Effects of nicotine pretreatment on dopaminergic and behavioral responses to conditioned fear stress in rats: dissociation of biochemical and behavioral effects

65 years of research on dopamine's role in classical fear conditioning and extinction: A systematic review

Dopamine, a catecholamine neurotransmitter, has historically been associated with the encoding of reward, whereas its role in aversion has received less attention. Here, we systematically gathered the vast evidence of the role of dopamine in the simplest forms of aversive learning: classical fear conditioning and extinction. In the past, crude methods were used to augment or inhibit dopamine to study its relationship with fear conditioning and extinction. More advanced techniques such as conditional genetic, chemogenic and optogenetic approaches now provide causal evidence for dopamine's role in these learning processes. Dopamine neurons encode conditioned stimuli during fear conditioning and extinction and convey the signal via activation of D1-4 receptor sites particularly in the amygdala, prefrontal cortex and striatum. The coordinated activation of dopamine receptors allows for the continuous formation, consolidation, retrieval and updating of fear and extinction memory in a dynamic and reciprocal manner. Based on the reviewed literature, we conclude that dopamine is crucial for the encoding of classical fear conditioning and extinction and contributes in a way that is comparable to its role in encoding reward.

Smoking trajectories from adolescence to early adulthood as a longitudinal predictor of mental health in adulthood: evidence from 21 years of a nationally representative cohort

AIMS

To measure the prospective relationship between smoking trajectories from adolescence to young adulthood and mental health in later adulthood and test whether this relationship was mediated by concurrent co-use of alcohol and marijuana.

DESIGN

Longitudinal study using data drawn from rounds 1 to 18 of the National Longitudinal Survey of Youth 1997 (NLSY97), a nationally representative cohort study spanning 21 years.

SETTING

United States.

PARTICIPANTS

The analytical sample included those who completed survey items about smoking behaviors on at least half the data collection opportunities in adolescence and young adulthood (n = 8570, 48.9% female, 66.2% white).

MEASUREMENTS

Mental health in adulthood was measured using the five-item Mental Health Inventory (MHI-5; range = 0-100) at round 18. Seven trajectories of smoking from adolescence to young adulthood were identified by group-based multi-trajectory modeling, using data over 11 years from rounds 1 to 11.

FINDINGS

Late-onset moderate smokers [β = -1.95, 95% confidence interval (CI) = -3.61 to -0.29], late-onset accelerated smokers (β = -2.53, 95% CI = -4.28 to -0.78), early-onset heavy smokers (β = -3.72, 95% CI = -5.59 to -1.85) and early-onset moderate smokers (β = -2.66, 95% CI = -4.48 to -0.84) showed poorer regression-adjusted mean MHI-5 scores in later adulthood than stable abstainers, even after controlling for baseline mental health and covariates. Whether or not a difference in MHI-5 scores was present between quitters and stable abstainers was inconclusive. The concurrent co-use of alcohol and marijuana in young adulthood significantly mediated the relationship between smoking trajectory and mental health.

CONCLUSIONS

Continued smoking, especially early-onset and heavy smoking from adolescence to young adulthood, appears to increase the risk of poor mental health later in mid-adulthood, and quitting smoking in young adulthood may mitigate such risk even among early-onset smokers. Mediation analyses underscore the role of using multiple substances in this pathway.

Cigarette Smoking and Depressive Symptoms: A Longitudinal Study of Adolescents and Young Adults

Cigarette smoking and depressive symptoms have been shown to be related in previous research. This paper examined the relationship between cigarette smoking and depressive symptoms in a longitudinal sample of 688 adolescents and young adults through surveys conducted over 13 yr. The results indicate that a history of earlier cigarette smoking in adolescence predicts later depressive symptoms in the late twenties. The study also suggests that depressive symptoms during adolescence predict cigarette smoking in the late twenties but not above and beyond prior smoking. These results help clarify and expand current knowledge on the links between cigarette smoking and depression. The results point to several clinical implications for treatment of both cigarette smoking and depressive symptoms among both adolescents and young adults.

Acute administration of nicotine into the higher order auditory Te2 cortex specifically decreases the fear-related charge of remote emotional memories

Nicotine elicits several behavioural effects on mood as well as on stress and anxiety processes. Recently, it was found that the higher order components of the sensory cortex, such as the secondary auditory cortex Te2, are essential for the long-term storage of remote fear memories. Therefore, in the present study, we examined the effects of acute nicotine injection into the higher order auditory cortex Te2, on the remote emotional memories of either threat or incentive experiences in rats. We found that intra-Te2 nicotine injection decreased the fear-evoked responses to a tone previously paired with footshock. This effect was cue- and dose-specific and was not due to any interference with auditory stimuli processing, innate anxiety and fear processes, or with motor responses. Nicotine acts acutely in the presence of threat stimuli but it did not determine the permanent degradation of the fear-memory trace, since memories tested one week after nicotine injection were unaffected. Remarkably, nicotine did not affect the memory of a similar tone that was paired to incentive stimuli. We conclude from our results that nicotine, when acting acutely in the auditory cortex, relieves the fear charge embedded by learned stimuli.

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Nicotine reliefs fear memories.

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Nicotine acts on long-term memories.

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Nicotine modulates memory in auditory cortex.

Stress during the gestational period modifies pups' emotionality parameters and favors preference for morphine in adolescent rats

Experimental animal studies have shown that early life periods are highly vulnerable to environmental factors, which may exert prolonged impact on HPA axis function and on subsequent neurochemical and behavioral responses in adulthood. Here we evaluated the influence of environmental stressful situations in two different early life stages on stress-related behaviors, and morphine-conditioned place preference (CPP), which is indicative of addiction. While in the gestational stress (Gest-S) dams were exposed to daily sessions of chronic mild stress (CMS) for 2 weeks, in the postnatal stress (post-NS) the offspring were exposed daily to neonatal isolation from postnatal day (PND) 2 to PND 9 for 60 min. Animals exposed to post-NS showed lesser anxiety in different behavioral paradigms (elevated plus maze-EPM and defensive burying test-DBT) as well as increased exploratory behavior (open-field task-OFT), and no preference for morphine in CPP. In contrast, animals exposed to Gest-S showed increased corticosterone plasma levels together with anxiety symptoms and greater preference for morphine following three days of drug withdrawal. Our findings indicate that the gestational period is critical for stress, whose effects may be manifest throughout life. On the other hand, post-NS can trigger neuroadaptations able to overcome emotional consequences of early life. We hypothesized that Gest-S is able to modify responses to opioids along adulthood, which may facilitate development of addiction to these drugs.

Effects of nicotine dependence and depressive symptoms on smoking cessation: a longitudinal study among adolescents

INTRODUCTION

Nicotine dependence has been shown to hamper successful smoking cessation in adolescents. Nicotine dependence and depression are highly comorbid, but the relation between depression and smoking cessation is not yet fully understood. Therefore, the present study examines both the longitudinal reciprocal relation between nicotine dependence and depressive symptoms, and the longitudinal effect of these factors on successful smoking cessation and number of quit attempts.

METHODS

A 2-wave longitudinal study was conducted among 535 adolescents aged 13-18. Written self-report questionnaires were administered in a classroom setting. Two models were tested, examining the mutual relation between nicotine dependence and depressive symptoms, as well as the predictive value of these factors on smoking cessation (n = 535), and number of quit attempts (n = 473) 1 year later.

RESULTS

Adolescents with more depressive symptoms have significantly higher levels of nicotine dependence 1 year later. Higher levels of nicotine dependence negatively predicted subsequent successful smoking cessation, whereas depressive symptoms did not. In contrast, depressive symptoms predicted a higher number of unsuccessful quit attempts in the following year, whereas nicotine dependence did not.

CONCLUSIONS

The findings suggest that adolescents tend to smoke cigarettes in order to diminish their depressive feelings, which might provide some support for the self-medication theory. Smoking cessation programs aiming at adolescents should not only focus on symptoms of nicotine dependence but should also pay attention to depressive feelings, since these feelings are related to a higher number of unsuccessful quit attempts.

Anxiolytic-like effect of neuropeptide S in the rat defensive burying

Neuropeptide S (NPS) has been recently identified as the endogenous ligand of a previously orphan G-protein-coupled receptor now named NPSR. Both NPS and its receptor are expressed in the brain, where they modulate different functions. In particular, it has been demonstrated that intracerebroventricular (i.c.v.) injection of NPS in rodents increases wakefulness and promotes anxiolytic-like effects. In the present study we used the defensive burying (DB) test in rats to further investigate the action of human NPS (0.1-10 nmol, i.c.v.) on anxiety-related behaviors. Diazepam (1.5mg/kg, i.p.) and caffeine (20mg/kg, i.p.) were used in parallel experiments as standard anxiolytic and anxiogenic drugs, respectively. None of the tested drugs produced statistical differences in the latency to contact the probe, burying behavior latency, number of shocks received or immobility/freezing duration. Caffeine increased cumulative burying behavior and the buried bedding height in a statistically significant manner thus promoting anxiogenic like effects. Opposite results were obtained with diazepam that significantly reduced these behavioral parameters. The anxiolytic-like action of diazepam was mimicked by NPS that reduced cumulative burying behavior in a dose dependent manner. Collectively, robust anxiolytic-like effects were recorded in response to NPS in the DB test. These results are of particular interest since the outcome of this assay is marginally influenced by drug effects on locomotor activity. In conclusion, we provide further evidence that NPS evokes genuine anxiolytic-like effects in the rat; therefore NPSR selective agonists are worthy of development as innovative drugs for the treatment of anxiety disorders.

Activation of nicotinic acetylcholine receptors increases the frequency of spontaneous GABAergic IPSCs in rat basolateral amygdala neurons

The basolateral amygdala (BLA) is a critical component of the amygdaloid circuit, which is thought to be involved in fear conditioned responses. Using whole cell patch-clamp recording, we found that activation of nicotinic acetylcholine receptors (nAChRs) leads to an action potential-dependent increase in the frequency of spontaneous GABAergic currents in principal neurons in the BLA. These spontaneous GABAergic currents were abolished by a low-Ca2+/high-Mg2+ bathing solution, suggesting that they are spontaneous inhibitory postsynaptic currents (sIPSCs). Blockade of ionotropic glutamate receptors did not prevent this increased frequency of sIPSCs nor did blockade of alpha7 nAChRs. Among the nAChR agonists tested, cystisine was more effective at increasing the frequency of the sIPSCs than nicotine or 1,1-dimethyl-4-phenyl piperazinium iodide, consistent with a major contribution of beta4 nAChR subunits. The nicotinic antagonist, dihydro-beta-erythroidine, was less effective than d-tubocurarine in blocking the increased sIPSC frequency induced by ACh, suggesting that alpha4-containing nAChR subunits do not play a major role in the ACh-induced increased sIPSC frequency. Although alpha2/3/4/7 and beta2/4 nAChR subunits were found in the BLA by RT-PCR, the agonist and antagonist profiles suggest that the ACh-induced increase in sIPSC frequency involves predominantly alpha3beta4-containing nAChR subunits. Consistent with this, alpha-conotoxin-AuIB, a nAChR antagonist selective for the alpha3beta4 subunit combination, inhibited the ACh-induced increase in the frequency of sIPSCs. The observations suggest that nicotinic activation increases the frequency of sIPSCs in the BLA by acting mainly on alpha3beta4-containing nicotinic receptors on GABAergic neurons and may play an important role in the modulation of synaptic transmission in the amygdala.

The neurobiology and control of anxious states

Fear is an adaptive component of the acute "stress" response to potentially-dangerous (external and internal) stimuli which threaten to perturb homeostasis. However, when disproportional in intensity, chronic and/or irreversible, or not associated with any genuine risk, it may be symptomatic of a debilitating anxious state: for example, social phobia, panic attacks or generalized anxiety disorder. In view of the importance of guaranteeing an appropriate emotional response to aversive events, it is not surprising that a diversity of mechanisms are involved in the induction and inhibition of anxious states. Apart from conventional neurotransmitters, such as monoamines, gamma-amino-butyric acid (GABA) and glutamate, many other modulators have been implicated, including: adenosine, cannabinoids, numerous neuropeptides, hormones, neurotrophins, cytokines and several cellular mediators. Accordingly, though benzodiazepines (which reinforce transmission at GABA(A) receptors), serotonin (5-HT)(1A) receptor agonists and 5-HT reuptake inhibitors are currently the principle drugs employed in the management of anxiety disorders, there is considerable scope for the development of alternative therapies. In addition to cellular, anatomical and neurochemical strategies, behavioral models are indispensable for the characterization of anxious states and their modulation. Amongst diverse paradigms, conflict procedures--in which subjects experience opposing impulses of desire and fear--are of especial conceptual and therapeutic pertinence. For example, in the Vogel Conflict Test (VCT), the ability of drugs to release punishment-suppressed drinking behavior is evaluated. In reviewing the neurobiology of anxious states, the present article focuses in particular upon: the multifarious and complex roles of individual modulators, often as a function of the specific receptor type and neuronal substrate involved in their actions; novel targets for the management of anxiety disorders; the influence of neurotransmitters and other agents upon performance in the VCT; data acquired from complementary pharmacological and genetic strategies and, finally, several open questions likely to orientate future experimental- and clinical-research. In view of the recent proliferation of mechanisms implicated in the pathogenesis, modulation and, potentially, treatment of anxiety disorders, this is an opportune moment to survey their functional and pathophysiological significance, and to assess their influence upon performance in the VCT and other models of potential anxiolytic properties.

Smoking, stress, and negative affect: correlation, causation, and context across stages of smoking

This transdisciplinary review of the literature addresses the questions, Do stress and negative affect (NA) promote smoking? and Does smoking genuinely relieve stress and NA? Drawing on both human and animal literatures, the authors examine these questions across three developmental stages of smoking--initiation, maintenance, and relapse. Methodological and conceptual distinctions relating to within- and between-subjects levels of analyses are emphasized throughout the review. Potential mechanisms underlying links between stress and NA and smoking are also reviewed. Relative to direct-effect explanations, the authors argue that contextual mediator-moderator approaches hold greater potential for elucidating complex associations between NA and stress and smoking. The authors conclude with recommendations for research initiatives that draw on more sophisticated theories and methodologies.

Donepezil for memory dysfunction in schizophrenia

A case is reported of a 54-year-old female patient with schizophrenia and cognitive impairment. Her memory dysfunction improved following the addition of donepezil to quetiapine. The possible implications for future studies are reviewed.

Effect of nicotine and nicotinic receptors on anxiety and depression

Nicotine has been shown to have effects on anxiety and depression in both human and animal studies. These studies suggest that nicotinic acetylcholine receptors (nAChRs) can modulate the function of pathways involved in stress response, anxiety and depression in the normal brain, and that smoking can result in alterations of anxiety level and mood. The effects of nicotine are complex however, and nicotine treatment can be either anxiolytic or anxiogenic depending on the anxiety model tested, the route of nicotine administration and the time course of administration. The paradoxical effects of nicotine on emotionality are likely due to the broad expression of nAChRs throughout the brain, the large number of nAChR subtypes that have been identified and the ability of nicotine treatment to both activate and desensitize nAChRs. Activation of nAChRs has been shown to modulate many systems associated with stress response including stress hormone pathways, monoaminergic transmission and release of classical neurotransmitters throughout the brain. Local administration studies in animals have identified brain areas that may be involved in the anxiogenic and anxiolytic actions of nicotine including the lateral septum, the dorsal raphe nuclei, the mesolimbic dopamine system and the hippocampus. The ensemble of studies to date suggest that under certain conditions nicotine can act as an anxiolytic and an antidepressant, but that following chronic use, adaptations to nicotine can occur resulting in increased anxiety and depression following withdrawal.