An OERP Experiment Study On Olfactory Function Of Rabbits

【Background】In recent years,the case complained of anosmia increase quickly in medico-legal expertise. Relevant reports record that about 5% - 10% of patients with cranial trauma will happen to have anosmia [1]. According to related standards of evaluating mild injuries and grading disability due to injury used in medico-legal investigation, it demands an objective examination for evaluating anosmia. Because the anatomy of the nasal cavity and olfactory pathway has not been totally clarified yet, so the clinical examination of dysosphresia mainly relies on subjective judgment of a patient, subjective randomness cannot be avoided. So, it is not a dependable and stable enough test .Adding the other aspect of patient's compensation psychology, malingering is also difficult to avoid, and have directly limited its application in the medico-legal expertise. Accordingly it has important practical significance and application value to set up objective examination in medico-legal expertise.OERP (Olfactory Event-Related Potentials) is a specific brain electric potential evoked by stimulating olfactory mucosa with pharmaceutical smell and recorded from specific location on scalp adopting international 10/20 standards[2]. OERP mainly reflect sensory conduction function and the cognition function. As a nerve electrophysiological index for olfactory assessment, it has objectivity and can be applied to qualitative analysis. But the technique is just in experimental stage, and most studies use electrical stimulation [3, 4] or damaging olfactory bulb [5] to the OERP test, and this does not correspond to normal olfactory physiology. This experiment uses gaseous pharmaceutical smell as the stimulation according to the olfactory physiological characteristic. With the help of the professors and students of our institute, we collectively participated in the biomedical engineered synchronous olfactory stimulator. Then some specific OERP components were explored and we tried to establish a standardized OERP detection method in hope to offer a reliable and objective index for testing ability in medico-legal expertise【Purpose】Devise a preliminary experimental study to test for the feasibility and dependability of Olfactory Evoked Potential using isoamyl acetate as chemical stimuli that induces particular olfactory evoked potential on the scalp Cz of the rabbit, by comparing the difference of waveform between air control group and isoamyl stimuli group, and the difference in the incubation period and amplitude between different intensities of isoamyl, and proving the stability and repetitiveness of the OERP【Method】Part one: Make synchronous olfactory stimulator. 11 normal volunteers were tested in order to verify stability and dependability of the instrument. Part two: Utilize VikingQuest evoked potential instrument produced by Nicolet Company and synchronous olfactory stimulator, 20 normal adult rabbits were tested by olfactory stimulating tasks with isoamyl and air. Isoamyl group were randomized into two groups: full dose group and half dose group. Then analyze amplitude and latency between the groups, to compare the effect of different doses. Adopt SPSS11.5 to analyze.【Result】(1) Can educe obvious OERP waveform on the particular position of scalp of volunteer with the home-made olfactory stimulator, the stability and the repetitiveness of waveform is better. (2) Among isoamyl stimuli group, the OERP waveform between volunteers and rabbits is mainly composed"positive-negative-positive-negative " four waves, named respectively as P1, N1, P2, N2 according to relevant research, differently individual waveforms are basically similar, among them P1 is not obvious in some experimenters, sometimes the third wave P3 can be recorded. And N1, P2, N2 wave are more invariable in every waveform. (3) Relatively half dosage group obviously shorter in incubation period of every composition to the full dosage group, every composition (N1, P2, N2) of OERP waveform among two dosage groups is obvious statistics difference (P<0.01), The difference between the amplitude is not obvious (P>0.05); Have not seen the obvious statistics difference (P>0.05) between the full dosage group and half dosage group in another index N1/P2 peak-peak value, And the variability among the individuals is low; But the air control group has not elicited the obvious waveform.【Conclusion】The synchronous olfactory stimulator can elicit the stable OERP waves. Accompanying dose increase showed shortened latency. N1, P2, N3 are stable indexes. Peak-peak value between N1 and P2 is not affected by dose within the specific limits. This could be used as a physiological index to evaluate the olfactory function obstacle in medico-legal expertise.