Alejandro Higuera-Matas

Cannabidiol, a nonpsychotropic component of cannabis, inhibits cue-induced heroin-seeking and normalizes discrete mesolimbic neuronal disturbances

There remains debate regarding the impact of cannabis on neuropsychiatric disorders. Here, we examined the effects of cannabidiol (CBD), a nonpsychoactive constituent of cannabis, on heroin self-administration and drug-seeking behavior using an experimental rat model. CBD (5–20 mg/kg) did not alter stable intake of heroin self-administration, extinction behavior, or drug seeking induced by a heroin prime injection. Instead, it specifically attenuated heroin-seeking behavior reinstated by exposure to a conditioned stimulus cue. CBD had a protracted effect with significance evident after 24 h and even 2 weeks after administration. The behavioral effects were paralleled by neurobiological alterations in the glutamatergic and endocannabinoid systems. Discrete disturbances of AMPA GluR1 and cannabinoid type-1 receptor expression observed in the nucleus accumbens associated with stimulus cue-induced heroin seeking were normalized by CBD treatment. The findings highlight the unique contributions of distinct cannabis constituents to addiction vulnerability and suggest that CBD may be a potential treatment for heroin craving and relapse.

Augmented acquisition of cocaine self-administration and altered brain glucose metabolism in adult female but not male rats exposed to a cannabinoid agonist during adolescence.

Marijuana consumption during adolescence has been proposed to be a stepping-stone for adult cocaine addiction. However, experimental evidence for this hypothesis is missing. In this work we chronically injected male and female Wistar rats with either the cannabinoid agonist CP 55,940 (CP; 0.4 mg/kg) or its corresponding vehicle. Adult acquisition (seven 30 min daily sessions) and maintenance (fourteen 2 h daily sessions) of cocaine self-administration (1 mg/kg), food-reinforced operant learning under conditions of normal (ad libitum access to food), and high motivation (food-restriction schedule) were measured. Additionally, brain metabolic activity was analyzed by means of [18F]-fluorodeoxyglucose positron emission tomography. During the acquisition phase, female CP-treated rats showed a higher rate of cocaine self-administration as compared to vehicle-treated females and males; no differences were found between both male groups. This effect disappeared in the maintenance phase. Moreover, no differences among groups were evident in the food-reinforced operant task, pointing to the cocaine-specific nature of the effect seen in self-administration rather than a general change in reward processing. Basal brain metabolic activity also changed in CP-treated females when compared to their vehicle-treated counterparts with no differences being found in the males; more specifically we observed a hyper activation of the frontal cortex and a hypo activation of the amygdalo-entorhinal cortex. Our results suggest that a chronic exposure to cannabinoids during adolescence alters the susceptibility to acquire cocaine self-administration, in a sex-specific fashion. This increased susceptibility could be related to the changes in brain metabolic activity induced by cannabinoids during adolescence.

Enhancement of hippocampal long-term potentiation induced by cocaine self-administration is maintained during the extinction of this behavior.

Drug addiction may involve learning and memory processes requiring the participation of hippocampal formation. One of the best studied examples of hippocampal synaptic plasticity is the long-term potentiation (LTP) which usually occurs when hippocampal synapses are stimulated with high-frequency stimulation. The aim of this work has been to study the effect of extinction of cocaine self-administration behavior on synaptic plasticity in rat hippocampal slices. LTP was induced using a tetanization paradigm consisting of a single train of high-frequency (100 Hz) stimulation for one second. This tetanization protocol evoked a greater and more perdurable LTP in slices obtained after 10 days of extinction of cocaine self-administration (1 mg/kg/injection) than that elicited in slices from saline self-administering (0.9% NaCl) animals. In addition, this LTP facilitation in animals which have followed the cocaine self-administration extinction protocol was very similar to that obtained in slices from cocaine self-administering animals. These results suggest that chronic cocaine self-administration induces enduring neuroadaptive changes in hippocampal synaptic plasticity which last even after the extinction of this behavior and that they may be involved in cocaine dependence.

Sex-dependent effects of periadolescent exposure to the cannabinoid agonist CP-55,940 on morphine self-administration behaviour and the endogenous opioid system

Early cannabinoid consumption may predispose individuals to the misuse of addictive drugs later in life. However, there is a lack of experimental evidence as to whether cannabinoid exposure during adolescence might differently affect opiate reinforcing efficacy and the opioid system in adults of both sexes. Our aim was to examine whether periadolescent chronic exposure to the cannabinoid agonist CP-55,940 could exert sex-dependent effects on morphine reinforcing and the opioid system in adulthood. Morphine reinforcing was studied under a progressive ratio (PR) reinforcement schedule in adult male and female rats that previously acquired morphine self-administration under a fixed ratio 1 (FR1) schedule. Binding levels and functionality of mu-opioid receptors were also evaluated. Periadolescent cannabinoid exposure altered morphine self-administration and the opioid system in adult rats in a sex-dependent manner. CP-55,940-exposed males exhibited higher self-administration rates under a FR1, but not under a PR schedule. In females, CP-55,940 did not modify morphine self-administration under either schedule. Moreover, CP-55,940 also increased mu-opioid receptor levels in the subcallosal streak of pre-treated animals and decreased mu-opioid receptor functionality in the nucleus accumbens shell but again, only in males. Our data indicate that adult male rats exposed to the cannabinoid in adolescence self-administer more morphine than females, but only when the demands required by the schedule of reinforcement are low, which might be related to the decrease in mu-opioid receptor functionality in the NAcc-shell observed in these animals.

Modulation of the endogenous opioid system after morphine self-administration and during its extinction: a study in Lewis and Fischer 344 rats.

Lewis (LEW) and Fischer 344 (F344) rats show differential morphine self-administration rates. In this study, after animals of both strains self-administered morphine (1mg/kg) or extinguished this behaviour for 3, 7 or 15days, we measured the binding to, and functional state of mu opioid receptors (MORs) as well as proenkephalin (PENK) mRNA content in several brain regions. The results showed that in most brain areas: 1) LEW rats had less binding to MORs in basal conditions than F344 rats; 2) after morphine self-administration, either one of the strains or both (depending on the brain area) showed increased levels of binding to MORs as compared to basal groups; and 3) these binding levels in morphine self-administration animals came down in each extinction group. Moreover, F344 rats exhibited, in general, an increased functionality of MORs after morphine self-administration, as compared to basal groups, which also went down during extinction. Finally, the basal content of PENK mRNA was lower in LEW rats than in F344 rats and it decreased more after self-administration; during extinction, the levels of PENK mRNA got normalized in this strain. This differential modulation of the endogenous opioid system might be related to the different rates of morphine self-administration behavior exhibited by both inbred rat strains.

Chronic periadolescent cannabinoid treatment enhances adult hippocampal PSA-NCAM expression in male Wistar rats but only has marginal effects on anxiety, learning and memory

Pubertal and adolescent exposure to cannabinoids is associated with enduring alterations in anxiety and memory. However, periadolescence virtually remains unexplored. Here, we measured anxiety in the Elevated Plus Maze (EPM) in adult Wistar rats treated at periadolescence (P28-P38) with the cannabinoid agonist CP 55,940 (CP) (0.4 mg/kg; 2 ml/kg i.p., 1 daily injection), and we also defined their recognition memory in the novel object paradigm and spatial learning and memory in the water maze. Additionally, we measured the expression of hippocampal PSA-NCAM (Polysialic Acid-Neural Cell Adhesion Molecule) and long-term potentiation (LTP) as well as, given their role in mnemonic processing, the levels of plasma corticosterone and estradiol. We found that CP had no robust effects on anxiety or in recognition memory. In the water maze, only a slight decreased percentage of failed trials in the reference memory task and an improvement in an indirect index of attention were observed. However, we detected an up-regulation of hippocampal PSA-NCAM expression, only in CP-males, although this effect was not related to changes in LTP. No hormonal alterations were evident. Based on our data, minimal long-term effects on anxiety, learning and memory appear to result from cannabinoid exposure during the periadolescent period.

Differential cocaine-induced modulation of glutamate and dopamine transporters after contingent and non-contingent administration

Although dopamine and glutamate transmission has been implicated in cocaine dependence, the effects of the extinction of cocaine self-administration on protein transporters in both of these neurotransmitter systems remain unknown. We have used a yoked-box procedure to simultaneously test rats in triads, one rat that actively self-administered cocaine (CONT), while the other two received yoked injections of either cocaine (NON-CONT) or saline (SALINE). The brains in each triad were removed and processed for quantitative autoradiography immediately after the last session of cocaine self-administration (Day 0), or after 1, 5, or 10 days of extinction, and excitatory amino acid transporters (EAATs) and dopamine transporter (DAT) binding was examined. When compared to NON-CONT and SALINE animals, binding of radioligand to EAATs was significantly lower in the hippocampal CA1 field and the cerebellar cortex of CONT rats on Day 0, although it was significantly higher after 1 day of extinction in the infralimbic cortex. No differences in EAAT binding were observed after 5 or 10 days of extinction in any of the brain regions analyzed. In contrast and at all the time points of extinction, binding to DAT was significantly enhanced in CONT animals when compared to SALINE and NON-CONT rats in different forebrain and mesencephalic regions, including the nucleus accumbens, ventral tegmental area or caudate putamen. These results suggest that changes in protein transporter binding after cocaine self-administration and extinction are transient for EAAT while they are more enduring for DAT, and that they depend on the type of access to cocaine.

Strain differences in the dose–response relationship for morphine self-administration and impulsive choice between Lewis and Fischer 344 rats

Dose–response studies are thought to be a valuable tool to predict the most genetically drug-vulnerable individuals. However, dose–response curves for morphine self-administration have not yet been examined and nor strain differences might be evident. Therefore, this study aimed to define the dose–response curve for morphine self-administration (0.25, 0.5, 1 and 2 mg/kg) in Lewis (LEW) rats and their histocompatible Fischer-344 (F344) rats. In addition, impulsivity has been suggested as one of the genetic factors contributing most to the initiation of drug use. Therefore, the impulsive choice of both rat strains in the presence or absence of the same morphine doses was also analysed. LEW rats self-administered significantly more morphine whatever the dose tested and they exhibited greater basal impulsive choice compared with F344 rats. The F344 strain showed a preference for the dose of 0.5 mg/kg, while any of the doses used had a differential reinforcing effect in the LEW strain. The basal pattern of strain differences in impulsive choice was not affected by morphine administration. These data suggest that the LEW strain has a highly drug-vulnerable phenotype and they point to the strength of impulsivity as a pre-existing behavioural trait that might make this rat strain more vulnerable to the reinforcing effects of drugs and, therefore, to develop addiction.

Hippocampal Synaptic Plasticity and Water Maze Learning in Cocaine Self‐Administered Rats

Abstract:  Previously, we have shown that long‐term potentiation (LTP) in hippocampus of Lewis rats was significantly modulated by cocaine self‐administration. Using a single train of high‐frequency stimulation of 100 Hz for 1s (HFS), we found an enhancement of LTP after cocaine self‐administration that was maintained even during the extinction of this behavior. However, the effects of cocaine self‐administration on a hippocampal‐dependent spatial learning task were unknown. Therefore, in the present study our first objective was to analyze if cocaine self‐administration might affect the performance in a hippocampus‐dependent task, such as the Morris water maze test. Male adult Lewis (LEW) rats self‐administered cocaine (1 mg/kg/injection) or saline (0.9% NaCl) for 3 weeks. Three hours after finishing the last self‐administration session, animals were submitted to Morris water maze training for 3 consecutives days. A memory test was carried out 24 h after the last training session. No significant differences were found in escape latencies and time spent in the quadrant where the platform was located during training. Given that we did not find any cocaine effect on this spatial learning task, our second objective was to estimate indirectly if brain cocaine levels have failed to modulate LTP in animals that were performing the water maze trials. To this end, we tested if cocaine application to hippocampal slices of naïve subjects was able to evoke LTP. The results indicated that cocaine produced an enhanced LTP in these hippocampal slices. Taking together, the results of the present study suggest that hippocampal LTP‐like processes generated after cocaine self‐administration are not related to spatial learning hippocampal‐dependent tasks, such as the water maze test.

Mice with Decreased Cerebral Dopamine Function following a Neurotoxic Dose of MDMA (3,4-Methylenedioxymethamphetamine, “Ecstasy”) Exhibit Increased Ethanol Consumption and Preference

MDMA (3,4-methylenedioxymethamphetamine, “ecstasy”) administration to mice produces relatively selective long-term neurotoxic damage to dopaminergic pathways. There is strong evidence indicating that the dopamine system plays a key role in the rewarding effects of ethanol and modulates ethanol intake. Using a two-bottle free-choice paradigm, we examined the voluntary consumption and preference for ethanol in mice deficient in cerebral dopamine concentration and dopamine transporter density by previous repeated MDMA administration. The current study shows that mice pre-exposed to a neurotoxic dose of MDMA exhibited a higher consumption of and preference for ethanol compared with saline-treated animals. The D1 receptor full agonist SKF81297 [(6-chloro-7,8-dihydroxy-1-phenyl-2,3,4,5-tetrahydro-1H-3-benzazepine hydrobromide)] attenuated the enhanced ethanol intake, an effect that was reversed by SCH23390 [((R)-(+)-7-chloro-8-hydroxy-3-methyl-1-phenyl-2,3,4,5-tetrahydro-1H-3-benzazepine hydrochloride], a D1 receptor antagonist. MDMA-exposed mice also showed a reduced release of basal dopamine in the nucleus accumbens compared with saline-injected animals and a modest increase in D1 receptor density in caudate-putamen and nucleus accumbens. Intraperitoneal administration of ethanol elevated extracellular dopamine release in the nucleus accumbens of saline-treated mice, but this effect was almost abolished in MDMA-treated mice. Differences between saline- and MDMA-treated animals did not appear to be secondary to changes in acute ethanol clearance. These results indicate that mice with reduced dopamine activity following a neurotoxic dose of MDMA exhibit increased ethanol consumption and preference and suggest that animals might need to consume more alcohol to reach the threshold for the rewarding effects of ethanol.