The dose-effect functions for all treatments are summarized in Fig. 3, collapsing across delays; only AM3506 had a significant effect, and this was only at the highest dose. Responding in the side holes is not explicitly required during the delay period, but it appears to serve a rehearsal-like mediating function, enhancing the accuracy of the non matching response . Rats show individual differences in whether their mediating behavior during the delay occurs in the matching or non matching hole. Logistic regression indicated that six of the rats in the present study were more likely to choose the correct hole if at least one response had occurred in the to-be-correct hole during the delay, while the other five rats were more likely to choose the correct hole if at least one response occurred in the other side hole during the delay; this analysis identified the B appropriate side hole for each rat. Neither AM3506 nor any of the other treatments had a significant effect on the rate of responding in the side holes or center hole during the delay , or the relative frequency of the four types of trials . However, AM3506 treatment [F=33.6, p<.0001] and trial type [F=12.96, p<.0001] had significant effects on accuracy ,indoor grow cannabis and paired comparisons revealed that the 3-mg/kg dose of AM3506 significantly decreased accuracy of the non matching response specifically in trials where at least one response occurred in the appropriate hole . To explore the mechanism of the AM3506 effect, we attempted to block it with the CB1 receptor antagonist, rimonabant; the PPAR-alpha antagonist, MK886; and the TRPV1 antagonist, capsazepine.The 3-mg/kg dose of AM3506 significantly impaired accuracy when it was given in combination with an injection of vehicle, MK886, or capsazepine. However, when AM3506 was combined with rimonabant, accuracy was significantly improved compared to when AM3506 was combined with vehicle.
Accuracy was not significantly affected by any of the antagonists when given alone .We tested several compounds that enhance endogenous levels of endocannabinoids and found that one compound, AM3506, produced THC-like impairments in a rodent model of working memory. The level of accuracy in the memory task after treatment with a 3-mg/kg dose of AM3506 in this study was comparable to the levels we observed in earlier studies after treatment with a 3-mg/kg dose of THC . Further testing with receptor-specific antagonists indicated that these impairments were mediated by cannabinoid CB1 receptors, but not by PPAR-alpha or TRPV1, which are known to be affected by anandamide and other fatty acid amides. These findings indicate that the impairments induced by AM3506 were due to the activation of CB1 receptors by anandamide, possibly in combination with slightly increased levels of 2-AG.A feature of the non matching-to-position procedure used here is that it allows automated recording of the rehearsal-like mediating behavior that occurs during the delay period . Like THC in earlier studies with this procedure, AM3506 did not change the rate or distribution of behavior during the delay period, but it seemed to make the mediating response less effective, impairing accuracy even when the most propitious behavior occurred during the delay. That is, AM3506 had significant effects on accuracy specifically in the trials in which the appropriate mediating response did occur. In this respect, THC and AM3506 clearly differ from scopolamine, which disrupts performance of the mediating response . FAAH and MGL are members of the serine hydrolase family, which includes over 200 members, many of which are not well characterized . AM3506 is a sulfonylfluoride inhibitor and might show substantial differences in cross-reactivity with serine hydrolases compared to the more typical carbamate/urea inhibitors of FAAH like URB597 and PF-04457845.
AM3506 mainly affects FAAH and to a lesser extent MGL and did not have Boff target effects when tested against a large number of serine hydrolases using activity-based proteomic methods . However, the differences in the effects of AM3506 and the other test compounds on memory might reflect inhibition of other serine hydrolases in addition to FAAH. Alternatively, in vivo AM3506 might irreversibly deactivate a significantly larger FAAH population compared to the other inhibitors. Squirrel monkeys are sensitive to the reinforcing effects of CB1 agonists and will intravenously self-administer solutions of THC , anandamide , or 2-AG . The FAAH and MGL inhibitors tested in the present study have all been assessed for reinforcing effects in squirrel monkeys , and it is interesting to note that there is only a partial correspondence between their effect in the memory and reinforcement models. That is, URB597 was not self-administered and did not impair memory; AM3506 was self-administered and did impair memory; but the other inhibitors were all self-administered at moderate to high levels and did not affect memory.Although it is not clear how doses compare across species, the lowest doses of AM3506, URB694, and ARN14633 that maintained significant rates of self-administration in squirrel monkeys were the same across drugs , and these were three times more potent than PF-04457845; thus, there was no indication that AM3506 was more potent than the other inhibitors. The doses selected for the present study were intended to be high enough to produce near-maximal inhibition of FAAH while maintaining selectivity for FAAH versus MGL. However, there has been no study in which the selectivity of all or even most of these drugs have been measured under the same conditions in any species, and it is most parsimonious at this point to assume that they all have the potential to inhibit both FAAH and MGL to some extent. For example, Seillier et al. found that doses of JZL184 ranging from 5 to 30 mg/kg increased 2-AG levels three- to fivefold in rat hippocampus, but doses of 15 or 30 mg/kg also increased anandamide levels more than twofold. Godlewski et al. found that a 1- mg/kg i.p. dose of AM3506 fully inhibited FAAH and increased anandamide in rat brain, but did not increase 2-AG; higher doses were not tested in rats, but a 3-mg/kg dose produced a moderate inhibition of MGL in mice.
One reason that selectivity is important is that treatment with a dual inhibitor of FAAH and MGL or with a selective FAAH inhibitor combined with a selective MGL inhibitor can produce THC-like effects in drug discrimination and short-term memory tests . Interestingly, Hruba et al. found that combined treatment with the FAAH inhibitor PF3845 plus the MGL inhibitor JZL184 produced THC-like discriminative effects in mice, but combined treatment with the FAAH inhibitor URB597 plus JZL184 did not. They suggest that this lack of interaction between URB597 and JZL184 might be due to URB597 decreasing levels of 2-AG. Goonawardena et al. used a delayed non matching to-position procedure that was similar to the one used in the present study, but used retractable levers instead of lighted nosepoke holes to present the samples and record the responses. Their behavioral procedure is sensitive to impairment by THC, and these impairments correlate with suppressed hippo campal cell firing around the time of the sample response, presumably representing disrupted encoding of the sample . Goonawardena et al. found that treatment with methanandamide or URB597 produced THC-like effects on memory and hippo campal cell firing. It is unclear why URB597 produced impairments in their procedure but not ours, but one difference is the use of Long–Evans rats in their study versus Sprague–Dawley rats in ours. They did not test other FAAH inhibitors, but they did find that the anandamide transport inhibitor AM404 only decreased accuracy of non matching at the longest delay and did not affect hippocampal firing. As noted above, FAAH inhibition and FAAH deletion have produced learning enhancements rather than impairments in some previous studies. It appears that aversively motivated learning is most sensitive to enhancement by FAAH manipulations,vertical grow system possibly due to effects of FAAH inhibition on anxiety or coping behavior . FAAH inhibition also increases endogenous levels of PPARalpha ligands that might play a role in these memory enhancements . With respect to the present study, it is worth noting that our delayed non matching-to-position procedure is not sensitive to enhancement effects. In past experiments, we did not observe memory enhancement with nicotine, caffeine, galantamine, or rimonabant, all of which have produced cognitive-enhancing effects in other procedures. We also did not observe either enhancement or impairment of memory in an earlier study when—in the same non matching task used in the present study—URB597 was tested in Long–Evans rats at doses that enhance passive avoidance learning ; the accuracy curves obtained at these lower doses closely resemble the curves for higher doses of URB597 shown in Fig. 2 of the present study. The insensitivity of our delayed non matching-to-position procedure to enhancement might be due to the fact that the rats are highly trained prior to drug testing, producing a ceiling effect. Consistent with this possibility, rimonabant produced a more robust enhancement in a delayed non matching procedure when extra-long delays were included during the test than when the tests used the same delay values as the baseline training schedule . In conclusion, we find that FAAH inhibitors vary in whether they produce THC-like amnestic effects in a rodent model of working memory. In other experiments, we have found that these same FAAH inhibitors vary in whether they produce THC-like reinforcing effects in the squirrel monkey model of cannabinoid self-administration. Puzzlingly, the profiles exhibited by these drugs in the memory-impairment and abuse-potential models do not fully match. These findings strongly suggest that FAAH inhibitors need to be evaluated on a case-by-case basis for different kinds of adverse effects.A core feature across autism spectrum disorder is impairment in social functioning.People with ASD restrict themselves to repetitive behaviors and show deficits in social reciprocity and communication.The underlying basis for social impairment in ASD is unknown, and no pharmacological treatment is available.
One theory—the social motivation theory—posits that the psychopathology of ASD is rooted in a decreased desire to be social.The neural substrates of normal social behavior are only now beginning to emerge.Perhaps the best account so far has come from the study of oxytocin. This neuropeptide is crucial in many aspects of social behavior, including affiliation and reward.Investigations are ongoing into the contributions of the oxytocin system to ASD and oxytocin-based therapies for ASD.Recent reports suggest that early treatment with oxytocin may be useful for improving social behavior in animal models as well as in human patients.Nevertheless, identifying the keyneural systems underlying social behavior and understanding how they interact with oxytocin remain an enormous challenge.5 One candidate is the endogenous cannabinoid system, a modulatory neurotransmitter system that may play an important role in social behavior. This signaling complex consists of lipid-derived messengers called ‘‘endocannabinoids,’’ whose actions in the brain are mainly, although not exclusively, mediated through CB1 cannabinoid receptors. A series of enzymes catalyze endocannabinoid synthesis and degradation to control the activity of these substances.Fatty acid amide hydrolase catalyzes the intracellular hydrolysis of the endocannabinoid anandamide. In an effort aimed at probing anandamide function in social behavior, we found that genetic removal of FAAH in mice increases direct social interactions,while Trezza et al. noted that pharmacological FAAH inhibition promotes social play in juvenile rats.More recently, we identified a signaling mechanism by which oxytocin drives anandamide-mediated signaling at CB1 receptors to control the rewarding properties of social interactions.Social contact among male mice stimulates the mobilization of anandamide in the nucleus accumbens , a key brain region for reward signaling, in an oxytocin-dependent manner. Conversely, in isolated male mice, specifically stimulating oxytocin neurons in the paraventricular nucleus of the hypothalamus drives anandamide mobilization in the NAc. Consequent activation of CB1 receptors is necessary and sufficient to regulate social reward. Anandamide enhancement offsets the effects of oxytocin receptor blockade on social reward and NAc activity.In addition, human studies also support the notion that the endocannabinoid system affects social behavior. Acutely intoxicated marijuana users enjoy interacting more and feel more connected and empathetic.Chakrabarti and Baron-Cohen reported that a polymorphism in the CB1 cannabinoid receptor gene modulates social gaze.Based on those studies, we hypothesized that enhancement of anandamide-mediated signaling at CB1 receptors might offer a therapeutic strategy for ASD-related social impairment.