A study conducted at Florida Atlantic University found that mice who were taken from the cage they lived in and later placed back in it caused a surge of dopamine "that mimics the response to a dose of cocaine."
From Science Daily:
The researchers questioned whether their findings reflected leaving an unappealing environment or if it truly was a response to the positive aspects of a known and safe environment. Therefore, they examined whether dopamine surges arise when the mice were relocated from the plexiglass recording chamber to a clean cage with natural bedding matching the one they had been living in prior to the study. Indeed, dopamine release occurred, however, this release was not as large as that observed when mice were transferred to the home cage and the dopamine surge was not as sustained.
"We weren't really exploring home cage effects," said Felix Mayer, Ph.D., a post-doctoral fellow in Blakely's lab and lead author of the study. "However, we were struck as to how reliable the manipulation was in evoking dopamine release particularly when placed in the context of little or no rise in dopamine when the mice were moved from the home cage to the test chamber. We are excited now to see if the genetic models of brain disorders we study will impact this effect."