NE/DA interactions in prefrontal cortex and their possible roles as neuromodulators in schizophrenia

Potential diagnostic biomarkers for schizophrenia

Schizophrenia (SCH) is a complex and severe mental disorder with high prevalence, disability, mortality and carries a heavy disease burden, the lifetime prevalence of SCH is around 0.7%-1.0%, which has a profound impact on the individual and society. In the clinical practice of SCH, key problems such as subjective diagnosis, experiential treatment, and poor overall prognosis are still challenging. In recent years, some exciting discoveries have been made in the research on objective biomarkers of SCH, mainly focusing on genetic susceptibility genes, metabolic indicators, immune indices, brain imaging, electrophysiological characteristics. This review aims to summarize the biomarkers that may be used for the prediction and diagnosis of SCH.

Noradrenergic Source of Dopamine Assessed by Microdialysis in the Medial Prefrontal Cortex

Previous results indicate that dopamine (DA) release in the medial prefrontal cortex (mPFC) is modified by α₂ adrenoceptor- but not D2 DA receptor- agonists and antagonists, suggesting that DA measured by microdialysis in the mPFC originates from noradrenergic terminals. Accordingly, noradrenergic denervation was found to prevent α₂-receptor-mediated rise and fall of extracellular DA induced by atipamezole and clonidine, respectively, in the mPFC. The present study was aimed to determine whether DA released by dopaminergic terminals in the mPFC is not detected by in vivo microdialysis because is readily taken up by norepinephrine transporter (NET). Accordingly, the D2-antagonist raclopride increased the electrical activity of DA neurons in the ventral tegmental area (VTA) and enhanced extracellular DOPAC but failed to modify DA in the mPFC. However, in rats whose NET was either inactivated by nisoxetine or eliminated by noradrenergic denervation, raclopride still elevated extracellular DOPAC and activated dopaminergic activity, but also increased DA. Conversely, the D2-receptor agonist quinpirole reduced DOPAC but failed to modify DA in the mPFC in control rats. However, in rats whose NET was eliminated by noradrenergic denervation or inhibited by locally perfused nisoxetine, quinpirole maintained its ability to reduce DOPAC but acquired that of reducing DA. Moreover, raclopride and quinpirole, when locally perfused into the mPFC of rats subjected to noradrenergic denervation, were able to increase and decrease, respectively, extracellular DA levels, while being ineffective in control rats. Transient inactivation of noradrenergic neurons by clonidine infusion into the locus coeruleus, a condition where NET is preserved, was found to reduce extracellular NE and DA in the mPFC, whereas noradrenergic denervation, a condition where NET is eliminated, almost totally depleted extracellular NE but increased DA. Both transient inactivation and denervation of noradrenergic neurons were found to reduce the number of spontaneously active DA neurons and their bursting activity in the VTA. The results indicate that DA released in the mPFC by dopaminergic terminals is not detected by microdialysis unless DA clearance from extracellular space is inactivated. They support the hypothesis that noradrenergic terminals are the main source of DA measured by microdialysis in the mPFC during physiologically relevant activities.

A possible key role of vision in the development of schizophrenia

Based on a brief overview of the various aspects of schizophrenia reported by numerous studies, here we hypothesize that schizophrenia may originate (and in part be performed) from visual areas. In other words, it seems that a normal visual system or at least an evanescent visual perception may be an essential prerequisite for the development of schizophrenia as well as of various types of hallucinations. Our study focuses on auditory and visual hallucinations, as they are the most prominent features of schizophrenic hallucinations (and also the most studied types of hallucinations). Here, we evaluate the possible key role of the visual system in the development of schizophrenia.

Persistent cognitive dysfunction after traumatic brain injury: A dopamine hypothesis

Traumatic brain injury (TBI) represents a significant cause of death and disability in industrialized countries. Of particular importance to patients the chronic effect that TBI has on cognitive function. Therapeutic strategies have been difficult to evaluate because of the complexity of injuries and variety of patient presentations within a TBI population. However, pharmacotherapies targeting dopamine (DA) have consistently shown benefits in attention, behavioral outcome, executive function, and memory. Still it remains unclear what aspect of TBI pathology is targeted by DA therapies and what time-course of treatment is most beneficial for patient outcomes. Fortunately, ongoing research in animal models has begun to elucidate the pathophysiology of DA alterations after TBI. The purpose of this review is to discuss clinical and experimental research examining DAergic therapies after TBI, which will in turn elucidate the importance of DA for cognitive function/dysfunction after TBI as well as highlight the areas that require further study.

Intrategmental infusion of cocaine decreases dopamine release and enhances norepinephrine release in the medial prefrontal cortex

We evaluated the effects of local cocaine infusion into the A10 (ventral tegmental area), the cell body of the mesocorticolimbic dopaminergic pathway, on the extracellular concentrations of dopamine and norepinephrine in the medial prefrontal cortex, one of its terminal fields. A 1-ml Hamilton syringe was used to infuse a cocaine solution, either 20 or 200 microM, into the ventral tegmental area of anesthetized rats for 120 min through a microdialysis probe. The pure artificial cerebrospinal fluid (0 microM cocaine) infusion served as a control and a lidocaine (100 microM) infusion was administered to prevent the local anesthetic effect of cocaine. After intrategmental cocaine infusion (either 20 or 200 microM), extracellular dopamine and norepinephrine in the ventral tegmental area both increased significantly to a steady state level (208 +/- 42 and 148 +/- 23% for low dose and 220 +/- 24 and 150 +/- 15% for high dose). Simultaneously, the 200-microM cocaine infusion caused a significant decrease in extracellular dopamine (77 +/- 5%) but an increase in norepinephrine (140 +/- 6%) in the medial prefrontal cortex. The local anesthetic, lidocaine, produced no effects on the dopamine or norepinephrine output (neither in the ventral tegmental area nor in the medial prefrontal cortex). This study not only supports recent findings of an increase in extracellular dopamine and norepinephrine in the ventral tegmental area on intrategmental cocaine infusion, but also demonstrates that cocaine infused locally in the ventral tegmental area can decrease dopamine and increase norepinephrine at a remote terminal area (medial prefrontal cortex). Finally, the introduction rate of cocaine into the ventral tegmental area by retrograde microdialysis was found to be 0.83 ng/min for the low dose and 8.14 ng/min for the high dose.