  We present some recent studies on the physical conditions and the chemistry
of the interstellar medium (ISM) in the Galactic center region (GCR). Large
scale shocks in the context of a bar potential can play a role in explaining
the observed properties, at least in some particular regions. Alternatively, we
propose that the observed properties (inhomogeneity, high temperatures of the
molecular gas, rich chemistry,...) of the GCR ISM can be the consequence of the
recent past ($10^6-10^7$ years ago) of massive star formation in the GCR.
