Evaluation of five antibiotic resistance genes in wastewater treatment systems of swine farms by real-time PCR.

Antibiotics are widely used in livestock for infection treatment and growth promotion. Wastes from animal husbandry are a potential environmental source of antibiotic-insensitive pathogens, and the removal efficiency of the resistance genotypes in current wastewater treatment plants (WWTPs) is unknown. In this study, quantitative PCR was used for evaluating antibiotic resistance genes in wastewater treatment processes. Six wastewater treatment plants in different swine farms were included in this study, and five antibiotic resistance genes (ARGs) were tested for each treatment procedure. All of the tested ARGs including tetA, tetW, sulI, sulII, and blaTEM genes were detected in six swine farms with considerable amounts. The results showed that antibiotic resistance is prevalent in livestock farming. The ARG levels were varied by wastewater treatment procedure, frequently with the highest level at anaerobic treatment tank and lowest in the activated sludge unit and the effluents. After normalizing the ARG levels to 16S rRNA gene copies, the results showed that ARGs in WWTP units fluctuated partly with the quantity of bacteria. Regardless of its importance in biodegradation, the anaerobic procedure may facilitate bacterial growth thus increasing the sustainability of the antibiotic resistance genotypes. After comparing the copy numbers in influx and efflux samples, the mean removal efficiency of ARGs ranged between 33.30 and 97.56%. The results suggested that treatments in the WWTP could partially reduce the spread of antibiotic-resistant bacteria, and additional procedures such as sedimentation may not critically affect the removal efficiency.

Stimulation of the lateral division of the dorsal telencephalon induces synaptic plasticity in the medial division of adult zebrafish.

In ray-finned fishes, the lateral (Dl) and medial (Dm) division of the dorsal telencephalon are important in learning and memory formation. Tract-tracing studies revealed that neural connections are formed between these regions via afferent Dl fibers projecting to the Dm. However, research analyzing Dl-Dm synaptic transmission is scant. We have used electrophysiological techniques to assess neurotransmission and synaptic plasticity in projections from the Dl to the Dm in zebrafish. We demonstrate that electrical stimulation of the Dl division evoked a negative field potential in the Dm division that could be inhibited by application of the AMPA/kainate receptor antagonist, CNQX (5µM). Pairs of stimuli, when delivered at brief inter-pulse intervals (IPI), elicited paired pulse facilitation (PPF). Long-term potentiation (LTP), induced through the application of three trains of high frequency stimulation (HFS; 100Hz for 1s), lasted for more than 1h and could be inhibited with DL-AP5 (40µM), an N-methyl-d-aspartate (NMDA) receptor antagonist. Our results suggest that the intratelencephalic connection between Dl and Dm may play an important role in the synaptic plasticity of the zebrafish brain. It also provides a new electrophysiological model for studying the neural mechanisms underlying learning and memory in zebrafish.

Effect of MK-801-induced impairment of inhibitory avoidance learning in zebrafish via inactivation of extracellular signal-regulated kinase (ERK) in telencephalon.

N-Methyl-D-aspartate (NMDA) receptors are implicated in a wide range of complex behavioral functions, including cognitive activity. Numerous studies have shown that using the repetitive administration of a noncompetitive NMDA receptor antagonist, MK-801, induces amnesia in rodents. In this study, the effect of a subchronic MK-801 treatment on the cognitive function of zebrafish was evaluated using a novel inhibitory avoidance task. First, we established a new system to investigate the inhibitory avoidance learning of zebrafish where they were trained to refrain from swimming from a shallow compartment to a deep compartment in order to avoid electric shock. Second, we found that blocking NMDA receptors by MK-801 could significantly attenuate the inhibitory avoidance behavior of the zebrafish and alter the telencephalic extracellular signal-regulated kinase (ERK) phosphorylation level 90 min after the inhibitory avoidance training. These results suggest that the formation of long-term emotional memory is possibly mediated by ERK activation in the telencephalon of zebrafish.