The Collaborative International Dictionary of English v.0.48:

Depressomotor \De*pres`so*mo"tor\, a. (Med.)
   Depressing or diminishing the capacity for movement, as
   depressomotor nerves, which lower or inhibit muscular
   activity. -- n. Any agent that depresses the activity of the
   motor centers, as bromides, etc.
   [1913 Webster]