The effects of prenatal nicotine on radial-arm maze performance in rats

Smoking during pregnancy: postnatal effects on arousal and attentional brain systems

Prenatal exposure to cigarette smoke is known to produce lasting arousal, attentional and cognitive deficits in humans. The pedunculopontine nucleus (PPN), as the cholinergic arm of the reticular activating system (RAS), is known to modulate arousal, waking and REM sleep. Rapid eye movement (REM) sleep decreases between 10 and 30 days postnatally in the rat, with the greatest decrease occurring at 12-21 days. Pregnant dams were exposed to 150 ml of cigarette smoke for 15 min, three times per day, from day E14 until parturition, and the pups allowed to mature. We analyzed (a) intrinsic membrane properties of PPN neurons in slices from pups aged 12-21 days, and (b) the sleep state-dependent P13 auditory evoked potential, which is generated by PPN outputs, in animals allowed to age to adolescence. We found significant changes in the intrinsic membrane properties of PPN cells in prenatally exposed animals compared to intact ones, rendering these cells more excitable. In addition, we found disturbances in the habituation to repetitive stimulation in adolescent, freely moving animals, suggestive of a deficit in the process of sensory gating. These findings could explain some of the differences seen in individuals whose parents smoked during pregnancy, especially in terms of their hypervigilance and increased propensity for attentional deficits and cognitive/behavioral disorders.

Undertaking positive control studies as part of developmental neurotoxicity testing: a report from the ILSI Research Foundation/Risk Science Institute expert working group on neurodevelopmental endpoints

Developmental neurotoxicity testing involves functional and neurohistological assessments in offspring during and following maternal and/or neonatal exposure. Data from positive control studies are an integral component in developmental neurotoxicity risk assessments. Positive control data are crucial for evaluating a laboratory's capability to detect chemical-induced changes in measured endpoints. Positive control data are also valuable in a weight-of-evidence approach to help determine the biological significance of results and provide confidence in negative results from developmental neurotoxicity (DNT) studies. This review is a practical guide for the selection and use of positive control agents in developmental neurotoxicology. The advantages and disadvantages of various positive control agents are discussed for the endpoints in developmental neurotoxicity studies. Design issues specific to positive control studies in developmental neurotoxicity are considered and recommendations on how to interpret and report positive control data are made. Positive control studies should be conducted as an integral component of the incorporation and use of developmental neurotoxicity testing methods in laboratories that generate data used in risk decisions.

Long-term behavioral and developmental consequences of pre- and perinatal nicotine

Research has shown that cigarette use during pregnancy can result in increased fetal mortality, sudden infant death syndrome, and behavioral and attentional disorders during childhood. Neurochemical and behavioral consequences of prenatal nicotine exposure have been well documented although few studies have examined long-term behavioral consequences that persist into adulthood. In this study, fifty-eight male and female Long-Evans rats were exposed to chronic nicotine prenatally and postnatally via subcutaneous infusions (0.96 mg/kg/day) in the dam. Nicotine exposure continued in the pups via maternal milk until the dams' osmotic mini-pumps became exhausted at approximately postnatal day (P) 11. At weaning, animals were group housed until behavioral testing at P60 to assess spatial learning and memory in the Morris water maze (MWM). Mild deficits in spatial learning were observed in nicotine-exposed females. These behavioral differences were accompanied by significant reduction in weight gain of nicotine-exposed females beginning at puberty, suggesting a hormonal interaction. Long-term effects of nicotine exposure were less striking in males. Nicotine-exposed males had significantly slower swim speeds than controls, but latency to reach the hidden platform was equal between groups by the conclusion of testing. Weight gain in males did not differ between groups as a result of prenatal nicotine exposure.

Effects of maternal intravenous nicotine administration on locomotor behavior in pre-weanling rats

Maternal tobacco use is associated with adverse developmental outcomes in offspring, including hyperactivity. Animal studies attempting to model this phenomenon have primarily used continuous s.c. nicotine infusion as the method of nicotine administration, which does not model the intermittent bolus delivery of nicotine associated with smoking in humans. The purpose of the present experiment was to examine the locomotor activity of pre-weanling offspring of pregnant rats exposed to an i.v. nicotine dosing protocol that approximates the pattern of nicotine exposure in moderate to heavy smokers. Pregnant rats were administered an i.v. bolus of 0.03 mg/kg nicotine (N=13) or saline (N=10) every 14 min for 16 h/day, resulting in a total daily dose of 2 mg/kg (base), from gestational day 4 to delivery. Pups from each litter were tested for spontaneous locomotor activity on postnatal days (PND) 19-21 and nicotine-induced locomotor activity on PND 22. Mean birth weight was significantly lower in nicotine-exposed pups compared to controls, but body weights were equivalent between groups by the time of behavioral testing. Mean total distance traveled, vertical counts, and stereotypy counts were lower on PND 19 in nicotine-exposed pups compared to controls, but only the difference in mean stereotypy counts was statistically significant. Within-session analysis revealed that both distance traveled and stereotypy were significantly decreased in nicotine-exposed pups in the first 5 min of the session on PND 19. Total time spent in the center of the field was also lower in nicotine-exposed pups. Nicotine-induced increases in activity on PND 22 did not differ according to gestational exposure. These findings demonstrate that prenatal nicotine exposure in a model that mimics the pattern of nicotine exposure from cigarette smoking in humans results in offspring that exhibit low birth weight and hypoactivity in a novel environment.

Molecular studies on the protective effect of nicotine in adult-onset hypothyroidism-induced impairment of long-term potentiation

We have recently shown that chronic nicotine treatment reverses hypothyroidism-induced learning and memory impairment. Chronic nicotine treatment also reverses the hypothyroidism-induced impairment of long-term potentiation (LTP). Analysis of LTP associated key signaling molecules revealed that chronic nicotine treatment prevented the hypothyroidism-induced reduction of the basal phosphotransferase activity of CaMKII and protein levels of P-CaMKII. In addition, the failure of high frequency stimulation to increase the levels of P-CaMKII in hypothyroid rats was reversed by nicotine treatment, suggesting that the neuroprotective effect of nicotine during hypothyroidism involved activation of CaMKII. Furthermore, chronic nicotine treatment reverses the hypothyroidism-induced elevated phosphatase activity and protein levels of calcineurin, a phosphatase that regulates CaMKII activation. We conclude that the neuroprotective effects of nicotine in adult-onset hypothyroidism may result from restoration of CaMKII and calcineurin activity.

Nicotine reverses adult-onset hypothyroidism-induced impairment of learning and memory: Behavioral and electrophysiological studies

Nicotine alleviates cognitive impairment associated with a variety of health conditions. We examined the effect of chronic nicotine treatment on adult-onset hypothyroidism-induced impairment of learning and memory in rats. Hypothyroidism was induced by surgical removal of thyroid glands (thyroidectomy). One month later, chronic nicotine treatment (1 mg/kg sc, twice/day) was instituted for 4-6 weeks. Test of hippocampus-dependent spatial learning and memory in the radial arm water maze showed that hypothyroidism impaired learning as well as short-term and long-term memory retention. Chronic nicotine treatment reversed the hypothyroidism-induced learning and memory impairment. In normal rats, chronic nicotine treatment had no effect on learning and memory. Extracellular recordings from the CA1 region of anesthetized hypothyroid rats showed severe reduction of both early-phase and late-phase long-term potentiation (LTP) magnitude, which was reversed in nicotine-treated hypothyroid rats. These results show that chronic nicotine treatment prevents hypothyroidism-induced impairment of spatial cognition and LTP.

Chronic neonatal nicotine upregulates heteromeric nicotinic acetylcholine receptor binding without change in subunit mRNA expression

Smoking during pregnancy chronically exposes the fetus to nicotine resulting in long-term behavioral and cognitive deficits. Nicotine binds to neuronal nicotinic acetylcholine receptors (nAChRs), pentameric ligand-gated ion channels widely expressed in the nervous system. Chronic nicotine upregulates high-affinity nAChRs in animals and smokers. Here we determined if chronic nicotine treatment during a developmental period corresponding to the human third trimester regulates nAChR expression. Rat pups were intubated orally three times per day with or without nicotine (6 mg/kg/day) from postnatal day 1 to 8. Subunit mRNA expression was assessed by in situ hybridization. Expression of heteromeric and homomeric nAChR receptor was evaluated by autoradiography using (125)I-epibatidine and (125)I-alphabungarotoxin, respectively. nAChR expression was analyzed in cortex, hippocampus, thalamus and medial habenula from autoradiograms using computer assisted image analysis. Nicotine induced significant upregulation of heteromeric but not homomeric nAChRs in hippocampus, cortex and thalamus without changes in subunit mRNA expression. No effect of chronic nicotine on receptor expression was detected in the medial habenula, suggesting that nicotine's effect was mainly on alpha4beta2-type heteromeric nAChRs. The nicotine-induced upregulation was reversed after nicotine withdrawal. Receptor blockade by DHbetaE, an antagonist for heteromeric alpha4/beta2 nAChRs, did not prevent upregulation but increased expression to a similar degree as nicotine. Combination of both drugs had a cumulative effect. Thus, although transient, intermittent nicotine exposure as seen in smoking mothers is sufficient to upregulate heteromeric nAChRs during a critical period of brain development and could contribute to the behavioral deficits found in children whose mother smoked.

alpha7 Nicotinic acetylcholine receptors and temporal memory: synergistic effects of combining prenatal choline and nicotine on reinforcement-induced resetting of an interval clock

We previously showed that prenatal choline supplementation could increase the precision of timing and temporal memory and facilitate simultaneous temporal processing in mature and aged rats. In the present study, we investigated the ability of adult rats to selectively control the reinforcement-induced resetting of an internal clock as a function of prenatal drug treatments designed to affect the alpha7 nicotinic acetylcholine receptor (alpha7 nAChR). Male Sprague-Dawley rats were exposed to prenatal choline (CHO), nicotine (NIC), methyllycaconitine (MLA), choline + nicotine (CHO + NIC), choline + nicotine + methyllycaconitine (CHO + NIC + MLA), or a control treatment (CON). Beginning at 4-mo-of-age, rats were trained on a peak-interval timing procedure in which food was available at 10-, 30-, and 90-sec criterion durations. At steady-state performance there were no differences in timing accuracy, precision, or resetting among the CON, MLA, and CHO + NIC + MLA treatments. It was observed that the CHO and NIC treatments produced a small, but significant increase in timing precision, but no change in accuracy or resetting. In contrast, the CHO + NIC prenatal treatment produced a dramatic increase in timing precision and selective control of the resetting mechanism with no change in overall timing accuracy. The synergistic effect of combining prenatal CHO and NIC treatments suggests an organizational change in alpha7 nAChR function that is dependent upon a combination of selective and nonselective nAChR stimulation during early development.

Prenatal exposure to cigarette smoke affects the physiology of pedunculopontine nucleus (PPN) neurons in development

Prenatal exposure to cigarette smoke is known to produce lasting arousal, attentional and cognitive deficits in humans. The pedunculopontine nucleus (PPN), as the cholinergic arm of the reticular activating system (RAS), is known to modulate arousal, waking and rapid eye movement (REM) sleep. REM sleep decreases between 10 and 30 days postnatally in the rat, especially at 12-21 days. Pregnant dams were exposed to 350 ml of cigarette smoke for 15 min, 3 times per day, from day E14 until birth, and the pups allowed to mature. Intracellularly recorded PPN neurons in 12-21 day rat brainstem slices were tested for intrinsic membrane properties, including the hyperpolarization-activated cation current Ih, which is known to drive oscillatory activity. Type II (A-current) PPN cells from 12-16 day old offspring of treated animals had a 1/2max Ih amplitude of (mean +/- SE) 4.1 +/- 0.9 mV, while 17-21 day cells had a higher 1/2max Ih of 9.9 +/- 1.1 mV (p < 0.0001). Cells from 12-16 day old control brainstems had a 1/2max Ih of 1.3 +/- 0.1 mV, which was lower (p < 0.05) than in cells from prenatally treated offspring; while 17-21 day old cells from controls had a 1/2max Ih of 3.3 +/- 0.3 mV, which was also lower (p < 0.01) than in cells from prenatally treated offspring. In addition, changes in resting membrane potential [control -65. +/- 0.9 mV (n=32); exposed -55.0 +/- 1.4 mV (n = 27) (p < 0.0001)], and action potential (AP) threshold [control -56.5 +/- 0.7 mV (n = 32), exposed -47.0 +/- 1.4 mV (n = 27) (p < 0.0001)], suggest that prenatal exposure to cigarette smoke induced marked changes in cells in the cholinergic arm of the RAS, rendering them more excitable. Such data could partially explain the differences seen in individuals whose parents smoked during pregnancy, especially in terms of their hypervigilance and increased propensity for attentional deficits and cognitive/behavioral disorders.

Event-related potentials in cocaine-exposed children during a Stroop task

OBJECTIVE

Prenatal cocaine-exposure may interfere with the ontogeny of prefrontal cortical executive functions due to cocaine's effect on the developing monoaminergic system. This study presents findings regarding cortical functioning in 29 prenatally cocaine-exposed (CE) and non-drug-exposed (NDE) 7- to 9-year-old children participating in event related potential (ERP) studies.

METHODS

ERPs were recorded using 128-electrode high-density arrays while children responded to a standard Stroop paradigm.

RESULTS

In the Stroop paradigm, CE children generated prolonged responses to the words while the NDE children produced briefer responses. Effects were noted in the region of the initial positive peak (P1), the second negative peak (N2) and the later positive peak (P3).

CONCLUSIONS

Early cocaine exposure may inhibit the specialization and streamlining of brain region involvement during cognitive processing such that task processing is slower to begin, requires more diverse cortical involvement, and requires more time to complete. ERP methodology has considerable potential for studying frontal maturation and may provide additional information to clarify generally the specific effects of prenatal CE on cortical functioning and the developmental course of cognitive functions.

An assessment of the long-term developmental and behavioral teratogenicity of prenatal nicotine exposure

Maternal tobacco use during pregnancy adversely affects prenatal and postnatal growth and increases the risk of developmental and behavioral deficits in children and adolescents. In the present study, the effects of prenatal nicotine exposure (infused at 6mg/kg/day) and maternal withdraw during neonatal development, was examined in Sprague-Dawley rats on an array of behavioral tasks during different stages of ontogenesis. Offspring of both genders were monitored for exploratory, locomotor, and novelty-seeking activity, anxiety, and learning and memory in an active-avoidance task. Nicotine-exposed animals showed growth retardation, hyperactivity, and poor adaptation in a new environment, increased level of anxiety during the early adolescent period, and robust cognitive deficits in early adulthood. In addition, the deficits were generally more severe in the female nicotine-exposed offspring. Cross-fostering also revealed that while maternal behavior and nicotine withdraw did not affect postnatal somatic growth retardation or cognitive ability of the offspring; measures of exploration and adaptation in a new environment were impacted during the post-weanling and early adolescence period. Nicotine-exposed offspring, and the saline-treated offspring cross-fostered to nicotine-exposed mothers, showed higher measures of anxiety in the elevated plus-maze and decreased novelty-seeking behavior on the hole-board apparatus. These studies demonstrated that prenatal nicotine exposure produced significant long-term developmental and behavioral teratogenic effects. The study design provides a model system for studying the mechanism(s) responsible for the decline in central nervous system function following prenatal nicotine exposure, as well as that of other neurological and behavioral teratogens during pregnancy.

Conditional expression in corticothalamic efferents reveals a developmental role for nicotinic acetylcholine receptors in modulation of passive avoidance behavior

Prenatal nicotine exposure has been linked to attention deficit hyperactivity disorder and cognitive impairment, but the sites of action for these effects of nicotine are still under investigation. High-affinity nicotinic acetylcholine receptors (nAChRs) contain the beta2 subunit and modulate passive avoidance (PA) learning in mice. Using an inducible, tetracycline-regulated transgenic system, we generated lines of mice with expression of high-affinity nicotinic receptors restored in specific neuronal populations. One line of mice shows functional beta2 subunit-containing nAChRs localized exclusively in corticothalamic efferents. Functional, presynaptic nAChRs are present in the thalamus of these mice as detected by nicotine-elicited rubidium efflux assays from synaptosomes. Knock-out mice lacking high-affinity nAChRs show elevated baseline PA learning, whereas normal baseline PA behavior is restored in mice with corticothalamic expression of these nAChRs. In contrast, nicotine can enhance PA learning in adult wild-type animals but not in corticothalamic-expressing transgenic mice. When these transgenic mice are treated with doxycycline in adulthood to switch off nAChR expression, baseline PA is maintained even after transgene expression is abolished. These data suggest that high-affinity nAChRs expressed on corticothalamic neurons during development are critical for baseline PA performance and provide a potential neuroanatomical substrate for changes induced by prenatal nicotine exposure leading to long-term behavioral and cognitive deficits.

Risks and benefits of nicotine to aid smoking cessation in pregnancy

Cigarette smoking during pregnancy is the single largest modifiable risk for pregnancy-related morbidity and mortality in the US. Addiction to nicotine prevents many pregnant women who wish to quit smoking from doing so. The safety and efficacy of nicotine replacement therapy (NRT) for smoking cessation during pregnancy have not been well studied. Nicotine is classified by the US Food and Drug Administration as a Pregnancy Category D drug. Animal studies indicate that nicotine adversely affects the developing fetal CNS, and nicotine effects on the brain may be involved in the pathophysiology of sudden infant death syndrome (SIDS). It has been assumed that the cardiovascular effects of nicotine resulting in reduced blood flow to the placenta (uteroplacental insufficiency) is the predominant mechanism of the reproductive toxicity of cigarette smoking during pregnancy. Short term high doses of nicotine in pregnant animals do adversely affect the maternal and fetal cardiovascular systems. However, studies of the acute effects of NRT in pregnant humans indicate that nicotine alone has minimal effects upon the maternal and fetal cardiovascular systems. Cigarette smoking delivers thousands of chemicals, some of which are well documented reproductive toxins (e.g. carbon monoxide and lead). A myriad of cellular and molecular biological abnormalities have been documented in placentas, fetuses, and newborns of pregnant women who smoke. The cumulative abnormalities produced by the various toxins in cigarette smoke are probably responsible for the numerous adverse reproductive outcomes associated with smoking. It is doubtful that the reproductive toxicity of cigarette smoking is primarily related to nicotine. We recommend the following. Efficacy trials of NRT as adjunctive therapy for smoking cessation during pregnancy should be conducted. The initial dose of nicotine in NRT should be similar to the dose of nicotine that the pregnant woman received from smoking. Intermittent-use formulations of NRT (gum, spray, inhaler) are preferred because the total dose of nicotine delivered to the fetus will be less than with continuous-use formulations (transdermal patch). A national registry for NRT use during pregnancy should be created to prospectively collect obstetrical outcome data from NRT efficacy trials and from individual use. The goal of this registry would be to determine the safety of NRT use during pregnancy, especially with respect to uncommon outcomes such as placental abruption. Finally, our review of the data indicate that minimal amounts of nicotine are excreted into breast milk and that NRT can be safely used by breast-feeding mothers.

Behavioral and neural consequences of prenatal exposure to nicotine

OBJECTIVE

To review evidence for the neurodevelopmental effects of in utero exposure to nicotine. Concerns about long-term cognitive and behavioral effects of prenatal exposure to nicotine arise from reports of increased rates of disruptive behavioral disorders in children whose mothers smoked during pregnancy. The relatively high rate of tobacco smoking among pregnant women (25% of all pregnancies in the U.S.) underlines the seriousness of these concerns.

METHOD

This review examines the largest and most recent epidemiological and clinical studies that investigated the association of prenatal nicotine exposure with health, behavioral, and cognitive problems. Because of the numerous potential confounding variables in human research, findings from animal studies, in which environmental factors are strictly controlled, are also discussed. Finally, neural and molecular mechanisms that are likely to underlie neurodevelopmental disruptions produced by prenatal nicotine exposure are outlined.

RESULTS

A dose-response relationship between maternal smoking rates and low birth weight (potentially associated with lower cognitive ability) and spontaneous abortion is consistently found, whereas long-term developmental and behavioral effects in the offspring are still controversial, perhaps because of the difficulty of separating them from other genetic and environmental factors. Despite the wide variability of experimental paradigms used in animal studies, common physical and behavioral effects of prenatal exposure to nicotine have been observed, including low birth weight, enhanced locomotor activity, and cognitive impairment. Finally, disturbances in neuronal pathfinding, abnormalities in cell proliferation and differentiation, and disruptions in the development of the cholinergic and catecholaminergic systems all have been reported in molecular animal studies of in utero exposure to nicotine.

CONCLUSIONS

Prenatal exposure to nicotine may lead to dysregulation in neurodevelopment and can indicate higher risk for psychiatric problems, including substance abuse. Knowledge of prenatal exposure to nicotine should prompt child psychiatrists to closely monitor at-risk patients.

Prenatal nicotine exposure is associated with an increase in [125I]epibatidine binding in discrete cortical regions in rats

Previously, it was reported that hyperactive male offspring of dams exposed to nicotine (6 mg/kg/day) during gestation had an increase in cortical alpha4-beta2 nicotinic receptor subtype density as determined by [3H]cytisine binding in tissue homogenate [Tizabi Y, Popke EJ, Rahman MA, Nespor SM, Grunberg NE. Hyperactivity induced by prenatal nicotine exposure is associated with an increase in cortical nicotinic receptors. Pharmacol, Biochem Behav 1997;58:141-6]. [125I]Epibatidine labels alpha4beta2 nicotinic receptors with higher affinity than [3H]cytisine. In the present study, using quantitative autoradiography, we evaluated the effects of in-utero exposure to nicotine (9 mg/kg/day) on [125I]epibatidine binding in 46 discrete brain regions of 36-day-old male offspring of Sprague-Dawley rats. This dosage of nicotine administered during pregnancy to same rats was shown to result in increased vertical activity in the male offspring [Tizabi Y, Russell LT, Nespor SM, Perry DC, Grunberg NE. Prenatal nicotine exposure: effects on locomotor activity and central [125I]alpha-BT binding in rats. Pharmacol, Biochem Behav (in press).]. Prenatal nicotine exposure resulted in increases in receptor densities of the somatosensory cortex (90%) and the visual cortex (107%) only. Moreover, these increases were restricted to cortical layer 1. Collectively, these results indicate that prenatal nicotine exposure affects specific nicotinic receptors in selective cortical regions of male offspring. These neurochemical effects may be responsible for some of the behavioral abnormalities seen in such offspring.

Nicotine exposure during the neonatal brain growth spurt produces hyperactivity in preweanling rats

Despite warning labels and increases in evidence of the adverse effects of tobacco use, women continue to use tobacco products during pregnancy. Cigarette smoking has been linked to increased prenatal mortality, increased incidence of SIDS, reductions in birth weight, and disruptions in CNS and behavioral development. Animal model systems have critically established the causal relationship between nicotine and adverse developmental outcome. The present study examines the behavioral effects of nicotine exposure in the rat during the third trimester equivalent of the human brain growth spurt, a period of rapid development of the cholinergic systems and a period during which the CNS is particularly vulnerable to a number of insults. Sprague-Dawley rat pups were exposed to nicotine (6.0 mg/kg/day) from postnatal days (PD) 4-9 via an artificial rearing procedure. This procedure ensures that observed effects are not due to nutritional deficits. Two control groups were employed, an artificially reared control group and a normally reared control group. Activity level was measured on PD 18-19. Nicotine-exposed subjects were significantly overactive compared to both control groups, which did not differ significantly from one another. This behavioral alteration was observed in the absence of nicotine-induced body weight deficits. These results suggest that women who use tobacco products during late gestation may place their fetuses at risk for hyperactivity later in life, particularly during early adolescence.

Prenatal nicotine exposure: effects on locomotor activity and central [125I]alpha-BT binding in rats

Maternal smoking during pregnancy or in utero exposure of the fetus to nicotine may result in learning difficulties and hyperactivity in the child. To elucidate possible involvement of the alpha(7) nicotinic receptor subtype in these behavioral impairments, pregnant dams were treated with nicotine (9 mg/kg/day) via osmotic minipumps throughout gestation. Male offspring were weaned at postnatal day 18, and were tested for locomotor activity at postnatal days 20-24. Pups were sacrificed on postnatal day 36-38 and 18 discrete brain areas were analyzed for [125I]alpha-bungarotoxin (alpha-BT) binding by quantitative autoradiography. Prenatal nicotine caused an elevation in locomotor activity (vertical movements) in offspring. [125I]alpha-BT binding was significantly reduced in the hippocampal CA1 region (29%), dentate gyrus (22%), and medial geniculate nucleus (29%). These findings suggest that some of the behavioral abnormalities induced by prenatal nicotine exposure may be due to a reduction of alpha(7) nicotinic receptors in discrete brain regions.

Neonatal nicotine exposure alters hippocampal EEG and event-related potentials (ERPs) in rats

A consensus is forming that nicotine can damage the developing rat central nervous system. However, few studies have assessed the electrophysiological effects of neonatal nicotine exposure in rodents in brain regions known to be sensitive to the teratogenic properties of nicotine. In a previous study it was reported that 1.0 and 4.0 mg/kg/day nicotine exposure from postnatal days 4-9, a developmental period corresponding to human third-trimester exposure, significantly altered hippocampal event-related potentials (ERPs) but did not effect cortical ERPs, cortical EEG, or hippocampal EEG. Because alterations in behavior and cortical/hippocampal neurochemistry and morphology have been reported following nicotine exposure, the present study used a higher dose of nicotine during the postnatal period (6.0 mg/kg/day) determine if functional changes in the EEG of these regions might contribute to behavioral changes that have been observed. Male Sprague-Dawley rats were exposed to 6. 0 mg/kg/day nicotine via gastric infusion using an artificial rearing, "pup-in-the-cup," technique for 6 consecutive days (postnatal days 4-9). At adulthood, EEG and auditory ERPs were recorded from the cortex and hippocampus. There were no significant differences in EEG or ERPs recorded from the cortex between nicotine-treated and control subjects. Examination of the hippocampal EEG revealed significantly decreased power in the 1-2-Hz frequency band of nicotine-treated rats. In addition, there was a significantly attenuated P300 ERP response to a noise tone in the nicotine-treated rats compared to controls. These data indicate that neonatal nicotine exposure alters functional activity in the hippocampus of adult rats. These effects are likely to be the result of synaptic disorganization in the hippocampus, and indicate that neonatal nicotine exposure exerts teratogenic effects on the developing central nervous system, particularly the hippocampus, which persist into adulthood.

Brain waves and brain wiring: the role of endogenous and sensory-driven neural activity in development

Neural activity is critical for sculpting the intricate circuits of the nervous system from initially imprecise neuronal connections. Disrupting the formation of these precise circuits may underlie many common neurodevelopmental disorders, ranging from subtle learning disorders to pervasive developmental delay. The necessity for sensory-driven activity has been widely recognized as crucial for infant brain development. Recent experiments in neurobiology now point to a similar requirement for endogenous neural activity generated by the nervous system itself before sensory input is available. Here we use the formation of precise neural circuits in the visual system to illustrate the principles of activity-dependent development. Competition between the projections from lateral geniculate nucleus neurons that receive sensory input from the two eyes shapes eye-specific connections from an initially diffuse projection into ocular dominance columns. When the competition is altered during a critical period for these changes, by depriving one eye of vision, the normal ocular dominance column pattern is disrupted. Before ocular dominance column formation, the highly ordered projection from retina to lateral geniculate nucleus develops. These connections form before the retina can respond to light, but at a time when retinal ganglion cells spontaneously generate highly correlated bursts of action potentials. Blockade of this endogenous activity, or biasing the competition in favor of one eye, results in a severe disruption of the pattern of retinogeniculate connections. Similar spontaneous, correlated activity has been identified in many locations in the developing central nervous system and is likely to be used during the formation of precise connections in many other neural systems. Understanding the processes of activity-dependent development could revolutionize our ability to identify, prevent, and treat developmental disorders resulting from disruptions of neural activity that interfere with the formation of precise neural circuits.

Exposure to prenatal nicotine transiently increases neuronal nicotinic receptor subunit alpha7, alpha4 and beta2 messenger RNAs in the postnatal rat brain

This study determined the effects of prenatal nicotine exposure (2 mg/kg/day) in Sprague Dawley CD rats via subcutaneously implanted osmotic minipumps, during gestational days 7-21, on postnatal levels of neuronal nicotinic receptor alpha4, alpha7 and beta2 subunit messenger RNAs. Northern analysis of postnatal day 1, 7, 14 and 28 hippocampal/septal and cortical total RNA using alpha-[32P]dCTP-labeled alpha4, alpha7 and beta2 complementary DNA probes identified a single (5.7-kb) alpha7 messenger RNA, three (2.4-, 3.8- and 8.0-kb) alpha4 messenger RNAs and four (3.7-, 5.0-, 7.5- and 10.0-kb) beta2 messenger RNAs. In comparison to prenatal saline, prenatal nicotine produced several significantly higher messenger RNA levels (cortical: 5.7-kb alpha7, 2.4-, 3.8- and 8.0-kb alpha4, 10.0-kb beta2; hippocampal/septal: 2.4- and 8.0-kb alpha4); these increases occurred predominantly on, but were not restricted to, postnatal day 14. Effects of nicotine were generally resolved by postnatal day 28. Collapsing the data across sex and age, a significant treatment effect indicated that hippocampal/septal and cortical 8.0-kb alpha4 messenger RNA levels and 10.0-kb beta2 messenger RNA levels were significantly higher following prenatal nicotine exposure. This is the first study indicating that prenatal nicotine produces alterations in developing postnatal rat neuronal nicotinic receptor messenger RNA levels, possibly by premature stimulation of neuronal nicotinic receptors. These results further implicate the teratogenic potential of nicotine in postnatal neuronal development.

Prenatal exposure to nicotine: effects on prepulse inhibition and central nicotinic receptors

The present experiment examined effects of prenatal nicotine exposure (6 mg/kg/day via osmotic minipump) throughout gestation on prepulse inhibition of the acoustic startle response (PPI) and on the density of nicotinic acetylcholine receptors (nAchRs) in the brains of 5-week-old Sprague-Dawley rats. A total of 117 male and 103 female offspring were used. Prenatal nicotine reduced subsequent percent PPI to a 98 dB stimulus in female but not in male offspring. There was an inverse correlation between the percent of PPI and nAchR density in the cortex of male rats and the striatum of female rats.

Prenatal nicotine exposure affects the development of the central serotonergic system as well as the dopaminergic system in rat offspring: involvement of route of drug administrations

The present study was undertaken to examine the effects of prenatal nicotine exposure by two different routes of drug administration, injection and infusion, on the development of monoaminergic systems and open field behavior in the neonatal and juvenile rat. The nicotine administration to pregnant Sprague-Dawley rats was carried out by subcutaneous injection (3 mg/kg twice daily) or infusion via implanted osmotic minipumps (6 mg/kg/day) from gestational day 4 (GD4) until GD20. At postnatal day 7 (PD7), 15 and 22, the contents of the neurotransmitters and their metabolites including noradrenaline (NA), dopamine (DA), dihydroxyphenylacetic acid (DOPAC), homovanilic acid (HVA), serotonin (5-HT) and 5-hydroxy-3-indolacetic acid (5-HIAA) were measured in the midbrain+pons - medulla (M + P - M), forebrain and cerebellum. Prenatal nicotine exposure caused a persistent reduction of DA turnover in the forebrain at PD15 and PD22. In addition, the 5-HT system was also affected by prenatal nicotine, and reductions of 5-HT turnover in the M + P - M at PD15 and in the forebrain and the cerebellum at PD22 were found. Although there was no effect of prenatal nicotine on NE contents, the involvement of this system remains uncertain since we measured only NE contents without metabolites. In the present study, we also found significant route-related changes in the contents of the monoamines and metabolites in the NA, DA and 5-HT systems in all brain regions in rat offspring besides the effects of prenatal nicotine. In addition, the difference in administration route reflected the results of the open field test and the number of ambulations in the injection-group was less than that in the infusion-groups with no relation to nicotine administration. Therefore, such effects of "prenatal stress" accompanied by drug administration are not negligible in considering the risk assessment of prenatal nicotine exposure.

Prenatal nicotine effects on memory in rats: pharmacological and behavioral challenges

Cigarette smoking during pregnancy has been shown in a variety of studies to be associated with cognitive deficits in the children. Nicotine administration to rats during gestation has been found to cause subtle cognitive effects in the offspring. Some individual differences in cognitive impairment may be related to prenatal nicotine effects on noradrenergic (NE) systems. In the current study, 10 Sprague-Dawley rat dams were infused with approximately 2 mg/kg/day of nicotine ditartrate via osmotic minipumps and 10 control dams were exposed to vehicle-containing minipumps from gestational day (GD) 4-20. Starting on postnatal day (PND) 50, the offspring were tested for T-maze rewarded spatial alternation with intertrial intervals of 0, 10, 20, or 40 s. There was a sex- and delay-dependent effect of prenatal nicotine exposure on T-maze alternation. Nicotine-exposed males showed a significant deficit at the 0 s delay. In radial-arm maze (RAM) acquisition training there were no significant nicotine effects. However, significant nicotine-related effects were seen with subsequent behavioral and pharmacological challenges in the RAM. Changing the RAM testing location to an identical maze in a different room elicited a significant choice accuracy deficit in the prenatal nicotine-exposed rats compared with controls. Acute nicotine challenge did not cause any differential effects in the prenatal nicotine and control groups. During the isoproterenol (beta-NE agonist) challenge phase there appeared a significant facilitation of choice accuracy and speeding of response in the prenatal nicotine exposure group which was not seen in the control group. The alpha-NE agonist phenylpropanolamine caused a significant deficit in control females but not in the females prenatally exposed to nicotine. No differential effects of the alpha-NE antagonist phenoxybenzamine were seen in the prenatal nicotine and control groups. Throughout RAM testing there was a significant sex effect with males having better choice accuracy than females. These results demonstrate that the persisting cognitive effects of prenatal exposure to 2 mg/kg/day cause subtle effects in cognitive performance which can be elicited with behavioral and pharmacological challenge. These results also support previous studies suggesting the involvement of NE systems in persisting effects of prenatal nicotine exposure.

Interactive effects of prenatal cocaine and nicotine exposure on maternal toxicity, postnatal development and behavior in the rat

Two experiments were performed to investigate the interactive effects of prenatal coadministration of cocaine hydrochloride (C) and nicotine tartrate (N). Experiment I was designed to determine doses of C and N that could be coadministered without altering maternal gestational parameters and/or fetal viability. Exposure of Sprague-Dawley rats to combined high-dose C (20 mg/kg) and high-dose N (5.0 mg/kg) on gestation days 8-21 was not more toxic to dam or fetus that that of exposure to C alone. Experiment II investigated pregnancy outcome, postnatal development, and behavior of the offspring following drug exposure to either high-dose cocaine (20 mg/kg: CS), high-dose nicotine (5.0 mg/kg: NS), or both (NC) on gestation days 8-21. N was administered by osmotic minipump and C by sc injection. Saline-injected dams, fitted with saline-fitted pumps (SS), and untreated dams, pair-fed (PF) to NC females, served as controls. Alterations in maternal variables were limited to a 10-15% decrease in food consumption in NC and CS groups. Pregnancy outcome and birth statistics were unaffected by prenatal treatment, as was offspring body weight during the first four postnatal weeks. However, the development of surface righting was delayed inC CS pups, and only CS offspring were underresponsive to the stimulatory effects of dopamine agonists on activity and stereotypy. Behavioral responses to N challenge were similar in all groups. In addition, only CS offspring showed altered behavioral responses in a spontaneous alternation task. Treatment effects on dopamine D1 and D2 binding in the caudate nucleus were not observed. The combination of N and C did not exacerbate any of the behavioral changes seen in CS offspring. These results support the hypothesis that C is a behavioral teratogen in rodents, and suggest that in the present model, nicotine can mitigate some of the consequences of in utero exposure to cocaine.

A role for the nicotinic alpha-bungarotoxin receptor in neurite outgrowth in PC12 cells

The addition of nicotine decreased neuritic outgrowth in PC12 cells in culture. This effect occurs as early as one day after addition of nicotine to the culture medium in a concentration-dependent manner. The nicotine-induced decline in neurite outgrowth was prevented by d-tubocurarine (10(-4) M) indicating that the effect was mediated through a nicotinic receptor. alpha-Bungarotoxin (10(-8) M) was also able to inhibit the nicotine-induced decrease in process formation in a dose-dependent manner. The concentrations of alpha-bungarotoxin required to affect process outgrowth correlated with those required to inhibit radiolabelled alpha-bungarotoxin binding. alpha-Bungarotoxin had no effect on [3H]noradrenaline release, a functional response mediated through the alpha-bungarotoxin-insensitive neuronal nicotinic acetylcholine receptor, suggesting that alpha-bungarotoxin specifically interacts with the neuronal alpha-bungarotoxin receptor. The present results suggest a functional role for the neuronal nicotinic alpha-bungarotoxin receptor in neurite outgrowth.