Radyasyonun Nörofizyolojik Etkileri
Özet
İyonlaştırıcı radyasyon maruziyeti, merkezi sinir sistemi üzerinde hem akut hem de uzun vadede ciddi nörofizyolojik hasarlara yol açmaktadır. Özellikle beyin kanserlerinin tedavisinde yaygın olarak kullanılan radyoterapi uygulamaları, sinir sisteminin göreceli direncine rağmen DNA hasarı, oksidatif stres, hücre ölümü ve sistemik inflamasyon gibi karmaşık hücresel değişiklikleri indüklemektedir. Bu süreç, öğrenme ve hafıza için kritik bir bölge olan hipokampus ile amigdaladaki nöral kök hücrelere zarar vererek postnatal nörogenezi ve sinaptik plastisiteyi olumsuz etkilemektedir. Hücresel düzeyde mikroglia, astrosit ve oligodendrosit gibi glial hücrelerin fonksiyonları bozularak proinflamatuar sitokinlerin salınımı artmakta, bu durum ilerleyici demiyelinizasyona ve beyaz cevher atrofisine neden olmaktadır. Hiroşima ve Çernobil gibi nükleer kazalara maruz kalanlar ile kraniyal ışınlama tedavisi gören hastalar üzerinde yapılan epidemiyolojik ve klinik çalışmalar; radyasyonun dozuna, süresine ve maruz kalınan yaşa bağlı olarak zeka geriliği, sözel/uzamsal bellek kayıpları, dikkat eksikliği ve hızlandırılmış yaşlanma gibi belirgin bilişsel gerilemeleri doğrulamaktadır. Deneysel in vivo ve in vitro kemirgen modelleri de radyasyonun kan-beyin bariyerini bozduğunu ve kalıcı öğrenme eksikliklerini tetiklediğini açıkça ortaya koymaktadır.
Exposure to ionizing radiation can induce severe acute and long-term neurophysiological damage within the central nervous system. Although the nervous system is relatively resistant, therapeutic cranial radiotherapy triggers a complex network of molecular and cellular disruptions, including DNA damage, oxidative stress, cell death, and neuroinflammation. This exposure profoundly impairs neural stem cells within the hippocampus and amygdala—regions crucial for spatial learning and memory—thereby hindering postnatal neurogenesis and neuroplasticity. At the cellular level, radiation disrupts glial cells such as microglia, astrocytes, and oligodendrocytes, accelerating the release of proinflammatory factors, progressive demyelination, and white matter atrophy. Clinical and epidemiological studies on individuals exposed to nuclear disasters like Hiroshima and Chernobyl, as well as patients undergoing cranial irradiation, demonstrate that radiation leads to severe cognitive decline, memory deficits, attention failure, and accelerated aging depending on the dose and exposure duration. Experimental in vivo and in vitro rodent models further confirm that cranial irradiation impairs blood-brain barrier functionality and causes persistent, progressive learning deficits.
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