  Let $V$ be a valuation domain of rank one with quotient field $K$. We study
the set of extensions of $V$ to the field of rational functions $K(X)$ induced
by pseudo-convergent sequences of $K$ from a topological point of view,
endowing this set either with the Zariski or with the constructible topology.
In particular, we consider the two subspaces induced by sequences with a
prescribed breadth or with a prescribed pseudo-limit. We give some necessary
conditions for the Zariski space to be metrizable (under the constructible
topology) in terms of the value group and the residue field of $V$.
