The possibility of endolymphatic hydrops in an animal migraine model created with nitroglycerin and analyses of the effects of migraine treatment on the cochlear and vestibular system

Background: VM is a different type of migraine with vestibular symptoms like vertigo and postural imbalance and also auditory symptoms like tinnitus, aural pressure, and muffled hearing. MD presents with vertigo, fluctuating hearing loss, tinnitus, and aural pressure. So, there are overlapping symptoms between these two diseases, and because of that, it can be challenging to make a diagnosis. There is not a single diagnostic test that can help to differantiate. MD's pathophysiology is still unclear, and the only pathological marker is ELH. ELH could also be seen with different etiologies, including VM . There is not much data on migraine's effect on the cochleovestibular system, and since MD's pathology is still unknown, MD could be thought of as a variant of VM. Clinical reports revealed that anti-migraine medications given to MD patients showed beneficial effects. There has recently been huge progress in the advancement of anti-migraine medications. Aim: In this thesis project, we first aimed to investigate the possibility of ELH in migraine. Furthermore, we included a CGRP receptor blocker as the treatment group to study its effects specifically on the cochleovestibular system. Methods: Our study included 30 male Wistar rats aged 2-5 months. Animals were divided randomly into three groups, 10 rats in each. Group 1 was the sham with saline injection. Group 2 was the migraine with diluted NTG injection at a dose of 10 mg/kg IP every other day for 9 days. Group 3 was the treatment group with Olcegepant in a volume of 1 mg/kg IP one hour and 15 minutes after the NTG injection every other day for 9 days. The hearing thresholds were determined by click and tone-burst ABR at 6, 12, 16, 20, and 32 kHz. DPOAE experiments were performed at 6, 8, 10, and 12 kHz. ECOG was performed, and SP/AP ratios were calculated. All the audiological evaluations were also done on day nine for the comparisons. The orofacial formalin test, OFT, tail hang reflex, and head circling tests were performed for behavioral analyses. Tail blood samples for measuring the levels of TNF-alpha, IL-6, and intracardiac blood samples for CGRP and CSF for the levels of HGMB1 were gathered on day nine. TG for the central, and organ of corti, saccule, stria vascularis for the peripheral immunohistochemical analyses were dissected after the perfusion. Half of the animal's cochleas (30 cochleas) were paraffin embedded for H&E staining. And the other half of the animals' cochleas were immunostained after the whole mount dissection. Image J program was used for the image analysis. Results: The immobility time that animals spent in OFT was measured and analyzed. A significant difference was detected between the migraine and the control group (p=0.001). The migraine group was more immobile, as expected. There was not a significant difference in the orofacial formalin test, and none of the groups had abnormal tail hang reflex or head circling. DPOAE results were extracted, and db SPL calculations at 6, 8, 10, and 12 kHz were higher on day nine compared to day one in the migraine group with a statistically significant difference (p=0.0006, p=0.002, p=0.009, p=0.014). On the other hand, there was a significant decrease in all the above frequencies in the treatment group (p=0.002, p=0.028, p=0.018, p=0.006). There was also a significant difference at 6 kHz between day nine and day one of tone-burst ABR thresholds between the control and the migraine and the migraine and the treatment groups (respectively p=0.038, p=0.018). In addition, at 12 and 20 kHz, there was a significant difference between the control and the migraine groups (p=0.030, p=0.018). Tone burst ABR thresholds were lower on day nine than on day one in the migraine group. There was no difference in click ABR thresholds. SP/AP ratios were compared within the groups on day one and day nine; the treatment group had a statistically significant lower ratio on day nine than day one (p=0.049). TNF-Alpha was significantly high in the migraine group (p=0.048). There was not any significant difference in IL-6 and CGRP results. The PSM was calculated through the H&E staining of the cochlea sections, and we did not see a significant difference between the groups. The only statistically significant difference was in the CGRP count, and the Glutamate R2 count at the whole mount dissected and immunostained IHCs. The CGRP count was higher in the treatment group and significantly different from that of the migraine group (p=0.02) and the control (p=0.006). Also, the glutamate R2 was significantly higher in the treatment group compared to the migraine group (p=0.012). Conclusion and Comment: NO has a beneficial effect on the central and peripheral auditory systems. The inhibition of NO lowers the SP/AP ratio. There is a signaling pathway of a reciprocal relationship of Glutamate with CGRP in the efferent system of LOC.