Itch

Question 1

Which histamine receptors are expressed on histaminergic neurons?

Answer 1

HR1 and HR4

Question 2

Where are the cell bodies of afferent nerves involved in itch located?

Answer 2

Dorsal root ganglia

Question 3

Where are H1 receptors mainly found?

Answer 3

Endothelial cells, smooth muscle as well as immune cells

Question 4

What role do H2 receptors have?

Answer 4

Involved in gastric acid production

Question 5

Where are H3 receptors mainly found?

Answer 5

In the central and peripheral nervous system

Question 6

Where are H4 receptors mainly found?

Answer 6

On haematopoetic cells (monocytes, dendritic cells, Langerhans cells, T-lymphocytes, eosinophils, basophils, mast cells) and on sensory neurons

Question 7

Repeated capsacin ‘numbs’ peripheral nerves by depleting stores of what?

Answer 7

Substance P

Question 8

Which nerve fibres transmit touch, pressure and vibration?

Answer 8

Alpha fibres

Question 9

Which nerve fibres transmit pain?

Answer 9

A delta fibres

Question 10

Which nerve fibres transmit itch?

Answer 10

Peptidergic and non-peptidergic C fibres

Question 11

Which non-peptidergic neurons are the most important in allergic skin disease?

Answer 11

NP3
Transmit inflammatory, chronic itch
Stimulated by IL-31, serotonin, histamine, LTC4, IL-4 and IL-13

Question 12

Which channels are important in transmission of itch?

Answer 12

TRPA1
TRPV1
Voltage gated Na channels

Question 13

Sensory neurons express three types of histamine receptors, which activate and promote pruritus and which inhibit it?

Answer 13

H1 and H4 activate

H3 inhibits

Question 14

Mast cells are more numerous in lesional atopic than normal canine skin, do they contain more histamine?

Answer 14

Yes, and histamine release is higher in atopic dogs

Question 15

Conventional antihistamines are inverse agonists of which receptor?

Answer 15

H1 receptor

Question 16

Selective H4 receptor antagonists in people; can they be useful for pruritus in AD?

Answer 16

No reduction in pruritus, did reduce clinical lesion scores

Question 17

Hydroxyzine in dogs should be effective at preventing pruritus at what dose?

Answer 17

2 mg/kg twice daily

Question 18

Is oral clemastine bioavailable following oral administration in dogs?

Answer 18

No

Question 19

Can H4R antihistamines prevent signs of cAD when used proactively?

Answer 19

No evidence of this

Question 20

IL-31 directly stimulates TRPV1 and ______ sensory neurons

Answer 20

TRPA1

Question 21

IL-31 induced pruritus is partly dependent on which other mediator?

Answer 21

Leukotriene B4 (secreted from keratinocytes due to IL-31 stimulation)

Question 22

IL-31 direct stimulation of sensory neurons can lead to release of _____ which stimulates keratinocytes to release inflammatory mediators

Answer 22

BNP

Question 23

IL-31 can induce pruritus in dogs in what time frame?

Answer 23

Within 30 mins and a delayed response after a few hours (induction of secondary pruritogens)