Investigating how postnatal inactivation of Smad proteins in dopaminergic neurons and how neonatal nicotine exposure affects the proper functioning of midbrain dopaminergic neurons and their synaptic projections into the striatum.
Kritzer, Eli C.
2023
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Midbrain dopaminergic neurons (mDAn) project to the striatum to establish dopaminergic synaptic connections in two distinct pathways: the nigrostriatal and mesolimbic pathways. In the nigrostriatal pathway, mDAn project from the ventral tegmental area (VTA) in the midbrain to the caudate putamen (CPu) in the striatum. In the mesolimbic pathway, mDAn project from the substantia nigra (SNc) in the ... read moremidbrain to the nucleus accumbens (NAc) in the striatum. Dysfunctional mesolimbic and nigrostriatal circuitry is implicated in many neuropsychiatric disorders including Parkinson’s, ADHD, and drug addiction. In order to regulate the establishment of nigrostriatal dopaminergic synaptic connections, Smad1 is phosphorylated by BMPR proteins in the CPu region of the striatum and regulates gene expression of mDAn as a transcription factor. In order to regulate the establishment of mesolimbic dopaminergic synaptic connections, Smad2 is phosphorylated by TGFβR proteins in the NAc region of the striatum and regulates gene expression of mDAn as a transcription factor. In the embryonic stage of development, transforming growth factor beta (TGFβ)superfamily signaling has been shown to plays critical roles in organizing the migration, survival, and growth of mDA neurons. However, in contrast to embryonic findings, I found that mice in which Smad1 or Smad2 was postnatally inactivated at P1 in DA neurons (Smad1cKO and Smad2cKO mice) exhibited no significant difference in mDAn survival, mDAn dendrite growth, or excitatory/inhibitory synaptogenesis onto mDAn dendrites compared to control mice. This reveals a stark contrast in the role of TGFβ superfamily signaling in mDAn during embryonic and postnatal developmental stages.I also examined potential genetic targets of Smad1 and Smad2 transcription factors.Increased D1R and D2R expression in the CPu of Smad1cKO mice suggested that perhaps in the nigrostriatal pathway, genes of mDAn that impact postsynaptic dopamine receptor expression could be affected by the Smad1 transcription factor. I found no significant difference between VMAT2 protein expression in the midbrain ofSmad1cKO or Smad2cKO in comparison to control mice which provided no support to the hypothesis of transcriptional regulation of the VMAT2 gene by Smad1 and Smad2. However, I found BMPR and TGFβR proteins to be preferentially expressed in SNc and VTA mDAn respectively, raising the possibility of BMPR and TGFβR genes as potential targets of Smad1 and Smad2.My results examining the effect of postnatal Smad1 or Smad2 inactivation in striatalastrocytes suggested that BMP/TGFβ Smad1/Smad2 signaling pathways could also potentially play a role in how astrocytes affect the establishment of dopaminergic synaptic connections in the striatum. Nicotine is an addictive psychoactive drug which is highly used in society. When pregnant mothers use nicotine, there are high rates of disorders in their offspring such as ADHD. Many of these disorders, such as ADHD, are largely mediated by dopaminergic circuitry so I examined the effect of nicotine usage during pregnancy on the establishment of mesolimbic and nigrostriatal dopaminergic synaptic connections in the brains of the offspring. Due to a slightly different time course of brain development in mice, In order to use an analogous animal model for this purpose, Akiko Terauchi and Lisa Kim neonatally administered either a low dose of nicotine (0.1 mg/kg), a high dose of nicotine (0.65 mg/kg), or saline as a control. Akiko Terauchi and Lisa Kim sacrificed the mice at P14 and P60 so I could examine both the short-term and long-term effects of neonatal nicotine usage on dopaminergic circuitry in mice.In the mesolimbic pathway, I observed that neonatal nicotine administration causedsignificant impairments in the establishment of dopaminergic synaptic connections (as assessed by VMAT2 immunostaining) and mDAn axon development (as assessed by TH immunostaining). I observed these impairments both immediately after nicotine treatment (at P14) and over the long-term (at P60). Additionally, I observed these impairments to be dose dependent, with higher doses generally causing more significant impairments.In the nigrostriatal pathway, I observed that neonatal nicotine administration at highdoses (and not low doses) immediately after neonatal nicotine treatment caused significant impairments in the establishment of dopaminergic synaptic connections, but not in mDAn axon development. Additionally, I observed that over the long-term both low doses and high doses caused significant impairments in the establishment of dopaminergic synaptic connections. However, I observed that only low doses appeared to cause significant impairments in mDAn axon development. The results of my research provides valuable insight into how maternal nicotine usage during pregnancy affects dopaminergic synapse formation and dopaminergic circuitry in the brain of the offspring and how this can lead to disorders such as ADHD for the offspring. This greater understanding can be potentially used in the future to create therapeutic treatments for those with ADHD or other disorders as a result of maternal nicotine usage during pregnancy.
Thesis (B.S.)--Tufts University, 2023.
Submitted to the Dept. of Biology.read less - ID:
- 0v838f06p
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