Champaen

1
Itchy and Scratchy

• Champaen
• Ambre
• Rose
• Donna

2
The Problem

• Your roommate Laura complains constantly of an
  itch that began shortly after she moved into your
  dorm room.
• She explains that she has a lot of allergies, and
  that its probably just another allergic reaction
  to something in the room.
• Youre not very sympathetic. You dont think her
  rash looks that bad (Ive had worse), but it
  has caused her to lose sleep, and her scratching
  has irritated her skin further.

3
Questions

• What is the pathogenesis of itch?
• What are possible paracrine messages that mediate
  the sensation?
• What is the nervous pathway that carries the
  information for perception?
• Is there a possible therapy aimed at controlling
  her hyperactive immune system?

4
Relevance

• Sensory receptors
• Nociceptors
• Pain/Itch pathways
• Modulation of signal pathways
• Agonist/Antagonist
• Local Control
• Paracrine messages

5
Pathogenesis of Itch

• Itch (pruritus) is an unpleasant cutaneous
  sensation which provokes the desire to scratch.
• Itch is similar to pain in that they both have a
  protective function, and follow the slow pain
  nerve pathway.
• There is no itch center in the brain itch is a
  perception.
• Sometimes itch has no obvious cause and can be
  either local or spanning the whole body.

6
Paracrine Messages

• Histamine
• released from dermal mast cells
• Substance P
• a neurotransmitter released at pain receptors
  causes the release of histamine from dermal mast
  cells
• Interleukin II
• produced by T lymphocytes for an immune response

7
Nerve Pathway
8
Therapy Control Hyperactive Immune System

• Antihistamines!!
• E.g. Benedryl
• Antihistamines block histamine receptors by
  acting as an antagonist which relieves symptoms.
• Corticosteroids
• E.g. Hydrocortisone
• Corticosteroids inhibit mast cell degranulation,
  which is the release of histamine from the
  granules.

9
Analogy

• Concept Both itch and pain share a pathway
• A dogs bark action potential
• Many successive barks will stimulate the pain
  perception and action
• A few barks will stimulate the slow pain pathway
  for itch perception
• Owner Somatosensory Cortex
• Highly annoyed by barking pain
• Slightly annoyed by barking itch