Prolonged decrease in hepatic connexin32 in chronic liver injury induced by carbon tetrachloride in rats

Body Weight Development in Adult Dogs Fed a High Level Resistant Starch Diet

This study investigated the effect of Dodamssal rice, which has a high content of resistant starch, on obesity and hematologic properties in dogs. In Experiment 1, 24 spayed dogs were divided into three feeding groups: normal-fat basal diet (control), high-fat diet with 12% normal amylose type rice (hNAR), and high-fat diet with 12% high amylose type rice (Dodamssal rice; hHAR). In Experiment 2, 8 spayed dogs were assigned to a normal amylose type rice (NAR) group and a high amylose type rice group (HAR) with a normal-fat basal diet. After 24 weeks, an increase in weight and blood cholesterol was observed in both high-fat diet groups for Experiment 1. Specifically, an increase in serum alanine aminotransferase was observed over time in the hNAR group compared with that of the control; however, no such patterns were present in the hHAR group. Further, a significant weight-loss effect was observed in the HAR group in Experiment 2 at 4 weeks. The effect on body weight was due to the reduced digestibility of amylose and thereby lower dietary ME content. Overall, this confirmed that Dodamssal rice had a positive effect on weight loss in dogs, and these results suggest that Dodamssal rice has potential value as a raw ingredient for preventing obesity in dogs.

Cholestasis Differentially Affects Liver Connexins

Connexins are goal keepers of tissue homeostasis, including in the liver. As a result, they are frequently involved in disease. The current study was set up to investigate the effects of cholestatic disease on the production of connexin26, connexin32 and connexin43 in the liver. For this purpose, bile duct ligation, a well-known trigger of cholestatic liver injury, was applied to mice. In parallel, human hepatoma HepaRG cell cultures were exposed to cholestatic drugs and bile acids. Samples from both the in vivo and in vitro settings were subsequently subjected to assessment of mRNA and protein quantities as well as to in situ immunostaining. While the outcome of cholestasis on connexin26 and connexin43 varied among experimental settings, a more generalized repressing effect was seen for connexin32. This has also been observed in many other liver pathologies and could suggest a role for connexin32 as a robust biomarker of liver disease and toxicity.

Targeting gap junctional intercellular communication by hepatocarcinogenic compounds

Gap junctions in liver, as in other organs, play a critical role in tissue homeostasis. Inherently, these cellular constituents are major targets for systemic toxicity and diseases, including cancer. This review provides an overview of chemicals that compromise liver gap junctions, in particular biological toxins, organic solvents, pesticides, pharmaceuticals, peroxides, metals and phthalates. The focus in this review is placed upon the mechanistic scenarios that underlie these adverse effects. Further, the potential use of gap junctional activity as an in vitro biomarker to identify non-genotoxic hepatocarcinogenic chemicals is discussed.

Gadolinium Chloride Restores the Function of the Gap Junctional Intercellular Communication between Hepatocytes in a Liver Injury

BACKGROUND

Gadolinium chloride (GdCl3) has been reported to attenuate liver injury caused by a variety of toxicants. Gap junctional intercellular communication (GJIC) is thought to be essential in controlling liver homeostasis and pathology. Here we evaluate the effects of GdCl3 on functional GJIC and connexin expression in mouse models and primary hepatocytes.

METHODS

Mice were administered GdCl3 intraperitoneally the day before a carbon tetrachloride (CCl4) injection or bile duct ligation (BDL) operation. Primary hepatocytes were treated with CCl4 or lipopolysaccharides (LPS), with or without GdCl3. A scrape loading/dye transfer assay was performed to assess the GJIC function. The expression of connexins was examined by real-time reverse transcription polymerase chain reaction (RT-PCR), western blot and immunofluorescent staining.

RESULTS

CCl4 treatment or the BDL operation led to the dysfunction of GJIC and a down-regulation of Cx32 and Cx26 in injured liver. GdCl3 administration restored GJIC function between hepatocytes by facilitating the transfer of fluorescent dye from one cell into adjacent cells via GJIC, and markedly prevented the decrease of Cx32 and Cx26 in injured liver. In primary hepatocytes, CCl4 or LPS treatment induced an obvious decline of Cx32 and Cx26, whereas GdCl3 pretreatment prevented the down-regulation of connexins. In vivo GdCl3 protected hepatocytes and attenuated the liver inflammation and fibrosis in liver injury mouse models.

CONCLUSION

GdCl3 administration protects functional GJIC between hepatocytes, and prevents the decrease of connexin proteins at mRNA and protein levels during liver injury, leading to the alleviation of chronic liver injury.

Gap junctions in liver disease: Implications for pathogenesis and therapy

In the normal liver, cells interact closely through gap junctions. By providing a pathway for the trafficking of low molecular mass molecules, these channels contribute to tissue homeostasis and maintenance of hepatic function. Thus, dysfunction of gap junctions affects a wide variety of liver processes, such as differentiation, cell death, inflammation and fibrosis. In fact, dysfunctional gap junctions have been implicated, for more than a decade, in cholestatic disease, hepatic cancer and cirrhosis. Additionally, in recent years there is an increasing body of evidence that these channels are also involved in other relevant and prevalent liver pathological processes, such as non-alcoholic fatty liver disease, acute liver injury and portal hypertension. In parallel to these new clinical implications the available data include controversial observations. Thus, a comprehensive overview is required to better understand the functional complexity of these pores. This paper will review the most recent knowledge concerning gap junction dysfunction, with a special focus on the role of these channels in the pathogenesis of relevant clinical entities and on potential therapeutic targets that are amenable to modification by drugs.

Connexin and Pannexin (Hemi)Channels: Emerging Targets in the Treatment of Liver Disease

Connexin proteins are the building blocks of hemichannels, which dock further between adjacent cells to form gap junctions. Gap junctions control the intercellular exchange of critical homeostasis regulators. By doing so, gap junctions control virtually all aspects of the hepatic life cycle. In the last decade, it has become clear that connexin hemichannels also provide a pathway for cellular communication on their own independent of their role as structural precursors of gap junctions, namely between the cytosol of an individual cell and its extracellular environment. In contrast to gap junctions, connexin hemichannels become particularly active in liver disease by facilitating inflammation and cell death. This equally holds true for cellular channels composed of pannexins, being connexin-like proteins recently identified in the liver that gather in structures reminiscent of hemichannels. This paper gives an overview of the involvement of connexin-based and pannexin-based channels in noncancerous liver disease.

Connexin32 deficiency exacerbates carbon tetrachloride-induced hepatocellular injury and liver fibrosis in mice

OBJECTIVE

Liver fibrosis results from the perpetuation of the normal wound healing response to several types of injury. Despite the wealth of knowledge regarding the involvement of intracellular and extracellular signaling pathways in liver fibrogenesis, information about the role of intercellular communication mediated by gap junctions is scarce.

METHODS

In this study, liver fibrosis was chemically induced by carbon tetrachloride in mice lacking connexin32, the major liver gap junction constituent. The manifestation of liver fibrosis was evaluated based on a series of read-outs, including collagen morphometric and mRNA analysis, oxidative stress, apoptotic, proliferative and inflammatory markers.

RESULTS

More pronounced liver damage and enhanced collagen deposition were observed in connexin32 knockout mice compared to wild-type animals in experimentally triggered induced liver fibrosis. No differences between both groups were noticed in apoptotic signaling nor in inflammation markers. However, connexin32 deficient mice displayed decreased catalase activity and increased malondialdehyde levels.

CONCLUSION

These findings could suggest that connexin32-based signaling mediates tissue resistance against liver damage by the modulation of the antioxidant capacity. In turn, this could point to a role for connexin32 signaling as a therapeutic target in the treatment of liver fibrosis.

Connexins and pannexins in liver damage

Connexins and pannexins are key players in the control of cellular communication and thus in the maintenance of tissue homeostasis. Inherent to this function these proteins are frequently involved in pathological processes. The present paper reviews the role of connexins and pannexins in liver toxicity and disease. As they act both as sensors and effectors in these deleterious events connexins and pannexins could represent a set of novel clinical diagnostic biomarkers and drug targets.

Immunohisto- and Cytochemistry Analysis of Connexins

Immunohistochemistry (IHC) is a ubiquitous used technique to identify and analyze protein expression in the context of tissue and cell morphology. In the connexin research field, IHC is applied to identify the subcellular location of connexin proteins, as this can be directly linked to their functionality. The present chapter describes a protocol for fluorescent IHC to detect connexin proteins in tissues slices and cells, with slight modifications depending on the nature of biological sample, histological processing, and/or protein expression level. Basically, fluorescent IHC is a short, simple, and cost-effective technique, which allows the visualization of proteins based on fluorescent-labeled antibody-antigen recognition.

Localization of connexin 32 in spontaneous liver lesions of mice

We examined the localization of connexin 32 (Cx32), a component of gap junctions, in 24-month-old male B6C3F1 mice with spontaneously occurring hepatocellular altered foci or tumors. Immunohistochemically, Cx32-staining intensity in cell-to-cell membranes of altered hepatocytes was decreased in eosinophilic foci and increased in basophilic foci as compared to those in intact hepatocytes. These alterations were enhanced in adenomas and carcinomas with both eosinophilic and basophilic cytoplasm. In cell membranes facing on the sinusoidal portions, the intensities increased in all lesions. Image analyses confirmed that the spot areas of Cx32 were decreased in eosinophilic foci, but increased in basophilic foci, adenomas and carcinomas. These results demonstrate that Cx32 shows different expression in different types of hepatic lesions.

Connexin and pannexin signaling in gastrointestinal and liver disease

Gap junctions, which mediate intercellular communication, are key players in digestive homeostasis. They are also frequently involved in gastrointestinal and liver pathology. This equally holds true for connexin (Cx) hemichannels, the structural precursors of gap junctions, and pannexin (Panx) channels, Cx-like proteins assembled in a hemichannel configuration. Both Cx hemichannels and Panx channels facilitate extracellular communication and drive a number of deteriorative processes, such as cell death and inflammation. Cxs, Panxs, and their channels underlie a wide spectrum of gastrointestinal and liver diseases, including gastritis and peptic ulcer disease, inflammatory intestinal conditions, acute liver failure, cholestasis, hepatitis and steatosis, liver fibrosis and cirrhosis, infectious gastrointestinal pathologies, and gastrointestinal and liver cancer. This could open promising perspectives for the characterization of new targets and biomarkers for therapeutic and diagnostic clinical purposes in the area of gastroenterology and hepatology.

Role of gap junctions modulating hepatic vascular tone in cirrhosis

BACKGROUND & AIMS

Gap junctions are formed by connexins (Cx), a family of proteins that couple endothelial and smooth muscle cells in systemic vessels. In this context, Cx allow the transmission of signals modulating vascular tone. Recently, vascular Cx have been observed in liver cells implicated in liver blood flow regulation. Here, we investigated the role of Cx in the regulation of intrahepatic vascular tone in cirrhosis.

METHODS

Livers of Sprague-Dawley control and cirrhotic (common bile duct ligation-CBDL and CCl4 ) rats were perfused, and concentration-effect curves in response to acetylcholine (ACh) precontracted with methoxamine were obtained in the presence of the specific Cx inhibitor 18-alpha-glycyrrhetinic acid or vehicle. Cx expression was assessed by immunofluorescence, western blot and reverse-transcription polymerase chain reaction in liver tissue, hepatic stellate cells, sinusoidal endothelial cells and hepatocytes isolated from control and cirrhotic rat livers. Cx protein expression was also determined in cirrhotic human tissue.

RESULTS

Gap junction blockade markedly attenuated relaxation of hepatic vasculature in response to ACh in control (maximal relaxation, -55 ± 10.5% vs. -95.3 ± 10% with vehicle; P < 0.01) and CBDL rats (50.9 ± 18.5% vs. -18.7 ± 5.5% with vehicle; P = 0.01). Livers from CBDL rats and patients with cirrhosis exhibited Cx overexpression. By contrast, CCl4 -cirrhotic rats did not show attenuated relaxation of hepatic vasculature after blockade and Cx expression was significantly lower than in controls.

CONCLUSIONS

Gap junctions may contribute to modulating portal pressure and intrahepatic vascular relaxation. Liver gap junctions may represent a new therapeutic target in cirrhotic portal hypertension.

Parenteral solution of nutritional hepatotrophic factors improves regeneration in thioacetamide-induced cirrhotic livers after partial hepatectomy

Liver resection is a suitable option for the treatment of certain hepatic conditions, particularly hepatocarcinomas, in patients with cirrhosis. However, this disease impairs liver regeneration, which increases the risk of liver failure and postoperative death. Supportive treatments for regeneration of the remaining liver may be useful for the recovery of these patients. We demonstrated that nutritional hepatotrophic factors (NHF) is an effective regenerative stimulus for cirrhotic livers in rats subjected to partial hepatectomy (PH). The rats with thioacetamide-induced cirrhosis were subjected to PH, and they were divided into 2 groups. One group received intraperitoneal administration of NHF, and the other group received saline solution. After 12 days, biometric data, collagen content, hepatocyte regeneration (proliferation cell nuclear antigen immunochemistry), and profibrotic gene expression (Collagen-α1, matrix metalloproteinase 2, tissue inhibitor of metalloproteinase 1, and transforming growth factor beta 1) were assessed. The results indicated that the rats treated with NHF after PH had an increased liver size, a reduced amount of collagen, and a higher hepatocyte proliferation index compared with the rats that underwent PH alone. In addition, collagen-α1 gene expression was decreased in the NHF-treated rats. Thus, postoperative improvement in the liver morphology following NHF treatment may cause a significant decrease in the risk of liver failure and mortality after hepatic resection.

Gap junctions and non-neoplastic liver disease

Because of their critical role as goalkeepers of hepatic homeostasis, gap junctions are frequent targets in liver disease. This concept has been demonstrated on many occasions in the light of hepatocarcinogenesis. Relatively little focus has been put on the fate of gap junctions in other liver pathologies, including hepatitis, liver fibrosis and cirrhosis, cholestasis and hepatic ischemia and reperfusion injury. The present paper provides an in-depth description of the multiple changes in expression, localization and function of connexins, the molecular constituents of gap junctions. The use of connexins as biomarkers and therapeutic targets in liver disease is also illustrated.

Biological role of connexin intercellular channels and hemichannels

Gap junctions (GJ) and hemichannels (HC) formed from the protein subunits called connexins are transmembrane conduits for the exchange of small molecules and ions. Connexins and another group of HC-forming proteins, pannexins comprise the two families of transmembrane proteins ubiquitously distributed in vertebrates. Most cell types express more than one connexin or pannexin. While connexin expression and channel activity may vary as a function of physiological and pathological states of the cell and tissue, only a few studies suggest the involvement of pannexin HC in acquired pathological conditions. Importantly, genetic mutations in connexin appear to interfere with GJ and HC function which results in several diseases. Thus connexins could serve as potential drug target for therapeutic intervention. Growing evidence suggests that diseases resulting from HC dysfunction might open a new direction for development of specific HC reagents. This review provides a comprehensive overview of the current studies of GJ and HC formed by connexins and pannexins in various tissue and organ systems including heart, central nervous system, kidney, mammary glands, ovary, testis, lens, retina, inner ear, bone, cartilage, lung and liver. In addition, present knowledge of the role of GJ and HC in cell cycle progression, carcinogenesis and stem cell development is also discussed.

Morphological and molecular pathology of CCL4-induced hepatic fibrosis in connexin43-deficient mice

Gap junction channels, formed by connexins (Cx), are involved in the maintenance of tissue homeostasis, cell growth, differentiation, and development. Several studies have shown that Cx43 is involved in the control of wound healing in dermal tissue. However, it remains unknown whether Cx43 plays a role in the control of liver fibrogenesis. Our study investigated the roles of Cx43 heterologous deletion on carbon tetrachloride (CCl(4))-induced hepatic fibrosis in mice. We administered CCl(4) to both Cx43-deficient (Cx43(+/-)) and wild-type mice and examined hepatocellular injury and collagen deposition by histological and ultrastructural analyses. Serum biochemical analysis was performed to quantify liver injury. Hepatocyte proliferation was analyzed immunohistochemically. Protein and messenger RNA (mRNA) expression of liver connexins were evaluated using immunohistochemistry as well as immunoblotting analysis and quantitative real-time PCR. We demonstrated that Cx43(+/-) mice developed excessive liver fibrosis compared with wild-type mice after CCl(4) -induced chronic hepatic injury, with thick and irregular collagen fibers. Histopathological evaluation showed that Cx43(+/-) mice present less necroinflammatory lesions in liver parenchyma and consequent reduction of serum aminotransferase activity. Hepatocyte cell proliferation was reduced in Cx43(+/-) mice. There was no difference in Cx32 and Cx26 protein or mRNA expression in fibrotic mice. Protein expression of Cx43 increased in CCl(4)-treated mice, although with aberrant protein location on cytoplasm of perisinusoidal cells. Our results demonstrate that Cx43 plays an important role in the control and regulation of hepatic fibrogenesis.

Gap junctional intercellular communication as a target for liver toxicity and carcinogenicity

Direct communication between hepatocytes, mediated by gap junctions, constitutes a major regulatory platform in the control of liver homeostasis, ranging from hepatocellular proliferation to hepatocyte cell death. Inherent to this pivotal task, gap junction functionality is frequently disrupted upon impairment of the homeostatic balance, as occurs during liver toxicity and carcinogenicity. In the present paper, the deleterious effects of a number of chemical and biological toxic compounds on hepatic gap junctions are discussed, including environmental pollutants, biological toxins, organic solvents, pesticides, pharmaceuticals, peroxides, metals and phthalates. Particular attention is paid to the molecular mechanisms that underlie the abrogation of gap junction functionality. Since hepatic gap junctions are specifically targeted by tumor promoters and epigenetic carcinogens, both in vivo and in vitro, inhibition of gap junction functionality is considered as a suitable indicator for the detection of nongenotoxic hepatocarcinogenicity.

Expression and distribution of connexin 32 in rat liver with experimentally induced fibrosis

The connexin 32 (Cx32) is a protein that forms the channels that promote the gap junction intercellular communication (GJIC) in the liver, allowing the diffusion of small molecules through cytosol from cell-to-cell. Hepatic fibrosis is characterized by a disruption of normal tissue architeture by cellular lesions, and may alter the GJIC. This work aimed to study the expression and distribution of Cx32 in liver fibrosis induced by the oral administration of dimethylnitrosamine in female Wistar rats. The necropsy of the rats was carried out after five weeks of drug administration. They presented a hepatic fibrosis state. Sections from livers with fibrosis and from control livers were submitted to immunohistochemical, Real Time-PCR and Western-Blot analysis to Cx32. In fibrotic livers the Cxs were diffusely scattered in the cytoplasm, contrasting with the control livers, where the Cx32 formed junction plaques at the cell membrane. Also it was found a decrease in the gene expression of Cx32 without reduction in the protein quantity when compared with controls. These results suggest that there the mechanism of intercellular communication between hepatocytes was reduced by the fibrotic process, which may predispose to the occurrence of a neoplastic process, taken in account that connexins are considered tumor suppressing genes.

A quantitative inverse relationship between connexin32 expression and cell proliferation in a rat hepatoma cell line

Gap junctions comprised of connexin proteins are involved in direct intercellular communication and the regulation of cell behaviour and homeostasis. Reduced connexin expression and loss of gap junction function is a characteristic of many cancer cells and of the effect of many non-genotoxic carcinogens that induce cell proliferation. Moreover, when certain cancer cell lines are transfected with specific connexin genes, cells can regain control over proliferation. We have employed RNA interference and dexamethasone to modulate connexin32 expression in MH(1)C(1) cells to a range of concentrations. This allowed the determination of the quantitative relationship between connexin32 protein expression and cell proliferation. The magnitude of cell proliferation, measured by bromodeoxyuridine incorporation, was inversely proportional to the level of connexin32 expression. Q-PCR indicated a lack of change of expression of a range of cell cycle-related genes at 24h. The inverse relationship between Cx32 expression and proliferation was continuous, and a threshold level of reduction of connexin32 was not observable for an influence on proliferation.

Biology and pathobiology of gap junctional channels in hepatocytes

The present review provides the state of the art of the current knowledge concerning gap junctional channels and their roles in liver functioning. In the first part, we summarize some relevant biochemical properties of hepatic gap junctional channels, including their structure and regulation. In the second part, we discuss the involvement of gap junctional channels in the occurrence of liver cell growth, liver cell differentiation, and liver cell death. We further exemplify their relevance in hepatic pathophysiology. Finally, a number of directions for future liver gap junctional channel research are proposed, and the up-regulation of gap junctional channel activity as a novel strategy in (liver) cancer therapy is illustrated.

Different mechanisms of modulation of gap junction communication by non-genotoxic carcinogens in rat liver in vivo

This is a comparative study of the mechanisms by which three different rodent non-genotoxic carcinogens modulate connexin-mediated gap junction intercellular communication in male rat liver in vivo. In the case of the peroxisome proliferating agent Wy-14,643, a non-hepatotoxic dose of 50mg/kg led to a marked loss of inter-hepatocyte dye transfer associated with a loss of both Cx32 and Cx26 protein expression. In contrast, p,p'-dichlorodiphenyltrichloroethane (DDT) at a non-hepatotoxic dose (25mg/kg) was not found to alter Cx32 or Cx26 expression or to produce a measurable Cx32 serine phosphorylation but did give a small, significant reduction of cell communication. Carbon tetrachloride (CCl(4)) did not affect cell communication (despite a small significant reduction of Cx32 content) at a non-hepatotoxic dose. Both loss of communication and Cx32 expression was observed only at a dose that caused hepatocyte toxicity as evidenced by increased serum alanine aminotransferase activity. Overall, the findings emphasise that loss of gap junctional communication in vivo can contribute to carcinogenesis by non-genotoxic carcinogens through different primary mechanism. In contrast to Wy-14,643 and DDT, the results with CCl(4) are consistent with a requirement for hepatotoxicity in its carcinogenic action.

Involvement of cell junctions in hepatocyte culture functionality

In liver, like in other multicellular systems, the establishment of cellular contacts is a prerequisite for normal functioning. In particular, well-defined cell junctions between hepatocytes, including adherens junctions, desmosomes, tight junctions, and gap junctions, are known to play key roles in the performance of liver-specific functionality. In a first part of this review article, we summarize the current knowledge concerning cell junctions and their roles in hepatic (patho)physiology. In a second part, we discuss their relevance in liver-based in vitro modeling, thereby highlighting the use of primary hepatocyte cultures as suitable in vitro models for preclinical pharmaco-toxicological testing. We further describe the actual strategies to regain and maintain cell junctions in these in vitro systems over the long-term.

A single evoked afterdischarge produces rapid time-dependent changes in connexin36 protein expression in adult rat dorsal hippocampus

Gap junctions between neurons contribute to synchronous neuronal firing and may play a role in the pathophysiology of epilepsy. We examined the expression of a number of gap junction subunits, including the neuronal gap junction forming protein connexin36 (Cx36), in the hippocampus at various time points following an electrically stimulated afterdischarge (AD) in freely-moving animals. Once recovered from electrode implantation, animals were tested with an escalating series of stimulations until an AD was evoked. Suprathreshold stimulation produced a brief AD with no convulsion. Groups of animals were sacrificed at 3, 12, and 24h post-stimulation, and connexin expression was assessed via semiquantitative immunoblotting. Compared to implanted non-stimulated controls, a significant decrease in Cx36 expression was observed in the stimulated dorsal hippocampus at 3h post-stimulation, which returned to control levels by 24h. No changes were seen in the ventral hippocampus. As well, no changes were seen in other selected connexin proteins including Cx26, Cx32, and Cx43, thought to be expressed primarily in glia, in either dorsal or ventral hippocampus. These data suggest that a relatively brief hypersynchronous neuronal discharge can produce rapid and specific changes in Cx36 expression, which may have implications for both normal brain function and the pathophysiology of epilepsy.

Differential gene expression profiles in the steatosis/fibrosis model of rat liver by chronic administration of carbon tetrachloride

Global gene expression profile was analyzed by microarray analysis of rat liver RNA after chronic carbon tetrachloride (CCl(4)) administration. Rats received 0.5 ml CCl(4)/kg three times a week, and the liver samples were obtained after 0, 30, 60, and 90 days of injection. Histopathologic studies of liver tissues enabled the classification of the CCl(4) effect into mild and severe fatty liver/steatosis (30 and 60 days, respectively) and fibrosis/cirrhosis (90 days) stages. The expression levels of 4,900 clones on a custom rat gene microarray were analyzed and the results were confirmed by semi-quantitative RT-PCR. Four hundred thirty-eight clones were differentially expressed with more than a 1.625-fold difference (which equals 0.7 in log2 scale) at one or more time points. Multiple genes involved in lipid metabolism and ribosome biogenesis showed differential transcript levels upon chronic CCl(4) administration, which was previously seen in acute rat model as well. In addition, a total of 149 clones were identified as fibrosis/cirrhosis-specific genes by either fold changes or Significance Analysis of Microarrays. In conclusion, we report microarray analysis results in rat liver upon chronic CCl(4) administration with a full chronological profile that not only covered fatty liver/steatosis but also later points of fibrosis/cirrhosis. These data will provide the insight of specific gene expression profiles that is implicated in the multistep process of fatty liver/steatosis and fibrosis/cirrhosis after chronic hepatotoxin exposure.

Extended cocaine self-administration and deprivation produces region-specific and time-dependent changes in connexin36 expression in rat brain

Cocaine addiction is a disease that develops over time, and it is thought that drug-induced neuro-adaptations underlie the changes in behavior seen across the addictive process. While a number of alterations in synaptic transmission have been identified, little is currently known regarding cocaine's effects on gap junctional communication between neurons. Here we examine the effects of a cocaine self-administration regimen, previously shown to increase the reinforcing efficacy of cocaine, on the expression of the neuron-specific gap junction-forming protein connexin36 (C x 36). Using real-time RT-PCR and immunoblotting, we show that binge cocaine self-administration produces region-specific and time-dependent changes in C x 36 mRNA and protein expression in the nucleus accumbens, prefrontal cortex, and hippocampus. A number of changes in C x 36 were present 1 day and 7 days following self-administration, and C x 36 mRNA and protein appeared to be differentially regulated in a region-specific manner. C x 36 protein was significantly decreased in the prefrontal cortex 7 days following self-administration, a time point when behavioral sensitization to the reinforcing effects of cocaine is observed. These results suggest that changes in neuronal gap junction expression may be one mechanism by which cocaine self-administration produces enduring changes in behavior.

Amphetamine withdrawal produces region-specific and time-dependent changes in connexin36 expression in rat brain

Repeated amphetamine treatment produces a long-lasting augmentation of locomotor behavior in rats, a phenomenon known as behavioral sensitization. This process is thought to be a correlate of the addictive process in humans, and it is believed that there are drug-induced neuroadaptations that underlie these behavioral changes. One mechanism by which amphetamine can alter brain function is by affecting direct intercellular communication between neurons via gap junctions. The purpose of the present study was to examine the effect of an amphetamine treatment regimen known to produce changes in dye coupling between neurons, a functional correlate of gap junction function, on the expression of the neuronal gap junction-forming protein, connexin36. Here we report that withdrawal from an extended amphetamine regimen produces region-specific and time-dependent changes in connexin36 expression in rat nucleus accumbens and prefrontal cortex, brain regions known play roles in sensitization and addiction. This is, to our knowledge, the first demonstration of pharmacological manipulation of connexin36 in vivo.