  Based on schematic two-level models extended to $a_1$-meson degrees of
freedom, we investigate possible mechanisms of chiral restoration in the
vector/axialvector channels in cold nuclear matter. In the first part of this
article we employ the massive Yang-Mills framework to construct an effective
chiral Lagrangian based on low-energy mesonic modes at finite density. The
latter are identified through nuclear collective excitations of `meson'-sobar
type such as $\pi\leftrightarrow [\Delta (1232)N^{-1}]\equiv\hat\pi$,
$\rho\leftrightarrow [N^* (1520)N^{-1}]\equiv\hat\rho$, etc.. In a mean-field
type treatment the in-medium gauge coupling $\hat g$, the (axial-) vector meson
masses and $\hat f_\pi$ are found to decrease with density indicating the
approach towards chiral restoration in the language of in-medium effective
fields. In the second part of our analysis we evaluate the (first) in-medium
Weinberg sum rule which relates vector and axialvector correlators to the pion
decay constant. Using in-medium $\rho$/$a_1$ spectral functions (computed in
the two-level model) also leads to a substantial reduction of the pion decay
constant with increasing density.
