The goal of this proposal is to determine the mechanisms underlying age-related changes in synaptic physiology at the neuromuscular junction. Acetylcholine (ACh) levels decrease with age. This manifests a change in the balance between synthesis and degradation. Thus, using sensitive gas chromatography/mass spectrometry, the rates of ACh synthesis and degradation will be measured to determine the nature of this age-related change. Intracellular Ca2+ levels may also be altered during aging. This will be tested using electrophysiological techniques. The kinetics of Ca2+ entry and clearance will be estimated from frequency histograms of synaptic delays. The relative amounts of Ca2+ entry will be measured using focal extracellular electrodes following pharmacological blocking of nerve-terminal K+ currents. The rate of clearance of intracellular Ca2+ will be estimated by measuring the time course for the decay of synaptic facilitation. Moreover, the sensitivity of the release mechanism to Ca2+ will be estimated from data relating quantal release to extracellular Ca2+ concentrations. Proteins weighing 125, 145, and 210 kDa are present in nerve terminals of 10-month but not 28-month rats. The 145 and 210 kDA molecules are quite probably neurofilament proteins. Using gel electrophoresis and immunoblot techniques, this identity will be tested. Similar techniques will be used to ascertain whether the failure to detect these proteins in aged rats is due to impaired axonal transport from the cell body or enhanced Ca2+-dependent degradation. In the postsynaptic membrane, there is an age-related increase in low-affinity, slow channel open time ACh receptors. Patch-clamp methods will be used to determine whether there are corresponding changes in mean channel conductance. Since these changes in receptor properties are similar to those following functional denervation, focal recording techniques will be used to test whether all nerve terminals are functional in the end plates of aged animals. These studies should elucidate the underlying causes of reduced ACh levels, altered synaptic efficacy, and changing end-plate structure during aging.

Agency
National Institute of Health (NIH)
Institute
National Institute on Aging (NIA)
Type
Research Project (R01)
Project #
2R01AG001572-07
Application #
3114227
Study Section
Neurological Sciences Subcommittee 1 (NLS)
Project Start
1979-07-01
Project End
1988-08-31
Budget Start
1985-09-01
Budget End
1986-08-31
Support Year
7
Fiscal Year
1985
Total Cost
Indirect Cost
Name
University of Wisconsin Madison
Department
Type
Schools of Medicine
DUNS #
161202122
City
Madison
State
WI
Country
United States
Zip Code
53715
Rosenheimer, J L (1990) Ultraterminal sprouting in innervated and partially denervated adult and aged rat muscle. Neuroscience 38:763-70
Smith, D O; Williams, K D; Emmerling, M (1990) Changes in acetylcholine receptor distribution and binding properties at the neuromuscular junction during aging. Int J Dev Neurosci 8:629-42
Rosenheimer, J L; Smith, D O (1990) Age-related increase in soluble and cell surface-associated neurite-outgrowth factors from rat muscle. Brain Res 509:309-20
Rosenheimer, J L (1990) Factors affecting denervation-like changes at the neuromuscular junction during aging. Int J Dev Neurosci 8:643-54
Williams, K D; Smith, D O (1989) Cholesterol conservation in skeletal muscle associated with age- and denervation-related atrophy. Brain Res 493:14-22
Smith, D O (1989) Evidence for increased calcium buffering in motor-nerve terminals of aged rats. Ann N Y Acad Sci 568:106-14
Smith, D O (1988) Muscle-specific decrease in presynaptic calcium dependence and clearance during neuromuscular transmission in aged rats. J Neurophysiol 59:1069-82
Smith, D O; Emmerling, M (1988) Biochemical and physiological consequences of an age-related increase in acetylcholinesterase activity at the rat neuromuscular junction. J Neurosci 8:3011-7
Smith, D O; Weiler, M H (1987) Acetylcholine metabolism and choline availability at the neuromuscular junction of mature adult and aged rats. J Physiol 383:693-709
Smith, D O; Chapman, M R (1987) Acetylcholine receptor binding properties at the rat neuromuscular junction during aging. J Neurochem 48:1834-41

Showing the most recent 10 out of 15 publications