Ethanol drinking experience attenuates (-)sulpiride-induced increases in extracellular dopamine levels in the nucleus accumbens of alcohol-preferring (P) rats

BACKGROUND: The reinforcing properties of ethanol may be partly mediated through the mesolimbic dopamine (DA) system. This study examines the effects of local application of the DA D(2) receptor antagonist (-)sulpiride (SUL) on ethanol drinking of alcohol-preferring (P) rats, and extracellular DA levels in the nucleus accumbens (NAc) of P rats that were either ethanol-naive or had been chronically drinking ethanol. METHODS: Microdialysis was used to sample NAc DA levels, and reverse microdialysis was used to locally administer the D(2) antagonist (-)sulpiride (SUL) into the NAc of adult female P rats that were either drinking ethanol (n = 17) or were ethanol-naive (n = 24). Stable intake of 15% (v/v) ethanol (>/=0.75 g/kg) was established for the ethanol-drinking group in daily 1-hr access periods over a minimum of 4 weeks before surgery. Naive and ethanol-drinking rats were implanted with bilateral guide cannulae aimed 4 mm above the NAc shell. After recovery from surgery, microdialysis probes (active area = 2 mm) were inserted bilaterally into the NAc. Two days later, rats in the ethanol-drinking and naive groups were each divided into two groups; one group was bilaterally perfused (1.0 microl/min) with artificial cerebrospinal fluid (aCSF) and the other group was further divided into three subgroups that were perfused with aCSF + either 50, 100, or 200 microM SUL for 240 min. During the last 60 min of perfusion, the ethanol-drinking rats were given their daily 1-hr ethanol access period. Following ethanol access, the aCSF + SUL subgroups were then given aCSF only. The entire perfusion procedure was repeated 24 hr later, but the aCSF only and aCSF + SUL group treatment conditions were transposed. RESULTS: In ethanol-drinking rats, 100 and 200 microM SUL increased extracellular NAc DA levels to approximately 200% of basal values, but did not significantly alter ethanol intake. In ethanol-naive P rats, 100 and 200 microM SUL increased extracellular NAc DA levels significantly more (450% of basal; p < 0.05) than in the ethanol-drinking group. CONCLUSIONS: The findings are consistent with the hypothesis that ethanol-drinking experience causes a desensitization or a down-regulation of D(2) autoreceptors in the NAc of P rats.     

Ethanol as a prodrug: brain metabolism of ethanol mediates its reinforcing effects--a commentary

Background: This commentary discusses a study by Karahanian and colleagues (2011) on the role of central nervous system acetaldehyde in the reinforcing effects of ethanol. The goal is to emphasize the importance of the study and to discuss future directions. Results: This important paper solidifies the idea that the levels of acetaldehyde in the central nervous system have profound effects in mediating the reinforcing actions of ethanol. This is accomplished by manipulating the brain levels of acetaldehyde produced from ethanol by the injection of lentivirus containing either an anti‐catalase shRNA construct or a rat liver alcohol dehydrogenase into the central nervous system and observing the effects on alcohol preference by high ethanol‐consuming rats. A factor not directly considered is that acetaldehyde is further metabolized to acetate, which also has some behavioral actions. Conclusions: The efficacy of lentivirus injections of enzyme inhibitors or enzymes themselves to alter a behavioral response to ethanol is clearly demonstrated here. The many other actions of ethanol that are postulated to be a result of the production of acetaldehyde in the brain remain to be investigated by similar techniques. Possible “therapeutic avenues to reduce chronic alcohol use” are envisioned.     

The reinforcing properties of salsolinol in the ventral tegmental area: evidence for regional heterogeneity and the involvement of serotonin and dopamine

Background:  Salsolinol (SAL), the condensation product of acetaldehyde and dopamine, may be a factor contributing to alcohol abuse. Previous research indicated that both ethanol and acetaldehyde are self-administered into the posterior ventral tegmental area (VTA). The current study examined SAL self-infusions into the VTA, and determined the involvement of dopamine neurons and 5-HT₃ receptors in this process.
Methods:  The intracranial self-administration technique was used to determine the self-infusion of SAL into the VTA of adult, male Wistar rats. The rats were placed in 2-lever (active and inactive) experimental chambers, and allowed to respond for the self-infusion of 0, 0.03, 0.1, 0.3, 1.0 or 3.0 μM SAL into the posterior or anterior VTA. In a second experiment, rats self-administered 0.3 μM SAL for the initial 4 sessions, co-administered SAL with ICS-205,930 (a 5-HT₃ receptor antagonist) or quinpirole (a D_2,3 receptor agonist) for sessions 5 and 6, and then only 0.3 μM SAL for session 7.
Results:  Wistar rats, given 0.03 to 0.3 μM SAL, received more infusions per session than did the group given artificial cerebrospinal fluid (aCSF) alone (e.g., 41 infusions for 0.1 μM SAL versus 9 infusions for the aCSF group), and responded more on the active than inactive lever. These effects were observed in the posterior but not in anterior VTA. Co-infusion of 100 μM ICS-205,930, or quinpirole significantly reduced self-infusions and active lever responding.
Conclusions:  SAL produces reinforcing effects in the posterior VTA of Wistar rats, and these effects are mediated by activation of DA neurons and local 5-HT₃ receptors.     

Intravenous Ethanol Self-administration in C57BL/6J and DBA/2J Mice

Two strains of mice, C57BL/6J (B6) and DBA/2J (D2) were allowed to self-administer intravenous (iv) ethanol. These two strains were selected because they differ greatly in their preference for drinking ethanol solutions: 86 mice are preferrers, whereas D2 mice are avoiders of ethanol. Of interest was whether these strains would also differ in self-administration of iv ethanol when taste factors presumably do not influence consumption. Mice were trained with either 60, 75, or 90 mg/kg per infusion. Mice from both strains acquired nosepoking for all of these doses on an FR-3 schedule of reinforcement during 2-hr daily sessions. Additionally, mice in both strains acquired an equal preference for nosepoking on the side resulting in ethanol infusions, compared with the side that had no scheduled consequence, although B6 mice took somewhat more ethanol early in training than did D2 mice. Mice in both strains achieved equal levels of responding at the conclusion of training, when response rates had stabilized. A subset of animals were then tested at doses of ethanol ranging from 25 to 125 mg/kg per infusion. Although their responding tended to decrease over time regardless of changes in the unit dose of ethanol, these mice showed lower response rates for higher doses of ethanol, and less responding for saline than for ethanol. Together, these findings imply that iv ethanol has reinforcing properties in both these strains, despite the strain difference in preference for oral ethanol. Self-administration of iv ethanol in mice may prove a valuable addition to existing animal models for the study of ethanol reward.     

Alcohol Self-Administration: Further Examination of the Role of Dopamine Receptors in the Nucleus Accumbens

One of the functions of the mesolimbic dopamine (DA) system is to regulate the process of reinforcement, a process that is thought to influence drug self-administration. This study tested the effects of centrally administered DA receptor ligands on ethanol self-administration behavior. Long-Evans rats were trained to lever press on a fixed-ratio 4 schedule of ethanol (10% v/v) reinforcement. DA agonists and antagonists were then bilaterally microinjected (0.5 μ/side) into the nucleus accumbens (N Acc) 10-min before sessions to test for effects on the onset, maintenance, and termination of ethanol self-administration. Infusions of the D₁-like agonist SKF 38393 (0.03 to 3.0 μg) produced no effect on ethanol self-administration. The D₁-like antagonist SCH 23390 (0.5 to 2.0 μg) reduced total responding by decreasing the time course of self-administration without altering response rate. The D₂-like agonist quinpirole produced a biphasic effect on self-administration. Quinpirole (1.0 μg) increased total responses and response rate, whereas higher doses (4.0 to 10.0 μg) decreased total responding as a result of early termination. The D₂-like antagonist raclopride (0.1 to 1.0 μg) reduced total responding by decreasing time course and response rate. Co-administration of either SKF 38393 or SCH 23390 with quinpirole prevented the behavioral effects observed with the low doses of quinpirole. Thus, in the N ACC either increased activation of D₁-like receptors or their blockade can affect the expression of the behavioral effects of the D₂-like agonist. This suggests that some intermediate level of D₁ activation is required to observe the D₂ effect. The decreases in total responding produced by raclopride were enhanced by co-administration of SKF 38393, but not altered by SCH 23390, thus suggesting that D₁-like and D₂-like receptors in the N Acc interact in the regulation of ethanol self-administration in a manner similar to their interactive regulation of other behaviors.     

Mouse Strain Differences in Oral Operant Ethanol Reinforcement under Continuous Access Conditions

The present experiment examined ethanol setf-administration in C57BL/6J (C57) and DBA/2J (DBA) mice using a continuous access operant procedure. Adult male C57 and DBA mice were initially trained to perform a lever press response to obtain access to 10% w/v sucrose solution. Subsequently, the mice were placed in operant chambers on a continuous (23 hr/day) basis with access to food (FR1), 10% v/v ethanol (FR4), and water from a sipper tube. C57 mice displayed greater rates of responding on the ethanol-associated lever compared with DBA mice. Responding on the food lever was the same in both strains, but DBA mice consumed greater amounts of water. C57 mice consistently displayed both prandial and nonprandial episodes (bouts) of ethanol responding. DBA mice did not respond for ethanol in bouts. Following 50 consecutive sessions, ethanol concentration was altered every 5 days. Response patterns were determined using 0, 5, 10, 20, and 30% v/v ethanol concentrations. C57 mice displayed concentration-dependent responding on the ethanol lever showing that ethanol was functioning as an effective reinforcer in this strain. In contrast, responding on the ethanol lever by DBA mice did not change as a function of ethanol concentration. Saccharin (0.2% w/v) was subsequently added to the ethanol mixture, and responding was examined at 0, 5, 10, and 20% ethanol concentrations. Overall, ethanol lever responding was increased in both strains. As before, C57 mice showed higher levels of ethanol responding, compared with DBA mice. C57 mice also showed higher responding for saccharin alone. These results are consistent with findings that suggest orally administered ethanol is a more effective reinforcer in C57 mice than in DBA mice. Furthermore, C57 mice engage in ethanol-reinforced responding over a broader range of conditions than DBA mice.     

Alcohol-related effects on automaticity due to experimentally manipulated conditioning

Background: The use of alcohol is associated with various forms of automatic processing, such as approach tendencies and attentional biases, which may play a role in addictive behavior. The development of such automaticity has generally occurred well before subjects perform tasks designed to detect them. Although it seems plausible that this development involves some form of alcohol‐related conditioning, this process is not usually included in the experimental procedure. Methods: The development of automaticity involving alcoholic or nonalcoholic stimuli was experimentally manipulated via a conditioning task. Subjects were presented with pairs of stimuli from a set of 4 stimuli: 2 pictures of alcoholic beverages, and 2 pictures of nonalcoholic beverages. One of the alcoholic and 1 of the nonalcoholic beverages was associated with reward, the other stimuli with punishment. Subjects had to learn to select the rewarded stimuli from pairs of 1 rewarded and 1 punished stimulus. The task, thus experimentally established reward versus punishment stimulus–response–outcome associations, for alcoholic and for nonalcoholic stimuli. Subsequently, a cued reversal task was used to test automaticity involving alcoholic versus nonalcoholic, and rewarded versus punished stimuli. Results: An association was found between heavier drinking and an alcohol‐related conditioning bias: heavier drinkers had more difficulty overcoming a conditioned response when it involved selecting a previously punished nonalcoholic stimulus over a previously rewarded alcoholic stimulus. Conclusions: The study provided novel information on secondary reinforcement involving alcoholic stimuli: heavier drinkers may more easily develop automaticity related to alcohol‐reward contingencies. This may have implications for interventions and the interpretation of findings concerning alcohol‐related automatic processing.     

Responding for Oral Ethanol after Naloxone Treatment by Alcohol-Preferring AA Rats

The present study examined the effect of a relatively nonselective opioid antagonist, naloxone, on lever pressing for oral ethanol by the alcohol-preferring AA rats. The AAs, housed continually in operant chambers with free access to food and water, learned to respond for 10% oral ethanol during daily 60-min alcohol access periods indicated by a stimulus light. The rats developed stable ethanol responding, resulting in mean ethanol intakes of 1.2 g/kg/60 min and measurable blood alcohol levels. In the first experiment, single systemic injections of naloxone (0.05–2.5 mg/kg) had no effect on the initial rate of responding; dose-dependent decreases were observed later during the alcohol access. The second experiment examined the effects of repeated injections of 0.5 and 2.5 mg/kg naloxone on 5 consecutive days. Naloxone suppressed responding dose-relatedly over the treatment days. In contrast to the effects of single injections, repeated injections with 2.5 mg/kg naloxone produced progressive decreases within the first minutes of access. The results suggest that naloxone may attenuate the reinforcing actions of ethanol.     

后巩膜加固术的组织学观察

目的：为进一步了解巩膜加固术后的组织学改变。方法：选用白色家兔为实验对象，采用人体巩膜施行巩膜加固术，于术后不同时期分批处死动物，并对手术区巩膜进行组织学检查结果：术后1－2周，为炎症浸润期：术后1－2个月为肉芽肿及新生血管增殖期，植片与巩膜粘连；术后3－6月，纤维母细胞形成，植片与巩膜完全愈合，形成“新巩膜”。实验结果为后巩膜加固术提供了理论根据。     

The emergence of saliency and novelty responses from Reinforcement Learning principles

Recent attempts to map reward-based learning models, like Reinforcement Learning [Sutton, R. S., & Barto, A. G. (1998). Reinforcement Learning: An introduction. Cambridge, MA: MIT Press], to the brain are based on the observation that phasic increases and decreases in the spiking of dopamine-releasing neurons signal differences between predicted and received reward [Gillies, A., & Arbuthnott, G. (2000). Computational models of the basal ganglia. Movement Disorders, 15(5), 762–770; Schultz, W. (1998). Predictive reward signal of dopamine neurons. Journal of Neurophysiology, 80(1), 1–27]. However, this reward-prediction error is only one of several signals communicated by that phasic activity; another involves an increase in dopaminergic spiking, reflecting the appearance of salient but unpredicted non-reward stimuli [Doya, K. (2002). Metalearning and neuromodulation. Neural Networks, 15(4–6), 495–506; Horvitz, J. C. (2000). Mesolimbocortical and nigrostriatal dopamine responses to salient non-reward events. Neuroscience, 96(4), 651–656; Redgrave, P., & Gurney, K. (2006). The short-latency dopamine signal: A role in discovering novel actions? Nature Reviews Neuroscience, 7(12), 967–975], especially when an organism subsequently orients towards the stimulus [Schultz, W. (1998). Predictive reward signal of dopamine neurons. Journal of Neurophysiology, 80(1), 1–27]. To explain these findings, Kakade and Dayan [Kakade, S., & Dayan, P. (2002). Dopamine: Generalization and bonuses. Neural Networks, 15(4–6), 549–559.] and others have posited that novel, unexpected stimuli are intrinsically rewarding. The simulation reported in this article demonstrates that this assumption is not necessary because the effect it is intended to capture emerges from the reward-prediction learning mechanisms of Reinforcement Learning. Thus, Reinforcement Learning principles can be used to understand not just reward-related activity of the dopaminergic neurons of the basal ganglia, but also some of their apparently non-reward-related activity.