Effects of sibutramine on anxiety-related behaviours in rats

Role of Nociceptin/Orphanin FQ-NOP Receptor System in the Regulation of Stress-Related Disorders

Nociceptin/orphanin FQ (N/OFQ) is a 17-residue neuropeptide that binds the nociceptin opioid-like receptor (NOP). N/OFQ exhibits nucleotidic and aminoacidics sequence homology with the precursors of other opioid neuropeptides but it does not activate either MOP, KOP or DOP receptors. Furthermore, opioid neuropeptides do not activate the NOP receptor. Generally, activation of N/OFQ system exerts anti-opioids effects, for instance toward opioid-induced reward and analgesia. The NOP receptor is widely expressed throughout the brain, whereas N/OFQ localization is confined to brain nuclei that are involved in stress response such as amygdala, BNST and hypothalamus. Decades of studies have delineated the biological role of this system demonstrating its involvement in significant physiological processes such as pain, learning and memory, anxiety, depression, feeding, drug and alcohol dependence. This review discusses the role of this peptidergic system in the modulation of stress and stress-associated psychiatric disorders in particular drug addiction, mood, anxiety and food-related associated-disorders. Emerging preclinical evidence suggests that both NOP agonists and antagonists may represent a effective therapeutic approaches for substances use disorder. Moreover, the current literature suggests that NOP antagonists can be useful to treat depression and feeding-related diseases, such as obesity and binge eating behavior, whereas the activation of NOP receptor by agonists could be a promising tool for anxiety.

Evaluation of the effect of acute sibutramine in female rats in the elevated T-maze and elevated plus-maze tests

Sibutramine is a serotonin and norepinephrine reuptake inhibitor indicated for the treatment of obesity. A pre-clinical study showed that acute administration of sibutramine promoted anxiolytic- and panicolytic-like effects in male rats. However, in clinical reports, sibutramine favoured the onset of panic attacks in women. In this study, the effect of sibutramine on experimental anxiety in females and the relevance of different oestrous cycle phases for this effect were analysed. In experiment 1, both male and female rats were submitted to acute intraperitoneal injection of sibutramine or vehicle 30 min. before testing in the elevated T-maze (ETM) and in the open-field test (OF). Females in the pro-oestrus (P), oestrus (E), early dioestrus (ED) and late dioestrus (LD) phases were tested in the ETM and OF (experiment 2) or in the elevated plus-maze (EPM) 30 min. after the injection of sibutramine. Sibutramine impaired the escape response in the ETM in both males and females. This effect was observed for P, E and ED, but not for LD females. Sibutramine altered neither the inhibitory avoidance in the ETM nor the behaviour of females in the EPM. Thus, sibutramine promoted a panicolytic-like effect in female rats cycling at P, E and ED, but not in the LD phase and did not alter behaviours related to anxiety in both ETM and EPM. Considering that pre-clinical studies aiming the screening of anxiolytic drugs employ male rodents, data here obtained reinforce the importance of better understanding the effects of drugs in females.

Absence of sibutramine effect on spontaneous anxiety in rats

INTRODUSTION: Sibutramine has been described as a drug recommended for treatment of obesity, since it has the ability to inhibit the reuptake of serotonin and noradrenaline in the central nervous system, thereby increasing energy expenditure.

OBJECTIVE

Investigate the anxiogenic and anxiolytic effects of acute and chronic treatment with sibutramine in rats submitted to the task of the elevated plus-maze.

METHODS

Diazepam was used as a positive control for the anxiolytic effect, and the task of the elevated plus-maze showed sensitivity to detect the effect. In the chronic treatment, sibutramine was ingested for a period of two months.

RESULTS

The acute and chronic treatments at the studied dose, which is described to produce a maximum effect of anti-obesity in rats, did not interfere with anxiety.

CONCLUSIONS

The acute and chronic administration of sibutramine is not related to anxiolytic or anxiogenic effects.

Anxiolytic and panicolytic effects of escitalopram in the elevated T-maze

Escitalopram is a highly selective inhibitor of serotonin re-uptake that is used to treat anxiety disorders. In the present study, we investigated the effects of acute, sub-chronic (14 days) and chronic (21 days) administration of escitalopram (2, 4 and 8 mg/kg, PO) on the performance of rats in the elevated T-maze. For comparison, imipramine (15 mg/kg, PO) was also studied. The apparatus is made of three elevated arms of equal dimension, one enclosed transversal to the two open arms. Inhibitory avoidance of the open arms, trained in the enclosed arm, has been related to generalised anxiety disorder, while one-way escape from one open arm, to panic disorder. After acute administration, the three doses of escitalopram impaired avoidance (anxiolytic effect), while imipramine was ineffective. Escape was unaffected by either drug. With subchronic administration, both drugs were ineffective on either avoidance or escape. After chronic treatment, avoidance was impaired by imipramine and by the two highest doses of escitalopram. In addition, escape was impaired (panicolytic effect) by imipramine and by the highest dose of escitalopram. Locomotion measured in a square arena was increased by the three doses of escitalopram, given chronically. Therefore, both imipramine and escitalopram had anxiolytic and panicolytic-like effects after chronic administration, but acutely only escitalopram decreased anxiety. Since no such effect was observed following subchronic administration, it is likely that the mechanisms of the early and late anxiolytic actions of escitalopram are different.

Elevated mazes as animal models of anxiety: effects of serotonergic agents

This article reviews reported results about the effects of drugs that act upon the serotonergic neurotransmission measured in three elevated mazes that are animal models of anxiety. A bibliographic search has been performed in MEDLINE using different combinations of the key words X-maze, plus-maze, T-maze, serotonin and 5-HT, present in the title and/or the abstract, with no time limit. From the obtained abstracts, several publications were excluded on the basis of the following criteria: review articles that did not report original results, species other than the rat, intracerebral drug administration alone, genetically manipulated rats, and animals having any kind of experimental pathology. The reported results indicate that the effect of drugs on the inhibitory avoidance task performed in the elevated T-maze and on the spatio temporal indexes of anxiety measured in the X and plus mazes correlate with their effect in patients diagnosed with generalized anxiety disorder. In contrast, the drug effects on the one-way escape task in the elevated T-maze predict the drug response of panic disorder patients. Overall, the drug effects assessed with the avoidance task in the T-maze are more consistent than those measured through the anxiety indexes of the X and plus mazes. Therefore, the elevated T-maze is a promising animal model of generalized anxiety and panic disorder.

Behavioral effects of sinomenine in murine models of anxiety

The present study was designed to investigate the putative anxiolytic-like effect of sinomenine in three experimental models of anxiety in male rats and mice. Use of the elevated plus-maze test revealed that sinomenine (20 and 40 mg/kg, p.o.) increased the percentage of open arm entries and diazepam (2 mg/kg, p.o.) increased the percentage of open arm entries, the percentage of time spent on open arms and total arm entries in mice. In the light/dark transition test, sinomenine (20 and 40 mg/kg, p.o.) increased time spent in the light area and diazepam (2 mg/kg, p.o.) increased time spent in the light area and the overall movements in mice. In the social interaction test, the sinomenine-treated animals significantly increased social interaction time in low light unfamiliar (7 mg/kg, p.o.) and high light unfamiliar conditions (7 and 14 mg/kg, p.o.) as well as diazepam (3 mg/kg, p.o.). Sinomenine (28 mg/kg, p.o.) can also decrease squares entered in rats in social interaction test under low light unfamiliar condition. In the open-field test, sinomenine (160 mg/kg) decreased squares entered in mice. Thus, these findings indicated that sinomenine exhibited anxiolytic-like effect.