Effects of combined pre- and postnatal treatment with nicotine on hypothalamic catecholamine nerve terminal systems and neuroendocrine function in the 4-week old and adult male and female diestrous rat

Varenicline, the clinically effective smoking cessation agent, restores probabilistic response reversal performance during withdrawal from nicotine

There is recognition that cognitive problems can contribute to renewed drug taking in former addicts. Our previous work has indicated that current smokers show reduced performance on a probabilistic reversal learning (PRL) task, relative to former smokers. To further explore PRL performance and its relevance to smoking, in addition to the role of nicotine, we developed a model of nicotine withdrawal-induced deficits in rodents. A second goal was to test varenicline, an α4β2 partial agonist, for its ability to restore any cognitive impairment. Acute effects of nicotine and varenicline on PRL performance in non-dependent animals were minimal and confined to speed of responding. When rats were made dependent on nicotine via osmotic minipumps implanted for 7 days (3.16 mg/kg/day), repeated tests at specified withdrawal time points revealed PRL disruption peaking at 12 and 24 hours following surgical removal of minipumps. Withdrawal was characterized by significant deficits in the number of reversals (P < 0.05), speed of responding (P < 0.01) and increases in omissions (P < 0.05). Nicotine (0.2 mg/kg SC) or varenicline (0.3 and 1.0 mg/kg SC) administered 10-minute prior to PRL test sessions during withdrawal, relieved the performance deficits. At 24-hour withdrawal, nicotine and varenicline (1 mg/kg) prevented decrements in reversals, in addition to ameliorating slower speed of responding. The high dose of varenicline only reduced omissions. These results confirm the role of nicotine in withdrawal-induced disruption of PRL performance and suggest that the model may be useful for investigating efficacy of potential new treatments for smoking cessation.

Early exposure to nicotine during critical periods of brain development: Mechanisms and consequences

Tobacco use during pregnancy continues to be a major problem with more than 16% of pregnant women in the United States continuing to smoke during pregnancy. Tobacco smoke is known to contain more than 4,000 different chemicals, and while many of these compounds have the potential to interfere with proper neurodevelopment, there is direct evidence that nicotine, the major psychoactive substance present in tobacco, acts as a neuroteratogen. Nicotine activates, and subsequently desensitizes, neuronal nicotinic acetylcholine receptor subtypes (AChRs), which are expressed in the developing central nervous system (CNS) prior to the in-growth of cholinergic neurons. Nicotinic AChRs are present by the first trimester of development in both humans and rodents, and activation of these receptors by acetylcholine is thought to play a critical role in CNS development. The purpose of the current review is to provide an overview of the role that nicotinic AChRs play in the developing CNS and to describe the effects of nicotine exposure during early development on neuronal cell biology, nicotinic AChR expression and neurotransmitter system (e.g., dopamine, norepinephrine, serotonin) function. In particular, differences that occur as a result of the timing and duration of nicotine exposure will be discussed. Emphasis will be placed on preclinical studies examining particular periods of time which correspond to periods of prenatal development in humans (i.e., first, second and third trimesters). Finally, the effects of early nicotine exposure on neurobehavioral development as it pertains to specific disorders, i.e., attention deficit hyperactivity disorder (ADHD), depression and addiction, will be discussed.

Regulation of endocrine function by the nicotinic cholinergic receptor

One important neuroendocrine action of nicotine in the male rat is an increase in the secretion of corticosterone which is seen upon acute and acute intermittent exposure to nicotine. Tolerance develops to this action of nicotine upon chronic exposure, and in the withdrawal phase serum corticosterone levels are substantially reduced. In contrast, no significant increases of serum corticosterone levels were observed upon acute intermittent treatment with nicotine in the dioestrous rat. Available evidence indicates that corticosterone can modulate dopamine transmission in the basal ganglia via glucocorticoid receptors within the nucleus accumbens and neostriatum, and via glucocorticoid receptor immunoreactivity in nigrostriatal and mesolimbic dopamine pathways. Through concerted pre- and postsynaptic actions glucocorticoids may decrease dopamine transmission, especially that mediated by D2 receptors in these regions. In view of the hypothesis that the mesolimbic dopamine pathways mediate the euphoric effects of nicotine, the secretion of corticosterone induced by nicotine in the smoking male may substantially influence the mood elevating activity of nicotine. Thus, individual smoking habits may depend on the ability of nicotine to induce corticosterone secretion, which obviously would also vary with the degree of stress. The glucocorticoids may in a similar way influence the arousal action of nicotine because of the high number of glucocorticoid receptors present both in noradrenaline cell bodies of the locus ceruleus and within the entire cerebral cortex.

Sex differences in nicotine effects and self-administration: review of human and animal evidence

Although both the human and animal literatures are notable for the general lack of attention paid to possible sex differences in drug self-administration behavior, evidence is accumulating to suggest that males and females may differ in factors that maintain tobacco smoking or nicotine self-administration. Self-administration of nicotine per se may be less robust in women, and women are less sensitive than men to some effects of nicotine that may be reinforcing. Compared to men, smoking behavior of women may be influenced more by non-nicotine stimuli associated with smoking, suggesting greater conditioned reinforcement of smoking in women. Moreover, nicotine replacement, the current standard treatment for smoking cessation, is sometimes less effective in women, further suggesting the need for greater consideration of non-nicotine factors that may maintain women's smoking. Very recent research on rats also indicates sex differences in nicotine self-administration. However, these differences are complex and suggest that nicotine-seeking behavior is composed of several components, including hedonic, incentive-motivational, and conditioning effects; males and females may differ in one or more of these components. Menstrual or estrous cycle phase effects on the maintenance of nicotine self-administration are not particularly apparent in humans or animals, although cycle phase may influence other stages of dependence (e.g., withdrawal symptoms during cessation). Future research should evaluate further the consistency of results across human and non-human species, identify the conditions and procedures under which sex differences are observed, and elucidate the specific components of reinforcement that may differ between males and females. Studies also should examine the possible generalizability of these sex differences to other drugs of abuse. Identification of specific factors responsible for these sex differences may lead to improved interventions for smoking cessation and other substance abuse in women.

Gender differences in the pharmacology of nicotine addiction

Smoking rates have declined in recent years less rapidly in women than in men. More adolescent girls than boys are currently smoking. Quitting smoking is reported in many studies to be more difficult in women than in men. These observations suggest that there may be gender differences in the nature of nicotine addiction. Gender differences in various pharmacological processes involved in nicotine addiction are reviewed. Women take in less nicotine from smoking per cigarette than men but, because of slower metabolism, nicotine levels in the body for a given number of cigarettes per day are similar in male and female smokers. Women tend to be less sensitive to the discriminative effects of nicotine and tend to regulate nicotine intake less precisely than men. On the other hand, women appear to be more sensitive to the effects of nicotine in reducing negative affect and reducing body weight. There is a strong association between depression and smoking, and this association appears to be stronger in women than in men. Women tend to respond more to environmental cues associated with smoking than do men. Thus, several lines of evidence suggest that nicotine addiction is different in women than in men. Understanding the basis for gender differences may be of utility in individualizing and optimizing smoking cessation therapy.

Estrogen differentially modulates nicotine-evoked dopamine release from the striatum of male and female rats

In the present experiment we examined the effects of an in vitro infusion of nicotine (10 microM) upon dopamine release from superfused striatum of castrated male and female rats treated or not treated with estrogen. Estrogen exerted bidirectional effects on nicotine-evoked dopamine release as a function of the sex of the animal. Nicotine-evoked dopamine release was increased in estrogen treated females and decreased in estrogen treated males. Peak nicotine-evoked dopamine output from estrogen treated females was significantly greater than that of estrogen treated males. These results may be related to the gender differences in response to nicotine and smoking behavior.