Combinatorial augmentation of voltage-gated KCNQ potassium channels by chemical openers

Noninactivating potassium current formed by KCNQ2 (Kv7.2) and KCNQ3 (Kv7.3) subunits resembles neuronal M-currents which are activated by voltage and play a critical role in controlling membrane excitability. Activation of voltage-gated potassium channels by a chemical opener is uncommon. Therefore, the mechanisms of action are worthy further investigation. Retigabine and zinc pyrithione are two activators for KCNQ channels but their molecular interactions with KCNQ channel remain largely elusive. Here we report that retigabine and zinc pyrithione recognize two different sites of KCNQ2 channels. Their agonistic actions are noncompetitive and allow for simultaneous binding of two different activators on the same channel complex, hence giving rise to combinatorial potentiation with characteristic properties of both openers. Examining their effects on mutant channels, we showed zinc pyrithione is capable of opening nonconductive channels and coapplication of zinc pyrithione and retigabine could restore a disease mutant channel similar to wild type. Our results indicate two independent activator binding sites present in KCNQ channels. The resultant combinatorial potentiation by multiple synthetic chemical openers indicates that KCNQ channels are accessible to various types and combinations of pharmacological regulation.     

美托洛尔对大鼠心肌梗死后钾通道Kv9.X基因表达的影响

探讨美托洛尔对心肌梗死后大鼠心室肌钾通道Kv9.X(Kv9.1、Kv9.2、Kv9.3)表达的影响。通过结扎大鼠左前降支近端建立心肌梗死模型,手术后存活大鼠随机分为心肌梗死组、美托洛尔组,同时设立相应假手术(SH)组。每组存活大鼠又分为两个亚组,分别于7天或30天时取心脏标本。应用半定量RT-PCR方法检测左室心肌(梗死者取非梗死心肌)钾通道Kv9.1、Kv9.2、Kv9.3mRNA量。结果:与假手术组比较,无论7天或30天,心肌梗死组钾通道Kv9.1、Kv9.2、Kv9.3mRNA均显著降低(P<0.05或P<0.01)。与假手术组比较,无论7天或30天,美托洛尔组钾通道Kv9.1、Kv9.2、Kv9.3mRNA均明显降低(P均<0.05);心肌梗死组30天时与7天时比较钾通道Kv9.1、Kv9.2、Kv9.3mRNA量下降(P<0.05)。与心肌梗死组比较,30天时美托洛尔组钾通道Kv9.1、Kv9.2、Kv9.3mRNA明显升高(P<0.05);美托洛尔组7天与30天比较无差别。结论:美托洛尔能够逆转钾通道Kv9.1、Kv9.2、Kv9.3表达的下调,且这一逆转作用是缓慢的。     

Reduced KCNQ4-encoded voltage-dependent potassium channel activity underlies impaired β-adrenoceptor-mediated relaxation of renal arteries in hypertension

KCNQ4-encoded voltage-dependent potassium (Kv7.4) channels are important regulators of vascular tone that are severely compromised in models of hypertension. However, there is no information as to the role of these channels in responses to endogenous vasodilators. We used a molecular knockdown strategy, as well as pharmacological tools, to examine the hypothesis that Kv7.4 channels contribute to β-adrenoceptor-mediated vasodilation in the renal vasculature and underlie the vascular deficit in spontaneously hypertensive rats. Quantitative PCR and immunohistochemistry confirmed gene and protein expression of KCNQ1, KCNQ3, KCNQ4, KCNQ5, and Kv7.1, Kv7.4, and Kv7.5 in rat renal artery. Isoproterenol produced concentration-dependent relaxation of precontracted renal arteries and increased Kv7 channel currents in isolated smooth muscle cells. Application of the Kv7 blocker linopirdine attenuated isoproterenol-induced relaxation and current. Isoproterenol-induced relaxations were also reduced in arteries incubated with small interference RNAs targeted to KCNQ4 that produced a ≈60% decrease in Kv7.4 protein level. Relaxation to isoproterenol and the Kv7 activator S-1 were abolished in arteries from spontaneously hypertensive rats, which was associated with ≈60% decrease in Kv7.4 abundance. This study provides the first evidence that Kv7 channels contribute to β-adrenoceptor-mediated vasodilation in the renal vasculature and that abrogation of Kv7.4 channels is strongly implicated in the impaired β-adrenoceptor pathway in spontaneously hypertensive rats. These findings may provide a novel pathogenic link between arterial dysfunction and hypertension.     

Celecoxib blocks cardiac Kv1.5, Kv4.3 and Kv7.1 (KCNQ1) channels: Effects on cardiac action potentials

Celecoxib is a COX-2 inhibitor that has been related to an increased cardiovascular risk and that exerts several actions on different targets. The aim of this study was to analyze the effects of this drug on human cardiac voltage-gated potassium channels (Kv) involved on cardiac repolarization Kv1.5 (I_Kur), Kv4.3 + KChIP2 (I_to1) and Kv7.1 + KCNE1 (I_Ks) and to compare with another COX-2 inhibitor, rofecoxib. Currents were recorded in transfected mammalian cells by whole-cell patch-clamp. Celecoxib blocked all the Kv channels analyzed and rofecoxib was always less potent, except on Kv4.3 + KChIP2 channels. Kv1.5 block increased in the voltage range of channel activation, decreasing at potentials positive to 0 mV. The drug modified the activation curve of the channels that became biphasic. Block was frequency-dependent, increasing at fastest frequencies. Celecoxib effects were not altered by TEA_out in R487Y mutant Kv1.5 channels but the kinetics of block were slower and the degree of block was smaller with TEA_in, indicating that celecoxib acts from the cytosolic side. We confirmed the blocking properties of celecoxib on native Kv currents from rat vascular cells, where Kv1.5 are the main contributors (IC₅₀ ≈ 7 μM). Finally, we demonstrate that celecoxib prolongs the action potential duration in mouse cardiac myocytes and shortens it in guinea pig cardiac myocytes, suggesting that Kv block induced by celecoxib may be of clinical relevance.     

Metabolic Mapping of the Effects of Oral Alcohol Self-Administration in Rats

The functional effects of the voluntary consumption of ethanol in rats were investigated using the quantitative autoradiographic 2-[¹⁴C]deoxyglucose method for measurement of rates of local cerebral glucose utilization. A modified sucrose-substitution procedure was used to train three groups of Wistar rats to self-administer water, a 5% sucrose solution, or a 10% ethanol/5% sucrose solution in daily sessions. Once stable rates of consumption were established, the 2-[¹⁴C]deoxyglucose method was applied immediately after completion of the final test session. Rats received a dose of ethanol equivalent to 0.5 g/kg (n= 6) on the day of the procedure or a comparable volume of sucrose solution (n= 6) or water (n= 5). Rates of local cerebral glucose utilization in rats that ingested water did not differ from those that rats consumed a 5% sucrose solution. In contrast, voluntary ethanol consumption produced a highly discrete pattern of changes in rates of glucose utilization. Ethanol ingestion increased cerebral metabolism, as compared with rates of metabolism in rats that consumed either water or sucrose in the rostral pole and shell of the nucleus accumbens, medial prefrontal cortex, lateral septum, basolateral and central nuclei of the amygdala, substantia nigra, and the ventral tegmental area. This pattern of alterations in functional activity is distinctly different from that observed when equivalent doses of ethanol are administered acutely, emphasizing the importance of self-administration in determining the changes in glucose utilization. Furthermore, within the nucleus accumbens, glucose utilization was selectively augmented in the rostral pole and shell subterritories, whereas cerebral metabolism in the core was unaffected. Finally, these data demonstrate that it is the simultaneous activation of an interconnected network of limbic brain regions that serves as the substrate of the effects of voluntarily ingested ethanol.     

Effect of naloxone on appetitive and consummatory phases of ethanol self-administration

BACKGROUND: The opioid system has been implicated in ethanol self-administration. Morphine, an opiate agonist, can sometimes increase the amount of ethanol consumed, and opiate antagonists such as naloxone and naltrexone decrease the amount of ethanol consumed in both animals and humans. The objective of this study was to examine the effect of naloxone on appetitive (or seeking) and consummatory behaviors by using an operant model developed to separate these two phases of self-administration. METHODS: Intraperitoneal injections of naloxone (0.3-10 mg/kg) or vehicle were given before operant self-administration sessions to assess the effect on lever pressing (appetitive behavior) and subsequent consumption. Effects were measured in two groups of rats: one self-administered a 3% sucrose solution and the other a 10% ethanol solution. RESULTS: Naloxone dose-dependently decreased ethanol and sucrose consumption by an earlier cessation of drinking in the session compared with vehicle injection days. There were some effects on appetitive responding after treatment with naloxone, but none was statistically significant. CONCLUSIONS: Naloxone may decrease ethanol self-administration by decreasing the postingestive or pharmacological effects of alcohol. This model provides a new method for examining the effects of potential pharmacotherapeutics on alcohol self-administration behavior.     

The CRF-1 receptor antagonist, CP-154,526, attenuates stress-induced increases in ethanol consumption by BALB/cJ mice

Background: Corticotropin‐releasing factor (CRF) signaling modulates neurobiological responses to stress and ethanol, and may modulate observed increases in ethanol consumption following exposure to stressful events. The current experiment was conducted to further characterize the role of CRF₁ receptor (CRF₁R) signaling in stress‐induced increases in ethanol consumption in BALB/cJ and C57BL/6N mice. Methods: Male BALB/cJ and C57BL/6N mice were given continuous access to 8% (v/v) ethanol and water for the duration of the experiment. When a baseline of ethanol consumption was established, animals were exposed to 5 minutes of forced swim stress on each of 5 consecutive days. Thirty minutes before each forced swim session, animals were given an intraperitoneal injection of a 10 mg/kg dose of CP‐154,526, a selective CRF₁R antagonist, or an equal volume of vehicle. The effect of forced swim stress exposure on consumption of a 1% (w/v) sucrose solution was also investigated in an ethanol‐naïve group of BALB/cJ mice. Results: Exposure to forced swim stress significantly increased ethanol consumption by the BALB/cJ, but not of the C57BL/6N, mice. Stress‐induced increases in ethanol consumption were delayed and became evident approximately 3 weeks after the first stressor. Additionally, forced swim stress did not cause increases of food or water intake and did not promote delayed increases of sucrose consumption. Importantly, BALB/cJ mice pretreated with the CRF₁R antagonist showed blunted stress‐induced increases in ethanol intake, and the CRF₁R antagonist did not influence the ethanol drinking of non‐stressed mice. Conclusions: The present results provide evidence that CRF₁R signaling modulates the delayed increase of ethanol consumption stemming from repeated exposure to a stressful event in BALB/cJ mice.     

Chronic Naltrexone Treatment and Ethanol Responsivity in Outbred Rats

Background: Acute naltrexone treatment in rats produces significant alterations in ethanol palatability (increase in the aversiveness of the solution) and ethanol consumption during tests of restricted access (decrease in consumption). The effects of chronic naltrexone exposure, accomplished by implantation of osmotic mini‐pumps, were examined in the present study. Methods: Rats were surgically implanted with intraoral fistulae for taste reactivity testing. The animals were given 2 bottles (distilled water and 10% ethanol, v/v) for 3, 2‐week phases: Pre‐Drug, Drug, and Post‐Drug. After the Pre‐Drug phase, rats were assigned to groups (counterbalanced based on ethanol intake) and implanted with a mini‐pump containing saline, 7.5 mg/kg/d naltrexone, or 15 mg/kg/d naltrexone. The pumps were removed 2 weeks later. During each 2‐week phase, taste reactivity tests with 10% ethanol were conducted at 1, 7, and 14 days (a total of 9 reactivity tests). Results: The 7.5 mg/kg/d dose produced only minor effects on 10% ethanol reactivity and consumption during the Drug phase. The 15 mg/kg/d naltrexone dose generally shifted taste reactivity responding to 10% ethanol in a negative direction and produced a transient decrease in ethanol consumption. The 15 mg/kg/d group significantly increased ethanol consumption beyond the level of consumption by the Saline group when the pumps were removed, although the increase was delayed 48 hours. By the end of the Post‐Drug period, this naltrexone group returned to control levels of ethanol consumption. Conclusions: Chronic naltrexone treatment at 15 mg/kg/d significantly decreased the palatability of a 10% ethanol solution, an effect seen even after drug withdrawal. Naltrexone had a minor effect on ethanol consumption during treatment but did decrease overall levels of fluid consumption. The significant increase in ethanol consumption postdrug by the high‐dose naltrexone group, presumably due to receptor up‐regulation during treatment, is important and understanding this effect and developing means of overcoming it within a clinical practice would be useful goals.     

Consumption of Sweet, Salty, Sour, and Bitter Solutions by Selectively Bred Alcohol-Preferring and Alcohol-Nonpreferring Lines of Rats

To determine whether selective breeding for high or low oral ethanol consumption is associated with different preferences for nonpharmacological solutions with various flavors, the oral intake of a range of concentrations of sucrose (0.5–64.0 g/100 ml), NaCl(0.025–3.2 g/100 ml), citric acid (0.008–2.048 g/liter), and sucrose octaacetate (0.002–0.512 g/liter) was studied in alcohol-preferring (P) and alcohol-nonpreferring (NP) rats. Separate groups of 7–8 rats from each line were tested for consumption of each of the four flavors. The flavored solutions were presented continuously with water and food always available, and the concentrations were doubled every 48 hr. Although rats from both lines showed a strong preference for the sucrose solutions, P rats consumed greater amounts than NP rats [F(7,98) = 5.57, p < 0.001], Rats of the P line drank less of the NaCl solutions than NP rats [F(7,98) = 3.88, p < 0.0011], but the effect was not as robust as the line differences seen with sucrose. The P and NP rats did not differ in citric acid or sucrose octaacetate intake at any of the concentrations tested. Selective breeding for high oral ethanol preference appears to be positively associated with consumption of sweet solutions and negatively associated with intake of salty solutions.     

Ethanol Intake of Chickens Treated with Fenfluramine, Fluoxetine, and Dietary Tryptophan

Male, white leghorn chickens fed a standard diet with or without tryptophan supplementation were treated with single injections of 8 mg/kg fenfluramine in one series of experiments, or 8 mg/kg fluoxetine in another series. The birds had been food- and water-deprived prior to injection. They were offered, following the drug or saline injection, water, a 5% ethanol solution, or an isocaloric sucrose solution (8.75%) for 1 hr. Both fluoxetine and fenfluramine significantly reduced consumption of the ethanol solution, an effect exacerbated by tryptophan supplementation. Water or sucrose solution intake was also significantly reduced, but significantly less so than ethanol after fenfluramine injection. Since the birds drank significantly more of the sucrose solution after saline injection than of water, the consumption decrease caused by fenfluramine resulted, nevertheless, in a higher intake than that of either water or ethanol. Body temperature was decreased by ethanol intake and/or fluoxetine injection. Fenfluramine injection had an opposite, body temperature-increasing effect. It appears that both fenfluramine and fluoxetine decrease ethanol intake in a manner more specific than for water or sucrose, and that this effect is amplified by dietary tryptophan supplementation.     

Patterns of Ethanol Consumption in a Continuous Access Situation: The Effect of Adding a Sweetener to the Ethanol Solution

The effect of the addition of sucrose to an ethanol solution upon daily intake patterns was examined in a continuous-access operant situation with Wistar rats. Rats were first initiated to self-administer orally a 10% ethanol (v/v) solution using the sucrose-substitution procedure in 30-min limited-access conditions. When then studied in a continuous-access operant situation (23 hr ethanol access), substantial increases in ethanol consumption were found when varying concentrations of sucrose were added to the ethanol solutions presented. This increased consumption was found to be a complex function of both an increase in the number of drinking occurrences each day and in the size of each drinking occurrence. When 2% sucrose was compared with 2% sucrose/10% ethanol, the consumption of the sweetened ethanol was greater than consumption of the sweetener alone, suggesting that the ethanol added to the ability of the solution to maintain behavior beyond that of the sucrose alone. This study supports the use of sweetened ethanol solutions for the study of ethanol drinking patterns, and as a model system for examining factors involved in the regulation of ethanol consumption.     

Long-term exogenous melatonin treatment modulates overall feed efficiency and protects ovarian tissue against injuries caused by ethanol-induced oxidative stress in adult UChB rats

Background: Chronic ethanol intake leads to reproductive damage including reactive oxygen species formation, which accelerates the oxidative process. Melatonin is known to regulate the reproductive cycle, food/liquid intake, and it may also act as a potent antioxidant indoleamine. The aim of this study was to verify the effects of alcoholism and melatonin treatment on overall feed efficiency and to analyze its protective role against the oxidative stress in the ovarian tissue of UChB rats (submitted to 10% [v/v] voluntary ethanol consumption). Methods: Forty adult female rats (n = 10/group) were finally selected for this study: UChB Co: drinking water only; and UChB EtOH: drinking ethanol at 2 to 6 ml/100 g/d + water, both receiving 0.9% NaCl + 95% ethanol 0.04 ml as vehicle. Concomitantly, UChB Co + M and UChB EtOH + M groups were infused with vehicle + melatonin (100 μg/100 g body weight/d) intraperitoneally over 60 days. All animals were euthanized by decapitation during the morning estrus (4 am ). Results: Body weight gain was reduced with ethanol plus melatonin after 40 days of treatment. In both melatonin‐treated groups, it was observed a reduction in food‐derived calories and liquid intake toward the end of treatment. The amount of consumed ethanol dropped during the treatment. Estrous cycle was longer in rats that received both ethanol and melatonin, with prolonged diestrus. Following to oxidative status, lipid hydroperoxide levels were higher in the ovaries of ethanol‐preferring rats and decreased after melatonin treatment. Additionally, antioxidant activities of superoxide dismutase, glutathione peroxidase activity, and glutathione reductase activity were increased in melatonin‐treated groups. Conclusions: We suggest that melatonin is able to affect feed efficiency and, conversely, it protects the ovaries against the oxidative stress arising from ethanol consumption.     

The effects of neuropeptide S on ethanol drinking and other related behaviors in alcohol-preferring and -nonpreferring rats

Background.  Neuropeptide S (NPS) is a 20-amino-acid peptide, identified in the brain and periphery, that is reported to regulate arousal, anxiety, and feeding behavior. Studies were conducted to determine whether this peptide would alter ethanol intake, sucrose intake, anxiety, and general motor activity in alcohol-preferring (P) and -nonpreferring (NP) rats.
Methods.  Experiment 1 : P and NP rats were given 8 weeks of continuous access to ethanol (15% w/v) and water. All rats were implanted with a cannula aimed at either the left or right lateral ventricle and 1 week later were infused with NPS (0.075, 0.3, 1.2 nmol) or artificial cerebrospinal fluid (aCSF) and tested for ethanol, food, and water intake. Experiment 2 : The same doses of NPS were administered to a group of P rats and intake of 2.5% (w/v) sucrose was measured. Experiment 3 : Infusions of NPS (1.2 nmol) or aCSF were administered to P rats prior to a 5-minute test on an elevated plus maze. Experiment 4 : Ethanol naive P and NP rats were infused with NPS (0.075, 0.15, 0.3, 0.6, and 1.2 nmol) or aCSF prior to a 20-minute test in activity monitors.
Results.  NPS reduced ethanol intake in P, but not in NP rats. It did not influence sucrose solution intake in P rats. However, an increase in food intake was seen in both rat lines following lower doses of the peptide. NPS did neither alter anxiety-like behavior in the elevated plus maze test nor was there an effect on general motor activity; however, there was an increase in the amount of time spent in the center of the activity monitors following infusions of 0.6 nmol of NPS in P, but not in NP rats, indicating anxioltyic actions of the peptide.
Conclusions.  These data suggest a role for NPS in the modulation of ethanol drinking and possibly anxiety-like behavior in rats selectively bred for high alcohol drinking.     

Blood Ethanol Concentrations in Rats Drinking Sucrose/Ethanol Solutions

BACKGROUND: The addition of sucrose to ethanol solutions results in a substantial increase in ethanol self-administration by rats that are deprived of neither food nor water. However, if sucrose alters ethanol absorption or metabolism, resulting in blood ethanol concentrations (BECs) not different from those resulting from lower intakes of ethanol/water solutions, then the usefulness of sucrose/ethanol mixtures in increasing ethanol consumption is questionable. The present study was conducted to determine whether the addition of sucrose to ethanol solutions altered BECs in an operant self-administration paradigm. METHODS: Tail blood (from male Long-Evans rats) was collected 30 min after the intake of four different solutions, i.e., 5% sucrose/20% ethanol, 5% sucrose/10% ethanol, 2% sucrose/10% ethanol, and 10% ethanol. RESULTS: Ethanol intakes (mean, 1.57+/-0.21 g/kg) and BECs (mean, 78.4+/-9.3 mg/100 ml) were highest when 5% sucrose was added to the ethanol solution. Moreover, the ratios between ethanol intakes and resulting BECs were approximately the same for all solutions. CONCLUSIONS: These findings indicate that, under the conditions of this procedure, the BEC reached is dependent on the amount of ethanol consumed and is not influenced by the addition of sucrose to the solution.     

Chronic ethanol drinking and food deprivation affect rat hypothalamic-pituitary-thyroid axis and TRH in septum

Because chronic ethanol ingestion may perturb thyroid function, we evaluated the effect of 4-wk of oral 10% ethanol ingestion on the hypothalamic-pituitary-thyroid (HPT) axis and septal thyrotropin-releasing hormone (TRH) in 200-g male Wistar rats. Animals were divided into three groups: absolute control receiving tap water and food ad libitum; ethanol group receiving food ad libitum and 10% ethanol as the sole source of drinking fluid; pair-fed group receiving tap water and an amount of food corresponding to the consumption of ethanol group. After 4-wk of treatment, the body weight of the ethanol group was 7% and of the pair-fed rats 19% lower than that of the absolute controls. Both chronic ethanol treatment and food deprivation produced a decrease in plasma thyroid-stimulating hormone (TSH). Pair-fed rats also had a lower plasma T₃. Type I iodothyronine 5′-deiodinase activity in the liver was increased in the pair-fed and even more in the ethanol-treated group. The content and secretion in vitro of TRH from the hypothalamic paraventricular nucleus and median eminence were unchanged. TRH content in the septum was increased in both the ethanol and pair-fed groups. TRH secretion from the septum in vitro was lower in the pair-fed, but unchanged in the ethanol group. These data suggest that 4-wk of peroral ethanol intake affects thyroid function mostly at the extrahypothalamic level and that there is a contribution of concomitant food deprivation. Both ethanol treatment and food deprivation increased TRH content in the septum.     

Naltrexone Suppresses Ethanol Intake in 6-Hydroxydopamine–Treated Rats

BACKGROUND: The suppressive effect of opioid antagonists, such as naltrexone, on ethanol intake has been suggested to be based on the interference with ethanol-induced stimulation of dopamine release in the nucleus accumbens. The aim of this study was to determine whether reduction of dopamine innervation to the nucleus accumbens with the neurotoxin 6-hydroxydopamine (6-OHDA) alters naltrexone-induced suppression of ethanol consumption. Because the mesolimbic dopaminergic neurons have also been implicated in ethanol reinforcement, the effects of 6-OHDA on the maintenance and acquisition of ethanol intake were also studied. METHODS: To damage accumbal terminals of the mesolimbic dopamine neurons, alcohol-preferring Alko Alcohol (AA) rats were given bilateral injections of 6-OHDA or vehicle into the nucleus accumbens after pretreatment with desipramine and pargyline. The effect of the lesion on the acquisition or maintenance of ethanol self-administration was studied in animals having continual access to ethanol solution (10% v/v) and water. Subsequently the effect of naltrexone on ethanol consumption was determined. RESULTS: Naltrexone (0.03-3.0 mg/kg subcutaneously) suppressed ethanol consumption in a dose-dependent manner both in 6-OHDA-treated and control animals given a daily 90-min access to ethanol solution. When the rats had continual access to ethanol, there was a clear day-to-day decline in ethanol intake during the first 5 days of the 7-day naltrexone treatment (10 mg/kg subcutaneously). 6-OHDA treatment had no effect on either the acquisition or maintenance of ethanol self-administration. Postmortem analysis of the brain dopamine content revealed approximately 92% depletion of dopamine in the nucleus accumbens of the 6-OHDA-treated rats. CONCLUSIONS: The suppressive effect of naltrexone does not depend on naltrexone's interaction with dopaminergic terminals in the nucleus accumbens. Furthermore, the role of the mesolimbic dopamine pathway is probably not central either in the acquisition or maintenance of ethanol self-administration in alcohol-preferring AA rats.     

Chronic intermittent ethanol administration differentially alters DeltaFosB immunoreactivity in cortical-limbic structures of rats with high and low alcohol preference

Background: The role of specific cerebral areas involved in alcohol use disorder, such as the amygdala, hippocampus and prefrontal cortex, has emerged as a subject of interest over recent years. Nevertheless, the role played by these regions is frequently confounded by different variables, among them are the patterns of alcohol consumption presented by the subjects.

Objectives: The present study verified the effects of chronic voluntary ethanol intake (20 sessions) on DeltaFosB immunoreactivity (DeltaFosB-ir) in the amygdala, hippocampus and prefrontal cortex of rats showing high and low preference for ethanol.

Methods: DeltaFosB-ir induced by chronic voluntary ethanol intake with a two-bottle intermittent access to 20% ethanol model in male Wistar rats was measured. Three groups of animals were analyzed: control (n = 6), low preference (n = 8) and high preference (n = 8) for ethanol, the latter two categorized from their pattern of voluntary consumption of the alcohol solution.

Results: Ethanol intake in high-preference rats increased DeltaFosB-ir in the central amygdala, CA1 and CA3 regions of the hippocampus and decreased DeltaFosB-ir in the prelimbic cortex and anterior cingulate cortex. On the other hand, in low preference rats, chronic voluntary ethanol intake decreased DeltaFosB-ir in the medial amygdala, basolateral amygdala, dentate gyrus and anterior cingulate cortex.

Conclusions: The present results suggest that different alcohol intake patterns are associated with a specific pattern of DeltaFosB-ir in brain structures that play a key role in controlling behavior and decision making, that is the amygdala, the hippocampus and the prefrontal cortex.     

Assessment of voluntary ethanol consumption and the effects of a melanocortin (MC) receptor agonist on ethanol intake in mutant C57BL/6J mice lacking the MC-4 receptor

Background: The melanocortin (MC) system is composed of peptides that are cleaved from the polypeptide precursor proopiomelanocortin (POMC). Recent evidence shows that chronic exposure to ethanol significantly blunts central MC peptide immunoreactivity and MC receptor (MCR) agonists protect against high ethanol intake characteristic of C57BL/6J mice. Here, we assessed the role of the MC‐4 receptor (MC4R) in voluntary ethanol intake and in modulating the effects of the nonselective MCR agonist melanotan‐II (MTII) on ethanol consumption. Methods: To assess the role of the MC4R, MC4R knockout (Mc4r^?/?) and littermate wild‐type (Mc4r^+/+) mice on a C57BL/6J background were used. Voluntary ethanol (3, 5, 8, 10, 15, and 20%, v/v) and water intake were assessed using standard two‐bottle procedures. In separate experiments, Mc4r^?/? and Mc4r^+/+ mice were given intracerebroventricular (i.c.v.) infusion of MTII (0, 0.5, or 1.0 μg/1 μl) or intraperitoneal (i.p.) injection of MTII (0 or 5 mg/kg/5 ml). The effects of MTII (0 or 0.5 μg/1 μl, i.c.v.) on 10% sucrose and 0.15% saccharin intake were assessed in C57BL/6J mice. Results: Mc4r^?/? mice showed normal consumption of ethanol over all concentrations tested. I.c.v. infusion of MTII significantly reduced ethanol drinking in Mc4r^+/+ mice, but failed to influence ethanol intake in Mc4r^?/? mice. When administered in an i.p. injection, MTII significantly reduced ethanol drinking in both Mc4r^?/? and Mc4r^+/+ mice. MTII attenuated consumption of caloric (ethanol, sucrose, and food) and noncaloric (saccharin) reinforcers. Conclusions: When given centrally, the MCR agonist MTII reduced ethanol drinking by signaling through the MC4R. On the other hand, MTII‐induced reduction of ethanol drinking did not require the MC4R when administered peripherally. Together, the present observations show that the MC4R is necessary for the central actions of MCR agonists on ethanol drinking and that MTII blunts the consumption natural reinforcers, regardless of caloric content, in addition to ethanol.     

Ethanol and sucrose seeking and consumption following repeated administration of the GABA(B) agonist baclofen in rats

BACKGROUND: Baclofen, a GABA(B) agonist, has been found to decrease alcohol craving in humans and to nonselectively decrease ethanol intake in some rodent models. This experiment assessed the effects of repeated administration of baclofen on reinforcer seeking and consumption using the sipper tube appetitive/consummatory model of ethanol access. METHODS: Subjects were divided into 2 groups and trained to make 30 lever press responses that resulted in access to either 10% ethanol or 2% sucrose in a sipper tube-drinking spout for 20 minutes. Three doses of baclofen were tested (0.3, 1.0, and 3.0 mg/kg) and each drug treatment was assessed using the following schedule: Monday, saline; Tuesday to Thursday, baclofen; and Friday, saline. RESULTS: The low dose of baclofen had no effect on the seeking or intake of either sucrose or ethanol, and the 1.0 mg/kg dose also had no effect on the appetitive, seeking response. However, the 1.0 mg/kg dose significantly decreased sucrose intake (from an average of 0.56 to 0.41 g/kg) and significantly increased ethanol intake (from an average of 0.77 to 1.00 g/kg). Similarly, the high dose (3.0 mg/kg) decreased sucrose intake and had a tendency to increase ethanol intake while decreasing both sucrose seeking and ethanol seeking. CONCLUSIONS: Overall, baclofen treatment affected reinforcer intake at doses that had no effect on reinforcer seeking, and effective doses decreased both sucrose seeking and ethanol seeking. Moreover, the effects on reinforcer intake were disparate, in that baclofen increased ethanol drinking and decreased sucrose drinking. The nonspecific effects of baclofen suggest that the GABA(B) system may be involved in general consummatory or drinking behaviors and does not appear to specifically regulate ethanol-motivated responding.     

Dissociation of ethanol and saccharin preference in sP and sNP rats

BACKGROUND: It has been proposed that ethanol intake and consumption of sweet tasting solutions are positively correlated in rodents. Experiment 1 of the present study investigated whether selectively bred ethanol-preferring (sP) and -nonpreferring (sNP) rats differed, consistently with the above hypothesis, as to saccharin intake and preference. Experiment 2 evaluated whether saccharin addition to the ethanol solution, likely resulting in a highly palatable fluid, would result in an increase in voluntary ethanol intake in sP rats. METHODS: The saccharin solution was offered, in free choice with water, at a fixed concentration of 1 g/liter for 6 consecutive days in Experiment 1A or at ascending concentrations (0.002 to 16.4 g/liter, doubling the concentration every day) in Experiment 1B. In Experiment 2, 1 g/liter saccharin was added to the standard 10% ethanol solution and offered to sP rats in free choice with water for 7 consecutive days. RESULTS: In both Experiments 1A and 1B, sP and sNP rats showed avidity for the saccharin solution with marginal line difference in saccharin intake and preference. In Experiment 2, daily ethanol intake remained stable at baseline levels (6-7 g/kg), irrespective of the saccharin addition to the ethanol solution. CONCLUSIONS: The results of Experiments 1A and 1B suggest that saccharin drinking behavior in sNP rats deviates from the hypothesis that saccharin and ethanol intakes may co-vary; thus, at least in sNP rats, saccharin and ethanol intakes do not appear to be influenced by the same genetic factors. The results of Experiment 2 provide further support to the existence of a central set-point mechanism that regulates daily ethanol intake in sP rats, likely based on the pharmacological effects of ethanol.