Browsing by Subject "serotonin"

Now showing 1 - 4 of 4
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    Anxiogenic CO2 Stimulus Elicits Exacerbated Hot Flash-like Responses in a Rat Menopause Model and Hot Flashes in Menopausal Women
    (Lippincott, Williams & Wilkins, 2016-11) Federici, Lauren M.; Roth, Sarah Dorsey; Krier, Connie; Fitz, Stephanie D.; Skaar, Todd C.; Shekhar, Anantha; Carpenter, Janet S.; Johnson, Philip L.; Anatomy and Cell Biology, School of Medicine
    Objective Since longitudinal studies determined that anxiety is a strong risk factor for hot flashes, we hypothesized that an anxiogenic stimulus that signals air hunger (hypercapnic, normoxic gas) would trigger an exacerbated hot flash-associated increase in tail skin temperature (TST) in a rat ovariectomy (OVEX) model of surgical menopause and hot flashes in symptomatic menopausal women. We also assessed TST responses in OVEX serotonin transporter (SERT)+/− rats that models a common polymorphism that is associated with increased climacteric symptoms in menopausal women and increases in anxiety traits. Methods OVEX and sham-OVEX rats (initial experiment) and wildtype and SERT+/− OVEX rats (subsequent experiment) were exposed to a 5 min infusion of 20%CO2 normoxic gas while measuring TST. Menopausal women were given brief 20% and 35%CO2 challenges, and hot flashes were self-reported and objectively verified. Results Compared to controls, OVEX rats had exacerbated increases in TST, and SERT+/− OVEX rats had prolonged TST increases following CO2. Most women reported mild/moderate hot flashes after CO2 challenges, and the hot flash severity to CO2 was positively correlated with daily hot flash frequency. Conclusions The studies demonstrate that this anxiogenic stimulus is capable of inducing cutaneous vasomotor responses in OVEX rats, and eliciting hot flashes in menopausal women. In rats, the severity of the response was mediated by loss of ovarian function and increased anxiety traits (SERT+/−), and, in women, by daily hot flash frequency. These findings may provide insights into anxiety related triggers and genetic risk factors for hot flashes in thermoneutral environments.
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    Chronic-Stress-Induced Behavioral Changes Associated with Subregion-Selective Serotonin Cell Death in the Dorsal Raphe
    (Society for Neuroscience, 2017-06-28) Natarajan, Reka; Forrester, Laura; Chiaia, Nicolas L.; Yamamoto, Bryan K.; Pharmacology and Toxicology, School of Medicine
    The current study examined the neurochemical mechanisms and neuroanatomical changes underlying coexisting behavioral effects associated with chronic-stress-induced alterations in serotonin (5HT) neurons. Chronic unpredictable stress (CUS) to adult male rats produced depression-like changes with cognitive dysfunction and selective cell death in the interfascicular nucleus of the dorsal raphe (DRif), resulting in decreased 5HTergic innervation of medial prefrontal cortex (mPFC). Twenty-one days of CUS decreased basal plasma levels of corticosterone and produced a shorter latency to immobility and longer durations of immobility in the force-swim test that persisted for 1 month after CUS. Deficits in acquisition, recall, perseveration, and reversal learning were evident 1 month after CUS. MK801 treatment during CUS blocked the changes in the forced-swim test and deficits in memory recall. These behavioral changes were associated with terminal deoxynucleotidyl transferase dUTP nick end labeling (TUNEL)-positive soma and the eventual loss of 5HT neurons in the DRif and its projections to the mPFC as evidenced by fewer labeled cells in the DRif after retrograde tracer injections into the mPFC of stressed rats. Similar to the effects of MK801 on behavior, MK801 pretreatment during stress blocked the CUS-induced decreases in 5HT soma within the DRif and its projections to the mPFC. Finally, the depression-like behaviors were blocked by acute injection of the 5HT2A/C agonist (−)-2,5-dimethoxy-4-iodoamphetamine hydrochloride into the mPFC before forced-swim testing. These results identify a cause and mechanism of 5HTergic dysfunction of the mPFC and associated mood and cognitive behaviors., SIGNIFICANCE STATEMENT Chronic stress causes persistent mood and cognitive changes typically associated with dysregulated serotonin (5HT) transmission in the medial prefrontal cortex (mPFC), but the cause of this dysregulation is unknown. Prior studies have focused on 5HTergic terminals in this region, but this study shows that chronic stress causes NMDA-receptor-dependent and subregion-specific cell death of 5HT neurons in the dorsal raphe. The consequent decreased 5HT innervation of the mPFC was associated with mood and cognitive changes that persisted long after the termination of stress. These findings identify a mechanism of subregion-selective death of 5HT neurons in the dorsal raphe, a defined neuroanatomical pathway, and a behavioral phenotype that mirror stress-associated diseases such as major depressive disorder.
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    Intraperitoneal injection of lipopolysaccharide prevents seizure-induced respiratory arrest in a DBA/1 mouse model of SUDEP
    (Wiley, 2020-05-31) Adhikari, Yadav; Jin, Xiaoming; Anatomy and Cell Biology, School of Medicine
    Objective Sudden unexpected death in epilepsy (SUDEP) is the cause of premature death of 50% patients with chronic refractory epilepsy. Respiratory failure during seizures is regarded as an important mechanism of SUDEP. Previous studies have shown that abnormal serotonergic neurotransmission is involved in the pathogenesis of seizure‐induced respiratory failure, while enhancing serotonergic neurotransmission in the brainstem suppresses it. Because peripheral inflammation is known to enhance serotonergic neuron activation and 5‐HT synthesis and release, we investigated the effect of intraperitoneal lipopolysaccharide (LPS)‐induced inflammation on the S‐IRA susceptibility during audiogenic seizures in DBA/1 mice. Methods After DBA/1 mice were primed by exposing to sound stimulation for three consecutive days, they were tested for seizure severity and seizure‐induced respiratory arrest (S‐IRA) induced by sound stimulation under different conditions. We determined the dose and time course of the effects of intraperitoneal administration of LPS on audiogenic seizures and S‐IRA. The effects of blocking TLR4 or RAGE receptors and blocking 5‐HT receptors on the LPS‐induced effect on S‐IRA were investigated. Statistical significance was evaluated using the Kruskal‐Wallis test. Results Intraperitoneal injection of LPS significantly had dose‐dependent effects in reducing the incidence of S‐IRA as well as seizure severity in DBA/1 mice. The protective effect of LPS on S‐IRA peaked at 8‐12 hours after LPS injection and was related to both reducing seizure severity and enhancing autoresuscitation. Blocking TLR4 or RAGE receptor with TAK‐242 or FPS‐ZM1, respectively, prior to LPS injection attenuated its effects on S‐IRA and seizure severity. Injection of a nonselective 5‐HT receptor antagonist, cyproheptadine, or a 5‐HT3 receptor antagonist, ondansetron, was effective in blocking LPS‐induced effect on S‐IRA. Immunostaining results showed a significant increase in c‐Fos‐positive serotonergic neurons in the dorsal raphe. Significance This is the first study that demonstrates the effect of intraperitoneal LPS injection‐induced inflammation on reducing S‐IRA susceptibility and provides additional evidence supporting the serotonin hypothesis on SUDEP. Our study suggests that inflammation may enhance brainstem 5‐HT neurotransmission to promote autoresuscitation during seizure and prevent SUDEP.
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    Physical Weight Loading Induces Expression of Tryptophan Hydroxylase 2 in the Brain Stem
    (2014-01) Shim, Joon W.; Dodge, Todd R.; Hammond, Max A.; Wallace, Joseph M.; Zhou, Feng C.; Yokota, Hiroki
    Sustaining brain serotonin is essential in mental health. Physical activities can attenuate mental problems by enhancing serotonin signaling. However, such activity is not always possible in disabled individuals or patients with dementia. Knee loading, a form of physical activity, has been found to mimic effects of voluntary exercise. Focusing on serotonergic signaling, we addressed a question: Does local mechanical loading to the skeleton elevate expression of tryptophan hydroxylase 2 (tph2) that is a rate-limiting enzyme for brain serotonin? A 5 min knee loading was applied to mice using 1 N force at 5 Hz for 1,500 cycles. A 5-min treadmill running was used as an exercise (positive) control, and a 90-min tail suspension was used as a stress (negative) control. Expression of tph2 was determined 30 min – 2 h in three brain regions ––frontal cortex (FC), ventromedial hypothalamus (VMH), and brain stem (BS). We demonstrated for the first time that knee loading and treadmill exercise upregulated the mRNA level of tph2 in the BS, while tail suspension downregulated it. The protein level of tph2 in the BS was also upregulated by knee loading and downregulated by tail suspension. Furthermore, the downregulation of tph2 mRNA by tail suspension can be partially suppressed by pre-application of knee loading. The expression of tph2 in the FC and VMH was not significantly altered with knee loading. In this study we provided evidence that peripheral mechanical loading can activate central tph2 expression, suggesting that physical cues may mediate tph2-cathalyzed serotonergic signaling in the brain.