Antioxidant role of oleuropein on midbrain and dopaminergic neurons of substantia nigra in aged rats

Oleuropein is a phenolic compound which is present in the olive leaf extract. The purpose of the present study was to investigate the neuroprotective effect of oleuropein as an antioxidant agent on the substantia nigra in aged rats. Twenty 18-month-old Wistar rats [450-550 g] were randomly divided into control and experimental groups. The experimental group received a daily single dose of 50 mg/kg of oleuropein by oral gavage for 6 months. The control group received only distilled water. All rats were sacrificed two hours after the last gavage and the brains were removed and midbrains were cut. One part of the midbrains were homogenized and centrifuged. The tissue supernatant was assayed for lipid peroxidation [LPO] and antioxidant enzyme activities. The other part of midbrains fixed and embedded in paraffin, then processed for Nissl and immunohistochemistry [IHC] staining. Data was analyzed using SPSS by t-test. Differences were considered significant for P<0.05. The level of LPO in midbrain of the rats was decreased significantly in the experimental group, but superoxide dismutase, catalase and glutathione peroxidase activities were increased in experimental group compared to control group [P<0.05]. Morphometric analyses showed significantly that the experimental group had more neurons in substantia nigra pars compacta [SNc] either in Nissl or IHC staining when compared to control [P<0.05]. The results of the present study indicate that treatment of the old rats with oleuropein reduces the oxidative damage in SNc by increasing the antioxidant enzyme activities

Agonistic-like responses from the torus semicircularis dorsalis elicited by GABA A blockade in the weakly electric fish Gymnotus carapo

Findings by our group have shown that the dorsolateral telencephalon of Gymnotus carapo sends efferents to the mesencephalic torus semicircularis dorsalis (TSd) and that presumably this connection is involved in the changes in electric organ discharge (EOD) and in skeletomotor responses observed following microinjections of GABA A antagonist bicuculline into this telencephalic region. Other studies have implicated the TSd or its mammalian homologue, the inferior colliculus, in defensive responses. In the present study, we explore the possible involvement of the TSd and of the GABA-ergic system in the modulation of the electric and skeletomotor displays. For this purpose, different doses of bicuculline (0.98, 0.49, 0.245, and 0.015 mM) and muscimol (15.35 mM) were microinjected (0.1 æL) in the TSd of the awake G. carapo. Microinjection of bicuculline induced dose-dependent interruptions of EOD and increased skeletomotor activity resembling defense displays. The effects of the two highest doses showed maximum values at 5 min (4.3 ± 2.7 and 3.8 ± 2.0 Hz, P < 0.05) and persisted until 10 min (11 ± 5.7 and 8.7 ± 5.2 Hz, P < 0.05). Microinjections of muscimol were ineffective. During the interruptions of EOD, the novelty response (increased frequency in response to sensory novelties) induced by an electric stimulus delivered by a pair of electrodes placed in the water of the experimental cuvette was reduced or abolished. These data suggest that the GABA-ergic mechanisms of the TSd inhibit the neural substrate of the defense reaction at this midbrain level.