  We derive expressions for the intensity of the Brillouin polarized spectrum
of a molecular liquid formed of axially symmetric molecules. These expressions
take into account both the molecular dielectric anisotropy and the modulation
of the local polarisability by density fluctuations. They also incorporate all
the retardation effects which occur in such liquids. We show that the spectrum
splits into a q-independent rotational contribution and q-dependent term, which
reflects the propagation of longitudinal phonons. In the latter, the two light
scattering mechanisms enter on an equal footing and generate three scattering
channels. We study the influence of the two new channels and show that they may
substantially modify the Brillouin line-shape when the relaxation time of the
supercooled liquid and the phonon period are of the same order of magnitude.
