Pic of the day: Cortex

99 cortex - Copy.jpg

Reference: von Bonin, G. (1950). Essay on the cerebral cortex. Ed. Charles C. Thomas, Springfield. ISBN 10: 0398044252, ISBN 13: 9780398044251

Image credit: geralt.The whole image: Public Domain

By Neuronicus, 15 September 2016

The F in memory

"Figure 2. Ephs and ephrins mediate molecular events that may be involved in memory formation. Evidence shows that memory formation involves alterations of presynaptic neurotransmitter release, activation of glutamate receptors, and neuronal morphogenesis. Eph receptors regulate synaptic transmission by regulating synaptic release, glutamate reuptake from the synapse (via astrocytes), and glutamate receptor conductance and trafficking. Ephs and ephrins also regulate neuronal morphogenesis of axons and dendritic spines through controlling the actin cytoskeleton structure and dynamics" (Dines & Lamprecht, 2015, p. 3).
“Figure 2. Ephs and ephrins mediate molecular events that may be involved in memory formation. Evidence shows that memory formation involves alterations of presynaptic neurotransmitter release, activation of glutamate receptors, and neuronal morphogenesis. Eph receptors regulate synaptic transmission by regulating synaptic release, glutamate reuptake from the synapse (via astrocytes), and glutamate receptor conductance and trafficking. Ephs and ephrins also regulate neuronal morphogenesis of axons and dendritic spines through controlling the actin cytoskeleton structure and dynamics” (Dines & Lamprecht, 2015, p. 3).

When thinking about long-term memory formation, most people immediately picture glutamate synapses. Dines & Lamprecht (2015) review the role of a family of little known players, but with big roles in learning and long-term memory consolidation: the ephs and the ephrines.

Ephs (the name comes from erythropoietin-producing human hepatocellular, the cancer line from which the first member was isolated) are transmembranal tyrosine kinase receptors. Ephrines (Eph receptor interacting protein) bind to them. Ephrines are also membrane-bound proteins, which means that in order for the aforementioned binding to happen, cells must touch each other, or at least be in a very very cozy vicinity. They are expressed in many regions of the brain like hippocampus, amygdala, or cortex.

The authors show that “interruption of Ephs/ephrins mediated functions is sufficient for disruption of memory formation” (p. 7) by reviewing a great deal of genetic, pharmacologic, and electrophysiological studies employing a variety of behavioral tasks, from spatial memory to fear conditioning. The final sections of the review focus on the involvement of ephs/ephrins in Alzheimer’s and anxiety disorders, suggesting that drugs that reverse the impairment on eph/ephrin signaling in these brain diseases may lead to an eventual cure.

Reference: Dines M & Lamprecht R (8 Oct 2015, Epub 13 Sept 2015). The Role of Ephs and Ephrins in Memory Formation. International Journal of Neuropsychopharmacology, 1-14. doi:10.1093/ijnp/pyv106. Article | FREE FULLTEXT PDF

By Neuronicus, 26 October 2015

I’m not like you, inside and out

Credit: Dawn of the Planet of the Apes
Screenshot from “Dawn of the Planet of the Apes” (Director: Tim Burton, 2001)

One mistake than many neuroscientists make (myself included) is the implicit assumption that the human brain is a rodent brain scaled-up, plus a few more bits. Here is a remainder that “a rat is not a monkey is not a human”, in the famous words of A. D. (Bud) Craig (2009).

Mohan et al. (2015) analyzed a portion of the brain (Brodmann area 21) obtained from 28 individuals that had to undergo neurosurgery and have it removed for various illnesses. Using some good microscopy, fancy statistics, and 3-D modeling, they reconstructed the shape of individual neurons from that region. The main finding is that 88% of human pyramidal neurons were distinctly different than their mouse or macaque counterparts. Also, they managed to record the electrical activity of these neurons in less than 10 minutes after resection. So it appears that this morphological distinctness of ours results in unique electrical properties of human neurons, which may account for the “distinct cognitive capabilities of humans”, as the authors put it.

Approximate location of Brodmann Area 21, corresponding to gyrus temporalis medium. Credit: Brain template to _DJ_; Area tracing to Neuronicus
Approximate location of Brodmann Area 21, corresponding to gyrus temporalis medium. Credit: Brain template to _DJ_; Area tracing to Neuronicus

Citation: Mohan, H., Verhoog, M. B., Doreswamy, K. K., Eyal, G., Aardse, R., Lodder, B. N., Goriounova, N. A., Asamoah, B., B. Brakspear, A. B. C., Groot, C., van der Sluis, S., Testa-Silva, G., Obermayer, J., Boudewijns, Z. S., Narayanan, R. T., Baayen, J. C., Segev, I., Mansvelder, H. D., de Kock, C. P. (28 August 2015; Epub ahead of print). Dendritic and Axonal Architecture of Individual Pyramidal Neurons across Layers of Adult Human Neocortex. Cerebral Cortex, 1-15. doi: 10.1093/cercor/bhv188. Article + FREE PDF