PAIN TECHNIQUES

1. -Indirect

1. +Direct

   Annotations:

   • Direct measure of pain- records neural activity

1. +Direct

1. -Indirect

1. implanted electrode

   Annotations:

   • stimulates specific brain regions/ release of neurotransmitters
2. PAG only
3. PAG + heating

   Annotations:

   • shows whether PAG modulates C-fibre/ A-fibre evoked responses slow heating- activates C-fibres fast heating- activates Ad fibres
4. PAG + heating + cfos

   Annotations:

   • c-fos detection as a functional anatomical method point to dynamic changes in acute and chronic pain
5. chemical vs electrical stimul

   Annotations:

   • Waters and Lumb, 1997- stimulation by electrical or chemical means, at the same site of PAG>> led to non-selective and selective effects respectively 
   1. selective
   2. non-selective

1. LIMITATIONS

   Annotations:

   •       Remember, in sensory neurones action potentials initiate adjacent to sensory terminals..so changes determining spike initiation need to occur in this region.       However it is currently impossible to record intracellularly directly from the peripheral terminals of sensory neurones (too small)- even pretty hard to live image. ·         Thus, researchers study the sensory neurone cell-bodies [C1] as an experimental surrogate (very easy, very big).       It must always be considered how good a surrogate the cell body is for the terminal          For example we don’t even know the resting potential of the terminal (but we do Vrest of the cell body (~-55 mV - are they similar??)         
2. recording activity of injured nerves
   1. ectopic activity- indicates pain

      Annotations:

      • trains of ongoing (spontaneous) electrical nerve impulses, or impulses generated upon stimulation, for which the discharge originates at any location other than the normal location. The normal location for sensory impulse generation is the sensory ending of afferent neurons in the skin, viscera and other organs.
3. recording currents
   1. hyperexitability/ inward currents= pain
4. intracellular recordings
   1. impossible to record from peripheral terminals of sensory neurones

      Annotations:

      •   Remember, in sensory neurones action potentials initiate adjacent to sensory terminals..so changes determining spike initiation need to occur in this region.       However it is currently impossible to record intracellularly directly from the peripheral terminals of sensory neurones (too small)- even pretty hard to live image. ·         Thus, researchers study the sensory neurone cell-bodies [C1] as an experimental surrogate (very easy, very big).         It must always be considered how good a surrogate the cell  body is for the terminal For example we don’t even know the resting potential of the terminal (but we do Vrest of the cell body (~-55 mV - are they similar??)                 
      1. sensory neurone cell-bodies (DRG)
         1. is it a good measure??

Annotations:

•    Properties of sensory neurone cell bodies will depend on how the cells have been treated-   

1. • In vivo single cell recordings

   Annotations:

   • difficult to do – under anaesthesia[C1] , often a bit cool- 30C[C2]   [C1]What is the anaesthetic doing?  [C2]Not physiological temp   
2. • In vitro – intact ganglion

   Annotations:

   • tricky technique, published work often at room temp[C1]   [C1]Not physiological temp   
3. • In vitro dissociated

   Annotations:

   • various temps, evidence that dissociation increases excitability
4. various temperatures changes the excitability of neurons

1. Pain rating scales
   1. Numerical rating scales (NRS)

      Annotations:

      • discontinuous scale e.g. 1-10
      1. BEST

         Annotations:

         •  NRS and VRS are easier to complete by patients and have been shown to have less missing in the questionnaires because they are easier to understand   
   2. Visual analogue scales (VAS)

      Annotations:

      • continuous (a bar ------------------ in which you mark)
   3. McGill Pain Questionnaire (MPQ)

      Annotations:

      •    uses verbal descriptions, multidimensional, but it long and tiresome to complete   
   4. Verbal rating scales (VRS)

      Annotations:

      •   multi-dimensions- picking a word (qualitative, but may be quantified in some cases)   
   5. Brief Pain Inventory

      Annotations:

      • A combination of scales, picture and descriptions. Contains: Pain rating (NRS), % pain relief, what the pain interferes with (general activity, walking etc), location of pain >> commonly used in clinics
   6. LIMITATIONS
      1. Large inherent variability

         Annotations:

         • therefore need a large study size to show differences (a 30% change [C1] is considered meaningful)   [C1]Why? Because the change have to be significant for the patient to feel that there is a difference. Even 50% pain score still have pain.       
      2. VAS most powerful

         Annotations:

         • however patients prefer numerical rating
      3. uni-directional

         Annotations:

         • Pain can be on different dimensions e.g. unpleasantness some loss of compliance Therefore some scale testing would lose the multi-dimensional element of pain

1. quantitative sensory testing (QST)

   Annotations:

   • evoked responses to defined stimuli, may provide insights into mechanisms, less variation and so may be able to get results from smaller studies 
   1. cotton buds
   2. von frey hairs
   3. thermal testing
2. Measuring pain
3. Neural activity
   1. Peripheral nerve recordings
   2. fMRI
   3. PET
   4. MEG
   5. EEG

1. Capsaicin
   1. TRPV1 agonist
2. UV burn
   1. TRPV1 anta
3. Acid to oesophagus

   Annotations:

   • visceral sensitisation- heartburn
4. Electrical cutaneous stimulation
5. inducing pain
6. LIMITATIONS
   1. Mild pain

      Annotations:

      • not distressing
   2. Ethics

      Annotations:

      • not ethical to increase pain
   3. models conditions?

      Annotations:

      • Evoked pain is not the same as spontaneous pain- may not be useful for all types of pain Experimental studies in human volunteers are necessarily restricted to use non-injurious conditioning inputs, and therefore are limited to studying only the activity-dependent components of pain hypersensitivity elicited by sensory inputs, and not those transcription-dependent and structural changes that manifest after inflammation or nerve injury, which may have different mechanisms, time courses and presentations 
7. conditioned pain modulation (CPM)

   Attachments:

   • Descending control of pain

Attachments:

• Approaches to treating Pain

1. Behavioural testing
   1. von Frey hairs
   2. Hot plate/ tail flick
   3. Hargreave’s algesymeter
   4. acetone/cooled metal/ice
   5. Weight bearing
   6. Spontaneous foot lifting
   7. Withdrawal
   8. LIMITATIONS
      1. Common pitfalls
         1. Relevance

            Annotations:

            •    ·         How relevant is the behaviours that has been measured in the animals to the human symptom or disease?   
         2. Controls
         3. Experimental design unbiased?
         4. Drug doses

            Annotations:

            •    ·         Are the doses of the drug relevant to clinical doses? How does the dose used compared to the occupancy of the receptors in vivo?    What is the specificity of the drug used in the experimental at the doses administrated  
      2. Experimental design
         1. Experimental bias
         2. Species, strain and genetic modifications

            Annotations:

            • Choosing the right species and strain can have a great impact on result, so they have to be chosen carefully >> different strains may respond differently to behavioural testing >> This might lead to over-interpretation of results in genetically modified animals if they are not matched to the same strains in the controls
         3. Non-specific effects

            Annotations:

            •    ·         The use of drugs/ genetic modification could affect the sensory/ motor functioning of an animals and therefore it’s important that extra control tests are done to ensure that the drugs don’t affect other systems that might affect the results of the experiment (as behavioural tests are used they might perform better or worse because of the non-specific effect)   
            •    ·         Combining behavioural and pharmacological methods- when using drugs in a behavioural experiment the results are usually bell-shaped because when the dose of the drug is increased too much, the non-specific effects would counteract the effects of the drug, and therefore extra tests should be carried out to test whether the effect is due to targets of the drugs or the non-specific effects   
      3. Lack of feedback
      4. Validity
         1. Face

            Annotations:

            •    ·         Reflect the symptoms in man (face validity)   
         2. Construct

            Annotations:

            •    ·         Replicate the underlying biology (construct validity)   
         3. Predictive

            Annotations:

            •    ·         Predict treatments which will be effective in the human condition (predictive validity)   
         4. Translational

            Annotations:

            •    ·         How readily the data obtained from the animal model can be translated to a benefit in the clinic (translational validity)   
      5. confounding- motor behaviour

         Annotations:

         • Since pain assessment in experimental animal studies is commonly based on the expression of motor behavior (such as limb withdrawal or guarding), it is of importance to exclude potential confounding effects induced by a change in motor behavior when assessing antinociceptive actions of spinally administered noradrenergic compounds in animals.
      6. CONFOUNDING-NA agonists- motor

         Annotations:

         • Noradrenergic functions not directly related to pain may also provide confounding factors in the assessment of noradrenergic pain regulation. Since assessment of pain, particularly in animal studies, is commonly based on expression of pain-related motor behavior, a norepinephrine-induced change in the control of motor output may change pain-related behavioral response in a way that does not reflect the perception of pain (Fung et al., 1991 and Kauppila et al., 1998).
2. Transgenic/ genetically modified

   Attachments:

   • TECHNIQUES
   1. Examples
      1. Galanin overexpression in DRG
         1. >> neuropathic pain

            Annotations:

            • reduced pain threshold in transgenic mice
      2. Galanin-LacZ (blue)

         Annotations:

         • shows what areas of the genes are important for expression
      3. Galanin knockouts
         1. don't develop neuropathic/ inflammatory pain

Attachments:

• TECHNIQUES