The Barzan probe was an automated probe sent into the Barzan wormhole in early 2366.
As the Barzan had no manned space travel, they had to send a probe. The probe traveled all the way to the Gamma Quadrant, beyond the Denkiri Arm of the Milky Way Galaxy.
The findings of the probe were relatively limited though, as it was not possible to determine from the gathered data whether the wormhole would be stable or not. (TNG: "The Price")