Depression, Neuroplasticity and Neurotrophic Factors

Abstract

Depression is a common psychiatric disorder. There is still very little known about the neurobiological alterations that underlie the pathophysiology of depression. Recently, neuroplasticity hypothesis is added to monoamine hypothesis and neurotransmitter receptor hypothesis which are among the theories about the biological etiology of depression. Neuroplasticity can be defined as alterations in structural properties and functions of neurons and synapses depending on various internal and external stimuli. Neurotrophic factors are molecules important for development and protection of neurons. The neuron needs the neurotrophic factors synthesized by itself for survival, differentiation and neuroplasticity. Hippocampus is one of the brain regions with highest level of neuroplasticity. Brain imaging studies reveal that there is hippocampal volume reduction in depression. This reduction may be due to stress induced alterations in neurogenesis and neurotrophic factor expression in hippocampus. Pharmacologic and somatic antidepressant treatments increase adult hippocampal neurogenesis and neurotrophic factor expression and reverse effects of stress on hippocampal atrophy. Brain derived neurotrophic factor (BDNF) is the mostly studied neurotrophic factor in depression. There are data about decreased levels of BDNF in depression. Many studies suggest that BDNF is the "common final pathway" for actions of different antidepressants and chronic antidepressant treatment can enhance neurogenesis in adult hippocampus regulating plasticity and neurotrophin signalling pathways important in neuronal survival.

Keywords

• Depression, neuroplasticity, brain derived neurotrophic factor

Depresyon, Nöroplastisite ve Nörotrofik Faktörler

Öz

Yaygın bir psikiyatrik bozukluk olan depresyon patofizyolojisinin altında yatan nörobiyolojik değişiklikler hakkında halen çok az şey bilinmektedir. Depresyonun biyolojik etiyolojisi hakkında geliştirilen kuramlardan monoamin hipotezi ve nörotransmitter reseptör hipotezine son yıllarda depresyonun nöroplastisite hipotezi eklenmiştir. Nöroplastisite, çeşitli iç ve dış uyaranlara bağlı olarak beyindeki nöronların ve bunların oluşturduğu sinapsların yapısal özellikleri ve işlevlerindeki değişiklikler olarak tanımlanabilir. Nörotrofik faktörler; nöronların gelişimi ve korunması için büyük öneme sahip olan moleküllerdir. Nöron yaşamak, farklılaşmak ve nöroplastisite için kendi salgıladığı nörotrofik faktörlere gereksinim duymaktadır. Hipokampus nöroplastisitesi en yüksek beyin bölgelerinden biridir. Beyin görüntüleme çalışmaları; depresyonlu olgularda hipokampal hacim azalması olduğunu göstermektedir. Bu durum hipokampustaki nörogenez ve nörotrofik faktör ekspresyonunda stresle indüklenen değişikliklere bağlı olabilir. Farmakolojik ve somatik antidepresan tedaviler erişkin hipokampal nörogenezi ve nörotrofik faktör ekspresyonunu arttırmakta, dolayısıyla stresin hipokampal atrofi üzerine olan etkisini durdurup geriye döndürebilmektedir. Depresyonda üzerinde en çok çalışılan nörotrofik faktör olan beyin kaynaklı nörotrofik faktör (BDNF) düzeylerinin depresyon durumunda azaldığı yönünde veriler mevcuttur. Pek çok araştırma, BDNF'nin farklı antidepresan yaklaşımlar için "son ortak yol" olduğunu ileri sürmekte ve kronik antidepresan tedavinin erişkin hipokampusunda nörogenezi hızlandırdığını; plastisite ve nöronal hayatta kalımda rolü olan nörotrofin iletici yolakları düzenlediğini göstermektedir

Anahtar Kelimeler

• Depresyon, nöroplastisite, beyin kaynaklı nörotrofik faktör

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