Entorhinal transplants and spatial memory abilities in rats.

Transplants of embryonic entorhinal tissues, placed into the angular bundle region of adult rats, innervate appropriate areas of the host hippocampal formation and amygdala, provided that native entorhinal connections have been destroyed. In the present study, transplants were examined for their ability to restore spatial memory abilities which are lost following the bilateral destruction of native entorhinal connections. Animals were tested for their ability to perform an 8-arm radial maze task, for spontaneous alternation in a T-maze, and for their ability to learn to alternate in a T-maze for a food reward. Animals with lesions, and those with lesions + implants, remained impaired on all 3 tasks examined for as long as 6 months postimplantation. During this time, no transplant-induced behavioral recovery was observed, although behavioral stabilization was observed on the spontaneous alternation task at 6 months post-transplantation. The data suggest that these transplants may be limited in their ability to restore functions which are highly dependent upon the anatomical integrity of the damaged circuits and the precise organization of information flow through the damaged area.