Authoritative DNS server for 12.54.94.0/23 PTR

Hello Nanog Members, We have been having some issue doing reverse lookups for ip's in the 12.54.94.0/23 prefix. We know that this block is assigned to AT&T and AT&T has assigned that block to Siemens Medical (based on whois queries). We are now trying to find out who would be the authoritative DNS server that would resolve PTR queries for these IP addresses. Would someone from AT&T (or Siemens) or someone that has that info please contact me offline to discuss? Thanks Everyone, -- Michael Gatti cell.949.735.5612 ekim.ittag@gmail.com (UTC-8)