  We investigate a class of spectral multipliers for an Ornstein-Uhlenbeck
operator $\mathcal L$ in $\mathbb R^n$, with drift given by a real matrix $B$
whose eigenvalues have negative real parts. We prove that if $m$ is a function
of Laplace transform type defined in the right half-plane, then $m(\mathcal L)$
is of weak type $(1, 1)$ with respect to the invariant measure in $\mathbb
R^n$. The proof involves many estimates of the relevant integral kernels and
also a bound for the number of zeros of the time derivative of the Mehler
kernel, as well as an enhanced version of the Ornstein-Uhlenbeck maximal
operator theorem.
