what is pain
unpleasent sensory and emotional experience associated with actual or potential tissue damage or described in terms of such damage
pain is multi-dimensional
sensory-location, radiation, intensity
negative emotions-anxiety, depression
social-affects social structure, conspecifics in pain
environmental- being unable to hide, disturbed by environ can affect pain
pain perception and use
ability to detect noxious stimuli is essential to survival and well being
- pain is active process
- involves peripheral and central mechs
- multiple plastic changes determine pain experience
pain experience
- transmission of signal: noxious stim>brain (nociception)
- perception of unpleasant experience
- behavioural or cognitive response to pain
nociception
negative stimulus transfer and response in brain
-nociceptors are terminal endings of primary afferent nerve fibers
nociceptor types
- myelinated A-delta fibers
- non-myelinated C-fibers
- both synapse at DORSAL horn of spinal cord
Pain pathway, 4 processes
- transduction
- transmission
- modulation
- perception
transduction
-noxious stimuli translated to electrical activity at sensory nerve endings and nociceptors
transmission
propagation of impulses in nervous system, moves through sensory nerves nerves
modulation
amplification or suppression or nerve signals at spinal cord
perception
integration, processing, and recognition of nerve signals at brain
how do we know animals feel pain?
- similar nervous system with brain, spinal cord, and pain receptors
- show behaviour indicating pain, ie. vocal and flinching
- do signs go away when given drugs to remove pain?
types of pain
acute: immediate, severe pain, ie. colic
chronic: duller, over time pain, ie. arthritis
importance of pain assessment
underestimation of pain and ineffective analgesia can results in ethical obligations not being met
-limiting effect of pain in research is ethically vital
traditional assessments
subjective: appearance, posture, gait, demeanour
objective: activity, food/water intake, respiratory/heart rate, blood pressure
equine signs of pain
head down, on three legs, rolling, tucked abdomen, ached back, dropped ears, aggressive, kicking, striking, biting, fighting, defeated, docile, escaping, quiet, grunting moaning, lameness, slow, odd gait, non-weight bearing, reluctant to move, self-trauma, dull eyes
limitations of traditional assessments
- little evidence of how is it related to pain intensity
- requires detailed species knowledge
- requires a baseline of species/individual
- observers may vary interpretation
behavioural assessment
- improve effectiveness of pain assessment
- behaviour gives immediate cage assessment, and relationship between pain and behaviour
principles of behavioural assessments
- pain causes certain behaviours to be more or less frequent
- analgesics should therefore reduce the increase or decrease
- appropriate controls are necessary to ensure relationships and changes are in response to pain
problems with behavioural indicators
-few procedures assessed in small number of species
-time consuming process:
must establish which behaviours indicate pain, applying scoring system
-still only 80% accurate
facial expressions of pain
-established in humans, and validated tool for rats and mice as well
horse grimace scale
- back/sideways ears
- tension above eyes
- orbital tightening
- prominenet strained chewing muscles
- strained nostrils and mouth
