Cannabinoid effects on anxiety-related behaviours and hypothalamic neurotransmitters

Chronic treatment with cannabinoid agonists leads to tolerance. One possible mechanism for this is receptor internalization, but tolerance has also been reported with compounds that only cause internalization to a low degree. Furthermore, cannabinoid antagonist administration precipitates a characteristic withdrawal syndrome in tolerant subjects, accompanied by neuronal activation and enhanced release of corticotropin-releasing hormone (CRH) in the central amygdala. The underlying molecular mechanisms are unknown. We examined the role of cannabinoid tolerance and withdrawal for the expression of the cannabinoid 1 (CB1) receptor and of CRH in rats. Tolerance was first established functionally. An acute dose (100 mg/kg) of the CB1 agonist HU-210 suppressed locomotor activity, and had an anxiogenic-like effect on the elevated plus-maze. Both effects were absent following daily treatment with the same agonist or a lower (40 mg/kg) dose for 14 days. Next, withdrawal was reliably precipitated by a single dose (3 mg/kg) of the CB1 antagonist SR141716A in rats treated subchronically with 14-day HU-210. Using in situ hybridization, a robust suppression of CB1 mRNA expression was found in the caudate-putamen, indicating a downregulation of CB1 expression levels as one mechanism for tolerance to the locomotor suppressant effects of HU-210. The CRH transcript was upregulated in the central amygdala in precipitated withdrawal compared to nonwithdrawn tolerant subjects, suggesting that increased gene expression contributes to the previously reported CRH release in withdrawal. Most importantly, this increase occurred from a suppressed level in tolerant subjects, and behavioral signs of withdrawal, presumably mediated by CRH, were seen at the CRH expression that had only returned to normal nontolerant levels. This suggests the possibility of an allostatic shift, as previously proposed on theoretical grounds. The expression of CRH-R1, CRH-R2a, NPY, and its Y1 receptor mRNA was analyzed in search of neural substrates for the allostatic shift observed, but did not seem to contribute to the dysregulated state.

Section: Discussionsupporting

confidence: 85%

Corticotropin-Releasing Hormone (CRH) mRNA Expression in Rat Central Amygdala in Cannabinoid Tolerance and Withdrawal: Evidence for an Allostatic Shift?

Caberlotto

Rimondini

Hansson

et al. 2003

“…The observed anxiogenic effects of cannabinoids agree with previous results in the emergence and EPM tests (Rodriguez de Fonseca et al, 1996;Arevalo et al, 2001;Caberlotto et al, 2004;Marco et al, 2004) and the social interaction test (Genn et al, 2004). Adolescent behavior in rodents is characterized by greater social interaction and exploratory behavior relative to adults (Spear, 2000) and such effects were evident in control rats in the social interaction and EPM tasks in the present study.…”

Section: Acute Anxiogenic Effects Of Thcsupporting

confidence: 93%

Adolescent Rats Find Repeated Δ9-THC Less Aversive Than Adult Rats but Display Greater Residual Cognitive Deficits and Changes in Hippocampal Protein Expression Following Exposure

Quinn

Matsumoto

Callaghan

et al. 2007

274

226

The current study examined whether adolescent rats are more vulnerable than adult rats to the lasting adverse effects of cannabinoid exposure on brain and behavior. Male Wistar rats were repeatedly exposed to D-9-tetrahydrocannabinol (D 9 -THC, 5 mg/kg i.p.) in a place-conditioning paradigm during either the adolescent (post-natal day 28 + ) or adult (post-natal day 60 + ) developmental stages. Adult rats avoided a D 9 -THC-paired environment after either four or eight pairings and this avoidance persisted for at least 16 days following the final D 9 -THC injection. In contrast, adolescent rats showed no significant place aversion. Adult D 9 -THC-treated rats produced more vocalizations than adolescent rats when handled during the intoxicated state, also suggesting greater drug-induced aversion. After a 10-15 day washout, both adult and adolescent D 9 -THC pretreated rats showed decreased social interaction, while only D 9 -THC pretreated adolescent rats showed significantly impaired object recognition memory. Seventeen days following their last D 9 -THC injection, rats were euthanased and hippocampal tissue processed using two-dimensional gel electrophoresis proteomics. There was no evidence of residual D 9 -THC being present in blood at this time. Proteomic analysis uncovered 27 proteins, many involved in regulating oxidative stress/mitochondrial functioning and cytoarchitecture, which were differentially expressed in adolescent D 9 -THC pretreated rats relative to adolescent controls. In adults, only 10 hippocampal proteins were differentially expressed in D 9 -THC compared to vehicle-pretreated controls. Overall these findings suggest that adolescent rats find repeated D 9 -THC exposure less aversive than adults, but that cannabinoid exposure causes greater lasting memory deficits and hippocampal alterations in adolescent than adult rats.

“…McLaughlin et al (2005) found that a cannabinoid agonist decreased center-zone activity in an open field, an effect they interpreted as anxiogenic. In the elevated plus maze, cannabinoid agonists generally produce anxiogenic effects at high doses and anxiolytic effects at low doses (Arevalo et al, 2001;Berrendero and Maldonado, 2002;Marin et al, 2003;Marco et al, 2004). In the social interaction test (File, 1992;File and Seth, 2003;Genn et al, 2004) and defensive withdrawal test (Rodriguez de Fonseca et al, 1996;Yang et al, 1992), cannabinoid agonists and psychomotor stimulants can both produce anxiogenic effects.…”

Section: Discussionmentioning

confidence: 99%

Previous Exposure to THC Alters the Reinforcing Efficacy and Anxiety-Related Effects of Cocaine in Rats

Panlilio

Solinas

Matthews

et al. 2006

The hypothesis that prior cannabis exposure increases the likelihood of becoming addicted to other drugs can be evaluated by giving rats a history of tetrahydrocannabinol (THC) exposure, then allowing them to self-administer other drugs. In Experiment 1, THC preexposure did not alter the acquisition of cocaine self-administration or the amount of cocaine taken under a fixed-ratio 1 (FR1) schedule, with one response required for each injection. Under a progressive-ratio schedule, with the response requirement increasing exponentially with each injection, cocaine-seeking was significantly reduced in THC-exposed rats, suggesting that the regimen of THC exposure used in the present study caused cocaine to be devalued as a reinforcer. In contrast, in an earlier study that used the same regimen, a history of THC exposure did not alter the value of heroin as a reinforcer under the progressive-ratio schedule, but it increased heroin self-administration under the FR1 schedule. Experiment 2 examined how this regimen of THC pre-exposure alters the locomotor effects of cocaine and heroin. THC pre-exposure produced cross-tolerance to the motor-depressant effects of heroin; this may explain the shortened post-injection pauses exhibited by THC-exposed rats under FR1 heroin self-administration. When given cocaine, THCexposed rats exhibited normal increases in locomotion, but they avoided the center of the open field, suggesting that this THC preexposure regimen enhances the anxiogenic effects of cocaine. This enhanced anxiogenic effectFwhich was verified in Experiment 3 using another model of anxiety, the light-dark testFmay explain the reduced reinforcing value of cocaine observed in THC-exposed rats in Experiment 1.