Urea-induced myoclonus: medullary glycine antagonism as mechanism of action

Stimulus sensitive myoclonus is a prominent symptom of uremia in both man and animals. Intravenous injection of urea into cats had been previously reported to produce spike and sharp wave electrical discharges in the medullary reticular formation which correlated with the myoclonic movements. In the present investigations, intraperitoneal injections of 2 g/kg urea every 15 minutes for 4 injections produced myoclonus in rats accompanied by brain urea concentrations of 6.8 X 10(-2)M, which is sevenfold higher than normal. 10(-2) and 10(-1) M urea significantly reduced 3H-strychnine binding to rat medulla membranes by 30% and 43% respectively. Urea inhibition of 3H-strychnine binding was reversible and binding kinetics revealed that 10(-1)M urea decreased Bmax by 65% with no effect on the affinity. Brain glycine levels did not change after urea injections and urea had no effect on synaptosomal uptake of 3H-glycine. Urea did not alter 3H-GABA, 3H-glutamate and 3H-QNB receptor binding but decreased 3H-diazepam receptor binding in the medulla. Mannitol also reduced 3H-diazepam binding but had no effect on 3H-strychnine binding. Stereotaxic injection of the glycine receptor antagonist, strychnine, into the rat medullary reticular formation produced myoclonus, whereas Ro 15-1788, a benzodiazepine antagonist, had no effect. Urea may produce myoclonus by blockade of glycine receptors in the medullary reticular formation.

DDT myoclonus: sites and mechanism of action

Intragastric injection of the insecticide DDT produces a stimulus-sensitive myoclonus in mice and rats. Unilateral stereotaxic infusions of DDT into rat medullary reticular formation also induced generalized myoclonus, identical to that produced by systemic administration. Similar myoclonus, but of lesser intensity, occurred when DDT was injected into cerebellar nuclei, red nucleus, and the inferior olive. Multiple other regions of the brain were resistant to the myoclonic action of locally infused DDT. Direct infusions into the medullary reticular formation of allethrin, which has a similar action on neuronal membranes as DDT, or the glycine receptor antagonist, strychnine, also elicited myoclonus.

Cerebellar cyclic GMP in p,p'-DDT myoclonus: effects of antimyoclonic agents

The relationship of DDT myoclonus and antimyoclonic agents to the concentration of cGMP in the cerebellum was investigated. Intragastric administration of 600 mg/kg DDT increased mouse cerebellar cGMP levels about 4 fold. Antimyoclonic agents, such as L-5HTP plus fluoxetine, clonazepam, phenoxybenzamine, prostaglandin E2 and harmaline, all counteracted the elevation of cerebellar cGMP induced by DDT. Cinnanserin, a 5-HT receptor blocker, did not counteract the reduction of cerebellar cGMP produced by L-5HTP plus fluoxetine, clonazepam, and phenoxybenzamine, although cinnanserin abolished the antimyoclonic actions of these agents. Destruction of the inferior olive-climbing fiber pathway by 3-acetylpyridine in rats did not prevent the elevation of cerebellar cGMP levels by DDT. L-5HTP, clonazepam and phenoxybenzamine still significantly counteracted DDT-induced elevation of cerebellar cGMP levels in the inferior olive lesioned rats, although these agents no longer had any antimyoclonic action in these animals. These data indicate that 1) DDT-induced elevation of cerebellar cGMP and DDT-induced myoclonus are not related, and 2) antimyoclonic agents counteract DDT-induced elevation of cerebellar cGMP levels via pathways other than the olivo-cerebellar tract.

Fluoxetine in the treatment of intention myoclonus

Some types of intention myoclonus respond to serotonin precursor therapy (e.g., L-5-hydroxytryptophan, L-5HTP). Fluoxetine, a specific serotonin (5HT) uptake blocker, was found to have no antimyoclonic effect when administered by itself to four patients with intention myoclonus. However, in two patients with intention myoclonus responsive to L-5HTP and carbidopa, fluoxetine reduced the required dose of L-5HTP to approximately one-third, with greater antimyoclonic activity, decreased side effects, and reduction in platelet 5HT and plasma 5-hydroxyindoleacetic acid and L-5HTP concentrations. These findings further support the hypothesis that some forms of intention myoclonus are caused by a deficiency of brain 5HT, and suggest that the addition of fluoxetine to L-5HTP and carbidopa may improve antimyoclonic therapy.

Cleavage of Type II and III collagens with mammalian collagenase: site of cleavage and primary structure at the NH2-terminal portion of the smaller fragment released from both collagens

Collagenase cleavage of human Type II and III collagens has been studied using a highly purified preparation of rabbit tumor collagenase. Progress of the reactions in solution was followed by viscometry and the results indicated that under the conditions employed Type III collagen molecules were cleaved at approximately five times the rate of Type II molecules. Cleavage products of the reactions were isolated in denatured form by agarose molecular sieve chromatography. The molecular weights and amino acid compositions of the products demonstrated that Type II and III molecules had been cleaved at the characteristic three-quarter, one-quarter locus, giving rise to a large fragment derived from the NH2-terminal portion of the molecule and a smaller fragment representing the COOH-terminal region. The amino acid sequence at the NH2-terminal portion of the smaller fragment derived from Type II collagen was determined to be Ile-Ala-Gly-Gln-Arg, and the corresponding region from Type III collagen was found to have the sequence Leu-Ala Gly-Leu-Arg. These sequences for alpha1(II) and alpha1(III) chains adjacent to the site of collagenase cleavage along with previous data for alpha1(I) and alpha2 chains indicate that the minimum specific sequence required for collagenase cleavage is Gly-Ile-Ala or Gly-Leu-Ala. Inspection of the available sequence data for collagen alpha chains indicates that the latter sequences are found in at least three additional locations at which collagenase cleavage does not occur. Each of the sequences which are apparently not substrates for collagenase, however, are followed by a Gly-X-Hyp sequence. We suggest, then, that a minimum of five residues in collagen alpha chains COOH-terminal to the cleavage site comprise the substrate recognition site.

Proteins of the periodontium. Identification of collagens with the [alpha1(I)]2alpha2 and [alpha1(III)]3 structures in bovine periodontal ligament

Insoluble collagen was prepared from bovine periodontal ligament. Isolation and characterization of CNBr peptides originating from the alpha1(I), alpha2, and alpha1(III) chains showed that the tissue contained both type I and type III collagens. Further evidence for the presence of type III collagen was obtained by the isolation of alpha1(III) chains from pepsin-treated ligament collagen, with properties similar to those of human alpha1(III) chains. Estimates based on the amounts of certain CNBr peptides indicated that about one-fifth of the collagen of periodontal ligament is type III, the remainder being type I collagen.

Comparative electron-microscope studies on type-III and type-I collagens

Long-spacing-segment crystallites prepared from type III collagen with the chain composition [alpha1(III)]3 and type I collagen with the chain composition [alpha(I)]i12alpha2 have been compared in the electron microscope after positive. staining with phosphotungstic acid and uranyl acetate. The comparison revealed several differences in intensities of the cross-striation bands as well as significant differences in band positions. The latter occur most prominently in three distinct regions of the crystallites. Further, crystallites prepared from type III collagen contain an additional intensely staining band in an area corresponding to the carboxy-terminal end of the molecule. The latter band is still observed following limited pepsin digestion and presumably represents a slight elongation of the helical portion of the type III molecule when compared to the type I molecule. In spite of the somewhat altered distribution of charged groups as indicated in studies on the long-spacing-segment crystallites, type III molecules are capable of forming fibrils of the native type with a cross-striation pattern and periodicity virtually identical to that observed when type I molecules are precipitated as native fibers.

Collagen polymorphism: characterization of molecules with the chain composition (alpha 1 (3)03 in human tissues

Collagen moleculess with the chain comizposition [alpha1(III)](3), have been isolated from pepsin-solubilized collagen of dermis, aorta, and leiomlyoma of the uterus by differential salt precipitation. On denaturation, approximately 90 percent of this collagen is recovered as a gamma component (300,000 daltons). Reduction and alkylation of the high-molecular-weight component yields alpha1(III) chains (95,000 daltons). In addition to containing cysteine, alpha1(III) chains exhibit several other compositional differences when compared to alpha1(I), alpha1(II), or alpha2 chains from human tissues.