Anesthetic Evaluation of Geraniol and Citronellol in Tambaqui (Colossoma macropomum): Neuromuscular, Cardiorespiratory, and Chemoprotective Implications
Author: Ednara Ronise Lima de Araújo (Currículo Lattes)
Advisor: Dr. Luís André Nassr de Sampaio
Abstract
The study of new anesthetic agents will allow the proposition of alternative drugs that are effective, potentially less costly, without compromising the necessary safety and efficacy, with rapid action on the nervous system and no subsequent complications for the animal. In fish, the anesthetic activity of citronella essential oil (EO) has been demonstrated; however, there is no information in the literature regarding which major constituents of this oil are responsible for the biological and behavioral effects observed in anesthetized juveniles. In this context, the objective of this study was to evaluate the anesthetic efficacy of the isolated phytoconstituents from citronella EO, geraniol (GRL) and citronellol (CTL), in tambaqui juveniles, Colossoma macropomum, by assessing induction and recovery times through concentration-response assays, as well as evaluating their effects on behavior, muscle tone modulation, cardiorespiratory frequency and rhythm, cardiotoxic potential, capacity to induce central neuronal depression, and oxidative balance. For the evaluation of anesthesia and recovery (Chapter 1), the anesthetic efficacy of GRL and CTL was assessed through behavioral characterization and evaluation of electrophysiological markers. The fish (24.78 ± 2.50g) were divided into two experimental groups: I – Behavioral Evaluation: Six concentrations (10; 30; 50; 70; 90; and 110 µL L⁻¹) were tested for each compound, where effective concentrations were found for both products (70 µL L⁻¹ GRL and 90 µL L⁻¹ CTL). II – Electrophysiological Characterization: The concentrations determined in the first experiment were used for recordings of EMG, ECG, intensity and frequency of opercular beat (OBI and OBR), and heart rate (HR). Our results demonstrated that GRL and CTL promoted total body immobilization and presented muscle-relaxant properties, with alterations but no compromise of cardiac function. In the cardiological characterization and cardiotoxic potential assessment (Chapter 2), changes in cardiac response patterns of animals exposed to GRL and CTL and during recovery were evaluated. Juvenile tambaqui (13.9 ± 1.4g) were exposed to the same concentrations determined in the first chapter, and electrocardiographic recordings (ECG) lasted five minutes. Parameters investigated included heart rate (HR) (beats min⁻¹), amplitude recording (mV), RR interval (s), QT interval (s), and QRS complex duration (s). Animals exposed to GRL, despite presenting a negative chronotropic effect, maintained sinus rhythm. In contrast, those exposed to CTL exhibited pronounced bradycardia and arrhythmia, which were reversible during the recovery phase, which was rapid for both anesthetics. For neuronal depression assessment (Chapter 3), aimed at observing the anesthetic depth and reversibility of effects promoted by GRL and CTL on the central nervous system (CNS), fish (35.2 ± 9.4g) were exposed to the anesthetics and EEG recordings of induction and recovery were conducted for 300 seconds. Irregularities in the traces were observed; however, GRL allowed regular traces, while animals exposed to CTL exhibited patterns incompatible with an adequate anesthesia condition. For oxidative balance assessment during transport under sedation (Chapter 4), animals (26.97 ± 3.73 g) were subjected to simulated transport for 2, 6, and 10 hours, using sedative doses corresponding to 15% of the effective dose found in the first chapter of this work (GRL – 10.5 µL L⁻¹ and CTL – 13.5 µL L⁻¹). At the end of transport, antioxidant capacity (ACAP), glutathione concentration (GSH), sulfhydryl group (P-SH), and lipid peroxidation levels (TBARS) were evaluated in gills, brain, liver, and muscle. The highest concentrations of GSH and P-SH were found in the gills in the presence of the anesthetics. Conversely, LPO levels were considerably higher in muscle of animals transported with the addition of CTL in the water, regardless of transport time. We concluded that GRL added to transport water in sedative doses would be a good option to mitigate oxidative damage, especially in the gills. On the other hand, CTL demonstrated a pro-oxidant action, with high levels of LPO in the muscle of post-transported animals.