Descending Control Systems Ronald Dubner, D.D.S., Ph.D. · IP3 SRC NMDA mGluR NK1 Glu Glu SP....

Descending Control SystemsRonald Dubner, D.D.S., Ph.D.

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Descending Control Systems

1

Ronald Dubner, D.D.S., Ph.D.Department of Neural and Pain Sciences

University of Maryland Dental School

• Sensory coding

• Sensory modulation

• Activity-dependent plasticity

2

Transmission Modulation

3



V4

SOLC1

V4

4Oliveras et al., 1975

TB

P

P 6

SOMC1

7M

P 7.1

7M

7L

PPR

P 8.5

Powerful analgesia No analgesia

Off-cell

5

On-cell

Activity-dependent plasticity

RVM

PAG

6

DH



Sp5

NRM

7n

P 11.30

Py

14

( 7 )5 7 DHT(s)

7Timepre-CFA 2h 5h 24h

4

6

8

10

12

2

******

CFA

( n = 7 ) 5,7-DHT

Vehicle ( n = 9 )

CFA

Paw

with

draw

al la

tenc

y

P 11.30

NGC

NGCαPy

S5

NRM7n

cy (s

) 12

8

Vehicle ( n = 5 )

IBO - NGC ( n = 5 )

Time

Paw

with

draw

al la

tenc

4

6

8

10

2pre-CFA 2h 5h 24h

CFA

**

CFA

+++++

Descending modulation: facilitation or inhibition?

• Site of injury

• Type of injury (tissue or nerve)

• Duration of injury

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• Type of hyperalgesia: 1° or 2°, thermal or mechanical

• Deep or superficial tissue

• Cognitive and emotional factors



Effects of RVM lesion on behavior

Ipsilateral Contralateral

Sham ( n = 4 )Saline ( n = 6 )RVM-X ( n = 6 )

100

80 **

10

60

40

20

0pre 24h 3d 1w 2w pre 24h 3d 1w 2w

Time post-CFA injectionTime post-CFA injection

**

Pain modulatory circuitry hyperexcitability

Thalamus & cortex

∆ Pain

11Dorsal horn hyperexcitability

Injuryinput

+ -

• Increase in RVM excitability

• Increase in EAA receptor sensitivity

• Increases in EAA receptor subunit expression and phosphorylation

• Changes in neuronal phenotype

12

• Activity-dependent plasticity at the level of the RVM



Dynamic shifts in descending

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modulation after inflammation

Brain stem

MI R

RVM

ES

Experimental set up

14PW/TF

Spinal cordHeat

1 h-CFA24 h-CFA

15

3 h-CFA

RVM Stimulus intensity ( μA )



NMDA AMPA

#

#

#

120

150

180

120

150

180

3 h

24 h

16Dose (pmol)

#### #

**** #

#

#

#* *

**

0 0.1 1.0 10 100 1000 0 0.1 1.0 10 100 1000

0

-30

30

60

90

0

-30

30

60

90

Changes in gene expression?

Changes in receptor protein expression?

Changes in receptor phosphorylation?

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Dorsal hornneuron

Axonterminal

PKCMg2+

P

P

AMPA

BDNF

Glu

Trk B

18

Ca2+

IP3

SRCNMDA

mGluR

NK1

Glu

Glu

SP



M3M1

M2M3

M1

M2

Mg2+

Ca2+Na+

H2NNH2

DTT

SHHS

NMDA receptor ion channel complex

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M4M2

M4M2

NR1 NR2

COOHHOOC

300

N 10’ 2h30’ 3d 7d 14d

-180kDa

-180kDa

PY-NR2B

NR2B

20

Rel

ativ

e pr

otei

n le

vels

( % N

aïve

)

10’ 30’ 2h 3d 7d 14d0

50

100

150

200

250

Time post-CFA

* **

*

Changes in NMDA receptor subunit

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expression in the RVM



2h 5h 1d 3d 7d 14dN

Time after CFA

NR2A

M

GAPDH

22

Changes in NMDA receptor protein

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expression in the RVM

10000

8000evel

s

2h 5h 1d 3d 7d 14dN

Time after CFA

NR2A180 kDa

**

24

6000

8000

2h 5h 1d 3d 7d 14d

Time after CFA

Rel

ativ

e P

rote

in le

( % o

f naï

ve )

4000

2000

0

*



Changes in NMDA NR2 receptor subunit

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phosphorylation after inflammation

PY-NR2A

NR2A 180 kDa

180 kDa

Naive 10 min 30 min 24 h 7 d 14 d

-

-

*

els 250

300

**

26Time post-CFA

Rel

ativ

e pr

otei

n le

ve(%

nai

ve)

0

50

100

150

200

*

10 min 30 min 24 h 7 d 14 d

10 min 30 min 24 h 7 d 14 d

- 180 kDa

- 180 kDaPY-NR2B

NR2B

Naive

vels

250

300

vels

250

300

250

300

27Time post-CFA

Rel

ativ

e pr

otei

n le

v(%

nai

ve)

0

50

100

150

200

10 min 30 min 24 h 7 d 14 d

Time post-CFA

Rel

ativ

e pr

otei

n le

v(%

nai

ve)

0

50

100

150

200

0

50

100

150

200

10 min 30 min 24 h 7 d 14 d



Neuronal activity in the RVM

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Neuronal activity in the RVM

20 H 25 H

ON - cell OFF - cell

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20 Hz

5 s

25 Hz

5 s

9 h post-CFA

5 s14.5 h post-CFA

30

25 H

z

5 s

2 h post-CFA h post-CFA5.5



Time post-CFA ON-like OFF-like Neutral-like

1.5-11 h 10 5 15

Changes in RVM neuronal activity during the development of inflammation

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5.5-16.5 h 16 10 4

Total = 30Chi Square P < 0.01

Treatment ON-like OFF-like Neutral-like

Naive 11 (15%) 10 (14%) 51 (71%)

Total

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Distribution of RVM neuronal types in ratswith inflamed versus non-inflamed paws

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Naive 11 (15%) 10 (14%) 51 (71%)

24 h CFA 30 (32%) 26 (28%) 37 (40%)

Chi Square P < 0.001

72

93

60

80

100

activ

ity (

% b

asel

ine

)

P < 0.001

B. Off-like cells

nse

( Hz

)

P < 0.05

A. On-like cells

60

80

33

0

20

40

Red

uctio

n of

neu

rona

l a

CFA( n=26 )

Naive ( n=10 )

Naive ( n=11 )

Peak

resp

on

CFA( n=30 )

0

20

40



Brain-derived neurotrophic factor (BDNF) (1)

• A member of the NGF family of neurotrophins

• A modulator of synaptic plasticity

• Involved in central sensitization in the spinal dorsal horn (Mannion et al 1999; Kerr et al 1999)

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(Mannion et al., 1999; Kerr et al., 1999)

• A role in brain stem descending circuitry?

Brain-derived neurotrophic factor (BDNF) (2)

• BDNF-containing neurons in the PAG project to and release BDNF in the RVM

• Inflammation induces an enhanced expression of PAG BDNF and RVM TrkB phosphorylation

35

p p y

• Knockdown of TrkB and suppression of BDNF attenuate inflammatory hyperalgesia

• Microinjection of BDNF into RVM produces hyperalgesia and is dependent upon activation of NMDA receptors

Upregulation of BDNF in PAG neurons

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PAG BDNF-containing neurons project to RVM

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Upregulation of TrkB in the RVM

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PAG stimulation activates TrkB in RVMControl TBS +

40

Effect of neutralizing BDNF in the RVM

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Effect of exogenous BDNF in RVM

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NMDAR antagonist blocksBDNF-induced facilitation

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BDNF induces NR2A tyr-P in the RVM

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Inflammation induces NR2A tyr-P in RVM

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Cellular mediators of BDNF-induced NR2A tyr-P

ba

46

dc

Ca2+

47

Ca2+

Increased Transcription

• PAG-RVM BDNF-containing neurons are upregulated after inflammation

• Intra-RVM sequestration of BDNF and knockdown of TrkB attenuates inflammatory hyperalgesia

• Intra-RVM BDNF at physiological concentrations (10-100 fmol) facilitates nociception, which is dependent on the activation

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of NMDARs

• BDNF induces NR2A try-P via a signal transduction cascade that involves IP3, PKC and Src

• Supraspinal BDNF-TrkB signaling contributes to descending pain facilitation after injury



Pain modulatory circuitry hyperexcitability

Thalamus & cortex

∆ Pain

49Dorsal horn hyperexcitability

Injuryinput

+ -

Normal function of the brain

• Peripheral sensitization

• Central sensitization

• Descending modulation

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• Temporomandibular disorders

• Fibromyalgia

• Low back pain

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Acknowledgements• Ke Ren

• Wei Guo

• Feng Wei

• Stacey LaGraize

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Stacey LaGraize

• Hu Wang

• Shiping Zou

• Kun Yang

Thank you for your interest!

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Descending Control Systems Ronald Dubner, D.D.S., Ph.D. · IP3 SRC NMDA mGluR NK1 Glu Glu SP....

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