| Background and ObjectivesOlfactory is the only body sense directly correlated with cerebrum, and olfactory neural system has direct correlation with the animals instinct capabilities, such as predating, mating partner, discriminating safety and danger, communicating sentiment with each other. However, olfactory is the least known to human beings. It is reported that the functions of olfactory neural system have close relations with the learning-and-memory capability of the brain and some correlations have been found out: eg: the correlations between odor-exposure and consolidating and integrating the declarative memories in the slow-wave sleep period; the correlations between synaptic modifications induced by odor-related memory and behavioral performance . Besides, olfactory center itself was found to be involved in learning-and-memory process. It was worked out that eugenol could improve learning-and- memory of the Kunming mice in before researches in our institution. Based on the correlation between learning-and-memory, olfactory, and inhaling eugenol, a series of neuroethological methods plus establishing olfactory bulbectomy models, were used to observe effect of eugenol inhaling. To discuss the relations between olfactory pathway and learning-and-memory capability, and try to develop eugenol into one of the medicines that could improve learning-and-memory and prevent neural and mental disease, such as AD and so on, electrophysiology test was used to record different olfactory nerve-evoked field potentials when the mice inhale different odors: eugenol, formaldehyde, acetic acid, toluene and then expression of ChAT, GABA and Glu were detected by immunohistochemistry.MethodsThe mice were selected by neuroethology methods, and then some of them were selected to be established olfactory bulbectomy models. The mice were divided into five groups: control group (blank group), bogus operation group, olfactory bulbectomy model group, eugenol inhaling group, and model plus eugenol inhaling group(sample group). The mice were detected olfactory six-arms maze test, olfaction discrimination memory test, autonomic activities box test. The test of electrophysiology is used to detect olfactory nerve-evoked field potentials by eugenol-inhaling in different concentration and compare the spontaneous potential with the induced potential after inhaling different eugenol, formaldehyde, acetic acid, toluene. Then, each mouse was sacrificed and brains were removed. The slices of hippocampus and cortex were stained with HE's staining, Nissl's staining and detected the expression of ChAT, GABA and Glu by immunohistochemistry.Results1. Olfactory inhaling group can strengthen the learning and memory ability compared with the other groups (Blank group; SO group and Sample group)in olfactory six- arms maze test and olfaction discrimination memory test. The latter two groups (SO group and Sample group) had more frequencies of automatic activities than the Blank group.2. The consequence of electrophysiology test is that OB can bring out different olfactory nerve-evoked field potentials when the mice inhaling different eugenol, formaldehyde, acetic acid, toluene. OB induced potential's frequency and amplitude had not changed after inhaling different density's eugenols.3. According to the immunohistochemistry results, the capability of eugenol's improvement on learning memory is known to relate to the increasing of transmitters of cortex and hippocamp, such as ChAT, Glu, but not GABA.Conclusions1. The mechanisms of eugenol's improvement on learning-and-memory have something to do with olfactory pathway.2. eugenol inhaling through olfactory pathway can obviously improve learning-and- memory of the Kunming mice.3. Olfactory nerve-evoked field potentials is that OB can bring out specified induced potential when the mice inhale eugenol.4. The capability of eugenol's improvement on learning and memory is related to the changes of transmitters of cortex and hippocamp, such as ChAT, Glu.
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