Bidirectional changes in the consumption of food produced by beta-carbolines

GABA(A) receptor modulation during adolescence alters adult ethanol intake and preference in rats

BACKGROUND

To address the hypothesis that GABA(A) receptor modulation during adolescence may alter the abuse liability of ethanol during adulthood, the effects of adolescent administration of both a positive and negative GABA(A) receptor modulator on adult alcohol intake and preference were assessed.

METHODS

Three groups of adolescent male rats received 12 injections of lorazepam (3.2 mg/kg), dehydroepiandrosterone (DHEA, 56 mg/kg), or vehicle on alternate days starting on postnatal day (PD) 35. After this time, the doses were increased to 5.6 and 100 mg/kg, respectively, for 3 more injections on alternate days. Subjects had access to 25 to 30 g of food daily, during the period of the first 6 injections, and 18 to 20 g thereafter. Food intake of each group was measured 60 minutes after food presentation, which occurred immediately after drug administration on injection days or at the same time of day on noninjection days. When subjects reached adulthood (PD 88), ethanol preference was determined on 2 separate occasions, an initial 3-day period and a 12-day period, in which increasing concentrations of ethanol were presented. During each preference test, intake of water, saccharin, and an ethanol/saccharin solution was measured after each 23-hour access period.

RESULTS

During adolescence, lorazepam increased 60-minute food intake, and this effect was enhanced under the more restrictive feeding schedule. DHEA had the opposite effect on injection days, decreasing food intake compared with noninjection days. In adulthood, the lorazepam-treated group preferred the 2 lowest concentrations of ethanol/saccharin more than saccharin alone compared with vehicle-treated subjects, which showed no preference for any concentration of ethanol/saccharin over saccharin. DHEA-treated subjects showed no preference among the 3 solutions.

CONCLUSIONS

These data demonstrate that GABA(A) receptor modulation during adolescence can alter intake and preference for ethanol in adulthood and highlights the importance of drug history as an important variable in the liability for alcohol abuse.

Pharmacology of the beta-carboline FG-7,142, a partial inverse agonist at the benzodiazepine allosteric site of the GABA A receptor: neurochemical, neurophysiological, and behavioral effects

Given the well-established role of benzodiazepines in treating anxiety disorders, beta-carbolines, spanning a spectrum from full agonists to full inverse agonists at the benzodiazepine allosteric site for the GABA(A) receptor, can provide valuable insight into the neural mechanisms underlying anxiety-related physiology and behavior. FG-7,142 is a partial inverse agonist at the benzodiazepine allosteric site with its highest affinity for the alpha1 subunit-containing GABA(A) receptor, although it is not selective. FG-7,142 also has its highest efficacy for modulation of GABA-induced chloride flux mediated at the alpha1 subunit-containing GABA(A) receptor. FG-7,142 activates a recognized anxiety-related neural network and interacts with serotonergic, dopaminergic, cholinergic, and noradrenergic modulatory systems within that network. FG-7,142 has been shown to induce anxiety-related behavioral and physiological responses in a variety of experimental paradigms across numerous mammalian and non-mammalian species, including humans. FG-7,142 has proconflict actions across anxiety-related behavioral paradigms, modulates attentional processes, and increases cardioacceleratory sympathetic reactivity and neuroendocrine reactivity. Both acute and chronic FG-7,142 treatment are proconvulsive, upregulate cortical adrenoreceptors, decrease subsequent actions of GABA and beta-carboline agonists, and increase the effectiveness of subsequent GABA(A) receptor antagonists and beta-carboline inverse agonists. FG-7,142, as a partial inverse agonist, can help to elucidate individual components of full agonism of benzodiazepine binding sites and may serve to identify the specific GABA(A) receptor subtypes involved in specific behavioral and physiological responses.

Effects of GABA modulators on the repeated acquisition of response sequences in squirrel monkeys

The present study investigated the effects of positive and negative GABA(A) modulators under three different baselines of repeated acquisition in squirrel monkeys in which the monkeys acquired a three-response sequence on three keys under a second-order fixed-ratio (FR) schedule of food reinforcement. In two of these baselines, the second-order FR schedule and the discriminative stimuli for the response sequence were manipulated ("chain-strained" and "tandem-strained"). In the third baseline condition, response-independent tail shock was presented during acquisition of the response sequence. All of these baselines maintained high error levels and produced slow rates of acquisition. Under both the chain-strained and tandem-strained conditions, the positive GABA(A) modulator triazolam (0.0032-0.1 mg/kg) and the negative GABA(A) modulators beta-CCE (ethyl-beta-carboline-3-carboxylate; 0.01-1 mg/kg), beta-CCM (methyl-beta-carboline-3-carboxylate; 0.0032-0.1 mg/kg), and FG-7142 (methyl-beta-carboline-3-carboxamide; 0.18-10 mg/kg) dose-dependently decreased overall response rate compared to administration of saline (control). Under the same two conditions, triazolam and the negative GABA(A) modulators also increased the percentage of errors; however, the effects on accuracy frequently depended on the baseline condition and the particular modulator. In contrast, triazolam only decreased errors and enhanced acquisition in the presence of concurrent response-independent tail shock when compared to saline administration under this condition. The neutral GABA(A) modulator, flumazenil (1 mg/kg), had no effect on rate or accuracy of responding when administered alone, but antagonized the rate-decreasing and error-increasing effects produced by the negative GABA(A) modulators. Together, these data suggest that the effects of both the positive and negative GABAA modulators on acquisition can be similar in squirrel monkeys (i.e., both types of modulator may produce rate-decreasing and error-increasing effects) and that their effects on acquisition depend, in part, on the environmental conditions maintaining acquisition.

??CCM enhances retrieval of serial contextual but not of serial spatial memory in mice

The effects of inverse agonists of the gamma-aminobutyric acid (GABA)/benzodiazepine receptors such as beta-carboline-3-carboxylate (betaCCM) on retrieval processes have not been studied extensively. This study investigates the effects in mice of an acute betaCCM injection on retrieval of previously acquired serial discriminations, involving distinct contextual cues (Contextual Serial Discrimination, CSD) or identical cues (Serial Spatial Discrimination, SSD) in a four-hole board. Animals submitted to CSD were also evaluated for emotional reactivity in an elevated-plus maze. In both the CSD and the SSD tasks, mice were injected with saline before the learning session began. Twenty-four hours later, mice were replaced on the hole-board following a single dose of saline or betaCCM (0.5 mg/kg or 1.5 mg/kg) injected 20 min before testing. The highest dose of betaCCM improved performance of the first discrimination in the contextual task but not in the spatial task. Moreover, the higher dose of betaCCM produced anxiety-like reactivity in an elevated-plus maze, and scores of 'anxiety' were positively correlated with memory scores. Overall, the data show that the betaCCM enhancement of memory processes depends on: (1) the cues associated with the to-be-remembered information; and (2) the emotional effects of the drug.

Tryptophan-N-glucoside in fruits and fruit juices

In extracts prepared from various fruits as well as in fruit juices a single tryptophan glycoconjugate was detected by HPLC-MS analysis. Product ion spectra demonstrated the N-glycosidic linkage of a hexose moiety to the indole nitrogen. For structure elucidation, the novel tryptophan glycoside was isolated from pear juice and identified as N(1)-(beta-D-glucopyranosyl-(4)C(1))-L-tryptophan by (1)H, HH-COSY and (13)C NMR spectroscopy. Finally, we disclosed the biosynthetic origin of the novel tryptophan metabolite by demonstrating the enzymatic glycosylation of deuterium-labeled tryptophan, which was applied to pear fruit.

Effects of diazepam or chronic alcohol treatment on spatial reversal learning in mice

Mice submitted to chronic alcohol consumption (CAC; 11 months) or to systemic diazepam administration were trained in a spatial reversal learning task. Although CAC-treated mice were able to learn the initial acquisition at normal rates, they were impaired during the first reversal of the discrimination and subsequent reversal sessions. In contrast, diazepam administration induced no deficits for any behavioral measure. In conclusion, CAC, but not diazepam administration, induces an exaggerated sensitivity to proactive interference. The two treatments spared, however, the development of the learning set curve. These results are congruent with clinical data showing that nondeclarative or implicit forms of memory processes are spared in diazepam-treated subjects or in chronic alcoholics.

Food intake in Prader-Willi syndrome and controls with obesity after administration of a benzodiazepine receptor agonist

Benzodiazepine receptor (BZR) agonists, used extensively for their anxiolytic effects, have been shown to increase food intake in many mammalian species. Little information, however, is available on the effects of BZR agonists on feeding behaviors of humans. Food intake was evaluated in a 60-minute free-feeding standardized test after the acute administration of the BZR agonist chlordiazepoxide (CDP, Librium; 5 mg or 20 mg) or placebo. Subjects were 12 individuals with the Prader-Willi syndrome (PWS), a disorder characterized by extreme hyperphagia and morbid obesity, and 11 controls with obesity. PWS subjects showed the characteristic hyperphagia associated with the appetite disorder, consuming more than six times as many sandwiches as controls with obesity. Results revealed no significant effect of either dose of CDP on the food intake of either group. Serum assays revealed that dose-dependent, clinically effective levels of CDP and active metabolites were achieved. These results suggest that acute administration of the BZR agonist CDP, at the therapeutic levels used, may not increase food intake in populations with obesity. However, the chronic effects of CDP on appetite in human populations still need to be explored.

Benzodiazepine receptor ligands modulate ethanol drinking in alcohol-preferring rats

The effects of benzodiazepine receptor ligands with different intrinsic activity profiles were studied on voluntary ethanol consumption in the selectively bred alcohol-preferring AA (Alko, Alcohol) rat line, and compared to those of an opiate antagonist, naloxone, and a serotonin uptake inhibitor, citalopram. The rats were first allowed to develop a strong preference for 10% (v/v) ethanol solution in tap water over plain water until their ethanol consumption stabilized. Thereafter, the period when ethanol solution was available for the rats was gradually reduced to 4 h, 3 times a week, every second working day. The acute effects of positive allosteric modulators (agonists) of the gamma-aminobutyric acid type A (GABAA)/benzodiazepine receptor [midazolam, abecarnil, ethyl 5-benzyloxy-4-methoxymethyl-beta-carboline-3-carboxylate (ZK 91296), bretazenil, and 2,5-dihydro-2-(4-methylphenyl)-3H-pyrazolo[4,3-C]quinolin-3(5H)-on e (CGS 9895)] and of negative allosteric modulators [inverse agonists, ethyl 8-azido-5,6-dihydro-5-methyl-6-oxo-4H-imidazo[1,5- a][1,4]benzodiazepine-3-carboxylate (Ro 15-4513) and t-butyl 5,6-dihydro-5-methyl-6-oxo-4H-imidazo[1,5-a]thieno[2,3- f][1,4]diazepine-3-carboxylate (Ro 19-4603)] were tested after i.p. injections of three different drug doses using saline injections as a control treatment. The benzodiazepine agonists had rather modest effects on ethanol intake, measured 1 and 4 h after the injections, whereas the inverse agonists and naloxone strongly decreased ethanol consumption. Acute citalopram had no clear effect on ethanol drinking, but it slightly decreased the consumption of novel food during the 4-h session, as did all other benzodiazepine agonists except bretazenil. Neither the inverse agonists nor naloxone had any significant effect on food intake.(ABSTRACT TRUNCATED AT 250 WORDS)

"Anxiolytic" and "anxiogenic" benzodiazepines and beta-carbolines: effects on aggressive and social behavior in rats and squirrel monkeys

Ethopharmacological studies on the behavior of socially housed rats and squirrel monkeys were conducted to explore the role of the benzodiazepine GABAA-coupled ionophore receptor complex in aggressive and social interactions. Benzodiazepine receptor (BZR) antagonists, ZK 93426 (1-10 mg/kg) and flumazenil (3-10 mg/kg), the partial agonist, ZK 91296 (1-10 mg/kg) and the partial inverse agonists Ro 15-4513 (0.3-10 mg/kg), were administered to (1) squirrel monkeys prior to 1 h focal observations within established social groups or to (2) resident male rats before confrontations with a naive male intruder in their home cage for 5 min. Aggression was modified in a similar manner in both species, although squirrel monkeys were more sensitive to BZR challenges. Specifically, resident male rats showed dose dependent reductions in attack bites directed at intruder males that were significant at the highest dose of ZK 93426 (10 mg/kg). In squirrel monkeys, ZK 93426 (3 and 10 mg/kg) reduced aggressive grasps, threats and displays, as well as reducing the duration of being the target of aggression from untreated group members (1-10 mg/kg). The BZR partial agonist, ZK 91296 and the antagonist, flumazenil produced few effects on social behavior, low and high intensity aggression and motor activity in both species. Flumazenil (10-30 mg/kg) and ZK 91296 (10 mg/kg), but not ZK 93426, produced significant increases in foraging and feeding behaviors in squirrel monkeys. The hyperphagic effects of ZK 91296 and flumazenil, that are typical of BZR agonists compounds, were not observed in rats.(ABSTRACT TRUNCATED AT 250 WORDS)

Prevention of the pro-aggressive effects of alcohol in rats and squirrel monkeys by benzodiazepine receptor antagonists

Pharmacological manipulations at the benzodiazepine-GABAA-chloride ionophore receptor complex modify some of the behavioral and physiological actions of alcohol (ethanol). The interactions between alcohol, benzodiazepines and aggression were examined in similar ethopharmacological studies in squirrel monkeys and in rats in confrontations with conspecifics. Dominant male squirrel monkeys were tested (1) within their social groups, and (2) in dyadic confrontations with "rival" males from a different social group, and resident male rats were tested in their home cage in confrontations with an inexperienced male intruder. Low doses of alcohol (0.1-0.3 g/kg) increased aggressive behaviors in dominant squirrel monkeys and a subgroup of resident rats, whereas high doses of alcohol (1-3 g/kg) decreased aggression and produced marked motor incoordination. Individuals that showed alcohol-enhanced aggression were selected, and pretreated with benzodiazepine antagonists (flumazenil, ZK 93426) prior to alcohol administration. Both ZK 93426 (3 mg/kg) and flumazenil (10 mg/kg) blocked the aggression-enhancing effects of alcohol in dominant squirrel monkeys and resident rats in confrontations with conspecifics. Neither compound altered the reductions in aggression and increases in inactivity produced by high doses of alcohol. Interestingly, agonist-like increased feeding and inverse agonist-like reductions in social behaviors were observed simultaneously at the same dose of flumazenil, in the same individual and testing situation. ZK 93426 did not alter feeding but also reduced social behaviors. The two antagonists were also not equipotent in their interactions with alcohol. ZK 93426 reduced alcohol-induced motor incoordination in squirrel monkeys, whereas flumazenil did not. In fact, flumazenil potentiated the effects of low doses of alcohol.(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of the benzodiazepine receptor inverse agonist, DMCM, on the behaviour of mice: an ethopharmacological study

Ethopharmacological procedures and a two-compartment black and white test box were used to examine behavioural effects produced by the benzodiazepine receptor inverse agonist, methyl-6,7-dimethoxy-4-ethyl-beta-carboline-3-carboxylate (DMCM), when given by intraperitoneal injection (0.4 and 1.0 mg/kg) to pair-housed adult CD1 male mice. Control mice received injections of the solvent. Behaviour in the light-dark box was examined at 30 min after the injection and behaviour during encounters with an untreated group-housed male, in a neutral cage, was then assessed by ethological procedures. In dominant mice, aggressive behaviour was significantly reduced and the ratio of flight, relative to aggression received, was significantly increased by DMCM at 0.4 mg/kg. At 1 mg/kg but not 0.4 mg/kg, DMCM decreased time spent by dominant mice in the light compartment of the test box. In both dominant and subordinate mice, flight was increased by DMCM at 1 mg/kg to a level close to statistical significance. Treatment with DMCM had no other detectable effect on the behaviour of subordinate animals. It is suggested that anxiogenic activity of this compound might induce a shift of agonistic behaviour from aggression to "fear-induced flight".

Inverse agonist properties of the FG 7142 discriminative stimulus

A two-lever, food-motivated discrimination was established between the benzodiazepine receptor partial inverse agonist FG 7142 (5.0 mg/kg) and its vehicle. The FG 7142 discriminative stimulus was pharmacologically characterized by testing trained rats with a variety of benzodiazepine receptor ligands. Administration of the inverse agonist DMCM (0.15-0.30 mg/kg) dose-dependently mimicked the FG 7142 stimulus. In contrast, the benzodiazepine receptor agonist chlordiazepoxide, partial agonist ZK 91 296, mixed agonist/antagonist CGS 9896 and antagonist RO 15-1788 blocked the FG 7142 cue. These results indicate that the FG 7142 discriminative stimulus is based on its inverse agonist activity. The generalization of FG 7142 to the anxiogenic/convulsant compound pentylenetetrazole (PTZ), but not to the anorectic agent norfenfluramine, indicates that the anxiogenic properties of FG 7142, rather than its anorectic actions, may underlie the FG 7142 discriminative stimulus.

Body temperature discriminates between full and partial benzodiazepine receptor agonists

The benzodiazepine full agonist loprazolam and the beta-carboline ZK 93423 produced hypothermia in mice (1-30 mg/kg i.p.). Maximal effects were seen at relatively low doses of these compounds. In contrast, the partial agonists Ro 17-1812 (a benzodiazepine) and ZK 91296 (a beta-carboline), did not modify rectal temperature at doses up to 30 mg/kg i.p. (which would be receptor saturating). Body temperature may therefore be a useful test for discriminating between full and partial agonists at the benzodiazepine receptor.

Effects of midazolam, DMCM and lindane on potentiated startle in the rat

Forty-eight male Wistar rats were exposed to contingent light-shock combinations and 48 rats received light and shock stimuli in a random order. One day after fear conditioning the animals were tested for startle potentiation after injection of midazolam (0, 0.5, 1.0, 2.0 mg/kg, IP) or DMCM (methyl-6,7-dimethoxy-4-ethyl-beta-carboline-3-carboxylate; 0, 0.1, 0.2, 0.4 mg/kg IP) or lindane (0, 7.5, 15.0, 30.0 mg/kg PO). Midazolam attenuated potentiated startle dose dependently and the inverse benzodiazepine agonist DMCM had the opposite effect. The effects of lindane on startle amplitudes were identical to those of DMCM, indicating that lindane has anxiogenic effects on behavior. It is suggested that the anxiogenic effects of lindane are mediated by an effect at the GABA-ionophore complex.

Effects of Ro 15-4513, fluoxetine and desipramine on the intake of ethanol, water and food by the alcohol-preferring (P) and -nonpreferring (NP) lines of rats

The effects of the IP administration of RO 15-4513 (1, 2 and 4 mg/kg), fluoxetine (5 and 10 mg/kg) and desipramine (5 and 10 mg/kg) on the intake of 10% ethanol, H2O and food were determined in the selectively bred alcohol-preferring (P) and -nonpreferring (NP) lines of rats with daily access to fluids being limited to single 2-hour sessions. The imidazobenzodiazepine Ro 15-4513 (a partial inverse benzodiazepine agonist) significantly reduced the intake of 10% ethanol by the P rats to 50-60% of control levels in the first 30 minutes without altering food or H2O intake. The attenuating actions of 2 mg/kg Ro 15-4513 on ethanol intake could be completely blocked by the central benzodiazepine receptor antagonist Ro 15-1788 (10 mg/kg). Ro 15-1788, by itself, produced no effects on alcohol and H2O consumption. The 5 mg/kg dose of fluoxetine significantly reduced 10% ethanol intake by the P rats to 20% of control values without altering either H2O or food consumption. The 10 mg/kg dose of fluoxetine further reduced ethanol intake by the P rats, but this dose also reduced daily food intake to approximately 70% of normal. Desipramine at both doses significantly (p less than 0.05) reduced both ethanol and food uptake by the P rats and had a tendency to reduce H2O consumption as well. In general, the three drugs had effects in the NP rats similar to those observed for the P group, although the effects on 10% ethanol intake were difficult to compare because of the low, variable intake of alcohol by the NP group.(ABSTRACT TRUNCATED AT 250 WORDS)