3. Umbruch 4.4..2005 - Online Pot

Cannabinoids: effects on vomiting and nausea in animal models 191
psychoactive ∆ 9 -THC and the nonpsychoactive CBD, effectively suppress
lithium- and cisplatin-acute vomiting in Suncus at appropriate doses.
Conclusion
Until recently, there were few experimental studies that evaluated the
anti-emetic properties of cannabinoids, probably for two reasons: (1) the
mechanism of action of cannabinoids has only recently been discovered and
(2) animal models of emesis relied on large animals, since rodents do not
vomit. The recent work using the shrew provides the opportunity to evaluate
the potential anti-emetic properties of drugs using smaller animal models.
Conditioned gaping in shrews: a model for ANV
ANV often develops over the course of repeated chemotherapy sessions [1, 2,
10, 11, 14, 20–22]. For instance, Nesse et al. [21] described the case of a
patient who had severe nausea and vomiting with each treatment. After his
third treatment, the patient became nauseated as soon as he walked into the
clinic building and noticed a “chemical smell”, that of isopropyl alcohol. He
experienced the same nausea when returning for routine follow-up visits, even
though he knew he would not receive treatment. The nausea gradually disappeared
over repeated follow-up visits. Nesse et al. [21] reported that about
44% of the patients being treated for lymphoma demonstrated such anticipatory
nausea. He suggested that “this syndrome of pretreatment nausea can be
understood as a classically conditioned response” ([21], p. 33); certain odors
have become aversive because of their association with chemotherapy-induced
illness. Indeed, Bernstein [72] has clearly demonstrated that the flavor of foods
also becomes aversive to patients receiving chemotherapy treatment.
Since it is best understood as a classically conditioned response [21, 73],
control over ANV could be exerted at the time of conditioning or at the time
of re-exposure to the conditioned stimulus (CS). If an anti-emetic drug is presented
at the time of conditioning, then a reduction in ANV would be the result
of an attenuated unconditioned response (UCR); that is, reduced nausea and
vomiting produced by the toxin at the time of conditioning thereby attenuating
the establishment of the conditioned response (CR). Indeed, when administered
during the chemotherapy session, the 5-HT 3 antagonist granisetron has
been reported to reduce the incidence of ANV in repeat cycle chemotherapy
treatment [2]. On the other hand, if a drug is delivered prior to re-exposure to
cues previously paired with the toxin-induced nausea and vomiting, then suppressed
ANV would be the result of attenuation of the expression of the CR
(conditioned nausea and/or vomiting); the 5-HT 3 antagonists are ineffective at
this stage [1, 10, 11, 14, 20].