Tori Collins
Pain and Stress
Chronic pain is an inescapable stress Many patients with chronic pain
suffer from depression Depressed patients have an altered
perception of pain Biggest risk factor for depression is
chronic stress Blackburn-Munros & Blackburn-Munro
2001
Pain integration
Descending control of nociception plays a role in how we experience acute and chronic pain
Nociceptive input is prioritized relative to other homeostatic needs
Descending control can be stimulatory or inhibitory Can depend on behavioral, emotional
and pathological states
Pain integration
Descending inhibition: intense stress and fear are associated with hypoalgesia
Descending facilitation: inflammation, nerve injury, sickness, chronic opioid exposure are associated with hyperalgesia
Pain integration
The RVM can produce both analgesia and hyperalgesia Opiods, OFF-cells: analgesia CCK, ON-cells: hyperalgesia
Rivat C et. al.
Chronic stress induces transient spinal neuroinflammation, triggering sensory hypersensitivity and long-lasting anxiety-induced hyperalgesia
Intro
After repetitive and sustained stress adaptation is impaired Hypercortisolism Hypertension Neuropsychiatric disorders
Immune system can be affected Increased inflammatory response Excess of COX-2 leads to neuronal
damage
Intro
Social defeat is a model for psychological chronic stress
Animals display anxiety/depression-like behaviors
Methods
Intruders (male Sprague-Dawley rats 300-325g)
Residents (male Long-Evans rats, 700-800g)
Rats were divided into defeated intruders and non-defeated intruders each receiving either vehicle or drug
Social defeat
Intruders were placed into resident’s cage for 45 min periods on 4 consecutive days Period 1: no physical contact Period 2: either intruder was defeated by
resident or resident was removed and intruder allowed to explore freely (non-defeated group)
Experimental design
Elevated plus maze
Methods
Nociceptive sensitivity was assessed with von Frey and Randall-Selitto tests
Methods
Formalin was injected under the skin on the dorsal surface of the hindpaw and pain responses were recorded for 70 min
Pain is assessed on a 5 level scale according to posture Ex. 0 = normal posture, 4 = shaking,
licking or biting of paw
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Discussion
Psychological stress produced a transient plastic change in the spinal cord
Spinal inflammation was correlated with mechanical sensory hypersensitivity RVM-CCK dependent descending pathways Distinct mechanisms for sensory
hypersensitivity and formalin-induced hyperalgesia
Discussion
Spinal neuroinflammation was related to sensory hypersensitivity mediated by iNOS and COX-2 but not to anxiety
The inflammation was linked to the stress itself, not the anxiety state produced by the stress
Discussion
The decrease in pain threshold in the rats exposed to social defeat was related to CCK-dependent facilitatory pathways from the RVM A CCK-2 receptor antagonist may
provide pain relief in the context of anxiety-induced hyperalgesia
FIGHT THE POWER
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