Human chorionic gonadotropin decreases the phosphorylated tau protein level in streptozotocin-Alzheimeric male rats’ hippocampus

Introduction
The pharmacological suppression of luteinising hormone or human chorionic gonadotropin (hCG) can reduce Aβ plaques in the brains of rats and mice, but the effects of hCG on the phosphorylated tau protein level in the hippocampus have not been studied. Therefore, we investigated the effects of hCG on the phosphorylated tau protein level and its effect on hCG receptor-immunoreactive neuron density in the hippocampus of Alzheimer’s disease (AD) model rats (streptozotocin [STZ] injected intracerebroventricularly).

Material and methods
The rats were administered hCG (50, 100, and 200 IU/200 µl saline, intraperitoneally) or vehicle once/day for three days after injection of STZ. The passive avoidance memory test was performed 6 hours after the last hCG injection. The phosphorylated tau protein level in the hippocampus was measured by ELISA, and hCG receptor-immunoreactive neurons were shown by immunohistochemical technique in areas of hippocampus.

Results
Treatment with hCG attenuated memory deficiencies and reduced the level of phosphorylated tau protein in the hippocampus. hCG also improved the density of hCG receptor-immunoreactive neurons. The high dose of hCG hormone (200 IU/200 µl saline) seemed to have a significant effect on passive avoidance memory, phosphorylated tau protein concentration, and accumulation of hCG receptor-immunoreactive neurons in Alzheimeric rats’ hippocampus.

Conclusions
In conclusion, hCG can provide protection against memory deficits induced by STZ and it can inhibit accumulation of tau hyperphosphorylation in the hippocampus. Furthermore, hCG can increase the hCG receptor-ir neurons number in the rats hippocampus after ICV injection of STZ.