With their mission drawing to a close, space shuttle Columbia's astronauts wrapped up their animal experiments Friday and expressed a reluctance to come home.

"It really doesn't feel like we've been here for two weeks. It feels like we just got here," said astronaut Kay Hire. "I'm not ready to come home yet. I'd like to stay up here another couple weeks."Columbia's brain research mission, called Neurolab, was due to end with a Sunday touchdown.

The astronauts took their last crack at a ball-catching experiment intended to see how their nervous systems adapt in space. They also observed young rats scampering around a small jungle gym.

In the final dissections of the mission, Columbia's medics administered an anesthetic overdose to six young rats that had undergone minor leg surgery on Wednesday.