Cocaine exposure during adolescence affects anxiety in adult mice

The effects of cocaine exposure in adolescence: Behavioural effects and neuroplastic mechanisms in experimental models

Drug addiction is a devastating disorder with a huge economic and social burden for modern society. Although an individual may slip into drug abuse throughout his/her life, adolescents are at higher risk, but, so far, only a few studies have attempted to elucidate the underlying cellular and molecular bases of such vulnerability. Indeed, preclinical evidence indicates that psychostimulants and adolescence interact and contribute to promoting a dysfunctional brain. In this review, we have focused our attention primarily on changes in neuroplasticity brought about by cocaine, taking into account that there is much less evidence from exposure to cocaine in adolescence, compared with that from adults. This review clearly shows that exposure to cocaine during adolescence, acute or chronic, as well as contingent or non‐contingent, confers a vulnerable endophenotype, primarily, by causing changes in neuroplasticity. Given the close relationship between drug abuse and psychiatric disorders, we also discuss the translational implications providing an interpretative framework for clinical studies involving addictive as well as affective or psychotic behaviours.

Social isolation at adolescence: a systematic review on behaviour related to cocaine, amphetamine and nicotine use in rats and mice

Adolescence is known for its high level of risk-taking, and neurobiological alterations during this period may predispose to psychoactive drug initiation and progression into more severe use patterns. Stress is a risk factor for drug consumption, and post-weaning social isolation increases drug self-administration in rodents. This review aimed to provide an overview of the effects of adolescent social isolation on cocaine, amphetamine and nicotine use-related behaviours, highlighting the specific period when animals were submitted to stress and these drugs. We wondered if there was a specific period during adolescence that isolation stress would increase drug use vulnerability. A total of 323 publications from the Scopus, Web of Science and PubMed (Medline) electronic databases were identified using the words "social isolation" and "adolescence" and "drug" or "cocaine" or "amphetamine" or "nicotine", resulting in 24 articles after analyses criteria following the PRISMA statement. The main points raised were social isolation during adolescence increased cocaine self-administration, amphetamine and nicotine locomotor activity. We did not observe a pattern of a specific moment during the adolescent period that could lead to an increased vulnerability to drug use. The precise conditions under which adolescent social stress alters drug use parameters are complex and likely depend on several factors.

Cocaine treatment before pregnancy differentially affects the anxiety and brain glucose metabolism of lactating rats if performed during adulthood or adolescence

Cocaine exposure disrupts the maternal behavior of lactating rats, yet it is less known whether it alters the affective changes that accompany motherhood. As the long-term action of cocaine on anxiety varies according to the developmental stage of the individuals, this study aimed to compare the effect of a chronic treatment with cocaine to adult and adolescent non-pregnant females on their anxiety-like behavior and basal brain metabolic activity during lactation. Thus, adult and adolescent virgin rats were exposed to cocaine (0.0 or 15.0 mg/kg ip) during 10 days and were mated four days later. Anxiety behavior was evaluated on postpartum days 3-4 in the elevated plus maze test, and the basal brain glucose metabolism was determined on postpartum days 7-9 by means of [¹⁸F] fluorodeoxyglucose positron emission tomography. Cocaine treatment during adulthood increased the anxiety-like behavior of lactating females whereas its administration during adolescence decreased it. Also, the basal glucose metabolism of the medial prefrontal cortex differed between lactating females treated with cocaine during adulthood and adolescence. These differential effects of cocaine, according to the age at which the drug was administered, support the idea that the adolescent and adult brains have a distinct susceptibility to this drug, which leads to divergent long-term changes in the neural circuits that regulate anxiety during lactation.

Pharmacological modulation of the behavioral effects of social defeat in memory and learning in male mice

RATIONALE

Previous studies have demonstrated that repeated social defeat (RSD) stress only induces cognitive deficits when experienced during adulthood. However, RSD increases cocaine-rewarding effects in adult and adolescent mice, inducing different expressions of proBDNF in the ventral tegmental area.

OBJECTIVE

The aim of the present study was to evaluate the effect of cocaine administration in socially defeated adult or adolescent mice on learning, memory, and anxiety. Additionally, the role of BDNF was also studied.

METHODS

Adolescent and young adult mice were exposed to four episodes of social defeat or exploration (control), being treated with a daily injection of four doses of saline or 1 mg/kg of cocaine 3 weeks after the last social defeat. Other groups were treated with the TrkB receptor antagonist ANA-12 during this 21-day period. After this treatment, their cognitive and anxiogenic profiles were evaluated, along with the expression of BDNF, pCREB, and pERK1/2 in the dentate gyrus (DG) and basolateral amygdala (BLA).

RESULTS

Cocaine induced an increased expression of pCREB and BDNF in the DG and BLA only in defeated animals. Although RSD did not affect memory, the administration of cocaine induced memory impairments only in defeated animals. Defeated adult mice needed more time to complete the mazes, and this effect was counteracted by cocaine administration. RSD induced anxiogenic effects only when experienced during adulthood and cocaine induced a general anxiolytic effect. Blockade of Trkb decreased memory retention without affecting spatial learning and modified anxiety on non-stressed mice depending on their age.

CONCLUSION

Our results demonstrate that the long-lasting effects of social defeat on anxiety and cognition are modulated by cocaine administration. Our results highlight that the BDNF signaling pathway could be a target to counteract the effects of cocaine on socially stressed subjects.

Effects of paternal deprivation on cocaine-induced behavioral response and hypothalamic oxytocin immunoreactivity and serum oxytocin level in female mandarin voles

Early paternal behavior plays a critical role in behavioral development in monogamous species. The vast majority of laboratory studies investigating the influence of parental behavior on cocaine vulnerability focus on the effects of early maternal separation. However, comparable studies on whether early paternal deprivation influences cocaine-induced behavioral response are substantially lacking. Mandarin vole (Microtus mandarinus) is a monogamous rodent with high levels of paternal care. After mandarin vole pups were subjected to early paternal deprivation, acute cocaine- induced locomotion, anxiety- like behavior and social behavior were examined in 45day old female pups, while hypothalamic oxytocin immunoreactivity and serum oxytocin level were also assessed. We found that cocaine increased locomotion and decreased social investigation, contact behavior and serum oxytocin level regardless of paternal care. Cocaine increased anxiety levels and decreased oxytocin immunoreactive neurons of the paraventricular nuclei and supraoptic nuclei in the bi-parental care group, whilst there were no specific effects in the paternal deprivation group. These results indicate that paternal deprivation results in different behavioral response to acute cocaine exposure in adolescents, which may be in part associated with the alterations in oxytocin immunoreactivity and peripheral OT level.

Timing of amphetamine exposure in relation to puberty onset determines its effects on anhedonia, exploratory behavior, and dopamine D1 receptor expression in young adulthood

Non-medical use of amphetamine (AMPH) among adolescents is prevalent, which is problematic given the potential consequences of developmental drug exposure on brain function and behavior. Previously we found in adult male rats that AMPH exposure starting before puberty induces a persistent decrease in dopamine D₁ receptor (D₁R) function in the medial prefrontal cortex (mPFC). Here we investigated if this dysfunction was associated with changes in D₁R expression in the mPFC and nucleus accumbens (NAc). We also determined if starting drug exposure well before or near the onset of puberty would influence AMPH-induced changes in D₁R expression and behavior. Male and female Sprague-Dawley rats were treated once every other day (10 injections total) with saline or 3mg/kg AMPH (i.p.) from either postnatal day (P) 27 to 45 (pre-puberty groups; Pre-P) or P37 to 55 (peri-puberty groups; Peri-P). After 1, 7 and 21days of withdrawal, sucrose preference tests were performed to assess anhedonia. Exploratory behavior was studied in an open-field arena and on an elevated plus maze (EPM). Rats were then sacrificed for Western blot analysis of D₁R expression. We found that AMPH withdrawal induced decreases in sucrose preference that persisted in rats with Peri-P onset treatment. Pre-P onset AMPH exposure led to increased open-arm exploration in the EPM test, as well as a decreased D₁R level in the mPFC but not NAc. Our results demonstrated that AMPH exposure starting at different developmental stages resulted in distinct neurobehavioral abnormalities, suggesting an important role of exposure timing in drug-induced plasticity.

Concordance and incongruence in preclinical anxiety models: Systematic review and meta-analyses

Rodent defense behavior assays have been widely used as preclinical models of anxiety to study possibly therapeutic anxiety-reducing interventions. However, some proposed anxiety-modulating factors - genes, drugs and stressors - have had discordant effects across different studies. To reconcile the effect sizes of purported anxiety factors, we conducted systematic review and meta-analyses of the literature on ten anxiety-linked interventions, as examined in the elevated plus maze, open field and light-dark box assays. Diazepam, 5-HT1A receptor gene knockout and overexpression, SERT gene knockout and overexpression, pain, restraint, social isolation, corticotropin-releasing hormone and Crhr1 were selected for review. Eight interventions had statistically significant effects on rodent anxiety, while Htr1a overexpression and Crh knockout did not. Evidence for publication bias was found in the diazepam, Htt knockout, and social isolation literatures. The Htr1a and Crhr1 results indicate a disconnect between preclinical science and clinical research. Furthermore, the meta-analytic data confirmed that genetic SERT anxiety effects were paradoxical in the context of the clinical use of SERT inhibitors to reduce anxiety.

Aggression and anxiety in adolescent AAS-treated hamsters: A role for 5HT3 receptors

Previously, we have shown that anabolic androgenic steroid (AAS) exposure throughout adolescence stimulates offensive aggression while also reducing anxious behaviors during the exposure period. Interestingly, AAS exposure through development correlates with alterations to the serotonin system in regions known to contain 5HT3 receptors that influence the control of both aggression and anxiety. Despite these effects, little is known about whether these separate developmental AAS-induced behavioral alterations occur as a function of a common neuroanatomical locus. To begin to address this question, we localized 5HT3 receptors in regions that have been implicated in aggression and anxiety. To examine the impact these receptors may have on AAS alterations to behavior, we microinjected the 5HT3 agonist mCPBG directly into a region know for its influence over aggressive behavior, the lateral division of the anterior hypothalamus, and recorded alterations to anxious behaviors using the elevated plus maze. AAS exposure primarily reduced the presence of 5HT3 receptors in aggression/anxiety regions. Accordingly, mCPBG blocked the anxiolytic effects of adolescent AAS exposure. These data suggest that the 5HT3 receptor plays a critical role in the circuit modulating developmental AAS-induced changes to both aggressive and anxious behaviors, and further implicates the lateral division of the anterior hypothalamus as an important center for the negative behavioral effects of developmental AAS-exposure.

Differences in cocaine-induced place preference persistence, locomotion and social behaviors between C57BL/6J and BALB/cJ mice

C57BL/6J and BALB/cJ mice display significant differences in sociability and response to drugs, but the phenotypic variability of their susceptibility to cocaine is still not well known. In this study, the differences between these two mice strains in the persistence of cocaine-induced conditioned place preference (CPP), as well as the locomotion and social behaviors after the 24-hour withdrawal from a four-day cocaine (20 mg/kg/day) administration were investigated. The results showed that the cocaine-induced CPP persisted over two weeks in C57BL/6J mice, while it diminished within one week among BALB/cJ mice. After 24-hours of cocaine withdrawal, high levels of locomotion as well as low levels of social interaction and aggressive behavior were found in C57BL/6J mice, but no significant changes were found in BALB/cJ mice, indicating that cocaine-induced CPP persistence, locomotion and social behavior are not consistent between these two strains, and that overall C57BL/6J mice are more susceptible to cocaine than BALB/cJ mice at the tested doses.

Higher sensitivity to the conditioned rewarding effects of cocaine and MDMA in High-Novelty-Seekers mice exposed to a cocaine binge during adolescence

RATIONALE

Exposure to drugs during adolescence can induce alterations in the central nervous system. The novelty-seeking personality trait influences differences observed among individuals exposed to drugs of abuse.

OBJECTIVES

Long-term effects of intensive pre-treatment with cocaine during adolescence or adulthood were evaluated in High- and Low-Novelty Seeker (HNS and LNS) mice. It was hypothesized that a cocaine binge during adolescence would increase sensitivity to the rewarding effects of cocaine and MDMA, especially in HNS animals, and modify the spontaneous behaviour of adult animals.

METHODS

Adolescent (PND 33) and adult (PND 60) mice were identified as HNS or LNS according to their performance in the hole-board test. Subsequently, they received pre-treatment with cocaine (three injections per day of an increasing dose for 10 days) or saline. Three weeks later, the mice performed the hole-board, elevated plus maze, spontaneous locomotor activity and cocaine- (1 mg/kg) or MDMA- (1.25 mg/kg) induced conditioning place preference (CPP) tests. In another set of mice, the effects of pre-treatment of cocaine during adulthood on MDMA- or cocaine-induced CPP were also evaluated 3 weeks later.

RESULTS

Only HNS mice treated with cocaine during adolescence acquired MDMA- or cocaine-induced CPP in adulthood. Moreover, pre-exposure to cocaine during adolescence caused subsequent behavioural alterations, including reduced exploratory behaviour and increased locomotor reactivity.

CONCLUSIONS

Cocaine binge administration during adolescence induces a higher sensitivity to the rewarding effects of MDMA and cocaine in HNS mice in adulthood. This may explain the greater vulnerability often seen among individuals exposed early in life to drugs of abuse.

Increased conditioned place preference for cocaine in high anxiety related behavior (HAB) mice is associated with an increased activation in the accumbens corridor

Anxiety disorders and substance use disorders are strongly associated in humans. Accordingly, a widely held but controversial concept in the addiction field, the so-called “self-medication hypothesis,” posits that anxious individuals are more vulnerable for drug dependence because they use drugs of abuse to alleviate their anxiety. We tested this hypothesis under controlled experimental conditions by quantifying the conditioned place preference (CPP) to 15 mg/kg i.p. cocaine given contingently (COCAINE) in CD1 mice selectively bred for high anxiety-related behavior (HAB) vs. normal anxiety-related behavior (NAB). Cocaine was conditioned to the initially non-preferred compartment in an alternate day design (cocaine vs. saline, four pairings each). HAB and NAB mice were also tested for the effects of non-contingent (NONCONT) cocaine administration. HAB mice showed a slightly higher bias for one of the conditioning compartments during the pretest than NAB mice that became statistically significant (p = 0.045) only after pooling COCAINE and NONCONT groups. Cocaine CPP was higher (p = 0.0035) in HAB compared to NAB mice. The increased cocaine CPP was associated with an increased expression of the immediate early genes (IEGs) c-Fos and Early Growth Related Protein 1 (EGR1) in the accumbens corridor, i.e., a region stretching from the anterior commissure to the interhemispheric border and comprising the medial nucleus accumbens core and shell, the major island of Calleja and intermediate part of the lateral septum, as well as the vertical limb of the diagonal band and medial septum. The cocaine CPP-induced EGR1 expression was only observed in D1- and D2-medium spiny neurons, whereas other types of neurons or glial cells were not involved. With respect to the activation by contingent vs. non-contingent cocaine EGR1 seemed to be a more sensitive marker than c-Fos. Our findings suggest that cocaine may be more rewarding in high anxiety individuals, plausibly due to an anxiolytic effect.

Adolescent amphetamine exposure elicits dose-specific effects on monoaminergic neurotransmission and behaviour in adulthood

Despite the growing non-medical consumption of amphetamine (Amph) during adolescence, its long-term neurobiological and behavioural effects have remained largely unexplored. The present research sought to characterize the behavioural profile and electrophysiological properties of midbrain monoaminergic neurons in adult rodents after Amph exposure during adolescence. Adolescent rats were administered vehicle, 0.5, 1.5, or 5.0 mg/kg.d Amph from postnatal day (PND) 30-50. At adulthood (PND 70), rats were tested in an open-field test (OFT) and elevated plus maze (EPM), paralleled by in-vivo extracellular recordings of serotonin (5-HT), dopamine (DA) and norepinephrine (NE) neurons from the dorsal raphe nucleus, ventral tegmental area, and locus coeruleus, respectively. 5-HT firing in adulthood was increased in rats that had received Amph (1.5 mg/kg.d) during adolescence. At this regimen, DA firing activity was increased, but not NE firing. Conversely, the highest Amph dose regimen (5.0 mg/kg.d) enhanced NE firing, but not DA or 5-HT firing rates. In the OFT, Amph (1.5 mg/kg.d) significantly increased the total distance travelled, while the other doses were ineffective. In the EPM, all three Amph doses increased time spent in the open arms and central platform, as well as the number of stretch-attend postures made. Repeated adolescent exposure to Amph differentially augments monoaminergic neuronal firing in a dose-specific fashion in adulthood, with corresponding alterations in locomotion, risk assessment (stretch-attend postures and central platform occupancy) and risk-taking behaviours (open-arm exploration). Thus, adolescent Amph exposure induces long-lasting neurophysiological alterations that may have implications for drug-seeking behaviour in the future.

Regionalized loss of parvalbumin interneurons in the cerebral cortex of mice with deficits in GFRalpha1 signaling

Inhibitory interneurons are crucially important for cerebral cortex function and behavior. The mechanisms controlling inhibitory interneuron diversification and allocation to distinct cortical areas remain poorly understood. GDNF (glial cell line-derived neurotrophic factor) and its receptor GFRalpha1 have been implicated in the development of GABAergic precursors but, because of the early lethality of null mutants, their roles in postnatal maturation and function of cortical interneurons are unknown. "cis-only" mutant mice lack GFRalpha1 only in cells that do not express the RET signaling receptor subunit and survive to adulthood. At birth, both null mutants and cis-only mice showed a specific loss of GABAergic interneurons in rostro- and caudolateral cortical regions but not in more medial areas. Unexpectedly, the adult cortex of cis-only mice displayed a complete loss of parvalbumin (PV)-expressing GABAergic interneurons in discrete regions (PV holes) interspersed among areas of normal PV cell density. PV holes predominantly occurred in the visual and frontal cortices, and their size could be affected by neuronal activity. Consistent with deficits in cortical inhibitory activity, these mice showed enhanced cortical excitability, increased sensitivity to epileptic seizure, and increased social behavior. We propose that GFRalpha1 signaling guides the development of a subset of PV-expressing GABAergic interneurons populating discrete regions of the cerebral cortex and may thus contribute to the diversification and allocation of specific cortical interneuron subtypes.

X11-like protein deficiency is associated with impaired conflict resolution in mice

Understanding how emotion is generated, how conflicting emotions are regulated, and how emotional states relate to sophisticated behaviors is a crucial challenge in brain research. Model animals showing selective emotion-related phenotypes are highly useful for examining these issues. Here, we describe a novel mouse model that withdraws in approach-avoidance conflicts. X11-like (X11L)/Mint2 is a neuronal adapter protein with multiple protein-protein interaction domains that interacts with several proteins involved in modulating neuronal activity. X11L-knock-out (KO) mice were subordinate under competitive feeding conditions. X11L-KO mice lost significantly more weight than cohoused wild-type mice without signs of decreased motivation to eat or physical weakness. In a resident-intruder test, X11L-KO mice showed decreased intruder exploration behavior. Moreover, X11L-KO mice displayed decreased marble-burying, digging and burrowing behaviors, indicating aberrant ethological responses to attractive stimuli. In contrast, X11L-KO mice were indistinguishable from wild-type mice in the open field, elevated plus maze, and light/dark transition tests, which are often used to assess anxiety-like behavior. Neurochemical analysis revealed a monoamine imbalance in several forebrain regions. The defective ethological responses and social behaviors in X11L-KO mice were rescued by the expression of X11L under a Camk2a promoter using the Tet-OFF system during development. These findings suggest that X11L is involved in the development of neuronal circuits that contribute to conflict resolution.

Behavioural and neurotoxic long-lasting effects of MDMA plus cocaine in adolescent mice

The poly-drug pattern is the most common among MDMA users, with cocaine being a frequently associated drug. The aim of the present work was to evaluate the behavioural and neurotoxic long-term effects of exposure during adolescence to MDMA alone or plus cocaine. Mice of 28 to 30 days of age received a treatment of two daily injections of an identical dose of MDMA (5, 10 or 20 mg/kg), alone or plus cocaine (25 mg/kg), for 3 days (6 administrations). Three weeks after receiving MDMA, an increase in the time dedicated by the animals to social contacts with their conspecifics was observed, whilst their behaviour in the elevated plus maze showed no differences from that of non-treated mice. After being exposed to MDMA plus cocaine, mice spent more time in social contacts during the interaction test, as well as exhibiting an anxiolytic profile in the elevated plus maze, with an increase in the time and number of entries in the open arms. The activity of mice treated with cocaine alone or plus MDMA remained constant; the decrease observed among the rest of the animals after the second hour was absent in their case. The level of dopamine in the striatum was diminished in mice treated with 20 mg/kg of MDMA, but this neurotransmitter was not affected in animals exposed to the same dose plus cocaine. The present results highlight pronounced alterations in the behaviour of adult mice after exposure to MDMA and cocaine during adolescence, and demonstrate that these long-term effects can occur without the dopaminergic system becoming affected.

Anxiogenesis in adult rats treated chronically with cocaine during adolescence: effects of extended abstinence and 8-OH-DPAT treatment

Our laboratory has recently observed the development of an anxiogenic response after a short abstinence period ( approximately 10 days) in young adult rats treated repeatedly with cocaine during adolescence. The present study was conducted to determine if this effect persists into adulthood following extended durations of abstinence and whether it could be modulated with the 5-HT(1A) agonist (+/-)-8-hydroxy-2-(dipropylamino)tetralin hydrobromide (8-OH-DPAT). Accordingly, 30-day-old rats were injected with either 10mg/kg cocaine or saline for 8 consecutive days. Approximately 8 weeks after the final injection, anxiety levels in subjects were assessed with an elevated zero maze with a second assessment performed 4 weeks thereafter. Shortly prior to each test session, half the subjects in each of the two adolescent drug conditions received injections of 300 microg/kg 8-OH-DPAT while the other half received injections of the vehicle. Based on total time spent in the open areas of the maze, the results obtained at the first abstinent duration indicated that adolescent cocaine treatment did not induce an anxiogenic response. Assessment of maze behavior at the second abstinent duration was aided with a digital tracking and computerized scoring system (LimeLight, Actimetrics). Similar to the results obtained at the first abstinent duration, the amount of time spent in the open areas of the maze was unrelated to prior cocaine treatment. However, cocaine-treated rats did show evidence of an anxiogenic response at this abstinent duration based on more frequent entries into and out of the open and enclosed areas of the maze, more frequent and longer durations of exploratory bouts beyond the perimeter of the maze, excessive number of cautious protrusions into the open areas, and faster running velocities through the open areas. These results were not artifacts of generalized motor activation in that comparable total distance traveled scores were noted for all subjects. Treatment with 8-OH-DPAT shortly prior to elevated zero maze testing normalized these behaviors induced by adolescent cocaine. It is concluded that the anxiogenic response produced by cocaine exposure during adolescence persists 12 weeks beyond cessation of drug treatment and that this effect is reversible with 8-OH-DPAT. In addition, the results underscore the importance of taking multiple measures when assessing anxiety in experimental animals. Implications for the neurobiology of drug abuse and the role of serotonin are discussed.