3. Umbruch 4.4..2005 - Online Pot

194 L.A. Parker et al.
specific to nausea-induced gaping. In fact, ondansetron suppressed conditioned
gaping elicited by exposure to a lithium-paired saccharin solution even during
a drinking test, but it did not modify the amount consumed. Therefore, the
effects of ondansetron on conditioned gaping, but not conditioned taste avoidance,
cannot simply be attributed to differences in the delivery of the taste when
using the two measures (e.g. [98]); conditioned gaping is suppressed by
ondansetron whether the taste is presented by bottle or by intraoral infusion.
Subsequently, Limebeer and Parker [89] demonstrated a very similar pattern
following pretreatment with the 5-HT 1A autoreceptor antagonist, 8-hydroxy-2di-N-propylaminotetraline
(8-OH-DPAT), that also reduces serotonin availability
and serves as an anti-emetic agent in animal models. Most recently,
Limebeer et al. [99] report that lesions of the dorsal and median raphe that
reduce forebrain serotonin availability interfere with the establishment and the
expression of conditioned gaping consistent with reports that reduced serotonin
availability interferes with nausea [99]. Since rats are incapable of vomiting, we
have argued that the gape represents an incipient vomiting response. As is evident
in Figure 1, the orofacial characteristics of the rat gape are very similar to
those of the shrew just before it vomits [87].
Using the conditioned gaping measure of nausea in rats, we have demonstrated
that a low dose (0.5 mg/kg, ip) of ∆ 9 -THC interferes with the establishment
and the expression of cyclophosphamide-induced conditioned gaping
[36]. Most recently, we found that CBD (5 mg/kg, ip), as well as its synthetic
dimethylheptyl homolog (5 mg/kg, ip), suppressed the establishment and the
expression of lithium-induced conditioned gaping, but not taste avoidance
[38]. Finally, the potent agonist HU-210 (0.001–0.01 mg/kg) also suppressed
lithium-induced conditioned gaping [37, 39] and this suppression was reversed
by the CB 1 antagonist SR-141716, suggesting that the effect of HU-210 was
mediated by its action at CB 1 receptors [39]. Although SR-141716 did not pro-
Figure 1. The rat gape is topographically similar to the shrew gape just before it vomits.