Assessment of the Role of the Glutamatergic System in the Activation of Melanin-Concentrating Hormone Neurons

Öz

The hypothalamus is the part of the central nervous system that contains many neuropeptide and neurotransmitter systems. It functions as an integrative center for peripheral and central signals that control appetite and regulate energy homeostasis. Neurons located in various nuclei of the hypothalamus regulate feeding behavior with the many different hormones and peptides they synthesize. While some of these molecules have orexigenic effects that stimulate food intake, others have anorexigenic effects that suppress food intake. One orexigenic peptide is melanin-concentrating hormone (MCH). The mammalian melanin-concentrating hormone is a nineteen-amino acid neuropeptide produced in the lateral hypothalamic area (LHA) and incerto-hypothalamic area (IHA) in the brain and exerts its orexigenic effects through MCHR1 receptors. In our study, we investigated the relationship between the glutamatergic system and MCH neurons histologically. In the experiments, double immunohistochemical labeling with anti-MCH and anti-pCREB antibodies was performed on sections from rat brains injected with glutamate agonists and antagonists. CREB phosphorylation (pCREB) was used as a marker of neuronal activation in the experiments. In male rats, an increased proportion of MCH neurons expressing pCREB was observed in the lateral hypothalamic nucleus after injection of all three agonists. Applying the specific antagonist before injections of all three agonists led to a statistically significant decrease in the number of activated MCH neurons. This study shows that intracellular pathways that require p-CREB protein expression are used to activate MCH neurons. Additionally, for the first time in the literature, the presence of phosphorylated CREB protein in MCH neurons was determined. New information has been added to the literature on glutamatergic regulation of MCH neurons.

Anahtar Kelimeler

• Melanin-concentrating hormone (MCH)
• pCREB
• Glutamate
• Hypothalamus
• Immunohistochemistry
• Rat

Glutamaterjik Sistemin Melanin Yoğunlaştırıcı Hormon Nöronlarının Aktivasyonundaki Rolünün Değerlendirilmesi

Öz

Hipotalamus, çok sayıda nöropeptit ve nörotransmitter sistemin yer aldığı merkezi sinir sistemi bölümüdür. İştahın kontrol edilmesi ve enerji homeostazisinin düzenlenmesini sağlayan periferal ve merkezi sinyaller için integratif bir merkez olarak fonksiyon görür. Hipotalamusun çeşitli çekirdeklerinde yerleşik nöronlar, sentezledikleri çok sayıda farklı hormon ve/veya peptit ile beslenme davranışı üzerinde düzenleme yapmaktadırlar. Bu moleküllerin bir kısmı besin alımını tetikleyici oreksijenik etki gösterirken, bir bölümü de baskılayıcı anoreksijenik etkiye sahiptirler. Oreksijenik peptitlerden biri de melanin konsantre edici hormondur (MCH). Memeli MCH'ı, beyinde lateral hipotalamik alan (LHA) ile inserto-hipotalamik alanda (IHA) üretilen on dokuz amino asitli bir nöropeptiddir ve oreksijenik etkilerini MCHR1 reseptörleri üzerinden göstermektedir. Çalışmamızda glutamaterjik sistemle MCH nöronları arasındaki ilişki histolojik olarak araştırılmıştır. Deneylerde glutamat agonisti ve antagonisti verilen sıçan beyinlerinden elde edilen kesitlere, anti-MCH ve anti-pCREB antikorlarıyla ikili immünohistokimyasal işaretlemeler yapılmıştır. Çalışmalarda CREB fosforilasyonu (pCREB) nöronal aktivasyon belirteci olarak kullanılmıştır. Erkek deneklerde, lateral hipotalamik çekirdekte her üç agonistin enjeksiyonu sonrasında pCREB’i eksprese eden MCH nöronlarının oranının arttığı gözlenmiştir. Her üç agonistin enjeksiyonlarından önce özgün antagonist uygulanması, aktive olan MCH nöron sayısında istatistiksel olarak anlamlı bir azalmaya yol açmıştır. Bu çalışma ile MCH nöronlarının aktivasyonunda p-CREB protein ekspresyonunu gerektiren hücre içi yolakların kullanıldığı gösterilmiştir. Ayrıca literatürde ilk kez MCH nöronlarında fosforile CREB proteininin varlığı belirlenmiştir. MCH nöronlarının glutamaterjik regülasyonu açısından literatüre yeni bilgiler kazandırılmıştır.

Anahtar Kelimeler

• Melanin konsantre edici hormon (MCH)
• p-CREB
• Glutamat
• Hipotalamus
• İmmünohistokimya
• Sıçan

Kaynakça

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