MSDTC and NT AUTHORITY\NETWORK SERVICE vs NT AUTHORITY\NetworkService

We encountered a very strange issue with MSDTC recently. We were getting an error when trying to execute a remote stored procedure, which appeared to be security related. We were using NT AUTHORITY\NETWORK SERVICE, which didn't work, but then found that NT AUTHORITY\NetworkService did. I was not even aware that the NetworkService account existed, as I had always used NETWORK SERVICE. I can't seem to find anything that explains the difference and why you must use NetworkService for MSDTC. I would love to hear from someone that can explain that to me.