Cholinergic transmission in the central nervous system of the dystrophic mouse (MDX): studies on the ligand properties and presynaptic modulatory effects of the neuronal nicotinic receptors

Abstract

Duchenne Muscle Dystrophy (DMD) is a progressive X-linked muscle disease caused by mutation of the dystrophin gene and lack of the protein expression. Dystrophin is a subsarcolemal protein of the striated muscle fibers involved in the mechanical stability of the muscle fibers. The lack of protein expression causes microruptures in the sarcolema during contractile activity leading to muscle degeneration and necrosis. Dystrophin is also expressed in neuronal cells and its absence has been related to structural and neurotransmission changes associated with cognitive and memory dysfunctions in both DMD and MDX mice. Previous studies by the group revealed the presence of the embryonic type nicotinic acetylcholine receptors (nAChR) in the diaphragm muscles of the MDX mouse, which are normally expressed during muscle development and in denervated muscles (Souccar et al., 2002). Taking in account the involvement of central cholinergic nicotinic pathways in cognition and memory, we hypothesized a possible relationship of similar changes in neuronal nAChR and the reported dementia symptoms and memory alteration in both DMD and MDX mouse. To test this hypothesis this work aims to assess the concentration and ligand properties of neuronal nAChR of the main subtypes, alfa 7 and alfa 4beta 2 in the brain of MDX mice and to evaluate their modulatory presynaptic actions. Brain regions that contain dystrophin (cortex, hippocampus, cerebellum) from 4 month-old (young adult) and 12 month-old (adult) control and MDX mice will be used in all studies to investigate : 1) the ligand properties of alfa7 and alfa4beta2 nAChR of the cortex, hyppocampus and cerebellum membrane preparations from control and MDX at both ages,using radioligand binding techniques; 2) presynaptic nicotinic modulation of the neurotransmiter release by measurements of [3H]ACh , [3H]Dopamine and [14C]GABA effluxes in synaptossomes preparations of all three brain, regions in control and MDX mice; 3) the pharmacological properties of the nAChR subtypes involved in presynaptic modulation of the neurotransmitter release in all three brain regions from both control and MDX groups; 4) total acetylcholinesterase activity of all three brain regions from both control and MDX groups; 5) the presence of transcripts coding for both muscular and neuronal nAChR using polymerase chain reaction (PCR) on RNA extracted from diaphragm muscle, cortex, hippocampus and cerebellum from control and MDX mice; 6) the cognitive function of both control and MDX mice in parallel to the evaluation of their motor performance using validated behavioral models. (AU)