Experimental serotonin myopathy

Evidence that serotonin affects female sexual functioning via peripheral mechanisms

A review of the literature indicates that serotonin is active in several peripheral mechanisms that are likely to affect female sexual functioning. Serotonin has been found in several regions of the female genital tract in both animals and humans. In the central nervous system (CNS), serotonin acts primarily as a neurotransmitter, but in the periphery, serotonin acts primarily as a vasoconstrictor and vasodilator. Since, in the periphery, the principal component of sexual arousal is vasocongestion of the genital tissue, it is likely that serotonin participates in producing normal sexual arousal. In addition, serotonin administration produces contraction of the smooth muscles of the genito-urinary system and is found in nerves innervating the sexual organs. Taken together, this evidence suggests that peripheral serotonergic activity may be involved in the normal sexual response cycle. In addition, exogenous substances that alter serotonin activity, such as selective serotonin uptake inhibitors (SSRIs) and the atypical antipsychotics, can produce sexual dysfunction. It is possible that sexual side effects seen with these drugs may result, at least in part, from their action on peripheral mechanisms.

Experimental serotonin myopathy as an animal model of muscle degeneration and regeneration in muscular dystrophy

Degenerating and regenerating muscle fibers, in serotonin-induced myopathy (SM) of rats, were investigated histochemically, immunohistochemically and electron microscopically with polyclonal antibodies against dystrophin, type IV collagen and laminin. The myopathy produced was characterized by grouping of degenerating and regenerating muscle fibers, and degeneration of capillary endothelial cells. Dystrophin disappeared in an early stage of muscle degeneration and reappeared in an early stage of regeneration. On the other hand, type IV collagen and laminin were well preserved throughout the degeneration and regeneration processes, even on the shrunk and wrinkled basement membrane of empty muscle fibers after phagocytosis. Muscle fiber regeneration was completed within each tube of the preserved basement membrane through the fusion of myoblasts derived from satellite cells of single necrotic fibers, myotubes already being visible on the 1st or 2nd day of regeneration on light microscopy. These small regenerating myotubes did not fuse with each other at all. The findings in the present experimental SM study are compatible with those in Duchenne muscular dystrophy, especially at the preclinical stage.

Vascular alterations in Fukuyama type congenital muscular dystrophy

Blood vessels in muscle biopsy specimens from 6 Fukuyama type congenital muscular dystrophy (FCMD) patients were examined by electron microscopy and compared with ones in non-diagnostic biopsy specimens from age-matched controls and patients with childhood neuromuscular disorders. The most striking feature was the blister-like swelling of vascular endothelial cells in the biopsied muscle specimens from 5 of the 6 patients with FCMD. Morphometric analysis of capillaries in biopsied muscles showed the extremely greater capillary, endothelial and pericyte areas in the FCMD patients than in controls. These phenomena are quite similar to those found in Duchenne muscular dystrophy (DMD) at the preclinical stage and suggest an as yet undetermined process in blood vessels in FCMD as well as DMD. An immunohistochemical study involving dystrophin antibodies showed positive staining in FCMD.

Polyamine biosynthetic decarboxylases in muscles of rats with different experimental myopathies

The activities of the two polyamine biosynthetic decarboxylases (PBD), L-ornithine decarboxylase (ODC) and S-adenosyl-L-methionine decarboxylase (SAMD), have been measured in quadriceps femoris of rats killed at different times after the induction of calciphylaxis- or serotonin(5-HT)-induced myopathy. Decreases in both PBD levels were observed at early times after both myotoxic treatments. Subsequent progressive increases in both enzyme levels were observed to nearly control values by 4 days after 5-HT administration. In the 5-HT-treated rats, the effects on the myocardial PBD activities were different from those in skeletal muscle, with no effect on ODC but much on SAMD, when rats were killed shortly after 5-HT injection. These results demonstrate that the time-course of the changes in PBD activities in quadriceps femoris mirrors quite well the successive occurrence of degenerative and regenerative processes during the calciphylaxis-induced myopathy and the 5-HT-induced myopathy; it is 5-HT that is mainly responsible for the decreases in PBD levels observed in both experimental myopathies, since dihydrotachysterol alone was without any effect on PBD activity levels and 5-HT alone was effective; myocardial ODC reacts more slowly to 5-HT than quadriceps femoris ODC.

Dipeptidyl peptidases in the soleus muscle of the rat before and after treatment with 5-hydroxytryptamine

A moderate peptidase activity against L-lysyl-L-proline-4-methoxy-beta-napththylamide was detected histochemically in unfixed sections of soleus muscle fibres of inbred male Wistar rats using two variants of the semipermeable membrane technique. One variant involved simultaneous coupling with tetrazotised 3,3'-dimethoxybenzidine, the other post-coupling. The activity at pH 6 increased approximately three-fold in many fibres showing signs of insult in rats that had been given a single low dose of 5-hydroxytryptamine (10 mg/kg body weight) 48-72 h earlier. The hydroxytryptamine treatment was found to induce a selective myopathy. Some of the increased peptidase activity within insulted muscle fibres appeared to arise from invading mononuclear cells, but the majority seemed endogenous to muscle fibres. The peptidase activity persisted in some fibres 21-28 days after 5-hydroxytryptamine administration, by which time the whole muscle appeared histologically normal. The variation of the activity of the peptidase with pH in the presence of various inhibitors was investigated in both control and insulted muscle fibres. From its sensitivity and behaviour towards Zn2+, Hg2+, Cu2+, puromycin, benzethonium chloride and phenylmethylsulphonyl fluoride and its indifference towards Co2+, Cd2+, Mn2+ and o-phenanthroline, it is concluded that the activity can be attributed to a mixture of at least two peptidases, dipeptidyl peptidase II and an unidentified neutral dipeptidyl peptidase. The possible role of the peptidase(s) in muscle regeneration in discussed.

Vascular endothelial cell injury and platelet embolism in Duchenne muscular dystrophy at the preclinical stage

Blood vessels in muscle biopsy specimens from 4 Duchenne muscular dystrophy (DMD) patients (including 3 at the preclinical stage) were examined by electron microscopy and compared with those in non-diagnostic biopsy specimens from age-matched controls and cases of other childhood neuromuscular disorders. The most striking feature was the blister-like swelling of vascular endothelial cells in the biopsied muscle specimens from the 3 preclinical stage DMD patients, which was observed in 23-39% of the small blood vessels examined. Other noticeable features in the preclinical DMD patients were: (1) replication of the basement membrane, there being more than 3 layers in 30% of the capillaries; (2) many degenerating and regenerating capillaries; and (3) platelet adhesion and aggregation in small blood vessels including small arteries and veins. Morphometric analysis showed that the capillary and endothelial cell areas were much greater in the preclinical DMD patients than in the controls or the cases of the other neuromuscular disorders. These phenomena strongly suggest an as yet undetermined process in blood vessels in preclinical DMD.

Distribution of muscle changes in experimental ischemic myopathy

The distribution of ischemic changes was examined in the medial gastrocnemius muscle of the cat, following transient simultaneous clamping of the aorta and femoral artery. Initial changes occurred in the middle portion of the muscle, in the areas corresponding to watershed zones of the primary arteries of the muscle. The superficial layers of the muscle, the regions close to the main stem of the primary arteries, and the entire distal portion of the muscle were the most resistant to ischemic damage. These studies demonstrate that in the feline medial gastrocnemius muscle, the vascular pattern is the primary factor in determining the distribution of ischemic changes. The role of differential muscle fiber vulnerability is only secondary.

Some histochemical observations on invasive cells in a myopathy induced in rats with 5-hydroxytryptamine

The enzyme cytochemistry and proportion of mononuclear cells exclusively present within degenerating muscle fibres of the soleus of rats 24 h after a single intraperitoneal injection of 5-hydroxytryptamine (5-HT) (10 mg/kg) were studied. The following enzymes displayed strong cytochemical activities within these cells: non-specific esterase (against naphthol AS-D acetate and alpha-naphthylacetate), aminopeptidase (against leucine-4-methoxy-2-naphthylamide) and dipeptidyl peptidase II. A peroxidatic activity was also present, but was found to arise from cytochrome oxidase in phagocytosed muscle mitochondria. The aminopeptidase activity in the monocytic cells increased by roughly 50% between 6 and 24 h after 5-HT administration. Dipeptidyl peptidase II was found, by the use of appropriate inhibitors, to be present in both mononuclear cells and muscle fibres and may be implicated in degrading the basal lamina of muscle fibres, thereby permitting access to the mononuclear cells. The morphological, enzyme histochemical and electron microscopical evidence suggest that the cells which invade muscle fibres in the early stages of a myopathy induced by 5-HT in rats are actively phagocytosing, mature macrophages.

Pathogenesis of rheumatoid arthritis: a vascular hypothesis

Past research into the pathogenesis of RA has generally concerned itself with established inflammation. The present review summarizes alterations in microvascular anatomy and function which occur during the hypoxic state, in various experimental and disease conditions. It further shows that tissue hypoxia is a common finding in RA and that the microvascular alterations of RA are similar to those produced by experimental hypoxia. The available data suggest that microcirculatory compromise, concomitant with an increase in metabolic needs of synovial tissue, may initiate tissue injury via anoxia and acidosis, resulting in hydrolytic enzyme release, increased vascular permeability and acceleration of inflammatory processes. It is further believed that the microcirculatory abnormality may be generalized, accounting for the systemic manifestations often seen in RA. Factors effecting arteriolar blood flow obstruction are reviewed to identify areas for future investigation in RA and other disorders involving microvasculopathy. The multitude of longknown and newly recognized factors predisposing to vasospasm and vasodilatation have been outlined as a guide to possible mechanisms which may be operative in RA. An attempt has been made to gather and synthesize the available data in the hope that it may stimulate other investigators to pursue more definitive research into specific areas which may show early microvascular abnormalities in the pathophysiology of RA. Identification of factors operative early in the pathogenesis of RA, before it becomes self-perpetuating, may well be a step in the direction of preventing the ravages of this disease, or providing insight to more effective control.

Experimental ischemic myopathy. Effects of aortic ligation and serotonin

Support for the hypothesis that biogenic amines are involved in the production of muscle diseases comes from a report that rat muscle is damaged by combining distal aortic ligation with serotonin injection. Our studies explore the role of serotonin in the production of the myopathic changes in the aortic ligation-serotonin model. Twenty-six young Sprague-Dawley rats were subjected either to aortic ligation alone, aortic ligation followed by injection of serotonin (40 mg/kg, i.p.), or injection of serotonin alone. Following sacrifice 7--14 days later, 10 micrometer frozen sections of the soleus muscle were stained by trichrome, NADH-TR, and ATPase methods. Focal necrosis and phagocytosis or focal regeneration were seen after aortic ligation with, or without, subsequent serotonin injection. Serotonin alone produced only occasional mild changes in muscle. Therefore, we conclude that the significant damage to muscle in the ligation-serotonin model is provided by the aortic ligation, not the serotonin injection.

Delayed functional disability in dystrophic chickens receiving chemotherapy

Line 413 early-onset, genetically homozygous dystrophic chickens were given twice-daily intraperitoneal injections of the antiserotoninergic drug cinanserin, alone or in combination with methysergide. Other trials consisted of penicillamine treatment in combination with either methysergide or cyproheptadine. Chemotherapy significantly prolonged the righting ability of treated dystrophic chickens, as measured by a periodic standardized flip-test procedure. Plasma creatine kinase activities were not affected by any of the various drug treatments. However, the blood serotonin levels of the dystrophic chickens (grand mean 1.47 microgram serotonin/ml blood) were found to be significantly higher (p less than 0.001) than those in the corresponding normal chickens (0.99 microgram/ml). This finding may partially account for the antiserotoninergic drug enhancement in righting ability that was demonstrated in the drug-treated dystrophic chickens.