Summary OBJECTIVE : To study the effects of repetitive transcranial magnetic stimulation (rTMS) on conditional fear memory in rats with cerebral infarction. METHODS : Forty male adult Sprague-Dawley rats, weighing 200-250 g, were treated with modified Zea longa suture method to prepare a model of cerebral infarction in the right middle cerebral artery occlusion. Successfully modeled rats were randomly divided into model group and 40% (0.76 T), 60% (1.14 T), 80% (1.52 T) intensity stimulation group, 8 in each group, and 8 sham-operated groups. Rats in each stimulation group received magnetic stimulation according to the set parameters on the 5th day after successful modeling. For 5 consecutive days, the sham operation group and the model group were placed in the same magnetic field environment, but magnetic stimulation was not accepted. After the end of treatment, rats in each group were given the same foot shock (55 V, 2 s), and the duration of stiffness in the rats was measured within 24 min after 24 h. Results The duration of stiffness of the rats in each stimulation group was significantly higher than that in the model group after 24 hours of receiving electric shock (P < 0.01), and the duration of stiffness after 24 hours was also obvious with the increase of stimulation intensity. Growth (P < 0.01). Conclusion: rTMS can promote the recovery of memory function in rats with cerebral infarction, and with the increase of stimulation intensity, the recovery of memory ability of rats is also enhanced. Cerebral infarction refers to localized ischemic necrosis or softening caused by ischemia and hypoxia due to blood supply disorders in the brain. As a disease with high morbidity and high disability, cerebral infarction poses a threat to human health and life, and it also affects patients' daily life ability, which places a heavy burden on society and families. Repetitive transcranial magnetic stimula-tion, rTM S is a pulsed magnetic field acting on the central nervous system (mainly the brain), changing the membrane potential of cortical neurons, causing them to induce currents and affecting the brain. Internal magnetic metabolism and neuroelectric activity, which cause a series of physiological and biochemical reactions, as a new neuropsychiatric treatment technology, it has the advantages of painless, non-invasive, safe and easy to operate, and has been widely used in the treatment of Pa Clinical treatment of diseases such as Jinsen disease, epilepsy, depression, cerebral infarction, spinal cord injury, etc., and achieved good results. The formation of conditional fear is a process of learning and memory, this study aims to pass the brain The observation of conditional fear memory in rats after infarction to study the recovery effect of rTM S on learning and memory function in rats after cerebral infarction, and to explore the relationship between treatment intensity and functional recovery degree, so that rTMS can be better applied to clinical cerebral infarction in the future. The patient's treatment provides a basis for guidance. Materials and Methods 1.1 experimental animals SPF adult SD male rats weighing approximately 200-250 (provided by the Experimental Animal Center of the Third Military Medical University), 12 weeks old, 12 h light/dark cycle in the cage, free access to water and food. Eight rats were randomly selected as the sham operation group, and the other rats were made into the right middle cerebral artery occlusion cerebral infarction model. The successful rats were randomly divided into model group and 40% (0.76 T), 60% (1.14 T). 80% (1.52 T) intensity stimulation group, 8 in each group. 1.2 Instrument Magnetic field stimulator (CCY-1 type) produced by Wuhan Yiruide Co., Ltd.; Shanghai Xinsoft superfcs conditional fear experiment system 1.3 Production of animal models of cerebral infarction The right middle cerebral artery ischemia model was made with reference to the modified Zea longa line plug method. After the animal wakes up, it shows the left front forelimb flexion during tailing; the same side Homer's sign; the left side of the circle when crawling; the left side is dumped when standing. Those who have the above signs are included in the study. A total of 100 rats were shared, and 32 of them were eligible for inclusion and survived for a prescribed period of time. The sham operation group only used the right internal carotid artery ligation, and there was no pathological behavior change after operation. 1.4 treatment methods The stimulation group was treated with rTM S on the 2nd day after successful modeling, and the rat's head was fixed to keep it awake, quiet and comfortable during the stimulation. The center of the magnetic field coil is 0.5 cm from the right side of the rat meat door. The stimulation parameters were designed as: stimulation frequency 1 Hz, stimulation intensity 40% (0.76 T), 60% (1.14 T), 80% (1.52 T) output intensity; 3 groups/d, 5 sequences/group, 20 times/sequence Each sequence was separated by l0s, each group was 60 s apart, continuous stimulation was performed for 5 days, and stimulation was performed every day from 14:00 to 15:00. The sham operation group and the model group were placed in the same magnetic field environment, but magnetic stimulation was not accepted. 1.5 memory ability evaluation The experiment was divided into two parts: training and testing. Each group of rats underwent a scene conditional fear test on the 2nd day after the end of treatment. Wipe the bottom of the box and the wire with 95% ethanol before each use of the shock box. Place the rats in a test chamber with no sound and no special smell. After 3 minutes, start giving a short foot shock (SSV, 2s) for 6 times. The average time of the two foot clicks was 90 s (60-120 s random change), and the rats were returned to the cage 30 s after the last shock. The test of memory formation and retention ability was carried out 24 h after the end of the training. Rats were placed in the same electric shock box without electrical stimulation, and the time of the Freezing reaction in the rats was observed and recorded with a stopwatch. The criterion for stiffness is that after the animal receives the stimulation signal, except for the respiratory movement, all other body movements of the whole body are stopped. In this behavioral model, the length of the stiffness response reflects the degree of fear memory of the rat in the scene of the shock. 1.6 statistical analysis Data processing was performed using SPSS 17.0 statistical software package. The data of each group were expressed by the mean standard deviation. The comparison of multiple samples was analyzed by one-way ANOVA. The comparison between groups was performed by LSD test, P < 0.05. has statistical significane. 2 results Compared with the sham operation group, the fear memory ability of the model group was significantly decreased, and the fear memory ability of the rats in the rTMS group was significantly higher than that of the model group. The difference between the groups was statistically significant (P < 0.01). With the increase of stimulation intensity, the rat's stiffness time at 24 h also increased significantly, and the difference was statistically significant (P < 0.01). See Table 1. 3 Discussion Repetitive transcranial magnetic stimulation (rTM S ) is a new neuroelectrophysiological technique developed on the basis of transcranial magnetic stimulation in 1991. It is painless, non-invasive, easy to operate, safe and reliable, and can affect local and distant cortical function and achieve cortical layer. Functional regional reconstruction, affecting a variety of neurotransmitters and gene expression levels, is currently widely used in the clinical treatment of depression, Parkinson's disease, epilepsy, nerve J wow pain, spinal cord injury and stroke diseases. Clinical studies have shown that rTMS can promote the recovery of limb function and improve the daily living ability of patients with cerebral infarction [n}. At present, the study of learning and memory behaviors in rats with cerebral infarction is mainly based on Y-maze and water maze [A-9]. The formation of conditional fear is also a process of learning and memory. This study uses conditional fear memory as the test. Learning and memory evaluation experiments showed that rTMS can promote the recovery of memory function in rats with cerebral infarction, and with the increase of stimulation intensity, the recovery of memory ability of rats with cerebral infarction is also enhanced. At present, there are many researches on the possible mechanism of rTMS in promoting the recovery of memory in rats with cerebral infarction. It has been reported that rTMS can promote the expression of synaptophysin (Syn) in hippocampus of rats with cerebral infarction. Syn is a specific marker membrane protein of synaptic vesicles, and its quantity and distribution density can indirectly reflect the density of synapses. Synapses, as functionally connected parts of neurons, increase in density, and the transmission and association between neurons in the hippocampus area increases. In addition, magnetic stimulation can also increase brain-derived neurotrophic factor in the lateral cortex of cerebral infarction. (BDNF) expression, promotes neuronal regeneration, stimulates axon sprouting and new synapse formation, inhibits pro-apoptotic proteins Bax, BAD, etc., thereby producing various neuroprotective effects on cerebral infarction mo; , rTMS treatment can also inhibit the apoptosis of ischemic nerve cells and increase neuroplasticity, and can be used for the treatment of memory function recovery in subacute phase after cerebral infarction; in addition, rTMS can regulate miR-25/p57 signaling pathway and promote cerebral infarction Proliferation of adult neural stem cells in the subventricular zone and strengthening self-repairing ability after cerebral infarction. The effect of rTMS on patients with cerebral infarction is related to many factors. The main factors are the setting of stimulation parameters such as intensity, frequency, duration of stimulation, etc. This experiment is found to be consistent with the stimulation intensity under the premise of ensuring the same parameters except strength. Strengthening, the degree of recovery of memory in rats is also enhanced. It has been reported in the literature that this may be related to the influence of magnetic stimulation on the migration of astrocytes, and the astrocyte migration ability is enhanced with the increase of stimulation intensity. Under the premise of ensuring the safety of treatment, this study only explored the effects of repeated intensity transcranial magnetic stimulation on conditional fear memory in rats after cerebral infarction, and the dose-effect relationship of other parameters such as frequency and total amount of stimulation on cerebral infarction treatment. 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Effects of transcranial magnetic stimulation with different intensities on conditional fear memory in rats with cerebral infarction