tetrodotoxin and Muscular-Dystrophy--Duchenne

Duchenne muscular dystrophy (DMD), a genetic disease due to dystrophin gene mutation and characterised by skeletal muscle failure, is associated with non-progressive cognitive deficits. In human and mouse brain, full-length dystrophin is localised postsynaptically in neocortical, hippocampal and cerebellar neurons. Evidence obtained in the CNS of dystrophic mice (mdx) suggested alterations of the GABAergic system. However, a direct functional evaluation of GABAergic synaptic transmission in mdx mice has not been conducted in the hippocampus, which is involved in cognitive processes and is rich in full-length dystrophin. Here, we investigated evoked and miniature inhibitory postsynaptic currents (IPSCs) in CA1 pyramidal neurons of mdx mice with patch clamp recording techniques. Results showed an increased frequency of miniature spontaneous IPSCs in mdx mice compared with controls, whereas evoked IPSCs did not show significant variations. Paired-pulse facilitation (PPF) analysis showed lack of facilitation at short intervals in mdx mice compared with that in wild-type mice. Analysis of density of synapses that innervate CA1 pyramidal cell bodies did not indicate significant differences between mdx mice and controls. Therefore, we suggest that increased miniature spontaneous IPSC frequency is due to altered pre-synaptic release probability. The present findings are discussed in the light of the accrued evidence for alterations of inhibitory synaptic transmission in the brain of dystrophic mice.

Topics: Animals; gamma-Aminobutyric Acid; Hippocampus; Inhibitory Postsynaptic Potentials; Membrane Potentials; Mice; Mice, Inbred C57BL; Mice, Inbred mdx; Microscopy, Electron; Muscular Dystrophy, Animal; Muscular Dystrophy, Duchenne; Patch-Clamp Techniques; Pyramidal Cells; Sodium Channel Blockers; Tetrodotoxin

To explore the origin of diarrhea or constipation in human Duchenne muscular dystrophy (DMD), the effect of the inhibition of e- , i-, and n-nitric oxide synthase (NOS) on the motility of proximal and distal segments of colon of muscular dystrophy (mdx) and control mice was studied. The frequency of migrating motor complexes (MMC) was higher in the proximal than in the distal segments in mdx colon (0.56 vs. 0.25 cpm) and in the control colon (0.7 vs. 0.25 cpm), and there was no difference when mdx was compared to control segments. High concentrations of NOS inhibitors, including 1,3-PBIT dihydrobromide (1,3-PBIT) and spermine, inhibited MMC. The dose of spermine required to inhibit MMC was lower for the proximal mdx colon than for the distal mdx or control colon. In the presence of tetrodotoxin, spermine (1 mM) and 1,3-PBIT (5 mM) reduced the magnitude of local, rhythmic contractions (LC) paced by the interstitial cells of Cajal (ICC), but 1,3-PBIT (50 microM) increased their magnitude. There was no difference in the effect of spermine and 1,3-PBIT on the LC between mdx and control colon. The results suggest an inhibition of MMC by high concentrations of e-, i-, and n-NOS inhibitors, modulation of ICC activity by e-NOS, and greater susceptibility of MMC to n-NOS inhibition in the mdx proximal than in the control colon, which is very likely because of a deficit in n-NOS in the mdx smooth muscle affecting the MMC pacemaker. A deficit in the effect of mdx smooth muscle n-NOS on an MMC pacemaker may be the origin of diarrhea or constipation in human DMD.

Topics: Animals; Colon; Enzyme Inhibitors; Gastrointestinal Motility; Hexamethonium; Male; Mice; Mice, Inbred mdx; Muscular Dystrophy, Duchenne; Myoelectric Complex, Migrating; Nerve Tissue Proteins; NG-Nitroarginine Methyl Ester; Nitric Oxide Synthase; Nitric Oxide Synthase Type I; Nitric Oxide Synthase Type II; Nitric Oxide Synthase Type III; Nitroso Compounds; Spermine; Tetrodotoxin; Thiourea

This study examined whether alterations of the spontaneous and evoked mechanical activity are present in the stomach of the mdx mouse, the animal model for Duchenne muscular dystrophy. The gastric mechanical activity from whole-organ of normal and mdx mice was recorded in vitro as changes of intraluminal pressure. All gastric preparations developed spontaneous tone and phasic contractions, although the tone of the mdx preparations was significantly greater. Atropine reduced the tone of the two preparations by the same degree. Nomega-nitro-l-arginine methyl ester (l-NAME) significantly increased the tone and spontaneous contractions only in the stomach from normal animals, but did not affect on the mdx preparations. Effects ofl-NAME on tone and contractility were preserved in the presence of tetrodotoxin. In both types of tissues electrical field stimulation (EFS) induced a biphasic response: cholinergic contraction followed by slow relaxation. In nonadrenergic noncholinergic conditions, EFS induced a rapid relaxation followed by a slow component in both types of tissues. l-NAME abolished the rapid component, reduced the slow component and unmasked tachychinergic contractions. No significant difference was found in evoked responses. The enteric neurotransmission is preserved in mdx gastric preparations, although alterations in the ongoing production of nitric oxide are present.

Topics: Anesthetics, Local; Animals; Carbachol; Cholinergic Agonists; Electric Stimulation; Enzyme Inhibitors; Male; Mice; Mice, Inbred mdx; Muscle Contraction; Muscle, Smooth; Muscular Dystrophy, Animal; Muscular Dystrophy, Duchenne; NG-Nitroarginine Methyl Ester; Nitric Oxide; Nitric Oxide Donors; Nitroprusside; Organ Culture Techniques; Stomach; Tetrodotoxin