CO₂ induced pH_i changes in the brain of polar fish: a TauCEST application

Abstract

Chemical exchange saturation transfer (CEST) from taurine to water (TauCEST) can be used for in vivo mapping of taurine concentrations as well as for measurements of relative changes in intracellular pH (pH i ) at temperatures below 37°C. Therefore, TauCEST offers the opportunity to investigate acid-base regulation and neurological disturbances of ectothermic animals living at low temperatures, and in particular to study the impact of ocean acidification (OA) on neurophysiological changes of fish.Here, we report the first in vivo application of TauCEST imaging. Thus, the study aimed to investigate the TauCEST effect in a broad range of temperatures (1-37°C) and pH (5.5-8.0), motivated by the high taurine concentration measured in the brains of polar fish. The in vitro data show that the TauCEST effect is especially detectable in the low temperature range and strictly monotonic for the relevant pH range (6.8-7.5).To investigate the specificity of TauCEST imaging for the brain of polar cod (Boreogadus saida) at 1.5°C simulations were carried out, indicating a taurine contribution of about 65% to the in vivo expected CEST effect, if experimental parameters are optimized. B. saida was acutely exposed to three different CO 2 concentrations in the sea water (control normocapnia; comparatively moderate hypercapnia OA m = 3300 μatm; high hypercapnia OA h = 4900 μatm). TauCEST

Studying the cardiovascular system of a marine crustacean with magnetic resonance imaging at 9.4 T

“…While seawater-induced signal loss increased at high field strengths, this can be partially overcome by the use of improved high-power amplifiers in combination with RF hardware purpose-built for high-conductivity samples. The negative effects of the high conductivity and the volume of the surrounding seawater are the main reasons for signal losses in MR images, particularly for spin-echo sequences at 9.4 T. Nevertheless, fast spin-echo sequences achieve highquality images of marine fish, when the seawater content between RF coil and region of interest is minimized [13]. MR techniques benefit from a much lower body fluid osmolarity in teleost fish, compared to crustacea or other marine invertebrates.…”

“…The gills are located on both sides lateral to the heart with Velcro © . The chamber was attached to a retractable arm for positioning, and thus had no contact to the inner surface of the MRI scanner, the gradient system nor the RF resonator, similar to a setup used by Wermter et al [13]. Water was continuously supplied to the chamber as described by Bock et al [35].…”

“…3b). Spin-echo sequences could not replicate the high image quality of images of marine fish brains [13] or of crustacea at lower field strength [20]. Image quality on larger, highly conductive samples at 9.4 T is limited by signal losses, in particular close to the center of the image (Online Source 1).…”

“…Standard instruments come with high-performance radio-frequency (RF) antennae, gradient systems and powerful electronics that are especially suitable for cardiac MRI [4] and cardiovascular imaging [5]. Recently, MRI has been used to answer more fundamental, biological research questions in morphological studies [6][7][8][9][10][11] and in comparative physiology of aquatic animal models [12,13]. Present applications of cardiac MRI to aquatic model organisms were thus far limited in resolution because of lower field strength [14][15][16] or usage of very small organisms (< 5 cm) [17][18][19].…”

Exploring New Frontiers in Marine Radioisotope Tracing – Adapting to New Opportunities and Challenges

“…Mainly, two in vivo techniques have been used: proton magnetic resonance spectroscopy ( 1 H-MRS) and 31 P magnetic Resonance Spectroscopy ( 31 P-MRS). 1 H-MRS is able to quantify the abundance of neurochemicals, such as neurotransmitters and metabolites like amino acids, but also anaerobic end products, such as lactate, and is also used for fat and lipid analysis (Bock et al, 2017;Wermter et al, 2018). 31 P-MRS measures phosphorus-containing metabolites that play an essential role in physiology.…”