Electrophysiological evaluation of oxytocin’s effects on basolateral amygdala
Ejder Saylav Bora1, Mümin Alper Erdoğan2, Oytun Erbaş3
1İzmir Katip Çelebi Üniversitesi Atatürk Eğitim ve Araştırma Hastanesi, Acil Tıp Anabilim Dalı, İzmir, Türkiye
2İzmir Katip Çelebi Üniversitesi Atatürk Eğitim ve Araştırma Hastanesi, Fizyoloji Anabilim Dalı, İzmir, Türkiye
3İstanbul Bilim Üniversitesi Tıp Fakültesi Fizyoloji Anabilim Dalı, İstanbul, Türkiye
Keywords: Amygdala; anxiety; electroencephalography; oxytocin
Abstract
Objectives: This study aims to evaluate the effects of oxytocin on basolateral amygdala in spontaneous electroencephalography (EEG).
Materials and methods: The study included seven Sprague Dawley type adult male rats (weighing, 250-300 g). Ketamine (40 mg/kg) and xylazine (4 mg/kg) were used for the anesthesia of the rats. Under anesthesia, a window was opened in the cranium with the aid of a drill and insulated bipolar EEG electrode was placed in basolateral amygdala (coordinates AP: -2.8 mm, L: +4.8 mm, V: -8.5 mm [Paxinos]) with stereotaxic method taking the bregma as reference. Electrodes were fixed in cranium using dental cold acrylic and prophylactic penicillin injection was performed. Three days later, rats’ basolateral amygdala records were obtained spontaneously (for 10 minutes) while the rats were awake in their cages. The records that were obtained with Biopac MP30 (BIOPAC Systems Inc., CA, USA) system were evaluated with Fast Fourier Transform and Power Spectral Analysis methods. Delta 1-4 Hz, theta 4-8 Hz, alpha 8-12 Hz, and beta 12-20 Hz were accepted and percentage dominances of EEG waves were evaluated. On the first day, rats were performed 0.9% intraperitoneal (IP) sodium chloride in oxytocin volume and rats’ EEG records were obtained for 10 minutes while in their cages. On the second day, rats were performed 10 IU/kg IP oxytocin (Synpitan amp 5 IU) and five minutes after the administration, rats’ EEG records were obtained for 10 minutes while in their cages. Percentage dominances of EEG waves were reevaluated with the same methods.
Results: The dominant frequency as percentage in spontaneous amygdala activity was 1-4 Hz (delta). Anxiety and stress due to isotonic injection caused suppression at 1-4 Hz and increase at 4-8 Hz in amygdala frequency. Compared to isotonic injection, oxytocin injection caused significant increase at amygdala’s 1-4 Hz frequency (p<0.05) and significant decrease at 4-8 Hz frequency (p<0.05).
Conclusion: Oxytocin decreased the increasing activity in amygdala due to injection anxiety. This finding validated electrophysiologically the anxiolytic effect of oxytocin demonstrated in behavior and functional magnetic resonance imaging studies.