brain plasticity: more on synapses (Introduction)

by David Turell , Saturday, February 06, 2016, 00:49 (3215 days ago) @ David Turell

Spines on dendrites can come and go based on need for contact:-http://medicalxpress.com/news/2016-02-day-life-synapse-reveals-facets.html-"A neuron is bombarded with signals from hundreds of presynaptic partners. Synapses act as conduits for these incoming signals. Excitatory neurotransmitters flow from the presynaptic to the postsynaptic neuron at synaptic locations that are on bulbous protrusions with a rounded head and thin neck, termed spines. The long branching dendrites of a single neuron can display hundreds of spines like leaves on a tree branch. -"When spines appear and disappear, a neuron can gain new connections or lose existing ones. "If spines disappear, they rarely come back to the same location; new spines seek out alternative locations," says biology graduate student Katherine Villa, co-first author on the study. "It's as if after deciding that a connection is not worth keeping neurons will try to replace it with a different contact."-***-"Directly visualizing inhibitory synapses revealed the surprising fact that while many reside on the shaft of dendritic branches, approximately 30 percent reside on dendritic spines alongside excitatory synapses. Another surprise was that when inhibitory synapses are removed, they return again and again to the same location. "Clearly, the goal here is not to change partners as we see for excitatory connections," says biology graduate student Kalen Berry, Villa's co-first author. "We think that inhibitory synapses can act as a kind of gatekeeper, flickering on and off to shut down excitatory connections as needed."-"Interestingly, the dual-purpose spines are large and extremely stable, as are the excitatory connections onto them. "This is essentially a hard-wired part of the circuit," Nedivi says. "But we still have the potential to modify it via the nearby inhibitory synapse."-"These findings raise questions about why some excitatory connections on singly innervated spines can be restructured while those on dually innervated spines cannot. How does the structural plasticity of inhibitory synapses alter excitatory circuit properties, and what enables their rapid insertion and removal at stable sites? The answers to these questions could shed light on ways to enhance plasticity in the adult brain and synapse-related disorders."-Comment: It shows how the brain has many ways to modify contacts in networks.