We present the radial profiles of the H{alpha}, Mg and Fe line-strength indices for a sample of eight spiral galaxies with a low-surface-brightness stellar disc and a bulge. The correlations between the central values of the line-strength indices and velocity dispersion are consistent with those known for early-type galaxies and bulges of high-surface-brightness galaxies. The age, metallicity and {alpha}/Fe enhancement of the stellar populations in the bulge-dominated region are obtained using stellar population models with variable element abundance ratios.