Propofol and essential oil of Nepeta cataria induce anaesthesia and marked myorelaxation in tambaqui Colossoma macropomum: Implications on cardiorespiratory responses

Highlights

• This is the first study using Nepeta cataria essential oil as an anaesthetic for fish.

• Propofol and N. cataria essential oil blunted muscle contraction power in Colossoma macropomum.

• Exposure to short-term baths using propofol and N. cataria essential oil did not compromise cardioventilatory function.

Abstract

This study aimed at characterizing the modulation of skeletal muscle contraction and cardiorespiratory response of tambaqui, Colossoma macropomum submitted to baths using anaesthetic concentrations (capable of inducing fast, i.e. < 5 min, and full body immobilization) of propofol (PRP) and essential oil of Nepeta cataria (EON). For the evaluation of electromyography, electrocardiographic data, and opercular beat intensity (OBI) and rate (OBR), fish (5.6 ± 1.8 g, 8.0 ± 0.3 cm, total length) were assigned to the following groups: a) control (basal recording), b) ethanol-exposed fish (vehicle control), c) fish submitted to induction with EON at 175 μL L⁻¹ and subsequent recovery, and d) fish submitted to induction with PRP at 4 μL L⁻¹ and subsequent recovery. Eight fish (n = 8) per group were used. Both products induced full body immobilization and suppressed (99.9%) dorsal muscle contraction power, determining a general anaesthesia-like state. During exposure to either anaesthetic, cardiac function was transiently affected, with decreased heart rates (42–43%) and a mild arrhythmia in PRP recovering fish. Moreover, ventilatory capacity was reduced with this drug (85.3% and 59.6% decrease in OBI and OBR, respectively), yet without mortality. On the other hand, EON did not alter ECG tracings, allowing for the maintenance of normal ventilation intensity during exposure, albeit a slight increment in OBR occurred during deep anaesthesia. This study confirms propofol anaesthesia in fish and presents N. cataria essential oil as a novel and safe natural anaesthetic for juvenile Colossoma macropomum and potentially for other teleost species.

Introduction

Farmed fish are often submitted to several stressors such as handling for biometrics, artificial spawning and transportation. Hence, the use of stress relieving agents are commonplace in modern aquaculture (Velíšek et al., 2009). In this sense, anaesthetics are frequently used to promote sedation, complete immobilization, prevent physical injuries, and thus attenuate the stress response in fish (Ross and Ross, 2008; Kiessling et al., 2009; Weber 3rd., 2011).

Many of the drugs currently presented as new fish anaesthetics and/or muscle relaxant agents, are regarded as such, based on mechanical stimuli tests and visual assessment during exposure to anaesthetic baths (Ross and Ross, 2008). However, Barbas et al. (2017) have warned that the sole use of behavioural markers, such as the registration of latency to loss of the righting reflex or full immobilization, does not prove a state of general anaesthesia, analgesia or myorelaxation.

The extent of muscle relaxation attained during fish anaesthesia can be objectively measured by the electromyogram (EMG) (Fujimoto et al., 2017), which corresponds to the technique of detection, recording, and analysis of the electrical signal originating from muscle contraction (Webster, 1978, Webster, 1988). In the case invasive procedures are necessary, e.g., for surgical procedures, general anaesthesia should be accompanied by muscle relaxation as a result of an effective neuromuscular blockade, for it will decrease the movements, and thus facilitate the surgery conditions (Barbas et al., 2017).

Another relevant indicator for the monitoring of anaesthesia is the electrocardiogram (ECG), which consists of recording the electrical impulses generated by the cardiac pacemaker tissue. In order for the cardiac fibres to contract, a stimulus is required. Such stimulus triggers an action potential that propagates through the fibres and can be detected on the surface of the skin by appropriate electrodes. The ECG corresponds to the sum of the cardiac action potentials that emanate from the body surface (Guimarães et al., 2003; Ganong, 2003). Although some studies on the cardiorespiratory monitoring of fish under anaesthesia are available (Sandblom et al., 2013; Seth et al., 2013; Barbas et al., 2017), these are still relatively scarce. The ECG together with the monitoring of the respiratory capacity will allow for the verification of impacts such as arrhythmia, excessive bradycardia, cardiac arrest, and severe hypoventilation during induction, maintenance and return from anaesthesia (Ross and Ross, 2008). This monitoring will ultimately shed light on the interplay between cardiac and ventilatory responses and clarify the compatibility of a given anaesthetic with life, mainly in those cases where novel products are proposed for fish anaesthesia. Since the early seventies (Randall, 1970) it is well known that cardiac and ventilatory rates in fish are functionally linked and, in many circumstances, neurophysiologically synchronized. Thus, monitoring of such markers is important for the assessment of the anaesthesia process per se.

Propofol (2,6-diisopropylphenol) is a widely used parenteral class anaesthetic of ultra-short duration in mammals. It is a relatively water-soluble chemical compound that has been already tested on several aquatic species, including fish (Fleming et al., 2003; Valença-Silva et al., 2014; Miller et al., 2005; Gholipour and Ahadizadeh, 2013; Valentim et al., 2016), however, no thorough reports are available to date on the cardiac, respiratory and skeletal muscle responses of fish submitted to anaesthesia with this drug.

Many plant extractives have a vast potential for use as alternative anaesthetics in fish farming (Hoseini et al., 2018). Specifically, the herbaceous Nepeta cataria, popularly known as “catnip” belongs to the Lamiaceae family, has succulent leaves and presents a slight smell of mint. Its major compound is nepetalactone (Sarkar et al., 1995; Webb and Russell, 2007). In folk medicine it is widely used because of its antiseptic, astringent, antitussive/anti-cough, anti-spasmodic, anti-asthmatic, anti-thermal, diuretic, analgesic, antinociceptive and sedative potentials (Jackson and Reed, 1969; Sherry and Hunter, 1979; Mairesse, 1981; Hart and Leedy, 1985; Osterhoudt et al., 1997; Aydin, 1998; Micelli et al., 2005; Smitherman et al., 2005). Extractives from this plant species are widely available to purchase worldwide, especially in its essential oil form.

The tambaqui fish, Colossoma macropomum is native to South America, where it inhabits floodplain areas of the Orinoco and Amazon river basins; after pirarucu, Arapaima gigas (Osteoglossidae) the tambaqui is considered the second biggest Amazonian freshwater scaled fish (Sousa et al., 2016) reaching more than one metre in length and weighing >30 kg (Valladão et al., 2016) in natural environments. Its good adaptation to captivity, disease resistance, and high market acceptance have made it one of the most reared and marketed species in south America, mainly in Brazil (de Gomes et al., 2010; Valladão et al., 2016). Recent studies have emphasized the use of this species as a good animal model for the screening of new anaesthetics in tropical freshwater fish due to its handling resistance and high sensitivity to drug testing (Barbas et al., 2016a; Barbas et al., 2016b; Barbas et al., 2017; Baldisserotto et al., 2018).

In a pilot behavioural study of our research group, N. cataria oil presented promising properties as an anaesthetic, as it rendered juvenile tambaqui rapidly immobilized (< 3 min) and unresponsive to mechanical and visual stimuli. Animals were fully recovered after being moved to anaesthetic-free water and no mortality occurred post-anaesthesia. Therefore, we hypothesized herein that exposure to this oil in an anaesthetic bath will exert loss of muscle tonus without a compromise to cardioventilatory responses. Further, the same hypothesis was proposed for propofol-anaesthetized fish, in which data attained could also be used for comparison purposes between anaesthetics.

Thus, the objective of this study was to characterize, through selected electrophysiological markers, the modulation of skeletal muscle contraction and cardiorespiratory response during anaesthetic induction and recovery of tambaqui juveniles, C. macropomum submitted to baths with anaesthetic concentrations of propofol and essential oil of Nepeta cataria.