found in the human and rat brain. In Rats, OCT3 is the only known monoamine transporter inhibited by physiological concentrations of corticosteroids. We hypothesized that CORT- mediated inhibition of OCT3 blocks the clearance of serotonin (5-HT) leading to an increase 5-HT receptor-mediated signaling. In experiment 1, due to conflicting reports on the location of OCT3 mRNA in the rat brain, in situ hybridization was performed on brain tissue sections. RNA was extracted from rat brain tissue, reverse transcribed into cDNA, and then polymerase chain reaction (PCR) was performed to generate riboprobe templates. The riboprobe templates were then used for in vitro transcription of digoxigenin (DIG)-labeled riboprobes complementary to OCT3. In experiment 2, 12 rats from an identical cohort were exposed to a chronic restraint stress paradigm (two hours/day for seven days, STRESS group), while the other 12 remained in their home cages (CTRL group). Twenty-four hours after the last stressor, all animals were euthanized and their brains immediately removed and frozen. Bilateral tissue punches were collected from 300μm coronal sections from the CA1 region of the dorsal hippocampus, basolateral amygdala (BLA), and dorsomedial hypothalamus (DMH). The relative OCT2, OCT3, and 5HT2a mRNA levels from each tissue punch were determined via quantitative real-time polymerase chain reaction (qPCR). The results of experiment 1 confirmed the presence of OCT3 mRNA in the CA1, amygdala, and the DMH. The results of experiment 2 show that chronic restraint stress did not alter gene expression for 5-HT2A, OCT2, and OCT3. These data may help reveal new information involving OCT3’s role in the hippocampus, amygdala and DMH in regards to localization and mRNA expression levels after exposure to a stressor.
This hypothesis is supported by previous studies demonstrating that stress-induced elevation of glucocorticoids increases the transcription of C4. I propose that activated glucocorticoid receptors directly increase C4 protein expression as a transcription factor activator. Additionally, I propose that activated glucocorticoid receptors inhibit the expression of the transcription factor nuclear factor-light-chain-enhancer of activated B cells (NF-κB), thereby leading to decreased expression of the C4 inhibitor CUB and Sushi multiple domains 1 (CSMD1).
Glucocorticoid receptors and C4 are richly expressed in the hippocampus, a region critical in memory consolidation, spatial, and declarative memory. I propose that stress-induced upregulation of C4 activity in the hippocampus promotes excessive synaptic pruning, contributing to specific deficits and hippocampal shrinkage seen in schizophrenia. Stress exposure during fetal development and adolescence likely acts through the proposed mechanisms to increase hippocampal C4 activity and subsequent schizophrenia risk. These mechanisms may reveal novel interactions between environmental and genetic risk factors in the etiology of schizophrenia through complement activation.
Background: HIV-1 Clade C (Subtype C; HIV-1C) is responsible for greater than 50% of infections worldwide. Unlike clade B HIV-1 (Subtype B; HIV-1B), which is known to cause HIV associated dementia (HAD) in approximately 15% to 30% of the infected individuals, HIV-1C has been linked with lower prevalence of HAD (0 to 6%) in India and Ethiopia. However, recent studies report a higher prevalence of HAD in South Africa, Zambia and Botswana, where HIV-1C infections predominate. Therefore, we examined whether Southern African HIV-1C is genetically distinct and investigated its neurovirulence. HIV-1 Tat protein is a viral determinant of neurocognitive dysfunction. Therefore, we focused our study on the variations seen in tat gene and its contribution to HIV associated neuropathogenesis.
Results: A phylogenetic analysis of tat sequences of Southern African (South Africa and Zambia) HIV isolates with those from the geographically distant Southeast Asian (India and Bangladesh) isolates revealed that Southern African tat sequences are distinct from Southeast Asian isolates. The proportion of HIV - 1C variants with an intact dicysteine motif in Tat protein (C30C31) was significantly higher in the Southern African countries compared to Southeast Asia and broadly paralleled the high incidence of HAD in these countries. Neuropathogenic potential of a Southern African HIV-1C isolate (from Zambia; HIV-1C(1084i)), a HIV-1C isolate (HIV-1(IndieC1)) from Southeast Asia and a HIV-1B isolate (HIV-1(ADA)) from the US were tested using in vitro assays to measure neurovirulence and a SCID mouse HIV encephalitis model to measure cognitive deficits. In vitro assays revealed that the Southern African isolate, HIV-1C(1084i) exhibited increased monocyte chemotaxis and greater neurotoxicity compared to Southeast Asian HIV-1C. In neurocognitive tests, SCID mice injected with MDM infected with Southern African HIV-1C(1084i) showed greater cognitive dysfunction similar to HIV-1B but much higher than those exposed to Southeast Asian HIV - 1C.
Conclusions: We report here, for the first time, that HIV-1C from Southern African countries is genetically distinct from Southeast Asian HIV-1C and that it exhibits a high frequency of variants with dicysteine motif in a key neurotoxic HIV protein, Tat. Our results indicate that Tat dicysteine motif determines neurovirulence. If confirmed in population studies, it may be possible to predict neurocognitive outcomes of individuals infected with HIV-1C by genotyping Tat.
Decreased serotonin (5-HT) function is associated with numerous cognitive and affective disorders. Women are more vulnerable to these disorders and have a lower rate of 5-HT synthesis than men. Serotonergic neurons in the dorsal raphe nucleus (DRN) are a major source of 5-HT in the forebrain and play a critical role in regulation of stress-related disorders. In particular, polymorphisms of tryptophan hydroxylase-2 (TpH2, the brain-specific, rate-limiting enzyme for 5-HT biosynthesis) are implicated in cognitive and affective disorders. Administration of 17β-estradiol (E2), the most potent naturally circulating estrogen in women and rats, can have beneficial effects on cognitive, anxiety-like, and depressive-like behaviors. Moreover, E2 increases TpH2 mRNA in specific subregions of the DRN.
Although conjugated equine estrogens (CEE) are a commonly prescribed estrogen component of hormone therapy in menopausal women, there is a marked gap in knowledge regarding how CEE affects these behaviors and the brain 5-HT system. Therefore, we compared the effects of CEE and E2 treatments on behavior and TpH2 mRNA. Female Sprague-Dawley rats were ovariectomized, administered either vehicle, CEE, or E2 and tested on a battery of cognitive, anxiety-like, and depressive-like behaviors. The brains of these animals were subsequently analyzed for TpH2 mRNA. Both CEE and E2 exerted beneficial behavioral effects, although efficacy depended on the distinct behavior and for cognition, on the task difficulty.
Compared to CEE, E2 generally had more robust anxiolytic and antidepressant effects. E2 increased TpH2 mRNA in the caudal and mid DRN, corroborating previous findings. However, CEE increased TpH2 mRNA in the caudal and rostral, but not the mid, DRN, suggesting that distinct estrogens can have subregion-specific effects on TpH2 gene expression. We also found differential correlations between the level of TpH2 mRNA in specific DRN subregions and behavior, depending on the type of behavior. These distinct associations imply that cognition, anxiety-like, and depressive-like behaviors are modulated by unique serotonergic neurocircuitry, opening the possibility of novel avenues of targeted treatment for different types of cognitive and affective disorders.