  Although thick stellar discs are detected in nearly all edge-on disc
galaxies, their formation scenarios still remain a matter of debate. Due to
observational difficulties, there is a lack of information about their stellar
populations. Using the Russian 6-m telescope BTA we collected deep spectra of
thick discs in three edge-on S0-a disc galaxies located in different
environments: NGC4111 in a dense group, NGC4710 in the Virgo cluster, and
NGC5422 in a sparse group. We see intermediate age (4-5 Gyr) metal rich ([Fe/H]
$\sim$ -0.2 - 0.0 dex) stellar populations in NGC4111 and NGC4710. On the other
hand, NGC5422 does not harbour young stars, its disc is thick and old (10 Gyr),
without evidence for a second component, and its $\alpha$-element abundance
suggests a 1.5-2 Gyr long formation epoch implying its formation at high
redshift. Our results suggest the diversity of thick disc formation scenarios.
