Effects of vagus nerve stimulation on parafascicular nucleus neuronal activities in rats

BACKGROUND： Vagal nerve fibers have many projections to the central nervous system. The anti-epileptic effects of vagus nerve stimulation （VNS） are associated with the thalamus, insular cortex, and other brain regions. OBJECTIVE： To validate the inhibitory effects of vagus nerve stimulation on firing activities of parafascicular nucleus （Pf） neurons in rats. DESIGN, TIME, AND SETTING： The experiment was performed in the Electrophysiological Laboratory of Department of Neurobiology, Liaoning Medical University between September 2006 and September 2007 with multiple-factor self-controlled design. MATERIALS： Twenty-two healthy adult male Sprague Dawley rats were obtained for this experiment. Main instruments： A320R constant electrical stimulation was made by United States World Precision Instruments, Spike2 Biological Signal Processing Systems was provided by British CED Company. METHODS： Under general anesthesia, the left cervical vagus nerve of rats was separated by approximately 1.0 cm. A stimulation electrode was deployed on the vagus nerve, with various settings for VNS parameters. MAIN OUTCOME MEASURES： ① Firing rates of Pf before and after various VNS parameters were measured according to effect （R） ≥ 20%： excited effect, R ≤ -20%： inhibited effect, -20% 〈 R 〈 20%： no effect. ② Firing rates of excited Pf neurons after various VNS parameters were measured. RESULTS： ① One rat died prior to recording, another was recorded in the wrong brain location, but the remaining 20 rats were included in the final analysis. ② A total of 221 Pf neurons in healthy rats were recorded. The spontaneous firing rats were （6.70 ± 0.56） Hz and varied between 0.34-52.5 Hz. The spontaneous firing rates were significantly increased in 146 neurons （66.1%）, increasing from （5.36 ± 0.59） Hz to （8.22 ± 0.81） Hz （P 〈 0.01）. A total of 40 （18.1%） neurons did not respond, and 35 （15.8%） neurons were inhibited. ③ The excitation rates of Pf neurons did not increase with increasing current intensity from 3.0 mA to 5.0 mA. ④ When the current intensity was set to 3.0-4.0 mA, excitation rates of Pf neurons decreased with increasing stimulation frequency of 30 -50 Hz. The excitation ratios were not reduced by an intensity of 5.0 mA. CONCLUSION： VNS may result in excited Pf neurons that may inhibit cerebral cortical activities.

EFFECT OF ELECTROACUPUNCTURE ON DISCHARGES OF PAIN-REACTION NEURONS IN CAUDATE NUCLEUS AND PARAFACICULAR NUCLEUS IN RATS WITH CEREBRAL HEMORRHAGE

Objective: To study the bidirectional adjustment effe ct of ele ctroacupuncture (E A) on the electrical activities of neurons in caudate nucleus (CN) and parafasci cular nucleus (PFN) in rats with acute cerebral hemorrhage (ACH). Methods: ① 32 male Wistar rats were evenly randomize d into normal, EA+normal, model and model +EA groups for observing the effect of EA on pain reaction; ② another 40 male Wi star rats were equally randomized into control, saline, model and EA groups for comparing the effects of EA on discharges of pain-reaction neurons in CN and P FN . ACH model was established by intracerebral injection of the rat’s own arteria l blood sample (30μL) into CN and PFN. Pain reaction was tested by using tail -flicking (TF) reflex induced by radiation-heat irradiation. Extra-cellular d ischarges of neurons of CN and PFN were recorded by using glass micropipettes. E A (1 V, 15 Hz and duration of 10 min) was applied to "Baihui"(百会 GV 20) and "Taiyang" (太阳 EX-HN 5). Frequency of discharges of CN and PFN neurons was calculated be fore and after intracerebral injection of blood sample, heat nociceptive stimula tion and EA respectively. Results: Compared with con trol group and pre-EA in the same group, TF latency (TFL) values of normal rats increased significantly; compared w ith pre-injection of blood, TFL of model group also increased pronouncedly ( P<0.0 1). In comparison with model group, TFL values of EA group decreased significant ly (P<0.01), indicating that EA of GV 20 and EX-HN 5 could suppress ACH induced increase of TFL. In ACH rats, the latency of pain-excitement response of disch ar ges of CN and PFN neurons increased significantly, while the net increase values of pain-excitement response decreased significantly in model group (P< 0.05～0.01 ), the duration of pain-inhibitory response and the net decrease values of dis ch arges of CN and PFN neurons increased clearly. Comparison between model and EA groups showed that the latency values of the pain-excitement reaction of disch ar ges of CN and PFN neurons in EA group were significantly lower than those in mod el group (P<0.01), while the net increase values of discharges of CN and PFN neu rons in EA group were considerable higher than those in model group (P< 0.01); th e latency and net decrease values of pain-inhibitory CN and PFN neurons in EA gr oup were clearly lower than those in model group. It indicated that EA could pro l ong the latency of pain-excitatory reaction and shorten the duration of pain-i nhi bitory reactions of the neurons induced by cerebral hemorrhage and raise the exc itement degree of CN and PFN neurons. Conclusion: EA can reduce the excitability of pain-excitement neurons (PEN) and lower the inhibitory degree of pain -inhibitory neurons (PIN) in both CN and PFN, an d thus possesses a bidirectional regulation effect on cerebral hemorrhage-induced c hanges of the electrical activities of neurons in both CN and PFN.

EFFECT OF ELECTROACUPUNCTURE OF SCALP-POINTS ON ABNORMAL DISCHARGES OF NEURONS AROUND THE CEREBRAL HEMORRHAGE FOCUS IN THE RAT

Objective: To study the mechanism of electroacupuncture (EA) of scalp-points for regulating abnormal discharges of neurons in different regions around the cerebral hemorrhage focus by using neuro-electrophysiological methods. Methods: 80 Wistar rats (anesthetized with 20% urethane 1 g/kg, i.p.) were randomly divided into normal, saline, model and EA groups, with 20 cases in each group. Cerebral hemorrhage model was established by intracerebral injection of the rat’s own arterial blood sample (40 uL). In rats of saline group, the same volume of saline was given for intracerebral injection. Extracellular electrical activity of neurons of the caudate nucleus and parafascicular nucleus and Tail flicking latency (TFL) were used as the indexes. “Baihui”(百会 GV 20) and “Taiyang”(太阳 EX-HN 5) were punctured from GV 20 towards EX-HN 5 with filiform needles and stimulated electrically with stimulating parameters of strength of 1 V, frequency of 15 Hz and duration of 15 min. Results: Compared with normal group, TFL values of model group and EA group increased significantly (P<0.01); and compared with model group, those of EA group decreased significantly (P<0.01), suggesting that the pain threshold increased significantly in cerebral hemorrhage rats while after acupuncture stimulation, it lowered strikingly. Compared with normal and saline groups, the latency values of the pain excitement and inhibitory responses of the cellular discharges of the caudate and parafascicular nuclei in model and EA groups increased significantly (P<0.05～0.01), while after EA, it recovered apparently (P<0.01), showing an apparent regulative effect of EA on the abnormal changes of discharges of neurons around the cerebral hemorrhage focus. Conclusion: Scalp-acupuncture possesses an apparent regulatory effect on the abnormal electrical activity of neurons around the cerebral hemorrhage focus which may favor the early recovery of functional activity of neurons near the focus tissues.