Full NameDesigner Receptors Exclusively Activated by Designer Drugs
CategoryChemogenetic Neuromodulation
Activation MethodPharmacological (CNO, deschloroclozapine)
Clinical StatusPreclinical / Translational Research
ApplicationsCircuit mapping, Seizure control, Movement disorders
Designer Receptors Exclusively Activated by Designer Drugs (DREADDs) are a chemogenetic technology that allows precise control of neuronal activity through the administration of synthetic ligands. Originally derived from human muscarinic acetylcholine receptors, DREADDs provide a non-invasive method to modulate specific neural circuits with high temporal and spatial precision.
Unlike optogenetics, which requires genetic modification and light delivery, DREADDs can be activated systemically by administering a ligand (typically clozapine-N-oxide or deschloroclozapine), making them suitable for studies in deeper brain regions and for chronic experiments.
¶ Origin and Evolution
The DREADD technology was pioneered by Dr. Bryan Roth and colleagues at the University of North Carolina:
| Year |
Milestone |
| 2007 |
First generation DREADDs (hM3, hM4) developed |
| 2012 |
hM3Dq and hM4Di widely adopted |
| 2015 |
Cre-dependent DREADDs developed |
| 2020 |
Improved ligands (DCZ, compound 21) introduced |
| 2021 |
High-efficiency DREADD ligands |
First Generation (2007):
- hM3Dq and hM4Di derived from human muscarinic receptors
- Activated by clozapine-N-oxide (CNO)
- Limited brain penetration
Second Generation (2015):
- Cre-dependent expression systems
- Improved viral delivery vectors
- Application to specific cell types
Third Generation (2020):
- Deschloroclozapine (DCZ) — improved brain penetration
- Compound 21 — alternative high-affinity ligand
- Enhanced receptor stability
DREADDs work through the following mechanism:
- Receptor Expression: Viral vectors (AAV) deliver hM3Dq (excitatory) or hM4Di (inhibitory) DREADD genes to target neurons
- Ligand Binding: Administration of CNO or DCZ (deschloroclozapine) binds to the engineered receptor
- Signal Transduction:
- hM3Dq activates Gq signaling → increases neuronal firing
- hM4Di activates Gi signaling → decreases neuronal firing
- Effects: Neuronal activity is modulated for 2-6 hours post-administration
| DREADD |
G Protein |
Effect |
Duration |
| hM3Dq |
Gq |
Excitation (↑ firing) |
2-6 hours |
| hM4Di |
Gi |
Inhibition (↓ firing) |
2-6 hours |
| rM3D (rat) |
Gs |
Modulation |
Variable |
| KORD |
Gi |
Inhibition |
4-8 hours |
hM3Dq (Excitatory):
- Activates phospholipase C (PLC)
- Increases intracellular calcium
- Depolarizes neuronal membrane
- Enhances neurotransmitter release
hM4Di (Inhibitory):
- Opens G protein-gated inward rectifier potassium (GIRK) channels
- Hyperpolarizes neuronal membrane
- Reduces action potential firing
- Decreases neurotransmitter release
| Ligand |
Dose |
Brain Penetration |
Half-life |
| Clozapine-N-oxide (CNO) |
1-10 mg/kg |
Low |
2-4 hours |
| Deschloroclozapine (DCZ) |
0.1-1 mg/kg |
High |
6-12 hours |
| Compound 21 |
0.1-3 mg/kg |
High |
4-8 hours |
- Motor circuit modulation: DREADDs can be used to modulate the basal ganglia circuitry in PD models
- Dyskinesia research: Used to study L-DOPA-induced dyskinesias
- Therapeutic target validation: Used to test circuit hypotheses before invasive interventions
- Subthalamic nucleus modulation: Investigating STN hyperactivity in PD
- Memory circuit mapping: DREADDs enable investigation of memory circuits (hippocampus, entorhinal cortex)
- Neuroinflammation studies: Targeting microglia for modulation of neuroinflammatory responses
- Neuronal network restoration: Testing whether modulating specific circuits can restore cognitive function
- Entorhinal cortex dysfunction: Modeling early AD vulnerability
¶ Epilepsy and Seizure Control
- Acute seizure suppression: hM4Di can suppress seizure activity in focal epilepsy models
- Chronic epilepsy: Potential for on-demand seizure control through systemic ligand administration
- Circuit-specific targeting: Modulating excitatory/inhibitory balance
¶ ALS and Motor Neuron Disease
- Motor neuron circuit modulation: Targeting spinal cord circuits
- Respiratory circuit control: Potential for modulating brainstem respiratory centers
- Cortical hyperexcitability: Investigating mechanisms of motor neuron degeneration
- Striatal neuron modulation: Investigating striatal dysfunction
- Motor behavior control: Testing circuit contributions to chorea
- Cognitive circuit mapping: Understanding executive dysfunction
¶ Advantages and Limitations
- Non-invasive activation: Systemic ligand administration reaches deep brain structures
- Long-term studies: Suitable for chronic experiments spanning weeks to months
- Cell-type specificity: Cre-dependent expression allows precise targeting
- No light requirement: No fiber implantation needed, reducing tissue damage
- Chronic implantation not required: Unlike optogenetics, no hardware remains in brain
- Dose control: Effects can be titrated by ligand dose
- Reversibility: Effects wear off as ligand clears
- Off-target effects: Clozapine, used as a DREADD ligand, has activity at endogenous receptors
- Temporal resolution: Onset is slower than optogenetics (minutes vs. milliseconds)
- Variable expression: Viral delivery efficiency varies across brain regions
- Clinical translation: CNO does not cross the blood-brain barrier effectively; DCZ shows promise but is still preclinical
- Receptor trafficking: DREADD expression may be internalized over time
- Immune response: Potential immune reaction to foreign proteins
| Feature |
DREADDs |
Optogenetics |
| Temporal precision |
Minutes |
Milliseconds |
| Spatial precision |
Cell-type specific |
Cell-type specific |
| Invasiveness |
Low (injection) |
High (fiber implants) |
| Deep brain access |
Yes |
Limited by fiber length |
| Chronic studies |
Excellent |
Limited by fiber durability |
| Hardware requirements |
None |
Fiber optics, lasers |
| Clinical translation |
Moderate |
Challenging |
Use DREADDs when:
- Studying deep brain regions
- Needing chronic modulation over weeks/months
- Working with large animal models
- Combining with other surgical procedures
Use Optogenetics when:
- Requiring millisecond precision
- Studying rapid neural dynamics
- Bidirectional control needed simultaneously
- Circuit connectivity mapping
- Gi-DREADD for seizures: hM4Di showing efficacy in preventing seizure spread in temporal lobe epilepsy models
- hM3Dq for memory enhancement: Activation of specific hippocampal engram cells enhances memory recall in AD models
- Microglia targeting: New DREADD variants allow selective modulation of microglia for neuroinflammation studies
- KORD (Kappa opioid receptor DREADD): Alternative inhibitory DREADD using salvinorin B as ligand
- Dual DREADD systems: Simultaneous excitation and inhibition in different cell populations
| Application |
DREADD Used |
Model System |
| Memory formation |
hM3Dq |
Hippocampal engram cells |
| Seizure suppression |
hM4Di |
Temporal lobe epilepsy |
| Feeding behavior |
hM4Di |
Arcuate nucleus |
| Sleep-wake control |
hM3Dq/hM4Di |
Hypothalamus |
| Mood regulation |
hM3Dq |
Prefrontal cortex |
DREADDs have been adapted for non-neuronal cells:
- P2X7-DREADD: Targeting microglia via P2X7 promoter
- CX3CR1-DREADD: Microglia-specific expression
- Effects: Modulating cytokine release, phagocytosis
Carson et al. (2020) demonstrated astrocyte-specific DREADDs:
- Calcium modulation: Controlling astrocytic signaling
- Metabolic regulation: Impacting neuronal support
- Neurovascular coupling: Modulating blood flow
DREADDs have been applied beyond the CNS:
- Cardiac control: Modulating heart rate via vagal neurons
- Gastrointestinal: Controlling gut motility
- Immune system: Modulating peripheral immune cells
DREADDs remain in preclinical and translational research stages. The main clinical applications being explored include:
- Seizure control devices (though not DREADDs directly, the principle of chemogenetics)
- Targeted neuromodulation approaches that could complement or replace invasive DBS
| Challenge |
Current Status |
Potential Solutions |
| BBB penetration |
CNO poor, DCZ moderate |
Novel ligand development |
| Long-term expression |
Limited by immune response |
Immunosuppression, newer vectors |
| Specificity |
Off-target ligand effects |
Engineered receptors |
| Clinical-grade ligand |
Not available |
Pharmaceutical development |
While direct clinical DREADD therapy remains years away:
- Epilepsy: Implantable systems delivering CNO/DCZ to seizure foci
- Movement disorders: Potential DBS alternative with chemogenetic modulation
- Pain management: Targeting pain circuits with inhibitory DREADDs
- AAV vector selection: Serotype 2/9 for CNS targeting
- Promoter choice: Synapsin (neurons), GFAP (astrocytes), CX3CR1 (microglia)
- Injection volume: 0.5-1 μL per site
- Expression time: 2-4 weeks for peak expression
¶ Ligand Administration
| Route |
Dose (CNO) |
Dose (DCZ) |
Onset |
| Intraperitoneal |
0.1-1 mg/kg |
0.01-0.1 mg/kg |
30-60 min |
| Subcutaneous |
0.1-1 mg/kg |
0.01-0.1 mg/kg |
30-60 min |
| Intravenous |
0.1-0.5 mg/kg |
0.01-0.05 mg/kg |
15-30 min |