Individual differences in responses to nicotine: tracking changes from adolescence to adulthood

Long-term impacts of prenatal maternal immune activation and postnatal maternal separation on maternal behavior in adult female rats: Relevance to postpartum mental disorders

Early life adversities are known to exert long-term negative impacts on psychological and brain functions in adulthood. The present work examined how a prenatal brain insult and a postnatal stressor independently or interactively influence the quality of maternal care of postpartum female rats and their cognitive and emotional functions, as a way to identify the behavioral dysfunctions underlying childhood trauma-induced postpartum mental disorders (as indexed by impaired maternal care). Sprague-Dawley female offspring born from mother rats exposed to polyinosinic:polycytidylic acid (PolyI:C, 4.0-6.0 mg/kg) intended to cause gestational maternal immune activation (MIA) or saline were subjected to a repeated maternal separation stress (RMS, 3 h/day) or no separation for 9 days in the first two weeks of life (a 2 × 2 design). When these offspring became mothers, their attentional filtering ability (as measured in the prepulse inhibition of acoustic startle reflex test), positive hedonic response (as measured in the sucrose preference test), and negative emotional response (as measured in the startle reflex and fear-potentiated startle test) were examined, along with their home-cage maternal behavior. Virgin littermates served as controls in all the behavioral tests except in maternal behavior. Results showed that mother rats who experienced RMS displayed impaired nest building and crouching/nursing activities. RMS also interacted with MIA to alter pup retrieval latency and startle reactivity, such that MIA-RMS dams demonstrated significantly slower pup retrieval latency and higher startle magnitude compared to either RMS-only and MIA-only mothers. MIA also disrupted attentional filtering ability, with significantly lower prepulse inhibition. However, neither prenatal MIA nor postnatal RMS impaired sucrose preference or the acquisition of fear-potentiated startle. These results indicate that prenatal stress and postnatal adversity could impair maternal behavior individually, and interact with each other, causing impairments in attention, emotion and maternal motivation.

An α7 nAChR approach for the baseline-dependent modulation of deviance detection in schizophrenia: A pilot study assessing the combined effect of CDP-choline and galantamine

BACKGROUND

Cognitive operations including pre-attentive sensory processing are markedly impaired in patients with schizophrenia (SCZ) but evidence significant interindividual heterogeneity, which moderates treatment response with nicotinic acetylcholine receptor (nAChR) agonists. Previous studies in healthy volunteers have shown baseline-dependency effects of the α7 nAChR agonist cytidine 5'-diphosphocholine (CDP-choline) administered alone and in combination with a nicotinic allosteric modulator (galantamine) on auditory deviance detection measured with the mismatch negativity (MMN) event-related potential (ERP).

AIM

The objective of this pilot study was to assess the acute effect of this combined α7 nAChR-targeted treatment (CDP-choline/galantamine) on speech MMN in patients with SCZ (N = 24) stratified by baseline MMN responses into low, medium, and high baseline auditory deviance detection subgroups.

METHODS

Patients with a stable diagnosis of SCZ attended two randomized, double-blind, placebo-controlled and counter-balanced testing sessions where they received a placebo or a CDP-choline (500 mg) and galantamine (16 mg) treatment. MMN ERPs were recorded during the presentation of a fast multi-feature speech MMN paradigm including five speech deviants. Clinical measures were acquired before and after treatment administration.

RESULTS

While no main treatment effect was observed, CDP-choline/galantamine significantly increased MMN amplitudes to frequency, duration, and vowel speech deviants in low group individuals. Individuals with higher positive and negative symptom scale negative, general, and total scores expressed the greatest MMN amplitude improvement following CDP-choline/galantamine.

CONCLUSIONS

These baseline-dependent nicotinic effects on early auditory information processing warrant different dosage and repeated administration assessments in patients with low baseline deviance detection levels.

Impact of acute nicotine exposure on monoaminergic systems in adolescent and adult male and female rats

Adolescence is a period of risk for beginning tobacco addiction. Differential neural response to nicotine in adolescents vs. adults may help explain the increased vulnerability to nicotine self-administration seen with adolescent onset. We indexed the effects of acute nicotine ditartrate (0.4 mg/kg, salt weight) administration on dopamine (DA) and serotonin (5HT) as well as the DA metabolite 3,4-dihydroxyphenylacetic acid (DOPAC) in several brain regions (nucleus accumbens, striatum and frontal cortex) of 6-week old (adolescent) and 10-week old (young adult) Sprague-Dawley rats. When nicotine was administered DA concentrations in the accumbens were significantly higher in adults than in adolescents, whereas there was no age-related difference without nicotine. However neither age group showed a significant effect of nicotine vs. age-matched controls. DA turnover in the accumbens was significantly greater in adolescent females in response to nicotine, but adult females did not show this effect and neither did males of either age group. DA turnover in the striatum was significantly higher in adolescents than adults regardless of nicotine administration. In the frontal cortex, there was a more complex effect. Without nicotine, adult male rats had higher DA concentrations than adolescent males, whereas female rats did not differ from adolescent to adult ages. When given nicotine, the age effect was no longer seen in males. However, there was not a significant effect of nicotine vs. age-matched controls in either age group. No age or nicotine effects were seen in females. 5HT in the accumbens was significantly increased by nicotine administration in adults but not in adolescents. Altered neural responsivity of adolescents to nicotine-induced neural effects particularly in accumbens DA and 5HT may be related to the increased nicotine dose concentrations they self-administer.

The impact of adolescent nicotine exposure on alcohol use during adulthood: The role of neuropeptides

Nicotine and alcohol abuse and co-dependence represent major public health crises. Indeed, previous research has shown that the prevalence of alcoholism is higher in smokers than in non-smokers. Adolescence is a susceptible period of life for the initiation of nicotine and alcohol use and the development of nicotine-alcohol codependence. However, there is a limited number of pharmacotherapeutic agents to treat addiction to nicotine or alcohol alone. Notably, there is no effective medication to treat this comorbid disorder. This chapter aims to review the early nicotine use and its impact on subsequent alcohol abuse during adolescence and adulthood as well as the role of neuropeptides in this comorbid disorder. The preclinical and clinical findings discussed in this chapter will advance our understanding of this comorbid disorder's neurobiology and lay a foundation for developing novel pharmacotherapies to treat nicotine and alcohol codependence.

CDP-choline and galantamine, a personalized α7 nicotinic acetylcholine receptor targeted treatment for the modulation of speech MMN indexed deviance detection in healthy volunteers: a pilot study

RATIONALE

The combination of CDP-choline, an α7 nicotinic acetylcholine receptor (α7 nAChR) agonist, with galantamine, a positive allosteric modulator of nAChRs, is believed to counter the fast desensitization rate of the α7 nAChRs and may be of interest for schizophrenia (SCZ) patients. Beyond the positive and negative clinical symptoms, deficits in early auditory prediction-error processes are also observed in SCZ. Regularity violations activate these mechanisms that are indexed by electroencephalography-derived mismatch negativity (MMN) event-related potentials (ERPs) in response to auditory deviance.

OBJECTIVES/METHODS

This pilot study in thirty-three healthy humans assessed the effects of an optimized α7 nAChR strategy combining CDP-choline (500 mg) with galantamine (16 mg) on speech-elicited MMN amplitude and latency measures. The randomized, double-blinded, placebo-controlled, and counterbalanced design with a baseline stratification method allowed for assessment of individual response differences.

RESULTS

Increases in MMN generation mediated by the acute CDP-choline/galantamine treatment in individuals with low baseline MMN amplitude for frequency, intensity, duration, and vowel deviants were revealed.

CONCLUSIONS

These results, observed primarily at temporal recording sites overlying the auditory cortex, implicate α7 nAChRs in the enhancement of speech deviance detection and warrant further examination with respect to dysfunctional auditory deviance processing in individuals with SCZ.

A drug-drug conditioning paradigm reveals multiple antipsychotic-nicotine interactions

Clinical studies indicate a reciprocal impact between nicotine use and antipsychotic medications in patients with schizophrenia. The present study used a conditioned avoidance response (CAR) test (a behavioral test of antipsychotic effect) and examined the specific drug-drug interactions between nicotine and haloperidol or clozapine. Following acquisition of the avoidance response, rats were first tested under either vehicle, nicotine (0.2, 0.4 mg/kg, sc), haloperidol (0.025, 0.05 mg/kg, sc), clozapine (5.0, 10.0 mg/kg, sc), or a combination of nicotine and haloperidol or nicotine and clozapine for seven consecutive days. Afterward, they were challenged with nicotine (0.2 mg/kg), haloperidol (0.025 mg/kg), or clozapine (5.0 mg/kg) in the CAR to assess if haloperidol or clozapine affected the behavioral effect of nicotine on avoidance response and if nicotine altered the avoidance suppressive effect of haloperidol and clozapine. During the seven avoidance drug test days, nicotine did not alter the avoidance suppressive effect of haloperidol or clozapine. However, in the challenge test, prior nicotine treatment (0.2 mg/kg) attenuated haloperidol's (0.05 mg/kg) sensitized effect on avoidance response. On the other hand, prior haloperidol treatment increased nicotine's (0.2 mg/kg) avoidance disruptive effect, and even engendered nicotine 0.4 mg/kg to exhibit an "acquired" avoidance suppressive effect. The combined nicotine and clozapine treatment did not produce any detectable interactive effects on avoidance response and motor activity. These findings suggest that nicotine is capable of altering the long-term antipsychotic efficacy of haloperidol, while haloperidol can alter the behavioral effects of nicotine. Clozapine and nicotine are less likely to influence each other.

The Serotonin 2C Receptor Agonist Lorcaserin Attenuates Intracranial Self-Stimulation and Blocks the Reward-Enhancing Effects of Nicotine

Lorcaserin, a serotonin (5-hydroxytryptamine, 5-HT) 2C receptor agonist, was recently approved for the treatment of obesity. We previously suggested that 5-HT2C receptor agonists affect reward processes and reduce the rewarding effects of drugs of abuse. Here, we determined whether lorcaserin (1) decreases responding for brain stimulation reward (BSR) and (2) prevents nicotine from enhancing the efficacy of BSR. Rats were trained on the intracranial self-stimulation (ICSS) paradigm to nosepoke for BSR of either the dorsal raphé nucleus or left medial forebrain bundle. In Experiment 1, lorcaserin (0.3-1.0 mg/kg) dose-dependently reduced the efficacy of BSR. This effect was blocked by prior administration of the 5-HT2C receptor antagonist SB242084. In Experiment 2, separate groups of rats received saline or nicotine (0.4 mg/kg) for eight sessions prior to testing. Although thresholds were unaltered in saline-treated rats, nicotine reduced reward thresholds. An injection of lorcaserin (0.3 mg/kg) prior to nicotine prevented the reward-enhancing effect of nicotine across multiple test sessions. These results demonstrated that lorcaserin reduces the rewarding value of BSR and also prevents nicotine from facilitating ICSS. Hence, lorcaserin may be effective in treating psychiatric disorders, including obesity and nicotine addiction, by reducing the value of food or drug rewards.

Modulation of auditory deviance detection by acute nicotine is baseline and deviant dependent in healthy nonsmokers: a mismatch negativity study

OBJECTIVE

Cognitive enhancement resulting from nicotinic acetylcholine receptor stimulation may be evidenced by increased efficiency of the auditory-frontal cortex network of auditory discrimination, which is impaired in schizophrenia, a cognitive disorder associated with excessive tobacco use. Investigating automatic (preattentive) detection of acoustic change with the mismatch negativity (MMN) brain event-related potential in response to nicotine in individuals with varying baseline levels of auditory discrimination may provide useful insight into the cholinergic regulation of this neural network and its potential amelioration with novel nicotinic agents.

METHODS

Sixty healthy, non-smoking male volunteers were presented with an 'optimal' multi-feature MMN paradigm in a randomized, placebo controlled double-blind design with 6 mg of nicotine gum.

RESULTS

Participants with low, medium, and high baseline amplitudes responded differently to nicotine (vs. placebo), and nicotine response was feature specific. Whereas MMN in individuals with high amplitudes was diminished by nicotine, MMN increased in those with low amplitudes. Nicotine effects were not shown in medium amplitude participants.

CONCLUSIONS

These findings provide preliminary support for the role of nicotinic neurotransmission in sensory memory processing of auditory change and suggest that nicotinic receptor modulation can both enhance and diminish change detection, depending on baseline MMN and its eliciting stimulus feature.

Neonatal MK-801 treatment differentially alters the effect of adolescent or adult MK-801 challenge on locomotion and PPI in male and female rats

Schizophrenia is a neurodevelopmental disorder and is typically "triggered" by subsequent insults in life. The N-methyl-D-aspartate (NMDA) receptor antagonist dizocilpine (MK-801) induces locomotor hyperactivity and prepulse inhibition (PPI) deficits, which can mimic the schizophrenia phenotype. In this experiment, we assessed whether neonatal exposure to MK-801 (postnatal days 5-14) could induce sensitization to both hyperactivity and PPI deficit caused by later-life acute MK-801 treatment during adolescence or adulthood. Our results showed that the hyperactivity induced by an acute MK-801 challenge was enhanced in male and female rats after neonatal MK-801 treatment. Notably, in the PPI test, adult female rats neonatally exposed to MK-801 exhibited a significantly greater reduction in PPI in response to acute MK-801 administration, whereas male rats receiving neonatal MK-801 treatment expressed attenuated PPI disruption in adulthood. Our data indicate that a combination of neonatal and later-life NMDA receptor blockades could induce sensitization in the locomotor activity of both sexes in adolescence and adulthood. In addition, a sex difference was observed in the effects of this treatment regime on PPI.

Effects of intravenous nicotine on prepulse inhibition in smokers and non-smokers: relationship with familial smoking

RATIONALE

The reinforcing properties of nicotine may be, in part, derived from its ability to enhance certain forms of cognitive processing. Several animal and human studies have shown that nicotine increases prepulse inhibition (PPI) of the startle reflex. However, it remains unclear whether these effects are related to smoking susceptibility.

OBJECTIVES

The current study examined the effects of intravenously delivered nicotine on PPI in smokers and non-smokers, as well as its association with a quantitative index of familial smoking.

METHODS

The sample consisted of 30 non-smokers and 16 smokers, who completed an initial assessment, followed on a separate day by a laboratory assessment of PPI prior to and following each of two intravenous nicotine infusions. Separate doses were used in smoker and non-smoker samples.

RESULTS

Analyses indicated that both nicotine infusions acutely enhanced PPI among non-smokers, and this enhancement was positively related to the degree of smoking among first and second-degree relatives. Smokers also displayed PPI enhancement after receiving the first infusion, but this effect was unrelated to familial smoking.

CONCLUSIONS

These data suggest that the PPI paradigm may have utility as an endophenotype for cognitive processes which contribute to smoking risk.

Iptakalim Preferentially Decreases Nicotine-induced Hyperlocomotion in Phencyclidine-sensitized Rats: A Potential Dual Action against Nicotine Addiction and Psychosis

Objective

Iptakalim is a putative ATP-sensitive potassium (K_ATP) channel opener. It is also a novel nicotinic acetylcholine receptor (nAChR) blocker and can antagonize nicotine-induced increase in dopamine release in the nucleus accumbens. Our recent work also shows that iptakalim exhibits a clozapine-like atypical antipsychotic profile, indicating that iptakalim may possess a dual action against nicotine addiction and schizophrenia.

Methods

The present study examined the potential therapeutic effects of iptakalim on nicotine use in schizophrenia. We created an animal model of comorbidity of nicotine addiction and schizophrenia by injecting male Sprague-Dawley rats with nicotine (0.40 mg/kg, subcutaneously[sc]) or saline, in combination with phencyclidine (PCP, 3.0 mg/kg, sc) or saline daily for 14 consecutive days.

Results

During the PCP/nicotine sensitization phase, PCP and nicotine independently increased motor activity over time. PCP also disrupted prepulse inhibition (PPI) of acoustic startle response. Acute nicotine treatment attenuated the PCP-induced hyperlocomotion and PCP-induced disruption of PPI, whereas repeated nicotine treatment potentiated these effects. Importantly, pretreatment with iptakalim (10-20 mg/kg, intraperitoneally) reduced nicotine-induced hyperlocomotion in a dose-dependent fashion. This reduction effect was highly selective: it was more effective in rats previously sensitized to the combination of PCP and nicotine, but less effective in rats sensitized to saline, nicotine alone or PCP alone.

Conclusion

To the extent that the combined nicotine and PCP sensitization mimics comorbid nicotine addiction in schizophrenia, the preferential inhibitory effect of iptakalim on nicotine-induced hyperlocomotion suggests that iptakalim may be a potential useful drug for the treatment nicotine abuse in schizophrenia.

Startle reactivity and prepulse inhibition in prodromal and early psychosis: effects of age, antipsychotics, tobacco and cannabis in a vulnerable population

The use of biomarkers in the study of the prodrome and first episode of psychosis provides a means of not only identifying individuals at greatest risk for psychosis but also understanding neurodevelopmental abnormalities early in the course of illness. Prepulse inhibition (PPI), a marker that is deficient in schizophrenia and after developmental manipulations in animal models, was assessed in 75 early psychosis (EP), 89 at risk (AR) for psychosis and 85 comparison subjects (CS) at baseline and 6 months. Consistent with findings in chronic schizophrenia, PPI was stable with repeated assessment and EP subjects had reduced PPI but this was most evident in tobacco smokers. A significant positive PPI and age association in AR and EP samples, but not CS, demonstrated potential neurodevelopmental differences in early psychosis. Unexpected findings included the fact that medication naive EP subjects, as well as AR subjects who later developed psychosis, had greater PPI, introducing the possibility of early compensatory changes that diverge from findings in chronic patients. In addition, subjects with a history of cannabis use had greater startle reactivity while EP and AR subjects who used cannabis and were also taking an antipsychotic had greater PPI, again highlighting the potentially important cannabis/psychosis association.

Multiple 'hits' during postnatal and early adulthood periods disrupt the normal development of sensorimotor gating ability in rats

In the present study, we evaluated a multiple-hit animal model of schizophrenia in an attempt to capture the complex interactions among various adverse developmental factors in schizophrenia. Sprague-Dawley rats were assigned to receive either repeated daily 3-h maternal separation for eight days (first 'hit') on postnatal days (PND) 3 to 10, and/or avoidance conditioning for six days (second 'hit') on PND 49-56, and/or repeated phencyclidine treatment (third 'hit', 3.0 mg/kg, sc) immediately after each daily avoidance conditioning. Prepulse inhibition (PPI) of acoustic startle reflex was assessed at late adolescence (PND 41-43) and early adulthood (PND 62-63). The change in %PPI from the adolescence phase to adulthood phase was used to index the maturation-related improvement of sensorimotor gating ability. Maternal separation, avoidance conditioning and PCP treatment had a complex three-way interaction on the functional improvement of sensorimotor gating. Maternal separation impaired PPI improvement preferentially in the saline rats that were not subjected to avoidance conditioning. Avoidance conditioning had no effect on PPI improvement in the non-maternally separated rats, but restored the maternal separation-induced disruption. However, this restoration effect was abolished by PCP treatment. The present study also identified a number of behavioral, emotional and learning abnormalities caused by these three developmental insults which may precede their interactive disruption of normal development of sensorimotor gating ability.

Nicotine: alcohol reward interactions

It is well established that the continued intake of drugs of abuse is reinforcing-that is repeated consumption increases preference. This has been shown in some studies to extend to other drugs of abuse; use of one increases preference for another. In particular, the present review deals with the interaction of nicotine and alcohol as it has been shown that smoking is a risk factor for alcoholism and alcohol use is a risk factor to become a smoker. The review discusses changes in the brain caused by chronic nicotine and chronic alcohol intake to approach the possible mechanisms by which one drug increases the preference for another. Chronic nicotine administration was shown to affect nicotine receptors in the brain, affecting not only receptor levels and distribution, but also receptor subunit composition, thus affecting affinity to nicotine. Other receptor systems are also affected among others catecholamine, glutamate, GABA levels and opiate and cannabinoid receptors. In addition to receptor systems and transmitters, there are endocrine, metabolic and neuropeptide changes as well induced by nicotine. Similarly chronic alcohol intake results in changes in the brain, in multiple receptors, transmitters and peptides as discussed in this overview and also illustrated in the tables. The changes are sex and age-dependent-some changes in males are different from those in females and in general adolescents are more sensitive to drug effects than adults. Although nicotine and alcohol interact-not all the changes induced by the combined intake of both are additive-some are opposing. These opposing effects include those on locomotion, acetylcholine metabolism, nicotine binding, opiate peptides, glutamate transporters and endocannabinoid content among others. The two compounds lower the negative withdrawal symptoms of each other which may contribute to the increase in preference, but the mechanism by which preference increases-most likely consists of multiple components that are not clear at the present time. As the details of induced changes of nicotine and alcohol differ, it is likely that the mechanisms of increasing nicotine preference may not be identical to that of increasing alcohol preference. Stimulation of preference of yet other drugs may again be different -representing one aspect of drug specificity of reward mechanisms.

Inter-individual differences in neurobiology as vulnerability factors for affective disorders: implications for psychopharmacology

Susceptibility to affective disorders is individually different, and determined both by genetic variance and life events that cause significant differences in the CNS structure and function between individual subjects. Therefore it is plausible that search for the inter-individual differences in endophenotypes that mediate the effects of causal factors, both genetic and environmental, will reveal the substrates for vulnerability, help to clarify pathogenetic mechanisms, and possibly aid in developing strategies to discover better, more personalized treatments. This review first examines comparatively a number of animal models of human affect and affect-related disorders that rely on persistent inter-individual differences, and then highlights some of the neurobiological findings in these models that are compatible with much of research in human behavioural and personality traits. Many behaviours occur in specific combinations in several models, but often remarkable dissociations are observed, providing a variety of constellations of traits. It is concluded that more systematic comparative experimentation on behaviour and neurobiology in different models is warranted to reveal possible "building blocks" of affect-related personality common in animals and humans. Looking into the perspectives in psychopharmacology the focus is placed on probable associations of inter-individual differences with brain structure and function, personality and coping strategies, and psychiatric vulnerability, highlighting some unexpected interactions between vulnerability endophenotypes, adverse life events, and behavioural traits. It is argued that further studies on inter-individual differences in affect and underlying neurobiology should include formal modeling of their epistatic, hierarchical and dynamic nature.