Cortical Interneurons

Question 1

How many neurons are generated during proliferation peak?

Answer 1

around 250.000 per minute

Question 2

Neural stem cells divide symmetrically and asymmetrically. What’s the difference?

Answer 2

symmetrically (early stage): two new stem cells

asymmetrically (later stage): one stem cell and one “post-mitotic” neuroblast (immature nerve cell)

Question 3

for excitatory neurons (i.e., mainly pyramidal cells), cell divisions happens close to …………, from where neuroblasts migrate to surface

Answer 3

the ventricles (“ventricular zone”, VZ)

Question 4

What’s the ratio (in percent) between excitatory vs inhibitory neurons?

Answer 4

excitatory neurons (approx. 70-80 % of all cortical neurons)

inhibitory neurons (approx. 20-30 % of all cortical neurons)

Question 5

Name four differences between excitatory (=Projection Neurons; PN) and inhibitory neurons (=InterNeurons; IN)

Answer 5

PN:
1. long axons
2. target other cortical areas or non-cortical structures (basal ganglia, thalamus, spinal cord, etc.),
3. mediating communication between brain areas
4. main neurotransmitter: glutamate

IN:
1. short axons;
2. target local cells,
3. regulating activity of nearby PNs and INs (->local computation)
4. main neurotransmitter: γ-amino butyric acid (GABA)

Question 6

What are the three major types of interneurons (in rodents)?

And what’s the ratio between them (in percent)?

Answer 6

parvalbumin (PV) ≈ 40%

somatostatin (SST) ≈ 30%

5HTR3a serotonin receptors ≈ 30%

Question 7

What are subtypes of parvalbumin-positive interneurons?

Answer 7

1. basket cells
2. chandelier cells
3. translaminar cells

Question 8

What are subtypes of somatostatin-positive interneurons?

Answer 8

Martinotti and Non-martinotti cells

Question 9

Interneuron types differ in how they are produced in neurogenesis and migration during early development.

Temporal dynamics of 5HTR3a neurons less understood.

How do parvalbumin+ and somatostatin+ cells differ with respect to their genesis?

Answer 9

parvalbumin+ cells are produced more extendedly and continuously

somatostatin+ cells show peak proliferation during early embryonic phase

Question 10

After migrating to their final destination, some interneurons become functional and survive, others don’t. What is a simple reason for that?

Answer 10

SIMPLE ANSWER:
INs become functional and survive based on STIMULATION received from other neurons

NOT SO SIMPLE:
After arrival at final destination, INs begin to synapse onto neighboring neurons (PNs and INs) and initiate neuronal activity, prompted by thalamic input

30-40 % of INs undergo programmed cell death after settling (cf. 12 % of PNs), which is prevented in some IN subtypes by strong input from PNs

Question 11

Within cortex, how do interneurons first migrate to destined area, before allocating radially to correct layer?

Answer 11

tangentially (parallel to surface)

Question 12

In spawning cells, what’s the main difference between
- LATERAL ganglionic eminence (LGE) and
- MEDIAL/ CAUDAL ganglionic eminence (MGE/ CGE)?

Answer 12

lateral ganglionic eminence (LGE) spawns cells of olfactory bulb and striatum

medial and caudal ganglionic eminences (MGE and CGE) spawn different types of cortical interneurons

Question 13

In early brain development, what’s the difference between pallium and subpallium?

Answer 13

PALLIUM:
future cortex (allocortex and isocortex), amygdala, and claustrum
neurogenesis of glutamatergic projection neurons
radial migration towards from VZ to surface

SUBPALLIUM:
future striatum, pallidum, and other nuclei
neurogenesis of inhibitory cortical neurons