Gene Expression In Ventral Tegmental Area Research Articles

Thyroid hormones mediate the impact of early-life stress on ventral tegmental area gene expression and behavior

Proper thyroid function is essential to the developing brain, including dopamine neuron differentiation, growth, and maintenance. Stress across the lifespan impacts thyroid hormone signaling and anxiety disorders and depression have been associated with thyroid dysfunction (both hypo- and hyper-active). However, less is known about how stress during postnatal development impacts thyroid function and related brain development. Our previous work in mice demonstrated that early-life stress (ELS) transiently impinged on expression of a transcription factor in dopamine neurons, Otx2, shown to be regulated by thyroid hormones. We hypothesized that thyroid hormone signaling may link experience of ELS with transcriptional dysregulation within the dopaminergic midbrain, and ultimately behavior. Here, we find that ELS transiently increases thyroid-stimulating hormone levels (inversely related to thyroid signaling) in both male and female mice at P21, an effect which recovers by adolescence. We next tested whether transient treatment of ELS mice with synthetic thyroid hormone (levothyroxine, LT4) could ameliorate the impact of ELS on sensitivity to future stress, and on expression of genes related to dopamine neuron development and maintenance, thyroid signaling, and plasticity within the ventral tegmental area. Among male mice, but not females, juvenile LT4 treatment prevented hypersensitivity to adult stress. We also found that rescuing developmental deficits in thyroid hormone signaling after ELS restored levels of some genes altered directly by ELS, and prevented alterations in expression of other genes sensitive to the second hit of adult stress. These findings suggest that thyroid signaling mediates the deleterious impact of ELS on VTA development, and that temporary treatment of hypothyroidism after ELS may be sufficient to prevent future stress hypersensitivity.

Restriction and hyperlipidic diets during pregnancy, lactation and adult life modified the expression of dopaminergic system related genes both in female mice and their adult offspring

The neurocircuitry underlying hunger, satiety, motivation to eat and food reward is complex, however a lot of mechanisms are still unknown. Two main cerebral areas are responsible for controlling feeding through hunger and food reward: the hypothalamus (HPT) and the ventral tegmental area (VTA), respectively. The dopaminergic system modulates both these areas and is essential to control food ingestion. Therefore, we aim to evaluate the effects of restrictive and hyperlipidic diets during pregnancy, lactation and during adult life of the offspring, on the expression of dopaminergic system genes in VTA and HPT of mice dams and their adult male offspring. We also measured diets’ effect in locomotor activity in the open field (OF) test. Female mice were divided into control (CONT), restriction (RD) and hyperlipidic (HD) dietary groups, and mated with isogenic male mice. On the 9th postpartum day (PPD), dams were tested in the OF, and on the 22nd PPD cerebral areas were collected. After weaning, the offspring also were divided into one of three diet groups, independently of the diets provided to their dams. In the 80th PPD, the offspring was tested in the OF, and at 100th PPD, VTA and HPT were collected. Gene expression was analyzed by quantitative reverse transcription real-time polymerase chain reaction. The correlation between gene expression and locomotor activity was also assessed. In dams’ VTA, both diets upregulated the expression of Th, Slc6a3/Dat1, Drd1 and Drd2 genes. In opposition, in the offspring the maternal diet was associated with a reduction in Th and Ddc gene expression. In the HPT, mice dams that received restriction or hyperlipidic diets had increased Th mRNA levels, but reduced the expression of Drd4 gene. The offspring diet had no effect on the expression of the studied genes in their adult lives. Both diets increased mice dam’s locomotion in the OF, however none of them altered the offspring locomotor activity. We detected a positive correlation between the duration of total locomotion in the OF and Slc6a3/Dat1 gene expression in VTA of mice dams. In the HPT, a negative correlation of locomotion and Drd4 mRNA levels, and a positive correlation with Th gene expression was observed. Our results show that restriction and hyperlipidic diets alter mice dams’ locomotor activity in the OF and modify the expression of dopaminergic system genes in VTA and HPT of mice dams and in VTA of the offspring.

Complex patterns of dopamine-related gene expression in the ventral tegmental area of male zebra finches relate to dyadic interactions with long-term female partners.

Dopaminergic projections from the ventral tegmental area (VTA) to multiple efferent targets are implicated in pair bonding, yet the role of the VTA in the maintenance of long-term pair bonds is not well characterized. Complex interactions between numerous neuromodulators modify activity in the VTA, suggesting that individual differences in patterns of gene expression in this region may explain individual differences in long-term social interactions in bonded pairs. To test this hypothesis we used RNA-seq to measure expression of over 8000 annotated genes in male zebra finches in established male-female pairs. Weighted gene co-expression network analysis identified a gene module that contained numerous dopamine-related genes with TH found to be the most connected gene of the module. Genes in this module related to male agonistic behaviors as well as bonding-related behaviors produced by female partners. Unsupervised learning approaches identified two groups of males that differed with respect to expression of numerous genes. Enrichment analyses showed that many dopamine-related genes and modulators differed between these groups, including dopamine receptors, synthetic and degradative enzymes, the avian dopamine transporter and several GABA- and glutamate-related genes. Many of the bonding-related behaviors closely associated with VTA gene expression in the two male groups were produced by the male's partner, rather than the male himself. Collectively, results highlight numerous candidate genes in the VTA that can be explored in future studies and raise the possibility that the molecular/genetic organization of the VTA may be strongly shaped by a social partner and/or the strength of the pair bond.

Comparison of chronic physical and emotional social defeat stress effects on mesocorticolimbic circuit activation and voluntary consumption of morphine

Chronic social defeat stress (CSDS) is a well-established rodent model of depression that induces persistent social avoidance. CSDS triggers molecular adaptations throughout the mesocorticolimbic reward circuit, including changes in the activity of dopamine neurons in the ventral tegmental area (VTA), that may also influence drug reward. One limitation of traditional, physical CSDS (PS) is that injury complicates the study of opiate drugs like morphine. Thus, we sought to characterize a variation of CSDS, termed emotional CSDS (ES), that eliminates this confound. We assessed the effect of PS and ES on mesocorticolimbic circuit activation, VTA gene expression, and morphine intake. We found that PS and ES similarly induced ΔFosB in the hippocampus, but only PS significantly increased ΔFosB expression in the prefrontal cortex and striatum. In contrast, cFos expression was similarly reduced by both PS and ES. Interestingly, we found that PS and ES similarly increased voluntary morphine consumption immediately following stress, despite differences in the magnitude of the depressive phenotype and striatal ΔFosB expression at this time point. Combined, these data suggest that both stress paradigms may be useful for investigation of stress-induced changes in drug behavior.

Juvenile Administration of Concomitant Methylphenidate and Fluoxetine Alters Behavioral Reactivity to Reward- and Mood-Related Stimuli and Disrupts Ventral Tegmental Area Gene Expression in Adulthood

There is a rise in the concurrent use of methylphenidate (MPH) and fluoxetine (FLX) in pediatric populations. However, the long-term neurobiological consequences of combined MPH and FLX treatment (MPH + FLX) during juvenile periods are unknown. We administered saline (VEH), MPH, FLX, or MPH + FLX to juvenile Sprague Dawley male rats from postnatal day 20 to 34, and assessed their reactivity to reward- and mood-related stimuli 24 h or 2 months after drug exposure. We also assessed mRNA and protein levels within the ventral tegmental area (VTA) to determine the effect of MPH, FLX, or MPH + FLX on the extracellular signal-regulated protein kinase-1/2 (ERK) pathway--a signaling cascade implicated in motivation and mood regulation. MPH + FLX enhanced sensitivity to drug (i.e., cocaine) and sucrose rewards, as well as anxiety (i.e., elevated plus maze)- and stress (i.e., forced swimming)-eliciting situations when compared with VEH-treated rats. MPH + FLX exposure also increased mRNA of ERK2 and its downstream targets cAMP response element-binding protein (CREB), BDNF, c-Fos, early growth response protein-1 (Zif268), and mammalian target of rapamycin (mTOR), and also increased protein phosphorylation of ERK2, CREB, and mTOR 2 months after drug exposure when compared with VEH-treated rats. Using herpes simplex virus-mediated gene transfer to block ERK2 activity within the VTA, we rescued the MPH and FLX-induced behavioral deficits seen in the forced-swimming task 2 months after drug treatment. These results indicate that concurrent MPH + FLX exposure during preadolescence increases sensitivity to reward-related stimuli while simultaneously enhancing susceptibility to stressful situations, at least in part, due to long-lasting disruptions in ERK signaling within the VTA.

THE EFFECTS OF ACUTE AND CHRONIC METHYLPHENIDATE TREATMENT ON STEREOTYPIC BEHAVIOR AND BASAL GANGLIA GENE EXPRESSION IN RATS. † 366

Methylphenidate (MPH) is frequently used in the treatment of Attention-Deficit / Hyperactivity Disorder, a common neurodevelopmental diagnosis in school-aged children. A concerning side effect is the induction of tics and other stereotypic behaviors. MPH is a dopamine re-uptake blocker with effects on mesocorticolimbic and mesostriatal dopamine (DA) systems. Mesocorticolimbic DA cell bodies are located in the ventral tegmental area(VTA) and project to the nucleus accumbens (NA) and frontal cortex. Mesostriatal DA cell bodies are located in the substantia nigra pars compacta(SNc) and project to the striatum (or caudate-putamen, STR). To identify neuronal subgroups involved in MPH effects, in situ hybridization histochemistry was performed after acute (at 7 wks) or chronic treatment(twice daily, 4-7 wks) with saline, low- (1.25 mg/kg) or high-dose (12.5 mg/kg) MPH in young rats. mRNA labelling for tyrosine hydroxylase, the rate-limiting enzyme in DA synthesis, and DA2 receptors was quantified in the VTA and SNc, and glutamic acid decarboxylase 67, the rate-limiting enzyme in GABA synthesis, DA1 and DA2 receptors and preproenkephalin labelling was quantified in the NA and STR. Locomotor activity, stereotypy and rearing were measured on days 1, 7, 14 and 21. After acute treatment, all behaviors were increased in the high-dose group (p's < 0.005) and there were no changes in mRNA labelling. With chronic treatment, activity was highest in the high-dose group (p= 0.0005), and effects were largest on day 1 (p's < 0.004). Stereotypy showed dose-dependent increases(p < 0.00005) without time effects. Rearing was increased in the high-dose group (p= 0.0006), with marginal effects on day 21. Chronic treatment with either dose resulted in increased tyrosine hydroxylase labelling in the VTA and SNC (p's < 0.05). High-dose treatment resulted in increased labelling for preproenkephalin in the STR (p < 0.01). Mazindol binding was unchanged suggesting that this was not due to loss of DA terminals. Chronic MPH treatment alters gene expression in VTA and SNc DA neurons and STR efferent neurons which express preproenkephalin. Supported by Tourette Syndrome Association, HD28815 and HD26979.