Journal
AQUACULTURE
Volume 350, Issue -, Pages 91-97Publisher
ELSEVIER
DOI: 10.1016/j.aquaculture.2012.04.012
Keywords
Essential oil; Benzodiazepine; GABA; Tolerance; Anesthesia
Categories
Funding
- Fundacao de Amparo a Pesquisa do Estado do Rio Grande do Sul (FAPERGS/PRONEX) [10/0016-8]
- Conselho Nacional de Pesquisa e Desenvolvimento Cientifico (CNPq) [470964/2009-0]
- Coordena ao de Aperfeicoamento de Pessoal de Nivel Superior (CAPES)
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The aim of this study was to determine the time until anesthetic induction and recovery in silver catfish (Rhamdia quelen) exposed to the essential oil of Ocimum gratissimum L. (EO), its potential mechanism of action via GABAergic transmission and the development of tolerance. The EO was obtained from the aerial parts of O. gratissimum L. by hydrodistillation and analyzed by gas chromatograph coupled to mass spectrometer (GC-MS). Eugenol (73.6%) and beta-bisabolene (18.3%) are the major compounds of the EO. Juvenile silver catfish were placed in aquaria containing different concentrations of the EO (10, 20, 30, 40, 50, 60, 70, 150 and 300 mg L-1) to determine the point at which anesthesia was induced and the length of the recovery period. In the following experiments, the anesthetic effect of the EO (10, 20 and 40 mg L-1) in association with benzodiazepine (BDZ) was determined. The GABAergic-like action and development of tolerance were assessed in fish exposed to BDZ (diazepam 150 mu M), EO (40 mg L-1) or both EO and BDZ (EO + BDZ) at the same concentrations. After the induction of anesthesia, juveniles were transferred to an anesthetic-free aquarium containing either the classic BDZ antagonist flumazenil (5 mu M) or water to assess their recovery. The development of tolerance was evaluated in two experiments. In the first, juveniles were exposed to the EO twice in a 30-day interval, and in the second five exposures, weekly intervals were performed. Fish exposed to concentrations above 30 mg L-1 of the EO were effectively anesthetized without experiencing side effects or mortality. Fast anesthesia (<4 min) could be obtained using 150 and 300 mg L-1 of the EO. Synergism was detected for EO + BDZ at the lower concentrations tested. Juveniles exposed to all tested drugs showed a faster recovery in flumazenil than those that recovered in water. The development of tolerance was observed in fish exposed to the EO or BDZ separately after the fifth exposure. Two exposures were sufficient to sensitize the fish to the action of these drugs. However, repeated exposure to EO + BDZ did not induce tolerance and/or sensitization. In conclusion, the EO of O. gratissimum is an effective and safe anesthetic for silver catfish, and its mechanism seems to be related to an interaction with the GABA(A)-benzodiazepine receptor. (C) 2012 Elsevier B.V. All rights reserved.
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