Nicotine-exposed Animals Research Articles

Osseointegration of implants with superhydrophilic surfaces in rats with high serum levels of nicotine.

This study aimed to evaluate the effect of nicotine administration on the osseointegration of a superhydrophilic implants surface on rat tibiae. Thirty-two rats were used and divided into 2 groups according to the administration or not of nicotine: HH - Installation of implants with superhydrophilic surfaces in healthy animals; and HN - Installation of implants with superhydrophilic surfaces in animals subjected to nicotine administration. The animals were euthanized 15 and 45 days after implant placement (n = 8). Osseointegration was assessed by means of biomechanical analyses (removal torque), microcomputed tomography (volume of bone around the implants- %BV/TV), and histomorphometry (bone-implant contact -%BIC and the bone area between implant threads -%BBT). The animals subject to the nicotine administration presented lower removal torque than the control animals at the 45-day period (21.88 ± 2.80 Ncm vs. 17.88 ± 2.10 Ncm). The implants placed in the control rats presented higher %BIC (54.26 ± 6.59% vs. 39.25 ± 4.46%) and %BBT (50.57 ± 5.28% vs. 32.25 ± 5.24%) than the implants placed in nicotine animals at 15-day period. The nicotine administration reduces the osseointegration at 15 days, however, the superhydrophilic surface equalized the osseointegration in nicotine-exposed animals compared with healthy animals after 45 days of implant placement.

Fetal and Postnatal Nicotine Exposure Modifies Maturation of Gonocytes to Spermatogonia in Mice.

Studies in laboratory animals have shown that male offspring from dams, exposed to nicotine during pregnancy and postnatal periods, show alterations in fertility, although the origin of this is still uncertain. In this study, we examined in a mouse model if the process of gonocyte maturation to spermatogonia was affected in male offspring from dams with nicotine administration during pregnancy and postnatal periods. BALB/C mice, with and without nicotine administrations in pregnancy and postnatal periods, were studied. The animals were euthanized at 3, 7, 10, 16, and 35 days postpartum (dpp). Testicular tissue samples were processed for histological, ultrastructural, and immunohistochemical studies; and testicular lipoperoxidation was determined. It was observed that in the nicotine-exposed animals, there was increased apoptosis and a reduction in the number of gonocytes that matured to spermatogonia. This gonocyte-spermatogonia maturation reduction was associated with a greater immunoreactivity to nicotinic acetylcholine receptors in the germ cells. Lipoperoxidation was similar in both groups until 16 dpp, with significant reduction at 35 dpp. Our findings suggest that nicotine intake during pregnancy and postnatal periods can affect the process of maturation of gonocytes to spermatogonia and the pool of available spermatogonia for spermatogenesis.

The impact of chronic daily nicotine exposure and its overnight withdrawal on the structure of anxiety-related behaviors in rats: Role of the lateral habenula

Tobacco smoking is a serious health problem worldwide and a leading cause of mortality. Nicotine, the addictive component of tobacco, affects a range of emotional responses, including anxiety-related behaviors. Although perceived by smokers to be anxiolytic, evidence suggests that smoking increases anxiety and that mood fluctuates with nicotine intake. Thus, nicotine addiction may depend on easing the psychobiological distress caused by its abuse. The lateral habenula (LHb) has been implicated as a neural substrate for acute nicotine-induced anxiety, but its role in anxiety-like behaviors associated with chronic nicotine exposure has not been explored. Here, we assessed the effect of chronic nicotine exposure and its subsequent overnight withdrawal on anxiety-like behavior using both quantitative and multivariate T-pattern analysis in rats tested using the hole-board apparatus. Additionally, we explored the role of the LHb by comparing the behavioral effects of short-term nicotine withdrawal in chronically treated LHb-lesioned rats. Quantitative analysis revealed increased anxiety-like behavior in chronically treated overnight nicotine-deprived rats, as manifested in reduced general and focused exploratory behaviors, which was eased in animals that received nicotine. Quantitative analysis failed to reveal a role of the LHb in overnight nicotine deprivation-induced anxiety. Conversely, T-pattern analysis of behavioral outcomes revealed that chronic nicotine-treated rats still show anxiety-like behavior following nicotine challenge. Moreover, it demonstrated that the LHb lesion induced a stronger anxiolytic-like response to the acute challenge of nicotine in chronically nicotine-exposed animals, implicating the LHb in the anxiogenic effect of chronic nicotine exposure. These data further highlight the LHb as a promising target for smoking cessation therapies and support the importance of T-pattern analysis for behavioral analysis.

Enduring effects of perinatal nicotine exposure on murine sleep in adulthood.

The long-term consequences of early life nicotine exposure are poorly defined. Approximately 8-10% of women report smoking during pregnancy, and this may promote aberrant development in the offspring. To this end, we investigated potential enduring effects of perinatal nicotine exposure on murine sleep and affective behaviors in adulthood (~13-15 wk of age) in C57Bl6j mice. Mothers received a water bottle containing 200 µg/ml nicotine bitartrate dihydrate in 2% wt/vol saccharin or pH-matched 2% saccharin with 0.2% (vol/vol) tartaric acid throughout pregnancy and before weaning. Upon reaching adulthood, offspring were tested in the open field and elevated plus maze, as well as the forced swim and sucrose anhedonia tests. Nicotine-exposed male (but not female) mice had reduced mobility in the open field, but no differences were observed in anxiety-like or depressive-like responses. Upon observing this male-specific phenotype, we further assessed sleep-wake states via wireless EEG/EMG telemetry. Following baseline recording, we assessed whether mice exposed to nicotine altered their homeostatic response to 5 h of total sleep deprivation and whether nicotine influenced responses to a powerful somnogen [i.e., lipopolysaccharides (LPS)]. Males exposed to perinatal nicotine decreased the percent time spent awake and increased time in non-rapid eye movement (NREM) sleep, without changes to REM sleep. Nicotine-exposed males also displayed exaggerated responses (increased time asleep and NREM spectral power) to sleep deprivation. Nicotine-exposed animals additionally had blunted EEG slow-wave responses to LPS administration. Together, our data suggest that perinatal nicotine exposure has long-lasting effects on normal sleep and homeostatic sleep processes into adulthood.

Neurohistochemical studies of adolescent rats' prefrontal cortex exposed to prenatal nicotine

Background: Exposure to tobacco has frequently been associated with adverse implications on many body organs and systems. Maternal smoking can influence fetal development, causing intrauterine growth restriction, preterm birth, or even fetal death and spontaneous abortion. Objectives: We investigated the effects of prenatal exposure to nicotine on the prefrontal cortex in adolescent rats. Materials and Methods: Twenty-four mature female Wistar rats were time mated and grouped according to Trimester into Control and Treated groups. Nicotine was administered intra-peritoneally to pregnant Wistar rats in the treated groups, while normal saline was given to the control groups, at each of the three Trimesters. The animals were allowed to litter and the pups were allowed to grow till postnatal day 35, when they were sacrificed and the brain removed and weighed. The prefrontal cortex was excised and either fixed in 4% paraformaldehyde for tissue histology or homogenized in sucrose solution for enzyme studies (alkaline phosphatase, lactate dehydrogenase and glucose-6-phosphate dehydrogenase). Results: Enzyme studies showed derangement in biochemical status of the prefrontal cortex of all the nicotine-exposed animals compared with their respective controls, and corresponding morphological and histological alterations, especially in animals exposed to nicotine during their 2nd and 3rd weeks of fetal life. Conclusions: The morphohistological and biochemical derangements that occur during neurodevelopment of nicotine-exposed offspring persist into adolescent life, and could underlie the neurological dysfunctions associated with such individuals.

Prenatal nicotine exposure enhances the trigeminocardiac reflex via serotonin receptor facilitation in brainstem pathways

In this study we used a rat model for prenatal nicotine exposure to test whether clinically relevant concentrations of brain nicotine and cotinine are passed from dams exposed to nicotine to her pups, whether this changes the trigeminocardiac reflex (TCR), and whether serotonergic function in the TCR brainstem circuitry is altered. Pregnant Sprague-Dawley dams were exposed to 6 mg·kg(-1)·day(-1) of nicotine via osmotic minipumps for the duration of pregnancy. Following birth dams and pups were killed, blood was collected, and brain nicotine and cotinine levels were measured. A separate group of prenatal nicotine-exposed pups was used for electrophysiological recordings. A horizontal brainstem slice was obtained by carefully preserving the trigeminal nerve with fluorescent identification of cardiac vagal neurons (CVNs) in the nucleus ambiguus. Stimulation of the trigeminal nerve evoked excitatory postsynaptic current in CVNs. Our data demonstrate that prenatal nicotine exposure significantly exaggerates both the TCR-evoked changes in heart rate in conscious unrestrained pups, and the excitatory neurotransmission to CVNs upon trigeminal afferent nerve stimulation within this brainstem reflex circuit. Application of the 5-HT1A receptor antagonist WAY 100635 (100 μM) and 5-HT2A/C receptor antagonist ketanserin (10 μM)significantly decreased neurotransmission, indicating an increased facilitation of 5-HT function in prenatal nicotine-exposed animals. Prenatal nicotine exposure enhances activation of 5-HT receptors and exaggerates the trigeminocardiac reflex.

Hyperactivity, increased nicotine consumption and impaired performance in the five-choice serial reaction time task in adolescent rats prenatally exposed to nicotine

Prenatal exposure to nicotine has been linked to accelerated risk for different psychiatric disorders, including conduct disorder, attention deficit hyperactivity disorder (ADHD) and drug abuse. We examine a potential link between prenatal nicotine exposure, hyperactivity, anxiety, nicotine consumption, and cognitive performance in rats. Adolescent offspring of females exposed during pregnancy to 0.06 mg/ml nicotine solution as the only source of water and of a group of pair-fed females, used as a control for anorexic effects of nicotine, were evaluated in a battery of tests, including locomotor activity, the elevated plus maze, two-bottle free-choice nicotine solution consumption, the five-choice serial reaction time test (5-CSRTT) and a delay-discounting test. All tests were conducted between postnatal day (PND) 25 and PND 50. Nicotine-exposed animals expressed hyperactivity, increased number of open arms entries in the elevated plus maze and increased numbers of anticipatory responses in the 5-CSRTT. Decreased aversion for nicotine solution in the free-choice test and decreased numbers of omission errors in the 5-CSRTT were observed both in nicotine-exposed and pair-fed offspring. Neither nicotine exposure nor pair-feeding had an effect on impulsive choice in a delay-discounting test. Our study confirms deleterious effects of prenatal nicotine exposure on important aspects of behaviour and inhibitory control in adolescent rats and supports epidemiological findings that show increased levels of symptoms of ADHD and related disorders among those whose mothers smoked during their pregnancy. It also suggests a link between food restriction during pregnancy and addiction-related behaviours in offspring.

Neuroplasticity of the central hypercapnic ventilatory response: teratogen-induced impairment and subsequent recovery during development.

Neuroventilation is highly plastic and exposure to either of two distinct teratogens, nicotine or ethanol, during development results in a similar loss of the neuroventilatory response to hypercapnia in bullfrog tadpoles. Whether this functional deficit is permanent or transient following nicotine or ethanol exposure was unknown. Here, we tested the persistence of hypercapnic neuroventilatory response impairments in tadpoles exposed to either 30 microg/L nicotine or 0.12-0.06 g/dL ethanol for 10 weeks. Brainstem breathing-related neural activity was assessed in tadpoles allowed to develop teratogen-free after either nicotine or ethanol exposure. Nicotine-exposed animals responded normally to hypercapnia after a 3-week teratogen-free period but the hypercapnic response in ethanol-exposed tadpoles remained impaired. Tadpoles allowed to develop for only 1 week nicotine free after chronic exposure were unable to respond to hypercapnia. The hypercapnic response of ethanol-exposed tadpoles returned by 6 weeks following chronic ethanol exposure. These findings suggest that some nicotine- and ethanol-induced impairments can be resolved during early development. Understanding both the disruptive effects of nicotine and ethanol exposure and how impaired responses return when teratogen exposure stops may offer insight on the function and plasticity of respiratory control.

Prenatal nicotine-exposure alters fetal autonomic activity and medullary neurotransmitter receptors: implications for sudden infant death syndrome

During pregnancy, exposure to nicotine and other compounds in cigarette smoke increases the risk of the sudden infant death syndrome (SIDS) two- to fivefold. Serotonergic (5-HT) abnormalities are found, in infants who die of SIDS, in regions of the medulla oblongata known to modulate cardiorespiratory function. Using a baboon model, we tested the hypothesis that prenatal exposure to nicotine alters 5-HT receptor and/or transporter binding in the fetal medullary 5-HT system in association with cardiorespiratory dysfunction. At 87 (mean) days gestation (dg), mothers were continuously infused with saline (n = 5) or nicotine (n = 5) at 0.5 mg/h. Fetuses were surgically instrumented at 129 dg for cardiorespiratory monitoring. Cesarean section delivery and retrieval of fetal medulla were performed at 161 (mean) dg for autoradiographic analyses of nicotinic and 5-HT receptor and transporter binding. In nicotine-exposed fetuses, high-frequency heart rate variability was increased 55%, possibly reflecting increases in the parasympathetic control of heart rate. This effect was more pronounced with greater levels of fetal breathing and age. These changes in heart rate variability were associated with increased 5-HT(1A) receptor binding in the raphé obscurus (P = 0.04) and increased nicotinic receptor binding in the raphé obscurus and vagal complex (P < 0.05) in the nicotine-exposed animals compared with controls (n = 6). The shift in autonomic balance in the fetal primate toward parasympathetic predominance with chronic exposure to nicotine may be related, in part, to abnormal 5-HT-nicotine alterations in the raphé obscurus. Thus increased risk for SIDS due to maternal smoking may be partly related to the effects of nicotine on 5-HT and/or nicotinic receptors.

In Utero and Lactational Exposure to Nicotine Alters the Intra-Ovarian IGF System in Adult Female Rats

In humans there is evidence that in utero exposure to cigarette smoke results in decreased fertility in female offspring. We have demonstrated in rats that fetal and neonatal exposure to nicotine alone results in impaired fertility and increased follicular atresia in the adult female offspring. In mammals, the insulin-like growth factor-I and -II (IGF-I and -II) and their binding proteins (IGFBPs) are considered stimulators and inhibitors of follicular growth and maturation. Therefore we hypothesized that dysregulation of the intra-ovarian IGF system could be implicated in the impaired fertility observed in nicotine-exposed offspring. Nulliparous female Wistar rats were exposed to nicotine (1 mg/kg/d) for 2 weeks prior to mating until weaning. Ovaries were collected on the morning of estrus from sexually mature saline- and nicotine-exposed offspring. Protein expression of IGF ligands and receptors (IGFR-I and IGFR-II) were quantified by western blot and immunohistochemistry. The expression of IGF-I, IGF-II; IGFR-I, IGFR-II; and IGFBP1–6 mRNA in the ovary was deter- mined by semi-quantitative reverse transcriptase-PCR. Results showed that nicotine exposure significantly reduced IGF-I, IGF-II and IGFR-I protein expression (p < 0.01) relative to saline controls. Furthermore, nicotine-exposed offspring had significantly reduced IGFR-II mRNA expression (p < 0.01) in the ovary. Data from this study suggest that the decreased fertility and increased follicular atresia in nicotine-exposed animals may be due, in part, to disruption of IGF regulation in the ovary.

Fetal and Neonatal Nicotine Exposure in Wistar Rats Causes Progressive Pancreatic Mitochondrial Damage and Beta Cell Dysfunction

Nicotine replacement therapy (NRT) is currently recommended as a safe smoking cessation aid for pregnant women. However, fetal and neonatal nicotine exposure in rats causes mitochondrial-mediated beta cell apoptosis at weaning, and adult-onset dysglycemia, which we hypothesize is related to progressive mitochondrial dysfunction in the pancreas. Therefore in this study we examined the effect of fetal and neonatal exposure to nicotine on pancreatic mitochondrial structure and function during postnatal development. Female Wistar rats were given saline (vehicle control) or nicotine bitartrate (1 mg/kg/d) via subcutaneous injection for 2 weeks prior to mating until weaning. At 3–4, 15 and 26 weeks of age, oral glucose tolerance tests were performed, and pancreas tissue was collected for electron microscopy, enzyme activity assays and islet isolation. Following nicotine exposure mitochondrial structural abnormalities were observed beginning at 3 weeks and worsened with advancing age. Importantly the appearance of these structural defects in nicotine-exposed animals preceded the onset of glucose intolerance. Nicotine exposure also resulted in significantly reduced pancreatic respiratory chain enzyme activity, degranulation of beta cells, elevated islet oxidative stress and impaired glucose-stimulated insulin secretion compared to saline controls at 26 weeks of age. Taken together, these data suggest that maternal nicotine use during pregnancy results in postnatal mitochondrial dysfunction that may explain, in part, the dysglycemia observed in the offspring from this animal model. These results clearly indicate that further investigation into the safety of NRT use during pregnancy is warranted.

Rosiglitazone prevents diabetes by increasing beta‐cell mass in an animal model of type 2 diabetes characterized by reduced beta‐cell mass at birth

Interventions that preserve or increase beta-cell mass may also prevent type 2 diabetes. Rosiglitazone prevents diabetes in people with high glucose levels who have impaired glucose tolerance and/or impaired fasting glucose. The effect of this drug on both glucose levels and beta-cell mass was studied in a rat model of diabetes, characterized by reduced beta-cell mass at birth with normoglycaemia, and progression to dysglycaemia with age. Female Wistar rats were given either saline (vehicle) or nicotine during pregnancy and lactation. Offspring of saline-exposed dams were given vehicle and offspring of nicotine-exposed dams were randomized to receive either vehicle or rosiglitazone starting at weaning. Beta-cell mass, proliferation and apoptosis were determined at birth and at 4 and 26 weeks of age. Glucose homeostasis was examined following sequential oral glucose tolerance tests (OGTT). Rosiglitazone treatment prevented the development of dysglycaemia in nicotine-exposed animals. The ability of rosiglitazone to preserve normoglycaemia appeared to be because of its ability to increase beta-cell mass through a combination of enhanced beta-cell proliferation and decreased beta-cell apoptosis. These results suggest that if rosiglitazone administration is started prior to the onset of glucometabolic abnormalities, it prevents the onset of dysglycaemia by partially restoring beta-cell mass in animals with reduced beta-cell mass at birth.

Nicotinic Receptor Activation Occludes Purinergic Control of Central Cardiorespiratory Network Responses to Hypoxia/Hypercapnia

Prenatal nicotine exposure alters the cardiorespiratory network responses to hypoxia/hypercapnia; however the mechanism(s) responsible for these cardiorespiratory network responses and their alteration by prenatal nicotine exposure are unknown. We used an in vitro medullary slice that allows simultaneous examination of rhythmic respiratory-related activity and excitatory synaptic neurotransmission to cardioinhibitory vagal neurons (CVNs). Respiratory related increases in glutamatergic neurotransmission only occurred on recovery from hypoxia/hypercapnia in unexposed animals. These responses were not altered by nicotinic antagonists but were mediated in part by activation of P2 purinergic receptors. Prenatal nicotine exposure transformed central cardiorespiratory responses to hypoxia/hypercapnia; CVNs received a respiratory related glutamatergic neurotransmission during periods of hypoxia and hypercapnia, whereas increases in glutamatergic neurotransmission during recovery were absent. The excitatory neurotransmission to CVNs during hypoxia/hypercapnia in prenatal nicotine-exposed animals were wholly dependent on nicotinic receptor activation. In the presence of nicotinic antagonists, the responses in prenatal nicotine animals reverted to the pattern of responses in unexposed animals in which an increase in glutamatergic neurotransmission occurred not during but only on recovery from hypoxia/hypercapnia, and this recruited excitatory pathway was blocked by P2 receptor antagonists. These data identify a new functional role for purinergic receptors in the cardiorespiratory responses to hypoxia/hypercapnia and their role in occluding nicotinic receptor activation with prenatal nicotine exposure.

Influence of prenatal nicotine exposure on development of ventilatory responses to hypoxia and asphyxia.

Ventilatory responses to 3 minutes of hypoxia (16, 12 and 10 % inspired O2, balance N2), asphyxia (12% O2, 5% CO2, balance N2) and normoxia were studied in neonatal rats that were exposed to either nicotine (nicotine tartrate, 6 mg/kg/day) or saline in the prenatal period. Measurements were obtained on postnatal days (P) 3, 6, 9, 12 and 18, using head-out body plethysmography. Plethysmograph temperature was servocontrolled within the thermoneutral zone for neonatal rats (33 +/− 0.1 degrees C). Normoxic pulmonary ventilation (VI) increased progressively as the animals grew, with no between-group differences at any age. With 16% O2, nicotine-exposed rats had a lower VI than saline-exposed rats on P9, and a higher VI on P18. In response to 12% O2, nicotine-exposed rats had a higher VI on P12. With 10% O2, VI was lower in nicotine-exposed rats on P3, but higher on P12 and P18. Prenatal nicotine exposure did not alter the response to asphyxia with the exception of a reduced response on the 9th day of life. The increase in body mass with age was similar in both groups, with the exception of a slightly higher weight in nicotine-exposed animals on P18. Prenatal nicotine exposure causes complex developmental changes in hypoxic sensitivity, expressed as attenuation over the first 9 days of life, and facilitation on days 12–18. The developmental switch between P9-P12 is consistent with a major readjustment of brainstem neurotransmitter receptor densities near P12 (Liu et al, JAP. 98: 1442, 2005). Support: AHA 0255970Z

Nicotine Effect on Cardiovascular System and Ion Channels

Smoking is a leading cause of cardiovascular disease, hypertension, myocardial infarction, and stroke. Nicotine is one of the components of cigarette smoke. Nicotine effects on the cardiovascular system reflect the activity of the nicotine receptors centrally and on peripheral autonomic ganglia. It has been found that cigarette smoke extract-induced contraction of porcine coronary arteries is related to superoxide anion-mediated degradation of nitric oxide. Treatment of rabbit aortas with an oxygen free radicals scavenger attenuated cigarette smoke impairment of arterial relaxation. Treatment of smokers with vitamin C, an antioxidant, improved impaired endothelium-dependent reactivity of large peripheral arteries. Thus it appears that chronic smoking and acute exposure to cigarette smoke extract may alter endothelium-dependent reactivity via the production of oxygen derived free radicals. This review discusses the effects of nicotine on resistance arterioles, compliance arteries, smooth muscle cells, and ion channels in the cardiovascular system. We discuss studies performed on humans, nicotine-exposed animals, and cell cultures yielding varying and inconsistent results that may be due to differences in experimental design, species, and the dose of exposure. Nicotine exposure appears to induce a combination of free radical production, vascular wall adhesion, and a reduction of fibrinolytic activity in the plasma.

Cardiorespiratory effects of nicotine exposure during development

Exposure to tobacco smoke is a major risk factor for the sudden infant death syndrome. Nicotine is thought to be the ingredient in tobacco smoke that is responsible for a multitude of cardiorespiratory effects during development, and pre- rather than postnatal exposure is considered to be most detrimental. Nicotine interacts with endogenous acetylcholine receptors in the brain and lung, and developmental exposure produces structural changes as well as alterations in neuroregulation. Abnormalities have been described in sympathicovagal balance, arousal threshold and latency, breathing pattern at rest and apnea frequency, ventilatory response to hyperoxia or hypoxia, heart rate regulation and ability to autoresuscitate during severe hypoxia. This review discusses studies performed on infants of smoking mothers and nicotine-exposed animals yielding varying and sometimes inconsistent results that may be due to differences in experimental design, species and the dose of exposure. Taken together however, developmental nicotine exposure appears to induce vulnerability during hypoxia and a potential inability to survive severe asphyxia.

Brain Uptake Kinetics of Nicotine and Cotinine after Chronic Nicotine Exposure

Blood-brain barrier (BBB) nicotine transfer has been well documented in view of the fact that this alkaloid is a cerebral blood flow marker. However, limited data are available that describe BBB penetration of the major tobacco alkaloids after chronic nicotine exposure. This question needs to be addressed, given long-term nicotine exposure alters both BBB function and morphology. In contrast to nicotine, it has been reported that cotinine (the major nicotine metabolite) does not penetrate the BBB, yet cotinine brain distribution has been well documented after nicotine exposure. Surprisingly, therefore, the literature indirectly suggests that central nervous system cotinine distribution occurs secondarily to nicotine brain metabolism. The aims of the current report are to define BBB transfer of nicotine and cotinine in naive and nicotine-exposed animals. Using an in situ brain perfusion model, we assessed the BBB uptake of [3H]nicotine and [3H]cotinine in naive animals and in animals exposed chronically to S-(-)nicotine (4.5 mg/kg/day) through osmotic minipump infusion. Our data demonstrate that 1) [3H]nicotine BBB uptake is not altered in the in situ perfusion model after chronic nicotine exposure, 2) [3H]cotinine penetrates the BBB, and 3) similar to [3H]nicotine, [3H]cotinine BBB transfer is not altered by chronic nicotine exposure. To our knowledge, this is the first report detailing the uptake of nicotine and cotinine after chronic nicotine exposure and quantifying the rate of BBB penetration by cotinine.

Periadolescent nicotine exposure causes heterologous sensitization to cocaine reinforcement

There is increasing concern that abuse of tobacco during periadolescence increases the potential for later abuse of other drugs. To test this hypothesis, Sprague–Dawley rats received once-daily injections of either water or 0.4 mg/kg nicotine from postnatal day 35 through 44. Beginning on postnatal day 80, animals were tested in a 12-day cocaine-induced conditioned place preference (CPP) paradigm. Prior nicotine treatment enhanced the dose–response to cocaine. CPP training with 3.0 mg/kg i.p. cocaine increased time in drug-paired chambers by 50% in control rats and 94% in nicotine-exposed animals. Thus, periadolescent nicotine exposure produced long-term sensitization to an indirect-acting dopamine agonist.

Prenatal nicotine exposure increases the strength of GABAA receptor‐mediated inhibition of respiratory rhythm in neonatal rats

Infants born to mothers that smoke while pregnant have a relatively high incidence of central respiratory control abnormalities. Recent studies have shown that prenatal nicotine exposure increases GABA release and the frequency of GABAergic currents, leading to an up-regulation of GABA(A) receptors in central neurones. Activation of GABA(A) receptors inhibits ventilatory activity, with intense activation causing apnoea. These observations lead us to hypothesize that prenatal nicotine exposure alters GABAergic control of respiratory motor pattern in the early neonatal period. Osmotic minipumps were implanted in pregnant Sprague-Dawley rats on the fifth day of gestation, and filled with nicotine (6 mg kg(-1) day(-1), 2.5 microl h(-1)) or physiological saline (2.5 microl h(-1)). Brainstem-spinal cord preparations from 1- to 3-day-old neonates were studied under in vitro conditions. Electrical activity was recorded from the fourth cervical ventral root (C4 VR), which contains the axons of phrenic motoneurones. Bath application of GABA(A) receptor agonists muscimol (250 microM) or pentobarbital sodium (60 microM) to the brainstem led to consistent, reversible and significant reductions in C4 VR burst frequency. In saline-exposed animals, frequency (bursts min(-1)) fell from 6.8 +/- 0.4 to a nadir of 2.8 +/- 0.5 with muscimol, and from 6.5 +/- 0.3 to a nadir of 2.9 +/- 0.3 for pentobarbital; in nicotine-exposed animals, frequency fell from 6.3 +/- 0.4 to 1.0 +/- 0.4 with muscimol and from 6.4 +/- 0.2 to 1.7 +/- 0.4 with pentobarbital (P < 0.05 in all cases). The decrease in C4 VR frequency was significantly greater in nicotine-exposed compared to saline-exposed preparations with both muscimol and pentobarbital (P < 0.001 for both). There were no changes in the amplitude of C4 VR bursts under any condition. The GABA(A) receptor antagonist bicuculline methiodide (8 microM) did not change C4 VR frequency or amplitude in either group, although it was effective in reversing the effects of muscimol. These experiments demonstrate that prenatal nicotine exposure alters the GABAergic regulation of respiratory rhythm in a reduced preparation. The results may lead to a better understanding of the perturbed breathing pattern observed in neonates that are exposed to nicotine in utero.

Influence of prenatal nicotine exposure on postnatal development of breathing pattern.

To determine if prenatal nicotine exposure alters the postnatal development of the ventilatory pattern and the frequency and duration of apneas, we recorded respiratory airflow with head-out body plethysmography in awake neonates on postnatal days 1, 2, 6, 10, 14, and 18. Data from 12 nicotine-exposed animals were compared with data from 12 saline-exposed animals. Nicotine (6 mg/kg of nicotine tartrate per day) or saline exposure was induced by osmotic minipumps that were implanted subdermally on the fifth day of gestation in Sprague-Dawley Dams. Although both saline- and nicotine-exposed pups gained weight at the same rate throughout the studies, there were subtle differences in ventilatory indices between the two groups. Nicotine-exposed animals had a significantly higher breathing frequency on day 10, and a lower tidal volume on days 14 and 18. Although ventilation tended to be lower in the nicotine-exposed animals, the difference was not significant. There was a significantly higher frequency of apneas in the nicotine-exposed compared with the saline-exposed animals on postnatal days 1 and 2, but the apnea duration did not differ between the groups. No apneas were observed in any of the animals after the sixth postnatal day. Prenatal nicotine exposure is associated with a greater incidence of apneas on the first two postnatal days, and then an altered breathing pattern that manifests at a later stage of development.