Hypoinsulinemia regulates amphetamine-induced reverse transport of dopamine

Molecular mechanisms of psychostimulant-induced structural plasticity

Drug addiction is characterized by persistent behavioral and cellular plasticity throughout the brain's reward regions. Among the many neuroadaptations that occur following repeated drug administration are alterations in cell morphology including changes in dendritic spines. While this phenomenon has been well documented, the underlying molecular mechanisms are poorly understood. Here, within the context of drug abuse, we review and integrate several of the established pathways known to regulate synaptic remodeling, and discuss the contributions of neurotrophic and dopamine signaling in mediating this structural plasticity. Finally, we discuss how such upstream mechanisms could regulate actin dynamics, the common endpoint involved in structural remodeling in neurons.

A closer look at amphetamine-induced reverse transport and trafficking of the dopamine and norepinephrine transporters

Amphetamine (AMPH) and its derivatives are regularly used in the treatment of a wide array of disorders such as attention-deficit hyperactivity disorder (ADHD), obesity, traumatic brain injury, and narcolepsy (Prog Neurobiol 75:406-433, 2005; J Am Med Assoc 105:2051-2054, 1935; J Am Acad Child Adolesc Psychiatry 41:514-521, 2002; Neuron 43:261-269, 2004; Annu Rev Pharmacol Toxicol 47:681-698, 2007; Drugs Aging 21:67-79, 2004). Despite the important medicinal role for AMPH, it is more widely known for its psychostimulant and addictive properties as a drug of abuse. The primary molecular targets of AMPH are both the vesicular monoamine transporters (VMATs) and plasma membrane monoamine-dopamine (DA), norepinephrine (NE), and serotonin (5-HT)-transporters. The rewarding and addicting properties of AMPH rely on its ability to act as a substrate for these transporters and ultimately increase extracellular levels of monoamines. AMPH achieves this elevation in extracellular levels of neurotransmitter by inducing synaptic vesicle depletion, which increases intracellular monoamine levels, and also by promoting reverse transport (efflux) through plasma membrane monoamine transporters (J Biol Chem 237:2311-2317, 1962; Med Exp Int J Exp Med 6:47-53, 1962; Neuron 19:1271-1283, 1997; J Physiol 144:314-336, 1958; J Neurosci 18:1979-1986, 1998; Science 237:1219-1223, 1987; J Neurosc 15:4102-4108, 1995). This review will focus on two important aspects of AMPH-induced regulation of the plasma membrane monoamine transporters-transporter mediated monoamine efflux and transporter trafficking.

Neurotrophic factors and structural plasticity in addiction

Drugs of abuse produce widespread effects on the structure and function of neurons throughout the brain's reward circuitry, and these changes are believed to underlie the long-lasting behavioral phenotypes that characterize addiction. Although the intracellular mechanisms regulating the structural plasticity of neurons are not fully understood, accumulating evidence suggests an essential role for neurotrophic factor signaling in the neuronal remodeling which occurs after chronic drug administration. Brain-derived neurotrophic factor (BDNF), a growth factor enriched in brain and highly regulated by several drugs of abuse, regulates the phosphatidylinositol 3'-kinase (PI3K), mitogen-activated protein kinase (MAPK), phospholipase Cgamma (PLCgamma), and nuclear factor kappa B (NFkappaB) signaling pathways, which influence a range of cellular functions including neuronal survival, growth, differentiation, and structure. This review discusses recent advances in our understanding of how BDNF and its signaling pathways regulate structural and behavioral plasticity in the context of drug addiction.

PI3K signaling supports amphetamine-induced dopamine efflux

The dopamine (DA) transporter (DAT) is a major molecular target of the psychostimulant amphetamine (AMPH). AMPH, as a result of its ability to reverse DAT-mediated inward transport of DA, induces DA efflux thereby increasing extracellular DA levels. This increase is thought to underlie the behavioral effects of AMPH. We have demonstrated previously that insulin, through phosphatidylinositol 3-kinase (PI3K) signaling, regulates DA clearance by fine-tuning DAT plasma membrane expression. PI3K signaling may represent a novel mechanism for regulating DA efflux evoked by AMPH, since only active DAT at the plasma membrane can efflux DA. Here, we show in both a heterologous expression system and DA neurons that inhibition of PI3K decreases DAT cell surface expression and, as a consequence, AMPH-induced DA efflux.

Fetal cytomegalovirus infection associated with cerebral hemorrhage, hydrops fetalis, and echogenic bowel: case report

We describe some fetal ultrasound findings associated with intrauterine cytomegalovirus (CMV) infection. We report a 38-year-old gravida 3, para 2 at 16 weeks of gestation who underwent ultrasound examination for anomaly screening. The scan revealed an extensive irregular echogenic area in the fetal brain, especially at the level of lateral ventricles, suggestive of intraventricular and cerebral hemorrhage. Cardiomegaly, hepatomegaly, and mild ascites as well as an echogenic bowel were demonstrated. Abnormal chromosomes and hemoglobin Bart disease were excluded by analysis of fetal blood. Follow-up ultrasound at 20 weeks of gestation showed frank hydrops fetalis, and termination of the pregnancy was performed based on the couple's decision, giving stillbirth to a male fetus weighing 450 g. Autopsy findings showed intracerebral hemorrhage (right cerebral hemisphere) and hydrops fetalis with hepatosplenomegaly. Microscopic investigation showed typical changes of CMV infection in several organs, including brain, thyroid gland, lung, liver, kidney, heart, pancreas, and placenta. Sonographically, the combination of hydrops fetalis, cerebral hemorrhage, and hyperechoic bowel should raise the possibility of a CMV infection, particularly in cases with no obvious cause of hydrops fetalis.