Hippocampal levels of gamma-enolase, C-1-tetrahydrofolate synthase and serotransferrin fluctuate over the estrous cycle in the rat.

Hippocampal functions vary across the estrous cycle but metabolic changes at the protein level have not been systematically studied so far. It was therefore the aim of the study to screen expression of metabolic proteins mainly represented by metabolic enzymes in the hippocampus over the estrous cycle and in males. Female and male OFA Sprague-Dawley rats were used and female estrous phases were determined by vaginal smears, according to which females were separated into groups of proestrous, estrous, early and late metestrous and diestrous. Proteins were extracted from hippocampal tissue and separated on two-dimensional gel electrophoresis followed by identification with mass spectrometry methods (MALDI-TOF-TOF and nano-LC-ESI-MS/MS). Comparative analysis of protein levels was carried out by quantifying protein spot volumes by means of specific software. Levels of one expression form of gamma-enolase were different between diestrous and early metestrous; C-1-tetrahydrofolate synthase levels were elevated in proestrous as compared with estrous and serotransferrin levels were increased in diestrous as compared with proestrous, estrous, metestrous and in males. The outcome of estrous cycle- and gender-dependent protein fluctuations is relevant for the interpretation of previous and future work as well as for the design of further studies at the protein level in the hippocampus.