fast-scan cyclic voltammetry

Stages

1. 1.
   Sensor expression in caudate-putamen(library_build)

   The glutamate sensor had to be expressed in the caudate-putamen region before multiplexed measurements could be performed in slices.

   Selection: Expression of the genetically encoded glutamate sensor in the target region

2. 2.
   Brain slice multiplexed recording setup(functional_characterization)

   This stage establishes the multiplexed assay geometry needed to compare dopamine and glutamate release in the same slice region.

   Selection: Placement of a carbon fiber microelectrode near cells expressing the glutamate sensor to monitor stimulated dopamine release alongside glutamate sensing

3. 3.
   Local adenosine perturbation and response measurement(secondary_characterization)

   The stage probes the neuromodulatory effect of adenosine on both neurotransmitter outputs in the multiplexed slice assay.

   Selection: Measure how local exogenous adenosine changes stimulated dopamine and glutamate release

4. 4.
   A1 receptor antagonist confirmation(confirmatory_validation)

   This confirmatory stage tests the receptor mechanism underlying the observed inhibitory effect.

   Selection: Test whether DPCPX blocks the adenosine inhibition of dopamine and glutamate release

Steps

1. 1.
   Express iGluSnFR3.v857 in caudate-putamenglutamate sensor

   Enable fluorescent glutamate measurement in the target region.

   Sensor expression is required before slice-based multiplexed measurements can be performed.

2. 2.
   Implant a carbon fiber microelectrode near sensor-expressing cells in the brain slicemultiplexed recording components

   Monitor electrically stimulated dopamine release near cells reporting glutamate release.

   After sensor expression, the electrochemical recording hardware is positioned to create the simultaneous multimodal measurement geometry.

3. 3.
   Apply exogenous adenosine locally and measure transient effects on stimulated dopamine and glutamate releasemultiplexed assay

   Test the spatial and temporal effects of adenosine neuromodulation on both neurotransmitter outputs.

   The perturbation is performed after the multiplexed recording setup is established so both neurotransmitter responses can be measured simultaneously.

4. 4.
   Apply DPCPX to test whether A1 receptor antagonism blocks adenosine inhibition

   Confirm the receptor mechanism responsible for the observed inhibition.

   Mechanistic confirmation follows observation of the inhibitory phenotype so the authors can test whether the effect depends on A1 receptor signaling.

Stages

1. 1.
   Targeted optogenetic transduction(library_build)

   This stage establishes selective expression of the optogenetic construct in the neuronal population whose transmitter output will be tested.

   Selection: Injection site was used to target either nigrostriatal neurons or striatal TH interneurons in TH-Cre mice.

2. 2.
   Functional dopamine release testing(functional_characterization)

   This stage directly tests the central assumption that striatal TH interneurons are dopaminergic.

   Selection: Measure whether optical or electrical stimulation elicits dopamine release in striatal slices.

3. 3.
   Marker colocalization analysis(secondary_characterization)

   This stage tests whether striatal TH interneurons possess the enzymes and transporters necessary to operate as dopaminergic neurons.

   Selection: Assess colocalization of dopamine-related markers with EGFP in TH-labeled neurons.

4. 4.
   Optogenetic circuit output validation(confirmatory_validation)

   This stage validates an alternative functional identity for striatal TH interneurons after dopamine release and marker analyses argue against a dopaminergic phenotype.

   Selection: Test whether optogenetic activation of striatal EGFP-TH interneurons produces inhibitory output onto spiny neurons.

Steps

1. 1.
   Inject Cre-dependent ChR2-EYFP virus into unlesioned midbrain or striatumoptogenetic targeting construct

   Target either nigrostriatal neurons or striatal TH interneurons for selective stimulation.

   Selective transduction is required before stimulation-based testing can distinguish the output of different TH-expressing populations.

2. 2.
   Measure evoked dopamine release in striatal slices by fast-scan cyclic voltammetry during optical or electrical stimulationdopamine release assay

   Directly test whether targeted stimulation elicits striatal dopamine release.

   After selective targeting is established, dopamine release can be compared across nigrostriatal and striatal TH interneuron conditions.

3. 3.
   Assess colocalization of dopamine-related markers with EGFP in TH-labeled neurons by fluorescence immunocytochemistry

   Determine whether striatal TH interneurons express the molecular machinery required for dopaminergic function.

   This follows the negative dopamine-release result to test a mechanistic explanation for why striatal TH interneurons fail to behave as dopaminergic neurons.

4. 4.
   Optogenetically activate striatal EGFP-TH interneurons and test for inhibition of spiny neuronsoptogenetic actuator

   Validate whether striatal TH interneurons function as inhibitory GABAergic interneurons.

   After evidence argues against dopaminergic identity, this step tests the alternative circuit function supported by the data.