Allan Flowers, a designer who worked for both GM and Nissan, recently submitted a bunch of his sketches to Dean's Garage. This is his Nissan work:
http://www.deansgarage.com/2015/alla...-ndi-designer/
I linked his GM work is in another thread.
It looks like most of this was never seriously considered for production. However there are some interesting proposals for the first Altima here as well as the second generation Pulsar/NX.