Synthesis of Kainate Receptor Subunits in Oxytocin Neurons: An Immunohistochemical Study

Öz

Oxytocin neurons are the most important part of the neuroendocrine mechanism which starts and maintains the parturition as well as the milk ejection. These neurons are localized in the hypothalamic supraoptic (SON) and paraventricular (PVN) nuclei and glutamatergic system plays an important role in the regulation of these neurons in the central nervous system. Glutamate exerts its effects by binding and activating its receptors on the plasma membrane. There is a lack of knowledge in the literature on the synthesis of kainate receptors, as one of the glutamatergic subfamilies, by oxytocin neurons. In this study the aim is to determine if the kainate receptor subunits (GluK1, GluK2, GluK3, GluK5) were expressed in oxytocin neurons. For this purpose, double immunofluorescence labeling technique was employed in order to assess the co-localization of oxytocin with respective receptor in the female rat hypothalamus. The results of this staining showed that almost the vast majority of oxytocin neurons were immuno-reactive for GluK5 protein in both SON and PVN. It was determined that almost half of the oxytocin neurons in both of the nuclei synthesize GluK2. Analyses of the preparations revealed no expression of GluK1 and GluK3 proteins in the oxytocin neurons. As a result, the determination of the oxytocin neurons can synthesize kainate receptor subunits which can form functional kainate receptor channels suggests that the endogenous glutamate can exert its effects on oxytocin neurons by binding these receptors. We anticipate that showing the oxytocin neurons express kainate receptor subunits would be an important addition to the literature. The future physiological and/or pharmacological studies as well as the possible findings from the transgenic animals would enlighten the role of kainate receptors in the regulation of oxytocin synthesis and/or releasing mechanism.

Anahtar Kelimeler

• oxytocin,
• glutamate
• kainate receptors
• GluK2
• GluK5
• immunohistochemistry

Oksitosin Nöronlarında Kainat Reseptör Alt Birimlerinin Sentezi: İmmünohistokimyasal Çalışma

Öz

Oksitosin nöronları, gebe dişide doğumu başlatan ve sürdüren, ayrıca meme bezlerinden süt enjeksiyonunu sağlayan nöroendokrin mekanizmanın en önemli kısmını oluştururlar. Hipotalamik supraoptik (SON) ve paraventriküler (PVN) çekirdeklerde yerleşik olan bu nöronların regülasyonunda merkezi sinir sisteminde yer alan glutamaterjik sistemin önemli rolü olduğu bilinmektedir. Glutamat etkisini hücre membranları üzerinde bulunan reseptörlerine bağlanıp onları aktive ederek gösterir. Bu reseptörlerin üç ayrı alt grubundan biri olan kainat reseptörlerine ait alt birim proteinlerinin oksitosin nöronlarınca sentezlendiğine dair bilgi henüz raporlanmamıştır. Bu çalışmada, oksitosin nöronlarında kainat reseptör alt birimlerinin (GluK1, GluK2, GluK3, GluK5) eksprese edilip edilmediğinin belirlenmesi amaçlandı. Bu amaçla dişi sıçan hipotalamusunda oksitosin ve reseptör ko-lokalizasyonunun belirlenmesinde ikili immünofloresan işaretleme tekniği kullanıldı. Bu boyamaların sonucunda, SON ve PVN’deki oksitosin nöronlarının sayıca çok büyük bir kısmının aynı zamanda GluK5 proteini sentezledikleri belirlendi. Her iki çekirdekte yer alan tüm oksitosin nöronlarının yaklaşık yarısının GluK2 sentezlendiği görüldü. Preparatların incelenmesi sonucunda oksitosin nöronlarında GluK1 ve GluK3 proteinlerinin ekspresyonu izlenmedi. Sonuç olarak çalışmamızda oksitosin nöronlarının fonksiyonel reseptör kanalı oluşturabilecek kainat reseptör alt birimleri eksprese ettiklerinin belirlenmesi, endojen glutamatın oksitosin nöronları üzerindeki etkilerini bu reseptörlere bağlanarak gerçekleştirebileceğini düşündürmektedir. Oksitosin nöronlarında kainat reseptör alt birimlerinin ekspresyonun gösterilmesi bu konudaki literatüre önemli katkılar sağlayacağı ön görüsündeyiz. Gelecekte yapılacak olan fizyolojik ve farmakolojik çalışmalarla veya transgenik hayvanlardan elde edilebilecek bulgulara çalışmamızda elde ettiğimiz sonuçlar eklendiğinde, kainat reseptörlerinin oksitosin sentez ve salgılama mekanizmasındaki rolü açıklığa kavuşacaktır.

Anahtar Kelimeler

• oksitosin
• glutamat
• kainat reseptörleri
• GluK2
• GluK5
• immünohistokimya

Kaynakça

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