensions of a specific ocular tissue. The presence of the third eyelid presents unique and significant advantages, as it benefits the maintenance of the orientation of the eye, which is important for understanding eye physiology following any localized intervention or in studies involving ocular analysis relating to the eye's spatial topography.
In this method, we enucleated the eyeball at the socket along with the third eyelid by carefully and slowly cutting through the extraocular muscles and severing the optic nerve. The eyeball was pierced through the corneal limbus using a microblade. The incision was used as the point of entry, allowing for cutting along the corneal-scleral junction by inserting micro-scissors through the incision point. Small and continuous cuts along the circumference were made until the cups separated. These could be further dissected by gently peeling the translucent layer of the neural retina using Colibri suturing forceps to obtain the neural retina and RPE layers. Further, three/four equidistant cuts were made from the periphery perpendicularly to the optic center until the optic nerve was reached. This opened the hemispherical cups into a floret shape so that they fell flat and could be easily mounted. This technique has been used in our lab for corneal wholemounts and retinal sections. The presence of the third eyelid delineates the nasal-temporal orientation, which allows for the study of various cell therapy interventions post-transplantation and, thus, the targeted physiological validation vital for visualization and accurate representation in such studies.
Introduction
Ocular dissection is an important technique in ophthalmic research and has allowed investigators to access the segments of the eye for targeted studies. Previously, ocular researchers relied on the ocular tissue from diseased individuals for their studies. However, the progressively growing number of strains of ophthalmic rodent models1 over the years has diminished the need for human ocular tissue. These mouse strains have permitted a deeper understanding of ocular disease and interventions. Yet, they have also generated a need for innovative techniques of ocular micro-dissection. The small size and limited area of operation severely constrain effective access to the ocular sub-parts. Further, owing to the homogenous cellular assembly of the posterior and anterior eyecups, it is difficult to conduct targeted interventions post-dissection. The current micro-dissection techniques of laser2 and surgical microdissection3,4 are inadequate in meeting such requirements of ocular research. Laser micro-dissection is very effective in single-cell analysis, but the specific tissue needs to be micro-dissected before the laser procedure2. The technique can isolate small regions of interest from a pre-dissected tissue for molecular analysis. Thus, the technique is not suitable for preparing wholemounts or for the isolation of axially packed ocular layers for optimum visualization.
The surgical method is the most widely used technique; this method involves immobilizing the eye via the optic nerve5 and then performing the dissection. This practice is arduous and can damage any fragile tissue, as the spherical eye continues to move during dissection. Despite being beneficial for isolating the various sections of the retinal layers, the technique cannot demarcate the spatial orientation of the tissue upon dissection.
During dissection, maintaining the presence of the attached nictitating membrane or the third eyelid (Figure 1) presents unique and significant advantages. In this method, first, the eyeball is enucleated with the third eyelid. Then, the third eyelid is used to immobilize the eye6 (Figure 2A). This is followed by piercing the eyeball through the corneal limbus and using the incision as the point of entry (Figure 2B,C). Then, the eyecups are separated by cutting along the circumference anteriorly and posteriorly (Figure 2D–G). By dissecting the posterior eyecup further, the translucent layer of the neural retina can be identified and gently peeled off. Three or four equidistant cuts are then made in the obtained hemispherical anterior and posterior cups, which allow these flower-shaped cups to fall flat onto a slide (Figure 2H).
The third eyelid aids in easy and efficient handling during the dissection, thus ensuring minimal damage to the tissue while accessing the various ocular layers and when producing wholemounts. Further, the presence of the third eyelid helps to locate and examine localized interventions during visualization.
The procedure, in our lab, has been performed on a CBA/J or an rd1 mouse strain at P28 of any sex. The procedure can be performed on any strain, age, or sex of animal and has no bias according to these characteristics.
The animals were procured from commercial sources (see Table of Materials) and maintained at the Small Animal Facility (SAF) at the National Institute of Immunology (NII). They were kept in individual ventilated cages (IVC) and received ad libitum access to acidified autoclaved water and food. They were maintained at 21-23 °C and with a 14 h/10 h light/dark cycle.
Given below is a modified surgical method for the micro-dissection of a mouse eye.
Protocol
Representative Results
Discussion
Ocular microdissection has been found to be a difficult task owing to the small size and spherical shape of the rodent eye, and the rodent eye requires innovative techniques for efficient handling8.
In the current demonstrated method, the enucleated mouse eyeball is obtained with the third eyelid attached for effective and easy handling. Using the third eyelid, the eyeball can be immobilized completely, which allows the dissection to proceed with ease and with minimal …
Offenlegungen
The authors have nothing to disclose.
Acknowledgements
Dr. Alaknanda Mishra, Department of Cell Biology and Human Anatomy, University of California Davis, USA, trained us in this method at the National Institute of Immunology, New Delhi. This work was supported by the core grant received from the Department of Biotechnology, Government of India to the National Institute of Immunology, New Delhi. P.S. was granted a research fellowship by the Department of Biotechnology.
Materials
| Acetaminophen (Biocetamol) | EG Pharmaceuticals | No specific Catalog Number (Local Procurement) | |
| Alkaline Phosphatase Kit (DEA) | Coral Clinical System, India | No specific Catalog Number (Local Procurement) | |
| Automated analyser | Tulip, Alto Santracruz, India | Screen Maaster 3000 | Biochemical analyser for liver functional test |
| Betadine (Povidon-Iodine Solution) | Win-Medicare; India | No specific Catalog Number (Local Procurement) | |
| Biological safety cabinet ( Class I) | Kartos international; India | No specific Catalog Number (Local Procurement) | |
| Bright Field Microscope | Olympus, Japan | LX51 | |
| CBA/J inbred mice | The Jackson Laboratory | Stock No. 000654 | |
| Cefotaxime (Taxim) | AlKem ; India | cefotaxime sodium injection, No specific Catalog Number (Local Procurement) | |
| Cell Strainer | Sigma ; US | CLS431752 | |
| Collagenase Type I | Gibco by Life Technologies | 17100-017 | |
| Cotton Buds | Pure Swabs Pvt Ltd ; India | No specific Catalog Number (Local Procurement) | |
| DPX Mountant | Sigma ; US | 6522 | |
| Drape Sheet | JSD Surgicals, Delhi, India | No specific Catalog Number (Local Procurement) | |
| Eosin Y solution, alcoholic | Sigma ; US | HT110132 | |
| Forceps | Major Surgicals; India | No specific Catalog Number (Local Procurement) | |
| Gas Anesthesia System | Ugo Basile; Italy | 211000 | |
| Glucose | Himedia, India | GRM077 | |
| Hair removing cream (Veet) | Reckitt Benckiser , India | No specific Catalog Number (Local Procurement) | |
| Hematoxylin Solution, Mayer's | Sigma ; US | MHS16 | |
| Heparin sodium salt | Himedia; India | RM554 | |
| Hyaluronidase From Sheep Testes | Sigma ; US | H6254 | |
| I.V. Cannula (Plusflon) | Mediplus, India | Ref 1732411420 | |
| Insulin Syringes | BD ; US | REF 303060 | |
| Isoflurane ( Forane) | Asecia Queenborough | No B506 | Inhalation Anaesthetic |
| Ketamine (Ketamax) | Troikaa Pharmaceuticals Ltd. | Ketamine hydrochloride IP, No specific Catalog Number (Local Procurement) | |
| Meloxicam (Melonex) | Intas Pharmaceuticals Ltd; India | No specific Catalog Number (Local Procurement) | |
| Micro needle holders straight & curved | Mercian ; England | BS-13-8 | |
| Micro needle holders straight & curved |
Mercian ; England | BS-13-8 | |
| Microtome | Histo-Line Laboratories, Italy | MRS3500 | |
| Nylon Thread | Mighty ; India | No specific Catalog Number (Local Procurement) | |
| Paraformaldehyde | Himedia; India | GRM 3660 | |
| Percoll | GE Healthcare | 17-0891-01 | |
| Refresh Tears/Eyemist Gel | Allergan India Private Limited/Sun Pharma, India | P3060 | No specific Catalog Number |
| RPMI | Himedia; India | No specific Catalog Number (Local Procurement) | |
| Scalpel | Major Surgicals; India | No specific Catalog Number (Local Procurement) | |
| Scissors | Major Surgicals; India | No specific Catalog Number (Local Procurement) | |
| SGOT (ASAT) KIT | Coral Clinical System, India | No specific Catalog Number (Local Procurement) | |
| SGPT (ALAT) KIT | Coral Clinical System, India | No specific Catalog Number (Local Procurement) | |
| Shandon Cryotome E Cryostat | Thermo Electron Corporation ; US | No specific Catalog Number | |
| Sucrose | Sigma ; US | S0389 | |
| Surgical Blade No. 22 | La Medcare, India | No specific Catalog Number (Local Procurement) | |
| Surgical Board | Locally made | No specific Catalog Number (Local Procurement) | |
| Surgical White Tape | 3M India ; India | 1530-1 | Micropore Surgical Tape |
| Sutures | Ethicon, Johnson & Johnson, India | NW 5047 | |
| Syringes (1ml, 26 G) | Dispo Van; India | No specific Catalog Number (Local Procurement) | |
| Trimmer (Clipper) | Philips | NL9206AD-4 DRACHTEN QT9005 | |
| Weighing Machine | Braun | No specific Catalog Number (Local Procurement) | |
| William's E Media | Himedia; India | AT125 | |
| Xylazine (Xylaxin) | Indian Immunologicals Limited | Sedative, Pre-Anaesthetic, Analgesic and muscle relaxant |
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