Abstract
Hippocampal slices were obtained from C3H/HeN mice of 22-week-old (4 estrus/ 5 metestrus/ 6 diestrus females, and 5 males). After stimulating the molecular layer of the dentate gyrus (DG) by single square-wave pulse with intensities increased stepwisely from 10 to 900 μA, field potentials were recorded from the molecular layer and the granule cell (GC) layer simultaneously. The input-output (I-O) relationship of the field excitatory postsynaptic potential (fEPSP) was compared among the three phases of estrous cycle. In the case of stimulation with lower current (10–100 μA), the fEPSP slopes measured in the GC layer showed similar patterns across the phases whereas those in the molecular layer showed different patterns between estrus and non-estrus phases; in the slice from non-estrus mice the I-O curve of slope did not show a simple sigmoid form but a delayed rise or a decrease into negative value. Moreover, pattern of the increase in male mice resembles that in estrus mice. This variation across estrous phases may be due to a sex hormone-dependent change of excitability of interneurons that extend axonal fibers within DG molecular layer, such as molecular layer perforant path-associated cells (MOPP cells). [J Physiol Sci. 2007;57 Suppl:S156]
