ABSTRACT: The effects of acupuncture on the sensory evoked conical potentials were investigated in 31 rabbits anaesthetized with urethane of conscious, so as to see what happened to the functional state of cerebral cortex in the meantime. The visual, auditory and somatosensory evoked potentials as well as raw EEGs were recorded from the animal's scalp. In most cases, an electro-acupuncture instrument was used instead of manual acupuncture. The main component amplitudes of evoked potentials, the frequency band powers and the total integral values of raw EEGs were analyzed. Results showed that during acupuncture the main components of evoked potentials were significantly depressed and the raw EEGs appeared desynchronized while the experimental animals were slightly activated. Moreover, both the total integral values of raw EEGs and the powers of lower frequency waves (1 -- 3. 99 Hi) were decreased and positively correlated well with the amplitudes of main components of the evoked potentials. Therefore, the possibility that the effects of acupuncture on the evoked potentials are secondary to the changes of raw EEGs remains to be ruled oaf, and it is suggested that the inhibition of evoked potentials during acupuncture does not necessarily mean that the cerebral cortex is in an inhibitory state.

KEY WORDS: Evoked conical potentials Auditory evoked potentials Somatosensory evoked potentials Visual evoked potentials Powers spectrum analysis

It is well known that the spontaneous brain waves (EEGs) as well as evoked conical potentials are changed during sleep or in anaesthetized state. In humans, the evoked conical potential amplitudes are somewhat correlated to the ongoing EEGs. Now, what the relation would be between them under the influence of acupuncture. Possibly, the acupuncture changes the functional state of the brain and thus changes the EEGs, resulting in the changes of evoked conical potentials, i. e., the latter change secondarily to the EEG changes. If this is true, in the study on the functional state of the cerebral cortex influenced by the acupuncture, etc., the evoked potential method should not be used solely without simultaneously monitoring the raw EEGs. In the present work, the visual, auditory and somatosensory potentials (VEPs, AEPs and SEPs), and raw EEGs were investigated in rabbits conscious or anaesthetized with urethane which partially inactivated the mesencephalon reticular formation. The effects of acupuncture on the functional state of cerebral cortex and the relationship between the evoked potentials and raw EEGs were studied.

MATERIALS AND METHODS
In 31 adult rabbits, 25 of them were anaesthetized with 20% urethane, 1 g/kg, i.v.. However in 6 experiments the animals were immobilized 1% flaxedil, 4 mg/kg, i. v., repeatedly if necessary, and kept conscious on artificial breath. Procedures for recording evoked potentials and acupuncture, etc., were as follows:

1. VEPs The animal's pupil of one eye was dilated with 2% atropine. A small neon lamp placed near the eye was lighted by an electric pulse of 150 V, 3 ms and 1 Hz. A couple of small iron nails were used as recording electrodes to record the brain waves. The active electrode was inserted into the bone 3 mm before the lambda .and 5 mm lateral to the sagittal suture, contralateral to the eye stimulated, while the reference one was placed in the middle of the nasal bone (Same arrangements of the reference electrodes in the following SEP and AEP experiments).

2. SEPs The left or right posterior tibial nerve was exposed and stimulated by an electric pulse of 0. 2 ms width, at 1 Hz and the intensity adjusted to produce an obvious plantar movement. The active electrode was placed 1 -- 2 mm behind the coronary suture and 2 -- 4 mm lateral to the sagittal suture, contralateral to the stimulated nerve.

3. AEPs The stimulus was a click delivered from a loudspeaker set off by an electric pulse of 0. 1 ms, 150 V and 0.. 5 Hz. The active electrode was placed in the temporal bone 1 cm behind the lateral canthus.

The brain electric responses evoked by the three modality stimuli respectively were amplified and then processed by a computer averager. Generally, each 10 responses elicited by flash lights were processed to make up an averaged VEP, and each 10 -- 20 responses for an AEP, and 32 responses for a SEP. Four averaged responses were recorder respectively before, during and after the acupuncture. The interval between 2 averaged responses was 2 -- 5 minutes. In the meantime the raw EEGs were monitored and recorded for frequency analysis and integration.

4. Acupuncture
The acupoints were picked out anatomically according to those on the human body. In VEP experiments the bilateral Hegu (LI 4 ) or Guangming (GB 37 ), in SEP experiments the contralateral or homeolateral , Zusanli (ST 36 ) and .Huantiao (GB 30), and in AEP experiments the bilateral Xiaxi (GB 43 ), were punctured respectively. In most cases a G-6805 electro-acupuncture stimulator which delivered unsymmetrical biphasic recurrent pulses of 68 -- 110 V, at 7. 1 Hz through the acupuncture needles was used to stimulate the acupoints. During the stimulation the muscles neighboring the acupoints twitched slightly. In some cases weak stimuli of 5 -- 45V, at 3. 2 Hz were preferred. The acupuncture continued for 10 -- 15 minutes usually. In a few cases the acupuncture was done by hand. During the acupuncture, the behavioral state of experimental animals was noticed. The latencies and amplitudes of the evoked potential components, the frequency band powers and the total integral values of raw EEGs before, during and after the acupuncture were respectively compared with each other by paired T test to see if there were significant differences between them. The main component amplitudes of evoked potentials, the frequency band powers and the total integral values of raw EEGs were analyzed with multiple linear regression method to see if there were significant correlations among themselves.

RESULTS:
A. The effects of acupuncture on the evoked conical potentials.
The evoked conical potential recorded in this work appeared to be a composite and polyphasic wave composed of N1, P1, N2, P2, N3 and P3 components (see Figs. 1, 2 and 3). The waveforms recorded from the urethane anaesthetized animals were about the same as those recorded from the conscious and flaxedil immobilized ones. Among them the N2 and P2 occurred inconsistently, and were indiscernible sometimes. Thus they were neglected to be analyzed in this work. The P2 -- N3 amplitude was measured from the baseline to the peak of N3 because of the inconsistent P2. Others were determined from peak to peak.

(1)VEPs During acupuncture the N1--P1 and P2 -- N3 amplitudes decreased respectively from 31.3± 14.3 and 68.3±23.1 to 16.0±8. 6 and 43. 0±26. 5µV (P 0. 5), and the N3 -- P3 amplitudes were not significantly affected (P >0. 05). In addition, the inhibitory effects of acupuncture on the VEP amplitudes were the strongest when the acupuncture began, and then became weaker and weaker with the lapse of time. Namely, the percentaged amplitudes of N1-- P1 were 40. 8, 60. 4 and 68. 8% when the acupuncture began, after 5 min and 10 min later respectively; those of P2 -- N3 were 51. 9, 63. 3 and 68. 2% After the acupuncture ended, the N1  P1 recovered to 100% in 15 min and the P2 -- N3 in 5 -- 10 min. However, with acupuncture done by hand the inhibitory effects on VEP amplitudes were relatively persistent and some after effect remained even after acupuncture ended

(2) SEPs the control values of SEPs were:
　　N1 - P1, 12. 2 ±8. 2 µV
　　P2 - N3, 40. 5 ±22. 1 µV
　　N3 - P3, 42. 0 ±28. 3µV
　　N3, 78. 5 ± 17. 4 ms
　　During the acupuncture all these values were reduced, i. e.,
　　N1 - P1, 7. 6 ±5. 8µV
　　P2 - N3, 26. 7 ±19. 4 µV
　　N3 - P3, 25. 3±17. 5 µV
　　N3, 72. 6 ± 17. 1 ms.

Statistically, they were significantly different from the controls (P 0. 2).
(3) AEPs The acupuncture resulted in reduction of N1  P1 and N3 -- P3 amplitudes Of AEPs from 15. 0 ±7. 9 and 10. 1±2. 8 to 10. 1 ± 7. 2 and 7. 5 ±2. 6 µV respectively (P 0. 2).

B. The influences of acupuncture in the total integral values and the frequency band powers of raw EEGs. When the sensory evoked potentials were inhibited by the acupuncture the raw EEG appeared to be desynchronized. By the automatic analysis, it was found that during the acupuncture the total integral values and the powers of 1 -- 3. 99 Hz band of raw were both significantly decreased while those of other frequency bands were relatively increased. The results of VEP experiment were shown in Table 1. The same results were found in the SEP and AEP experiments.

C. The relationships among the chief component amplitudes of EPs, raw EEG integral values and frequency band powers. In animals conscious, anaesthetized or under acupuncture influences, the N1  P1 amplitudes were positively correlated with the raw EEG integral values (P0. 5), neither in the rabbit's behavior.

DISCUSSION:
It was reported that the flash evoked potentials in humans were larger when the monitored EEGs prior to the photic stimulation became comparatively slow in frequency or high in amplitude. In cats, the evoked responses to acoustic stimulation and to light flash were smaller in waking state than those in spindle activity or in high-voltage, slow wave sleep. So were the evoked potentials in low-voltage, fast wave sleep, etc.. These facts had been neglected by some authors in the study of acupuncture effects on the evoked responses. The present results revealed that the amplitudes of certain components were positively correlated with the total integral values of raw EEGs and so with the powers of 1-- 3. 99 Hz band, while negatively correlated with those of 13 -- 30 Hz band. In acupuncture experiments, the evoked potentials were inhibited while the total integral values Of raw EEGs and the powers of 1 -- 3. 99 Hz band were decreased, and, on the contrary, those of 13 -- 30Hz band were relatively increased. This suggests that are parallel effects on the evoked potentials and the raw EEGs. Thus, the possibility that by acupuncture the induced changes in evoked potentials may be secondary to the alterations of raw EEGs could not be ruled out. Nevertheless, there may not be such relationship between them. Perhaps the acupuncture effects on them were through different mechanisms. The EEGs desychronization induced by acupuncture stimulation must be due to the activation of ascending reticular activating system. Clearly, the acupuncture was essentially of somatic modality stimulation which may affect the conveying impulses elicited by flashes, clicks or electric shocks to the nerves and the consequent neural processes at certain levels in the central nervous system and the cortex as well. According to several research works, this presumption might be true. The problem that either mechanism stated above or both of them would be correct needs to be clarified in the future study. Besides, another fact that should be emphasized, is that, during the acupuncture the animal's behavior could be aroused to a certain extent while the raw EEGs appeared desynchronized and the evoked responses were apparently inhibited. Therefore, the inhibition of evoked responses does not necessarily mean that the cerebral cortex is in an inhibitory state. The results that the peak latencies of VEP N3 P3 and SEP N3 were decreased in the acupuncture experiments are probably in favor of this presumption. It was reported that weak Stimulation of acupoints had facilitory effects on the VEPs. In another report it was shown that in rabbits when the dorsal spinal cord was being stimulated by electric pulses of low voltage at 10 or 100 Hz (This was considered the analogue of electro-acupuncture at acupoints of Du meridian) the animal’s EEGs tended to be synchronized. This EEG synchronization was readily induced in relaxed, waking state and hardly occurred at highly arousal state. No such event had happened in the present work except in one case. What the reason is remains to be studied. So the result just stated suggests that in another functional state of the cortex the EP changes are still correlated well with the raw EEGs and the acupuncture exerts parallel effects on them both.

By Zhang Wenbin, Shen Xuesong,etc.