Endocannabinoids render exploratory behaviour largely independent of the test aversiveness: role of glutamatergic transmission.
Genes, Brain and Behavior. 2009-10-01; 8(7): 685-698
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1. Genes Brain Behav. 2009 Oct;8(7):685-98. doi: 10.1111/j.1601-183X.2009.00512.x.
Epub 2009 May 28.
Endocannabinoids render exploratory behaviour largely independent of the test
aversiveness: role of glutamatergic transmission.
Jacob W(1), Yassouridis A, Marsicano G, Monory K, Lutz B, Wotjak CT.
(1)Max Planck Institute of Psychiatry, D-80804 Munich, Germany.
To investigate the impact of averseness, controllability and familiarity of a
test situation on the involvement of the endocannabinoid system in the regulation
of exploratory behaviour, we tested conventional and conditional cannabinoid
receptor type 1 (CB1)-deficient mice in behavioural paradigms with different
emotional load, which depended on the strength of illumination and the ability of
the animals to avoid the light stimulus. Complete CB1 null-mutant mice
(Total-CB1-KO) showed an anxiogenic-like phenotype under circumstances where they
were able to avoid the bright light such as the elevated plus-maze and the
light/dark avoidance task. Conditional mutant mice lacking CB1 expression
specifically in cortical glutamatergic neurons (Glu-CB1-KO), in contrast, failed
to show a similar phenotype under the same experimental conditions. However, both
mutant lines showed increased avoidance of open arm exploration during a second
exposure to the elevated plus-maze. If tested in situations where the fear
eliciting light could not be avoided, Total-CB1-KO mice showed increased
thigmotaxis in an open field, decreased social investigation and decreased novel
object exploration under aversive light conditions, but not under non-aversive
low light. This time, Glu-CB1-KO also showed decreased exploratory behaviour
towards objects and conspecific juveniles and increased thigmotaxis in the open
field. Taking into consideration that the behavioural performance of wild-type
mice was only marginally affected by changes in light intensities, these data
indicate that the endocannabinoid system renders exploratory behaviour largely
independent of the test averseness. This process differentially involves
endocannabinoid-controlled glutamatergic transmission, depending on the
controllability of the test situation.
PMID: 19563475 [Indexed for MEDLINE]