Cocaine withdrawal enhances pentobarbital-induced sleep in rats: Evidence of GABAergic modulation

Central nervous system evaluation of an ethanol extract of Bidens odorata Cav (Asteraceae) leaves, and its antinociceptive interaction with paracetamol and naproxen

INTRODUCTION

Bidens odorata Cav (Asteraceae) is a medicinal plant employed for the treatment of pain, anxiety, and depression. This study aimed to evaluate some neuropharmacological effects of an ethanol extract of B. odorata (BOE) and assess its antinociceptive interaction with naproxen and paracetamol.

MATERIALS AND METHODS

The following neuropharmacological effects were evaluated with the ethanolic extract of B. odorata leaves (BOE) (10-200 mg/kg p.o.): the strychnine-induced-convulsion assay (anticonvulsant effect), rotarod test (locomotor activity), tail suspension test (anti-depressant-like activity), cylinder exploratory test (anxiolytic-like actions), and pentobarbital-induced sleep test (sedative effect). The interaction of the BOE-paracetamol and BOE-naproxen combinations were evaluated with the acetic acid-induced writhing test. The ED₅₀ value of each drug was estimated and the combinations of paracetamol and naproxen with BOE were calculated.

RESULTS

BOE (100-200 mg/kg) showed anti-convulsant activity by increasing the latency to occurrence of strychnine-induced convulsions, antidepressant-like effects by 28% and 33%, respectively, exerted anxiolytic actions (ED₅₀ = 125 mg/kg), but did not affect motor locomotion. The pre-treatment with 2 mg/kg flumazenil or 20 mg/kg pentylenetetrazol partially reverted the anxiolytic activity shown by BOE alone. BOE (200 mg/kg) prolonged the duration of sleep with similar effect in comparison to clonazepam (1.5 mg/kg). The combinations of BOE-paracetamol (1:1) and BOE-naproxen (1:1) showed antinociceptive synergism.

CONCLUSION

BOE induces sedative and anticonvulsant effects. The anxiolytic actions shown by BOE are probably induced by the participation of the GABAergic system. BOE exerts antinociceptive synergistic interaction with paracetamol and naproxen probably by the participation of nitric oxide and ATP-sensitive K⁺ channels, respectively.

Antidepressive effects of ginsenoside Rg1 via regulation of HPA and HPG axis

BACKGROUND

Hypothalamic-pituitary-adrenal (HPA) axis hyperactivity is a well-established pathological feature of major depression, accompanied by the persistent increase of glucocorticoid level and the dysfunction of hypothalamic-pituitary-gonadal (HPG) axis. Ginsenoside Rg1 (Rg1) is one of the most active ingredients of Panax ginseng, which has various biological activity.

OBJECTIVE

This study aimed to investigate the antidepressive effects of Rg1 and elucidate its impact on neuroendocrine system.

METHODS

The antidepressive effects of Rg1 were first analysed in mice, and was further identified in the chronic-unpredictable-mild-stress (CUMS) model and the gonadectomized (GDX) model. The effects of Rg1 on depression-like behaviour were analysed by the forced swimming test (FST), tail suspension test (TST), sucrose preference test, and measurement of pentobarbital-induced sleep. The serum corticosterone and testosterone levels were detected by ELISA. The protein levels of glucocorticoid receptor (GR) and androgen receptor (AR) were analysed by western blot and immunohistochemistry analysis.

RESULTS

Rg1 significantly decreased the immobility time of mice in FST and TST. Furthermore, Rg1 alleviated anhedonia and hopelessness, decreased serum corticosterone level, and increased serum testosterone level, and the GR protein level in the PFC and hippocampus of the CUMS-treated rats. Moreover, Rg1 improved sleep disruption, down-regulated the serum corticosterone level, and increased AR protein level in the PFC of the GDX-treated mice.

CONCLUSION

Together, these studies suggest that Rg1 displayed antidepressant activity through the modulation of the HPA and the HPG axis. These findings provide new mechanism involved in the antidepressive effects of Rg1 and propose theoretical clues for clinical therapies.

New perspectives on using brain imaging to study CNS stimulants

While the recent application of brain imaging to study CNS stimulants has offered new insights into the fundamental factors that contribute to their use and abuse, many gaps remain. Brain circuits that mediate pleasure, dependence, craving and relapse are anatomically, neurophysiologically and neurochemically distinct from one another, which has guided the search for correlates of stimulant-seeking and taking behavior. However, unlike other drugs of abuse, metrics for tolerance and physical dependence on stimulants are not obvious. The dopamine theory of stimulant abuse does not sufficiently explain this disorder as serotonergic, GABAergic and glutamagergic circuits are clearly involved in stimulant pharmacology and so tracking the source of the "addictive" processes must adopt a more multimodal, multidisciplinary approach. To this end, both anatomical and functional magnetic resonance imaging (MRI), MR spectroscopy (MRS) and positron emission tomography (PET) are complementary and have equally contributed to our understanding of how stimulants affect the brain and behavior. New vistas in this area include nanotechnology approaches to deliver small molecules to receptors and use MRI to resolve receptor dynamics. Anatomical and blood flow imaging has yielded data showing that cognitive enhancers might be useful adjuncts in treating CNS stimulant dependence, while MRS has opened opportunities to examine the brain's readiness to accept treatment as GABA tone normalizes after detoxification. A desired outcome of the above approaches is being able to offer evidence-based rationales for treatment approaches that can be implemented in a more broad geographic area, where access to brain imaging facilities may be limited. This article is part of the Special Issue entitled 'CNS Stimulants'.

Differential effects of methylphenidate and cocaine on GABA transmission in sensory thalamic nuclei

Methylphenidate (MPH) is widely used to treat children and adolescents diagnosed with attention deficit/hyperactivity disorder. Although MPH shares mechanistic similarities to cocaine, its effects on GABAergic transmission in sensory thalamic nuclei are unknown. Our objective was to compare cocaine and MPH effects on GABAergic projections between thalamic reticular and ventrobasal (VB) nuclei. Mice (P18-30) were subjected to binge-like cocaine and MPH acute and sub-chronic administrations. Cocaine and MPH enhanced hyperlocomotion, although sub-chronic cocaine-mediated effects were stronger than MPH effects. Cocaine and MPH sub-chronic administration altered paired-pulse and spontaneous GABAergic input differently. The effects of cocaine on evoked paired-pulse GABA-mediated currents changed from depression to facilitation with the duration of the protocols used, while MPH induced a constant increase throughout the administration protocols. Thalamic reticular nucleus GAD67 and VB Ca(V) 3.1 protein levels were measured using western blot to better understand their link to increased GABA release. Both proteins were increased by sub-chronic administration of cocaine. MPH showed effects on GABAergic transmission that seems less disruptive than cocaine. Unique effects of cocaine on postsynaptic VB calcium currents might explain deleterious cocaine effects on sensory thalamic nuclei. These results suggest that cocaine and MPH produced distinct presynaptic alterations on GABAergic transmission.

Increased non-rapid eye movement sleep by cocaine withdrawal: possible involvement of A2A receptors

This study attempted to clarify whether cocaine withdrawal altered sleep architecture and the role of adenosine receptors in this process. Cocaine (20 mg/kg) was administered subcutaneously once per day for 7 days to rat implanted with sleep/wake recording electrode. Polygraphic signs of undisturbed sleep/wake activities were recorded for 24 h before cocaine administration (basal recording as control); withdrawal-day 1 (after 1 day of repeated cocaine administration), withdrawal-day 8 (after 8 days of repeated cocaine administration), and withdrawal-day 14 (after 14 days of repeated cocaine administration), respectively. On cocaine withdrawal-day 1, wakefulness was significantly increased, total sleep was decreased, non-rapid eye movement sleep was markedly reduced, and rapid eye movement sleep was enhanced. Sleep/wake cycles were also increased on cocaine withdrawal day 1. However, non-rapid eye movement sleep was increased on withdrawal-day 8 and 14, whereas rapid eye movement sleep was decreased and no significant changes were observed in the total sleep and sleep/wake cycles during these periods. Adenosine A(2A) receptors expression was increased on withdrawal-day 8 and 14, whereas A(1) receptors levels were reduced after 14 days of withdrawal and the A(2B) receptors remained unchanged. Our findings suggest that alterations of sleep and sleep architecture during cocaine subacute and subchronic withdrawals after repeated cocaine administration may be partially involved in A(2A) receptors over-expression in the rat hypothalamus.

Effects of T-type calcium channel blockers on cocaine-induced hyperlocomotion and thalamocortical GABAergic abnormalities in mice

RATIONALE

Repetitive cocaine exposure has been shown to induce GABAergic thalamic alterations. Given the key role of T-type (Ca(V)3) calcium channels in thalamocortical physiology, the direct involvement of these calcium channels in cocaine-mediated effects needs to be further explored.

OBJECTIVE

The objective of this study was to investigate the effect of T-type calcium channel blockers on acute and repetitive cocaine administration that mediates thalamocortical alterations in mice using three different T-type blockers: 2-octanol, nickel, and mibefradil.

METHODS

During in vitro experiments, whole-cell patch-clamp recordings were conducted in ventrobasal (VB) thalamic neurons from mice treated with acute repetitive cocaine administration (3 x 15 mg/kg, i.p., 1 h apart), under bath application of mibefradil (10 μM), 2-octanol (50 μM), or nickel (200 μM). After systemic administration of T-type calcium channel blockers, we evaluated locomotor activity and also recorded GABAergic neurotransmission onto VB neurons in vitro.

RESULTS

Bath-applied mibefradil, 2-octanol, or nickel significantly reduced both GABAergic neurotransmission and T-type currents of VB neurons in cocaine-treated mice. In vivo i.p. pre-administration of either mibefradil (20 mg/kg and 5 mg/kg) or 2-octanol (0.5 mg/kg and 0.07 mg/kg) significantly reduced GABAergic mini frequencies onto VB neurons. Moreover, both mibefradil and 2-octanol were able to decrease cocaine-induced hyperlocomotion.

CONCLUSION

The results shown in this study strongly suggest that T-type calcium channels play a key role in cocaine-mediated GABAergic thalamocortical alterations, and further propose T-type channel blockers as potential targets for future pharmacological strategies aimed at treating cocaine's deleterious effects on physiology and behavior.

Neural substrates of psychostimulant withdrawal-induced anhedonia

Psychostimulant drugs have powerful reinforcing and hedonic properties and are frequently abused. Cessation of psychostimulant administration results in a withdrawal syndrome characterized by anhedonia (i.e., an inability to experience pleasure). In humans, psychostimulant withdrawal-induced anhedonia can be debilitating and has been hypothesized to play an important role in relapse to drug use. Hence, understanding the neural substrates involved in psychostimulant withdrawal-induced anhedonia is essential. In this review, we first summarize the theoretical perspectives of psychostimulant withdrawal-induced anhedonia. Experimental procedures and measures used to assess anhedonia in experimental animals are also discussed. The review then focuses on neural substrates hypothesized to play an important role in anhedonia experienced after termination of psychostimulant administration, such as with cocaine, amphetamine-like drugs, and nicotine. Both neural substrates that have been extensively investigated and some that need further evaluation with respect to psychostimulant withdrawal-induced anhedonia are reviewed. In the context of reviewing the various neurosubstrates of psychostimulant withdrawal, we also discuss pharmacological medications that have been used to treat psychostimulant withdrawal in humans. This literature review indicates that great progress has been made in understanding the neural substrates of anhedonia associated with psychostimulant withdrawal. These advances in our understanding of the neurobiology of anhedonia may also shed light on the neurobiology of nondrug-induced anhedonia, such as that seen as a core symptom of depression and a negative symptom of schizophrenia.