CHAPTER 9
LABORATORY ANIMALS
2. REFINEMENT
“Refine experiments to cause the minimum pain, distress and las4ng harm”
2.1. LAB ANIMAL HUSBANDRY
• Lab animal husbandry: right housing and environmental condi6ons, good health, good welfare
CAGE MATES
CAGE STRUCTURE CAGE
DIMENSIONS BEDDING
SCENTS
SOUNDS
LIGHT
HUMIDITY TEMPERATURE
PATHOGENS
OTHER SPECIES
PEOPLE
FOOD & WATER
VENTILATION NH3, CO2
2.1. LAB ANIMAL HUSBANDRY
• Microbiological status of lab animals • Germ-‐free: completely free from micro-‐organisms • GnotobioEc: harbour a fully known microflora • Specific pathogen-‐free (SPF): free from a number of specified (poten6ally) pathogenic micro-‐organisms • ConvenEonal: microbiological status unknown and uncontrolled
• Sources of infec6on: animals, staff, biological materials, insects and vermin • Disinfec6on and sterilisa6on
2.1. LAB ANIMAL HUSBANDRY
• Examina6on of an animal’s physical appearance is essen6al for health and welfare assessment. When evalua6ng an animal’s physical condi6on, one should look at: • Body condi6on (“fit not fat”)
hMp://www.ahwla.org.uk/site/Tutorials.html
2.1. LAB ANIMAL HUSBANDRY
• Body condi6on (“fit not fat”) • Changes in body shape • Posture • Fur and feathers • Facial expression • Skin • Mucous membranes • Eyes, ears, nose, mouth, perineum
2.2. ENRICHMENT
• Environmental enrichment = method employed to increase the biological relevance of a cap6ve environment with a view to improve overall welfare • Used to combat boredom and frustra6on, encourage explora6on, normal foraging and to reduce destruc6ve and aberrant behaviours
• Social enrichment: intra-‐ and interspecific interac6ons (e.g. contact with cage mates and humans)
2.2. ENRICHMENT
• Dietary enrichment: different ways of presen6ng food; novel foods; hay or straw for foraging • Sensory enrichment: auditory (sounds), visual, olfactory (smells)
2.2. ENRICHMENT
• Physical enrichment: cage dimensions and design, novel toys, increasing the complexity of an enclosure
2.2. ENRICHMENT
• The recovery environment can contribute posi6vely to aMenuate the need for pain relief in animals submiMed to invasive procedures.
(Pham et al., Physiol. Behav. 2010, 99: 663-‐668)
Non-‐enriched, isolated
Enriched, isolated
Non-‐enriched, grouped
Enriched, grouped
(Cao et al., Cell 2010, 142: 52-‐64)
2.2. ENRICHMENT
• Simple environmental enrichment (EE) decreases figh6ng in aggressive males, decreases aggression in certain inbred mouse strains, decreases barbering in mice, makes mice more easier to handle, etc. • Does not affect outcomes of experiments
2.4. NON-INVASIVE METHODS
• CT (computed tomography) or CAT (computed axial tomography) scan • Based on differences in damping of X rays through different 6ssues; mostly used for 6ssues with high density (e.g. bone) • Several images are taken and processed by the computer • Painless (animal is anaesthe6sed) • If animals are followed for longer periods of 6me, the high radia6on level may cause tumours to develop.
2.4. NON-INVASIVE METHODS
• CT (computed tomography) or CAT (computed axial tomography) scan
2.4. NON-INVASIVE METHODS
• PET (positron emission tomography) scan • Makes use of tracer; decay of tracer results in emission of two photons that are detected in two direc6ons • Very sensi6ve, but gives bad anatomical detail (usually combined with CT) • Painless
2.4. NON-INVASIVE METHODS
• MRI (magne6c resonance imaging) • Relies on powerful magne6c fields and radiofrequency pulses • MRI provides good contrast between the different soe 6ssues of the body → useful for imaging brain, muscles, heart, tumours
2.5.1. ANAESTHESIA
• Anaesthesia = reversible lack of awareness • Pharmacologically induced and reversible state of amnesia, analgesia, loss of responsiveness, loss of skeletal muscle reflexes or decreased fight-‐or-‐flight response, or all simultaneously. • This allows pa6ents to undergo surgery and other procedures without the distress and pain they would otherwise experience.
2.5.1. ANAESTHESIA
• General anaesthesia: reversible repression of central nervous system • Analgesia — loss of response to pain • Amnesia — loss of memory • Immobility — loss of motor reflexes, skeletal muscle relaxa6on • Hypnosis — loss of consciousness
• Single anaesthe6c (e.g. pento-‐barbital, ketamine) or combina6on of different pharmaceu6cals • Mode of ac6on of general anaesthe6cs not well understood; affect the GABA and NMDA systems in the brain
2.5.1. ANAESTHESIA
• Phases of general anaesthesia:
PREPARATION (PREANAESTHESIA) (PREMEDICATION/SEDATION)
INTRODUCTION (INDUCTION)
MAINTENANCE
RECOVERY (EMERGENCE)
2.5.1. ANAESTHESIA
• Anaesthe6c premedicaEon consists of a drug or combina6on of drugs that serve to complement or otherwise improve the quality of the anaesthe6c. • e.g. reduce saliva secre6on, bradycardia, bronchoconstric6on
• SedaEon: tranquilising (to calm down nervous animals) • e.g. benzodiazepines (like diazepam, midazolam): enhance effects of GABA • Anxioly6c (= fear-‐reducing) • Seda6ve • Hypno6c • An6convulsant • Muscle relaxant • Amnesic
2.5.1. ANAESTHESIA
• Stages of anaesthesia • Stage I: InducEon stage
• Period between the ini6al administra6on of the induc6on agents and loss of consciousness; animal progresses from analgesia without amnesia to analgesia with amnesia (fear, urina6on, defaeca6on, struggling, disorienta6on)
• Stage II: Excitement stage • Respiratory and heart rate may become irregular, many reflexes are enhanced, increased muscle tension, pupil dila6on, increased tear and saliva produc6on, vocalisa6on
• Stage III: Surgical anaesthesia • Concentra6on of anaesthe6c in brain increases: respiratory rate and depth decrease, pupil narrower, eyelid and cornea reflexes slower and disappear, muscle tension and toe reflex decrease → reflexes absent, anaesthesia sufficiently deep
• Stage IV: Overdose • Vital brain centres repressed, respiratory arrest, circulatory collapse, death within 1-‐5 mins
2.5.1. ANAESTHESIA
• Judge depth of anaesthesia by • Respiratory rate and depth • Heart rate • Reac6on to pain s6muli • Tes6ng of reflexes
• Righ6ng (turn-‐around) reflex
• Eyelid reflex (= palpebral or blink
reflex)
• Swallowing reflex
• Pupil reflex (= pupillary light
reflex)
• Tail pinch reflex and toe reflex in
mice and rats
2.5.1. ANAESTHESIA
• Local anaesthesia • To induce the absence of sensa6on in part of the body, generally for the aim of inducing local analgesia (= local insensi6vity to pain); structurally related to cocaine
• Regional anaesthesia • Affec6ng only a large part of the body, such as a limb • Plexus block: complete innerva6on area of nerve • Epidural block: complex of nerves • Diagnosis of navicular disease in horses, lameness
• Influence on physiological processes outside anaesthe6sed area minimal; safer in many situa6ons • DissociaEve anaesthesia
• Reduces or blocks signals to the conscious mind from other parts of the brain → animal no longer feels connected to and aware of its environment • Hallucinogenic, amnesia, analgesia • Most used: ketamine
2.5.1. ANAESTHESIA
• Important: • Ill animals have a bigger chance to drop out during anaesthesia • Anaesthe6cs influence physiological parameters (blood pressure, heart rate, respira6on, thermoregula6on) → experiment! • Interac6on of anaesthe6c with other pharmaceu6cals (e.g. an6bio6cs) • Long-‐las6ng anaesthesia → hypothermia
2.5.1. ANAESTHESIA
• Response of the animal to the administered anaesthe6cs depends on species, age, strain, weight, basal metabolism, sex, fat %, feeding condi6on, heath condi6on, previous exposure to pharmaceu6cals • Doses of anaesthe6cs are not the same for all species (par6ally because of varia6on in body composi6on)! • Species-‐specific reac6ons, e.g.
• Hamsters are less sensi6ve to Nembutal than other rodents. • Mice and cats react excited to morphine. • About 30% of rabbits does not respond to atropine premedica6on.
Top Related