ABCB1	ATP-Binding Cassette Subfamily B Member 1
AD	Alzheimer’s Disease
ADHD	Attention-Deficit/Hyperactivity Disorder
AES	Apathy Evaluation Scale
APA	American Psychological Association
BA	Behavioral Activation
BBB	Blood–Brain Barrier
BDI	Beck Depression Inventory
BDNF	Brain-Derived Neurotrophic Factor
BMI	Body Mass Index
CBT	Cognitive Behavioral Therapy
CESD-10	Center for Epidemiologic Studies Depression Scale (10-item version)
CNS	Central Nervous System
CRP	C-Reactive Protein
CSF	Cerebrospinal Fluid
CSVD	Cerebral Small Vessel Disease
CYP2C19	Cytochrome P450 2C19
CYP2D6	Cytochrome P450 2D6
CYP450	Cytochrome P450
DAMPs	Damage-Associated Molecular Patterns
DLPFC	Dorsolateral Prefrontal Cortex
DSM-5	Diagnostic and Statistical Manual of Mental Disorders, Fifth Edition
dTMS	Deep Transcranial Magnetic Stimulation
ECT	Electroconvulsive Therapy
EOD	Early-Onset Depression
ESC/MEM	Escitalopram + Memantine
FDA	U.S. Food and Drug Administration
FTD	Frontotemporal Dementia
GDS	Geriatric Depression Scale
HAM-D	Hamilton Depression Rating Scale
HDRS	Hamilton Depression Rating Scale
HDRS-21	21-item Hamilton Depression Rating Scale
HPA	Hypothalamic–Pituitary–Adrenal (axis)
HTR2A	5-Hydroxytryptamine (Serotonin) Receptor 2A Gene
IADL	Instrumental Activities of Daily Living
IL-6	Interleukin-6
IPT	Interpersonal Therapy
LLD	Late-Life Depression
LOD	Late-Onset Depression
MADRS	Montgomery–Åsberg Depression Rating Scale
MDD	Major Depressive Disorder
MDE	Major Depressive Episode
MEM	Memantine
MRI	Magnetic Resonance Imaging
MT	Motor Threshold
NDRI	Norepinephrine–Dopamine Reuptake Inhibitor
NMDA	N-Methyl-D-Aspartate
NLRP3	NOD-, LRR-, and Pyrin Domain-Containing Protein 3
NSAIDs	Nonsteroidal Anti-Inflammatory Drugs
OMEGA-3	Omega-3 Polyunsaturated Fatty Acids
PET	Positron Emission Tomography
PROSPECT	Prevention of Suicide in Primary Care Elderly: Collaborative Trial
RCT	Randomized Controlled Trial
ROS	Reactive Oxygen Species
rTMS	Repetitive Transcranial Magnetic Stimulation
SLC6A4	Solute Carrier Family 6 Member 4 (Serotonin Transporter Gene)
SNRI	Serotonin–Norepinephrine Reuptake Inhibitor
SSRI	Selective Serotonin Reuptake Inhibitor
TMS	Transcranial Magnetic Stimulation
TNF-α	Tumor Necrosis Factor-Alpha
TRD	Treatment-Resistant Depression
TR-LOD	Treatment-Resistant Late-Onset Depression
WMH	White Matter Hyperintensities