  We present integral field spectroscopic observations of the central region of
the active galaxy NGC 4258 obtained with the fibre IFU system INTEGRAL. We have
been able to detect cold neutral gas by means of the interstellar NaD doublet
absorption and to trace its distribution and kinematics with respect to the
underlying disc. The neutral gas is blue-shifted with projected velocities in
the 120--370 km/s range. We have also detected peculiar kinematics in part of
the ionized gas in this region by means of a careful kinematic decomposition.
The bipolar spatial distribution of the broader component is roughly coincident
with the morphology of the X-ray diffuse emission. The kinematics of this gas
can be explained in terms of expansion at very high (projected) velocities of
up to 300 km/s. The observations also reveal the existence of a strip of
neutral gas, parallel to the major kinematic axis, that is nearly coincident
with a region of very high [SII]/H$\alpha$ ratio tracing the shocked gas. Our
observations are consistent with the jet model presented by \cite{wilsonetal01}
in which a cocoon originating from the nuclear jet is shocking the gas in the
galaxy disc. Alternatively, our observations are also consistent with the
bipolar hypershell model of \cite{Sofue80} and \cite{SofueandVogler01}. On
balance, we prefer the latter model as the most likely explanation for the
puzzling features of this peculiar object.

Astrophysics of Galaxies;High Energy Astrophysical Phenomena