A single exposure to cocaine during development elicits regionally-selective changes in basal basic Fibroblast Growth Factor (FGF-2) gene expression and alters the trophic response to a second injection

Neurological Disorders Induced by Drug Use: Effects of Adolescent and Embryonic Drug Exposure on Behavioral Neurodevelopment

Clinical studies demonstrate that the risk of developing neurological disorders is increased by overconsumption of the commonly used drugs, alcohol, nicotine and cannabis. These drug-induced neurological disorders, which include substance use disorder (SUD) and its co-occurring emotional conditions such as anxiety and depression, are observed not only in adults but also with drug use during adolescence and after prenatal exposure to these drugs, and they are accompanied by long-lasting disturbances in brain development. This report provides overviews of clinical and preclinical studies, which confirm these adverse effects in adolescents and the offspring prenatally exposed to the drugs and include a more in-depth description of specific neuronal systems, their neurocircuitry and molecular mechanisms, affected by drug exposure and of specific techniques used to determine if these effects in the brain are causally related to the behavioral disturbances. With analysis of further studies, this review then addresses four specific questions that are important for fully understanding the impact that drug use in young individuals can have on future pregnancies and their offspring. Evidence demonstrates that the adverse effects on their brain and behavior can occur: (1) at low doses with short periods of drug exposure during pregnancy; (2) after pre-conception drug use by both females and males; (3) in subsequent generations following the initial drug exposure; and (4) in a sex-dependent manner, with drug use producing a greater risk in females than males of developing SUDs with emotional conditions and female offspring after prenatal drug exposure responding more adversely than male offspring. With the recent rise in drug use by adolescents and pregnant women that has occurred in association with the legalization of cannabis and increased availability of vaping tools, these conclusions from the clinical and preclinical literature are particularly alarming and underscore the urgent need to educate young women and men about the possible harmful effects of early drug use and to seek novel therapeutic strategies that might help to limit drug use in young individuals.

A single dose of cocaine raises SV2A density in hippocampus of adolescent rats

OBJECTIVE

Cocaine is a highly addictive psychostimulant that affects synaptic activity with structural and functional adaptations of neurons. The transmembrane synaptic vesicle glycoprotein 2A (SV2A) of pre-synaptic vesicles is commonly used to measure synaptic density, as a novel approach to the detection of synaptic changes. We do not know if a single dose of cocaine suffices to affect pre-synaptic SV2A density, especially during adolescence when synapses undergo intense maturation. Here, we explored potential changes of pre-synaptic SV2A density in target brain areas associated with the cocaine-induced boost of dopaminergic neurotransmission, specifically testing if the effects would last after the return of dopamine levels to baseline.

METHODS

We administered cocaine (20 mg/kg i.p.) or saline to rats in early adolescence, tested their activity levels and removed the brains 1 hour and 7 days after injection. To evaluate immediate and lasting effects, we did autoradiography with [3H]UCB-J, a specific tracer for SV2A, in medial prefrontal cortex, striatum, nucleus accumbens, amygdala, and dorsal and ventral areas of hippocampus. We also measured the striatal binding of [3H]GBR-12935 to test cocaine's occupancy of the dopamine transporter at both times of study.

RESULTS

We found a significant increase of [3H]UCB-J binding in the dorsal and ventral sections of hippocampus 7 days after the cocaine administration compared to saline-injected rats, but no differences 1 hour after the injection. The [3H]GBR-12935 binding remained unchanged at both times.

CONCLUSION

Cocaine provoked lasting changes of hippocampal synaptic SV2A density after a single exposure during adolescence.

Recency memory is altered in cocaine-withdrawn adolescent rats: Implication of cortical mTOR signaling

In humans, cocaine abuse during adolescence poses a significant risk for developing cognitive deficits later in life. Among the regions responsible for cognitive processes, the medial prefrontal cortex (mPFC) modulates temporal order information via mechanisms involving the mammalian-target of rapamycin (mTOR)-mediated pathway and protein synthesis regulation. Accordingly, our goal was to study the effect of repeated cocaine exposure during both adolescence and adulthood on temporal memory by studying the mTOR pathway in the mPFC. Adolescent or adult rats underwent repeated cocaine injections for 15 days and, after two weeks of withdrawal, engaged in the temporal order object recognition (TOOR) test. We found that repeated cocaine exposure during adolescence impaired TOOR performance, while control or adult-treated animals showed no impairments. Moreover, activation of the mTOR-S6-eEF2 pathway following the TOOR test was diminished only in the adolescent cocaine-treated group. Notably, inhibition of the mTOR-mediated pathway by rapamycin injection impaired TOOR performance in naïve adolescent and adult animals, revealing this pathway to be a critical component in regulating recency memory. Our data indicate that withdrawal from cocaine exposure impairs recency memory via the dysregulation of protein translation mechanisms, but only when cocaine is administered during adolescence.

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.

Electro-acupuncture alleviates adolescent cocaine exposure-enhanced anxiety-like behaviors in adult mice by attenuating the activities of PV interneurons in PrL

We recently found that adolescent cocaine exposure (ACE) resulted in an enhancement of the γ-aminobutyric acid (GABA) neurotransmitter system in the prelimbic cortex (PrL) of adult mice. Here, we aim to further investigate the role of GABAergic transmission, especially parvalbumin (PV) interneurons within PrL in the development of ACE-induced anxiety-like behavior, and to assess whether and how electro-acupuncture (EA) therapeutically manage the ACE-induced abnormal behaviors in adulthood. ACE mice exhibited the enhanced anxiety-like behaviors in their adulthood, accompanied by increased GABAergic transmission and PV interneurons in PrL. Chemogenetic blocking PV interneurons in PrL alleviated ACE-enhanced anxiety-like behaviors in mice. Importantly, 37-day EA treatments (mixture of 2 Hz/100 Hz, 1 mA, 30 minutes once a day) at the acupoints of Yintang (GV29) and Baihui (GV20) also alleviated ACE-induced anxiety-like behaviors, and rescued ACE-impaired GABAergic neurotransmitter system and PV interneurons in PrL. In parallel, EA treatments further suppressed the activities of pyramidal neurons in PrL, suggesting that EA treatments seem to perform it beneficial effects on the ACE-induced abnormal emotional behaviors by "calming down" the whole PrL. Collectively, these findings revealed that hyper-function of GABAergic transmission, especially mediating by PV interneurons in PrL may be key etiology underlying ACE-induced anxiety-like behaviors. At least by normalizing the function of GABAergic and PV interneurons, EA may represent a promising therapeutic strategy for managing adolescent substance use-related emotional disorders.

Anhedonic-like behavior and BDNF dysregulation following a single injection of cocaine during adolescence

We have previously demonstrated that a single exposure to cocaine during adolescence causes several behavioural and neurobiological changes, highlighting the unique vulnerability of this period of life. The purpose of our work was to investigate whether a single exposure to cocaine during brain development is sufficient to shape a negative emotional state in adolescent rats. A single injection of cocaine during adolescence followed by measurement of sucrose consumption, a measure of anhedonia, identifies two separate groups of rats, i.e. anhedonic (AN) and non anhedonic (NON-AN) rats. AN rats show reduced ability to synthesize, traffic and translate the neurotrophin BDNF at synaptic level, reduced activation of hippocampal BDNF signaling, reduced BDNF plasma levels and a steep rise of corticosterone secretion. Conversely, NON-AN rats exhibit reduced trafficking of BDNF while up-regulating hippocampal BDNF synthesis and stabilizing its downstream signaling with no changes of BDNF and corticosterone plasma levels. Adult rats exposed to cocaine showed no signs of anhedonia, an increase of BDNF both in hippocampus and plasma and decreased levels of corticosterone. In conclusion, our findings reveal a complex central and peripheral dysregulation of BDNF-related mechanisms that instead are preserved in NON-AN rats, suggesting that BDNF modulation dictates behavioural vulnerability vs. resiliency to cocaine-induced anhedonia, a profile uniquely restricted to adolescent rats.

Repeated cocaine exposure during adolescence impairs recognition memory in early adulthood: A role for BDNF signaling in the perirhinal cortex

The perirhinal cortex (PrhC) is critical for object recognition memory; however, information regarding the molecular mechanisms underlying this type of memory following repeated exposure to drugs of abuse during adolescence is unknown. To this end, adolescent or adult rats were exposed to cocaine from postnatal day (PND) 28 to PND 42 or PND 63 to PND 77, respectively. Two weeks later, rats were subjected to the cognitive test named Novel Object Recognition (NOR) test. We found that adolescent, but not adult, cocaine exposure caused a significant impairment in the NOR test, independently from changes in the stress response system. In adolescent saline-treated rats, NOR test up-regulated BDNF and its downstream signaling whereas a downregulation of the same pathway was observed in cocaine-treated rats together with a reduction of Arc/Arg3.1 and PSD95 expression, indicating reduced pro-cognitive structural adaptations in the PrhC. Of note, cocaine-treated adult rats correctly performed in the NOR test indicating intact recognition memory mechanisms, despite a significant cocaine-induced reduction of BDNF levels in the PrhC, suggesting that recognition memory is heavily dependent on BDNF during adolescence whereas during adulthood other mechanisms come into play.

Adolescent cocaine exposure enhances the GABAergic transmission in the prelimbic cortex of adult mice

We have recently shown in rats that adolescent cocaine exposure induces prolonged modifications on synapses in medial prefrontal cortex (mPFC), which might contribute to long-term behavioral outcomes in adulthood. In this study, we further investigated the molecular mechanisms underlying adolescent cocaine exposure-related psychiatric problems in adulthood, especially focusing on the alterations of GABAergic transmission in prelimbic cortex (PrL), 1 subregion of mPFC. Consistent with a previous study, adolescent cocaine-exposed mice exhibited enhanced anxiety-like behaviors in their adulthood. In the same mice models, depression-like behaviors increased as well, but the conditioned place preference formed normally. In parallel, activities of pyramidal neurons at layer V of PrL were reduced after adolescent cocaine exposure, accompanied by an increase in the percentage of symmetric synapses in PrL of adult mice. Additionally, miniature inhibitory postsynaptic currents rather than miniature excitatory postsynaptic currents were increased on these pyramidal neurons, and increased levels of GABA were found in adult PrL. The molecules in the GABAergic system in adult PrL were also changed by adolescent cocaine use, as indicated by increased glutamate decarboxylase 67 kDa, GABA_A-α1, and decreased GABA transporter 1. In the same mice, some regulators to GABAergic transmission such as neuregulin 1/ErbB4 signals were heightened as well. Collectively, these findings revealed that adolescent cocaine exposure results in permanent enhancement of GABAergic transmission on pyramidal neurons in PrL, which subsequently attenuate the activities of these neurons and ultimately contributes to the development of psychiatric disorders in later life.-Shi, P., Nie, J., Liu, H., Li, Y., Lu, X., Shen, X., Ge, F., Yuan, T.-F., Guan, X. Adolescent cocaine exposure enhances the GABAergic transmission in the prelimbic cortex of adult mice.

Short-term withdrawal from repeated exposure to cocaine during adolescence modulates dynorphin mRNA levels and BDNF signaling in the rat nucleus accumbens

BACKGROUND

Early-life stressful events affect the neurobiological maturation of cerebral circuitries including the endogenous opioid system and the effects elicited by adolescent cocaine exposure on this system have been poorly investigated. Here, we evaluated whether cocaine exposure during adolescence causes short- or long-term alterations in mRNAs codifying for selected elements belonging to the opioid system. Moreover, since brain-derived neurotrophic factor (BDNF) may undergo simultaneous alterations with the opioid peptide dynorphin, we also evaluated its signaling pathway as well.

METHODS

Adolescent male rats were exposed to cocaine (20 mg/kg/day) from post-natal day (PND) 28 to PND42, approximately corresponding to human adolescence. After short- (PND45) or long-term (PND90) abstinence, prodynorphin-κ-opioid receptor (pDYN-KOP) and pronociceptin-nociceptin receptor (pN/OFQ-NOP) gene expression were evaluated in the nucleus accumbens (NAc) and hippocampus (Hip) together with the analysis of BDNF signaling pathways.

RESULTS

In the NAc of PND45 rats, pDYN mRNA levels were up-regulated, an effect paralled by increased BDNF signaling. Differently from NAc, pDYN mRNA levels were down-regulated in the Hip of PND45 rats without significant changes of BDNF pathway. At variance from PND45 rats, we did not find any significant alteration of the investigated parameters either in NAc and Hip of PND90 rats.

CONCLUSIONS

Our results indicate that the short-term withdrawal from adolescent cocaine exposure is characterized by a parallel pDYN mRNA and BDNF signaling increase in the NAc. Given the depressive-like state experienced during short abstinence in humans, we hypothesize that such changes may contribute to promote the risk of cocaine abuse escalation and relapse.

A single cocaine administration alters dendritic spine morphology and impairs glutamate receptor synaptic retention in the medial prefrontal cortex of adolescent rats

The brain is still maturing during adolescence and interfering with such a vulnerable period may lead to structural and functional consequences. We investigated the effect of a single cocaine exposure on dendritic spine structure and glutamate dynamics in the medial prefrontal cortex (mPFC) of adolescent rats 7 days after a single cocaine administration. We found a reduced number of dendritic spines, suggesting that cocaine lowers the density of dendritic spines in the mPFC of adolescent rats. Since dendritic spines are postsynaptic glutamatergic protrusions, we investigated the main determinants of glutamate postsynaptic responsiveness. In the postsynaptic density, cocaine reduced the expression of the NMDA receptor subunits GluN1, GluN2A and GluN2B as well as of the AMPA GluA1 and GluA2 subunits. Cocaine also impaired their synaptic stability since the expression of the scaffolding proteins SAP102 and SAP97, critical for the anchoring of such receptors at the postsynaptic membrane, was reduced as well. The expression of PSD-95 and Arc/Arg3.1, which play structural and functional roles in glutamate neurons, was also similarly reduced. Such changes were not found in the whole homogenate, ruling out a translational effect of cocaine and implying, rather, an impaired synaptic retention at the active zones of the synapse. Notably, neither these critical glutamate determinants nor the density and morphology of the dendritic spines were altered in the mPFC of adult animals, suggesting that a single cocaine exposure selectively impairs the developmental trajectory of the glutamate synapse. These results indicate a dynamic impairment of mPFC glutamate homeostasis during a critical developmental window that persists for at least one week after a single cocaine administration. Our results identify dysfunctional glutamate synapse as a major contributor to the mechanisms that distinguish adolescent vs. adult outcomes of a single cocaine exposure.

Adolescent cocaine exposure induces prolonged synaptic modifications in medial prefrontal cortex of adult rats

Substance used during adolescent period increases the risk of psychiatric disorders in later life, but the underlying neural mechanisms remain unclear. We hypothesize that synaptic remodeling and changes of homeostasis in the medial prefrontal cortex (mPFC) following adolescent cocaine exposure may last for a long time, and these modifications may contribute to behavioral deficiencies in adulthood. To address this hypothesis, rats were exposed to cocaine hydrochloride from postnatal day 28 (P28) to P42. When reared to adulthood, rats were subjected to behavioral tests. On P75 and P76, cocaine-experienced rats exhibited increased locomotive and anxiety-like behaviors, as well as impaired non-selective attention. In the cocaine-experienced rats, both levels of synapse-related proteins (synapsin I and PSD-95) and density of synapse and dendrite spine in mPFC were significantly decreased when compared to controls. Unexpected, the expression of molecules related to oxidative stress, inflammation and apoptosis showed no significant changes in mPFC following adolescent cocaine exposure. These findings suggested that adolescent exposure to cocaine induce long-term modification on synapses in mPFC, which might contribute to long-term behavioral outcomes in adulthood.

Developmental Exposure to Cocaine Dynamically Dysregulates Cortical Arc/Arg3.1 Modulation in Response to a Challenge

During adolescence, the medial prefrontal cortex (mPFC) is still developing. We have previously shown that developmental cocaine exposure alters mPFC's ability to cope with challenging events. In this manuscript, we exposed rats developmentally treated with cocaine to a novelty task and analyzed the molecular changes of mPFC. Rats were exposed to cocaine from post-natal day (PND) 28 to PND 42 and sacrificed at PND 43, immediately after the novel object recognition (NOR) test. Cocaine-treated rats spent more time exploring the novel object than saline-treated counterparts, suggesting an increased response to novelty. The messenger RNA (mRNA) and protein levels of the immediate early gene Arc/Arg3.1 were reduced in both infralimbic (IL) and prelimbic (PL) cortices highlighting a baseline reduction of mPFC neuronal activity as a consequence of developmental exposure to cocaine. Intriguingly, significant molecular changes were observed in the IL, but not PL, cortex in response to the combination of cocaine exposure and test such as a marked upregulation of both Arc/Arg3.1 mRNA and protein levels only in cocaine-treated rats. As for proteins, such increase was observed only in the post-synaptic density and not in the whole homogenate, suggesting psychostimulant-induced changes in trafficking of Arc/Arg3.1 or an increased local translation. Notably, the same profile of Arc/Arg3.1 was observed for post-synaptic density (PSD)-95 leading to the possibility that Arc/Arg3.1 and PSD-95 bridge together to promote aberrant synaptic connectivity in IL cortex following repeated exposure to cocaine during brain development.

Region-specific effects of developmental exposure to cocaine on fibroblast growth factor-2 expression in the rat brain

RATIONALE

Adolescence is a period of high vulnerability to drugs of abuse and alterations of the proper developmental trajectory via psychostimulant exposure might change the physiological brain homeostasis.

OBJECTIVE

By microdissection of brain areas via punching, we investigated whether repeated exposure to cocaine during adolescence (from postnatal day 28 [PND28] to PND42) has altered fibroblast growth factor-2 (FGF-2) messenger RNA (mRNA) levels in selected brain subregions critical for the action of cocaine.

RESULTS

We found a reduction of FGF-2 mRNA levels in ventral tegmental area (VTA), where mesocortical and mesolimbic pathways originate. The analysis of the trophic factor levels in the distal projecting regions revealed a selective reduction of FGF-2 mRNA levels in infralimbic (IL) subregion of the medial prefrontal cortex (the terminal region of the mesocortical pathway) and in the nucleus accumbens core (cNAc) (the terminal region of the mesolimbic pathway). Last, we found reduced FGF-2 mRNA levels also in brain regions which, although in a different manner, contribute to the reward system, i.e., the central nucleus of amygdala (cAmy) and the ventral portion of hippocampus (vHip).

CONCLUSION

The widespread and coordinated reduction of FGF-2 mRNA levels across the brain's reward neurocircuitry might represent a defensive strategy set in motion to oppose to the psychostimulant properties of cocaine. Moreover, given the role of FGF-2 in modulating mood disorders, the reduced trophic support here observed might sustain the negative emotional state set in motion by repeated exposure to cocaine.

Redox-based epigenetic status in drug addiction: a potential contributor to gene priming and a mechanistic rationale for metabolic intervention

Alcohol and other drugs of abuse, including psychostimulants and opioids, can induce epigenetic changes: a contributing factor for drug addiction, tolerance, and associated withdrawal symptoms. DNA methylation is a major epigenetic mechanism and it is one of more than 200 methylation reactions supported by methyl donor S-adenosylmethionine (SAM). Levels of SAM are controlled by cellular redox status via the folate and vitamin B12-dependent enzyme methionine synthase (MS). For example, under oxidative conditions MS is inhibited, diverting its substrate homocysteine (HCY) to the trans sulfuration pathway. Alcohol, dopamine, and morphine, can alter intracellular levels of glutathione (GSH)-based cellular redox status, subsequently affecting SAM levels and DNA methylation status. Here, existing evidence is presented in a coherent manner to propose a novel hypothesis implicating the involvement of redox-based epigenetic changes in drug addiction. Further, we discuss how a “gene priming” phenomenon can contribute to the maintenance of redox and methylation status homeostasis under various stimuli including drugs of abuse. Additionally, a new mechanistic rationale for the use of metabolic interventions/redox-replenishers as symptomatic treatment of alcohol and other drug addiction and associated withdrawal symptoms is also provided. Hence, the current review article strengthens the hypothesis that neuronal metabolism has a critical bidirectional coupling with epigenetic changes in drug addiction exemplified by the link between redox-based metabolic changes and resultant epigenetic consequences under the effect of drugs of abuse.