Prenatal nicotine exposure does not cause Purkinje cell loss in the developing rat cerebellar vermis

Impact of prenatal nicotine on the structure of midbrain dopamine regions in the rat

In utero exposure of rats to nicotine (NIC) provides a useful animal model for studying the impact of smoking during pregnancy on human offspring. Certain sequelae of prenatal NIC exposure suggest an impact on the development of the midbrain dopamine (DA) system, which receives a robust cholinergic innervation from the mesopontine tegmentum. We therefore investigated whether prenatal NIC induced structural changes in cells and synapses within the midbrain that persisted into adulthood. Osmotic minipumps delivering either sodium bitartrate (vehicle; VEH) or NIC bitartrate at 2 mg/kg/day were implanted into nine timed-pregnant dams at E4. At birth, rat pups were culled to litters of six males each, and the litters were cross-fostered. Plasma levels of NIC and cotinine from killed pups provided evidence of NIC exposure in utero. Pups separated from dams at weaning showed a trend toward reduced locomotor activity at this time point but not when tested again in adulthood. Adult rats were killed for anatomical studies. Estimates of brain size and volume did not vary with NIC treatment. Midbrain sections stained for Nissl or by immunoperoxidase for tyrosine hydroxylase and analyzed using unbiased stereology revealed no changes in volume or cell number in the substantia nigra compacta or ventral tegmental area as a result of NIC exposure. Within the ventral tegmental area, electron microscopic physical disector analysis showed no significant differences in the number of axon terminals or the number of asymmetric (putative excitatory) or symmetric (putative inhibitory) synapses. Although too infrequent to estimate by unbiased stereology, no obvious difference in the proportion of cholinergic axons was noted in NIC- versus VEH-treated animals. These data suggest that activation of nicotinic receptors during prenatal development induces no significant modifications in the structure of cells in the ventral midbrain when assessed in adulthood.

Prenatal exposure to nicotine stimulates neurogenesis of orexigenic peptide-expressing neurons in hypothalamus and amygdala

Animal and clinical studies show that gestational exposure to nicotine increases the propensity of offspring to consume nicotine, but the precise mechanism mediating this behavioral phenomenon is unclear. The present study in Sprague Dawley rats examined the possibility that the orexigenic peptide systems, enkephalin (ENK) and orexin (OX), which are stimulated by nicotine in adult animals and promote consummatory behavior, may be similarly responsive to nicotine's stimulatory effect in utero while having long-term behavioral consequences. The results demonstrated that nicotine exposure during gestation at low doses (0.75 or 1.5 mg/kg/d) significantly increased mRNA levels and density of neurons that express ENK in the hypothalamic paraventricular nucleus and central nucleus of the amygdala, OX, and another orexigenic peptide, melanin-concentrating hormone, in the perifornical lateral hypothalamus in preweanling offspring. These effects persisted in the absence of nicotine, at least until puberty. Colabeling of the cell proliferation marker BrdU with the neuronal marker NeuN and peptides revealed a marked stimulatory effect of prenatal nicotine on neurogenesis, but not gliogenesis, and also on the number of newly generated neurons expressing ENK, OX, or melanin-concentrating hormone. During adolescence, offspring also exhibited significant behavioral changes, increased consumption of nicotine and other substances of abuse, ethanol and a fat-rich diet, with no changes in chow and water intake or body weight. These findings reveal a marked sensitivity during gestation of the orexigenic peptide neurons to low nicotine doses that may increase the offspring's propensity to overconsume substances of abuse during adolescence.

Effects of nicotine exposure during prenatal or perinatal period on cell numbers in adult rat hippocampus and cerebellum: a stereology study

Smoking during pregnancy poses a potential risk to unborn children. The present study examined the long-term effects of early nicotine exposure on the number of pyramidal and granule cells in the hippocampus, and Purkinje cells in the cerebellar vermis. The loss of neurons is the most severe form of brain injury with significant functional implications. In this study, rats were exposed to nicotine during either the prenatal (PRE) period or both the prenatal and early postnatal (PERI) period. It was hypothesized that nicotine treatment would result in long-term decreases in neuronal numbers, and that PERI treatment would be more detrimental to these cell populations than the PRE treatment. The results showed that neither PRE nor PERI nicotine exposure reduces the numbers of pyramidal, granule or Purkinje cells. Neither the regions where these cells reside, nor the cell densities were affected by nicotine. Although no significant cell loss was observed, the current nicotine exposure regimens may lead to alterations in cellular functions or cytoarchitectures. The present results in conjunction with previous reports showing significant cell loss from nicotine exposure during the brain growth spurt suggest that "patch-like" nicotine exposure during prenatal period may alter the sensitivity or the responsiveness of the developing brain to the injurious effects of nicotine during the most vulnerable stage of brain development - the brain growth spurt. Furthermore, the current stereology cell counting results are not in agreement with some reports in the literature, and this discrepancy may simply be a function of different cell counting techniques used.

Gender-related response in open-field activity following developmental nicotine exposure in rats

Smoking during pregnancy may lead to low birthweight and behavioral alterations in the offspring. In this study, the effects of developmental nicotine exposure on the somatic growth of the offspring and the behavioral performance in the open-field test were examined. Sprague-Dawley female rats were implanted with nicotine (35 mg for 21-day time release; NIC 35) or placebo pellets on gestational day (GD) 8 (postblastocyst implantation). A normal control group with no pellet implant was also included. There was a significantly higher maternal weight gain in the placebo group possibly due to a larger litter size. However, there were no significant differences in body weights among all three treatment groups for male and female offspring. The amount of activity, measured by the total number of crossings in the open-field test, indicated a gender difference in baseline level and pattern of ambulatory activity, with less activity (lower number of crossings) in male offspring and an increase in the activity of the female offspring as a function of testing day. The increase in the ambulatory activity of the female offspring was observed in the placebo and normal, but not the NIC 35 group suggesting that developmental nicotine exposure interferes with open-field activity, and this behavioral alteration is gender related.

Interactive Effect of Alcohol and Nicotine on Developing Cerebellum: An Investigation of the Temporal Pattern of Alcohol and Nicotine Administration

BACKGROUND

Among individuals who use alcohol and tobacco products, pregnant women represent a unique subpopulation that generates a greater concern because of the toxic effects of alcohol and nicotine (from cigarettes and tobacco products) on the health of both the pregnant woman and her fetus. Therefore, it is imperative to understand the interactive effects of these two substances on the fetus. Previously, we found that concurrent exposure to alcohol and nicotine did not result in the loss of greater numbers of Purkinje cells compared with each drug treatment alone, possibly as a result of a nicotine-mediated decline in peak blood alcohol concentration (BAC). The present study tested the validity of this hypothesis.

METHODS

On postnatal day (PD) 4, Sprague-Dawley rat pups were assigned to five groups, GC (no alcohol [ALC], no nicotine [NIC]), ALC (4 g/kg/day), NIC (6 mg/kg/day), ALC/NIC (ALC and NIC given concurrently), or ALC-NIC (NIC administered 6 hr after ALC exposure). These rat pups were reared in an artificial-rearing apparatus from PDs 4 to 9, and the cerebellar tissues were obtained on PD 10. The total number of cerebellar Purkinje cells in the vermis was estimated using stereological methods.

RESULTS

The results showed that alcohol significantly reduced Purkinje cell numbers. The coexposure of alcohol and nicotine did not lead to further reduction in Purkinje cell number regardless of administration method, concurrent or sequential. However, alcohol and nicotine administered concurrently but not sequentially significantly lowered the BAC.

CONCLUSION

These findings suggest that the lack of increased Purkinje cell loss after the coexposure of alcohol and nicotine is independent of nicotine's ability to lower the BAC. An alternative hypothesis might be that alcohol and nicotine target the same subpopulation of Purkinje cells; therefore, no additional Purkinje cells were lost from the coexposure of these two drugs.