Uptake and release of catecholamines in sympathetic nerve fibers in the spleen of the cod, Gadus morhua.

The effects of denervation or pretreatment with reserpine or 6-hydroxydopamine on the contractile responses of the cod spleen have been studied. The contraction produced by tyramine is abolished by pretreatment with reserpine or 6-hydroxydopamine and by denervation. The response to tyramine is restored in reserpine-treated strips after exposure to noradrenaline, but this is not the denervated or 6-hydroxydopamine-treated strips. The response to noradrenaline is potentiated by 6-hydroxydopamine treatment or denervation, while neither acute (2 days) nor chronic (8 days) reserpine treatment have any detectable effect. The effects of 6-hydroxydopamine and denervation are probably due to specific supersensitivity caused by the loss of the presynaptic uptake mechanisms on destruction of the nerve terminals, but contribution by a non-specific postsynaptic supersensitivity is not completely excluded. The effect of acetylcholine is also significantly potentiated by pretreatment with 6-hydroxydopamine or denervation, but not by reserpine, while the dose-response curve for carbachol is not affected by the specific cholinesterase inhibitor BW 284 C51, denervation or 6-hydroxydopamine. The degree of potentiation of the acetylcholine curve caused by both denervation and 6-hydroxydopamine treatment is very similar to that produced by BW 284 C51. It is concluded therefore, that the cholinesterase is associated with nerve fibres which are destroyed by denervation and 6-hydroxydopamine. Although the cod spleen receives both cholinergic and adrenergic sympathetic innervation all responses to nerve stimulation of the perfused spleen are abolished after 6-hydroxydopamine treatment. The possibility is suggested that the sympathetic fibres to the cod spleen represent a primitive type of neuron, with both catecholamines and acetylcholine present within the same terminals.