Abstract
Chronic nicotine exposure during pregnancy has been shown to induce physiological and anatomical alterations in offspring. Previously, we investigated the complexity of dopamine (DA) neuron firing in the sub-regions of the ventral tegmental area (VTA) following perinatal nicotine exposure. Using approximate entropy, we found that within the middle sub-region, the parainterfascicular nucleus (PIF), there was higher complexity indicating more random neural firing and a less homogeneous neuron population. Therefore, we sought to investigate the neuron populations within the sub-regions of the VTA following perinatal nicotine exposure. We used real time PCR in order to find the relative quantity of glutamate to γ-aminobutyric acid (GABA), DA, and glutamate neurons within three sub-regions: the parabrachial pigmented nucleus (PBP), parainterfascicular nucleus (PIF), and paranigral nucleus (PN). Our results showed that the PIF region of the VTA contained a more diverse population of neurons resulting in a more complex system. In addition, we found that DA neurons are more activated in PN sub-region of the VTA, which mediates the rewarding effects of drugs including nicotine. Lastly, using immunohistochemistry, we observed an overall decrease in DA neurons following perinatal nicotine exposure.
Highlights
Maternal smoking during pregnancy is a major public health concern with women who continue smoking throughout their pregnancies[1]
The ventral tegmental area (VTA) sub-regions (PBP, parainterfascicular nucleus (PIF), and paranigral nucleus (PN)) were isolated from rat pups (4 weeks old) that were perinatally exposed to nicotine or saline through their mother via an osmotic pump as described in the methods section, in order to compare the genetic expressions between each sub-region of the VTA
Five candidate neuronal markers were selected based on their usage as neurotransmitters in gene expression studies and significance in neural mechanisms of addiction; Taqman Gene Expression Assays GAD1 and GAD2 playing role in the conversion of glutamate to glutamate to γ-aminobutyric acid (GABA), the inhibitory neurotransmitter in central nervous systems, Slc6a3, Tyrosine Hydroxylase (TH) and Slc17a6 playing in dopamine transport and Slc17a6 playing role in L-glutamate transmembrane transporter activity in glutamatergic pathway
Summary
Maternal smoking during pregnancy is a major public health concern with women who continue smoking throughout their pregnancies[1]. It has been revealed that after the nicotine injection, some VTA DA neurons showed different temporal changes on the firing rate These result suggested that detailed subgroups of VTA DA may exist within VTA, defined by physical function and/or anatomical sub-region[25,26,27,28] but several studies suggested that the posterior VTA, but not anterior VTA, centering around the PN mediates the rewarding effects of drugs including nicotine[28]. More information regarding the DA existence in different sub- regions of VTA investigating the effects of developmental nicotine exposure is needed to better understand potential targets for novel medical treatments In this current study, we investigated the nicotine-dependent activation of specific neurons within the VTA sub-regions to understand the effect of perinatal nicotine exposure. Real time PCR (RT-qPCR) was used to find the relative quantity of GABA, DA, and glutamate neuron markers and immunofluorescence staining was performed to visualize DA neurons based on their role in the reward/addiction pathway
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