Central Flashcards
Coderre and colleagues (1990)
Late-phase nociceptive responses were significantly reduced by spinal anaesthesia induced immediately prior to formalin injection, but not by spinal anaesthesia administered 5 minutes after formalin injection in rats
LaMotte and colleagues (1991)
Proximal anaesthetic block of the peripheral nerve in humans only prevented hyperalgesic responses to intradermal injection of capsaicin if the anaesthetic was administered prior to capsaicin
Pre-operative administration of analgesics
pre-operative administration of analgesics by a variety of routes reduces postoperative pain long after the clinical duration of action of the analgesics (Campbell et al.,1990; McGlew et al., 1991).
Cutaneous hyperalgesia
Typically, nociceptor sensitization associated with injury is restricted to about 5-10 mm of the site of injury (Fitzgerald, 1979) while, in contrast, cutaneous hyperalgesia spreads far beyond the site of injury.
Woolf 1983
Injected a rat paw with inflammatory agents and found heightened sensitivity in the contralateral paw where there was no inflammatory lesion
This sensitivity was maintained after the affected paw was injected with a LA, demonstrating that the driving force of this hypersensitivity was not peripheral but central
Campbell et al. 1988
LaMotte et al. 1992
Other studies have also shown that noxious mechanical and chemical stimuli produce extensive spreading hyperalgesia without producing the same degree of spreading sensitization of primary afferent nociceptors in monkeys (Campbell et al. 1988) or humans (LaMotte et al. 1992).
O’Neil and colleagues (2012)
O’Neil and colleagues (2012) compared the injection of a hypertonic saline solution to cause experimental cramp in control and chronic back pain (CBP) patients.
They found that the spatial distribution and intensity of pain was much larger in CBP patients, demonstrating objectively that nociceptive processing in chronic pain conditions is exaggerated and altered.
Expansion of receptive field is likely driven by dorsal horn neurons - why?
Dorsal horn neurons which show prolonged firing after repeated stimulation of C-fibers (Mendell, 1966) and expansion of receptive fields to incorporate the site of injury (McMahon and Wall, 1984).
Vast changes in the topographic organisation of the somatosensory and motor cortex
for example Karl et al., 2001
Ramachandran et al., 1992
Ramachandran found that in upper limb amputees, cortical regions representing the face had expanded into those that previously represented the amputated hand and that stimulation of the ipsilateral face region could induce phantom sensations
Flor and colleagues (1995)
Found that the degree of expansion correlated with the degree of pain experienced in PLP
Flor et al., 1997
Cortical reorganisation of the primary somatosensory cortex was observed in CBP patients whereby regions representing the back expanded into those that represent the lower limbs
CBP patients have demonstrated a reduction in
Grey matter density of the somatosensory cortex, PFC, thalamus and brainstem (Schmidt-Wilcke et al., 2006)(Apkarian et al., 2009).
Grey matter reductions were also found in patients with fibromyalgia
(Schmidt-Wilcke et al., 2007). These include the medial PFC, anterior cingulate cortex (ACC), insular cortex, amygdala and parahippocampal gyri.
CPM fibromyalgia
Staud and colleagues (2003) found that immersing one hand in a hot bath while the other is presented with noxious heat stimuli led to increased pain thresholds in female controls but not females with fibromyalgia
