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Cocaine on the BrainAlterations in D1/D2 Medium Spiny Neurons of the Nucleus Accumbens Shell Due to Cocaine Exposure
HMB420: Kathleen, Urshita, Majid
I can’t get enough of this stuff!
Goals- Understand what this neurobiological system is
- Basal Ganglia mNAc Anatomy and Connectivity
- Understand the research methods- Optogenetics; Pharmacogenetics; DREADS; Two-Photon
Microscopy, Patch-Clamps, Paired Pulse Facilitation, etc.
- Understand what was found- NAc D1/D2 changes due to cocaine- Inputs from V. Hippocampus and BL Amygdala
- Understand how this could shape behaviour - Theories for addiction
?
NAc
Action Initiation or Inhibition- Which of several possible
behaviors will be performed
Emotional & Motivational - reinforcement of wanted
behavior - suppression of unwanted
behavior
What are the Basal ganglia?- Striatum
- Putamen- Caudate
- Nucleus Accumbens (NAc)
- Medial Shell
Anatomy of the NAc● NAc Shell (medial, lateral & ventral)
○ limbic system - regulation of Reward behaviours
● Medium Spiny Neurons (MSN) ~90%○ GABA-ergic
■ D1 or D2 receptors○ large ∆ spine density, morphology excitability
■ ∆ behaviours (i.e. sensitization)
● Inputs from ○ Ventral Tegmental Area○ Prefrontal Cortex○ Basolateral Amygdala○ Ventral Hippocampus
Not as well understood
Direct and Indirect PathwaysDirect - GO!- NAc D1 MSNs= EPSP= facilitate action
Indirect - STOP!- NAc D2 MSNs=IPSP= facilitate action
Reason for Experimentation
Can such addiction related behaviour be seen as changes in the mNAc and associated circuits?
Is cocaine’s behavioural sensitization reflected in NAc D1/D2
MSN synaptic connectivity?
Question #1
Pilot Data; Confirmation- Rewarding/ addictive drugs increase locomotion in mice
- behavioral sensitization => addiction
- Ensured;- Behavioral sensitization and; - Synaptic changes of MSN post cocaine
- Patch clamp D1/D2 MSN mEPSCs- Recorded at −80 mV- TTX - block AP - Gabazine - block
GABAA receptors
Function/ Structure Change; Methods
Example of method; Whole cell patch using diffusion contrast + fluorescence in Purkinje neuron
- Two-photon microscopy:- D1/D2- MSNs with
fluorescent dye- 3D model to compare
density and volume
Example of 3D synapse modeling
Function/ Structure Change; Results - Cocaine increased D1-
mEPSCHz - No mEPSCAP change
- Cocaine increased D1-MSNs density
May reflect greater numbers of excitatory connections
Sensitization is strongly associated with functional and structural
changes in NAc D1-MSNs synaptic connectivity.
Answer #1
Question #2
Are cocaine induced changes restricted to certain cell types or
cortical inputs?
Input connectivity; Method - Optogenetics:
- AAV-ChR2 in the BLA, VH or PFC. - Only BLA, VH and PFC afferents to mNAc.
Input connectivity; Results- Enhanced BLA D1/2-EPSCs - Dampened VH D1/2-EPSCs - No change with PFC
“Initially stronger VH inputs got
weaker, and BLA inputs became
much stronger?! What does this
mean?!”
Hopefully you are thinking,
Answer #2
Cocaine differentially alters ratio of D1/D2-MSNs NAc afferents, with cell type and input specificity from BLA/
VH inputs.
Question #3
Is observed synaptic plasticity reflected as altered qEPSC
changes?
Postsynaptic Changes; Method - Use light evoked qEPSC visualized
with Extracellular Strontium uptake- Direct estimate qEPSC efficacy - Indirect estimate qEPSC connection
LTP
Spine#
- Paired-pulse experiment check
Postsynaptic Changes; Results - Increased BLA qEPSCHz at D1-MSNs
- unaltered BLA qEPSCAP
- VH qEPSCAP decreased at D1-MSNs- unaltered qEPSCHz for VH inputs
- Consistent with patch mEPSC recordings
- Not due to vesicle release differences - Specific postsynaptic effects at D1-MSNs
Suggest cocaine enhances BLA NAc afferents by more inputs, and
decreased VH inputs by dampened inputs onto D1-MSNs.
Answer #3
Question #4
Is observed BLA and VH input changes reflected as altered
synaptic structure?
Subcellular Changes; Method - Two-photon mapping:
- detect spine volume and synapse volume via Alexa Fluor 594
- detect synaptic calcium levels via calcium indicator (Fluo-4FF)
Subcellular Changes; Results- Cocaine selectively enhanced synapse density at D1-MSNs- Repeated exposure to cocaine selectively enhances the
number of BLA connections onto D1-MSNs.
- Spine volume was initially much larger at D1-MSNs for VH inputs in saline-treated mice
- Difference was abolished after repeated cocaine exposure (reduction in spine volume at D1-MSNs)
- Drug exposure suppresses the strength of VH connections onto D1-MSNs
- Synapse density similar at D1-MSNs and D2-MSNs
Answer #4
Repeated cocaine exposure enhances BLA inputs and
suppresses VH inputs onto D1-MSNs
Question #5
Is NMDAR activation required for behavioral sensitization and observed BLA/VH synaptic
plasticity?
Synaptic Induction; Method - In vivo Pharmacology:
- NMDAR antagonist (MK-801) to test for cocaine induced sensitization
- inject MK-801 to test cocaine induced EPSC changes at BLA and VH
- Test if NMDAR is required for the changes in synaptic connectivity
Synaptic Induction; Results - Long term MK-801
- Abolished sensitization - blocked changes to BLA & VH EPSCs
- Acute pretreatment MK-801 - Did not prevent sensitization
NMDAr needed for sensitization
Answer #5
NMDAR activation required for cocaine-induced behavioral
sensitization and changes to BLA/ VH connections onto MSNs.
Is BLA/VH activation responsible for observed sensitization, mEPSC
frequency, and synaptic remodeling of the mNAc?
Question #6
Structure/Function reversal; Method - In vivo pharmacology:
- DREADD (hM4D) with N-oxide (CNO)
- pre-treat CNO/ saline before cocaine - Measure light-EPSC from D1/D2-MSNs- Measure mEPSCHZ and mEPSCAP
- Two photon image for density and volume
Structure/Function reversal; Results Inhibiting BLA activity:
- Abolished behavioural sensitization & only altered BLA EPSCs
Inhibiting VH activity- Remain sensitized but altered VH EPSCs
BLA activity is necessary for cocaine sensitization- Inhibiting BLA activity:
- Eliminated cocaine-induced increase in mEPSCHz at D1-MSNs
- Abolished cocaine-induced increase in spine density at D1-MSNs
- BLA connectivity accounts increased D1 mEPSCHz and D1 spine density.
Supports BLA/ VH EPSCs being dissociable, with only BLA inputs
causing sensitization, through structural and functional BLA D1-
MSNs innervation.
Answer #6
Overall Findings1. Cocaine alters synaptic connectivity in the NAc
○ Sensitization = increased mEPSCHz & spine density at D1-MSNs
2. Connectivity changes are cell type and input specific○ Increased BLA D1 EPSC, dampened VH D1 EPSC
3. Number and strength of connections are altered○ Increased BLA D1 qESPCHz, dampened VH D1 qESPCAP
4. Subcellular structures are altered○ Increased BLA D1 spine density, reduced VH D1 spine volume
5. Connectivity depends on NMDA receptors○ NMDAR antagonist inhibits sensitization, BLA & VH EPSCs changes
6. Depend on amygdala activity○ Only BLA activity needed for sensitization, & altered BLA D1 EPSCs
7. Amygdala activity causes enhanced connectivity○ Only BLA activity needed to increase mEPSCHz, and spine density
NAc MSNs synaptic rearrangement
during sensitization is cell type and input-specific!
So… What does this mean?!● Goal-directed/ motivated behavior regulated by differential
activation of D1/ D2-MSNs in the NAc
● Drug exposure rebalances connectivity to BLA inputs○ VH inputs usually dominant onto D1 neurons○ Thus; motivated behavior may shift from VH contextual inputs to BLA
emotional inputs!
● Types of neurons and individual spines can have huge behavioral effects
● How neural circuits are reorganized in many neurological / neuropsychiatric diseases?
Huh! So maybe I develop more emotional based drive-learning
Where knowing something is bad does not matter, because doing it feels
right, so I keep doing it!
Criticisms/ Future workComparison to VTA?Relevance in overall circuit?Time dependent plasticity?D2 MSN interactions?
Any questions about me?
Andrew F MacAskill, John M Cassel & Adam G Carter . “Cocaine exposure reorganizes cell type– and input- specific connectivity in the nucleus accumbens. Naure Neuroscience. 2014
Will add Bibliography dropbox link
References