Characterizing the role of the endocannabinoid system’s catabolic enzymes FAAH and MAGL in the development of functional sensorimotor activities in zebrafish
Creators: Khara, Lakhan S
Publisher: name: University of Alberta Library
Year: 2022

<p>The endocannabinoid system (eCS) plays a critical role in a variety of homeostatic and developmental processes. Generally, the eCS relies on the naturally produced compounds known as endocannabinoids (eCBs), which are lipophilic signaling molecules that interact with cannabinoid receptors to regulate biological activities of the central and peripheral systems. In terms of its developmental roles, the eCS is becoming more well known for its involvement in neural development and motor function; however, the role of eCB signaling in functional sensorimotor development remains to be examined. One way to study the roles of eCB signaling is to perturb the system by targeting the enzymes responsible for degrading the eCBs. Thus, the two eCB catabolic enzymes known as fatty acid amide hydrolase (FAAH) and monoacylglycerol lipase (MAGL) are of interest in many studies that investigate the roles of eCB signaling. The two main eCBs are known as anandamide (AEA) and 2-arachidonoylglycerol (2-AG). FAAH is responsible for degrading AEA, while MAGL breaks down 2-AG. In this thesis, the catabolic enzymes FAAH and MAGL were inhibited either simultaneously, or individually, during the first ~24 hours of zebrafish embryogenesis, and the properties of contractile events and sensorimotor escape responses were studied in animals ranging in age from 1 day post-fertilization (dpf) to 10 weeks. This perturbation of the eCS resulted in alterations to contractile activity, which was observed at 1 dpf. Inhibition of MAGL using JZL 184, and dual inhibition of FAAH and MAGL using JZL 195 decreased escape swimming activity at 2 dpf. Treatment with JZL 195 also produced alterations in the properties of the 2 dpf short latency C-start escape response. Furthermore, animals treated with JZL 195 exhibited deficits in escape responses elicited by auditory/vibrational (A/V) stimuli at 5 and 6 dpf. A/V response deficits were also present during the juvenile developmental stage (8–10-week-old fish), thus demonstrating a prolonged impact to sensorimotor activities. Overall, from performing different sensorimotor assessments, the results indicate that MAGL has a more significant role than FAAH does in zebrafish sensorimotor development. These findings demonstrate that eCS perturbation affects sensorimotor function and underscores the importance of eCB signaling in the development of motor and sensory processes. </p>

<p>Since eCBs are known to interact with a variety of different receptor systems, the involvement of canonical and non-canonical cannabinoid receptors was also studied in this thesis. In particular, the CB1R and CB2R cannabinoid receptors, along with transient receptor potential (TRP) channels, and the Sonic Hedgehog (SHH) signaling pathway were examined for their potential roles in eCS-related sensorimotor development. To investigate the potential involvement of these receptor systems, developing animals were co-treated with pharmacological inhibitors of the CB1R, CB2R, TRPA1/TRPV1/TRPM8 channels, and a Smoothened (SMO) agonist, alongside the eCS enzyme inhibitors during the first ~24 hours of development. Escape swimming was then assessed at 2 dpf. The CB1R antagonist AM 251 prevented locomotor deficits caused by eCS perturbation, while the CB2R antagonist AM 630 was not effective in restoring locomotor activity. Inhibition of TRPA1/TRPV1/TRPM8 using AMG 9090 rescued the locomotor reductions caused by JZL 195, but not the reductions caused by JZL 184. The SMO agonist purmorphamine attenuated the effects of JZL 184 and JZL 195 on swimming distance, but not mean swimming velocity. After observing the involvement of these receptor systems on the eCS-related deficits in 2 dpf escape swimming, their roles in mediating the alterations to A/V-induced escape responses at 6 dpf were also assessed. Here, none of the co-treatments produced a detectable recovery to the reductions in A/V responsiveness caused by JZL 195. Overall, these findings provide one of the first investigations examining the interactions between the eCS and its non-canonical receptor systems in vertebrate sensorimotor development.</p>

<p>Taken together, this work provides an overview which demonstrates that the activity of the eCS enzymes FAAH and MAGL are essential for different aspects of sensorimotor development in zebrafish, and provides insight towards the canonical and non-canonical cannabinoid receptor mechanisms that mediate eCS-related motor development.</p>