Naloxone potentiates anxiolytic-like actions of diazepam, pentobarbital and meprobamate but not those of Ro19-8022 in the rat

Atypical anxiolytic-like response to naloxone in benzodiazepine-resistant 129S2/SvHsd mice: role of opioid receptor subtypes

“…they occurred in the absence of significant changes to other components of the behavioural repertoire (Table 1). Although the lack of effect of naloxone in C57 mice could simply be explained by their low anxiety baseline, this finding agrees well with numerous previous studies, demonstrating that classical opioid receptor antagonists are inactive irrespective of the anxiety baseline (Agmo et al 1995;Privette and Terrian 1995;Belzung and Agmo 1997a;Agmo et al 1999;Frussa-Filho et al 1999;Kang et al 1999;Belzung et al 2000;Filliol et al 2000;Silva and Frussa-Filho 2002). Indeed, where rare exceptions exist, anxiogenic-like effects have been reported for these compounds (e.g.…”

“…Belzung and Agmo 1997b;Frussa-Filho et al 1999;Belzung et al 2000;Silva and Frussa-Filho 2002). Interestingly, Belzung and colleagues (2000) have proposed that this latter action of naloxone may be due to antagonism of an EOP-induced inhibition of GABAergic neurons in areas such as the amygdala and hippocampus (Cohen et al 1992;Sugita and North 1993;Kieffer and Gaveriaux-Ruff 2002).…”

Involvement of opioidergic system of the ventral hippocampus, the nucleus accumbens or the central amygdala in anxiety-related behavior

“…The mechanism by which naloxone could exert such an anxiolytic effect may be the blockade of the tonic inhibitory influence of μ-opioid receptors upon GABAergic system (Belzung et al, 2000b). The opioid receptor activation may elicit an inhibitory effect in GABAergic activity in several brain areas (Cohen et al, 1992;Stanford and Cooper, 1999).…”

The role of delta opioid receptors in the anxiolytic actions of benzodiazepines

“…These behavioral studies show that opioid antagonists are able to block the anxiolytic effect of benzodiazepines in the elevated plus maze task or anticonflict tests (Billingsley and Kubena 1978;Koob et al 1980;Soubrie et al 1980;Agmo et al 1995;Tsuda et al 1996) and can increase shock-induced freezing in rats (Fanselow and Bolles 1979). In contrast, some studies indicate that the systemic administration of nonselective opioid antagonists actually enhance the anxiolytic actions of low doses of benzodiazepine agonists (diazepam, chlordiazepoxide), but not partial agonists (Belzung and Agmo 1997b;Frussa-Filho et al 1999;Belzung et al 2000). These prior studies suggest that both doses of opioids and benzodiazepines used in these studies (Agmo et al 1995;Belzung and Agmo 1997a), as well as the novelty of the testing situation (File and Rodgers 1979a;Frussa-Filho et al 1999) influence the ability of opioids agonists and antagonists to modify the anxiolytic influences of benzodiazepines.…”