ABSTRACT
Linalool oxide is a monoterpene that is found in some species of aromatic plants. The effects of the inhalation of linalool oxide (0.65%, 1.25%, 2.5% and 5.0% w/w) in the elevated plus-maze and light/dark box tests as animal models of anxiety were investigated in adult male mice and compared with the effects of the reference anxiolytic diazepam (0.5 and 2.0 mg/kg), administered intraperitoneally. Additionally, the effects of inhaled linalool oxide were investigated in the rotarod test. Linalool oxide significantly increased the number of visits to the open arms of the elevated plus-maze and the amount of time spent there as well as the total number of entries. In the light/dark box test, inhalation of linalool oxide led to an increase in the time spent by the mice in the brightly-lit chamber and in the number of times the animal crossed from one compartment to another. Performance on the rotarod was unaffected. Thus, inhaled linalool oxide was found to have anxiolytic properties in both animal models, without causing any motor deficit. These results suggest that inhalation of linalool oxide may be a useful means of counteracting anxiety.
Subject(s)
Anti-Anxiety Agents/therapeutic use , Anxiety/drug therapy , Disease Models, Animal , Monoterpenes/therapeutic use , Acyclic Monoterpenes , Administration, Inhalation , Animals , Anti-Anxiety Agents/administration & dosage , Behavior, Animal , Male , Mice , Monoterpenes/administration & dosageABSTRACT
Serotonin (5-HT) neurons located in the median raphe nucleus (MRN) may have a role in the development of behavioral changes to stress. The objective of the present work was to investigate the effects of a selective lesion of 5-HT neurons located in the MRN in previously stressed male Wistar rats submitted to the elevated plus maze (EPM). In an initial experiment, the animals (n=20-22) were submitted to one (acute) or seven (chronic) daily restraint stress periods (2 h) and tested in the EPM 24 h later. Results showed that acute restraint caused a significant decrease in the number of entries into the open arms, as compared to nonstressed controls. This effect disappeared when the animals were submitted to chronic restraint. In the next set of experiments, animals (n=6-8) received, 1 week before the behavioral studies, intra-MRN injection of 5,7-dihydroxytryptamine (5,7-DHT; 8 microg/1 microl). Neurochemical analysis showed that this treatment significantly decreases 5-HT and 5-hydroxy-indoleacetic acid (5-HIAA) levels in the hippocampus, but not in the striatum. No difference between lesioned and sham-operated animals in EPM performance was found in nonstressed animals or in those submitted to acute restraint. In chronically restrained animals, however, lesioned rats showed a significant decrease in the number of entries and time spent in the open arms. These results suggest that lesions of 5-HT neurons located in the MRN cause anxiogenic-like behavior in animals that have been chronically restrained.
