Endogenous opiates in the parabrachial nucleus mediate the electroacupuncture – induce sleep activities in rats

Abstract

Introduction Previous studies indicate that electroacupuncture (EA) of Anmian acupoint (EX 17) enhances vagal activity and changes the synaptic morphology in the nucleus tractus solitarius (NTS) by different EA stimulus frequencies. The goal of this study is to investigate the role of parabrachial nucleus (PBN), which receives afferents from NTS, in the EA-induced sleep alterations. Materials and methods Total of six male Sprague–Dawley rats, weighted 250–300 g, was used. We microinjected naloxone, an opioid receptor antagonist, into the PBN before the EA stimulation. A 30-min EA stimulation was performed at the beginning of the dark period in a 12:12 h light:dark cycle. The frequency of EA used in this experiment was 10 Hz, and the EEGs were recorded after EA stimulation and lasted for 24 h. Results Our preliminary results indicated that EA significantly enhanced non-rapid eye movement (NREM) sleep between the 6th and the 9th hour after the 30-min EA stimuli. The percentage of NREM sleep between 6- and 9-h of the dark period increased from 19.2 +/- 2.9% obtained after control to 43 +/- 3.6% (one-way ANOVA, p 0.05). Microinjection of naloxone (broad-spectrum opioid receptor antagonist) into the PBN 30 min prior to the EA stimulation reduced the percentage of NREM sleep to 30.3 +/- 3.7 % (one-way ANOVA, p 0.05 vs. the effect of EA). Conclusion Our results indicated that 10 Hz EA stimulation of Anmian acupoints increased spontaneous NREM sleep during the dark period, suggesting the sleep improvement for EA stimuli of Anmian acupoints. Microinjection of naloxone directly into the PBN blocked EA-induced enhancement of NREM sleep, indicating the role of endogenous opioids in the PBN. This observation further demonstrated endogenous opioids in the PBN, the relay nucleus of NTS, mediate EA-induced sleep alterations. Acknowledgements This study is supported by National Science Council grant ( NSC 101-2321-B-002-065 ).