ELECTROPHYSIOLOGY OF THE NEUROMUSCULAR-JUNCTION OF THE LAMININ-2 (MEROSIN) DEFICIENT C57 BL 6J DY(2J)/DY(2J) DYSTROPHIC MOUSE/

The C57 BL/6J dy(2J)/dy(2J) dystrophic mouse expresses an abnormal tru ncated form of the alpha 2 subunit of the protein laminin-2 (or merosi n), which is unable to form a stable link between the extracellular ma trix and the dystrophin-associated proteins, resulting in muscular dys trophy. Morphological abnormalities of the peripheral nervous system a nd neuromuscular junction have also been reported. The electrophysiolo gical properties of the neuromuscular junctions of diaphragm, extensor digitorum longus (EDL), and soleus from C57 BL/6J ny(2J)/dy(2J) mice and controls are described. No evidence for the presence of denervated fibres were found. Mean MEPP amplitudes were significantly increased in EDL and soleus but reduced in the diaphragm from affected mice. Mea n MEPP frequencies were raised in all the dy(2J)/dy(2J) muscles studie d. dy(2J)/dy(2J) muscles were paralysed by low concentrations of mu-co notoxin suggesting that embryonic (tetrodotoxin and mu-conotoxin resis tant) sodium channels are not widespread on dy(2J)/dy(2J) muscle as ha s previously been reported. EPP latencies were significantly prolonged in the diaphragm and EDL but not soleus from dy(2J)/dy(2J) mice. Quan tal contents were higher in all dy(2J)/dy(2J) muscles. In the dy(2J)/d y(2J) diaphragm failures in neurotransmission occurred and a faster ra te of rundown of EPPs was apparent. Some changes appear from a direct effect of dystrophy, whilst increased MEPP frequency and quantal conte nt, and failures in neurotransmission indicate neuronal abnormalities. (C) 1998 Elsevier Science B.V.