Objective: It has been shown by behavioral studies that oxytocin has anxiolytic effects and that oxytocin in nasal spray form suppresses amygdala activity, which is powered by anxiety as demonstrated in functional MRI studies in humans. The amygdala is a part of the limbic system and is activated in case of fear and anxiety. This study evaluated the effects of oxytocin on the basolateral amygdala using a spontaneous EEG. Material and Methods: The experiments performed in this study have been carried out according to the rules in the Guide for the Care and Use of Laboratory Animals adopted by National Institutes of Health (U.S.A) and have received consent from Ege University Animal Ethics Committee. The rats were maintained under controlled environmental conditions throughout the study: 22-24 °C ambient temperature, 12:12 light-dark cycle (light from 7:00-19:00), and standard laboratory food and tap water available ad libitum. In this study 7 Sprague-Dawley adult male rats were used, which were 8-12 weeks old. Under anesthesia a small hole was drilled. Then by taking the bregma as a reference using the stereotaxic method (coordinates Anteroposterior: - 2.8 mm, Lateral: + 4.8 mm, Ventral: - 8.5 mm) (Paxinos Rat Brain), an exterior insulated bipolar EEG electrode was placed in the basolateral amygdala. Electrodes were fixed by using a dental acrylic (numerous alloys are used in the making of dental restorations). The rats were anesthetized using ketamine (40 mg/kg) and xylazine (4 mg/kg) intraperitoneally (IP). Electrodes were placed and 3 days later, while the animals were awake in their cages, spontaneous EEG recordings were taken from the amygdala. Then, 0.9% isotonic NaCl solution was injected intraperitoneally into the rats (n = 7), and the EEG was recorded from the amygdala while they were in their cages. One day later to the same rats (n=7) oxytocin 10 IU/Kg (Synpitan 5 IU) was given IP, and 5 minutes later the oxytocin EEG records were taken in their own cage. The system recordings were taken for 20 minutes by a Biopac MP30 amplifier system in the range of the 1-60 Hz band, with 10,000 amplification. During this process Delta 1-4 Hz Theta 4-8 Hz, alpha 8-12 Hz and beta 12-20 Hz waves in the EEG were accepted as the ratio of percentage in PSA (Power Spectral Analyses) methods. We affirmed electrode location histologically following euthanisation.
Results: There was significant (p<0.05) diminution in delta frequency (64.4 ± 10.9) in the rats given normal saline than in the spontaneous EEG records (79.5% ± 12.8). There was a significant (p<0.05) increase in delta frequency (76.8 ± 12.5) in rats given oxytocin one day after the normal saline was injected (64.4% ± 10.9)(Figure I)
Conclusion: Anxiety caused by injection of a normal saline solution augmented EEG frequency when compared with resting EEG records. Oxytocin diminished the EEG frequency of rats that had injection anxiety. This results show electrophysiologically that oxytocin is a powerful anxiolytic.