Introduction The kappa-opioid receptor (KOR) has been implicated in mediating the behavioral and biochemical effects associated with nicotine reward and withdrawal, however, its underlying mechanisms remain to be further explored. Methods Adult male Sprague-Dawley rats were used to established a nicotine dependence and withdrawal model by injecting nicotine (3 mg/kg/day, s.c.) or vehicle for 14 days, followed by the termination of nicotine for 7 days. Body weight gain, pain behaviors and withdrawal scores were assessed in succession. MicroRNA (miRNA) sequencing was performed, and quantitative real-time PCR (RT-qPCR) was used to detect the expression of candidate miRNAs and Oprk1. Western blotting was performed to examine KOR protein expression of KOR. Luciferase assay was conducted to validate the relationship of certain miRNAs/Oprk1. Results The behavioral results shown that nicotine dependence and withdrawal induced behavioral changes. Biochemical analyses demonstrated that miR-144-3p expression decreased and Oprk1/KOR expression increased in the prefrontal cortex, nucleus accumben, and hippocampus. Further investigation suggested that miR-144-3p exerted an inhibitory effect on Oprk1 expression in PC12 cells. Conclusions This study revealed that miR-144-3p/Oprk1/KOR might be a potential pathway underlying the adverse effects induced by nicotine dependence and withdrawal, and might provide a novel therapeutic target for smoking cessation. Implications This study demonstrate an impact of nicotine dependence and nicotine withdrawal on behavioral outcomes and the expressions of miR-144-3p/Oprk1/KOR in male rats. These findings have important translational implications given the continued use of nicotine and the difficulty in smoking cessation worldwide, which can be applied to alleviated the adverse effects induced by nicotine dependence and withdrawal, thus assist smokers to quit smoking.

Nicotine use is highly prevalent and brings a huge burden on individuals, society, health-care systems and economic development. The existing mechanisms underlying nicotine’ actions can’t illuminate all basic and clinical problems thoroughly. Transfer RNA-derived small RNAs (tsRNAs) is a novel class of small non-coding RNAs (sncRNAs), possessing potential regulatory functions in various diseases. However, the roles of tsRNAs in nicotine exposure have not been determined yet. In this study, firstly we established nicotine exposure model by subcutaneously injecting (sc.) with 0.5mg/kg of nicotine twice daily for 14 consecutive days, and conducted some behavioral observations (the pain threshold and body weight gains). Secondly, we identified the differentially expressed profiles of tsRNAs in rat hippocampus on saline or nicotine delivery conditions by using ncRNA-Seq, and then predicted the promising functions of the putative genes of the tsRNAs by bioinformatic method. The results shown that there were 26 differentially expressed tsRNAs (7 up-regulated and 19 down-regulated tsRNAs) (Fold change > 1.5; P < 0.05), of which the tRF-5 was the most common type. Eight tsRNAs were selected to validate the sequencing result by RT-qPCR. Then, based on the sequencing and RT-qPCR data, five candidate tsRNAs (tRF-1-T28-His-GTG-1, tRF-5c-Glu-CTC-1, tRF-5c-Glu-CTC-3, tRF-5c-Gly-GCC-2-M2, tRF-5c-Glu-TTC-4) were finally selected for further bioinformatic analysis. The GO and KEGG pathway enrichment analysis suggested that the five candidate tsRNAs might play regulatory roles through the cholinergic synapse pathways, dopaminergic synapse pathways, etc. In conclusion, our results indicated that tsRNAs were dysregulated in the rat hippocampus after nicotine exposure, and among them, tRF-5c-Glu-CTC-1 was the most promising one, which might lay a novel foundation for further research into nicotine’ actions.