[Chemokines as new actors in the dopaminergic system]

Early-life exposure to alcohol and the risk of alcohol-induced liver disease in adulthood

Alcohol consumption remains prevalent among pregnant and nursing mothers despite the well-documented adverse effects this may have on the offspring. Moderate-to-high levels of alcohol consumption in pregnancy result in fetal alcohol syndrome (FAS) disorders, with brain defects being chief among the abnormalities. Recent findings indicate that while light-to-moderate levels may not cause FAS, it may contribute to epigenetic changes that make the offspring prone to adverse health outcomes including metabolic disorders and an increased propensity in the adolescent-onset of drinking alcohol. On the one hand, prenatal alcohol exposure (PAE) causes epigenetic changes that affect lipid and glucose transcript regulating genes resulting in metabolic abnormalities. On the other hand, it can program offspring for increased alcohol intake, enhance its palatability, and increase acceptance of alcohol's flavor through associative learning, making alcohol a plausible second hit for the development of alcohol-induced liver disease. Adolescent drinking results in alcohol dependence and abuse in adulthood. Adolescent drinking results in alcohol dependence and abuse in adulthood. Alterations on the opioid system, particularly, the mu-opioid system, has been implicated in the mechanism that induces increased alcohol consumption and acceptance. This review proposes a mechanism that links PAE to the development of alcoholism and eventually to alcoholic liver disease (ALD), which results from prolonged alcohol consumption. While PAE may not lead to ALD development in childhood, there are chances that it may lead to ALD in adulthood.

Ethanol and Cytokines in the Central Nervous System

The innate immune system plays a critical role in the ethanol-induced neuroimmune response in the brain. Ethanol initiates the innate immune response via activation of the innate immune receptors Toll-like receptors (TLRs, e.g., TLR4, TLR3, TLR7) and NOD-like receptors (inflammasome NLRs) leading to a release of a plethora of chemokines and cytokines and development of the innate immune response. Cytokines and chemokines can have pro- or anti-inflammatory properties through which they regulate the immune response. In this chapter, we will focus on key cytokines (e.g., IL-1, IL-6, TNF-α) and chemokines (e.g., MCP-1/CCL2) that mediate the ethanol-induced neuroimmune responses. In this regard, we will use IL-1β, as an example cytokine, to discuss the neuromodulatory properties of cytokines on cellular properties and synaptic transmission. We will discuss their involvement through a set of evidence: (1) changes in gene and protein expression following ethanol exposure, (2) association of gene polymorphisms (humans) and alterations in gene expression (animal models) with increased alcohol intake, and (3) modulation of alcohol-related behaviors by transgenic or pharmacological manipulations of chemokine and cytokine systems. Over the last years, our understanding of the molecular mechanisms mediating cytokine- and chemokine-dependent regulation of immune responses has advanced tremendously, and we review evidence pointing to cytokines and chemokines serving as neuromodulators and regulators of neurotransmission.

Role of chemokines in Parkinson's disease

Parkinson's disease (PD) is a chronic progressive neurodegenerative disorder with an increasing incidence year by year, particularly as the population ages. The most common neuropathologic manifestation in patients with Parkinson's disease is dopamine neurons degeneration and loss in substantia nigra of middle brain. The main neurochemistry problem is the lack of the neurotransmitter dopamine. Clinically, PD patients may also have higher levels of glutamate, gamma-aminobutyric acid, acetylcholine and other neurotransmitters. At present, many data have shown that some chemokines are involved in regulating the release and transmission of neurotransmitters, and the growth and development of related neurons. In recent years, most of the studies relative to PD is based on immune and inflammatory mechanisms, and chemokines is also the focus on this mechanism. Chemokines are a class of cytokines that have definite chemotaxis effects on the different target cells. They might be involved in the pathogenesis of PD by inducing neuronal apoptosis and microglia activation. Clinical data has shown that the levels of chemokines in plasma and cerebrospinal fluid of PD patients have corresponding changes compared with the healthy persons. This review summarizes recent studies on chemokines and their receptors in Parkinson's disease: (i) to explore the role of chemokines in Parkinson's disease; (ii) to provide new indicators for clinical diagnosis of PD; (iii) to provide new targets for drug research and development in the treatment of Parkinson's disease.

Chronic Intracerebroventricular Infusion of Monocyte Chemoattractant Protein-1 Leads to a Persistent Increase in Sweetened Ethanol Consumption During Operant Self-Administration But Does Not Influence Sucrose Consumption in Long-Evans Rats

BACKGROUND

Among the evidence implicating neuroimmune signaling in alcohol use disorders are increased levels of the chemokine monocyte chemoattractant protein-1 (MCP-1) in the brains of human alcoholics and animal models of alcohol abuse. However, it is not known whether neuroimmune signaling can directly increase ethanol (EtOH) consumption, and whether MCP-1 is involved in that mechanism. We designed experiments to determine whether MCP-1 signaling itself is sufficient to accelerate or increase EtOH consumption. Our hypothesis was that increasing MCP-1 signaling by directly infusing it into the brain would increase operant EtOH self-administration.

METHODS

We implanted osmotic minipumps to chronically infuse either one of several doses of MCP-1 or vehicle into the cerebral ventricles (intracerebroventricular) of Long-Evans rats and then tested them in the operant self-administration of a sweetened EtOH solution for 8 weeks.

RESULTS

There was a significant interaction between dose of MCP-1 and sweetened EtOH consumed across the first 4 weeks (while pumps were flowing) and across the 8-week experiment. Animals receiving the highest dose of MCP-1 (2 μg/d) were the highest consumers of EtOH during weeks 3 through 8. MCP-1 did not influence the acquisition of self-administration (measured across the first 5 days), the motivation to consume EtOH (time to lever press or progressive ratio), withdrawal-induced anxiety, or the consumption of sucrose alone.

CONCLUSIONS

We provide novel evidence that neuroimmune signaling can directly increase chronic operant EtOH self-administration, and that this increase persists beyond the administration of the cytokine. These data suggest that EtOH-induced increases in MCP-1, or increases in MCP-1 due to various other neuroimmune mechanisms, may further promote EtOH consumption. Continued research into this mechanism, particularly using models of alcohol dependence, will help determine whether targeting MCP-1 signaling has therapeutic potential in the treatment of alcohol use disorders.

CRF-amplified neuronal TLR4/MCP-1 signaling regulates alcohol self-administration

Alcohol dependence is a complex disorder that initiates with episodes of excessive alcohol drinking known as binge drinking. It has a 50-60% risk contribution from inherited susceptibility genes; however, their exact identity and function are still poorly understood. We report that alcohol-preferring P rats have innately elevated levels of Toll-like receptor 4 (TLR4) and monocyte chemotactic protein-1 (MCP-1) that colocalize in neurons from the central nucleus of the amygdala (CeA) and ventral tegmental area (VTA). To examine the potential role of a TLR4/MCP-1 signal, we used Herpes Simplex Virus (HSV) vectors (amplicons) that retain in vivo neurotropism. Infusion of amplicons for TLR4 or MCP-1 siRNA into the CeA or VTA from the P rats inhibited target gene expression and blunted binge drinking. A similarly delivered amplicon for scrambled siRNA did not inhibit TLR4 or MCP-1 expression nor reduce binge drinking, identifying a neuronal TLR4/MCP-1 signal that regulates the initiation of voluntary alcohol self-administration. The signal was sustained during alcohol drinking by increased expression of corticotropin-releasing factor and its feedback regulation of TLR4 expression, likely contributing to the transition to alcohol dependence.