Temperature effects on the cardiorespiratory control of American bullfrog tadpoles based on a non-invasive methodology

Abstract

Temperature effects on cardiac autonomic tonus in amphibian larval stages have never been investigated. Therefore, we evaluated the effect of different temperatures (15, 25 and 30°C) on the cardiorespiratory rates and cardiac autonomic tonus of premetamorphic tadpoles of the bullfrog, To this end, a non-invasive method was developed to permit measurements of electrocardiogram (ECG) and buccal movements (; surface electromyography of the buccal floor). For evaluation of autonomic regulation, intraperitoneal injections of Ringer solution (control), atropine (cholinergic muscarinic antagonist) and sotalol (β-adrenergic antagonist) were performed. Ringer solution injections did not affect heart rate () or across temperatures. Cardiorespiratory parameters were significantly augmented by temperature (: 24.5±1.0, 54.5±2.0 and 75.8±2.8 beats min at 15, 25 and 30°C, respectively; : 30.3±1.1, 73.1±4.0 and 100.6±3.7 movements min at 15, 25 and 30°C, respectively). A predominant vagal tone was observed at 15°C (32.0±3.2%) and 25°C (27.2±6.7%) relative to the adrenergic tone. At 30°C, the adrenergic tone increased relative to the lower temperature. In conclusion, the cholinergic and adrenergic tones seem to be independent of temperature for colder thermal intervals (15-25°C), while exposure to a hotter ambient temperature (30°C) seems to be followed by a significant increase in adrenergic tone and may reflect cardiovascular adjustments made to match oxygen delivery to demand. Furthermore, while excluding the use of implantable electrodes or cannulae, this study provides a suitable non-invasive method for investigating cardiorespiratory function (cardiac and respiratory rates) in water-breathing animals such as the tadpole.

A survey of fish behaviour quantification indexes and methods in aquaculture

“…2020), water quality (Braun & Perry 2010; Longhini et al . 2017; Saari et al . 2018), and breeding density (Hong et al .…”

Thermal Acclimation to the Highest Natural Ambient Temperature Compromises Physiological Performance in Tadpoles of a Stream-Breeding Savanna Tree Frog

“…Tadpoles were placed into the respirometer for habituation at the first test temperature (15 • C) for at least one hour, which is sufficiently long for recovery from handling stress (Kern et al, 2014;Seebacher and Grigaltchik, 2014;Longhini et al, 2017). After one hour, the respirometer was sealed and ṀO 2 was determined in duplicates at each test temperature (15, 20, 25, 30, and 34 • C), always ensuring that O 2 saturation was kept above 80% (Jensen et al, 2013) during each cycle.…”

“…To study the autonomic control of heart rate (f H ), atropine (cholinergic muscarinic antagonist; 3.0 mg kg −1 ) and sotalol (β-adrenergic antagonist; 3.0 mg kg −1 ) were purchased from Sigma-Aldrich (St Louis, MO, United States) and dissolved in amphibian Ringer solution (composition in mmol l −1 : 46.9 NaCl; 21.0 KCl; 2.40 CaCl; 1.29 MgCl; 3.14 NaHCO 3 ; according to Zena et al, 2016;Longhini et al, 2017). Drugs and doses were chosen based on previous studies performed on both tadpole and adult anuran amphibians (Zena et al, 2016;Longhini et al, 2017).…”

“…A different sub-sample of tadpoles was used to study the autonomic control for each acclimation group (T acc18 : N = 8; T acc25 : N = 8). Heart rate was measured using a noninvasive methodology as previously described (Longhini et al, 2017). Briefly, we coupled two parallel electrodes, made from hypodermic needles (40 mm × 1.20 mm, 18G), to a 20 mL plastic syringe positioned inside the experimental tank and connected to a recirculation pump to ensure adequate water exchange between the outside and the inside of the syringe.…”

“…At first, the blockage was induced in each individual in their respective acclimation group (T acc18 and T acc25 ), that is, at their respective acclimation temperatures, 18 and 25 • C. After 7 days, each tadpole was again subjected to the autonomic blockade, but in this case in the form of an acute exposure to the opposite temperature of acclimation, i.e., T acc18 was exposed to 25 • C for 1 h and T acc25 was exposed to 18 • C for 1 h before the pharmacological blockade. At the end of the experiments, tadpoles were euthanized by placing them in a solution of benzocaine hydrochloride (250 mg L −1 ) buffered to pH 7.7 with sodium bicarbonate (Longhini et al, 2017). All tadpoles survived to experiments performed for the autonomic blockade, excepted one animal (5%) from T acc25 , which died during the habituation to the experimental apparatus when acutely exposed to 18 • C.…”