Δ 9 -tetrahydrocannabinol (THC) is the intoxicating constituent of cannabis and is responsible for the drug's reinforcing effects. Retrospective human studies suggest that cannabis use during adolescence is linked to long-term negative psychological outcomes, but in such studies it is difficult to distinguish the effects of THC from those of coexisting factors. Therefore, translationally relevant animal models are required to properly investigate THC effects in adolescents. However, though the relevance of these studies depends upon human-relevant dosing, surprisingly little is known about THC pharmacology and its effects on behavior and brain activity in adolescent rodents-especially in females. Here, we conducted a systematic investigation of THC pharmacokinetics, metabolism and distribution in blood and brain, and of THC effects upon behavior and neural activity in adolescent Long Evans rats of both sexes. We administered THC during an early-middle adolescent window (postnatal days 27-45) in which the brain may be particularly sensitive to developmental perturbation by THC. We determined the pharmacokinetic profile of THC and its main first-pass metabolites (11-hydroxy-THC and 11-nor-9-carboxy-THC) in blood and brain following acute injection (0.5 or 5 mg/kg, intraperitoneal). We also evaluated THC effects on behavioral assays of anxiety, locomotion, and place conditioning, as well as c-Fos expression in 14 brain regions. Confirming previous work, we find marked sex differences in THC metabolism, including a female-specific elevation in the bioactive metabolite 11-hydroxy-THC. Furthermore, we find dose-dependent and sexdependent effects on behavior, neural activity, and functional connectivity across multiple nodes of brain stress and reward networks. Our findings are relevant for interpreting results of rat adolescent THC exposure studies, and may lend new insights into how THC impacts the brain in a sex-dependent manner.

Accumulating evidence indicates significant consequences for astrocytes associated with drug abuse. For example, reductions in structural features and synaptic colocalization of male rat nucleus accumbens (NAc) astrocytes are observed following short-access (ShA, 2 hours/day) self-administration and extinction from cocaine, methamphetamine, and heroin. However, it is unknown whether these observations extend to other rodent models of drug abuse, how enduring these effects may be, and whether similar effects are observed in female rats. Here we assess the effects of long-access (LgA, 6 hours/day) cocaine self-administration and abstinence on NAc astrocytes separately in male and female rats, employing a commonly used behavioral approach to investigate the incubation of cocaine craving. NAc astrocytes from male rats exhibit extensive (~40%) reductions in surface area, volume, and postsynaptic colocalization 45 days, but not 24 hours after the last self-administration session. In contrast, no effect of self-administration and abstinence was observed in astrocytes from female rats. Moreover, no effect of LgA selfadministration and abstinence was observed on NAc GLT-1 expression in female rats, an effect that has been well described in males. These results indicate striking and sexually dimorphic effects of abstinence subsequent to LgA self-administration on astrocytes. Taken together, these results indicate a pivotal role of prolonged abstinence in the effects of cocaine selfadministration on NAc astrocytes, and extend a growing body of evidence regarding sex differences in the cellular consequences of drug self-administration in the brain. Effects of cocaine abstinence on astrocytes 3 Significance StatementPrevious studies have reported changes in astrocytes following short-access (ShA, 2 hours/day) cocaine self-administration and extinction. However, it is unknown if these changes occur following other rodent models of drug intake. Accordingly, we examined the morphometric properties and synaptic colocalization of NAc astrocytes in male rats following long-access (LgA, 6 hours/day) cocaine self-administration and prolonged abstinence (45 days).NAc astrocytes demonstrated a profound decrease (~40%) in surface area, volume, and synaptic colocalization. Importantly, these changes are greater following LgA and abstinence, vs. ShA and extinction. Furthermore, these changes are not observed 24 hours following LgA cocaine self-administration and not observed in female rats. These results indicate abstinence and sexdependent changes in NAc astrocytes following prolonged abstinence from LgA cocaine selfadministration.

Accumulating evidence indicates significant consequences for astrocytes associated with drug abuse. For example, reductions in structural features and synaptic colocalization of male rat nucleus accumbens (NAc) astrocytes are observed following short-access (ShA, 2 hours/day) self-administration and extinction from cocaine, methamphetamine, and heroin. However, it is unknown whether these observations extend to other rodent models of drug abuse, how enduring these effects may be, and whether similar effects are observed in female rats. Here we assess the effects of long-access (LgA, 6 hours/day) cocaine self-administration and abstinence on NAc astrocytes separately in male and female rats, a commonly used behavioral approach to investigate the incubation of cocaine craving. NAc astrocytes from male rats exhibit extensive (~40%) reductions in surface area, volume, and postsynaptic colocalization 45 days, but not 24 hours after the last self-administration session. In contrast, no effect of self-administration was observed in astrocytes from female rats. Moreover, no effect of LgA self-administration and abstinence was observed on NAc GLT-1 expression in female rats, an effect that has been well described in males. The results indicate striking and sexually dimorphic effects of abstinence subsequent to LgA self-administration on astrocytes. Taken together, these results indicate a pivotal role of prolonged abstinence in the effects of cocaine self-administration on NAc astrocytes, and extend a growing body of evidence regarding sex differences in the cellular consequences of drug self-administration in the brain.