CBD:
In rats, CBD injected straight into the dorsal hippocampus (10-30 pmol) impaired consolidation of fear memory when given immediately or one hour after fear conditioning, but not 3 hours after conditioning. The immediate effect of CBD was fully blocked by CB1 and CB2 antagonists, partially blocked by 5-HT1A and A2A antagonists and unchanged by PPARg antagonists. After one hour, the effect was blocked only by PPARg antagonists. FAAH inhibition blocked fear consolidation when applied immediately, but not after one hour (Raymundi et al., 2019). The results suggest than CBD can impair fear memory consolidation up to one hour after conditioning at least partially via AEA, mediated in a time-dependent manner via CB1, CB2 and PPARg, and to some degree via 5-HT1A and A2A receptors. Similar results were obtained with intraperitoneal injection of 3 to 30 mg/kg CBD (Stern et al., 2017).
Similar to CBD, THC (0.3-10 mg/kg intraperitoneal) can also disrupt fear memory consolidation. Moreover, in sub-effective doses, the combination of CBD and THC (10 : 1) could attenuate the maintenance of fear memories suggesting this combination could be used to reduce anxiety without eliciting psychotropic effects (Stern et al., 2015).
In a similar experiment in rats the effect of oral CBD (50 mg/kg), THC (5 or 50 mg/kg) and background material (residual extract after isolation of THC and CBD, 21.5 or 43 mg/kg) on fear memory reconsolidation was tested either alone or in combination. CBD, administered immediately after contextual recall, significantly and persistently (at least 7 days) reduced fear memory reconsolidation. Interestingly, background material had the same effect. THC on the other hand only reduced fear memory consolidation in combination with either CBD or background material (Murkar et al., 2019), suggesting a significant entourage effect on anxiety.
In another stress experiment in rats, intraperitoneal administration of THC (1 mg/kg) was found to be anxiogenic while CBD (5 mg/kg) and CBDA (0.1 to 100 mg/kg) were found to be anxiolytic although they could not alter the anxiogenic response to THC (Rock et al., 2017). Especially the low effective dose of CBDA is surprising.
In streptozotocin-induced diabetic rats, intraperitoneal administration of 30 mg/kg CBD had both anti-depressant and anxiolytic effects. While the anti-depressant effects were blocked by CB1, CB2 and 5-HT1A antagonists, the anxiolytic effects were only blocked by CB1 and 5-HT1A antagonists. CBD also had a positive effect on glycemic control which was CB2-dependent (Chaves et al., 2021).
In another rat experiment intraperitoneal injection of CBD (10 mg/kg) enhanced fear extinction when the conditioning stimulus was strong (6 foot shocks) but impaired fear extinction when the stimulus was relatively weak (2 foot shocks)(Song et al., 2016), suggesting the effect of CBD may be dependent on stress level.
In spontaneously hypertensive rats a low dose of 1 mg/kg intraperitoneal CBD increased social interaction (Almeida et al., 2013), suggesting an anxiolytic effect. Interestingly, the same study found that CBD was not antipsychotic in doses up to 60 mg/kg.
In rats, direct injection of 100 nmol CBD into the ventromedial hypothalamus decreased panic attack-like behavior (induced by local injection of NMDA) and unconditioned fear-induced anti-nociception in a CB1-dependent way (Khan et al., 2020).
In rats, direct injection of 5 mg CBD into the substantia nigra suppressed aversive/anxious behavior induced by GABAergic blockade in the superior colliculus in a CB1-dependent manner (da Silva et al., 2015).
In mice, 10 mg/kg CBD intraperitoneal, administered 24h after fear conditioning, disrupted cued fear memory expression but not generalized anxiety-related behavior. The same dose of CBDA on the other hand disrupted generalized anxiety-related behavior but not cued fear memory expression. Neither CBD nor CBDA affected contextual fear expression (Assareh et al., 2020).
In chronically stressed mice, concomitant chronic administration of 30 mg/kg CBD was anxiolytic by reducing FAAH activity (increasing AEA) and in a CB1 and CB2-dependent manner. In addition, CBD prevented the stress-induced decrease in dendritic remodeling and neurogenesis (Fogaça et al., 2018).
In Xenopus oocytes CBD was found to enhance GABA-A receptor mediated currents up to 4-fold at sub-micromolar concentrations (Bakas et al., 2017) which may also help explain the anti-convulsant and anxiolytic actions of CBD.
In an insightful review it was concluded that CBD can reduce fear expression acutely and by disrupting fear memory consolidation directly via stimulation of the 5-HT1A receptor and indirectly via stimulating AEA action on CB1 and CB2 and possibly Adenosine action on A2A receptors (Lee et al., 2017). While CBD may also act on receptors like TRPV1, TRPA1, TRPV2, TRPM8, GPR55 or PPARg, these effects are not yet substantially supported by experimental data.
Another review concluded that the anxiolytic effects of CBD involve the endocannabinoid system and depend on the used dose (with intermediate doses being more effective than low or high doses), the age, sex, species and strain of laboratory animal and thus that more research is required into the anxiolytic potential of CBD (García-Gutiérrez et al., 2020).
Other:
GPR55 is downregulated in mice after chronic restraint stress and its activation reduced anxiety-like behaviors, involving also PLC-PKC and RhoA-ROCK pathways (Shi et al., 2017)
MAGL inhibitors showed potential therapeutic action to treat cancer, neurodegenerative diseases, ischemic injuries, inflammation, pain, anxiety, nausea and drug-withdrawal symptoms (Chen et al., 2012; Kohnz & Nomura, 2014; Mulvihill & Nomura, 2013)
DAGLα knockout mice showed a reduction of 80% of 2-AG, reduction of AEA and increased fear and anxiety responses (Jenniches et al., 2016).
In Spontaneously Hypertensive Rats CBD was found to have anxiolytic but not anti-psychotic effects (Almeida et al., 2013)
Literature:
Almeida, V., Levin, R., Peres, F.F., Niigaki, S.T., Calzavara, M.B., Zuardi, A.W., Hallak, J.E., Crippa, J.A., and Abílio, V.C. (2013). Cannabidiol exhibits anxiolytic but not antipsychotic property evaluated in the social interaction test. Prog. Neuropsychopharmacol. Biol. Psychiatry 41, 30–35.
Assareh, N., Gururajan, A., Zhou, C., Luo, J.L., Kevin, R.C., and Arnold, J.C. (2020). Cannabidiol disrupts conditioned fear expression and cannabidiolic acid reduces trauma-induced anxiety-related behaviour in mice. Behav Pharmacol.
Bakas, T., van Nieuwenhuijzen, P.S., Devenish, S.O., McGregor, I.S., Arnold, J.C., and Chebib, M. (2017). The direct actions of cannabidiol and 2-arachidonoyl glycerol at GABAA receptors. Pharmacol. Res. 119, 358–370.
Chaves, Y.C., Genaro, K., Crippa, J.A., da Cunha, J.M., and Zanoveli, J.M. (2021). Cannabidiol induces antidepressant and anxiolytic-like effects in experimental type-1 diabetic animals by multiple sites of action. Metab Brain Dis.
Fogaça, M.V., Campos, A.C., Coelho, L.D., Duman, R.S., and Guimarães, F.S. (2018). The anxiolytic effects of cannabidiol in chronically stressed mice are mediated by the endocannabinoid system: Role of neurogenesis and dendritic remodeling. Neuropharmacology 135, 22–33.
García-Gutiérrez, M.S., Navarrete, F., Gasparyan, A., Austrich-Olivares, A., Sala, F., and Manzanares, J. (2020). Cannabidiol: A Potential New Alternative for the Treatment of anxiety, depression, and Psychotic Disorders. Biomolecules 10, 1575.
Khan, A.U., Falconi-Sobrinho, L.L., Dos Anjos-Garcia, T., de Fátima Dos Santos Sampaio, M., de Souza Crippa, J.A., Menescal-de-Oliveira, L., and Coimbra, N.C. (2020). Cannabidiol-induced panicolytic-like effects and fear-induced antinociception impairment: the role of the CB1 receptor in the ventromedial hypothalamus. Psychopharmacology (Berl.).
Lee, J.L.C., Bertoglio, L.J., Guimarães, F.S., and Stevenson, C.W. (2017). Cannabidiol regulation of emotion and emotional memory processing: relevance for treating anxiety-related and substance abuse disorders. Br. J. Pharmacol.
Murkar, A., Kent, P., Cayer, C., James, J., Durst, T., and Merali, Z. (2019). Cannabidiol and the Remainder of the Plant Extract Modulate the Effects of Δ9-Tetrahydrocannabinol on Fear Memory Reconsolidation. Front Behav Neurosci 13, 174.
Raymundi, A.M., da Silva, T.R., Zampronio, A.R., Guimarães, F. da S., Bertoglio, L.J., and Stern, C.A.J. (2019). A time-dependent contribution of hippocampal CB1, CB2, and pparγ receptors to cannabidiol-induced disruption of fear memory consolidation. Br. J. Pharmacol.
Rock, E.M., Limebeer, C.L., Petrie, G.N., Williams, L.A., Mechoulam, R., and Parker, L.A. (2017). Effect of prior foot shock stress and Δ9-tetrahydrocannabinol, cannabidiolic acid, and cannabidiol on anxiety-like responding in the light-dark emergence test in rats. Psychopharmacology (Berl.) 234, 2207–2217.
da Silva, J.A., Biagioni, A.F., Almada, R.C., de Souza Crippa, J.A., Cecílio Hallak, J.E., Zuardi, A.W., and Coimbra, N.C. (2015). Dissociation between the panicolytic effect of cannabidiol microinjected into the substantia nigra, pars reticulata, and fear-induced antinociception elicited by bicuculline administration in deep layers of the superior colliculus: The role of CB1-cannabinoid receptor in the ventral mesencephalon. Eur. J. Pharmacol. 758, 153–163.
Song, C., Stevenson, C.W., Guimaraes, F.S., and Lee, J.L.C. (2016). Bidirectional Effects of Cannabidiol on Contextual Fear Memory Extinction. Front Pharmacol 7, 493.
Stern, C.A.J., Gazarini, L., Vanvossen, A.C., Zuardi, A.W., Galve-Roperh, I., Guimaraes, F.S., Takahashi, R.N., and Bertoglio, L.J. (2015). Δ(9)-Tetrahydrocannabinol alone and combined with cannabidiol mitigate fear memory through reconsolidation disruption. Eur Neuropsychopharmacol.
Stern, C.A.J., da Silva, T.R., Raymundi, A.M., de Souza, C.P., Hiroaki-Sato, V.A., Kato, L., Guimarães, F.S., Andreatini, R., Takahashi, R.N., and Bertoglio, L.J. (2017). Cannabidiol disrupts the consolidation of specific and generalized fear memories via dorsal hippocampus CB1 and CB2 receptors. Neuropharmacology.
Almeida, V., Levin, R., Peres, F.F., Niigaki, S.T., Calzavara, M.B., Zuardi, A.W., Hallak, J.E., Crippa, J.A., and Abílio, V.C. (2013). Cannabidiol exhibits anxiolytic but not antipsychotic property evaluated in the social interaction test. Prog. Neuropsychopharmacol. Biol. Psychiatry 41, 30–35.
Chen, R., Zhang, J., Wu, Y., Wang, D., Feng, G., Tang, Y.-P., … Chen, C. (2012). Monoacylglycerol lipase is a therapeutic target for Alzheimer’s disease. Cell Reports, 2(5), 1329-1339. https://doi.org/10.1016/j.celrep.2012.09.030
Jenniches, I., Ternes, S., Albayram, O., Otte, D. M., Bach, K., Bindila, L., … Zimmer, A. (2016). anxiety, Stress, and Fear Response in Mice With Reduced endocannabinoid Levels. Biological Psychiatry, 79(10), 858-868. https://doi.org/10.1016/j.biopsych.2015.03.033
Kohnz, R., & Nomura, D. K. (2014). Chemical Approaches to Therapeutically Target the Metabolism and Signaling of the endocannabinoid 2-AG and Eicosanoids. Chemical Society reviews, 43(19), 6859-6869. https://doi.org/10.1039/c4cs00047a
Mulvihill, M. M., & Nomura, D. K. (2013). Therapeutic Potential of Monoacylglycerol Lipase Inhibitors. Life sciences, 92(8-9), 492-497. https://doi.org/10.1016/j.lfs.2012.10.025
Shi, Q.-X., Yang, L.-K., Shi, W.-L., Wang, L., Zhou, S.-M., Guan, S.-Y., … Yang, Q. (2017). The novel cannabinoid receptor GPR55 mediates anxiolytic-like effects in the medial orbital cortex of mice with acute stress. Molecular Brain, 10(1), 38. https://doi.org/10.1186/s13041-017-0318-7