Subject: How does catnip cause the 'playful' behaviors in cats?

What kind of plant is made into catnip?  How does the catnip
make a cat behave so funny (e.g. sniffing, rubbing its chin, rolling on
its back etc.)?  Is it anything like a halicinogen or some sort of 
"drug" to cats?  What is the cellular/molecular basis that triggers
these behaviors in cats? (e.g. some molecules in the plants binds to
certain neurological receptor in cats thus stimulating a set of responses
etc.etc.)

thank you!

Re: How does catnip cause the 'playful' behaviors in cats?