Planarians have mammalian-like neurotransmitter systems
and have been established as a novel in
vivo model for neuropharmacology. In previous research, planarians that
have been exposed to the cannabinoid receptor (CB-R) agonist WIN 55,212-2 for 1
h displayed abstinence-induced withdrawal when tested in drug-free, but not in
drug-containing, water. The goals of the present study were to extend previous
work and to further establish a cannabinoid behavioral model with planarians.
The results showed 1) four different CB-R antagonists (AM251, AM281, SLV319 and
SR144528) dose-relatedly blocked development of physical dependence induced by
two different CB-R agonists (WIN 55,212-2 and JWH251); 2) none of the same four antagonists (AM251, AM281, SLV319 or SR144528)
precipitated withdrawal; 3) short wavelength (254
nm), but not long wavelength (366 nm), ultraviolet (UV) light attenuated
abstinence-induced withdrawal from WIN 55,212-2, while short wavelength UV
light induced moderate withdrawal behavior. The results confirm the use of a
planarian model as a simple yet robust way to study development of physical
dependence to cannabinoid agonists. The effect of UV irradiation adds to the
evidence that the results are receptor-related. The results also give rise to
the surprising suggestion, within the limitations of the methodology, that
development of cannabinoid physical dependence and antagonist-induced
precipitated withdrawal might be separable phenomena in planarians.