All of these are graduate degrees and will not get your GPA any higher. Moreover, much less attention is paid to graduate school grades so even if you ace your coursework, no one will be particularly impressed.
The degrees themselves will do little to help you. A MS program in neuroscience is more relevant at the residency stage when they may care about research in neuro that you've done or papers/presentations, etc etc. You've got to get into medical school first. The MPH could give you some nice stuff to talk about as far as experience and knowledge with public health or health policy, but again, this isn't going to compensate for weaknesses in your application as there are many people that get these degrees. Similar for MHA (which has even less of a connection to medical school coursework). These shouldn't dissuade someone from pursuing these degrees; if you really like this stuff, you should do the degrees. Just don't do them to make up for weaknesses in your application because they're not really effective for that.