Diagnostic Necropsy and Selected Tissue and Sample Collection in Rats and Mice

Summary

This article describes the procedures for conducting a basic postmortem examination of a mouse or rat, and the collection of basic organs, as well as more challenging sample types from for histological, microbiological, and PCR evaluation.

Abstract

There are multiple sample types that may be collected from a euthanized animal in order to help diagnose or discover infectious agents in an animal colony. Proper collection of tissues for further histological processing can impact the quality of testing results. This article describes the conduct of a basic gross examination including identification of heart, liver, lungs, kidneys, and spleen, as well as how to collect those organs. Additionally four of the more difficult tissue/sample collection techniques are demonstrated. Lung collection and perfusion can be particularly challenging as the tissue needs to be properly inflated with a fixative in order for inside of the tissue to fix properly and to enable thorough histologic evaluation. This article demonstrates the step by step technique to remove the lung and inflate it with fixative in order to achieve optimal fixation of the tissue within 24 hours. Brain collection can be similarly challenging as the tissue is soft and easily damaged. This article demonstrates the step by step technique to expose and remove the brain from the skull with minimal damage to the tissue. The mesenteric lymph node is a good sample type in which to detect many common infectious agents as enteric viruses persist longer in the lymph node than they are shed in feces. This article demonstrates the step by step procedure for locating and aseptically removing the mesenteric lymph node. Finally, identification of infectious agents of the respiratory tract may be performed by bacterial culture or PCR testing of nasal and/or bronchial fluid aspirates taken at necropsy. This procedure describes obtaining and preparing the respiratory aspirate sample for bacterial culture and PCR testing.

Protocol

1. Preparation for the necropsy

1. Important parts of any gross postmortem examination (gross necropsy) are the history of the animal and the description of the findings.
2. A veterinary pathologist reading your histopathology slides may not have seen the animal and is relying on you for the background information.
3. Describe exactly what you see before you euthanize the animal. For example, "female mouse; one of five in the cage; C57BL/6N; head tilted to the right" or "brown male rat; strain unknown; animal is scratching; there is patchy hair loss on the dorsum, near the tail and head".
4. Use clear, descriptive, objective langua....

Discussion

Data collection at the end of a study may require a postmortem examination of animals. Describe well what is seen and remember to examine all tissues. These procedures are designed primarily to optimize necropsy and sample collection for infectious disease surveillance, but most are easily adapted to focused investigations of suspected disease incidents or outbreaks in which perhaps only a subset of the procedures would be employed. Many of the procedures are also relevant to necropsies more commonly performed at the .......

Materials

List of materials used in this article

Name	Company	Catalog Number	Comments
Cutting board	Thermo Fisher Scientific, Inc.	Cat #36114
Small scissors	Roboz Surgical Instruments Co.	RS-5910, G204	23mm blades, 3.5" length, straight
Medium scissors	Roboz Surgical Instruments Co.	RS-6808, G207	5"
Large scissors	Roboz Surgical Instruments Co.	RS-6826, G65"	6.25"
Forceps-Curved	Roboz Surgical Instruments Co.	RS-8254 (M1/21004)	4.5", serrated, slight curve
Forceps-Microdissecting	Roboz Surgical Instruments Co.	RS-5238	Hudson-(EWALD)
Forceps-Tissue Forceps	Roboz Surgical Instruments Co.	RS--8160	Rat tooth
Flame sterilizer	Oxford Labware	Bacti-Cinerator #5889-001007
Scalpel	Cancer Diagnostics, Inc.	Finger Scalpels #60, Cat#FS0060
Pipettes	VWR international	Pasteur Pipet 5 3/4", Cat#14672-400
Autoclave bags	Propper Manufacturing Company	Sterilizer Bag Paper Pouches Cat#021002(3100923)E09110	For Pasteur pipettes
Pipette bulb	VWR international	Cat#56310-240
Eppendorf tubes	Sarstedt Ltd	SafeSeal microtube 2mL, Ref#72.695
Eppendorf tubes	Argos	5mL microtube Cat#T20765-C
Syringe	BD Biosciences	1ml-309602 3 ml-300910 5ml-309603 10mL Cat#309604 20mL Cat#309661
Needles	BD Biosciences	26G-309625 18G-305195
Neutral buffered formalin	VWR international	20L 10% NBF, Cat#16004-128
Saline	Thermo Fisher Scientific, Inc.	Buffered Blood Bank Saline, Cat#23-309-178
Trypticase soy broth	BD Biosciences	TSB: Dehydrated, Cat#211825
Phosphate buffered saline	Sigma-Aldrich	HA Buffer, Cat#P3813-10PAK
Formalin cups	VWR international	4oz Cat#36318-852 8oz Cat#36318-860 16oz Cat#36318-858
Large formalin cups	OakRidge Products	32oz container Cat#0432-1100
Extra large formalin cup	VWR international	HDPE Multipurpose 160oz container Cat#89038-282
Suture material	Henry Schein	Braided silk surgical suture, Ref#100-5000, M766750	For mouse lung inflation
Twine	Staples	Cat#QUA-46173	For rat lung inflation