Delayed neuronal death and damage of GDNF family receptors in CA1 following focal cerebral ischemia

Abstract

Delayed neuronal death (DND) of pyramidal neurons in the CA1 and CA3 regions of the hippocampus has been extensively studied following global brain ischemia, whereas only little is known about DND in this highly vulnerable brain region after focal brain ischemia. In the present study, the distribution and time course of hippocampal neuronal apoptosis were studied following transient middle cerebral artery occlusion (MCAO) in rats 1, 3, 7, 14, and 30 days after the insult. In 60% of the animals, more than 90% of CA1 pyramidal neurons showed strong nick-end labeling (TUNEL) staining at day 3 with fragmentation and marginalization of the nuclei in approximately 40% of these cells. The number of TUNEL-positive cells decreased within the next days, but 30 days after MCAO, some apoptotic neurons were still present. Analysis of the expression of the glial cell line-derived neurotrophic factor (GDNF) and its receptors GFRα1, GFRα2, and GFRα3 using triple immunofluorescence and confocal laser scanning microscopy revealed that in all animals showing marked hippocampal DND, the neuronal staining for GFRα1, GFRα3, and GDNF decreased prior to the onset of TUNEL staining in CA1. After 7 days, some apoptotic neurons still expressed GFRα3, whereas only few showed GFRα1 immunoreactivity, indicating that GFRα1 may be beneficial for the survival of hippocampal neurons. The data suggest that reduced expression of GDNF and impairment of GFRα1/3 may contribute to hippocampal DND after focal brain ischemia.