Adolescent delta-9-tetrahydrocannabinol (THC) exposure fails to affect THC-induced place and taste conditioning in adult male rats

Illicit Drug Use and Smell and Taste Dysfunction: A National Health and Nutrition Examination Survey 2013–2014

Taste and smell dysfunction are suspected to be associated with substance use. However, representative epidemiological studies remain insufficient. This cross-sectional study explored the relationship between drug use (including cannabis or hashish, cocaine, heroin, and methamphetamine) and olfactory/gustatory dysfunction using data from the 2013–2014 National Health and Nutrition Examination Survey. In this study, participants who completed the smell examination with mean age of 59 were classified into four groups: cannabis users (n = 845), participants without cannabis use (n = 794), illicit drug users (n = 450), and participants without illicit drug use (n = 2000). Participants who completed the taste examination with mean age of 58 were also categorised into four groups: cannabis users (n = 810), participants without cannabis use (n = 714), illicit drug users (n = 428), and participants without illicit drug use (n = 1815). Logistic regression models investigated the association between cannabis or illicit drug use and smell or taste dysfunctions among study participants. Odds ratios and 95% confidence intervals were calculated. Finally, we did not find correlations between illicit drug use and dysfunction of taste or smell senses; our findings were consistent in many subgroup analyses. We recommend that further studies explore the mechanism and dose of illicit drug use that could have chemosensory impacts.

Impact of the Aversive Effects of Drugs on Their Use and Abuse

Drug use and abuse are complex issues in that the basis of each may involve different determinants and consequences, and the transition from one to the other may be equally multifaceted. A recent model of the addiction cycle (as proposed by Koob and his colleagues) illustrates how drug-taking patterns transition from impulsive (acute use) to compulsive (chronic use) as a function of various neuroadaptations leading to the downregulation of DA systems, upregulation of stress systems, and the dysregulation of the prefrontal/orbitofrontal cortex. Although the nature of reinforcement in the initiation and mediation of these effects may differ (positive vs. negative), the role of reinforcement in drug intake (acute and chronic) is well characterized. However, drugs of abuse have other stimulus properties that may be important in their use and abuse. One such property is their aversive effects that limit drug intake instead of initiating and maintaining it. Evidence of such effects comes from both clinical and preclinical populations. In support of this position, the present review describes the aversive effects of drugs (assessed primarily in conditioned taste aversion learning), the fact that they occur concurrently with reward as assessed in combined taste aversion/place preference designs, the role of aversive effects in drug-taking (in balance with their rewarding effects), the dissociation of these affective properties in that they can be affected in different ways by the same manipulations, and the impact of various parametric, experiential, and subject factors on the aversive effects of drugs and the consequent impact of these factors on their use and abuse potential.

Cannabinoids, Chemical Senses, and Regulation of Feeding Behavior

The herb Cannabis sativa has been traditionally used in many cultures and all over the world for thousands of years as medicine and recreation. However, because it was brought to the Western world in the late 19th century, its use has been a source of controversy with respect to its physiological effects as well as the generation of specific behaviors. In this regard, the CB1 receptor represents the most relevant target molecule of cannabinoid components on nervous system and whole-body energy homeostasis. Thus, the promotion of CB1 signaling can increase appetite and stimulate feeding, whereas blockade of CB1 suppresses hunger and induces hypophagia. Taste and flavor are sensory experiences involving the oral perception of food-derived chemicals and drive a primal sense of acceptable or unacceptable for what is sampled. Therefore, research within the last decades focused on deciphering the effect of cannabinoids on the chemical senses involved in food perception and consequently in the pattern of feeding. In this review, we summarize the data on the effect of cannabinoids on chemical senses and their influences on food intake control and feeding behavior.

Lasting effects of repeated ∆9 -tetrahydrocannabinol vapour inhalation during adolescence in male and female rats

BACKGROUND AND PURPOSE

Adolescents are regularly exposed to ∆⁹ -tetrahydrocannabinol (THC) via smoking and, more recently, vaping cannabis extracts. Growing legalization of cannabis for medical and recreational purposes, combined with decreasing perceptions of harm, makes it increasingly important to determine the consequences of frequent adolescent exposure for motivated behaviour and lasting tolerance in response to THC.

EXPERIMENTAL APPROACHES

Male and female rats inhaled THC vapour, or that from the propylene glycol (PG) vehicle, twice daily for 30 min from postnatal day (PND) 35-39 and PND 42-46 using an e-cigarette system. Thermoregulatory responses to vapour inhalation were assessed by radio-telemetry during adolescence and from PND 86-94. Chow intake was assessed in adulthood. Blood samples were obtained from additional adolescent groups following initial THC inhalation and after 4 days of twice daily exposure. Additional groups exposed repeatedly to THC or PG during adolescence were evaluated for intravenous self-administration of oxycodone as adults.

KEY RESULTS

Female, not male, adolescents developed tolerance to the hypothermic effects of THC inhalation in the first week of repeated exposure despite similar plasma THC levels. Each sex exhibited tolerance to THC hypothermia in adulthood after repeated adolescent THC. However, enhanced potency was found in females. Repeated THC male rats consumed more food than their PG-treated control group, without significant bodyweight differences. Adolescent THC did not alter oxycodone self-administration in either sex but increased fentanyl self-administration in females.

CONCLUSIONS AND IMPLICATIONS

Repeated THC vapour inhalation in adolescent rats has lasting consequences observable in adulthood.

Evaluation of reinforcing and aversive effects of voluntary Δ9-tetrahydrocannabinol ingestion in rats

Edible cannabis-infused products are an increasingly popular method of using cannabis in the United States. Yet, preclinical research to determine mechanisms underlying abuse of Δ⁹-tetrahydrocannabinol (THC), the primary psychoactive constituent of cannabis, has focused primarily on the effects of parenteral administration. The purpose of this study was to examine the rewarding and aversive effects of oral THC in a novel rodent voluntary ingestion model. Adult male and female Sprague Dawley rats were given access to sucrose-sweetened solutions during daily sessions. A range of THC concentrations, each paired with a unique flavor previously tested alone, was introduced into these solutions for four-session exposure periods and drinking volumes were measured. Injected (i.p.) THC doses were also paired with unique flavors to compare the effects of route of THC administration on drinking. Introduction of THC into sucrose solutions dose-dependently decreased drinking upon initial exposure, though drinking generally increased in subsequent sessions. By contrast, i.p. THC produced sustained dose-dependent decreases in drinking in rats of both sexes. Subsequent exposure to paired flavors in the absence of THC resulted in further decreases in drinking, suggesting route-specific aversion. Additional testing using saccharin-sweetened solutions in a two-bottle choice paradigm was also conducted, with THC producing sustained dose-dependent decreases in drinking after initial exposure in rats of both sexes. Though self-administration of ingested THC was not demonstrated, evidence of route-specific THC aversion was observed, which suggests that certain routes and/or rates of THC administration may mitigate some of its aversive effects.

Preclinical Studies of Cannabinoid Reward, Treatments for Cannabis Use Disorder, and Addiction-Related Effects of Cannabinoid Exposure

Cannabis use has become increasingly accepted socially and legally, for both recreational and medicinal purposes. Without reliable information about the effects of cannabis, people cannot make informed decisions regarding its use. Like alcohol and tobacco, cannabis can have serious adverse effects on health, and some people have difficulty discontinuing their use of the drug. Many cannabis users progress to using and becoming addicted to other drugs, but the reasons for this progression are unclear. The natural cannabinoid system of the brain is complex and involved in many functions, including brain development, reward, emotion, and cognition. Animal research provides an objective and controlled means of obtaining information about: (1) how cannabis affects the brain and behavior, (2) whether medications can be developed to treat cannabis use disorder, and (3) whether cannabis might produce lasting changes in the brain that increase the likelihood of becoming addicted to other drugs. This review explains the tactics used to address these issues, evaluates the progress that has been made, and offers some directions for future research.

Antagonism of the kappa opioid receptor attenuates THC-induced place aversions in adult male Sprague-Dawley rats

RATIONALE

Prior research with transgenic mice in which the kappa opioid receptor (KOR) has been suppressed or activated suggests that the aversive effects of THC are mediated by activity of this receptor subtype. If the activity of the KOR system is responsible for mediating the THC's aversive effects, then selective antagonism of the KOR by norBNI should block such aversive effects. To test this hypothesis, rats were pretreated with norBNI 24h prior to place conditioning with THC to assess its effect on the acquisition of THC-induced place aversions.

METHODS

In Experiment 1, rats pretreated with norBNI (0 or 15mg/kg) were exposed 24h later to one side of a place conditioning chamber and injected with THC (0, 0.56, 1 and 3.2mg/kg). On the next day, they were injected with vehicle and placed on the opposite side of the chamber. This was repeated for a total of five cycles followed by a test of the animal's aversion to the THC-paired side. In Experiment 2, rats were pretreated with norBNI (0 or 30mg/kg) prior to place conditioning 24h later with THC (0 or 3.2mg/kg).

RESULTS

In Experiment 1, THC produced dose-dependent place aversions that were unaffected by norBNI (15mg/kg). In Experiment 2, THC induced significant place aversions that were fully attenuated by norBNI (30mg/kg).

CONCLUSIONS

Although 15mg/kg norBNI was ineffective in antagonizing the aversive effects of THC, 30mg/kg norBNI blocked the ability of THC to induce a place aversion. The results of the latter assessment are consistent with prior research with transgenic manipulations of the KOR and provide further evidence for the role of the KOR system in the aversive properties of THC.

Sex as a biological variable: Drug use and abuse

The study of sex as a biological variable is a necessary emphasis across a wide array of endpoints, including basic neuroscience, medicine, mental health, physiology and behavior. The present review summarizes work from clinical and preclinical populations on sex differences in drug use and abuse, ranging from initiation to escalation/dysregulation and from drug cessation/abstinence to relapse. These differences are analyzed in the context of the addiction cycle conceptualization of Koob and his colleagues and address patterns of drug use (binge/intoxication), motivation underlying its use (withdrawal/negative affect) and likelihood and causes of craving and relapse of drug taking (preoccupation/anticipation). Following this overview, an assessment of the basis for the reported sex differences is discussed in the context of the affective (rewarding and aversive) properties of drugs of abuse and how such properties and their balance vary with sex and contribute to drug intake. Finally, the interaction of sex with several experiential (drug history) and subject (age) factors and how these interactions affect reward and aversion are discussed to highlight the importance of understanding such interactions in predicting drug use and abuse. We note that sex as a biological variable remains one of critical evaluation and that such investigations of sex differences in drug use and abuse continue and be expanded to assess all facets of their mediation, including these affective properties, how their balance may be impacted by the multiple conditions under which drugs are taken and how this overall balance affects drug use and addiction vulnerability.

Delta-9-tetrahydrocannabinol (THC) history fails to affect THC's ability to induce place preferences in rats

RATIONALE

In pre-clinical models of marijuana abuse, there is relatively limited evidence of delta-9-tetrahydrocannabinol's (THC) rewarding effects, as indexed by its general inability to induce a place preference. One explanation for this failure is that its rewarding effects are masked by its concurrently occurring aversive properties. Consistent with this explanation, THC pre-exposure, which presumably weakens its aversive effects, induces place preferences. Such demonstrations are limited to mice and given reported species differences in THC reactivity, it is unknown to what extent the same shift in affective properties would be evident in rats.

METHODS

The present experiment examined the effect of THC history (3.2mg/kg) on THC (1 or 3.2mg/kg) induced place preference conditioning in rats. An assessment of taste avoidance was also run to independently characterize THC's aversive effects and any changes that occurred with drug pre-exposure. These assessments were made in a combined taste avoidance/place preference procedure in which a novel saccharin solution and environment were paired with THC (0, 1 or 3.2mg/kg).

RESULTS

THC did not induce place conditioning, and a history of THC was ineffective in increasing THC's ability to do so, despite the fact that this same history significantly attenuated the aversive effects of THC.

CONCLUSIONS

The failure of THC to consistently induce place preferences has been argued to be a function of its concurrently occurring aversive effects masking its rewarding properties. The fact that pre-exposure to THC significantly reduced its aversive effects without impacting THC's ability to induce place preferences suggests that THC has weak rewarding effects and/or its residual aversive affects may have still masked its rewarding properties. An important area for future work will be characterizing under what conditions THC is rewarding and whether its overall reinforcing effects are impacted by the relationship between its affective properties.