BackgroundPraziquantel (PZQ) is an effective pesticide against monogeneans. Its pharmacokinetics in fish may be affected by water environment and temperature. The present study was designed to compare the pharmacokinetics, tissue distribution, and elimination of PZQ in freshwater-acclimated grass carp and brackish water cultured grass carp. Plasma and tissue PZQ concentrations were determined after a single 10 mg/kg oral PZQ dose.ResultsThe datas of plasma and tissues drug concentration was calculated by the software SPSS 13.0. According to the One-Way ANOVA, the results showed that the salinity had a significant effect on the drug concentration of plasma (p < 0.01), muscle (p < 0.01), liver (p < 0.01) and kidney (p < 0.01) in the all sampling time points between the brackish water grass carps and the freshwater grass carps, wherein, PZQ plasma and tissue concentrations in the brackish water group were constantly lower than that in the freshwater group. The peak PZQ levels of plasma, muscle, liver, and kidneys in the brackish water group were 0.76 μg/ml, 0.51 μg/g, 2.7 μg/g, and 2.99 μg/g, respectively; and that in the freshwater group were 0.91 μg/ml, 0.62 μg/g, 3.87 μg/g, and 3.39 μg/g, respectively. The elimination half-lives (t1/2β) in plasma and all tissues of the freshwater group were significantly longer than that in the brackish water group. The elimination half-lives (t1/2β) of plasma, muscle, liver and kidneys in brackish water grass carps were 56.46, 36.17, 15.31, and 132.64 h, respectively; and that in the freshwater grass carps were 71.15, 44.88, 23.86, and 150.23 h, respectively.ConclusionThese findings indicate that water environment affects the tissue distribution and elimination of PZQ in grass carps, the elimination in brackish water grass carps is more rapid than that in fresh water grass carps and tissue concentrations of brackish water grass carps are lower than that in freshwater grass carps after orally administrating the same dosage at the same water temperature. We speculate that the main excretion pathway of the drug is through renal elimination, and the decreased kidney function in brackish water grass carps is likely responsible for the considerable difference in pharmacokinetics between the two groups of grass carps.

Gamma-aminobutyric acid (GABA), a major inhibitory neurotransmitter in brain, is synthesized from glutamate and metabolized to succinic semialdehyde by glutamic acid decarboxylase (GAD) and GABA transaminase (GABA-T), respectively. The fast inhibitory effect of GABA is mediated by GABA type A (GABAA) receptors that are associated with several neurological disorders, and GABAA receptors are targets of several therapeutic agents. To date, information on the distribution and quantity of GABAA receptors in Carassius auratus gibelio is still limited. We investigated for the first time, the tissue-specific distribution of GABAARβ2a and GABAARβ2b, the two subunits of the predominant GABAA receptor subtype (α1β2γ2), and then, the expression of GABAARβ2a, GABAARβ2b, GAD, and quantified GABA-T genes in different tissues by quantitative real-time PCR method and compared different expressions between two developmental stages of C. auratus gibelio. Results showed that GABAARβ2a and GABAARβ2b genes expressed in both brain and peripheral organs using reverse transcription-polymerase chain reaction. In addition, the majority of GABAARβ2a, GABAARβ2b, GAD, and GABA-T were mainly synthesized in brain; however, a considerable amount of GABA-T was secreted from the peripheral tissues, especially in the liver. Moreover, the expression of GABAARβ2a and GABAARβ2b genes in different tissues varied with body weight change. This study provides a reference for further studies on GABA and GABAA receptors subunits and an insight on the possible pharmacological properties of the GABAA receptor in C. auratus gibelio.

Carassius auratus gibelio has been widely cultivated in fish farms in China, with avermectin (AVM) being used to prevent parasite infection. Recently, AVM was found to pass through the Carassius auratus gibelio blood-brain barrier (BBB). Although AVM acts mainly through a GABA receptor and specifically the α1 subunit gene, the most common isoform of the GABA A receptor, which is widely expressed in brain neurons and has been studied in other fish, Carassius auratus gibelio GABA A receptor α1 subunit gene cloning, and whether AVM passes through the BBB to induce Carassius auratus gibelio GABA A receptor α1 subunit gene expression have not been studied. The aim of this study was to clone, sequence, and phylogenetically analyze the GABA A receptor α1 subunit gene and to investigate the correlation of its expression with neurotoxicity in brain, liver, and kidney after AVM treatment by quantitative real-time reverse transcription polymerase chain reaction. The α1 subunit gene was 1550 bp in length with an open reading frame of 1380 bp encoding a predicted protein with 459 amino acid residues. The gene contained 128 bp of 5' terminal untranslated region (URT) and 72 bp of 3' terminal UTR. The α1 subunit structural features conformed to the Cys-loop ligand-gated ion channels family, which includes a signal peptide, an extracellular domain at the N-terminal, and four transmembrane domains. The established phylogenetic tree indicated that the α1 subunits of Carassius auratus gibelio and Danio rerio were the most closely related to each other. The α1 subunit was found to be highly expressed in brain and ovary, and the α1 mRNA transcription level increased significantly in brain. Moreover, the higher the concentration of AVM was, the higher the GABA A receptor expression was, indicating that AVM can induce significant neurotoxicity to Carassius auratus gibelio. Therefore, the α1 subunit mRNA expression was positively correlated with the neurotoxicity of AVM in Carassius auratus gibelio. Our findings suggest that AVM should be used carefully in Carassius auratus gibelio farming, and other alternate antibiotics with lower toxicity should be investigated with respect to toxicity via the induction of GABA A receptor expression for fish farming.

The aim of this study was to investigate the relationship between the administration of chitosan (CTS), expression of permeability glycoprotein (P-gp), and the metabolism of norfloxacin (NOR) in Grass Carp Ctenopharyngodon idella. Fish were administrated with a single dose of either NOR, CTS, 1:5 NOR-CTS or 1:10 NOR-CTS. The P-gp expression was analyzed by immunohistochemistry and real time-PCR. The concentration of NOR was determined using HPLC. The mRNA and protein expression of P-gp in the fish intestine was significantly enhanced following a single dosage of 40 mg/kg NOR, and peak expression occurred at 3 h after drug administration (P < 0.05). A single dosage of both 1:5 NOR-CTS and 1:10 NOR-CTS reduced the intestinal P-gp expression to levels significantly lower than that from NOR alone (P < 0.05), but significantly higher than that from the control (P < 0.05). Interestingly, CTS alone also led to a slight decrease in P-gp expression. In addition, pharmacokinetic assays revealed a marked increase in area under the curve (AUC) of NOR with 1:5 and 1:10 NOR-CTS, by approximately 1.5-fold and threefold, respectively. Finally, the relative bioavailability of NOR after a single oral dosage of 1:5 and 1:10 NOR-CTS was enhanced to 148.02% and 304.98%, respectively. In this study, we demonstrated that the transmembrane glycoprotein P-gp regulates NOR metabolism in the intestine of Grass Carp, suggesting that NOR may be a direct substrate of P-gp. More importantly, we showed that CTS can inhibit P-gp expression in a dose-dependent manner and improve the relative bioavailability of NOR in this species.

This study describes the effect of avermectin (AVM) on the expression of c-aminobutyric acid A receptor (GABA A R) in Carassius gibelio. To assess the specific expression of GABA A R in the brain, gonads, liver, kidneys, heart, muscles, and skin of C. gibelio, the expression of GABA A R a1 subunit (GABA A Ra1) was measured by Western blotting. To study the effects of AVM on the expression of GABA A R, the median lethal concentration (LC 50 ) at 24, 48, and 96 h of AVM was determined and the expression of GABA A R in the brain, liver, and kidneys of the corresponding C. gibelio evaluated by Western blotting and immunohistochemistry. The results show that GABA A R was expressed in the brain, gonads, liver, kidneys, heart, intestines, muscles, and skin, while primarily distributed in the central nervous system and moderately distributed in peripheral tissues. The expression of GABA A R in the brain, liver, and kidney tissues of C. gibelio was increased with the treatment of AVM at 24 h LC 50 , but attenuated by the treatment of AVM at 48 h LC 50 and 96 h LC 50 . This suggests a threshold effect of AVM.