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George E. Carvell, PhD, PT   University of Pittsburgh
M. Segal, E. Korkotian, and D.D. Murphy, Dendritic Spine Formation and Pruning: Common Cellular Mechanisms? Trends Neurosci 23: 53-57, 2000
Fig 2 p 55
This figure shows a dramatic effect of altering levels of Glutamate (Glu) on spine length in a cultured hippocampal neuron. Note changes in dendritic spine morphology when the neuropil is exposed to small (2 & 3) or larger (5 & 6) amounts of Glu.These changes are due to altered levels of intracellular Ca2+ (NMDA Receptors). Removing Ca2+ from the culture media nulls these effects. Changes may occur within a matter of minutes - not days, weeks or years.
      One might speculate that what you do as a therapist could potentially alter synaptic morphology within a single session of therapy (for better or worse, see fig 2)! The key of course is gaining access to the appropriate synapses and then providing the just right’ amount of altered activity- no small task for one attempting to adjust a microscopic system that is invisible to your therapeutic eye.
2 & 3 = short pulses of glutamate
5 & 6 = long pulses of glutamate
RAPID BRAIN MOTILITY I: Glu, Ca2+, & Spine Growth
Glutamate in “Goldilocks and The Three Bears”