Click on Topic Options at the top of the page and select Add Topic to your Watched Topics and you will receive an email every time there is a response with the content of the response in the email.
Actually, that's only the case if you go to
My Stuff ->
Edit Preferences and check the
Yes radio button under
By default should anything added to your Watch Lists be emailed to you? (be sure to click the
Submit button at the bottom of the page to implement the change)
or go to
My Stuff ->
Watch Lists ->
Watched Topics ->
Edit Watched Topics and check the
Immediately radio button under
Email Notification for the specific thread you want to receive reply notifications for (be sure to click the
Update Watched Topics button to implement the change).
By default, notification is turned off, both universally in your Preferences and case-by-case in your Watch Lists.