Effects of postnatal nicotine exposure on apoptotic markers in the developing piglet brain

Immunohistochemistry for acetylcholinesterase and butyrylcholinesterase in the dorsal motor nucleus of the vagus (DMNV) of formalin-fixed, paraffin-embedded tissue: comparison with reported literature

The majority of research regarding the expression of acetylcholinesterase (AChE) and butyrylcholinesterase (BuChE) in the brain has been conducted using histochemistry to identify enzymatic activity in frozen fixed tissue. However, retrospective human neurochemistry studies are generally restricted to formalin-fixed, paraffin-embedded (FFPE) tissues that are not suitable for histochemical procedures. The availability of commercially available antibody formulations provides the means to study such tissues by immunohistochemistry (IHC). In this study, we optimised IHC conditions for evaluating the expression of AChE and BuChE in the brainstem, focusing on the dorsal motor nucleus of the vagus, in human and piglet FFPE tissues, using commercially available antibodies. Our results were compared to published reports of histochemically determined AChE and BuChE expression. We varied antibody concentrations and antigen retrieval methods, and evaluated different detection systems, with the overall aim to optimise immunohistochemical staining. The primary findings, consistent across both species, are: (1) AChE and BuChE expression dominated in the neuronal somata, specifically in the neuronal cytoplasm; and (2) no change in the protocol resulted in axonal/neuropil expression of AChE. These results indicate that IHC is a suitable tool to detect AChE and BuChE in FFPE tissue using commercial antibodies, albeit the staining patterns obtained differed from those using histochemistry in frozen tissue. The underlying cause(s) for these differences are discussed in detail and may be associated with the principal components of the staining method, the antibody protein target and/or limitations to the detection of epitopes by tissue fixation.

Association of Maternal Tobacco Use During Pregnancy With Preadolescent Brain Morphology Among Offspring

IMPORTANCE

Maternal tobacco use during pregnancy has been associated with various health consequences, including suboptimal neurodevelopment in offspring. However, the effect of prenatal exposure to maternal smoking on child brain development has yet to be elucidated.

OBJECTIVE

To investigate the association between maternal smoking during pregnancy and offspring brain development in preadolescence as well as the mediating pathways.

DESIGN, SETTING, AND PARTICIPANTS

This prospective, population-based cohort study was embedded in the Generation R Study, Rotterdam, the Netherlands. The Generation R Study was launched in 2002, with follow-up ongoing. Child brain morphology was assessed at 9 to 11 years of age (ie, 10-12 years between exposure and outcome assessment). Data analysis was performed from March 1, 2021, to February 28, 2022, and at the time of manuscript revision. Participants included the singleton children of pregnant women residing in the study area with an expected date of delivery between April 1, 2002, and January 31, 2006; 2704 children with information on maternal smoking during pregnancy and structural neuroimaging at 9 to 11 years of age were included. A subsample of 784 children with data on DNA methylation at birth was examined in the mediation analysis.

EXPOSURES

Information on maternal smoking during pregnancy was collected via a questionnaire in each trimester. As a contrast, paternal smoking was assessed at recruitment.

MAIN OUTCOMES AND MEASURES

Brain morphology, including brain volumes and surface-based cortical measures (thickness, surface area, and gyrification), was assessed with magnetic resonance imaging. For mediation analysis, DNA methylation at birth was quantified by a weighted methylation risk score.

RESULTS

The 2704 participating children (1370 [50.7%] girls and 1334 [49.3%] boys) underwent brain imaging assessment at a mean (SD) age of 10.1 (0.6) years. Compared with nonexposed children (n = 2102), exposure to continued maternal smoking during pregnancy (n = 364) was associated with smaller total brain volume (volumetric difference [b] = -14.5 [95% CI, -25.1 to -4.0] cm3), cerebral gray matter volume (b = -7.8 [95% CI, -13.4 to -2.3] cm3), cerebral white matter volume (b = -5.9 [95% CI, -10.7 to -1.0] cm3), and surface area and less gyrification. These associations were not explained by paternal smoking nor mediated by smoking-associated DNA methylation patterns at birth. Children exposed to maternal smoking only in the first trimester (n = 238) showed no differences in brain morphology compared with nonexposed children.

CONCLUSIONS AND RELEVANCE

The findings of this cohort study suggest that continued maternal tobacco use during pregnancy was associated with lower brain volumes and suboptimal cortical traits of offspring in preadolescence, which seemed to be independent of shared family factors. Tobacco cessation before pregnancy, or as soon as pregnancy is known, should be recommended to women for optimal brain development of their offspring.

Early Postnatal Exposure to Intermittent Hypercapnic Hypoxia (IHH), but Not Nicotine, Decreases Reelin in the Young Piglet Hippocampus

This study evaluated the expression of reelin, an extracellular protein involved in lamination and migration of neurons, in the hippocampus of young piglets, and quantified to examine the following: (i) baseline levels within layers of the hippocampus and dentate gyrus (DG); (ii) differences between ventral and dorsal hippocampi; and (iii) changes attributable to postnatal exposure to continuous nicotine for 12 days, or intermittent hypercapnic hypoxia (IHH), with further analysis according to duration of IHH (1 vs 4 days). Additionally, we analysed whether any exposure altered DG morphology and whether it is related to altered reelin expression. Reelin was visualised via immunohistochemistry, and the number of positive reelin cells/mm² was measured in the CA4/Hilus, layers of the DG, and the CA1. The dorsal DG had significantly more reelin within the subgranular zone compared to the ventral DG (p < 0.01). There was no difference in reelin between nicotine (n = 5) and controls (n = 5). IHH exposed piglets (n = 10) had significantly lowered reelin in the CA1 (p = 0.05), specifically the stratum pyramidale (p = 0.04) and the hippocampal fissure (p = 0.02), compared to their controls (n = 7); the duration of IHH had no effect. No exposure was associated with an alteration in DG morphology. This study shows that postnatal IHH exposure decreased reelin expression in the developing piglet hippocampal CA1, suggesting that IHH may result in altered neuronal migration.

Immunostaining for NeuN Does Not Show all Mature and Healthy Neurons in the Human and Pig Brain: Focus on the Hippocampus

Neuronal nuclei (NeuN) is a neuron-specific nuclear protein, reported to be stably expressed in most postmitotic neurons of the vertebrate nervous system. Reduced staining has been interpreted by some to indicate loss of cell viability in human studies, while others suggest this may be because of changes in the antigenicity of the target epitope. Preliminary studies in our laboratory found low immunostaining for the NeuN antibody on formalin fixed and paraffin embedded (FFPE) human brain tissue. We report on the techniques and results used to enhance the staining for NeuN in that tissue. In parallel, we stained NeuN in piglet brain tissue, sourced from an experimental model where methodological parameters, including those for tissue fixation and storage, were tightly controlled. In human FFPE brain tissue, we were unable to enhance NeuN immunostaining to a degree sufficient for cell counting. In contrast, we found consistently high levels of staining in the piglet brain tissue. We conclude that processes used for fixation and storage of human FFPE brain tissue are responsible for the reduced staining. These results emphasize that a cautionary approach should be taken when interpreting NeuN staining outcomes in human FFPE brain tissue.

The α7 and β2 nicotinic acetylcholine receptor subunits regulate apoptosis in the infant hippocampus, and in sudden infant death syndrome (SIDS)

Apoptosis is increased in the hippocampus of infants who died of sudden infant death syndrome (SIDS), yet it is not known via which mechanism this has occurred. Following existing support for a role of the α7 and β2 nicotinic acetylcholine receptor (nAChR) subunits in apoptotic regulation, we aimed to determine whether these subunits are altered in the SIDS hippocampus and if they are correlated with cell death markers of active caspase-3 (Casp-3) and TUNEL. Further analyses were run according to the presence of major SIDS risk factors related to hypoxia (bed-sharing and prone sleeping), infection (presence of an upper respiratory tract infection (URTI)), cigarette smoke exposure and gender. Immunohistochemical expression of the markers was studied in 4 regions of the hippocampus (Cornu Ammonis (CA)1, CA2, CA3, CA4) and subiculum amongst 52 infants (aged 1-7 months) who died suddenly and unexpectedly (SUDI) and for whom the cause of death was explained (eSUDI; n = 9), or not and characterised as SIDS I (n = 8) and SIDS II (n = 35) according to the San Diego diagnostic criteria. Results showed that SIDS II infants had widespread increases in TUNEL compared with eSUDI and SIDS I infants, as well as increased α7 and Casp-3 in CA2 compared to eSUDI infants, although these changes were predominant amongst infants who did not bed-share. Cigarette smoke exposure had minimal effects on the markers, while an URTI was associated with changes in all markers (after accounting for bed-sharing). Our findings support the role of nAChRs in regulating apoptosis in the SIDS hippocampus, and highlight the need for separate analysis according to risk factors.

Histological effect of nicotine on adrenal zona fasciculata and the effect of grape seed extract with or without withdrawal of nicotine

Cigarette smoking is harmful to the health of both smokers and nonsmokers. It is a major cause of death. This study aimed to investigate the structural changes in the zona fasciculata of albino rats caused by nicotine and the protective effect of grape seeds with or without the stoppage of nicotine administration. Thirty-five adult male rats were used and equally divided into five groups: negative and positive control groups (Groups I and II), nicotine-treated group (Group III), nicotine- and grape seed extract-treated group (Group IV), and nicotine withdrawal and grape seed extract-treated group (Group V). Adrenal glands were dissected and prepared for histological studies. The majority of zona fasciculata cells of Group III showed striking changes in terms of swelling of the cells with marked cytoplasmic vacuolation, many pyknotic nuclei, and increased immunoexpression to caspase 3 antibodies. By electron microscopy, a marked increase in lipid deposition with its appearance in the capillary between zona fasciculata cells was noticed. Heterochromatic nuclei and dilated smooth endoplasmic reticulum were noted. Degenerated mitochondria and some mitochondria that had cavitation with a progressive loss of their cristae were seen. The zona fasciculata cells of Group IV were partially improved, while in Group V, those cells showed complete improvement. We can conclude that nicotine causes severe histological changes in zona fasciculata cells. Grape seed extract can partially ameliorate these changes, and complete recovery is achieved with grape seed extract after the stoppage of nicotine administration.

Developmental nicotine exposure enhances inhibitory synaptic transmission in motor neurons and interneurons critical for normal breathing

Nicotine exposure in utero negatively affects neuronal growth, differentiation, and synaptogenesis. We used rhythmic brainstems slices and immunohistochemistry to determine how developmental nicotine exposure (DNE) alters inhibitory neurotransmission in two regions essential to normal breathing, the hypoglossal motor nucleus (XIIn), and preBötzinger complex (preBötC). We microinjected glycine or muscimol (GABAA agonist) into the XIIn or preBötC of rhythmic brainstem slices from neonatal rats while recording from XII nerve roots to obtain XII motoneuron population activity. Injection of glycine or muscimol into the XIIn reduced XII nerve burst amplitude, while injection into the preBötC altered nerve burst frequency. These responses were exaggerated in preparations from DNE animals. Quantitative immunohistochemistry revealed a significantly higher GABAA receptor density on XII motoneurons from DNE pups. There were no differences in GABAA receptor density in the preBötC, and there were no differences in glycine receptor expression in either region. Nicotine, in the absence of other chemicals in tobacco smoke, alters normal development of brainstem circuits that are critical for normal breathing.

Orexin receptors in the developing piglet hypothalamus, and effects of nicotine and intermittent hypercapnic hypoxia exposures

Orexin and its receptors (OxR1 and OxR2) play a significant role in arousal and sleep regulation. Using developing piglets, we aimed to determine the effects of nicotine and Intermittent Hypercapnic Hypoxia (IHH), alone or in combination, on orexin receptor expression in the hypothalamus. Four piglet groups were studied: control (n=14), nicotine (n=14), IHH (n=10) and nic+IHH (n=14). Applying immunohistochemistry for OxR1 and OxR2 expression, eight nuclei/areas of the hypothalamus: dorsal medial nucleus (DMN), arcuate nucleus (ARC), perifornical area (PFA), paraventricular nucleus (PVN), lateral hypothalamic area (LHA), ventral medial nucleus (VMN), supraoptic nucleus, retrochiasmatic part (SONr) and tuberal mammillary nucleus (TMN), were studied. Compared to controls, OxR1 and OxR2 were increased due to exposures, however this was region dependent. Nicotine increased OxR1 in the DMN (P<0.001) and SONr (P=0.036), and OxR2 in the DMN (P<0.001), VMN (P=0.014) and the TMN (P=0.026). IHH increased OxR1 in the DMN, PVN, VMN and SONr (P<0.01 for all), and OxR2 in DMN (P<0.001), PFA (P=0.001), PVN (P=0.004), VMN (P=0.041) and the TMN (P<0.001). The nic+IHH exposure increased OxR1 expression in all nuclei (TMN excluded) however, the changes were not significantly different from IHH alone. For OxR2, the increased expression after nic+IHH was significant compared to IHH in the DMN, ARC and SONr. These results show that nicotine increases orexin receptor expression in a region dependent manner. IHH induced increases were specific to arousal and stress related regions and nic+IHH results suggest that for OxR1, nicotine has no additive effect whereas for OxR2 it does, and is region dependent.

The dorsal motor nucleus of the vagus (DMNV) in sudden infant death syndrome (SIDS): pathways leading to apoptosis

Sudden infant death syndrome (SIDS) remains the commonest cause of death in the post-neonatal period in the developed world. A leading hypothesis is that an abnormality in the brainstem of infants who succumb to SIDS, either causes or predisposes to failure to respond appropriately to an exogenous stressor. Neuronal apoptosis can lead to loss of cardiorespiratory reflexes, compromise of the infant's ability to respond to stressors such as hypoxia, and ultimately a sleep-related death. The dorsal motor nucleus of the vagus (DMNV) is a medullary autonomic nucleus where abnormalities have regularly been identified in SIDS research. This review collates neurochemical findings documented over the last 30 years, including data from our laboratory focusing on neuronal apoptosis and the DMNV, and provides potential therapeutic interventions targeting neurotransmitters, growth factors and/or genes.

Developmental hippocampal neuroplasticity in a model of nicotine replacement therapy during pregnancy and breastfeeding

RATIONALE

The influence of developmental nicotine exposure on the brain represents an important health topic in light of the popularity of nicotine replacement therapy (NRT) as a smoking cessation method during pregnancy.

OBJECTIVES

In this study, we used a model of NRT during pregnancy and breastfeeding to explore the consequences of chronic developmental nicotine exposure on cerebral neuroplasticity in the offspring. We focused on two dynamic lifelong phenomena in the dentate gyrus (DG) of the hippocampus that are highly sensitive to the environment: granule cell neurogenesis and long-term potentiation (LTP).

METHODS

Pregnant rats were implanted with osmotic mini-pumps delivering either nicotine or saline solutions. Plasma nicotine and metabolite levels were measured in dams and offspring. Corticosterone levels, DG neurogenesis (cell proliferation, survival and differentiation) and glutamatergic electrophysiological activity were measured in pups.

RESULTS

Juvenile (P15) and adolescent (P41) offspring exposed to nicotine throughout prenatal and postnatal development displayed no significant alteration in DG neurogenesis compared to control offspring. However, NRT-like nicotine exposure significantly increased LTP in the DG of juvenile offspring as measured in vitro from hippocampal slices, suggesting that the mechanisms underlying nicotine-induced LTP enhancement previously described in adult rats are already functional in pups.

CONCLUSIONS

These results indicate that synaptic plasticity is disrupted in offspring breastfed by dams passively exposed to nicotine in an NRT-like fashion.

Gestational nicotine treatment modulates cell death/survival-related pathways in the brains of adolescent female rats

Gestational exposure to nicotine affects brain development, leading to numerous behavioural and physiological deficits in the offspring during adolescence. To analyse the molecular mechanisms underlying these effects, a pathway-focused oligonucleotide microarray was used to determine gene expression profiles in five brain regions (i.e. amygdala, prefrontal cortex, nucleus accumbens, periventricular nucleus of the hypothalamus, and caudate putamen CPu) of adolescent rats that received nicotine or saline during gestation. Following appropriate statistical and Gene Set Enrichment Analyses, 24 cell death/survival-related pathways were found to be significantly modulated by gestational nicotine. On the basis of their biological functions, these pathways can be classified into three categories: growth factor, death receptor, and kinase cascade. We employed a quantitative real-time PCR array to verify the findings by measuring the expression of 29 genes involved in cell death/survival-related pathways. Together, our findings indicate that gestational nicotine exposure has significant effects on gene expression in cell death/survival-related pathways in the brains of adolescent offspring. Such effects appear to be brain region-specific and are realized through regulation of the expression of growth factors and receptors, caspases, kinases, and transcription factors. On the basis of these findings, we offer a hypothetical model to explain how gestational nicotine exposure may affect cell death and survival in the brains of adolescent offspring by regulating the balance between growth-factor and death-receptor pathways.

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.

The effects of nicotine on the alpha-7 and beta-2 nicotinic acetycholine receptor subunits in the developing piglet brainstem

Exposure to cigarette smoke is a major risk factor for sudden infant death syndrome (SIDS). We tested the hypothesis that nicotine increases expression of the nicotinic acetylcholine receptor (nAChR) subunits alpha7 and beta2 in a piglet model. Piglets exposed to 2mg/kg/day nicotine for 14 days postnatally (n=14) were compared to non-exposed controls (n=14), (equal gender proportions). Immunohistochemistry was performed to identify and quantify changes in, alpha7 and beta2 nAChR subunits in 8 nuclei of the medulla at both the rostral and caudal levels. Compared to controls, nicotine exposed piglets had decreased alpha7 in the rostral dorsal motor nucleus of the vagus (rDMNV) (p=0.01), and increased beta2 in the caudal DMNV (cDMNV) (p=0.05), caudal nucleus of the spinal trigeminal tract (cNSTT) (p=0.03) and caudal nucleus of the solitary tract (cNTS) (p=0.04). Analysis by gender showed that in the control group, compared to males, females had higher beta2 in the caudal hypoglossal (cXII) (p<0.01) and caudal inferior olivary (p=0.04) nuclei, while in the nicotine group females had higher beta2 in the cDMNV (p=0.02). Compared to control males, nicotine exposed males had lower beta2 in the cXII (p<0.01). Overall, changes in alpha7 were specific to nicotine exposure with no gender differentiation. Changes in beta2 were more widespread but showed gender-specific effects. These findings provide evidence that early postnatal exposure to nicotine significantly affects nAChR subunit expressions in the developing brainstem.

Effects of rosiglitazone on ovarian function and fertility in animals with reduced fertility following fetal and neonatal exposure to nicotine

We have previously shown that in utero nicotine exposure causes impaired fertility, follicle immaturity, and ovarian dysfunction in adult female rat offspring. These characteristics overtly resemble the clinical profile of polycystic ovarian syndrome (PCOS) and recent studies have shown that thiazolidinediones such as rosiglitazone improve fertility in women with PCOS but the mechanism is not well defined. Our goal was to examine whether rosiglitazone would (1) ameliorate the altered ovarian physiology that occurs following fetal and neonatal exposure to nicotine and (2) to examine whether this could be due to normalization of ovarian vascularization. At weaning, offspring of nicotine-exposed dams were given either vehicle (NV) or rosiglitazone (3 mg kg(-1) day(-1); NR). Offspring of saline-exposed dams received vehicle (SV). Tissues were collected when the female offspring reached 26 weeks of age. NV animals had reduced granulosa cell proliferation and increased ovarian cell apoptosis. Treatment with rosiglitazone increased proliferation, and decreased apoptosis, compared NV animals. NV animals had decreased ovarian vascularity relative to controls, whereas NR animals had an intermediate level of ovarian vessel density. Moreover, ovaries from NV animals had decreased levels of the pro-angiogenic growth factors vascular endothelial growth factor (VEGF) and endocrine gland-derived VEGF both of which were increased with rosiglitazone treatment. Rosiglitazone reversed some of the nicotine effects in the ovary and increased ovarian vascularization, follicle maturation and improved oocyte competence. Rosiglitazone may be an important treatment option for PCOS and the present study provides a potential mechanism by which rosiglitazone may have beneficial effects on fertility in these patients.

Tissue fixation effects on immunohistochemical staining of caspase-3 in brain tissue

Fixation methods for tissue often vary amongst clinical and research laboratories. To evaluate the effects of fixation method on studies of brain tissue, we examined immunohistochemical outcomes amongst 2 fixatives, 4 caspase-3 antibodies, and 2 species (human infants and piglets). Fixatives were 10% neutral buffered formalin (NBF) or 10% NBF and glacial acetic acid (FAA). Antibodies for caspase-3 were commercially obtained and included 2 for active caspase-3, and 2 for procaspase-3 (CASP3 and CPP32). Immunohistochemical staining of caspase-3 varied with fixation method, with the greatest effect of fixation method observed for the active caspase-3 antibodies and this effect was present in both species. In NBF-fixed tissue, active caspase-3 immunoreactivity was only visible microscopically, and was specific to neuronal cell bodies. In FAA-fixed tissue, active caspase-3 immunoreactivity was visible macroscopically, and predominantly present in fiber tracts and fasciculi compared with neuronal bodies. Fixation and species differences were also identified for the procaspase-3 antibodies, CASP3 and CPP32, where FAA-fixed pig tissue showed abundant staining of blood vessels that were not observed in the NBF-fixed pig tissue or in the human tissue. This study characterizes differences in immunohistochemical outcomes using commercially available antibodies for caspase-3, according to tissue fixation method and species.

Resuscitation with 21 or 100% oxygen in hypoxic nicotine-pretreated newborn piglets: possible neuroprotective effects of nicotine

BACKGROUND

Perinatal asphyxia is a major concern in perinatal medicine. Resuscitation and ways to prevent and minimize adverse outcomes after perinatal asphyxia are subject to extensive research.

OBJECTIVES

In this study we hypothesized that, prior to hypoxia, intravenously administered nicotine might have an effect on how newborn piglets tolerate hypoxia, with regard to the time and degree of damage inflicted, due to its suggested neuroprotective abilities, and further that resuscitation with 21 compared with 100% oxygen in nicotine-pretreated animals would cause less cerebral damage.

METHODS

Thirty anesthetized newborn piglets were randomized to either hypoxia or control groups, and pretreatment with either saline or nicotine. In addition, the nicotine/hypoxia group was randomized to resuscitation with either 21 or 100% oxygen for 15 min following hypoxia.

RESULTS

We found significantly more necrosis in the striatum and cortex combined (p = 0.036), and in the striatum alone (p = 0.026), in the animals pretreated with nicotine and resuscitated with 100% when compared to 21% oxygen. There was no significant difference in the cerebellum. We also found significantly increased tolerance to hypoxia as measured by the time interval that the animals endured hypoxia: 103.8 +/- 28.2 min in the nicotine-pretreated animals vs. 66.5 +/- 19.5 min in the saline-pretreated animals (p = 0.035).

CONCLUSION

Nicotine enhances newborn piglets' ability to endure hypoxia, and resuscitation with 21% oxygen inflicts less necrosis than 100% oxygen. The potential neuroprotective effects of nicotine in the newborn brain should be further investigated.

Nicotine and apoptosis

Cigarette smoking is associated with a plethora of different diseases. Nicotine is the addictive component of cigarette but also acts onto cells of the non-neuronal system, including immune effector cells. Although nicotine itself is usually not referred to as a carcinogen, there is ongoing debate whether nicotine functions as a 'tumor enhancer.' By binding to nicotinic acetylcholine receptors, nicotine deregulates essential biological processes like angiogenesis, apoptosis, and cell-mediated immunity. Apoptosis plays critical roles in a wide variety of physiologic processes during fetal development and in adult tissue and is also a fundamental aspect of the biology of malignant diseases. This review provides an overlook how nicotine influences apoptotic processes and is thus directly involved in the etiology of pathological conditions like cancer and obstructive diseases.

Prenatal nicotine exposure increases heart susceptibility to ischemia/reperfusion injury in adult offspring

In the present study we tested the hypothesis that prenatal nicotine exposure increases heart susceptibility to ischemia/reperfusion (I/R) injury in adult offspring. Nicotine was administered to pregnant rats via subcutaneous osmotic minipumps throughout gestation. Nicotine treatment resulted in a rapid and transient decrease in food-intake and a moderate decrease in maternal body weight gain. Hearts were isolated from adult male and female offspring and subjected to I/R in a Langendorff preparation. Nicotine significantly attenuated left ventricle (LV) developed pressure, heart rate, and coronary flow rate in female but not male hearts at baseline. Additionally, nicotine significantly increased LV infarct size and attenuated postischemic recovery of LV function in both male and female offspring with more pronounced effects in females. In female but not male hearts, nicotine significantly decreased the postischemic coronary flow rate. However, coronary nitric oxide release was decreased in male but not female hearts. Caspase-3, -8, and -9 levels were not significantly changed in either female or male hearts. However, nicotine caused a significant decrease in protein levels of protein kinase (PK) Cepsilon in both male and female hearts and a decrease in PKCdelta levels in female hearts only. Control studies of maternal food restriction showed that a moderate decrease in maternal body weight gain had no effect on female hearts but significantly improved postischemic recovery of LV function in male hearts. The results suggest that prenatal nicotine exposure causes in utero programming of the PKC isozyme gene expression pattern in the developing heart and increases heart susceptibility to I/R injury in adult offspring.

The neuroprotective effects of caffeic acid phenethyl ester (CAPE) in the hippocampal formation of cigarette smoke exposed rabbits

BACKGROUND

In this study, the neuroprotective effects of caffeic acid phenethyl ester (CAPE) in the hippocampus of cigarette smoke exposed rabbits were investigated.

MATERIALS AND METHODS

Eighteen rabbits were used as experimental subjects and divided into three equal groups. The control group (Group A) was exposed to clean air. Rabbits in the cigarette smoke (CS) group (Group B) were exposed to cigarette smoke 1 hour daily in a room within a glass chamber for 4 weeks. Animals in the CS+CAPE group (Group C) were exposed to cigarette smoke as in Group B and administered CAPE (10 micromol/kg/day) intraperitoneally for 4 weeks just before the exposure to cigarette smoke. Rabbits in all three groups were sacrificed with intraperitoneal administration of 100 mg/kg sodium pentothal and their brains were removed immediately. In the hippocampal formation samples of left hemispheres, the levels of malondialdehyde (MDA) and superoxide dismutase (SOD) were measured and the number of apoptotic neurons was counted by 'terminal transferase dUTP nick end labelling' (TUNEL) assay in the right hippocampal formation.

RESULTS

We found that MDA levels increased significantly in the Group B rabbits compared with the control group (Group A; p = 0.001). In contrast, SOD activities decreased significantly in Group B rabbits compared with the control group (p = 0.001). In the CAPE treated rabbits (Group C), MDA levels decreased and SOD activities increased significantly as compared with Group B rabbits (p = 0.002, p = 0.002, respectively). The number of apoptotic neurons (TUNEL+) in the CA1, CA2, CA3 and dentate gyrus areas of rabbits' hippocampal formation were significantly increased in Group B rabbits compared with the control group. On the other hand, the number of apoptotic neurons in the hippocampus areas was decreased significantly in Group C rabbits compared with Group B rabbits.

CONCLUSION

These findings suggest that cigarette smoking induces apoptosis in the hippocampal formation of rabbits and CAPE has a protective role against this induction.

Effects of chronic neonatal nicotine exposure on nicotinic acetylcholine receptor binding, cell death and morphology in hippocampus and cerebellum

Nicotine, the major psychoactive ingredient in tobacco interacting with nicotinic acetylcholine receptors (nAChR), is believed to have neuroprotective and neurotoxic effects on the developing brain. Neurotoxicity has been attributed to activation of homomeric alpha7 nAChRs, neuroprotection to heteromeric alpha4beta2 nAChRs. Thus, developmental nicotine could have opposite effects in different brain regions, depending on nAChR subtype expression. Here, we determined if chronic neonatal nicotine exposure (CNN), during a period of brain growth corresponding to the third human trimester, differentially regulates nAChR expression, cell death, and morphological properties in hippocampus and cerebellum, two structures maturing postnatally. Rat pups were orally treated with 6 mg/kg/day nicotine from postnatal day (P)1 to P7. On P8, expression for alpha4, alpha7 and beta2 mRNA was determined by in situ hybridization; nAChR binding sites by receptor autoradiography, dying neurons by TUNEL and Fluoro-Jade staining and morphological properties by analysis of Cresyl Violet-stained sections. In control cerebellum, strong expression of alpha4, beta2 mRNA and heteromeric nAChRs labeled with [125I]-epibatidine was found in granule cells, and alpha7 mRNA and homomeric nAChRs labeled with [125I]-alpha-bungarotoxin were in the external germinal layer. In control hippocampus, low expression of alpha4 mRNA and heteromeric nAChRs and high expression of alpha7 mRNA and homomeric nAChRs were detected. CNN increased heteromeric nAChR binding in hippocampus but not cerebellum and significantly decreased neuronal soma size and increased packing density in hippocampal principal cells but not in cerebellum. CNN did not increase the number of dying cells in any area, but significantly fewer TUNEL-labeled cells were found in CA3 strata oriens and radiatum and cerebellar granule layer. Thus, the hippocampus seems to be more sensitive than the cerebellum to CNN which could result from different nAChR subtype expression and might explain long-lasting altered cognitive functions correlated with gestational nicotine exposure due to changes in hippocampal cell morphology.

Identifying infants at risk for sudden infant death syndrome

PURPOSE OF REVIEW

This review examines recent research relevant to the underlying pathophysiology and risk factors for sudden infant death syndrome.

RECENT FINDINGS

Current research focuses on the linkage between known risk factors and vulnerability, genetic contributions, and the role of dysfunctional brainstem neurotransmission in the pathogenesis of this syndrome. While social inequalities, prematurity, maternal smoking, infant sleeping practices and sleep environment, arousal failures and environmental pollutants remain important risk factors, new evidence is emerging that certain genetic polymorphisms may contribute to vulnerability. New neuropathological studies have provided strong support for abnormal brainstem serotonergic function. Since serotonin influences a wide range of physiological systems including breathing, the cardiovascular system, temperature, and sleep-wake cycles, this finding strongly supports the hypothesis that sudden infant death syndrome is the result of dysregulation of the autonomic nervous system and provides biological plausibility for certain risk reduction strategies.

SUMMARY

Despite a putative diagnostic shift, sudden infant death syndrome remains the most common cause of death from 1 month to 1 year of age. Recent studies confirmed established risk factors and have suggested new genetic vulnerabilities. Finally, new evidence supports a key role for abnormalities in brainstem serotonin systems in the pathophysiology of this syndrome.

N-methyl-d-aspartate receptor 1 changes in the piglet braintem after nicotine and/or intermittent hypercapnic-hypoxia

Prone sleeping and cigarette smoke exposure are two major risk factors for the sudden infant death syndrome (SIDS). Utilizing piglet models of early postnatal nicotine and/or intermittent hypercapnic-hypoxia (IHH) exposure, we tested the hypothesis that these exposures, separately or combined, increase N-methyl-D-aspartate (NMDA) receptor 1 (NR1) expression in the brainstem medulla. We also tested for gender-specific effects. Three piglet exposure groups were compared against 14 controls; 1, nicotine [n = 14], 2, IHH [n = 10], and 3, nicotine+IHH [n = 14], with equal gender proportions in each group. Non-radioactive in situ hybridization and immunohistochemistry were performed for NR1 mRNA and protein expression, respectively, and were quantified in seven nuclei of the brainstem medulla. NR1 mRNA was significantly increased in the gracile and inferior olivary nucleus (ION) after nicotine exposure, in five of seven nuclei after IHH exposure, and in three of seven nuclei after nicotine+IHH. The increased mRNA changes were accompanied by increased protein only in the ION after IHH and nicotine+IHH (P = 0.019, and P = 0.008 respectively). By gender, control females had greater NR1 mRNA than males in the dorsal motor nucleus of vagus (P = 0.05) and for protein in the ION (P = 0.02). This gender difference was maintained after nicotine exposure in the ION with additional gender differences observed including greater mRNA in the cuneate nucleus (P = 0.04) and nucleus of the spinal trigeminal tract (P = 0.03) of males compared with females. Overall, more changes occurred at the mRNA level than protein, and IHH exposure induced more changes than nicotine or nicotine+IHH exposures. Together, these findings suggest that hypercapnic-hypoxic exposures (modeling prone sleeping or sleep apnea) are more likely to induce NMDA receptor changes in the developing brainstem than nicotine exposure alone.

Postnatal nicotine and/or intermittent hypercapnic hypoxia effects on apoptotic markers in the developing piglet brainstem medulla

The most important risk factors currently identified for the sudden infant death syndrome (SIDS) are prone sleeping and cigarette smoke exposure. In this study, we investigated the neuropathological sequelae of these risk factors by exposing piglets to intermittent hypercapnic-hypoxia (IHH) and/or nicotine (nic) in the early postnatal period. Our hypothesis was that either nic or IHH exposure could increase neuronal cell death, and that combined exposure (nic+IHH) would be additive. Four exposure patterns were studied: controls (n=14), IHH (n=10), nic (n=14), and nic+IHH (n=14). All groups had equal gender ratios. Nic exposure via an implanted osmotic minipump commenced within 48 h of birth and continued until age 13-14 days when animals were killed and brains collected. A total of 48 min of hypercapnic-hypoxia was delivered on the day immediately prior to killing in a pattern comprising 6 min of HH (8% O(2), 7% CO(2), balance N(2)) alternating with 6 min of air. Immunohistochemistry was performed to identify neurons positive for active caspase-3 and DNA fragmentation (terminal deoxynucleotidyl transferase-mediated dUTP nick-end labeling, TUNEL) in seven nuclei of the caudal medulla. Staining quantification showed that: 1. IHH induced neuronal death (increased both TUNEL and casapse-3) in more brainstem nuclei than nicotine. 2. Females were more severely affected by IHH than males. 3. Where IHH and nicotine were combined, TUNEL expression was approximately 5% less than IHH alone, but changes in caspase-3 were variable. We conclude that acute exposure to IHH in the postnatal period is more neurotoxic than exposure to nicotine alone. Combined exposure to IHH and nicotine produced variable responses with some results suggesting that nicotine can be neuroprotective. These results indicate that environmental insults attributable to prone sleeping can produce neurotoxic sequelae in SIDS, with some regional specificity in the response. However, no consistent relationship is evident when combining the two insults.

Long term environmental tobacco smoke activates nuclear transcription factor-kappa B, activator protein-1, and stress responsive kinases in mouse brain

Environmental tobacco smoke (ETS) is a key mediator of several diseases. Tobacco smoke contains a mixture of over 4700 chemical components many of which are toxic and have been implicated in the etiology of oxidative stress related diseases such as chronic obstructive pulmonary disease, Parkinson's disease, asthma, cancer and cardiovascular disease. However, the mechanism of action of cigarette smoke in the onset of these diseases is still largely unknown. Previous studies have revealed that the free radicals generated by cigarette smoke may contribute to many of these chronic health problems and this study sought to address the role of environmental tobacco smoke in oxidative stress related damage in different regions of the mouse brain. In this study, male mice were exposed for 7h/day, 7 days/week, for 6 months. Our results show that tobacco smoke led to increased generation of reactive oxygen species with an increase in NF-kappaB activation. Gel shift analysis also revealed the elevated level of the oxidative stress sensitive proinflammatory nuclear transcription factor-kappa B and activator protein-1 in different regions of the brain of cigarette smoke exposed mice. Tobacco smoke led to activation of COX-2 in all the regions of the brain. Activation of mitogen activated protein kinase and c-Jun N-terminal kinase were also observed in various regions of brain of ETS exposed mice. Overall our results indicate that exposure to long-term cigarette smoke induces oxidative stress leading to activation of stress induced kinases and activation of proinflammatory transcription factors.

Cigarette smoking induces heat shock protein 70 kDa expression and apoptosis in rat brain: Modulation by bacoside A

Cigarette smoking is associated with the development of several diseases and antioxidants play a major role in the prevention of smoking-related diseases. Apoptosis is suggested as a possible contributing factor in the pathogenesis of smoking-induced toxicity. Therefore the present study was designed to investigate the influence of chronic cigarette smoke exposure on apoptosis and the modulatory effect of bacoside A (triterpenoid saponin isolated from the plant Bacopa monniera) on smoking-induced apoptosis in rat brain. Adult male albino rats of Wistar strain were exposed to cigarette smoke and simultaneously administered with bacoside A (10 mg/kg b.w./day, orally) for a period of 12 weeks. Expression of brain hsp70 was analyzed by Western blotting. Apoptosis was identified by DNA fragmentation, terminal deoxynucleotidyl transferase-mediated deoxy uridine triphosphate nick end labeling (TUNEL) staining and transmission electron microscopy. The results showed that exposure to cigarette smoke induced hsp70 expression and apoptosis as characterized by DNA laddering, increased TUNEL-positive cells and ultrastructural apoptotic features in the brain. Administration of bacoside A prevented expression of hsp70 and neuronal apoptosis during cigarette smoking. We speculate that apoptosis may be responsible for the smoking-induced brain damage and bacoside A can protect the brain from the toxic effects of cigarette smoking.