Lecture 30: Neurotransmissions

Question 1

Parts of a neuron

Answer 1

1) Nucleus
2) Cell Body
3) Dendrites
4) Axon

Question 2

What are astrocytes?

What are their functions?

Answer 2

Star shaped Glial cells

• Astrocytes play important roles in physiological brain function beyond support

1. release and take up neurotransmitters (e.g. glutamate);
2. express receptors (e.g. NMDA);
3. regulate synaptic transmission;
4. conduc_t electrical events_ via gap junctions;
5. memory formation?;
6. produce and release neurotrophins (impt. during development and injury);
7. may generate new neurons? (in PNS?)

• Play important roles in brain pathology, e.g. form scars (impede axonal regrowth), immune activation, etc.

Question 3

Are astrocytes homogenous?

Answer 3

No

There are different types of astrocytes and even neuroanatomical differences.

There are at least 4 different types of astrocytes in the human cortex:

1. Protoplasmic astrocytes (Their function is support and regulate information processing at the synaptic level).
2. Interlaminar astrocytes
3. _Fibrous astrocytes (_Supprot role for neurons (rather than information processing) and also respond to brain injury)
4. Polarized astrocytes

Question 4

Describe 2 main types of astrocytes (+ name the other 2)

Answer 4

1) Protoplasmic astrocytes

• Most common type
• Reside in layers 2-6 of the neocortex
• Their GFAP-positive (marker) processes do not overlap (i.e. a domain organization) (separate from each other)
• The domain of one astrocyte might cover 10 nerve cell bodies, many synapses and 5 blood vessels. This puts these astrocytes in an important coordination position, e.g. to regulate blood flow in response to increased synaptic transmission. (Their function is support and regulate information processing at the synaptic level).
• Estimates are that the processes of 1 human astrocyte in the cortex, which can span 100-200µm, serves approx. 2 million synapses

2) Fibrous astrocytes

• Found in the white & gray matter
• Their processes intermingle (i.e. they do not form a domain structure).
• Probably they serve a support role for neurons (rather than information processing) and also r_espond to brain injury_ (form glial scar tissue).

3) Interlaminar astrocytes
4) Polarized astrocytes

Question 5

Describe Gliotransmission & Glioneuronal Functional Units

Answer 5

Gliotransmission & Glioneuronal Functional Units are the process of release of transmitters from astrocytes and a_cting on neurons._

Greatly enlarged the role of astrocytes in normal brain function.

• One hypothesis recently proposed suggests that memories may be encoded in astrocyte networks?
• Recent data shows that astrocytic adenosine release induces sleep via caffeine-sensitive receptors.
• Some hypothesize that the complexity of human protoplasmic astrocytes might provide a basis for the complexity of human brain function, distinct from other animals.

Question 6

Recent data shows that astrocytic _______ release induces _______ via_____________.

Answer 6

Recent data shows that astrocytic adenosine release induces sleep via caffeine-sensitive receptors.

Question 7

Describe the role of Microglia

Answer 7

Surveyors of the brains micro-environment, very sensitive to brain perturbations.

Resident macrophages of the brain.

• Mediate the brain immune response
• Phagocytize debris, f_oreign bodies_, toxict proteins, plaques in AD?
• Help s_culpt the brain_ during development
• May modulate neurotransmission and may modulate synaptic transmission

Question 8

_____ encase endothelial cells in brain capillaries and maintain the Blood-Brain Barrier

Answer 8

Pericytes

Question 9

Describe Pericytes

Answer 9

• Pericytes encase endothelial cells in brain capillaries and maintain the BBB
• It is thought that in many neurological disorders such as Alzheimer’s and stroke, the neurovascular unit and BBB is compromised, so many studies now directed at looking at the interaction of these cells.

Question 10

Termination of transmitter action is achieved by either _________and/or___________-

Answer 10

Termination of transmitter action is achieved by either metabolism and/or reuptake into neurons and/or glial cells (astrocytes) by specific transporter proteins.

Question 11

Defie Chemical neuroanatomy

Answer 11

The study of the _anatomical localization of neurotransmitter systems i_s known as chemical neuroanatomy.

Because the brain is a very complex organ composed of different anatomical regions that serve different functions, the action of a drug will not only depend upon which neurotransmitter(s) system it modulates or mimics, but also on the anatomical localization of the neurotransmitter system.

Question 12

What are 4 types of neurotransmitters

Answer 12

• Monoamines: serotonin, noradrenaline and dopamine.
• Amino acids derivatives: GABA, glutamate, glycine.
• Acetylcholine
• Neuropeptides: neuromodulators and cotransmitters.

Question 13

Name 3 monoamines

Answer 13

Monoamines: serotonin, noradrenaline and dopamine.

Question 14

Name 3 Amino-acid derivatives

Answer 14

Amino acids derivatives: GABA, glutamate, glycine.

Question 15

What are neuromodulators

Answer 15

A neuromodulator is a messenger released from a neuron in the central nervous system, or in the periphery, that affects groups of neurons, or effector cells that have the appropriate receptors.

It may not be released at synaptic sites, it often acts through second messengers and can produce long-lasting effects

A substance that, while not affecting the rate of firing or conduction of nerve impulses, can change the effect on a nerve of other neurotransmitters. Neuromodulators can control neurotransmitter synthesis or the amounts of neurotransmitter released in response to other stimuli. Adenosine is an example of a neuromodulator.

Question 16

What are neurotropic factors?

Answer 16

Neurotrophic factors are released by n_on-neuronal cells (astrocytes, microglia)_ and neurons and work over long time-scales.

Act on t_yrosine-kinase type receptors_ to mediate growth, morphology, functional properties, survival promoting effects in the nervous system (e.g. nerve growth factor, BDNF, IGF-1).

Question 17

Neuromodulators are releasd by __________

Neurotropic factors are released by _______

Answer 17

​

Neuromodulators produce slower pre and post-synaptic responses, released by nerve cells and astrocytes

Neurotrophic factors are released by non-neuronal cells (astrocytes, microglia)

Question 18

Neurotransmitters can have both fast and slow actions depending on __________

For example ___________

Answer 18

Neurotransmitters can have both fast and slow actions depending upon the receptor sub-type that they act on.

• Fast acting work via i_on channels_ (e.g. glycine, GABA, glutamate).
• Slow acting via G-protein coupled receptors (e.g. dopamine, neuropeptides, GABA, acetylcholine).

Question 19

• Pre-synaptic receptors __________*
• Astrocytes involve in ____________*
• Microglia modulate ___________*
• Pericytes __________*

Answer 19

• Pre-synaptic receptors modulate neurotransmitter release.*
• Astrocytes involve in neurotransmitter uptake and release as well as modulate neurotransmission at the synaptic level.*
• Microglia* act as the first and main form of active immune defence in the central nervous system
• Pericytes encases endothelial cells to form BBB.*