Original Article

Neuropeptide Y expression in mouse hippocampus and its role in neuronal excitotoxicity1

Yong-fei WU, Sheng-bin LI


Aim: To investigate neuropeptide Y (NPY) expression in mouse hippocampus
within early stages of kainic acid (KA) treatment and to understand its role in
neuronal excitotoxicity.
Methods: NPY expression in the hippocampus within
early stages of KA intraperitoneal (ip) treatment was detected by immunohistochemistry
(IHC) and in situ hybridization (ISH) methods. The role of NPY and
Y5, Y2 receptors in excitotoxicity was analyzed by terminal deoxynucleotidyl
transferase-mediated UTP nick end-labeling (TUNEL) assay.
Results: Using
IHC assay, in granule cell layer of the dentate gyrus (DG), NPY positive signals
appeared 4 h after KA injection, reached the peak at 8 h and leveled off at 16 and
24 h. In CA3, no positive signal was found within the first 4 h after KA injection,
but strong signal appeared at 16 and 24 h. No noticeable signal was detected in
CA1 at all time points after KA injection. Using the ISH method, positive signals
were detected at 4, 8, and 16 h in CA3, CA1, and hilus. In DG, much stronger
ISH signals were detected at 4 h, but leveled off at 8 and 16 h. TUNEL analysis
showed that intracerebroventricularly (icv) infusion of NPY and Y5, Y2 receptor
agonists within 8 h after KA insult with proper dose could remarkably rescue
pyramidal neurons in CA3 and CA1 from apoptosis.
Conclusion: NPY is an
important anti-epileptic agent. The preceding elevated expression of NPY in granule
cell layer of DG after KA injection might partially explain its different
excitotoxicity-induced apoptotic responses in comparison with the pyramidal neurons
from CA3 and CA1 regions. NPY can not only reduce neuronal excitability
but also prevent excitotoxicity-induced neuronal apoptosis in a time- and doserelated
way by activation of Y5 and Y2 receptors.