Background:
Background of this work was the investigation of the endocannabinoid system (ECS) in the Fmr1 knock- out (KO) mouse. The Fmr1- KO mouse is a mouse model for fragile X syndrome (FXS). FXS is the leading monogenic cause for autism spectrum disorders (ASD) in humans. The Fmr1- KO mouse displays autistic behavior such as an impaired social interaction, repetitive behavior, cognitive deficits, increased anxiety and aggressiveness. Alterations of the ECS have been suggested to play a key role in the etiopathology of a variety of neuropsychiatric disorders. Until today, little has been described about the involvement of the ECS in ASD.
Interrogation:
1. Evaluating the manifestation of typical cannabinoid- induced effects in the Fmr1- KO mouse
2. Investigating the influenceability of autistic symptoms with THC treatment in the Fmr1- KO mouse
3. Analyzing the signaling cascade of the stimulated and unstimulated ECS in different brain regions of the Fmr1- KO mouse
Material and Methods:
Experiments were carried out on adult (12±1 weeks old) male Fmr1- KO and Fmr1- wild- type (WT) mice from the C57BL/6J- (B6)- background. N= 15 mice received THC (10mg/kg bodyweight) and N= 16 received WIN55,212 (3mg/kg bodyweight). 30min after injection, the body temperature was measured and the distance animals moved in an open field during 15min was recorded (locomotion). Then, animals were placed with their forepaws onto a horizontally fixed bar and the time remaining in this position (catalepsy) was measured. Finally animals were placed on a preheated plate and the temperature at which a pain stimulus occurred was determined (testing analgesia). All 4 experiments are called tetrad experiment. Afterwards changes in body temperature, locomotion, catalepsy and analgesia of the animals was evaluated. To explore long-term effects of THC after the tetrad, N= 15 animals were tested in a social interaction test with a female contact mouse, 10 and 20 days after THC treatment. Therefore, the tested mouse and the contact mouse were placed together into a cage and the time mice spent in social interaction (nose, body and anogential sniffing, allogrooming and body contact) was manually quantified during 6min of recorded testing time. Another group of N= 19 received a premedication of rimonabant (Cannabinoid- receptor 1 (CB1) antagonist, 3mg/kg bodyweight) 30min prior to THC treatment. Rimonabant prevents THC from binding to CB1 and therefore allows the assessment of the involvement of CB1 in mediating social behavior. Furthermore the suggestibility of context-dependent fear conditioning with THC treatment has been tested on N= 13 mice. Animals were placed into a conditioning chamber that delivered 6 short electric shocks with a 30sec pause to their paws (conditioning phase). Immediately afterwards mice received THC or placebo. 24h later contextdependent fear was evaluated by quantification of the time mice spent freezing in the conditioning-chamber (fear) without receiving foot shocks. Intraneuronal signaling of the ECS was analyzed with N= 29 animals using western blots. Quantities of phosphorylated (“activated”) protein kinases (ERK, AKT and S6) from different brain homogenates (hippocampus, striatum, cortex and cerebellum) were therefore measured after THC or placebo injection (30 minutes prior to sacrificing).
Results:
Cannabinoids induced hypothermia, hypolocomotion, analgesia and catalepsy in WTmice. These effects were significantly less detectable in Fmr1- KO mice. Effects of both cannabinoids, THC and WIN55,212, were comparable with a slightly greater but not significant efficiency of THC. THC treated WT- mice exhibited further reduced social interaction 10 days after treatment, an effect that was partially prevented by premedication with rimonabant. THC increased social interaction in Fmr1- KO mice comparable to the level of untreated WT- mice. THC had no effect on behavior of WT- mice in context-dependent fear conditioning. Fmr1- KO mice showed significant less contextdependent fear conditioning compared to WT- mice. THC facilitated the recognition of an anxiety-correlated context in Fmr1- KO mice comparable to untreated WT- mice. In western blots significant changes in the THC- induced signaling cascade were detectable and depending on genotype, brain-region and analyzed protein-kinase. In the hippocampus there were no changes in untreated Fmr1- KO mice compared to WT- mice. THC had no effect on activation of protein-kinases in WT- and Fmr1- KO mice. In the striatum there were no changes in untreated Fmr1- KO mice compared to WTmice. THC significantly increased activity of ERK, AKT and S6 in WT-mice and not in Fmr1- KO mice. In the cortex of untreated Fmr1- KO mice AKT showed a significantly increased activity compared to WT- mice. THC significantly increased AKT activity in WT- mice without having an effect on KO- mice. In the cerebellum there were no changes in untreated Fmr1- KO mice compared to WT- mice. THC significantly increased ERK- activity in Fmr1- KO mice but had no effect on protein kinase activity in WT- mice.
Conclusion:
We observed physiological cannabinoid effects in WT- mice after treatment with THC and WIN55,212. These effects are significantly attenuated in Fmr1- KO mice. This may be interpreted as a desensitization of the ECS in the Fmr1- KO mouse. At the same time it was demonstrated that THC has the potential to improve context dependent memory consolidation and to increase social interaction in the Fmr1- KO mouse. In particular the influence of THC on impaired social interaction should be a target of further investigations to find possible therapeutic options for this typical symptom of Autism. Underlying molecular mechanisms remain unclear and the analysis of THC stimulated intraneuronal signaling gave no clear indication of possible molecular alterations in the Fmr1- KO mouse.
| Identifer | oai:union.ndltd.org:DRESDEN/oai:qucosa:de:qucosa:30677 |
| Date | 11 July 2017 |
| Creators | Lenz, Frederike |
| Contributors | Winter, Christine, Steiner, Barbara, Technische Universität Dresden |
| Source Sets | Hochschulschriftenserver (HSSS) der SLUB Dresden |
| Language | English |
| Detected Language | English |
| Type | doc-type:doctoralThesis, info:eu-repo/semantics/doctoralThesis, doc-type:Text |
| Rights | info:eu-repo/semantics/openAccess |
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