Tag Archives: enlargement of dendritic spines

Parts of your brain that move

Sick of COVID19 and omicron are you?  So am I.  It’s time for some hard core neuroscience.  Looking at slides or electron micrographs gives a very static picture of the brain.  There are parts of the brain that move.

Microglia are the macrophages of the brain.  They’re actually rather creepy, extending and retracting processes and feeling up neurons, removing synapses from processes.  They use receptors for ATP and ADP to detect when a neuron is in trouble.  A new cellular specialization is described — Somatic Purinergic Junctions — a combination of mitochondria, reticular membrane structures, vesicle-like membrane structures and clusters of a particular voltage gated potassium channel (Kv2.1).  You can actually watch this happening.   [ Science vol. 367 pp. 510 – 511, 528 – 537 ’20 ].

For about the past 20 years we’ve been able to observe dendritic spines for months in the living (rodent) brain.  In 1970, if you told me that, I’d have said you were smoking something.  The surprising finding is that dendritic spines are a work in progress, being newly formed and removed all the time.  The early literature (e.g. 10 years ago) is contentious about how long a given spine lasts, but most agree that spine plasticity is present every time it’s looked for.  Here are a few references [ Neuron vol. 69 pp. 1039 – 1041 ’11, ibid vol. 49 pp. 780 – 783, 877 – 887 ’06 ].

It is yet another reason why a wiring diagram of the brain wouldn’t help you understand it.   For much more on this please see — https://luysii.wordpress.com/2021/04/25/the-wiring-diagram-of-the-brain-takes-another-hit/

Now on to Long Term Potentiation — https://en.wikipedia.org/wiki/Long-term_potentiation.  This is basically a persistent strengthening of synapses based on recent patterns of activity. These are patterns of synaptic activity that produce a long-lasting increase in signal transmission between two neurons.One of the things that happens with long term potentiation is that the potentiated dendritic spines enlarge.  Now we know that there are all sorts of proteins crossing the synaptic cleft between presynaptic axon terminal and post-synaptic dendritic spine.  They hold the two together.

So the authors of Nature vol. 600 pp. 696 – 689 ’21 wondered if the enlargement of the spine changed neurotransmission.  They studied CA3 neurons in slice culture preparations of the rat hippocampus.  Synapses formed between axons and dendrites. The mimicked LTP (and produced dendritic spine enlargement) by two photon uncaging of glutamic acid.  Spine enlargement ensured which then pushed on the presynaptic bouton.  This caused increased release of glutamic acid by the presynaptic neuron.

This may actually be the mechanism behind long term potentiation.