Evaluation of limited and unlimited food intake during withdrawal in triazolam-dependent baboons

Comparison of the behavioral effects of bretazenil and flumazenil in triazolam-dependent and non-dependent baboons

Behavioral effects of the benzodiazepine receptor partial agonist bretazenil were compared with those of the benzodiazepine receptor antagonist flumazenil under conditions in which three baboons received continuous intragastric (i.g.) infusion of vehicle and then continuous i.g. infusion of triazolam (1.0 mg/kg/day). In each condition, acute doses of flumazenil (0.01-3.2 mg/kg) and bretazenil (0.01-10.0 mg/kg) were administered every 2 weeks (beginning after 30 days of treatment in the triazolam-dependent condition). Food pellets were available during daily 20-h sessions. Following test injections, 60-min behavioral observations were conducted followed by a fine motor assessment. During chronic vehicle administration, neither drug produced changes in observed behaviors. Bretazenil increased pellets earned and time to complete the fine-motor task (10.0 mg/kg dose). During chronic triazolam dosing, both bretazenil and flumazenil precipitated benzodiazepine withdrawal syndromes, characterized by vomiting, tremors/jerks, and a decrease in pellets earned. Thus, bretazenil can function as an antagonist under conditions of benzodiazepine physical dependence.

Laparophobia: a cognitive perspective on appetite control in anorexia nervosa

Decades of research have demonstrated that anorexia nervosa (AN) may be associated with aberrant cognition, yet, its role in maintaining stringent dieting has received relatively little attention from mainstream researchers of eating disorders. The purpose of the present article is to highlight cognitive ('top-down') factors that are considered responsible for anticipatory anxiety of stoutness and frank fat-phobia (laparophobia). A cognitive model proposed departs from the formulation suggesting that phobia of over-eating is superimposed on avoidant tendencies ('environmental autonomy syndrome'), whereas excessive exercising becomes a natural coping strategy with laparophobia, an instrument of reward. AN ideation involves complex neuronal circuitries and multiple neurochemical components that may conceivably represent a mirror image of those underlying obesity. The emphasis on phobia and aberrant membrane excitability akin to channelopathies behoves the clinicians to be aware of potential uses of drugs acting at the gamma-aminobutyric acid and the N-methyl-D-aspartate/AMPA [2-amino-3-(3-hydroxy-5-methylisoxazol-4-yl) propionic acid] receptors sites as the adjuncts to conventional agents in managing AN.

Palatability-dependent appetite and benzodiazepines: new directions from the pharmacology of GABA(A) receptor subtypes

This paper updates an early review on benzodiazepine-enhanced food intake, published in the first issue of Appetite, and describes the considerable advances since then in the pharmacology of benzodiazepines, their sites and mechanisms of action, and in understanding the psychological processes leading to the increase in food consumption. A great diversity of benzodiazepine receptor ligands have been developed, many of which affect food intake. Agonists can be divided into full agonists (which produce the full spectrum of benzodiazepine effects) and partial agonists (which are more selective in their effects). In addition, inverse agonists have been identified, with high affinity for benzodiazepine receptors but having negative efficacy: these drugs exhibit anorectic properties. Benzodiazepine receptors are part of GABA(A) receptor complexes, and ligands thereby modulate inhibitory neurotransmission in the brain. Molecular approaches have identified a palette of receptor subunits from which GABA(A) receptors are assembled. In all likelihood, benzodiazepine-induced hyperphagia is mediated by the alpha2/alpha3 subtype not the alpha1 subtype. Novel alpha2/alpha3 selective compounds will test this hypothesis. A probable site of action in the caudal brainstem for benzodiazepines is the parabrachial nucleus. Behavioural evidence strongly indicates that a primary action of benzodiazepines is to enhance the positive hedonic evaluation (palatability) of tastes and foodstuffs. This generates the increased food intake and instrumental responding for food rewards. Therapeutic applications may derive from the actions of benzodiazepine agonists and inverse agonists on food procurement and ingestion.

Involvement of gamma-hydroxybutyrate (GHB) and GABA-B receptors in the acute behavioral effects of GHB in baboons

RATIONALE

Gamma-hydroxybutyrate (GHB) is used for the treatment of narcolepsy, but it is also a drug of abuse. The behavioral pharmacology of GHB is not well defined.

OBJECTIVES

The current study was conducted to characterize the behavioral effects of a range of GHB doses in baboons (N=4) and to evaluate whether a GABA-B receptor antagonist and a GHB receptor antagonist would block a behaviorally active dose of GHB.

METHODS

In the first experiment, GHB (32-420 mg/kg) or vehicle was administered via an intragastric catheter. Sixty min after dosing, subjects were presented with a fine-motor task and observed. Food pellets were available under a fixed-ratio schedule of reinforcement 20-h/day. In the second experiment, the GABA-B antagonist CGP36742 (10-56 mg/kg), the putative GHB antagonist NCS-382 (0.1-10 mg/kg), or vehicle were administered alone and then in combination with GHB (320 mg/kg).

RESULTS

GHB dose-dependently decreased the number of food pellets earned. Performance in the motor task was also impaired and accompanied by signs of sedation and gastrointestinal discomfort. Pretreatment with CGP36742 antagonized GHB-induced suppression of food-maintained behavior and performance on the fine-motor task. Signs of abdominal discomfort, ataxia, and muscle relaxation produced by GHB were also reduced by pretreatment with CGP36742. In contrast, pretreatment with NCS-382 sometimes restored performance in the fine-motor task and increased food-maintained behavior, but the effect was variable across doses and baboons. Some doses of NCS-382 appeared to exacerbate ataxia and gastrointestinal discomfort produced by GHB in some subjects.

CONCLUSIONS

These data indicate that while GABA-B receptors play a significant role in mediating the behavioral effects of GHB in baboon, the role of GHB receptors is less clear.

Self-injection of flunitrazepam alone and in the context of methadone maintenance in baboons

Patients in methadone maintenance programs use benzodiazepines to "boost" methadone's subjective effects, and flunitrazepam has been prominent in this context. Self-administration of flunitrazepam (0.001-0.32 mg/kg i.v.) alone and during daily oral methadone administration was evaluated in three baboons. Flunitrazepam maintained self-injection as an inverted U-shaped function of dose at rates higher than those maintained by most other benzodiazepines under the same procedure. In the context of demonstrated physical dependence on 3.2 mg/kg/day p.o. methadone, flunitrazepam doses on the ascending limb of the dose-effect curve maintained greater rates of self-injection than before methadone in two baboons. When the methadone dose decreased to 1.8 mg/kg/day, self-injection remained higher for those baboons and became higher than before methadone for the third baboon. Self-injection remained higher when methadone decreased to 1.0 mg/kg/day, except self-injection of the lowest flunitrazepam dose returned to or below the pre-methadone rate for two baboons. After methadone was discontinued, the dose-effect curve shifted to the right in one baboon but remained to the left in two. Flunitrazepam thus served as a reinforcer alone and in the context of methadone maintenance. Lower doses maintained higher self-injection during and shortly after methadone maintenance. Further research should explore the duration of higher self-injection rates following methadone maintenance.

Zaleplon and triazolam physical dependence assessed across increasing doses under a once-daily dosing regimen in baboons

The ability of the GABA(A)-receptor-subtype-selective hypnotic zaleplon to produce physical dependence was compared to the nonselective benzodiazepine triazolam. Progressively increasing doses of zaleplon and triazolam were given to baboons by intragastric infusion once each day, with doses increasing every 17 days. Next, the highest dose was given for 10-34 additional days by continuous infusion. Both drugs produced increases in food-maintained lever pressing, ataxia, and time to complete a fine motor task. Plasma levels increased dose-dependently; drug was detectable 24 h after higher doses. Flumazenil produced a mild or intermediate precipitated-withdrawal syndrome on day 14 of all dosing conditions. When drug delivery ended after 85-100 days, a benzodiazepine-type withdrawal syndrome occurred. Physical dependence potential of zaleplon and triazolam appear similar.