Isolation reduces midbrain tryptophan hydroxylase activity in mice

Male C57 mice were divided into two experimental groups: "Isolated" and "Grouped". Isolated mice were housed individually for 30 or 45 days; Grouped mice were housed five per cage. Midbrain tryptophan hydroxylase activity was determined at the end of the isolation period. Isolated mice showed 35% less tryptophan hydroxylase activity than grouped mice (P<0.001). Prolongation of the isolation (45 vs 30 days) did not further reduce the enzyme activity. The changes in tryptophan hydroxylase activity may be related to behavioral changes induced by isolation.