The Neuroimmune System and the Cerebellum.

The recognition that there is an innate immune system of the brain, referred to as the neuroimmune system, that preforms many functions comparable to that of the peripheral immune system is a relatively new concept and much is yet to be learned. The main cellular components of the neuroimmune system are the glial cells of the brain, primarily microglia and astrocytes. These cell types preform many functions through secretion of signaling factors initially known as immune factors but referred to as neuroimmune factors when produced by cells of the brain. The immune functions of glial cells play critical roles in the healthy brain to maintain homeostasis that is essential for normal brain function, to establish cytoarchitecture of the brain during development, and, in pathological conditions, to minimize the detrimental effects of disease and injury and promote repair of brain structure and function. However, dysregulation of this system can occur resulting in actions that exacerbate or perpetuate the detrimental effects of disease or injury. The neuroimmune system extends throughout all brain regions, but attention to the cerebellar system has lagged that of other brain regions and information is limited on this topic. This article is meant to provide a brief introduction to the cellular and molecular components of the brain immune system, its functions, and what is known about its role in the cerebellum. The majority of this information comes from studies of animal models and pathological conditions, where upregulation of the system facilitates investigation of its actions.

Alcohol Enhances Responses to High Frequency Stimulation in Hippocampus from Transgenic Mice with Increased Astrocyte Expression of IL-6.

Recent studies show that alcohol exposure can induce glial production of neuroimmune factors in the CNS. Of these, IL-6 has gained attention because it is involved in a number of important physiological and pathophysiological processes that could be affected by alcohol-induced CNS production of IL-6, particularly under conditions of excessive alcohol use. For example, IL-6 has been shown to play a role in hippocampal behaviors and synaptic plasticity (long-term potentiation; LTP) associated with memory and learning. Surprisingly, in our in vitro studies of LTP at the Schaffer collateral to CA1 pyramidal neuron synapse in hippocampus from transgenic mice that express elevated levels of astrocyte produced IL-6 (TG), LTP was not altered by the increased levels of IL-6. However, exposure to acute alcohol revealed neuroadaptive changes that served to protect LTP against the alcohol-induced reduction of LTP observed in hippocampus from non-transgenic control mice (WT). Here we examined the induction phase of LTP to assess if presynaptic neuroadaptive changes occurred in the hippocampus of TG mice that contributed to the resistance of LTP to alcohol. Results are consistent with a role for IL-6-induced neuroadaptive effects on presynaptic mechanisms involved in transmitter release in the resistance of LTP to alcohol in hippocampus from the TG mice. These actions are important with respect to a role for IL-6 in physiological and pathophysiological processes in the CNS and in CNS actions of alcohol, especially when excessive alcohol used is comorbid with conditions associated with elevated levels of IL-6 in the CNS.

Alcohol alters IL-6 Signal Transduction in the CNS of Transgenic Mice with Increased Astrocyte Expression of IL-6.

Neuroimmune factors, including the cytokine interleukin-6 (IL-6), are important chemical regulators of central nervous system (CNS) function under both physiological and pathological conditions. Elevated expression of IL-6 occurs in the CNS in a variety of disorders associated with altered CNS function, including excessive alcohol use. Alcohol-induced production of IL-6 has been reported for several CNS regions including the cerebellum. Cerebellar actions of alcohol occur through a variety of mechanisms, but alcohol-induced changes in signal transduction, transcription, and translation are known to play important roles. IL-6 is an activator of signal transduction that regulates gene expression. Thus, alcohol-induced IL-6 production could contribute to cerebellar effects of alcohol by altering gene expression, especially under conditions of chronic alcohol abuse, where IL-6 levels could be habitually elevated. To gain an understanding of the effects of alcohol on IL-6 signal transduction, we studied activation/expression of IL-6 signal transduction partners STAT3 (Signal Transducer and Activator of Transcription), CCAAT-enhancer binding protein (C/EBP) beta, and p42/p44 mitogen-activated protein kinase (MAPK) at the protein level. Cerebella of transgenic mice that express elevated levels of astrocyte produced IL-6 in the CNS were studied. Results show that the both IL-6 and chronic intermittent alcohol exposure/withdrawal affect IL-6 signal transduction partners and that the actions of IL-6 and alcohol interact to alter activation/expression of IL-6 signal transduction partners. The alcohol/IL-6 interactions may contribute to cerebellar actions of alcohol, whereas the effects of IL-6 alone may have relevance to cerebellar changes occurring in CNS disorders associated with elevated levels of IL-6.

Increased IL-6 expression in astrocytes is associated with emotionality, alterations in central amygdala GABAergic transmission, and excitability during alcohol withdrawal.

Accumulating evidence from preclinical and clinical studies has implicated a role for the cytokine IL-6 in a variety of CNS diseases including anxiety-like and depressive-like behaviors, as well as alcohol use disorder. Here we use homozygous and heterozygous transgenic mice expressing elevated levels of IL-6 in the CNS due to increased astrocyte expression and non-transgenic littermates to examine a role for astrocyte-produced IL-6 in emotionality (response to novelty, anxiety-like, and depressive-like behaviors). Our results from homozygous IL-6 mice in a variety of behavioral tests (light/dark transfer, open field, digging, tail suspension, and forced swim tests) support a role for IL-6 in stress-coping behaviors. Ex vivo electrophysiological studies of neuronal excitability and inhibitory GABAergic synaptic transmission in the central nucleus of the amygdala (CeA) of the homozygous transgenic mice revealed increased inhibitory GABAergic signaling and increased excitability of CeA neurons, suggesting a role for astrocyte produced IL-6 in the amygdala in exploratory drive and depressive-like behavior. Furthermore, studies in the hippocampus of activation/expression of proteins associated with IL-6 signal transduction and inhibitory GABAergic mechanisms support a role for astrocyte produced IL-6 in depressive-like behaviors. Our studies indicate a complex and dose-dependent relationship between IL-6 and behavior and implicate IL-6 induced neuroadaptive changes in neuronal excitability and the inhibitory GABAergic system as important contributors to altered behavior associated with IL-6 expression in the CNS.

Neuroimmune regulation of neurophysiology in the cerebellum.

Recent studies have established the existence of an innate immune system in the central nervous system (CNS) and implicated a critical role for this system in both normal and pathological processes. Astrocytes and microglia, normal components of the CNS, are the primary cell types that comprise the innate immune system of the CNS. Basic to their role during normal and adverse conditions is the production of neuroimmune factors such as cytokines and chemokines, which are signaling molecules that initiate or coordinate downstream cellular actions. During adverse conditions, cytokines and chemokines function in defensive and repair. However, if expression of these factors becomes dysregulated, abnormal CNS function can result. Both neurons and glial cells of the CNS express receptors for cytokines and chemokines, but the biological consequence of receptor activation has yet to be fully resolved. Our studies show that neuroadaptive changes are produced in primary cultures of rat cerebellar cells chronically treated with the cytokine interleukin-6 (IL-6) and in the cerebellum of transgenic mice that chronically express elevated levels of IL-6 in the CNS. In the cerebellum in culture and in vivo, the neuroadaptive changes included alterations in the level of expression of proteins involved in gene expression, signal transduction, and synaptic transmission. Associated with these changes were alterations in neuronal function. A comparison of results from the cultured cerebellar cells and cerebellum of the transgenic mice indicated that the effects of IL-6 can vary across neuronal types. However, alterations in mechanisms involved in Ca(2+) homeostasis were observed in all cell types studied. These results indicate that modifications in cerebellar function are likely to occur in disorders associated with elevated levels of IL-6 in the cerebellum.

Impact of Elevated Brain IL-6 in Transgenic Mice on the Behavioral and Neurochemical Consequences of Chronic Alcohol Exposure.

Alcohol consumption activates the neuroimmune system of the brain, a system in which brain astrocytes and microglia play dominant roles. These glial cells normally produce low levels of neuroimmune factors, which are important signaling factors and regulators of brain function. Alcohol activation of the neuroimmune system is known to dysregulate the production of neuroimmune factors, such as the cytokine IL-6, thereby changing the neuroimmune status of the brain, which could impact the actions of alcohol. The consequences of neuroimmune-alcohol interactions are not fully known. In the current studies we investigated this issue in transgenic (TG) mice with altered neuroimmune status relative to IL-6. The TG mice express elevated levels of astrocyte-produced IL-6, a condition known to occur with alcohol exposure. Standard behavioral tests of alcohol drinking and negative affect/emotionality were carried out in homozygous and heterozygous TG mice and control mice to assess the impact of neuroimmune status on the actions of chronic intermittent alcohol (ethanol) (CIE) exposure on these behaviors. The expressions of signal transduction and synaptic proteins were also assessed by Western blot to identify the impact of alcohol-neuroimmune interactions on brain neurochemistry. The results from these studies show that neuroimmune status with respect to IL-6 significantly impacts the effects of alcohol on multiple levels.

Neuroimmune interactions with binge alcohol drinking in the cerebellum of IL-6 transgenic mice.

The neuroimmune system of the brain, which is comprised primarily of astrocytes and microglia, regulates a variety of homeostatic mechanisms that underlie normal brain function. Numerous conditions, including alcohol consumption, can disrupt this regulatory process by altering brain levels of neuroimmune factors. Alcohol and neuroimmune factors, such as proinflammatory cytokines IL-6 and TNF-alpha, act at similar targets in the brain, including excitatory and inhibitory synaptic transmission. Thus, alcohol-induced production of IL-6 and/or TNF-alpha could be important contributing factors to the effects of alcohol on the brain. Recent studies indicate that IL-6 plays a role in alcohol drinking and the effects of alcohol on the brain activity following the cessation of alcohol consumption (post-alcohol period), however information on these topics is limited. Here we used homozygous and heterozygous female and male transgenic mice with increased astrocyte expression of IL-6 to examined further the interactions between alcohol and IL-6 with respect to voluntary alcohol drinking, brain activity during the post-alcohol period, IL-6 signal transduction, and expression of synaptic proteins. Wildtype littermates (WT) served as controls. The transgenic mice model brain neuroimmune status with respect to IL-6 in subjects with a history of persistent alcohol use. Results showed a genotype dependent reduction in voluntary alcohol consumption in the Drinking in the Dark protocol and in frequency-dependent relationships between brain activity in EEG recordings during the post-alcohol period and alcohol consumption. IL-6, TNF-alpha, IL-6 signal transduction partners pSTAT3 and c/EBP beta, and synaptic proteins were shown to play a role in these genotypic effects.

Ethanol alters opioid regulation of Ca(2+) influx through L-type Ca(2+) channels in PC12 cells.

BACKGROUND: Studies at the behavioral and synaptic level show that effects of ethanol on the central nervous system can involve the opioid signaling system. These interactions may alter the function of a common downstream target. In this study, we examined Ca(2+) channel function as a potential downstream target of interactions between ethanol and µ or κ opioid receptor signaling. METHODS: The studies were carried out in a model system, undifferentiated PC12 cells transfected with µ or κ opioid receptors. The PC12 cells express L-type Ca(2+) channels, which were activated by K(+) depolarization. Ca(2+) imaging was used to measure relative Ca(2+) flux during K(+) depolarization and the modulation of Ca(2+) flux by opioids and ethanol. RESULTS: Ethanol, µ receptor activation, and κ receptor activation all reduced the amplitude of the Ca(2+) signal produced by K(+) depolarization. Pretreatment with ethanol or combined treatment with ethanol and µ or κ receptor agonists caused a reduction in the amplitude of the Ca(2+) signal that was comparable to or smaller than that observed for the individual drugs alone, indicating an interaction by the drugs at a downstream target (or targets) that limited the modulation of Ca(2+) flux through L-type Ca(2+) channels. CONCLUSIONS: These studies provide evidence for a cellular mechanism that could play an important role in ethanol regulation of synaptic transmission and behavior through interactions with the opioid signaling.

Altered hippocampal synaptic transmission in transgenic mice with astrocyte-targeted enhanced CCL2 expression.

Elevated expression of neuroinflammatory factors in the central nervous system (CNS) contributes to the cognitive impairment in CNS disorders such as injury, disease and neurodegenerative disorders. However, information on the role of specific neuroimmune factors in normal and abnormal CNS function is limited. In this study, we investigated the effects of chronic exposure to the chemokine CCL2 on hippocampal synaptic function at the Schaffer collateral-CA1 synapse, a synapse that is known to play an important role in cognitive functions such as memory and learning. Synaptic function was measured in vitro using hippocampal slices obtained from transgenic mice that express elevated levels of CCL2 in the CNS through astrocyte expression and their non-transgenic littermate controls. Extracellular field potential electrophysiological recordings showed a significant reduction in the magnitude of synaptic responses in hippocampal slices from the CCL2 transgenic mice compared with slices from non-transgenic littermate controls. Two forms of short-term synaptic plasticity (post-tetanic potentiation and short-term potentiation) thought to be important cellular mechanisms of short-term memory were enhanced in hippocampal slices from CCL2 transgenic mice compared to non-transgenic hippocampal slices, whereas long-term synaptic plasticity (LTP), which is critical to long-term memory formation, was not altered. Western blot analysis of hippocampus from the CCL2 transgenic mice and non-transgenic mice showed no change in level of neuronal specific enolase, a neuronal specific protein, GFAP, an astrocyte specific protein, and several synaptic proteins compared with non-transgenic littermate controls. These results show that CCL2, which is known to be chronically produced at elevated levels within the CNS in a number of CNS disorders, can significantly alter hippocampal function and implicate a role for CCL2 in the cognitive dysfunction associated with these CNS disorders.

Alcohol and IL-6 Alter Expression of Synaptic Proteins in Cerebellum of Transgenic Mice with Increased Astrocyte Expression of IL-6.

Recent studies indicate that neuroimmune factors, including the cytokine interleukin-6 (IL-6), play a role in the CNS actions of alcohol. The cerebellum is a sensitive target of alcohol, but few studies have examined a potential role for neuroimmune factors in the actions of alcohol on this brain region. A number of studies have shown that synaptic transmission, and in particular inhibitory synaptic transmission, is an important cerebellar target of alcohol. IL-6 also alters synaptic transmission, although it is unknown if IL-6 targets are also targets of alcohol. This is an important issue because alcohol induces glial production of IL-6, which could then covertly influence the actions of alcohol. The persistent cerebellar effects of both IL-6 and alcohol typically involve chronic exposure and, presumably, altered gene and protein expression. Thus, in the current studies we tested the possibility that proteins involved in inhibitory and excitatory synaptic transmission in the cerebellum are common targets of alcohol and IL-6. We used transgenic mice that express elevated levels of astrocyte produced IL-6 to model persistently elevated expression of IL-6, as would occur in alcohol use disorders, and a chronic intermittent alcohol exposure/withdrawal paradigm (CIE/withdrawal) that is known to produce alcohol dependence. Multiple cerebellar synaptic proteins were assessed by Western blot. Results show that IL-6 and CIE/withdrawal have both unique and common actions that affect synaptic protein expression. These common targets could provide sites for IL-6/alcohol exposure/withdrawal interactions and play an important role in cerebellar symptoms of alcohol use such as ataxia.

Chronic CXCL10 alters neuronal properties in rat hippocampal culture.

The chemokine CXCL10 is expressed in the central nervous system (CNS) during neuroinflammatory conditions. Neurons express CXCR3, the receptor for CXCL10, and neuronal function has been shown to be altered by acute exposure to CXCL10. Little is known about the effects of chronic exposure to CXCL10 on neuronal function. Results from our studies show that chronic exposure of cultured rat hippocampal neurons to CXCL10 results in altered levels of protein for GABA and glutamate receptors and altered synaptic network activity. These effects of CXCL10 may contribute to altered CNS function that occurs in some chronic neuroinflammatory conditions.

Emergence of NMDAR-independent long-term potentiation at hippocampal CA1 synapses following early adolescent exposure to chronic intermittent ethanol: role for sigma-receptors.

Adolescent humans who abuse alcohol are more vulnerable than adults to the development of memory impairments. Memory impairments often involve modifications in the ability of hippocampal neurons to establish long-term potentiation (LTP) of excitatory neurotransmission; however, few studies have examined how chronic ethanol exposure during adolescence affects LTP mechanisms in hippocampus. We investigated changes in LTP mechanisms in hippocamal slices from rats exposed to intoxicating concentrations of chronic intermittent ethanol (CIE) vapors in their period of early-adolescent (i.e., prepubescent) or late-adolescent (i.e., postpubescent) development. LTP was evaluated at excitatory CA1 synapses in hippocampal slices at 24 h after the cessation of air (control) or CIE vapor treatments. CA1 synapses in control slices showed steady LTP following induction by high-frequency stimulation, which was fully dependent on NMDAR function. By contrast, slices from early-adolescent CIE exposed animals showed a compound form of LTP consisting of an NMDAR-dependent component and a slow-developing component independent of NMDARs. These components summated to yield LTP of robust magnitude above LTP levels in age-matched control slices. Bath-application of the sigma-receptor antagonist BD1047 and the neuroactive steroid pregnenolone sulfate, but not acute ethanol application, blocked NMDAR-independent LTP, while leaving NMDAR-dependent LTP intact. Analysis of presynaptic function during NMDAR-independent LTP induction demonstrated increased presynaptic function via a sigma-receptor-dependent mechanism in slices from early-adolescent CIE-exposed animals. By contrast, CIE exposure after puberty onset in late-adolescent animals produced decrements in LTP levels. The identification of a role for sigma-receptors and neuroactive steroids in the development of NMDAR-independent LTP suggests an important pathway by which hippocampal synaptic plasticity, and perhaps memory, may be uniquely altered by chronic ethanol exposure during the prepubescent phase of adolescent development.

mGluR1 agonists elicit a Ca 2+ signal and membrane hyperpolarization mediated by apamin-sensitive potassium channels in immature rat purkinje neurons.

The type 1 metabotropic glutamate receptor (mGluR1) plays an import role in the synaptic physiology and development of cerebellar Purkinje neurons. mGluR1 expression occurs early in the developmental program of Purkinje neurons, at an age that precedes expression of the dendritic structure. Few studies have investigated the physiological response produced by mGluR1 activation in early-developing Purkinje neurons. To address this question, simultaneous recording of membrane potential and intracellular Ca(2+) was performed in immature cultured Purkinje neurons coupled with exogenous application of mGluR1 agonists. Membrane potential was measured using the perforated patch method of whole-cell recording, and intracellular Ca(2+) was measured using fura-2-based Ca(2+) imaging. Brief, 1-sec micropressure application of the group I mGluR-selective agonist (S)-3,5-dihydroxyphenylglycine (DHPG) evoked a prominent Ca(2+) signal and coincident fast hyperpolarization in the immature neurons. The mGluR1-selective antagonist 7-(hydroxyimino)cyclopropa[b]chromen-1a-carboxylate ethyl ester blocked the Ca(2+) signal and fast hyperpolarization, confirming the involvement of mGluR1s. Amplitude of the fast hyperpolarization varied as a function of membrane potential and intracellular Ca(2+) and was blocked by apamin, an antagonist of the small-conductance Ca(2+)-activated K(+) channel (SK), identifying this K(+) channel as an underlying mechanism. In similar experiments with mature cultured Purkinje neurons, DHPG elicited a Ca(2+) signal, but fast membrane hyperpolarization was not evident. These results suggest that mGluR1 activation and the resulting release of Ca(2+) from intracellular stores and activation of SK channels may be a mechanism through which mGluR1 can modulate neuronal excitability of Purkinje neurons during early development.

The chemokine CCL2 activates p38 mitogen-activated protein kinase pathway in cultured rat hippocampal cells.

Emerging evidence indicates that chemokines can regulate both the physiology and biochemistry of CNS neurons and glia. In the current study, Western blot analysis showed that in rat hippocampal neuronal/glial cultures the signal transduction pathway activated by CCL2, a chemokine expressed in the normal brain and at elevated levels during neuroinflammation, involves a G-protein coupled receptor, p38 MAPK as well as its immediate upstream kinase MKK3/6, and the downstream transcription factor CREB. ERK 1/2 and the transcription factors STAT1 and STAT3 do not play a prominent role. CCL2 also altered Ca(2+) influx and synaptic network activity in the hippocampal neurons. These results suggest an important role for p38 MAPK and CREB in hippocampal actions of CCL2.

Chronic CXCL10 alters the level of activated ERK1/2 and transcriptional factors CREB and NF-kappaB in hippocampal neuronal cell culture.

Signal transduction pathways may be important targets of chemokines during neuroinflammation. In the current study, Western blot analyses show that in rat hippocampal neuronal/glial cell cultures chronic CXCL10 increases the level of protein for ERK1/2 as well as for the transcriptional factors CREB and NF-kappaB. Bcl-2, an anti-apoptotic protein whose expression can be regulated by a pathway involving ERK1/2, CREB and NF-kappaB, was also increased in the CXCL10 treated cultures. These results implicate a role for ERK1/2, CREB and NF-kappaB in effects of CXCL10 on hippocampal cells and suggest that chronic CXCL10 may have a protective role during certain neuroinflammatory conditions.

Altered brain activity during withdrawal from chronic alcohol is associated with changes in IL-6 signal transduction and GABAergic mechanisms in transgenic mice with increased astrocyte expression of IL-6.

Interleukin-6 (IL-6) is an important neuroimmune factor that is increased in the brain by alcohol exposure/withdrawal and is thought to play a role in the actions of alcohol on the brain. To gain insight into IL-6/alcohol/withdrawal interactions and how these interactions affect the brain, we are studying the effects of chronic binge alcohol exposure on transgenic mice that express elevated levels of IL-6 in the brain due to increased astrocyte expression (IL-6 tg) and their non-transgenic (non-tg) littermate controls. IL-6/alcohol/withdrawal interactions were identified by genotypic differences in spontaneous brain activity in electroencephalogram (EEG) recordings from the mice, and by Western blot analysis of protein activation or expression in hippocampus obtained from the mice after the final alcohol withdrawal period. Results from EEG studies showed frequency dependent genotypic differences in brain activity during withdrawal. For EEG frequencies that were affected by alcohol exposure/withdrawal in both genotypes, the nature of the effect was similar, but differed across withdrawal cycles. Differences between IL-6 tg and non-tg mice were also observed in Western blot studies of the activated form of STAT3 (phosphoSTAT3), a signal transduction partner of IL-6, and subunits of GABAA receptors (GABAAR). Regression analysis revealed that pSTAT3 played a more prominent role during withdrawal in the IL-6 tg mice than in the non-tg mice, and that the role of GABAAR alpha-5 and GABAAR alpha-1 in brain activity varied across genotype and withdrawal. Taken together, our results suggest that IL-6 can significantly impact mechanisms involved in alcohol withdrawal.

Altered hippocampal synaptic function in transgenic mice with increased astrocyte expression of CCL2 after withdrawal from chronic alcohol.

CNS actions of the chemokine CCL2 are thought to play a role in a variety of conditions that can have detrimental consequences to CNS function, including alcohol use disorders. We used transgenic mice that express elevated levels of CCL2 in the CNS (CCL2-tg) and their non-transgenic (non-tg) littermate control mice to investigate long-term consequences of CCL2/alcohol/withdrawal interactions on hippocampal synaptic function, including excitatory synaptic transmission, somatic excitability, and synaptic plasticity. Two alcohol exposure paradigms were tested, a two-bottle choice alcohol (ethanol) drinking protocol (2BC drinking) and a chronic intermittent alcohol (ethanol) (CIE/2BC) protocol. Electrophysiological measurements of hippocampal function were made ex vivo, starting ∼0.6 months after termination of alcohol exposure. Both alcohol exposure/withdrawal paradigms resulted in CCL2-dependent interactions that altered the effects of alcohol on synaptic function. The synaptic alterations differed for the two alcohol exposure paradigms. The 2BC drinking/withdrawal treatment had no apparent long-term consequences on synaptic responses and long-term potentiation (LTP) in hippocampal slices from non-tg mice, whereas synaptic transmission was reduced but LTP was enhanced in hippocampal slices from CCL2-tg mice. In contrast, the CIE/2BC/withdrawal treatment enhanced synaptic transmission but reduced LTP in the non-tg hippocampus, whereas there were no apparent long-term consequences to synaptic transmission and LTP in hippocampus from CCL2-tg mice, although somatic excitability was enhanced. These results support the idea that alcohol-induced CCL2 production can modulate the effects of alcohol exposure/withdrawal on synaptic function and indicate that CCL2/alcohol interactions can vary depending on the alcohol exposure/withdrawal protocol used.

Transgenic mice with increased astrocyte expression of CCL2 show altered behavioral effects of alcohol.

Emerging research provides strong evidence that activation of CNS glial cells occurs in neurological diseases and brain injury and results in elevated production of neuroimmune factors. These factors can contribute to pathophysiological processes that lead to altered CNS function. Recently, studies have also shown that both acute and chronic alcohol consumption can produce activation of CNS glial cells and the production of neuroimmune factors, particularly the chemokine ligand 2 (CCL2). The consequences of alcohol-induced increases in CCL2 levels in the CNS have yet to be fully elucidated. Our studies focus on the hypothesis that increased levels of CCL2 in the CNS produce neuroadaptive changes that modify the actions of alcohol on the CNS. We utilized behavioral testing in transgenic mice that express elevated levels of CCL2 to test this hypothesis. The increased level of CCL2 in the transgenic mice involves increased astrocyte expression. Transgenic mice and their non-transgenic littermate controls were subjected to one of two alcohol exposure paradigms, a two-bottle choice alcohol drinking procedure that does not produce alcohol dependence or a chronic intermittent alcohol procedure that produces alcohol dependence. Several behavioral tests were carried out including the Barnes maze, Y-maze, cued and contextual conditioned fear test, light-dark transfer, and forced swim test. Comparisons between alcohol naïve, non-dependent, and alcohol-dependent CCL2 transgenic and non-transgenic mice show that elevated levels of CCL2 in the CNS interact with alcohol in tests for alcohol drinking, spatial learning, and associative learning.

Rapamycin-Sensitive Late-LTP is Enhanced in the Hippocampus of IL-6 Transgenic Mice.

The neuroimmune factor IL-6 has been shown to regulate hippocampal long-term potentiation (LTP), an activity-dependent enhancement of synaptic transmission that plays a central role in memory and learning. This IL-6 action was demonstrated with relatively short IL-6 exposure, and may reflect physiological actions of IL-6. IL-6 is also expressed chronically at elevated levels in the central nervous system (CNS) under pathological conditions such as neurological disorders. Little is known about the effects IL-6 on LTP under such conditions, an issue that we are addressing by electrophysiological recordings from CA1 pyramidal neurons of hippocampal slices from transgenic mice that persistently express elevated levels of IL-6 in the CNS (IL-6 tg). The current studies examined the long-lasting phase of LTP (late LTP; L-LTP) and the potential involvement mammalian target of rapamycin (mTOR), a known regulator of L-LTP and a downstream partner of IL-6 signal transduction pathways. Results show that basal synaptic transmission and L-LTP were increased in hippocampal slices from IL-6 tg mice compared to slices from non-transgenic (non-tg) control mice. An inhibitor of mTOR, rapamycin, reduced L-LTP in slices from both genotypes, and eliminated the difference in magnitude of L-LTP between IL-6 and non-tg hippocampus. There were no genotypic effect of rapamycin on basal synaptic transmission, but synaptic responses during the LTP induction protocol were reduced in IL-6 tg slices, an effect that could contribute to the reduction of L-LTP in the IL-6 tg slices. These results indicate that persistently increased levels of IL-6 can lead to alterations in mTOR regulation of L-LTP, possibly affecting learning and memory.

Impact of Increased Astrocyte Expression of IL-6, CCL2 or CXCL10 in Transgenic Mice on Hippocampal Synaptic Function.

An important aspect of CNS disease and injury is the elevated expression of neuroimmune factors. These factors are thought to contribute to processes ranging from recovery and repair to pathology. The complexity of the CNS and the multitude of neuroimmune factors that are expressed in the CNS during disease and injury is a challenge to an understanding of the consequences of the elevated expression relative to CNS function. One approach to address this issue is the use of transgenic mice that express elevated levels of a specific neuroimmune factor in the CNS by a cell type that normally produces it. This approach can provide basic information about the actions of specific neuroimmune factors and can contribute to an understanding of more complex conditions when multiple neuroimmune factors are expressed. This review summarizes studies using transgenic mice that express elevated levels of IL-6, CCL2 or CXCL10 through increased astrocyte expression. The studies focus on the effects of these neuroimmune factors on synaptic function at the Schaffer collateral to CA1 pyramidal neuron synapse of the hippocampus, a brain region that plays a key role in cognitive function.