Alpha1- and alpha2-containing GABAA receptor modulation is not necessary for benzodiazepine-induced hyperphagia

The use of midazolam as an appetite stimulant and anxiolytic in the common marmoset (Callithrix jacchus)

BACKGROUND

Food avoidance secondary to disease or stress can lead to weight loss and rapid deterioration of clinical condition in the common marmoset (Callithrix jacchus). Currently, there are no data supporting the use of any pharmaceuticals as an appetite stimulant in this species; however, benzodiazepines are frequently used for this purpose in other species.

METHODS

Six marmosets were used in a crossover study design to evaluate the benzodiazepine midazolam as an appetite stimulant and anxiolytic. Total food intake (TFI) and latency to eat (LTE) were measured following administration of oral and injectable midazolam in non-anxious and anxious states.

RESULTS

Injectable midazolam increased TFI and decreased LTE in anxious marmosets, but had no effect in non-anxious animals. Oral midazolam had no effect on appetite in either state.

CONCLUSIONS

Injectable midazolam may be an effective treatment for anxiety-induced inappetence in marmosets. Individual response to both oral and injectable midazolam may vary.

Selective stimulation of central GABAAα2,3,5 receptors increases intake and motivation to consume sucrose solution in rats

Benzodiazepines are one of the most commonly prescribed anxiolytic drugs in America, and between 2006 and 2015 prescription rates increased by an estimated 27.1%. Weight gain is a common side effect of these drugs and it may result from increased feeding caused by drug-enhanced food palatability. We investigated the role of specific GABA_A receptor subtypes involved with benzodiazepine-induced food consumption through third ventricle injections of L-838,417, a partial agonist of GABA_A α2, α3, and α5 subunits, and a full antagonist of the α1 receptor subunit. A microanalysis of the licking behavior of adult male rats to a sucrose solution was used to isolate drug effects on specific consummatory behaviors that include: hedonic taste evaluation, food approach behavior, and oromotor function. L-838,417 dose-dependently increased intake through increases in the motivation to approach the solution (shorter pause intervals between bouts of licking) and through enhancement of measures associated with hedonic taste evaluation. Oromotor depressant effects previously associated with broad-spectrum benzodiazepine receptor agonists were not observed. These results indicate that nuclei in proximity to the ventricles respond to GABA_A α2, α3, or α5 activation to induce motivation to feed, absent of α1 receptor subunit activation. Furthermore, activation of the α1 subunit is not necessary for benzodiazepine hyperphagia and may instead contribute to the oromotor depressant and sedative properties of classic benzodiazepine agonists. Hypothalamic nuclei such as the paraventricular nucleus may be involved in the benzodiazepine-increased motivation to feed, while the parabrachial nucleus of the hindbrain could contribute to benzodiazepine-induced enhancement of taste palatability.

Allopregnanolone involvement in feeding regulation, overeating and obesity

Obesity is strongly associated with ill health, primarily caused by consumption of excessive calories, and promoted (inter alia) by gamma-amino-butyric-acid (GABA) stimulating food intake by activating GABA_A receptors (primarily with α3 and α2 subunits) in the hypothalamic arcuate nucleus and paraventricular nucleus. Allopregnanolone is a potent positive GABA_A receptor modulating steroid (GAMS). As reviewed here, elevated allopregnanolone levels are associated with increases in food intake, preferences for energy-rich food, and obesity in humans and other mammals. In women with polycystic ovarian disease, high serum allopregnanolone concentrations are linked to uncontrolled eating, and perturbed sensitivity to allopregnanolone. Increases in weight during pregnancy also correlate with increases in allopregnanolone levels. Moreover, Prader-Willis syndrome is associated with massive overeating, absence of a GABA_A receptor (with compensatory >12-, >5- and >1.5-fold increases in α4, γ2, and α1, α3 subunits), and increases in the α4, βx, δ receptor subtype, which is highly sensitive to allopregnanolone. GABA and positive GABA-A receptor modulating steroids like allopregnanolone stimulates food intake and weight gain.

Injectable anaesthesia for adult cat and kitten castration: effects of medetomidine, dexmedetomidine and atipamezole on recovery

Objectives Rapid recovery from injectable anaesthesia benefits cat shelter neutering programmes. The effects of medetomidine, dexmedetomidine and atipamezole on recovery were evaluated in adult cats and kittens (⩽6 months old). Methods One hundred healthy male cats (age range 2-66 months, weight range 0.7-5.3 kg) admitted forneutering were randomly allocated to groups of 25. Anaesthesia was induced with 60 mg/m2 ketamine, 180 µg/m2 buprenorphine, 3 mg/m2 midazolam and either 600 µg/m2 medetomidine (groups M and MA) or 300 µg/m2 dexmedetomidine (groups D and DA) intramuscularly (IM). Groups MA and DA also received 1.5 mg/m2 atipamezole IM after 40 mins. Preparation time, surgical time, and times to sternal recumbency and standing were recorded. Data were analysed using the Kruskall-Wallis test, unpaired t-tests and ANOVA. Statistical significance was deemed to be P ⩽0.05. Results Groups did not differ significantly in age, body weight, preparation or surgical time. The time to sternal recumbency in group MA (64 ± 34 mins) was less than in group M (129 ± 32 mins), and in group DA it was less than in group D (54 ± 6 mins vs 110 ± 27 mins) ( P <0.001). There were no differences in duration of recovery to sternal recumbency between groups M and D or MA and DA. The time to standing in group MA (79 ± 51 mins) was less than in group M (150 ± 38 mins) ( P <0.001), and in group DA it was less than in group D (70 ± 22 mins vs 126 ± 27 mins) ( P <0.01). Time to standing in group D (126 ± 27 mins) was less than in group M (150 ± 38 mins) (P <0.05). Time to standing in groups DA and MA were not different. Kittens recovered faster than adults after atipamezole. Minimal adverse effects were seen. Conclusions and relevance Atipamezole reliably reduced recovery time after anaesthesia incorporating either dexmedetomidine or medetomidine; however, the choice of dexmedetomidine or medetomidine had little effect. Recovery was faster in kittens.

Neural basis of benzodiazepine reward: requirement for α2 containing GABAA receptors in the nucleus accumbens

Despite long-standing concerns regarding the abuse liability of benzodiazepines, the mechanisms underlying properties of benzodiazepines that may be relevant to abuse are still poorly understood. Earlier studies showed that compounds selective for α1-containing GABAA receptors (α1GABAARs) are abused by humans and self-administered by animals, and that these receptors may underlie a preference for benzodiazepines as well as neuroplastic changes observed in the ventral tegmental area following benzodiazepine administration. There is some evidence, however, that even L-838, 417, a compound with antagonistic properties at α1GABAARs and agonistic properties at the other three benzodiazepine-sensitive GABAA receptor subtypes, is self-administered, and that the α2GABAARs may have a role in benzodiazepine-induced reward enhancement. Using a two-bottle choice drinking paradigm to evaluate midazolam preference and an intracranial self-stimulation (ICSS) paradigm to evaluate the impact of midazolam on reward enhancement, we demonstrated that mice carrying a histidine-to-arginine point mutation in the α2 subunit which renders it insensitive to benzodiazepines (α2(H101R) mice) did not prefer midazolam and did not show midazolam-induced reward enhancement in ICSS, in contrast to wild-type controls, suggesting that α2GABAARs are necessary for the reward enhancing effects and preference for oral benzodiazepines. Through a viral-mediated knockdown of α2GABAARs in the nucleus accumbens (NAc), we demonstrated that α2 in the NAc is necessary for the preference for midazolam. Findings imply that α2GABAARs in the NAc are involved in at least some reward-related properties of benzodiazepines, which might partially underlie repeated drug-taking behavior.

Tests of unconditioned anxiety - pitfalls and disappointments

The plus-maze, the light-dark box and the open-field are the main current tests of unconditioned anxiety for mice and rats. Despite their disappointing achievements, they remain as popular as ever and seem to play an important role in an ever-growing demand for behavioral phenotyping and drug screening. Numerous reviews have repeatedly reported their lack of consistency and reliability but they failed to address the core question of whether these tests do provide unequivocal measures of fear-induced anxiety, that these measurements are not confused with measures of fear-induced avoidance or natural preference responses - i.e. discriminant validity. In the present report, I examined numerous issues that undermine the validity of the current tests, and I highlighted various flaws in the aspects of these tests and the methodologies pursued. This report concludes that the evidence in support of the validity of the plus-maze, the light/dark box and the open-field as anxiety tests is poor and methodologically questionable.

Diazepam promotes choice of abstinence in cocaine self-administering rats

When facing a choice between cocaine and a potent, albeit inessential, non-drug alternative (i.e. water sweetened with saccharin), most cocaine self-administering rats abstain from cocaine in favor of the non-drug pursuit, regardless of the dose available and even after extended drug use. Only a minority continues to take the drug despite the opportunity of making a different choice and increasing stakes. This pattern of individual variation could suggest that the majority of rats are resilient to addiction, taking cocaine by default of other options. Only a minority would be vulnerable to addiction. This study tested the hypothesis that rats choose to refrain from cocaine self-administration because cocaine would be conflictual, having both rewarding and anxiogenic properties. Contrary to this hypothesis, however, we report here that diazepam-a broad-spectrum benzodiazepine anxiolytic-did not decrease, but instead, further increased cocaine abstinence. Interestingly, although diazepam decreased locomotion, rats adapted to this effect by spending more time near the lever associated with the preferred reward, a behavior that minimized the need for locomotion at the moment of choice. When responding for cocaine or saccharin was analyzed separately, we found that diazepam decreased responding for cocaine without affecting responding for saccharin. Finally, the abstinence-promoting effects of diazepam were also induced in cocaine-preferring rats treated chronically with diazepam. Overall, this study demonstrates that abstinence from cocaine cannot be explained away by the anxiogenic effects of cocaine, thereby reinforcing the notion of resilience to addiction. It also supports the use of benzodiazepines in the treatment of cocaine addiction.

Contribution of GABA(A) receptors containing α3 subunits to the therapeutic-related and side effects of benzodiazepine-type drugs in monkeys

RATIONALE

Experimental evidence suggests that the differential behavioral effects of benzodiazepines depend on their relative actions at γ-aminobutyric acid type A (GABA(A)) receptors that contain either an α1, α2, α3, or α5 subunit.

OBJECTIVES

The present study was aimed at understanding the role of α3 subunit-containing GABA(A) (α3GABA(A)) receptors by examining the behavioral pharmacology of TP003 (4,2'-difluoro-5'-[8-fluoro-7-(1-hydroxy-1-methylethyl)imidazo[1,2-a]pyridine-3-yl]biphenyl-2-carbonitrile), which shows functional selectivity for α3GABA(A) receptors.

METHODS

First, a conflict procedure was used to assess the anxiolytic-like effects of TP003 and a representative clinically available benzodiazepine. TP003 was also administered before daily periods of sucrose pellet availability to evaluate potential hyperphagic effects. In separate experiments, observable behavioral effects were used to assess the motor and sedative effects of TP003.

RESULTS

Administration of TP003 produced robust anti-conflict effects without the rate-decreasing effects that were observed with the representative benzodiazepine. Unlike the reported effects of benzodiazepines, TP003 did not enhance palatable food consumption. However, increases in observable sleep-associated posture were induced by TP003, as were decreases in some species-typical behaviors (vocalization, locomotion, and environment-directed behaviors). When evaluated for its ability to induce a procumbent posture, TP003 failed to produce an effect.

CONCLUSIONS

Based on conflict and observation tests in monkeys, our results suggest that TP003 may have anxiolytic properties but lack ataxic, hyperphagic, and pronounced sedative effects characteristic of classical benzodiazepines. TP003 did induce myorelaxant-like effects and had relatively mild sedative effects. Collectively, these results suggest that α3GABA(A) receptors play an important role in the anxiolytic-like and motor effects of benzodiazepine-type drugs.

Help stop teenage pregnancy! Early-age neutering in cats

PRACTICAL RELEVANCE

neutering kittens at an early age, typically between 6 and 14 weeks, has received increasing attention and gained prominence in recent years, particularly in the United States and in shelter medicine in the UK. However, in private practice it has yet to be generally endorsed.

GLOBAL IMPORTANCE

among many of the animal welfare charities, early neutering is seen as a crucial step in conquering and controlling cat overpopulation.

CLINICAL CHALLENGES

physiological differences between kittens and adult cats are very important to consider before undertaking elective early neutering. Increased sensitivity to drugs, prolongation of effects and a limited capacity for cardiovascular compensation are the principal anaesthetic concerns in kittens.

EVIDENCE BASE

the optimal age for neutering, traditionally deemed to be between 5 and 8 months, is now questioned, as short- and longer-term studies demonstrate no significant behavioural and physical advantages conferred by traditional-age neutering. Furthermore, a number of safe anaesthetic and surgical protocols have been documented that produce lower morbidity and similar mortality rates in early-age neuters compared with traditional-age neuters.

Zolpidem-induced changes in activity, metabolism, and anxiety in rats

Gamma aminobutyric acid (GABA)-A receptor modulators constitute the majority of clinically relevant sedative-hypnotics. Zolpidem (Ambien) is a nonbenzodiazepine GABA-A receptor modulator that binds with high affinity to GABA-A receptors expressing alpha-1 subunits. The present study examined the effects of a new approach to the oral administration of zolpidem on locomotor activity, body weight, food intake, relative food intake, feed efficiency, anxiety, and visceral adiposity in rats. Effects of withdrawal associated with cessation of the drug were also recorded. A daily chronically administered oral 10 mg/kg dose of zolpidem caused a decrease in locomotor activity, an increase in food intake and relative food intake, and a more positive feed efficiency during the drug-administration period. Anxiety and visceral adiposity also increased in animals receiving the drug. During withdrawal of zolpidem, there was a decrease in body weight, food intake, relative food intake, and anxiety, as well as a negative feed efficiency. These results suggest that zolpidem can modulate locomotor activity, metabolism, and anxiety-related behavior. A highly positive feed efficiency and increased visceral adiposity associated with zolpidem intake were unique findings of this study.

Neural bases for addictive properties of benzodiazepines

Benzodiazepines are widely used in clinics and for recreational purposes, but will lead to addiction in vulnerable individuals. Addictive drugs increase the levels of dopamine and also trigger long-lasting synaptic adaptations in the mesolimbic reward system that ultimately may induce the pathological behavior. The neural basis for the addictive nature of benzodiazepines however remains elusive. Here we show that benzodiazepines increase firing of dopamine neurons of the ventral tegmental area through the positive modulation of GABA_A receptors in nearby interneurons. Such disinhibition, which relies on α1-containing GABA_ARs expressed in these cells, triggers drug-evoked synaptic plasticity in excitatory afferents onto dopamine neurons and underlies drug reinforcement. Taken together, our data provide evidence that benzodiazepines share defining pharmacological features of addictive drugs through cell type-specific expression of α1-containing GABA_ARs in the ventral tegmental area. The data also suggest that subunitselective benzodiazepines sparing α1 may be devoid of addiction liability.