Experimental Study of Itch Stimuli in Animals

Intracisternal Injection of Opioids Induces Itch-Associated Response through .MU.-Opioid Receptors in Mice.

“…Given that the body weight was 25 g, 0.3 nmol/mouse of morphine corresponds to about 0.005 mg/kg, which was about 150 times less than the i.c. dose of morphine (0.7 mg/kg) reported to produce facial scratching in several animals including cats (13). In human subjects, epidural injection of morphine at doses of 2-5 mg (cor responding to 0.04-0.1 mg/kg if body weight was 50 kg) was claimed to produce itching (1,21,22).…”

“…As regard to animal experiments, Koenigstein (13) mentioned that when injected into the cisterna magna, morphine produced scratching, a possible motor response to itch, in several species including the cat, dog, rabbit and guinea pig. Microinjection of an opioid agonist into the medullary dorsal horn produces facial scratching in monkeys (14) and rats (15).…”

Anaesthesia for daycase gynaecological laparoscopy: a survey of clinical practice in the United Kingdom

“…This concern has led to the removal of these preservatives from such solutions, but this has not influenced the experience of pruritus [21,26]. Opioids, which are clinically important pruritogens, probably act firstly by releasing histamine and secondly by stimulating a central encephalinergic mechanism [27,28]. Animal studies suggest the presence of a pruritus centre in the lower medulla involving the trigeminal nucleus.…”

Treatment of the pruritus of cholestasis: From unbearable lightness to substance

“…16,17 Morphine, which elicits its effect by binding to opioid receptors, is one of the most frequently used drugs in the management of acute pain. Clinical observations in human beings, behavioral studies in animals, and data from basic neurophysiology experiments suggest that activation of the endogenous opioid system also results in pruritus and scratching, as follows: (1) the central administration (e.g., intrathecally) of morphine is associated with pruritus in human beings, which can be effectively treated with opiate antagonists, 18,19,20 -22 (2) the central administration of morphine and the opiate agonist ligand D-ala2-MePhe4,gly-ol5-enkephalin is associated with scratching behavior in laboratory animals, [23][24][25][26] and (3) the stimulation of some neurons in the superficial dorsal horn of rats by morphine facilitates neuronal response to peripheral stimuli by histamine, a pruritogenic substance in human beings. 27 In cholestasis, there is evidence to suggest that central opioidergic neurotransmission is increased.…”