Repeated nicotine exposure in adolescent rats: Reduction of medial habenular activity and augmentation of nicotine preference

Nicotine neurotoxicity exacerbation following engineered Ag and Cu (50-60 nm) nanoparticles intoxication. Neuroprotection with nanowired delivery of antioxidant compound H-290/51 together with serotonin 5-HT3 receptor antagonist ondansetron

Nicotine abuse is frequent worldwide leading to about 8 millions people die every year due to tobacco related diseases. Military personnel often use nicotine smoking that is about 12.8% higher than civilian populations. Nicotine smoking triggers oxidative stress and are linked to several neurodegenerative diseases such as Alzheimer's disease. Nicotine neurotoxicity induces significant depression and oxidative stress in the brain leading to neurovascular damages and brain pathology. Thus, details of nicotine neurotoxicity and factors influencing them require additional investigations. In this review, effects of engineered nanoparticles from metals Ag and Cu (50-60 nm) on nicotine neurotoxicity are discussed with regard to nicotine smoking. Military personnel often work in the environment where chances of nanoparticles exposure are quite common. In our earlier studies, we have shown that nanoparticles alone induces breakdown of the blood-brain barrier (BBB) and exacerbates brain pathology in animal models. In present investigation, nicotine exposure in with Ag or Cu nanoparticles intoxicated group exacerbated BBB breakdown, induce oxidative stress and aggravate brain pathology. Treatment with nanowired H-290/51 a potent chain-breaking antioxidant together with nanowired ondansetron, a potent 5-HT3 receptor antagonist significantly reduced oxidative stress, BBB breakdown and brain pathology in nicotine exposure associated with Ag or Cu nanoparticles intoxication. The functional significance of this findings and possible mechanisms of nicotine neurotoxicity are discussed based on current literature.

Determining nicotine-related behavior changes in juvenile female rats through long-term maternal nicotine exposure

Nicotine replacement therapy (NRT) has been developed as a drug therapy for smoking cessation and has been considered a safe alternative to smoking during pregnancy. However, the effects of long-term nicotine exposure via NRT on the fetus are still being debated. Here, we determined the effects of long-term maternal nicotine exposure in gestation and lactation on nicotine-related behavior and drug vulnerability in dams and offspring rats. To expose long-term nicotine, on gestation day 14, pregnant rats were implanted with osmotic minipumps releasing nicotine tartrate (6 mg/kg/day, subcutaneously, equivalent to 2 mg nicotine-freebase) for 28 days. The concentration of cotinine in blood was 373.0 ± 109.0 ng/ml in dams and 12.50 ± 1.19 ng/ml in offspring rats. In dams, we found no significant differences in anxiety-like behaviors and various maternal behaviors such as touching, sniffing, pup licking, laying on pups, and retrieval between saline- and nicotine-exposed groups. Adolescent offspring female rats showed no significant differences in anxiety-like behavior and forced alcohol consumption between saline- and nicotine-exposed groups. Nicotine-exposed offspring rats showed more increased nicotine aversion than saline-exposed groups, but the effect was disturbed in the forced alcohol consumption condition on the first day of the nicotine consumption test. Taken together, these results suggest that, in the last gestation and lactation period corresponding to the second and third trimester of human pregnancy, long-term maternal nicotine exposure has a minor effect on dam and female offspring health and does not involve serious pathological changes in rat offspring, despite the presence of nicotine in their blood.

The role of pituitary adenylyl cyclase activating polypeptide in affective signs of nicotine withdrawal

Recent evidence implicates endogenous pituitary adenylyl cyclase activating polypeptide (PACAP) in the aversive effect of nicotine. In the present study, we assessed if nicotine-induced conditioned place preference (CPP) or affective signs of nicotine withdrawal would be altered in the absence of PACAP and if there were any sex-related differences in these responses. Male and female mice lacking PACAP and their wild-type controls were tested for baseline place preference on day 1, received conditioning with saline or nicotine (1 mg/kg) on alternate days for 6 days and were then tested for CPP the next day. Mice were then exposed to four additional conditioning and were tested again for nicotine-induced CPP 24 hr later. Controls were conditioned with saline in both chambers and tested similarly. All mice were then, 96 hr later, challenged with mecamylamine (3 mg/kg), and tested for anxiety-like behaviors 30 min later. Mice were then, 2 hr later, forced to swim for 15 min and then tested for depression-like behaviors 24 hr later. Our results showed that male but not female mice lacking PACAP expressed a significant CPP that was comparable to their wild-type controls. In contrast, male but not female mice lacking PACAP exhibited reduced anxiety- and depression-like behaviors compared to their wild-type controls following the mecamylamine challenge. These results suggest that endogenous PACAP is involved in affective signs of nicotine withdrawal, but there is a sex-related difference in this response.

The interaction of the Chrna5 D398N variant with developmental nicotine exposure

A single nucleotide polymorphism (SNP) in CHRNA5 (rs16969968, change from an aspartic acid [D] to asparagine [N] at position 398 of the human α5 nicotinic acetylcholine receptor subunit) has been associated with increased risk for nicotine dependence. Consequently, carriers of the risk variant may be at elevated risk for in utero nicotine exposure. To assess whether this gene-environment interaction might impact nicotine intake in developmental nicotine-exposed offspring, we utilized a mouse expressing this human SNP. D and N dams drank nicotine (100 μg/mL) in 0.2% saccharin water or 0.2% saccharin water alone (vehicle) as their sole source of fluid from 30 days prior to breeding until weaning of offspring. The nicotine (D Nic, N Nic) or vehicle (D Veh, N Veh) exposed offspring underwent a 2-bottle choice test between postnatal ages of 30 to 46 days. N Nic offspring consumed the most nicotine at the highest concentration (400 μg/mL) compared with all other groups. In contrast, D Nic offspring drank the least amount of nicotine at all concentrations tested. Nicotine-stimulated dopamine (DA) release measured from striatal synaptosomes was increased in D Nic offspring, while decreased in N Nic offspring relative to their genotype-matched controls. These data suggest that the α5 variant influences the effect of developmental nicotine exposure on nicotine intake of exposed offspring. This gene-environment interaction on striatal DA release may provide motivation for increased nicotine seeking in N Nic offspring and reduced consumption in D Nic offspring.

Alteration of adolescent aversive nicotine response and anxiety-like behavior in nicotine-exposed rats during late lactation period

Early nicotine exposure is an important cause of further habitual tobacco smoking. Although nicotine has not only rewarding but also aversive properties, the effects of early nicotine exposure on the distinct properties of nicotine are not well known. To reveal the effects of early adolescent nicotine exposure on further persistent tobacco smoking, we demonstrated developmental changes in nicotine-related appetitive and aversive behaviors of rats exposed to nicotine during the late lactation period. Sprague-Dawley rats were injected with saline or nicotine (2, 6 and 12mg/kg). We performed a two bottle free-choice test using escalating doses of nicotine (25, 50 and 100μg/ml), saccharin and quinine and the open field test in both adolescent and adult rats. The rats' aversive response to nicotine was increased according to the increase in nicotine concentration. Adolescent rats showed higher nicotine preference and consumption behaviors than did adult rats at an aversive dose of nicotine. Nicotine-exposed rats increased adolescent nicotine consumption when the nicotine concentration was 12mg/kg. We observed significant increases in anxious behaviors in adolescent nicotine-injected rats compared to saline-injected rats, but there were no alterations in adult rats. In both adolescent and adult rats, saccharin and quinine intake were not significantly different between groups. Taken together, it suggests that repeated nicotine exposure in late lactation period affect changes in aversive nicotine responses and anxious behaviors during adolescence but there is no difference in adults.

Differential effects of pair housing on voluntary nicotine consumption: a comparison between male and female adolescent rats

RATIONALE

Tobacco smoking occurs in a wide array of social circumstances. Social support for quitting is generally used to stop smoking, while peer interactions may be a crucial factor in triggering tobacco use among adolescents.

OBJECTIVES

To determine the role of social factors on nicotine dependence, we compared single- and pair-housed rats subjected to voluntary oral nicotine consumption tests.

METHODS

Six-week-old adolescent rats were subjected to experimental procedures and assigned to one of the following groups: a male single group, a male pair group with a sibling, a female single group, and a female pair group with a sibling. To measure voluntary nicotine intake, we adopted a two-bottle free-choice paradigm for each two days using 25 μg/ml and 100 μg/ml nicotine solution.

RESULTS

There were no differences in change in body weight or food intake between the two groups of either sex. Pair-housed female rats showed a reduction in nicotine consumption and preference for both low- and high-dose nicotine solution, while pair-housed male rats showed only reduced consumption and preference for high-dose nicotine solution, but not low-dose solution, as compared to single-housed male rats.

CONCLUSIONS

Nicotine consumption is sex-dependently controlled by the social circumstances of rats. This study broadens our perspectives on the role of social interactions as a therapeutic strategy to treat nicotine addiction-related behaviors depending on sex.

Nicotine pretreatment reduced cocaine-induced CPP and its reinstatement in a sex- and dose-related manner in adult C57BL/6J mice

Previous preclinical studies have shown that nicotine pretreatment during adolescence increases the reinforcing actions of cocaine. However, little is known about the effect of prior nicotine administration on cocaine-induced conditioned place preference (CPP) and its reinstatement in adult mice. Besides, little information is available regarding the role of sex in this cross-talk between nicotine and cocaine. Thus, we examined if nicotine administration during adulthood would differentially alter cocaine-induced CPP, its extinction and reinstatement in male versus female mice and if the dose of nicotine was important in this regard. To this end, mice were pretreated with saline or nicotine (0.25 or 1mg/kg; twice daily for seven days) and then tested for place preference before and after single and repeated conditioning with cocaine (15mg/kg). Mice were then exposed to extinction training and tested for reinstatement of CPP. Our results showed that male and female mice pretreated with saline and conditioned with cocaine each exhibited a robust CPP after a single cocaine conditioning. However, this response was blunted in mice pretreated with the lower but not higher dose of nicotine. Female mice pretreated with the lower dose nicotine also failed to show CPP after repeated conditioning. Reinstatement of cocaine-induced CPP was also blunted in these mice compared to their respective controls. Together, these results suggest that nicotine administration during adulthood exerts differential effects on cocaine-induced CPP and its reinstatement in male and female mice and the dose of nicotine is important in this regard.

Oxytocin attenuates aversive response to nicotine and anxiety-like behavior in adolescent rats

Initial tobacco use is initiated with rewarding and aversive properties of nicotine and aversive response to nicotine plays a critical role in nicotine dependency. Decrease of nicotine aversion increases the nicotine use that causes behavioral and neuronal changes of animals. Oxytocin influences drug abuse and reciprocally affect vulnerability to drug use. To assess the effect of oxytocin on initial nicotine aversion and anxiety, we examined voluntary oral nicotine intake and anxiety-like behavior following oxytocin treatment in adolescent rats. Sprague-Dawley male rats (4 weeks old) were used. For oxytocin administration, rats were injected subcutaneously with saline or oxytocin (0.01, 0.1 and 1mg/kg) according to the assigned groups. Voluntary oral nicotine consumption test was performed by two bottle free-choice paradigm. To examine anxiety-like behavior in rats, we performed a light/dark box test. Oxytocin not only significantly increased the nicotine intake but also alleviated nicotine aversion after acclimation to nicotine solution in a concentration dependent manner. Meanwhile, oxytocin significantly reduced anxiety-like behavior. We suggest that oxytocin itself mitigates aversive response toward initial nicotine intake and anxiety-like behavior. These results widen the psychophysiological perspective on oxytocin for better understanding of nicotine addiction related behaviors influenced by diverse social factors.

Optogenetic activation of septal GABAergic afferents entrains neuronal firing in the medial habenula

The medial habenula (MHb) plays an important role in nicotine-related behaviors such as nicotine aversion and withdrawal. The MHb receives GABAergic input from the medial septum/diagonal band of Broca (MS/DB), yet the synaptic mechanism that regulates MHb activity is unclear. GABA (γ -aminobutyric acid) is a major inhibitory neurotransmitter activating both GABA_A receptors and GABA_B receptors. Depending on intracellular chloride concentration, however, GABA_A receptors also function in an excitatory manner. In the absence of various synaptic inputs, we found that MHb neurons displayed spontaneous tonic firing at a rate of about ~4.4 Hz. Optogenetic stimulation of MS/DB inputs to the MHb evoked GABA_A receptor-mediated synaptic currents, which produced stimulus-locked neuronal firing. Subsequent delayed yet lasting activation of GABA_B receptors attenuated the intrinsic tonic firing. Consequently, septal GABAergic input alone orchestrates both excitatory GABA_A and inhibitory GABA_B receptors, thereby entraining the firing of MHb neurons.