Effects of benzodiazepine receptor ligands on the ingestion of sucrose, intralipid, and maltodextrin: An investigation using a microstructural analysis of licking behavior in a brief contact test.

Microstructural analysis of licking behavior in the rat was conducted (a) to describe in detail the characteristics of benzodiazopine-induced changes in ingestion and (b) to determine if the changes are consistent with an alteration in palatability. The effects of the benzodiazepine receptor (BZR) agonist midazolam (0.3–3 mg/kg), and the partial inverse agonist Ro 15-4513 (0.3–3 mg/kg), on licking for several concentrations of sucrose, Intralipid, and maltodextrin in a brief contact test were investigated. Midazolam increased the total number of licks for all 3 fluids; conversely, Ro 15-4513 decreased the total number of licks. Midazolam increased mean bout duration for sucrose and maltodextrin drinking and there was a trend toward a similar effect with Intralipid drinking. Ro 15-4513 reduced mean bout duration for all 3 test fluids. These data are discussed in terms of bidirectional changes in fluid palatability by drug actions at BZRs. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Benzodiazepine-GABA modulation of concurrent ethanol and sucrose reinforcement in the rat.

These experiments examined the role of the benzodiazepine (BZ)-GABA receptor complex in modulating ethanol consumption in rats. Lever presses were reinforced with concurrently available, isocaloric solutions: 10% ethanol-10% sucrose and 24% sucrose. Both reinforcers were available on independent, variable-interval 5-s schedules of reinforcement. In baseline sessions, rats earned approximately 110 sucrose reinforcers and 131 ethanol-sucrose reinforcers, equivalent to about 2 g ethanol per kilogram of body weight. Before experimental sessions, rats received injections of Ro 15-4513, Ro 15-1788, and Ro 15-4513 in combination with Ro 15-4513, chlordiazepoxide, picrotoxin, baclofen, and muscimol. Responding for the ethanol solution was significantly and selectively reduced by the BZ inverse agonist Ro 15-4513, and this effect was blocked by administration of the BZ antagonist Ro 15-1788. Conversely, responding for the ethanol solution increased following a low dose of the BZ agonist chlordiazepoxide. A low dose of baclofen significantly decreased responding for sucrose and increased consumption of ethanol. Picrotoxin and muscimol selectively reduced responding for the ethanol solution. These results are discussed in terms of the relationship between the BZ-GABA receptor complex and ethanol consumption. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Attenuation of the discriminative stimulus effects of ethanol by the benzodiazepine partial inverse agonist Ro 15-4513

The aim of the present study was to investigate whether ethanol training affects the ability of Ro 15-4513 to block the discriminative stimulus effects of ethanol dose differentially. Three different groups of rats were trained to discriminate 1.0 g/kg ethanol (n = 8), 1.5 g/kg ethanol (n = 7) or 2.0 g/kg ethanol (n = 8) from water in a two-lever, food-reinforced procedure. Ethanol and water were administered by gavage 20 min before the onset of the session. When the discrimination performance was stable, rats were pretreated with Ro 15-4513 (1-17 mg/kg; i.p.) 5 min before the administration of ethanol. Ro 15-4513 attenuated the discriminative stimulus effects of 1.0 and 1.5 g/kg ethanol but not 2.0 g/kg ethanol in each of the ethanol training groups. Overall, blockade of the discriminative stimulus effects of 1.0 and 1.5 g/kg ethanol by 5.6 mg/kg Ro 15-4513 occurred without significantly altering response rates or blood ethanol concentrations. A decrease in blood ethanol concentration was, however, found with 17 mg/kg Ro 15-4513 in combination with 2.0 g/kg ethanol. These results suggest that the benzodiazepine partial inverse agonist, Ro 15-4513, can attenuate the discriminative stimulus effects associated with low to moderate doses of ethanol (1.0-1.5 g/kg).     

Altered expression of bcl-2 and bax mRNA in amyotrophic lateral sclerosis spinal cord motor neurons

This study investigated the ability of the benzodiazepine inverse agonist, Ro 15-4513, to alter the expression of physical dependence on pentobarbital. Male Sprague-Dawley rats were made physically dependent on pentobarbital by continuous. IP, infusion of escalating doses of pentobarbital for 12 days. In Experiment 1, pentobarbital dependent rats received either vehicle or Ro 15-4513, in doses of 5, 10, or 15 mg/kg, IP, periodically during the pentobarbital abstinence period. As expected, Ro 15-4513 produced a significant, dose-dependent, exacerbation of withdrawal signs in the pentobarbital dependent rats. In Experiment 2, either vehicle or Ro 15-4513, at a dose of 15 mg/ kg, was administered, IP, once daily during the 12 days of continuous pentobarbital infusion. During the subsequent pentobarbital abstinence period it was noted that the withdrawal signs were significantly reduced in the rats receiving the daily administration of Ro 15-4513. It is hypothesized that the benzodiazepine inverse agonist, Ro 15-4513, may inhibit the development of physical dependence on pentobarbital through an opposing action on the GABA-A receptor.     

Effects of buprenorphine and Ro 15-4513 on delayed death and brain beta-endorphin levels in rats treated with cocaine or cocaine-ethanol

The present study was aimed at elucidating the relationship between brain beta-endorphin, which was estimated by the immunofluorescence method, and fatal drug toxicities due to cocaine and combined cocaine-ethanol administration, including the late fatal toxicities clinically noted. beta-endorphin is an endogenous opioid peptide, and its secretion has been suggested to be influenced by physiological stresses. Furthermore, since protection against these fatal toxicities has been previously reported to be provided by buprenorphine (a ligand for opioid receptors) and Ro 15-4513 (a ligand for benzodiazepine receptors), this study also focused on the relationship between the effects of these two ligands and the changes in brain beta-endorphin immunoreactivity. In the fatal toxicity study, a toxic dose (75 mg/kg, i.p.) of cocaine combined with and without ethanol (3 g/kg, i.p.) was administered to the rats, with and without buprenorphine (0.25, 0.5, 1 mg/kg, i.p.) or Ro 15-4513 (5, 10, 15 mg/kg, i.p.). All of the deaths that occurred in these animals were divided into two groups: early deaths with early toxic symptoms in which the drugs were detected in the tissue samples, and late deaths with late toxic symptoms in which no drugs were detected in the samples. Without the administration of buprenorphine or Ro 15-4513, the frequency of late deaths was higher in the cocaine group as compared to the cocaine-ethanol group. The total mortality rate was effectively attenuated by treatment with 0.25 mg/kg buprenorphine or 10 mg/kg Ro 15-4513. Following treatment with 1 mg/kg buprenorphine or 15 mg/kg Ro 15-4513, the frequency of late deaths was significantly enhanced in the cocaine group. The brain and liver cocaethylene concentrations were also attenuated in those groups in which the total mortality rates were attenuated. In the brain beta-endorphin immunoreactivity study, the number of beta-endorphin immunoreactive nerve cells at the arcuate nucleus was counted at 3 minutes or 24 hours after the drug treatment. At 3 minutes after the drug treatment, the number of weakly immunoreactive cells with photographic light absorption values greater than 50% was enhanced in the groups in which the frequency of late deaths had been increased. In the cocaine-ethanol groups treated with buprenorphine or Ro 15-4513, this enhancement of weakly immunoreactive cells was observed when the total mortality rate was increased, regardless of the type of death. At 24 hours after the drug treatment (50 mg/kg cocaine), an enhancement of the weakly immunoreactive cells only was observed in all of the groups in which the occurrence of toxicities had been enhanced, regardless of the type of toxicity. Therefore, it can be concluded that the enhancement of total brain beta-endorphin immunoreactivity was closely correlated with the increase in the frequency of total fatal toxicities, and that the enhancement of weakly immunoreactive cells was closely correlated with the increase in the frequency of delayed fatal toxicities.     

From contrast to reinforcement: Role of response contingency in anticipatory contrast.

Intake of a 0.15% saccharin solution is suppressed if access to the saccharin is followed by access to 32% sucrose in brief daily pairings. The present series of four experiments was concerned with factors that lead to this anticipatory contrast effect (suppressed saccharin intake) rather than a reinforcement effect. In Experiment 1, anticipatory contrast was obtained with an autoshaping procedure (no lick requirement on the initial tube), and degree of contrast did not vary as a function of intersolution interval in the range of 0–25 s. Experiments 2 and 3 showed that requirements of 10, 100, 200, or 400 licks on the first tube available led to a reinforcement effect in latency, but a requirement of 0 licks (autoshaping procedure) led to a contrast effect in licks and latency. In Experiment 4, a group with a 200-contingent-lick requirement showed a reinforcement effect in latency, but a group yoked to this contingent group showed a contrast effect in both latency and licks. Overall, the results suggest that anticipatory contrast occurs under conditions of a "relaxed" instrumental contingency. The data are discussed in terms of control of behavior by stimulus–stimulus, response–stimulus, and stimulus–response associations, and the results are related to behavioral contrast, to flavor–outcome associations, and to "misbehavior" produced by Pavlovian-instrumental interactions. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Identification of a unique domain in bovine brain GABAA receptors that is photoaffinity labelled by [3H]Ro15-4513

We have used photoaffinity labelling and protein cleavage techniques to identify the site of photoincorporation of [3H]Ro15-4513 into the alpha subunit of the bovine gamma-aminobutyric acid type A (GABAA) receptor. Bovine brain membranes were photoaffinity labelled with [3H]Ro15-4513 and after solubilization and denaturation, proteins were specifically cleaved at either cysteine or tryptophan residues. Peptides were resolved by sodium dodecyl sulphate polyacrylamide gel electrophoresis. Cleavage at cysteine residues generated a labelled peptide of Mr 6.5K, while cleavage at tryptophan residues generated a labelled peptide with an Mr of 5K. Cleavage products of this size indicate that the site of [3H]Ro15-4513 incorporation occurs between the end of the first transmembrane domain and the first four amino acids of the third transmembrane domain (residues 247-289). This region of the GABAA receptor has not previously been implicated in the formation of the benzodiazepine binding site and may be part of a unique recognition domain for inverse agonists.     

Determination of the absolute configuration of sugar residues using gas chromatography. Method with potential for elimination of references

The effects of the benzodiazepine receptor antagonist flumazenil (Ro 15-1799), the benzodiazepine receptor partial inverse agonist Ro 15-4513 and the benzodiazepine receptor inverse agonist beta-CCM on the behaviour of control and small platform stressed mice studied. Small platform stress was induced by placing the animals on small platforms (d = 3.5 cm) surrounded by water for 24 hours. This technique involves several factors of stress such as rapid eye movement sleep-deprivation, isolation, immobilization, falling into the water and soaking. In the plus-maze test small platform stress induced changes indicating anxiolytic action-an increase of the percentage of entries made onto and the percentage of time spent on the open arms. In control mice flumazenil (2.0 and 10.0 mg/kg), Ro 15-4513 (0.5; 1.0; 2.5; 5.0 and 10.0 mg/kg), and beta-CCM (1.0 and 2.0 mg/kg) exerted dose-dependent anxiogenic effect. The small platform stress induced an enhancement of the anxiogenic effect of flumazenil, but not that of Ro 15-4513 and beta-CCM. The selective enhancement of flumazenil's action may be explained with the mode of action of flumazenil. It is proposed that small platform stress causes changes in the concentration of the endogenous benzodiazepine receptor ligand with stress protective activity and flumazenil acts by blocking the effects of this endogenous ligand.     

Negative anticipatory contrast and preference conditioning: Flavor cues support preference conditioning, and environmental cues support contrast.

In 2 experiments, access to a .15% saccharin solution was followed on alternating days by access to a 32% sucrose solution and the same saccharin solution. In Exp 1, rats increased both intake of and preference for a flavored saccharin solution that predicted sucrose, but neither effect was found using a predictive odor cue alone. Exp 2 replicated the predictive flavor results but showed suppression of saccharin intake when environmental cues predicted sucrose. When both flavor and environment predicted sucrose, saccharin intake did not change, but preference for the predictive flavor increased. Discriminative taste cues appear to facilitate the development of preference conditioning, but environmental cues favor negative anticipatory contrast effects. Also, preference conditioning and contrast may develop concurrently and compete for expression. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Decremental carryover effects of sucrose ingestion in the negative anticipatory contrast procedure in rats.

To test for retrospective effects of sucrose ingestion in the anticipatory contrast procedure, 4 experiments examined intake of an initial 0.15% saccharin solution as a function of the unsignaled interspersing of days in which the 2nd solution was 32% sucrose or 0.15% saccharin. In Experiment 1, rats that received alternating saccharin-saccharin days and saccharin-sucrose days drank less saccharin on saccharin-only days, and on both days they drank less saccharin than a control group that received saccharin only. In Experiment 2, rats that received randomized saccharin-saccharin and saccharin-sucrose days drank less saccharin if, and only if, a sucrose day preceded. Experiments 3 and 4 used double and quadruple alternation of saccharin and sucrose days to examine persistence of the effects of a sucrose day. The results highlighted a retrospective carryover effect of sucrose that reduced intake of the initial saccharin solution and apparently was based on sucrose memories persisting over days. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Anticipation of future food: Suppression and facilitation of saccharin intake depending on the delay and type of future food.

A series of studies examined the (Sprague-Dawley) rat's tendency to suppress intake of .15% saccharin when it was followed by a second food after 4-, 16-, or 32-min delays. The second foods examined were 32% sucrose, 64% sucrose, lab chow, a Nutrasweet solution, skim milk, and chocolate milk. Saccharin intake was influenced by both the delay and the specific food available. Subsequent analysis showed that saccharin intake before the 4-min delay was an inverse function of the caloric value of the second food. However, saccharin intake before the 16-min delay was better predicted as an inverse function of the hedonic value of the second food. The results suggest that the caloric and hedonic values of a food may influence food selection across different time courses, and that the effective time horizon for the sequential comparison of foods depends on the specific foods that are compared. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Posttrial hippocampal, amygdaloid, and lateral hypothalamic electrical stimulation: Effects on short- and long-term memory of an appetitive experience.

52 Long-Evans male water-deprived rats were given 150 licks of a 10% sucrose solution, followed 4 sec later by 30 sec of low-intensity electrical brain stimulation applied in the dorsal hippocampus, amygdala, or lateral hypothalamus. Retention of the licking experience was then tested either 90 sec of 24 hrs after the lick experience by measuring the number of licks taken on an empty drinking tube. Ss that received hippocampal stimulation licked the empty tube less than the 17 controls did during the 24-hr, but not during the 90-sec, retention test. Data suggest that the hippocampus may be critically involved in processes (e.g., consolidation) mediating long-term, but not short-term, memory. Compared with controls, Ss that received amygdala stimulation did not exhibit any changes in licking at either retention test. Ss given lateral hypothalamic stimulation showed more licking compared with controls during the 90-sec, but not the 24-hr, test. Subsequent tests suggest that facilitation of short-term memory may have been influenced by stimulation-induced motivational changes. (20 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Benzodiazepine receptor ligands are elevated in an animal model of hepatic encephalopathy: relationship between brain concentration and severity of encephalopathy

Elevated levels of benzodiazepine receptor agonists are found in both animal models of hepatic encephalopathy and in humans with this syndrome. The present study investigated the relationship between agonist levels and the severity of the encephalopathy, as well as the potential reversibility of the syndrome by benzodiazepine receptor antagonists. The concentrations of benzodiazepine receptor ligands in rat brains were measured at several intervals during the induction of liver failure with thioacetamide. Six hours after the first dose of thioacetamide, brain concentrations of benzodiazepine receptor ligands were increased and open field activity decreased compared to control rats. However, the brain concentrations of benzodiazepine receptor ligands correlated better with the stage of hepatic encephalopathy than time after initiation of thioacetamide treatment. The benzodiazepine receptor ligands Ro 15-3505, Ro 15-4513 and CGS-8216 ameliorated motor abnormalities in rats with stage 3 hepatic encephalopathy. Only Ro 15-3505 improved motor activity in rats in stage 2 encephalopathy to levels observed in rats with stage 1 encephalopathy. Furthermore, although Ro 15-4513 and CGS 8216 significantly increased motor activity in stage 4 hepatic encephalopathy, this may reflect their partial inverse agonist properties. These findings support the hypothesis that increased brain levels of benzodiazepine receptor agonists contribute to the severity of hepatic encephalopathy and suggest that high-affinity benzodiazepine receptor antagonists are efficacious in reversing this syndrome.     

Inactivation of the median raphe nucleus increases intake of sucrose solutions: A microstructural analysis.

Previous studies have shown that microinjections of the GABA-A agonist muscimol into the median raphe nucleus (MR) result in large increases in the intake of solid foods. In the current study, we used microstructural techniques to characterize the effects of intra-MR muscimol injections on the consumption of either a 0.05 M or a 0.29 M sucrose solution. After injections of either saline or muscimol, animals consumed more of the 0.29 M than the 0.05 M solution, an effect which resulted primarily from increases in the initial rate of consumption with no change in the rate at which licking decayed across the test session. In contrast, intra-MR muscimol injections had little effect on the initial licking rate, but greatly increased meal duration, indicating that this treatment affected ingestion in a different way than did altering the sucrose concentration. Muscimol injections produced a significantly larger increase in the intake of the 0.29 M than of the 0.05 M solution. Intra-MR muscimol injections did not alter the within burst rate of licking, suggesting that they did not affect the functioning of the licking pattern generator. In contrast, these injections did increase the number of licks contained within “clusters,” that is groups of licks separated from each other by intervals of more than 0.5 sec. These findings show that inactivation of the MR produces a powerful effect on the intake of liquid diets, and that the nature of this effect is different from that produced here by changes in sucrose concentration and from those reported after pharmacological manipulations of a number of other brain systems. We additionally discuss several theoretical issues arising in the interpretation of microstructural data. (PsycINFO Database Record (c) 2011 APA, all rights reserved)     

Chronic morphine treatment exaggerates the suppressive effects of sucrose and cocaine, but not lithium chloride, on saccharin intake in Sprague-Dawley rats.

Three experiments examined the effect of chronic morphine treatment on cocaine-, sucrose-, and lithium chloride (LiCl)-induced suppression of saccharin intake in Sprague-Dawley rats. All rats were either water- or food-deprived and then implanted subcutaneously with 1 morphine (75 mg) or vehicle pellet for 5 days. They were then given brief access to 0.15% saccharin and soon thereafter injected with either cocaine (10 mg/kg sc) LiCl (0.009 M, 1.33 ml/100 g body weight ip), or saline, or in Exp 2, given a 2nd access period to either a preferred 1.0 M sucrose solution ot the same 0.15% saccharin solution. There was 1 taste–drug or taste–taste paring per day for a number of days. The results showed that a history of chronic morphine treatment exaggerated the suppressive effects of a rewarding sucrose solution and cocaine but not those of the aversive agent, LiCl. These data provide further support for the reward compairison hypothesis. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Gustatory thalamus lesions eliminate successive negative contrast in rats.

Neurologically intact rats expecting to receive a high-value reward (1.0 M sucrose), licked less for an unexpected low-value reward (0.15% saccharin) than did control subjects that only received the saccharin solution. This reward comparison effect, termed successive negative contrast, was eliminated after bilateral electrolytic lesions of the gustatory thalamus. The results are discussed in terms of disrupted memory processes that may have rendered the lesioned rats incapable of computing the relative reward value of the available solution (0. 15% saccharin) with respect to the memory of the preferred solution (1.0 M sucrose). (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Experiences of 23 patients > or = 90 years of age treated with radiation therapy

Previous studies showed that the 5-HT2 receptor antagonist, amperozide, is somewhat more potent than the opiate antagonist, naltrexone, in reducing alcohol drinking in high alcohol-preferring (P) rats. The purpose of this study was to determine in the P rat whether the effect of either drug could be due, in part, to an alteration in gustatory function. In an unlimited, 24-h free choice paradigm, P rats were offered water simultaneously with either a highly palatable 0.1% saccharin solution or a 1:4 dilution of Nestlé Sweet Success chocolate drink. Throughout all phases of the study, the P rats always consumed significantly greater volumes of the chocolate drink than of the saccharin solution, i.e., 526 ml/kg vs. 181 ml/kg, respectively. Successive 12-day experimental periods consisted of three phases: a 4-day predrug control interval; 4 days of administration of saline control vehicle or either drug; and a final 4 day postdrug interval. In a counterbalance design, saline, amperozide (1.0 or 5.0 mg/kg) or naltrexone (2.5 or 5.0 mg/kg) was administered subcutaneously twice daily at 1600 and 2200 h for 4 days. Amperozide and naltrexone significantly reduced the drinking of chocolate in a dose-dependent manner. Conversely, only the two higher doses of amperozide and naltrexone decreased the intake of saccharin significantly. Thus, these findings suggest that different populations of central serotonin and opioid receptors concurrently underpin, in part, the preferences for both palatable and/or nutrient fluids. Finally, because both the opiate and 5-HT2A antagonists reduce the ingestion of saccharin and chocolate solutions differentially, it is apparent that preferences for alternative palatable fluids should be examined when candidate drugs are screened for suppressing alcohol drinking and ultimately the treatment of alcohol abuse.     

Disruption of conditioned taste aversion in the rat by stimulation of amygdala: A conditioning effect, not amnesia.

Conducted 2 experiments with a total of 143 male Wistar rats to determine whether the disruption of conditioned taste aversion by amygdaloid brain stimulation (BST) during conditioning could be attributed to the stimulus properties of the BST. In Exp I, Ss receiving BST (a) while drinking saccharin, (b) during the onset of LiCl toxicosis, or (c) in the interval between taste exposure and toxicosis drank significantly more saccharin solution during a 48-hr retest than implanted or unoperated controls receiving similar taste–toxicosis pairings. In contrast, Ss receiving BST during both conditioning and retention trials developed a strong conditioned aversion. Exp II confirmed that BST formed a compound with the taste of the saccharin solution. A small but significant aversion was displayed by groups exposed to BST plus taste during conditioning and to either taste alone or BST alone during the retest. Again, the group presented with BST and taste prior to and following LiCl toxicosis displayed a strong conditioned aversion. Results suggest that disruption of conditioned taste aversion with amygdaloid BST represents a conditioning effect, not amnesia. (31 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Ovariectomy and estradiol affect postingestive controls of sucrose licking

Ovariectomy (OVX) has been shown to increase, and estradiol replacement to decrease, meal size in rats. Because little is known about how estradiol influences meals, we conducted two experiments to examine the effects of OVX and beta-estradiol 3-benzoate (EB) replacement on the microstructure of licking behavior. In both experiments, patterns of licking were analyzed in adult female Sprague-Dawley rats during an 0.8 M sucrose test meal. In Experiment 1, meal microstructure was determined preOVX and 10-12 days postOVX. Rate of licking following OVX was not changed during min 1 of the meal, but was significantly faster during min 2-4 of the meal (p < 0.03). The numbers of bursts (runs of licks separated by 250-500 ms) and numbers of clusters (runs of licks separated by > 500 ms) were significantly increased during min 2-4 (p < 0.05). In Experiment 2, OVX rats received EB replacement. Rate of licking after EB replacement was not changed during min 1 of the meal, but was significantly slower during the remainder of the meal (min 2-4, min 5-7, and min 8-10). Burst size, cluster size, and interburst interval were less after EB replacement during min 5-7 of the test meal (all p < 0.05). Because both OVX and EB replacement failed to alter the rate of licking during min 1, estrogen did not appear to alter the palatability of sucrose. OVX and EB replacement did appear to affect a postingestive mechanism(s) that is engaged within 2-4 min of meal onset.     

Sucrose-water preference reversal in the water-deprived rat.

Exposed 4 water-deprived male albino Carworth rats to each of 3 preference conditions. When given a 15-min preference test between a 7.4% sucrose solution and water, Ss ingested 81-91% of their total fluid intake from the sucrose bottle. When given a choice between 1 lick of water and 1 lick of the sucrose solution, Ss consistently preferred water. To determine if this water preference was related to dehydration, Ss were allowed to drink water immediately before the 1-lick preference test. In general, water preference was inversely proportional to amount of pretest drinking. (PsycINFO Database Record (c) 2010 APA, all rights reserved)