A portable infrared photoplethysmograph: heartbeat of Mytilus galloprovincialis analyzed by MRI and application to Bathymodiolus septemdierum

Hypertonic water reabsorption with a parallel-current system via the glandular and saccular renal tubules of Ruditapes philippinarum

We investigated the renal function of the brackish water clam, Ruditapes philippinarum, employing magnetic resonance imaging (MRI). The R. philippinarum kidney consists of two renal tubules, a glandular (GT) and a saccular (ST) tubule. After exposure to seawater containing manganese ion (Mn2+) at 20°C, the intensity of the T1-weighted MRI and longitudinal relaxation rates (1/T1=R1) of the kidney were increased. In the ST, haemolymph containing Mn2+ entered directly from the auricle, and the Mn2+ concentration ([Mn2+]) increased in the initial part of the ST. Thereafter, [Mn2+] was almost constant until the posterior end of the kidney. The GT received haemolymph from the pedal sinus via the visceral sinus. The GT runs parallel inside the ST, and [Mn2+] increased progressively until it merged with the ST. In a range of seawater with [Mn2+] from 1 to 30 µmol l-1, the [Mn2+] increased 12-fold in the posterior part of the ST, compared with the ambient [Mn2+]. Based on these results, the epithelium of the initial part of the ST reabsorbs water from luminal fluid, building up a higher osmotic pressure. Using this osmotic gradient, hypertonic water is reabsorbed via the epithelium of the GT to the ST, and then transferred to the haemolymph via the epithelium of the ST. Excess water is excreted as urine. This model was supported by the increases in [Mn2+] in the ST when the clams were exposed to seawater containing Mn2+ at salinity from 26.0 to 36.0‰, showing that the parallel-current system works in hypotonic seawater.

Monitoring Bivalve Behavior and Physiology in the Laboratory and Field Using Open Source Tools

Bivalve molluscs have been the focus of behavioral and physiological studies for over a century, due in part to the relative ease with which their traits can be observed. I review historical methods for monitoring behavior and physiology in bivalves and how modern methods with electronic sensors can allow for a number of parameters to be measured in a variety of conditions using low cost components and open source tools. Open source hardware and software tools can allow researchers to design and build custom monitoring systems to sample organismal processes and the environment, systems that can be tailored to the particular needs of a research program. The ability to leverage shared hardware and software can streamline the development process, providing greater flexibility to researchers looking to expand the number of traits they can measure, the frequency and duration of sampling, and the number of replicate devices they can afford to deploy.

Real-time automated behavioural monitoring of mussels during contaminant exposures using an improved microcontroller-based device

An improved microcontroller-based device for real-time biomonitoring of mussel behaviour is introduced in this study. Open source Arduino platforms were used as processing cores and infra-red (IR) sensors (with transistor output) and Hall sensors to record the cardiac activities and valve movements of mussels. Compared to the devices described in previous studies, this device has low cost, high throughput, and high portability, and can be applied to conduct real-time preliminary automatic data processing. Mediterranean mussels were exposed to Cu²⁺ and microplastics and their cardiac activities and valve movements were recorded. The results demonstrated that Cu²⁺ exposure caused valve closure and a drop in the heart rate, similar to the behaviour during natural periods of bradycardia in mussels. The microplastic exposures tended to cause high oscillations (low concentration of microplastics) and slow decreases (high concentration of microplastics) of the maximum valve open positions. Such oscillations and decreases appeared to reset and restart after the bradycardia period. The device has potential to measure and establish behavioural responses of mussels and other bivalves, to the stress of exposure from environmental contaminants.

Non-invasive quantification of cardiac stroke volume in the edible crab Cancer pagurus

Background

Brachyuran crabs can effectively modulate cardiac stroke volume independently of heart rate in response to abiotic drivers. Non-invasive techniques can help to improve the understanding of cardiac performance parameters of these animals. This study demonstrates the in vivo quantification of cardiac performance parameters through magnetic resonance imaging (MRI) on the edible crab Cancer pagurus. Furthermore, the suitability of signal integrals of infra-red photoplethysmographs as a qualitative tool is assessed under severe hypoxia.

Results

Multi-slice self-gated cardiac cinematic (CINE) MRI revealed the structure and motion of the ventricle to quantify heart rates, end-diastolic volume, end-systolic volume, stroke volume and ejection fraction. CINE MRI showed that stroke volumes increased under hypoxia because of a reduction of end-systolic volumes at constant end-diastolic volumes. Plethysmograph recordings allowed for automated heart rate measurements but determination of a qualitative stroke volume proxy strongly depended on the position of the sensor on the animal. Both techniques revealed a doubling in stroke volumes after 6 h under severe hypoxia (water PO₂ = 15% air saturation).

Conclusions

MRI has allowed for detailed descriptions of cardiac performance in intact animals under hypoxia. The temporal resolution of quantitative non-invasive CINE MRI is limited but should encourage further refining. The stroke volume proxy based on plethysmograph recordings is feasible to complement other cardiac measurements over time. The presented methods allow for non-destructive in vivo determinations of multiple cardiac performance parameters, with the possibility to study neuro-hormonal or environmental effects on decapod cardio physiology.

Size-selective filtration of the atrial wall estimated from the accumulation of tracers in the kidney of the mussel Mytilus galloprovincialis

In order to determine the molecular weight cut-off (MWCO) for the atrial wall filtration into kidneys of the Mytilus galloprovincialis, we employed five magnetic resonance (MR) tracers: manganese chloride (Mn²⁺), gadolinium chloride (Gd³⁺), manganese-ethylenediaminetetraacetic acid (MnEDTA), gadolinium-diethylenetriamine pentaacetic acid (GdDTPA) and oligomer-based contrast agent (CH3-DTPA-Gd). After injection of the MR tracers (1 or 2 mmol l^-1×0.1 ml) into the visceral mass, T ₁-weighted MR imaging (T _1w-MRI) and the longitudinal relaxation rates (1/T ₁=R ₁) were measured at 20°C. The MR tracers were distributed uniformly in the visceral mass within 1 h after injection. The T _1w-MRI intensity and R ₁ of the kidney (R _1K) were increased by Mn²⁺ and MnEDTA, with urine concentrations estimated at 210 and 65 µmol l^-1, respectively. The rest of the tracers showed only minimal or no increase. When the mussels were additionally incubated in seawater with 10 µmol l^-1 MnCl₂, R _1K was increased in the GdDTPA group, but not in the GdCl₃ group. Therefore, Gd³⁺ might have inhibited renal accumulation of Mn²⁺ and Gd³⁺ Incubation in seawater with 10 µmol l^-1 MnEDTA showed no increase in the R _1K, but additional incubation with 10 µmol l^-1 MnCl₂ caused an increase in R _1K It is suggested that injected MnEDTA was filtrated as MnEDTA per se, and not likely separated into free Mn²⁺ Thus, we concluded that the MWCO of the atrial wall of the M. galloprovincialis is around 0.5 kDa, which is almost 1/100 of that for vertebrate animals, and suggests a reduction in efforts to reabsorb metabolites and osmolytes from the urine.

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

OBJECTIVES

An approach is presented for high-field MRI studies of the cardiovascular system (CVS) of a marine crustacean, the edible crab Cancer pagurus, submerged in highly conductive seawater.

MATERIALS AND METHODS

Structure and function of the CVS were investigated at 9.4 T. Cardiac motion was studied using self-gated CINE MRI. Imaging protocols and radio-frequency coil arrangements were tested for anatomical imaging. Haemolymph flow was quantified using phase-contrast angiography. Signal-to-noise-ratios and flow velocities in afferent and efferent branchial veins were compared with Student's t test (n = 5).

RESULTS

Seawater induced signal losses were dependent on imaging protocols and RF coil setup. Internal cardiac structures could be visualized with high spatial resolution within 8 min using a gradient-echo technique. Variations in haemolymph flow in different vessels could be determined over time. Maximum flow was similar within individual vessels and corresponded to literature values from Doppler measurements. Heart contractions were more pronounced in lateral and dorso-ventral directions than in the anterior-posterior direction.

DISCUSSION

Choosing adequate imaging protocols in combination with a specific RF coil arrangement allows to monitor various parts of the crustacean CVS with exceptionally high spatial resolution despite the adverse effects of seawater at 9.4 T.

Roles of Keber's valve and foot chamber for foot manipulation in the mussel Nodularia douglasiae

In order to analyse the roles of Keber's valve for foot manipulation in the mussel Nodularia douglasiae, the anatomy and haemolymph flow in the cardiovascular system were detected by magnetic resonance imaging. The superficial layer of the foot was covered by a dense muscle layer, which extended to the dorsal side and connected with the shell. This closed space, the foot chamber, had an inlet (anterior aorta) and an outlet (Keber's valve). At rest, in the beginning of the systolic phase, flows in the anterior aorta and the pedal artery increased, followed by the pedal and visceral sinuses. Then these flows ceased at the end of the systolic phase, followed by inflow to the ventricle in the diastolic phase; therefore, the compliance of the foot chamber is low enough to transfer pressure pulses to the visceral sinus. Extension of the foot started with relaxation of the foot muscle, so the compliance of the foot chamber increased. Then, Keber's valve closed so that the haemolymph filled the foot haemocoel. Retraction of the foot is initiated by the opening of Keber's valve. Judging from these results Keber's valve and the foot chamber are essential for circulation at rest, foot extension and retraction.This article has an associated First Person interview with the first author of the paper.

Accumulation and excretion of manganese ion in the kidney of M ytilus galloprovincialis

T ₁-weighted magnetic resonance imaging (T _1w-MRI) was employed to detect the accumulation of manganese ion (Mn²⁺) in urine in the kidney of the mussel Mytilus galloprovincialis, and the longitudinal relaxation rates (1/T ₁=R ₁) were measured. When the mussel was exposed to seawater containing 10 µmol l^-1 Mn²⁺, the T _1w-MRI intensity and R ₁ of the kidney, stomach and digestive glands were increased. Mn²⁺ might be taken into the hemolymph via the gastrointestinal tract, and then filtrated into the pericardium via the auricles. Although the image intensity in the pericardium was not affected by manganese, an image intensity enhancement was observed in the distal part of the renopericardial communication canals between the pericardium and the kidneys, indicating Mn²⁺ was concentrated in the excretion pathway. As the seawater Mn²⁺ concentration ([Mn²⁺]_SW) was increased from 3 to 50 µmol l^-1, R ₁ of the kidney (R _1K) was elevated. When the mussels were immersed in 3-10 µmol l^-1 [Mn²⁺]_SW for 24 h, the Mn²⁺ concentration in the kidney ([Mn²⁺]_K) showed a 15-fold increase compared with the ambient [Mn²⁺]_SW In the range of [Mn²⁺]_SW from 10 to 50 µmol l^-1, R _1K reached a plateau level that corresponded to 200 µmol l^-1 [Mn²⁺]_K As [Mn²⁺]_K fell transiently, voluntary excretion of urine from the kidney was assumed. The decreases in intensity were not synchronized between the right and left kidneys, and the closure of the shells might not be essential for urinary excretion. The voluntary excretion suggested an additional explanation for the large range in metal concentratons in the kidneys of the mussel.