Characterization of the Effects of Reuptake and Hydrolysis Inhibition on Interstitial Endocannabinoid Levels in the Brain: An in Vivo Microdialysis Study

Abstract

The present experiments employed in vivo microdialysis to characterize the effects of commonly used endocannabinoid clearance inhibitors on basal and depolarization-induced alterations in interstitial endocannabinoid levels in the nucleus accumbens of rat brain. Compounds targeting the putative endocannabinoid transporter and hydrolytic enzymes (FAAH and MAGL) were compared. The transporter inhibitor AM404 modestly enhanced depolarization-induced increases in 2-arachidonoyl glycerol (2-AG) levels but did not alter levels of N-arachidonoyl-ethanolamide (anandamide, AEA). The transport inhibitor UCM707 did not alter dialysate levels of either endocannabinoid. The FAAH inhibitors URB597 and PF-3845 robustly increased AEA levels during depolarization without altering 2-AG levels. The MAGL inhibitor URB602 significantly enhanced depolarization-induced increases in 2-AG, but did not alter AEA levels. In contrast, the MAGL inhibitor JZL184 did not alter 2-AG or AEA levels under any condition tested. Finally, the dual FAAH/MAGL inhibitor JZL195 significantly enhanced depolarization-induced increases in both AEA and 2-AG levels. In contrast to the present observations in rats, prior work in mice has demonstrated a robust JZL184-induced enhancement of depolarization-induced increases in dialysate 2-AG. Thus, to further investigate species differences, additional tests with JZL184, PF-3845, and JZL195 were performed in mice. Consistent with prior reports, JZL184 significantly enhanced depolarization-induced increases in 2-AG without altering AEA levels. PF-3845 and JZL195 produced profiles in mouse dialysates comparable to those observed in rats. These findings confirm that interstitial endocannabinoid levels in the brain can be selectively manipulated by endocannabinoid clearance inhibitors. While PF-3845 and JZL195 produce similar effects in both rats and mice, substantial species differences in JZL184 efficacy are evident, which is consistent with previous studies.

2-AG promotes the expression of conditioned fear via cannabinoid receptor type 1 on GABAergic neurons

“…Currently, we do not know whether this discrepancy relates to different effects of the two drugs on locomotor activity or to subtle differences in blocking the uptake of AEA vs. 2-AG. In fact, AM404 seems to inhibit the uptake of 2-AG as well (Beltramo and Piomelli 2000;Bisogno et al 2001;Wiskerke et al 2012) by yet unknown mechanisms (Fowler 2012). Nevertheless, AM404 can also inhibit FAAH activity (Glaser et al 2003) which would have induced a higher increase in AEA levels than in 2-AG's.…”

Full Fatty Acid Amide Hydrolase Inhibition Combined with Partial Monoacylglycerol Lipase Inhibition: Augmented and Sustained Antinociceptive Effects with Reduced Cannabimimetic Side Effects in Mice

“…On the other hand, the use of whole brain extracts may have obfuscated the detection of regional differences in AA, as well as endocannabinoids in regions associated with pain (e.g., cingulate cortex, periaqueductal gray, rostral ventral medulla, spinal cord, dorsal root ganglia). Moreover, measurement of interstitial levels of AEA and 2-AG in relevant regions provides deeper insight regarding the relationship between inhibiting FAAH and MAGL and elevated endocannabinoid levels that are likely to play a role in cannabinoid receptor signaling than levels determined from whole brain lipid extracts or even from discrete regions (Wiskerke et al, 2012). Thus, combined blockade of FAAH and MAGL produces multiple neurochemical alterations that may account for increased antiallodynic effects compared with cannabimimetic effects (e.g., catalepsy, hypothermia, hypomotility, and THC substitution).…”

Fatty acid amide hydrolase inhibitors produce rapid anti-anxiety responses through amygdala long-term depression in male rodents

“…56 Our findings of astroglial CB 1 R 24 indicate that the interstitial space contains eCB that can directly stimulate astroglial CB 1 R. This idea is supported by in vivo microdialysis studies showing consistent baseline levels of interstitial AEA in various brain regions. [57][58][59] A systemic injection of the FAAH inhibitor URB597 or PF3845 significantly increased interstitial AEA but not 2-AG levels, [57][58][59] and mutant mice without the FAAH gene showed a 2-fold increase of interstitial AEA levels. 58 These data support the notion that amygdala interstitial AEA forms a basal AEA stream (similar to hippocampal interstitial 2-AG stream 25 ) with a constant supply and a continuous clearance by FAAH.…”