Influence of neurotransplantation on rats'' behavior with different conditions of reinforcement

Recently, we have reported a marked rat lateralization in the T-maze choice. Embryonic rat tissue from neocortex, hippocampus, hypothalamus and amygdala was transplanted into intact rat brains in various combinations: 1) neocortex and hypothalamus (Neo + Hyp); 2) hippocampus and amygdala (Hipp + Amyg); 3) neocortex and hippocampus (Neo + Hipp); and 4) hypothalamus and amygdala (Hyp + Amyg). Once under conditions in which reinforcement was equally qualitative and equally probable, rats in all groups chose the T-maze arm contralateral to the side of implantation. In a second set of experiments, rats were presented a choice between quality and probability of reinforcement. The right arm of the T-maze contained a cup of water 33% of the time (high-quality but low-probability reinforcement). The left sleeve contained a solution of 0.15% quinine in water 100% of the time (low quality but high probability of reinforcement). Rats that received Neo + Hyp transplants chose the T-maze arm that always contained a drink cup with water significantly more often than they chose the arm that always contained the drink cup with quinine solution. Rats that received Hipp + Amyg transplants chose the arm containing the drink cup with quinine solution much more often than the arm that sometimes contained a cup of water. Rats with transplanted Neo + Hyp generally were more active than rats with transplanted Hipp + Amyg. These data suggest that the behavior of rats can be affected by selective transplantation of different brain tissue.