In this study we have studied the initial stage of the nanosecond-pulsed discharge development in liquid phase. Modeling predicts that in the case of fast rising strong nonhomogeneous electric fields in the vicinity of high voltage pin electrode a region saturated with nanoscale non-uniformities may be developed. This phenomenon is attributed to the electrostriction mechanisms and may be used to explain development of breakdown in liquid phase. In this work, schlieren method was used in order to demonstrate formation of negative pressure region in liquids with different dielectric permittivity constants: water, ethanol and ethanol-water mixture. It is shown that this density perturbation, formed at the raising edge of the high voltage pulse, is followed by a generation of a shock wave propagating with the speed of sound away from the electrode, with negative pressure behind it.