Demonstration of denervation supersensitivity: a pharmacological approach.

1. Although the phenomenon of denervation supersensitivity has been extensively studied in peripheral cholinergically and adrenergically innervated organs, the consequences of denervation have not been studied in as much detail in serotonergically innervated s stems. This may be due in part to the difficulties associated with producing specific lesions of serotonergic systems and with quantifying physiological responses of the CNS due to serotonin. 2. Because the lateral ciliated cells of the gill of the bivalve mollusc, Mytilus edulis, are innervated by serotonergic motor neurons which are responsible for accelerating the beating rate of the cilia we used this as a model system with which to study the effects of denervation by physical transections of the branchial nerve and by pharmacological treatments with 5,6 dihydroxytryptamine. 3. Both treatments produced a supersensitive response of the ciliated cells to the superfusion of serotonin. Two mechanisms with different time courses may be responsible. 4. The initial faster acting component may be due to changes in re-uptake mechanisms for serotonin, while the later slowly developing component may be due to other causes, including a hyperplasia of postjunctional serotonin receptors.

The peripheral innervation of the gill of the marine mollusc demonstrated by the aluminium-formaldehyde (ALFA) histofluorescence method.

The aluminium-formaldehyde (ALFA) histofluorescence method was used to study the innervation of the gill of the marine bivalve mollusc Mytilus edulis and the results were contrasted with those obtained with the standard formaldehyde-induced-fluorescence (FIF) method. The ALFA method produced more fluorescing structures than the FIF method, thus revealing fine branches of the branchial nerve running beneath the gill epithelium which previously remained undetected. This study of marine invertebrates.

Characterization of the dopamine stimulated adenylate cyclase in the pedal ganglia of Mytilus edulis: interactions with etorphine, beta-endorphin, DALA, and methionine enkephalin.

The dopamine-stimulated adenylate cyclase activity was studied both in vivo and in vitro in the central nervous system of the bivalve mollusc Mytilus edulis. Dopamine, epinine, and apomorphine stimulated the enzyme system. Fluphenazine, haloperidol, chlorpromaxine, and to a lesser extent BOL inhibited the dopamine-stimulated adenylate cyclase. Etorphine, beta-endorphine, DALA, and methionine enkephalin depressed cyclic AMP levels. This phenomena was naloxone reversible. In addition, the opioids inhibited the stimulation of adenylate cyclase by dopamine. This phenomena was also naloxone reversible. The study demonstrates an interaction among dopamine, the opioids, and cyclic AMP.

The calcium-dependent neuronal release of serotonin and its antagonism by lithium.

The cilio-excitatory serotonergic innervation of lateral gill cilia of Mytilus edulis was studied in vivo. Peripheral serotonin release was dependent on the external calcium concentration. Serotonin release was inhibited by autodialyzing calcium from the tissue or by increasing the calcium concentration in the medium, as determined by measuring ciliary activity stroboscopically and by biochemical and radioassays of serotonin. Lithium also inhibited serotonin release when added to the external bathing medium. Concomitantly, altering calcium concentrations altered the degree of inhibition of serotonin release caused by lithium. The study demonstrates that the terminal release of the monoamine serotonin is a calcium-dependent mechanism. The pharmacological effects of lithium in this system appear to be interrelated with the calcium-dependent releasing mechanism.

Denervation produces supersensitivity of a serotonergically innervated structure.

The lateral ciliated gill epithelium of Mytilus edulis was denervated physically and chemically with 5,6-dihydroxytryptamine. Lateral ciliary activity which is under excitatory serotonergic control displayed an increased response to superfusion with serotonin after both treatment, as compared to controls. Endogenous serotonin levels were reduced by these treatments. An increase in maximal cilioexcitatory response was also noted.

Neurophysiological correlates of the dopaminergic cilio-inhibitory mechanism of Mytilus edulis.

The neurophysiological regulation of gill ciliary activity by the CNS of the bivalve mollusc Mytilus edulis was studied by recording electrophysiological activity of the branchial nerve while simultaneously observing ciliary activity of the lateral ciliated cells of the gill by stroboscopic microscopy. The addition of dopamine to the visceral ganglion slowed and stopped ciliary activity by increasing the firing rate of the cilio-inhibitory dopaminergic neurones of the visceral ganglion which innervate the gill. This could be antagonized at the ganglion by pre-applications of ergonovine or methysergide, or by prior treatments of intact animals with the neurotoxin 6-hydroxydopamine. The study confirms earlier work showing the inhibitory functioning of dopaminergic neurones of the CNS and demonstrates the manner in which they may exert their effects.

Correlation between acidic phospholipids and serotonin and between lysolecithin and dopamine in ganglia of the marine mussel, Mytilus edulis.

These studies have demonstrated a positive correlation between the acidic phospholipids and the serotonin content and between the lysolecithin and the dopamine content in the cerebral, pedal and visceral ganglia of Mytilus edulis. These relationships were further supported by experiments utilizing 6-hydroxydopamine and 5,6-dihydroxytryptamine.

The effects of temperature acclimation on monoamine metabolism.

Serotonin and dopamine content in the central nervous system of Mytilus edulis (Bivalvia) was assayed fluorometrically. Acclimating the animals for 2 to 4 days at a constant temperature higher than the environmental temperatures produced substantial increases in endogenous central nervous system serotonin and decreases in dopamine. p-Chlorophenylalanine and alpha-propyldopacetamide not only prevented this increase but reduced serotonin levels below those of unacclimated animals. Cycloheximide decreased the magnitude of the serotonin rise due to acclimation. Endogenous gill serotonin after acclimation also was higher. Gill filaments closest to the visceral ganglia were the first to increase. The study shows that hydroxylation of tryptophan is a temperature-sensitive step and axonal transport of tryptophan hydroxylase to the periphery accounts for terminal serotonin synthesis. A central pool of serotonin distinct from the peripheral pool was demonstrated. The study supports previous evidence of dopamine exerting a regulatory influence on serotonin metabolism in M. edulis.