R. Frussa-filho et al., Naltrexone potentiates the anxiolytic effects of chlordiazepoxide in rats exposed to novel environments, PSYCHOPHAR, 147(2), 1999, pp. 168-173
Rationale: Both novelty and naloxone have been reported to modify the anxio
lytic-like effect of benzodiazepines in the elevated plus maze. In addition
, it has been largely demonstrated that novelty alters endogenous opioid ac
tivity. Objectives: The present study was designed to examine a possible in
teraction between novelty and naltrexone effects on the behavior of chlordi
azepoxide-treated rats in two animal models of anxiety. Methods: Thirty min
utes after acute intraperitoneal treatment with saline or naltrexone and sa
line or chlordiazepoxide, male Wistar rats were exposed for the first time
to the elevated plus maze apparatus or the social interaction arena for the
quantification of the percentage of time spent in the open arms or the tim
e of active social interaction, respectively. The effects of naltrexone and
/or chlordiazepoxide on the plus maze and the social interaction tests were
also evaluated after previous exposure to the respective apparatus. Result
s: Naltrexone dose dependently increased the percentage of time spent in th
e open arms of the elevated plus maze in chlordiazepoxide-treated (5 mg/kg
i.p.) rats exposed for the first time to the apparatus. Similarly, naltrexo
ne (5 mg/kg i.p.) increased the time spent in active social interaction by
chlordiazepoxide-treated rats exposed to an unfamiliar arena. In both exper
iments, naltrexone had no effect when administered alone. When both the plu
s maze and the social interaction tests were conducted after previous expos
ure to the respective apparatus, naltrexone did not modify the behavior of
chlordiazepoxide- or saline-treated rats. Conclusions: These data suggest t
hat the anxiolytic-like effects of chlordiazepoxide can be modified by opio
id mechanisms in navel environments.