Cat loosing hair

Question
My male cat is 5 years old and recently has been shedding alot, i was brushing him tonight and he lost a ton of hair and i noticed that he has quarter size splotches on his back near his spine. I am just curious if this is normal because of the weather changes or is this an underlying medical problem.  Here is some information you might need to know...he is an indoor cat, he is fixed, and i have a 9 month old puppy that is constantly playing with the cat.  

thanks for any help

Answer
There are many possible causes of hair loss in cats, many of which may require medical attention. Here is an article which goes into this issue in depth:

http://www.peteducation.com/article.cfm?cls=1&cat=1338&articleid=195

As you can see, there is a great deal more analysis needed to ascertain what is going on both in terms of the detailed symptoms and tests your vet may need to do. I strongly urge you to take your cat to a vet and have him examined in order to get to the root of the problem and properly treat it. That is really the only way.