Antidepressant-like effect of bis-eugenol in the mice forced swimming test: evidence for the involvement of the monoaminergic system.

Dehydrodieugenol, known as bis-eugenol, is a eugenol ortho dimer, and both compounds were able to exhibit anti-inflammatory and antioxidant activities in previous studies. Furthermore, eugenol showed antidepressant-like effect; however, the biological actions of bis-eugenol on experimental models for screening antidepressant activity are still unknown. The present study investigated a possible antidepressant-like activity of bis-eugenol in the forced swimming test (FST) and tail suspension test (TST) in mice and the involvement in the monoaminergic system in this effect. In addition, a neurochemical analysis on brain monoamines of mice acutely treated with bis-eugenol was also conducted. Bis-eugenol decreased the immobility time in the FST and TST without accompanying changes in ambulation in the open field test at 10 mg/kg, i.p.. Nevertheless, it induced ambulation at 25 and 50 mg/kg doses. The anti-immobility effect of bis-eugenol (10 and 50 mg/kg, i.p.) was prevented by pretreatment of mice with p-chlorophenylalanine (PCPA, 100 mg/kg, i.p., an inhibitor of serotonin synthesis, for four consecutive days), yohimbine (1 mg/kg, i.p., an α2-adrenoceptor antagonist), SCH23390 (15 µg/kg, s.c., a dopamine D1 receptor antagonist) and sulpiride (50 mg/kg, i.p., a dopamine D2 receptor antagonist). Monoamines analysis using high-performance liquid chromatograph revealed significant increase in the 5-HT, NE and DA levels in brain striatum. The present study indicates that bis-eugenol possesses antidepressant-like activity in FST and TST by altering dopaminergic, serotonergic and noradrenergic systems function.

Doxycycline protects against pilocarpine-induced convulsions in rats, through its antioxidant effect and modulation of brain amino acids.

This work evaluated doxycycline (2nd generation tetracycline) protection against pilocarpine-induced convulsions in rats. The animals were treated with doxycycline (Dox: 10 to100 mg/kg, i.p., 7days), 30min before the pilocarpine injection (P: 300mg/kg, i.p.) and observed for cholinergic signs, latencies to the first convulsion and death. Amino acid concentrations, lipid peroxidation and nitrite levels in temporal cortices were determined as well as the radical scavenging activity. Doxycycline increased latencies to the first convulsion and death as compared to the untreated P300 group. It also decreased glutamate and aspartate, increased GABA, blocked nitrite formation, reduced TBARS contents and showed a radical scavenging activity. Finally, doxycycline decreased the number of degenerating neurons (evaluated by fluoro-jade staining) and increased the number of viable neurons (assessed by cresyl violet staining) as compared do the P300 group. The antioxidant effect associated with decreased levels of excitatory and increased levels of inhibitory amino acids could explain the neuroprotective effect of doxycycline.

Behavioral alterations and pro-oxidant effect of a single ketamine administration to mice.

A growing body of evidence has pointed to the ionotropic glutamate N-methyl-d-aspartate receptor (NMDA) as an important player in the etiology of psychopathologies, including anxiety and major depression. Clinical findings suggest that ketamine may be used for the treatment of major depression. There is evidence that reactive oxygen species also play an important role in the pathogenesis of many diseases, particularly those which are neurological and psychiatric in nature. This study examined the behavioral and oxidative stress alterations after a single administration of ketamine (5, 10 and 20mg/kg i.p.) in mice. Ketamine presented a significant anxiogenic effect in the elevated plus-maze model of anxiety, also increasing locomotor activity. In the forced swimming and tail suspension tests, a significant decrease in immobility time after ketamine administration was observed. In addition to the behavioral changes induced by ketamine, this drug also increased lipid peroxidation, nitrite content and catalase activity, while decreased GSH levels in mice prefrontal cortex. In conclusion, our results confirm the antidepressant effects of ketamine, also showing a pro-oxidant effect of this drug.

Effects of isopulegol on pentylenetetrazol-induced convulsions in mice: possible involvement of GABAergic system and antioxidant activity.

The present study investigated the effects of isopulegol, a monoterpene alcohol, in PTZ-induced convulsions and verified possible involved mechanisms. Saline, isopulegol or diazepam were intraperitonealy injected 30 min before PTZ. The latency for development of convulsions and mortality, as well as the mortality protection percentage was recorded. For investigating the involvement of GABAergic system, flumazenil was utilized. The activity of antioxidant enzyme catalase as well as the levels of reduced glutathione and lipid peroxidation were measured in brain hippocampus. Similarly to diazepam, isopulegol significantly prolonged the latency for convulsions and mortality of mice. All animals were protected against mortality at higher dose of isopulegol. Flumazenil pretreatment decreased the prolongation of seizure latency induced by both diazepam and isopulegol, although it was not able to reverse the latency and protection percent for mortality. Isopulegol also significantly prevented PTZ-induced increase in lipid peroxidation, preserved catalase activity in normal levels, and prevented the PTZ-induced loss of GSH in hippocampus of mice. These results suggest that the anticonvulsant and bioprotective effects of isopulegol against PTZ-induced convulsions are possibly related to positive modulation of benzodiazepine-sensitive GABA(A) receptors and to antioxidant properties.

Central nervous system activity of acute administration of isopulegol in mice.

Isopulegol is a monoterpene alcohol intermediate in the preparation of (-)-menthol and it is present in the essential oils of various plants. This work presents behavioral effects of isopulegol in animal models of open field, elevated plus maze (EPM), rota rod, hole board, barbiturate-induced sleeping time, tail suspension and forced swimming tests in mice. Isopulegol was administered intraperitoneally to male mice at single doses of 25 and 50 mg/kg, while diazepam 1 or 2 mg/kg and imipramine 10 or 30 mg/kg were used as standard drugs. The results showed that, similar to diazepam (1 mg/kg), both doses of isopulegol significantly modified all the observed parameters in the EPM test, without alter the general motor activity in the open field test. In the same way, both doses of isopulegol increased the number of head dips in the hole-board test. Forced swimming and tail suspension tests showed that isopulegol (25 and 50 mg/kg) was able to induce a significant increase in the immobility time, in opposite to imipramine, a recognized antidepressant drug. There was a decrease in the sleep latency time and prolongation of the pentobarbital-induced sleeping time with both doses of Isopulegol. Different from diazepam (2 mg/kg), isopulegol (25 e 50 mg/kg) had no effect on the motor coordination of animals in the rota rod test. These results showed that isopulegol presented depressant- and anxiolytic-like effects.