Effect of L-Tryptophan Feeding on Brain Mitochondrial Ion Transport in Net-Confined Climbing Perch (Anabas testudineus Bloch)

Serotonin (5-HT), a neurohormone with many physiological actions, is synthesized from the dietary essential amino acid tryptophan (TRP). However, the effects of TRP on neuronal ion transporters and its role in stress response have not yet been identified in the teleost fish. The effects of varied doses of TRP on the activities of mitochondrial (m) and cytosolic (c) ion transporters were examined in the forebrain (FB), midbrain (MB) and hindbrain (HB) segments of an air-breathing fish Anabas testudineus Bloch kept either in non-stressed or in stressed condition. Feeding the fish with varied doses of TRP (1, 2 and 4 mg g^-1 feed) for seven days produced dose-dependent effects on Na⁺, K⁺-ATPase and H⁺-ATPase activities in different regions of fish brain. A decrease in (P<0.001) Na⁺, K⁺-ATPase activity was found in FB and MB after seven days of TRP treatment. TRP decreased (P<0.001) H⁺-ATPase activity in the FB but increased Na⁺, K⁺ ATPase activity in all the three regions of the brain. In non-stressed fish, feeding 20 mg g^-1 TRP for two days produced a substantial rise (P<0.001) in cH⁺-ATPase activity in the FB and HB of the fish. But mH⁺-ATPase showed a reversed response to TRP feeding. On the contrary, TRP treatment in net-confined fish showed a decrease (P<0.001) in the cH⁺-ATPase activity in the FB and HB, whereas it produced an increase (P<0.001) in the MB. In non-stressed fish, cytosolic and mitochondrial Ca²⁺-ATPase activities in FB and MB decreased (P<0.001) after TRP feeding. Feeding TRP in stressed fish reduced (P<0.001) cCa²⁺- ATPase activity in the MB but produced an increase (P<0.001) in its activity in mitochondria. In non-stressed fish, TRP feeding decreased (P<0.001) mMg²⁺-ATPase activity in the FB and MB segments. TRP treatment, in stressed fish, however decreased (P<0.001) Mg²⁺-ATPase activity in the MB but not in other brain segments. The data indicate that TRP can regulate brain mitochondrial ion transport, and induction of stress may modify the TRP-induced mitochondrial ion transport response of air-breathing fish.