  This paper considers interactions between closed strings and open strings
satisfying either Neumann or constant (point-like) Dirichlet boundary
conditions in a BRST formalism in the critical dimension. With Neumann
conditions this reproduces the well-known stringy version of the Higgs
mechanism. With Dirichlet conditions the open-string states correspond to
either auxiliary or Lagrange multiplier target-space fields and their coupling
to the closed-string sector leads to constraints on the closed-string spectrum.
