Exposure of taste buds to potassium permanganate and formalin suppresses the gustatory neural response in the Nile tilapiaOreochromis niloticus(Linnaeus)

The effects of exposing the taste receptors to two common aquaculture therapeutants, potassium permanganate (KMnO4) and formalin, on the gustatory responses in the Nile tilapia Oreochromis niloticus (Linnaeus) were studied using an electrophysiological approach. Electrical responses to the stimuli before and after perfusing the receptors with the toxicants were compared. Responses to 1.0 mM l-methionine (l-met) were significantly reduced when the receptors were perfused with 2.0 mg L−1 KMnO4 or 200.0 mg L−1 formalin. KMnO4 suppressed the responses to 56%, whereas formalin reduced them to 83%. Both toxicants reduced the responses to l-arginine to a similar extent to that of l-met, indicating that the action of the toxicants is not specific for the receptor sites for amino acids. On the other hand, the toxicants suppressed the responses to quinine significantly more than those to amino acids, which indicates that the transduction pathways for bitter substances are much more sensitive. The suppressions were reversible, suggesting that these toxicants do not cause any permanent damage to the physiological features of the taste receptors, but only interfere with their normal functioning. The possible mechanisms of suppression and their consequences on the feeding process are discussed.