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

Sustained splenic contraction after daily cocaine administration in rats

The purpose of this study is to examine the effect of repeated cocaine administration on the whole body of rats. Rats (male, 6 weeks old, Sprague Dawley) were injected intraperitoneally with cocaine (50 mg/kg) once a day for 1, 3 or 7 days, and major organs (heart, liver, lung, brain, kidney, spleen) were excised from the sacrificed animals. During autopsy, we found a reduction in spleen size, but not other organs, in cocaine-administered rats as compared to control rats. This reduction became to be noticed at 3 day and easily perceived at 7 day. No marked changes were observed in other organs examined. H&E and EMG staining showed a tendency for a decrease in the number of red blood cells (RBCs) as well as an increase in collagen fibers in the spleens of rats treated repeatedly with cocaine. Transcriptome analysis indicated that repeated cocaine administration depletes RBCs from the spleen. Immunoblot analysis showed that cocaine increases the phosphorylation of myosin light chain (MYL) as well as the levels of transgelin, both of which are involved in the contraction of myofibrils. Collectively, these results show that repeated cocaine administration results in sustained contraction of the spleen, which leads to the release of RBCs from the spleen into circulation.

Nerve impulse-induced release of endogenous noradrenaline and adrenaline from the perfused cod spleen

Release of endogenous catecholamines (CA) by electrical nerve stimulation (NS) was studied in the isolated perfused spleen of the Atlantic cod, Gadus morhua. An HPLC-system for the analysis of endogenously released CA is described. Cocaine (COC) was used to block neuronal re-uptake of endogenous CA released by NS. Splanchnic NS at frequencies of 1-40 Hz for 20 s resulted in release of noradrenaline (NA) and adrenaline (A) with a maximal total overflow at 20 Hz for both amines. The release of CA was frequency-dependent. COC (0.1 mmol.l-1) increased NS-evoked (40 Hz) overflow of NA and A by 4.8 and 2.2 times, respectively. and reduced the overflow of dihydroxyphenylglycol (DOPEG) to spontaneous efflux levels or less. It can be concluded that the HPLC-technique used was adequate for measurement of NS-evoked release of endogenous CA and DOPEG from the isolated perfused cod spleen, and the model presented can therefore be used when studying adrenergic mechanisms in fish spleen.

The fate of noradrenaline and adrenaline in the perfused cod spleen

The time course of appearance of catecholamine metabolites was studied in the spleen of cod,Gadus morhua, during perfusion with radioactively labelled noradrenaline and adrenaline at 10°C. The tlag for appearance of the metabolites ranged between 1.78 and 6.76 min after onset of perfusion for both amines, indicating a rapid disposition of catecholamines. Perfusion with noradrenaline resulted in mainly MOPEG, VMA and DOMA formation, while perfusion with adrenaline additionally resulted in MN formation. There was still formation of deaminated metabolites after denervation, which indicates an additional non-neuronal site of deamination. It is concluded from the study that the fate of noradrenaline and adrenaline within the cod spleen depends on their affinities for the two uptake mechanisms and an extraneuronal site of deamination of great importance cannot be excluded.

Temperature effects on catecholamine accumulation in neuronal and extraneuronal compartments in the cod spleen

The effects of temperature on the accumulation of radiolabelled adrenaline and noradrenaline were studied in the perfused spleen of the Atlantic cod, Gadus morhua. A decrease in temperature from 20-24 to 10 degrees C showed a corresponding decrease in the neuronal and extraneuronal accumulation of both adrenaline and noradrenaline. The Q10-values for the neuronal accumulation of adrenaline and noradrenaline were 3.6 and 2.1, respectively. This indicates that adrenaline is accumulated neuronally by an active process. An increased perfusing time resulted in an even more pronounced difference in the neuronal accumulation between the two amines. The extraneuronal accumulation of both amines was only slightly affected by a 10 degree C decrease in temperature, and with increasing perfusion time, the accumulation increased as in a passive diffussion. There are strong indications that adrenaline and noradrenaline not only accumulate differently from each other in the adrenergic neurons of the cod spleen, but also that the adrenaline uptake mechanism neuronally might resemble the characteristic mammalian catecholamine uptake while noradrenaline seems to accumulate by a more primitive mechanism, not sensitive to a reduction in temperature. This might be physiologically important for the cod, since the spleen can synthetize adrenaline from noradrenaline and the uptake of adrenaline from the circulation is therefore less important.

Neuronal and extraneuronal uptake of L-3H-adrenaline and L-14C-noradrenaline in the fish spleen

The neuronal and extraneuronal uptake of adrenaline and noradrenaline in the isolated perfused spleen of the cod has been studied using radiolabelled amines. The neuronal uptake of adrenaline shows an optimum at 0.5 microgram/ml, but is less efficient than for noradrenaline in the concentration range 0.01-2.5 micrograms/ml. The neuronal uptake of noradrenaline accounts for 60-70% of the total (neuronal plus extraneuronal) uptake in the concentration range 0.01-1.0 microgram/ml. At higher concentrations (2.5-5.0 micrograms/ml) the importance of the extraneuronal uptake increases for both amines, to reach more than 90% of the total uptake at 5.0 micrograms/ml. The extraneuronal uptake shows equal efficiency for the two amines throughout the concentration range studied. It is concluded that the cod spleen possesses a neuronal uptake mechanism which shows a higher uptake efficiency for noradrenaline than for adrenaline, while the extraneuronal uptake mechanism shows no preference.

Neuropharmacology of adrenergic neurons in teleost fish

Although this brief review is based on relatively few types of experiments in few species of teleosts, it is possible to summarize some points of interest regarding the similarities and differences in the mechanisms of adrenergic neurotransmission in fish compared to the higher vertebrates. 1. There is a substantial mixing of cranial autonomic ("parasympathetic") and spinal autonomic ("sympathetic") pathways in the cranial nerves. This close relationship between the two systems and the differences in the nature of the neurons of cranial origin (cholinergic, and non-adrenergic, non-cholinergic) and spinal origin (adrenergic, cholinergic and mixed "polynergic") gives a basis in fish also for a complex pattern of innervation of the various organs. 2. Adrenaline is the major transmitter substance in the adrenergic neurons of most teleosts studied, but there are exceptions within the same species. For instance, in the swimbladder mucosa of the cod, noradrenaline dominates, while adrenaline is the major catecholamine in most other organs innervated by adrenergic neurons. The reasons for the regional differences are not known and further studies of the rate of catecholamine turn-over in the adrenergic neurons of fish are clearly indicated. 3. Adrenoceptors of both the alpha- and the beta-type show great similarities with those of mammals. Some differences in the potencies of certain compounds (e.g., clonidine and methoxamine) exist and receptor binding studies should add valuable information about the adrenoceptors of teleosts. The existence of a subtype of beta-adrenoceptor (beta 2) has been proposed and further work is needed to confirm or deny the applicability of the beta 1/beta 2 adrenoceptor terminology in fish. 4. There appears to be some differences in the mode of action of the so called "indirectly acting amines", such as tyramine, between teleosts and mammals. While the uptake of tyramine into the nerve terminals in mammals appears to take place via the cocaine-sensitive neuronal uptake system which is also responsible for catecholamine uptake (uptake 1), tyramine uptake in cod neurons appears to be via a separate pathway. 5. Presynaptic supersensitivity of the type seen in mammals has also been demonstrated in teleost adrenergic neurons. Both denervation (chemical or surgical) and blockade of the neuronal uptake mechanism by cocaine or desipramine produce this type of supersensitivity, while post-synaptic supersensitivity has so far not been described in teleosts. The effects of removal of the uptake system shows that the uptake process may be as important in teleosts as in mammals in the removal of adrenergic transmitter from the synaptic cleft. 6. In the total picture of adrenergic functions in fish, the circulating catecholamines take a special role...

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.