Tutorial 01 – Part 2

Question 1

What does „sugar“ commonly refer to?

Answer 1

Sucrose, a disaccharide consisting of one glucose and one fructose molecule

Question 2

Where is the intramolecular bond cleaved in?

Answer 2

The gut

Question 3

Via which pathways are glucose and fructose absorbed?

Answer 3

Via different metabolic pathways

Question 4

Sugar vs fructose (caloric value and physiological responses)

Answer 4

Sugar generally signals high caloric value and the physiological responses are generally much stronger to glucose than to fructose

Question 5

What is the only nutrient neurons/the brain can use for energy production?

Answer 5

Glucose

Question 6

How is sugar conditioning possible?

Answer 6

Even without tasting the sweetness (e.g. in direct intestinal infusion via gastric tube)

Question 7

Where are the cells necessary and sufficient for sugar conditioning found?

Answer 7

In the proximal small intestine (duodenum, jejunum)

Question 8

What is a cell type with neuron-like behavior in the mucosal lining of gut called?

Answer 8

Neuropod cells

Question 9

Where can neuropod cells be found?

Answer 9

In the mucolsal lining of gut

Question 10

What happens when neuropod cells bind to sodium-glucose co-transporter channels

Answer 10

Influx of sodium

Question 11

What happens after the influx of sodium (neuropod cells)?

Answer 11

Taste-receptor like receptors start second-messenger cascade with release of Ca2+ from intracellular storages, which opens a second set of Na+ channels

Question 12

What happens after the second set of Na+ channels are opened (neuropod)?

Answer 12

KATP-channels close on intracellular binding of ATP increase (after intracellular glucose metabolization)

Question 13

What do the three processes (influx of sodium, Na+ channels are open, KATP channels close on intracellular binding of ATP-increase) cause in neuropod cells?

Answer 13

Depolarization

Question 14

How are the extensions of neuropod cells and where do they go to (also what potentials does it cause)?

Answer 14

Axon-like extensions harbor vesicles with glutamate, which is released onto dendrites of the vagal nerve and cause excitatory post-synaptic potentials

Question 15

Where does the vagus nerve forward the signal to (neuropod)?

Answer 15

To the nucleus tractus solitarius (NTS) in the medulla

Question 16

What is taste receptor called (neuropod)?

Answer 16

T1R3

Question 17

What happens from T1R3 on?

Answer 17

• second messenger cascade
• Ca2+ release
  Na+ influx via TRPM5 channels

Question 18

What is the sodium-glucose co-transporter called and what does it do?

Answer 18

SGLT1: direct Na+ influx

Question 19

What closes upon ATP binding

Answer 19

KATP channels

Question 20

What are voltage-gated calcium channels doing?

Answer 20

VGCC amplify process and induce hormone release

Question 21

What are KATP channels doing?

Answer 21

Closes upon ATP binding

Question 22

What is responsible for direct Na+ influx?

Answer 22

SGLT1 (sodium-glucose co-transporter)

Question 23

Where does nucleus tractus solitarius receive input from?

Answer 23

Gut, but also oral cavity (sensation of sweetness and intestinal sugar signaling), as well as olfactory and visual cues (motivational)

Question 24

Where does the NTS (nucleus tractus solitarius) project to?

Answer 24

To the hypothalamus, central nucleus of amygdala, locus coeruleus (release of noradrenaline increases arousal), dorsal raphe (serotonin increases motivation and mood), SNc and VTA

Question 25

In which pathways does sugar intake increase activity?

Answer 25

In Mesolimbic and Nigrostriatal pathways

Question 26

Which pathway shows activity in sham-fed rats and which pathway does not (taste of sweetness, but no glucose intake)?

Answer 26

Mesolimbic activity increase but not nigrostriatal

Question 27

Which side of the vagus nerve causes increase in which activity?

Answer 27

Left vagus nerve shows increase in mesolimbic activity, right vagus nerve increases nigrostriatal activity

Question 28

How is the Nigrostriatal dopamine?

Answer 28

Post-ingestive only

Question 29

How is the mesolimbic dopamine?

Answer 29

Pre-ingestive and post-ingestive

Question 30

What can the midbrain dopaminergic system be divided into?

Answer 30

Substantia nigra pars compacta (SNc) and ventral tegmental area (VTA)
But separation is not strict with overlap and dopaminergic cells extending beyond boundaries

Question 31

Which pathways is the midbrain dopaminergic system origin of?

Answer 31

Nigrostriatal ( ventral SNc, important for locomotion), mesolimbic and mesocortical pathway (dorsal SNc and VTA, important for reward signaling

Question 32

By what is sugar perceived in the body?

Answer 32

Sugar is perceived by taste receptors in the mouth, but also by epithelial cells in the intestine that have neuron-like properties, e.g. the capacity to depolarize and release neurotransmitters onto dendrites of the vagus nerve

Question 33

Signals of sugar are conveyed to which part of the brain?

Answer 33

The nucleus tractus solitarius of the medulla and forwarded onto reward circuitry in midbrain, but also hypothalamus and amygdala

Question 34

Nigrostriatal dopamine pathway

Answer 34

Hepatic portal vain -> left vagus -> cNTS
Intestine -> right vagus -> cNTS -> PBN -> SNOc ->dorsal str -> cortex

Question 35

Mesolimbic dopamine pathway

Answer 35

1) hepatic portal vain -> left vagus -> cNTS
Intestine -> right vagus -> cNTS -> VTA -> ventral str -> cortex

2) tongue -> cranial nerves 7, 9, 10 ->rNTS -> VTA -> ventral str -> cortex

Question 36

Hoe does sugar travel trougj the body (simple)?

Answer 36

Gustation ( taste receptor cells) -> vagus nerve shows increase-> gut sense (neuropod cells)