Influence of ethanol on contrast in consummatory behavior

Frustrative nonreward and emotional self-medication:Factors modulating alcohol consumption following reward downshift in rats

Life experience involving unexpected incentive loss (e.g., loss of job or a significant other) may result in negative emotional reactions (frustration) and promote alcohol drinking. Similarly, animals exposed to a frustrative 32-to-4% sucrose downshift increase their preference for alcohol (2%) vs. water. This result was interpreted as reflecting emotional self-medication-the consumption of substances that reduce negative emotions. We conducted three experiments examining parametric manipulations of the animal model: (1) effects of a severe reward downshift (32-to-4% sucrose) on consumption of various alcohol concentrations (Experiment 1); (2) effects of different magnitudes of reward downshifts on consumption of 32% alcohol (Experiment 2); and (3) effects of partial reinforcement (an intervention that increases resistance to frustration) on 2% alcohol intake induced by a 32-to-4% sucrose downshift (Experiment 3). The results show that (1) a 32-to-4% sucrose downshift leads to an increase in alcohol intake over a wide range of alcohol concentrations; (2) the greater the reward downshift, the higher the relative increase in alcohol consumption; and (3) a treatment that increases resistance to frustration (partial reinforcement) also attenuates alcohol consumption after a sucrose downshift. These data are discussed in relation to the role of frustrative nonreward in alcohol consumption.

High Alcohol-Preferring Mice Show Reaction to Loss of Ethanol Reward Following Repeated Binge Drinking

BACKGROUND

Beyond yielding high blood ethanol (EtOH) concentrations (BECs), binge-drinking models allow examination of drinking patterns which may be associated with EtOH's rewarding effects, including front-loading and consummatory successive negative contrast (cSNC), a decrease in intake when only water is available to subjects expecting EtOH. The goals of the current study were to broaden our understanding of these reward-related behaviors during binge EtOH access in high alcohol-preferring (HAP) replicate lines (HAP2 and HAP3) of mice selectively bred to prefer alcohol. We hypothesized that both lines would show evidence of front-loading during binge EtOH access and that we would find a cSNC effect in groups where EtOH was replaced with water, as these results have been shown previously in HAP1 mice.

METHODS

HAP replicate 2 and replicate 3 female and male mice were given 2 hours of EtOH or water access in the home cage for 15 consecutive days using "drinking in the dark" (DID) procedures. Mice received the same fluid (either 20% unsweetened EtOH or water) for the first 14 days. However, on the 15th day, half of the mice from these 2 groups were provided with the opposite assigned fluid (EtOH groups received water and vice versa). Intake was measured in 1-minute bins using specialized sipper tubes, which allowed within-session analyses of binge-drinking patterns.

RESULTS

EtOH front-loading was observed in both replicates. HAP3 mice displayed front-loading on the first day of EtOH access, whereas front-loading developed following alcohol experience in HAP2 mice, which may suggest differences in initial sensitivity to EtOH reward. Consummatory SNC, which manifests as lower water intake in mice expecting EtOH as compared to mice expecting water, was observed in both replicates.

CONCLUSIONS

These findings increase confidence that defined changes in home cage consummatory behavior are driven by the incentive value of EtOH. The presence of cSNC across HAP replicates indicates that this reaction to loss of reward is genetically mediated, which suggests that there is a biological mechanism that might be targeted.

Sucrose exposure in juvenile rats produces long-term changes in fear memory and anxiety-like behavior

Sugar consumption has increased dramatically in our society, a phenomenon that is primarily associated with obesity and diabetes appearance. However, whether this overconsumption of sugar has an impact on the developing CNS remains unknown. This study investigated the long-term effects of unlimited access to sucrose using the two-bottle choice paradigm and the juvenile and adult effects were compared. Male Sprague Dawley rats had free access to water containing 10% sucrose and water during youth (PD 25-50) or adulthood (PD 75-100). Rats in the sucrose group, privileged to take sugary solution over the water. No weight differences were observed between the sucrose groups and their age-matched water controls. After treatment all animals drank only water for another 25 days. Frustration, measured as the amount of water drank after the sucrose period, was higher in young-exposed animals compared to adults. In addition, rats that consumed sucrose during youth travelled less the central zones of an open field. Sucrose consumption during youth also affected fear behavior as animals exhibited impaired extinction of fear memory compared to control, indicating that prefrontal and hippocampal function is impaired. In contrast, rats exposed to sucrose during adulthood did not behave significantly different from control on either task. The calretinin and parvalbumin GABAergic interneurons go through extensive remodeling during youth in the medial prefrontal cortex and the ventral hippocampus. Here, we found that rats exposed to sucrose during youth presented an increased expression of calretinin-immunoreactivity in the medial prefrontal cortex, but not in the ventral hippocampus, indicating that early sucrose consumption produces enduring effects on the GABA system. Altogether these results indicate that sugar overconsumption at early stages of life induces long-term effects on behaviors related to fear and anxiety in adulthood.

The effects of ethanol on diverse components of choice in the rat: reward discrimination, preference and relative valuation

Alcohol consumption impairs judgment and choice. How alcohol alters these crucial processes is primarily unknown. Choice can be fractionated into different components including reward discrimination, preference and relative valuation that can function together or in isolation depending upon diverse factors including choice context. We examined the diverse components and contextual effects by analyzing the effects of alcohol drinking on choice behavior in a task with a reduced level of temporal and spatial constraints. Rats were trained to drink 10% ethanol during 6 weeks of behavior testing using a combined sucrose-fade and two-bottle free-choice procedure. Two different sucrose pellet outcomes (e.g., constant vs. variable) were presented each week to examine the impact of voluntary drinking on reward-based decision-making. Behavioral contexts of single option, free choice and extinction were examined for each outcome set. Comparisons were made between alcohol and control groups and within the alcohol group over time to inspect choice profiles. Between-group results showed alcohol drinking animals expressed altered place preference and modified sucrose reward approach latencies. The within-group profile showed that alcohol drinking animals can express adequate reward discrimination, preference and incentive contrast during free choice. All of these components were significantly reduced during the context of extinction. Control animals were also impacted by extinction but not as severely. The findings point to a need for a greater focus on the context and the diverse components of choice when examining external and internal factors influencing decision-making during alcohol or other substance of abuse exposure.

Open-field exposure facilitates consummatory extinction

During extinction, the organism learns that a conditioned stimulus or a conditioned response is no longer associated with an unconditioned stimulus, and as a consequence, a decrement in the response is presented. The exposure to novel situations (e.g. exploration of a novel open field) has been used widely to modulate (i.e. either enhance or deteriorate) learning and memory. The aim of the present study was to test whether open-field exposure could modulate consummatory extinction. The results indicated that open-field exposure accelerated the extinction response (i.e. experimental animals provided novelty exposure had lower consummatory behavior than control animals) when applied before - but not after - the first extinction trial, or when applied before the second extinction trial. The results suggest that environmental treatments such as novelty exposure provide a valuable, nonpharmacological alternative to potentially modulate extinction processes.

Emotional reactivity to incentive downshift as a correlated response to selection of high and low alcohol preferring mice and an influencing factor on ethanol intake

Losing a job or significant other are examples of incentive loss that result in negative emotional reactions. The occurrence of negative life events is associated with increased drinking (Keyes, Hatzenbuehler, & Hasin, 2011). Further, certain genotypes are more likely to drink alcohol in response to stressful negative life events (Blomeyer et al., 2008; Covault et al., 2007). Shared genetic factors may contribute to alcohol drinking and emotional reactivity, but this relationship is not currently well understood. We used an incentive downshift paradigm to address whether emotional reactivity is elevated in mice predisposed to drink alcohol. We also investigated if ethanol drinking is influenced in High Alcohol Preferring mice that had been exposed to an incentive downshift. Incentive downshift procedures have been widely utilized to model emotional reactivity, and involve shifting a high reward group to a low reward and comparing the shifted group to a consistently rewarded control group. Here, we show that replicate lines of selectively bred High Alcohol Preferring mice exhibited larger successive negative contrast effects than their corresponding replicate Low Alcohol Preferring lines, providing strong evidence for a genetic association between alcohol drinking and susceptibility to the emotional effects of negative contrast. These mice can be used to study the shared neurological and genetic underpinnings of emotional reactivity and alcohol preference. Unexpectedly, an incentive downshift suppressed ethanol drinking immediately following an incentive downshift. This could be due to a specific effect of negative contrast on ethanol consumption or a suppressive effect on consummatory behavior in general. These data suggest that either alcohol intake does not provide the anticipated negative reinforcement, or that a single test was insufficient for animals to learn to drink following incentive downshift. However, the emotional intensity following incentive downshift provides initial evidence that this type of emotional reactivity may be a predisposing factor in alcoholism.

Behavioral neuroscience of psychological pain

Pain is a common word used to refer to a wide range of physical and mental states sharing hedonic aversive value. Three types of pain are distinguished in this article: Physical pain, an aversive state related to actual or potential injury and disease; social pain, an aversive emotion associated to social exclusion; and psychological pain, a negative emotion induced by incentive loss. This review centers on psychological pain as studied in nonhuman animals. After covering issues of terminology, the article briefly discusses the daily-life significance of psychological pain and then centers on a discussion of the results originating from two procedures involving incentive loss: successive negative contrast-the unexpected devaluation of a reward-and appetitive extinction-the unexpected omission of a reward. The evidence reviewed points to substantial commonalities, but also some differences and interactions between physical and psychological pains. This evidence is discussed in relation to behavioral, pharmacological, neurobiological, and genetic factors that contribute to the multidimensional experience of psychological pain.

Propranolol reverses open field effects on frustration

Reactivity to a reward is affected by prior experience with different reinforcer values of that reward, a phenomenon known as incentive relativity. Incentive relativity can be studied via the consummatory successive negative contrast (cSNC) paradigm, in which acceptance of 4% sucrose is assessed in animals that had been exposed to 32% sucrose. These downshifted animals usually exhibit significantly less sucrose acceptance than animals that always received the 4% sucrose solution. In previous work, we found that exploration of a novel open field (OF) before the first trial with the downshifted solution attenuated the contrast effect. The goal of the present experiments was to expand the knowledge on the effects of OF exposure on cSNC. We evaluated the effect OF exposure before the second downshift trial and assessed the mediational role of the adrenergic system in the effects of OF during the first and second trial of cSNC. The results indicate that OF applied before the first or second downshift trials exert opposite effects and that the adrenergic system is involved in the acquisition and consolidation of the OF information.

Incentive relativity in middle aged rats

Response to a reinforcer is affected by prior experience with different reward values of that reward, a phenomenon known as incentive relativity. Two different procedures to study this phenomenon are the incentive downshift (ID) and the consummatory anticipatory negative contrast (cANC), the former is an emotional-cognitive protocol and the latter cognitive one. Aged rodents, as also well described in aged humans, exhibit alterations in cognitive functions. The main goal of this work was to evaluate the effect of age in the incentive' assessment using these two procedures. The results indicated that aged rats had an adequate assessment of the rewards but their performance is not completely comparable to that of young subjects. They recover faster from the ID and they had a cognitive impairment in the cANC. The results are discussed in relation to age-related changes in memory and emotion.

Assessing appetitive, aversive, and negative ethanol-mediated reinforcement through an immature rat model

The motivational effects of drugs play a key role during the transition from casual use to abuse and dependence. Ethanol reinforcement has been successfully studied through Pavlovian and operant conditioning in adult rats and mice genetically selected for their ready acceptance of ethanol. Another model for studying ethanol reinforcement is the immature (preweanling) rat, which consumes ethanol and exhibits the capacity to process tactile, odor and taste cues and transfer information between different sensorial modalities. This review describes the motivational effects of ethanol in preweanling, heterogeneous non-selected rats. Preweanlings exhibit ethanol-mediated conditioned taste avoidance and conditioned place aversion. Ethanol's appetitive effects, however, are evident when using first- and second-order conditioning and operant procedures. Ethanol also devalues the motivational representation of aversive stimuli, suggesting early negative reinforcement. It seems that preweanlings are highly sensitive not only to the aversive motivational effects of ethanol but also to its positive and negative (anti-anxiety) reinforcement potential. The review underscores the advantages of using a developing rat to evaluate alcohol's motivational effects.

Anxiolytic-like effect of ejaculation upon frustration

In three experiments, we studied the consequences of ejaculation upon the frustrative or contrast response of male rats exposed to reward downshift situations (i.e., surprising changes from 32% to 4% sucrose solutions). Similar to what has been found after treatment with anxiolytic agents, consummatory suppression was partially reversed by previous ejaculations in a second postshift trial (Experiments 2 and 3), such a result not having been obtained in a first postshift trial (Experiment 1). Moreover, the effect of ejaculations upon males' behavior during a second postshift trial was transitory, disappearing when assessed during the third and fourth postshift trials (Experiment 3). These results are in accordance with both Amsel's (1958, 1992) frustration theory and Flaherty's (1996) multistage hypothesis of successive negative contrast; the diverse factors that are known to modulate contrast effects are considered, including an interpretation of the present data in terms of the anxiolytic-like effect of the ejaculation.

Evidence for zolpidem-induced hyperphagia, but not anxiolysis, in a successive negative contrast paradigm

Zolpidem is an imidazopyridine which binds to certain benzodiazepine receptor types with varying degrees of affinity. The effect of zolpidem on successive negative contrast was investigated in three experiments. In each experiment, a contrast group was given brief access to 32% sucrose for 10 days, then shifted to 4% sucrose for 2 days; a procedure that elicits anxiety primarily on the second postshift day. One control group was given only 4% sucrose. Experiments 2 and 3 included a 2% sucrose group as an intake rate-dependent control. In Experiment 1, zolpidem (4.0 and 0.5 mg/kg) dose-dependently reduced contrast on the two postshift days. Contrast occurred during the first postshift consummatory burst. Zolpidem prolonged the first postshift burst equally in both shifted and unshifted groups, suggesting a general facilitation of intake masked by a ceiling effect in controls. In Experiment 2, zolpidem's (4.0 mg/kg) anti-contrast action was equivalent to its hyperphagic effect in the 2% control group. Zolpidem prolonged the first postshift burst equally in all three groups, again consistent with general intake facilitation. In Experiment 3, 8.0 mg/kg zolpidem produced an anti-contrast effect not present in 2% controls on both postshift days. This does not appear attributable to anxiolysis, however, as the effect was equivalent during stressful and non-stressful phases of the postshift period, and zolpidem extended the duration of the first postshift burst equally in all three sucrose groups. Thus, unlike benzodiazepines, zolpidem is not anxiolytic in this paradigm.

Effects of nicotine and a cannabinoid receptor agonist on negative contrast: distinction between anxiety and disappointment?

RATIONALE

Animals trained to lick for a sucrose solution of a given incentive value that subsequently encounter an incentive downshift (i.e. 32-4% sucrose) display an exaggerated decrease in the amount consumed, relative to unshifted controls. This change has been classified as a successive negative contrast (SNC) effect. The emotional component to this robust behavioural change is dynamic and changes from post-shift day (PSD) 1 to 2. Anxiolytics block SNC, but the possible link between anxiety and SNC needs further exploration. Both nicotine and a cannabinoid receptor agonist have been reported to change anxiety and both have actions on the reward process, but their effects on SNC have not been investigated.

OBJECTIVES

To determine: (1) whether exposure to SNC evokes an anxiogenic response; (2) whether an anxiolytic dose of nicotine has the same effects on SNC as those of chlordiazepoxide; (3) the effects of a low (anxiolytic) and a high (anxiogenic) dose of the cannabinoid receptor agonist CP 55,940 on SNC.

METHODS

Two groups of animals were given access to high (32%) or low (4%) sucrose solutions for 5 min per day for 10 days. On PSD 1 and 2, the shifted group had access to a devalued incentive (from 32 to 4% sucrose) and the unshifted group remained at 4% sucrose. The volumes (ml) of sucrose solution consumed were measured pre-shift and on PSD 1 and 2. In experiment 1, immediately after SNC testing on PSD 1 and 2, the rats were tested in the social interaction and elevated plus-maze tests of anxiety. In experiment 2, the effects of chlordiazepoxide (5 and 7.5 mg/kg) and nicotine (0.1 mg/kg) were examined on PSD 1 and 2. In experiment 3, the effects of CP 55,940 (5 and 40 microg/kg) were examined on PSD 1 and 2.

RESULTS

There were no anxiogenic effects of shift in either test of anxiety on either test day. However, on PSD 1, the shifted group had significantly higher locomotor activity and spent a higher percentage of time on the open arms, perhaps reflecting search strategies. Nicotine was without significant effect on SNC on either test day. On PSD 1, chlordiazepoxide (5 mg/kg) and CP 55,940 (5 and 40 microg/kg, IP) blocked SNC. On PSD 2, both doses of chlordiazepoxide and the low, anxiolytic dose of CP 55,940 (5 microg/kg) blocked SNC, the high dose of CP 55,940 was without effect.

CONCLUSIONS

The pattern of results allows for the separation between effects on anxiety and SNC. The block of contrast on PSD 1 was independent of changes in anxiety, since both anxiolytic and anxiogenic drug doses were effective. It is suggested that this may provide an animal model of disappointment in which the cannabinoid system plays an important role. An anxiolytic action would seem to be a necessary, but not a sufficient, action to block SNC on PSD 2.

Mechanism of the antialcohol effect of gamma-hydroxybutyric acid

Treatment with gamma-hydroxybutyric acid has been reported to effectively decrease alcohol craving and consumption as well as alcohol withdrawal symptoms in alcoholics. We describe the results of animal studies demonstrating the ability of gamma-hydroxybutyric acid to reduce (1) the severity of ethanol withdrawal signs in rats rendered physically dependent on ethanol and (2) voluntary ethanol intake in selectively bred Sardinian alcohol-preferring rats. Furthermore, we review experimental data suggesting that gamma-hydroxybutyric acid and ethanol have several pharmacological effects in common. Relevant similarities are: (1) stimulation of firing rate of dopaminergic neurons and dopamine release in specific rat brain areas; (2) development of cross-tolerance to the motor-impairing effects after repeated administration in rats; 3) abuse potential, as indicated by self-administration of pharmacologically relevant doses of gamma-hydroxybutyric acid in rats and mice; (4) induction of anxiolytic effects in rats; and (5) induction of similar discriminative stimulus effects, as evidenced by symmetrical generalization in a drug discrimination study in rats. These lines of evidence are discussed in relation to gamma-hydroxybutyric acid exerting its antialcohol effects by a substitution mechanism.

Temporal dynamics of corticosterone elevation in successive negative contrast

A negative contrast effect in consummatory behavior that occurred when rats were shifted from 32% to 4% sucrose was accompanied by elevations in corticosterone that were measurable at 10 and 20 min but not at 40 min after the second postshift day. No corticosterone elevations were found to accompany contrast at 10 or 15 min after the first postshift day in these experiments nor immediately after the first postshift day in an earlier experiment. The present study also found an anticipatory elevation in plasma corticosterone in shifted animals just before their placement in the apparatus on the second postshift day. These results are discussed in terms of a multistage hypothesis of successive negative contrast. The anticipatory elevation is discussed in terms of uncontrollability and unpredictability of aversive events.

Lack of tolerance to contrast-reducing actions of chlordiazepoxide with repeated reward reductions

In each of eight cycles of repeated reward reduction, the performance of rats given brief access to 32% sucrose for 3 days, and then 4% sucrose for 2 days, was compared to rats that received 4% on all 5 days. Shifted rats consumed less than unshifted rats following each shift, with little evidence of diminution of negative contrast across the eight shifts. Acute administration of chlordiazepoxide (CDP, 8 mg/kg) on the second postshift day reduced contrast on each shift with no evidence of tolerance development to these anticontrast actions (Experiment 1a). Acute administration of CDP on the first postshift day had no effect on contrast through the first four shifts, but reliably reduced contrast on the following four shifts (Experiment 2a). There was tolerance to the sedative effects of CDP, as measured in an open field (Experiments 1b and 2b). The data thus show: a) that contrast is not lost with repeated shifts; b) no tolerance develops to the anticontrast actions of CDP and, instead, CDP gains anticontrast actions, in regard to initial contrast occurrence; c) but, concurrently, tolerance does develop to the sedative effects of CDP in an open field.

Sardinian alcohol-preferring rats: a genetic animal model of anxiety

The present study was designed to assess the anxiety profile of the selectively bred alcohol-preferring sP and alcohol-nonpreferring sNP rats. Rats were offered either water (ethanol-naive rats) or a free choice of 10% (v/v) ethanol and water (ethanol-experienced rats) for 14 consecutive days prior to the test. Spontaneous exploration of an elevated plus maze was used as a behavioral measure of anxiety. Ethanol-naive sP rats spent less time in and made fewer entries into the open arms of the maze than ethanol-naive sNP rats. These results suggest a higher innate degree of anxiety in sP than in sNP rats. Moreover, time spent in and number of entries into the open arms of the maze were higher in ethanol-experienced than in ethanol-naive sP rats. This finding suggests that ethanol consumed voluntarily produces anxiolytic effects in sP rats. The results of the present study are discussed in terms of (a) anxiety as a genetic trait related to ethanol-preference in sP rats and (b) self-medication of anxiety as a possible factor promoting voluntary ethanol consumption in sP rats.

Cyproheptadine prevents the initial occurrence of successive negative contrast

Rats shifted from 32% to 4% sucrose make fewer licks for 4% sucrose than rats having only experienced the lower reward. In Experiment 1, the occurrence of this contrast effect was prevented by the administration of the nonspecific serotonin antagonist cyproheptadine (3.0 or 6.0 mg/kg). These results of Experiments 2 and 3 demonstrated that the contrast-reducing action of cyproheptadine was not mediated by the antiserotonergic properties of the drug since systemic administration of the serotonin synthesis inhibitor, PCPA (150 or 300 mg/kg), failed to influence either the occurrence of contrast or the attenuation of contrast by cyproheptadine. The results of Experiment 4 indicated that the contrast-reducing action of cyproheptadine was not mediated by the antihistaminergic properties of the drug since the antihistamine, pyrilamine (6 or 12 mg/kg), also failed to prevent the occurrence of contrast. Finally, the contrast-reducing action of cyproheptadine was not due to rate-dependent and/or appetite stimulating effects since cyproheptadine did not serve to increase lick frequency in rate-dependent controls.

RO15-4513 antagonizes the anxiolytic effects of ethanol in a nonshock conflict task at doses devoid of anxiogenic activity

RO15-4513 is a partial benzodiazepine inverse agonist that has been reported to antagonize some of the biochemical and neurobehavioral actions of ethanol. However, whether this antagonistic action of RO15-4513 is dependent on the drug exerting its intrinsic (inverse agonist) properties is unclear at present. The purpose of the present study was to examine whether RO15-4513 was capable of antagonizing the anxiolytic effects of ethanol in a nonshock conflict task at doses that, by themselves, do not reveal the compound's intrinsic anxiogenic properties. The consummatory conflict task employed (negative contrast) involves quantifying how animals respond to an abrupt, unexpected reduction in reward (sucrose solution), and is particularly sensitive to the effects of anxiolytic agents, including ethanol. As previously demonstrated, depressed consummatory behavior engendered by reward reduction was significantly alleviated by ethanol (0.75 g/kg). This anxiolytic effect of ethanol, however, was antagonized dose dependently by RO15-4513 (0.1875-3.0 mg/kg). Only the highest dose of RO15-4513 (3.0 mg/kg) showed evidence of further response suppression. Lower doses of RO15-4513 tested did not exert an anxiogenic effect when given alone. Thus the antagonism of EtOH's anxiolytic (contrast-reducing) effects occurred at doses of RO15-4513 (0.375-1.5 mg/kg) that did not exhibit any intrinsic anxiogenic activity. As such, these results suggest that RO15-4513 interacts with the anxiolytic effects of ethanol in a nonadditive fashion in this test situation.

Bay K 8644 potentiates the anxiolytic effect of ethanol

The possible role of voltage-sensitive calcium channels (VSCCs) in the anxiolytic effect of ethanol was investigated using three different doses of ethanol (0.5, 1.0 and 2.0 g/kg) with calcium agonist Bay K 8644 (0.5 mg/kg) and calcium antagonist nifedipine (5 mg/kg) in rats. Ethanol produced an anxiolytic effect in a dose-dependent manner. The Bay K 8644-potentiated anxiolytic effect of ethanol, however, Bay K 8644 did not alter anxiety when used alone. Nifedipine itself showed an anxiolytic effect but did not change the ethanol-induced anxiolytic effect. This finding may lead to the consideration of the neurochemical mechanisms of the anxiolytic effects of ethanol and nifedipine as they vary from each other.

Valproate potentiates and picrotoxin antagonizes the anxiolytic action of ethanol in a nonshock conflict task

The purpose of this study was to examine the effects of the indirect GABA agonist valproate and the indirect GABA antagonist picrotoxin on the anxiolytic (anti-conflict) activity of ethanol in a behavioral conflict task that does not employ electroshock. This task (negative contrast) quantifies how animals respond to an abrupt, unexpected reduction in reward. Treatment with valproate alone did not elevated depressed behavior engendered by abrupt reduction in reward. However, when administered together with a sub-effective dose of ethanol (0.5 g/kg), valproate (50-200 mg/kg) dose-dependently potentiated the anxiolytic action of ethanol. Picrotoxin (2 mg/kg) antagonized the anxiolytic effects of a larger dose of ethanol (1.0 g/kg) given alone, as well as the ability of valproate to enhance the anxiolytic effects of smaller dose of ethanol (0.5 g/kg). As such, these data support a role for GABA in mediating the anxiolytic activity of ethanol.

Effect of serotonergic drugs on negative contrast in consummatory behavior

The effect of acute and chronic administration of the 5-HT1A agonist buspirone on successive negative contrast was investigated in Experiments 1-6. Contrast in consummatory behavior was induced by shifting rats from a 32% to a 4% sucrose solution. Experiments 1-5 showed that buspirone (0.125, 0.25, 0.5, 1.0, 2.0, 15.0 mg/kg) was ineffective in alleviating contrast or in facilitating recovery from contrast. The 15 mg/kg dose substantially decreased consummatory responding. Experiment 6 showed that the chronic (24 days) administration of buspirone (0.5, 2.0 mg/kg) also did not alleviate contrast. The chronic, but not the acute administration of the 2.0 mg/kg dose decreased consummatory behavior. In Experiment 7 the 5-HT1A agonist gepirone (2.5, 5.0 and 10.0 mg/kg) was also found to be ineffective in reducing contrast but, at the higher doses, decreased overall sucrose intake. Experiments 8 and 9 found that the 5-HT2 antagonists ketanserin (2.0 and 8.0 mg/kg) and ritanserin (0.63 and 2.5 mg/kg) also did not alleviate contrast. Midazolam (1.0 mg/kg), included as a positive control, eliminated contrast. These data suggest that serotonergic mechanisms are not involved in negative contrast.

Indomethacin does not antagonize the anxiolytic action of ethanol in the elevated plus-maze

The present study was designed to examine whether the prostaglandin (PG) synthesis inhibitor indomethacin (INDO) could antagonize the anxiolytic effects of ethanol (EtOH) in the elevated plus-maze test of anxiety. EtOH (1.6 g/kg) significantly increased the percentage of open arm entries and time spent on the open arms in both inbred C57BL/6J and outbred CD-1 mouse strains. However, this anxiolytic effect of EtOH was not significantly antagonized by pretreatment with INDO (5 and 10 mg/kg) in either strain. EtOH also significantly increased total arm entries in CD-1 mice, but not in the C57BL/6J strain. These data from C57BL/6J mice indicate that the low-dose stimulant properties of EtOH can be dissociated from the anxiolytic action of the drug in the plus-maze task. Finally, although INDO did not antagonize the stimulant effect of EtOH in the plus-maze task (in CD-1 mice), it did attenuate EtOH-induced stimulation of locomotor activity in an open-field arena. Taken together, these results suggest some specificity with regard to the role of PGs in mediating (or modulating) the neurobehavioral actions of EtOH, and further support the notion that the anxiolytic and stimulant effects of EtOH may be mediated by different mechanisms.

Effect of anxiolytics and antidepressants on extinction and negative contrast

Anxiolytics, particularly the benzodiazepines and barbiturates tend to retard, but not prevent, extinction, promote recovery from negative contrast, and elevate S- responding in discrimination training. Anxiolytics, administered during acquisition, tend to eliminate the partial reinforcement extinction effect, but this result is substantially influenced by parametric considerations. Behaviors that are energized in extinction may have a different pharmacological profile than behaviors that decline. Conclusions regarding the effects of antidepressants must be more tentative but, in general, acutely administered antidepressants are relatively ineffective in all of these paradigms. However, antidepressants may enhance the efficiency of responding on DRL schedules whereas anxiolytics tend to disrupt such behavior.

Rats (Rattus norvegicus) selectively bred to differ in avoidance behavior also differ in response to novelty stress, in glycemic conditioning, and in reward contrast

The behavior of the Syracuse high avoidance (SHA) and Syracuse low avoidance (SLA) rats, selectively bred by Brush (F. R. Brush, J. C. Froehlich, & P. Sakellaris, 1979, Behavior Genetics, 9, 309-316) to differ in avoidance behavior, was examined in several different tasks. The SLA rats showed a greater elevation in plasma glucose when exposed to a novel environment; after 7 days of exposure to this environment there was evidence of habituation in the SHA rats but not in the SLA rats; the SHA rats showed a hyperglycemic conditioned response in a glycemic conditioning procedure, the SLA rats showed no evidence of conditioning but had higher overall levels of plasma glucose; both strains showed reliable successive negative contrast effects in consummatory behavior when shifted from 32 to 4% sucrose, but the contrast was larger in the SLA rats; the administration of chlordiazepoxide eliminated negative contrast in the SLA rats but had no effect on contrast in the SHA rats; and the SLA rats were reliably heavier than the SHA rats. The behavioral differences were considered in the context of differences in emotional reactivity between the two strains.

Effect of clonidine on consummatory negative contrast and on novelty-induced stress

In Experiments 1 and 1a rats were shifted from 32% to 4% sucrose solutions. The resultant negative contrast effect in consummatory behavior was not alleviated by clonidine (3.12, 6.25, 12.5, 25.0 and 50.0 micrograms/kg). The lower dose of the drug had no effect on behavior, the higher doses reduced consumption in shifted and unshifted rats in a dose dependent fashion. In Experiment 2 clonidine (6.25, 12.5 micrograms/kg) raised plasma glucose levels in a dose dependent fashion when the animals were exposed to a novel environment. These results are at variance with those obtained with chlordiazepoxide (and other anxiolytics in the case of contrast effects) and suggest limits on the degree to which clonidine can be considered to function as an anxiolytic.

The effects of morphine in the consummatory contrast paradigm

Rats shifted from 32% to 4% sucrose show a negative contrast effect, licking significantly less than animals that receive only 4% sucrose. The effects of morphine sulfate (0.5, 1.0, 2.0, 4.0, 8.0, and 16.0 mg/kg) on negative contrast were investigated in four experiments. Contrast was reduced on both the 1st and 2nd postshift day by the 4.0 and 8.0 mg/kg doses, but the effects were less robust than those seen with the benzodiazepines. The effects of morphine on contrast were dissociable from simple increases in sucrose consumption. Naloxone (0.25, 0.5, and 1.0 mg/kg) had no effect on contrast or sucrose intake. However, the contrast-reducing effect of morphine (4.0 mg/kg) was blocked by pretreatment with naloxone (0.50 mg/kg). The results are discussed in terms of other anxiolytic screening paradigms that have obtained "partial anxiolytic effects" using morphine.

Effects of benzodiazepines on acquisition and performance: a critical assessment

Evidence related to the effects of benzodiazepines on learning and memory is reviewed in the contexts of human verbal learning studies and animal studies using both aversive and non-aversive paradigms. While the impairment of acquisition by benzodiazepines appears to be a robust phenomenon generalizing across species and experimental conditions, the impairment in the performance of an already-learned task by such drugs appears to be more restrictive and highly dependent upon experimental contingencies. Thus far, performance impairment appears to be found mainly in animal studies using non-aversive, food-motivated tasks, with such tasks being particularly well suited for investigating such a phenomenon. At present, there is a noticeable lack of knowledge regarding the neurochemical substrates underlying BDZ-induced impairment. Finally, some issues that may contribute to the presence or absence of a BDZ-induced performance impairment in published studies are briefly considered.

Comparison of the effects of the benzodiazepine midazolam and three serotonin antagonists on a consummatory conflict paradigm

A consummatory conflict procedure that involves an abrupt reduction in magnitude of an expected reward (negative contrast) has been shown to be particularly sensitive to the effects of anxiolytic agents. As previously reported with chlordiazepoxide, another benzodiazepine (BDZ), midazolam released suppressed consummatory performance in a dose-dependent manner. This effect was not due to a general appetitie stimulatory effect of the drug. The effects of three 5-HT antagonists on negative contrast were examined to evaluate the role serotonin may play in the anxiolytic action of BDZ. Methysergide was found to be ineffective, cinanserin tended to reduce contrast at two intermediate doses, and cyproheptadine eliminated the contrast effect in a similar fashion as midazolam. The effectiveness of cyproheptadine may not be attributed to its anticholinergic or antihistaminergic actions since scopolamine and pyrilamine did not produce similar effects. The results are discussed in terms of the role serotonin may play in the anti-conflict action of BDZ, as well as possible interactional effects of GABA.

Effects of chlordiazepoxide on novelty-induced hyperglycemia and on conditioned hyperglycemia

Moving rats from their home cages to a different environment for a twenty minute period tended to raise plasma glucose levels (PGLs). In general, the more different the novel environment was from the housing condition, the greater the rise in PGL. Stimulus contexts that have led to conditioned hyperglycemia in previous experiments caused a larger rise in PGLs than stimulus contexts that led to conditioned hypoglycemia in previous experiments. These glycemic effects of environmental novelty did not habituate across seven exposure periods. Experiment 2 showed that chlordiazepoxide (CDP) reduced PGLs in animals transported to novel environments. Experiment 2 also showed that conditioned hyperglycemia occurred when insulin was administered in the environment that led to the highest PGLs in Experiment 1, and that conditioned hypoglycemia occurred in this same environment when the animals were regularly pretreated with CDP. Administering insulin in an environment that did not initially elicit a large rise in PGL resulted in a tendency towards conditioned hypoglycemia that was not influenced by CDP.

Chlordiazepoxide and ethanol additively reduce gustatory negative contrast

Negative contrast that occurs when rats are shifted from 32% to 4% sucrose has been shown to be reduced by chlordiazepoxide (CDP) and ethanol (ETOH). In a previous experiment, doses of 0.75 and 1.0 g/kg ETOH substantially reduced contrast while doses of 0.25 and 0.5 g/kg ETOH were much less effective. In this study, doses of 6 and 8 mg/kg CDP were shown to attenuate the negative contrast effect while smaller doses (2 and 4 mg/kg) influenced contrast to a lesser degree. Evidence for an additive effect of CDP and ETOH on contrast reduction was obtained when 4 mg/kg CDP and 0.5 g/kg ETOH were administered together.