  We present measurements of the electrical conductance $G$ at room temperature
of mechanically controllable break junctions (MCBJ) fabricated from Au in
different solvents (octane, DCM, DMSO, and toluene) and compare with
measurements in air and vacuum. In the high conductance regime $G \agt
G_0=2e^2/h$, the environment plays a minor role, as proven by the measured
conductance histograms, which do not depend on the environment. In contrast,
the environment significantly affects the electrical properties in the low
conductance (tunneling) regime {$G << G_0$}. Here, we observe a systematic and
reproducible lowering of the tunneling barrier height $\phi$. At shorter
distances, a transition to a strongly suppressed apparent barrier height is
observed in octane, providing evidence for the layering of solvent molecules at
small inter-electrodes separations. The presented experimental configuration
offers interesting perspectives for the electrical characterization of single
molecules in a controlled environment.
