Table 1.

Terminology and definitions used in text

Terminology	Definition
Cannabinoids	Pharmacologically defined as a class of chemical compounds—comprising phytocannabinoids, chemically synthesized cannabinoids, and endocannabinoids—that bind to the cannabinoid CB1/CB2 receptor.
Primary reinforcer	An event that increases the probability of a behavioral response. In the context of drug addiction, an injection of heroin or a toke on a pipe might function as a primary reinforcer.
Secondary reinforcer	Also referred to as a “conditioned cue,” a stimulus that acquires reinforcing properties through Pavlovian associations. In the context of drug addiction, a syringe or a pipe might function as a secondary reinforcer.
Negative reinforcer	An event that increases the probability of a behavioral response resulting in the elimination or avoidance of the event.
Tonic dopamine	A steady-state dopamine level arising from dopamine neurons firing at low frequency (1–5 Hz) that is capable of occupying high-affinity dopamine D2 receptors.
Phasic dopamine	A significant, transient increase in dopamine concentration arising from dopamine neurons firing in high-frequency bursts (≥20 Hz) that is capable of occupying low-affinity dopamine D1 receptors.
Microdialysis	In the context of in vivo neurochemistry, a semipermeable probe is inserted into a brain region, artificial cerebral spinal fluid is infused, and dialysate containing neurotransmitters that passively diffuse into the probe is extracted and analyzed.
Fast-scan cyclic voltammetry (FSCV)	In the context of in vivo neurochemistry, a carbon fiber microelectrode is inserted into a brain region, and voltage is applied to the carbon fiber, resulting in the oxidation of surrounding chemicals; the resulting current flow is detected and analyzed.
Nucleus accumbens	A component of the basal ganglia that is commonly divided into two substructures, the core and the shell. All known drugs of abuse increase dopamine concentrations in the nucleus accumbens.
Ventral tegmental area	A group of neurons within the midbrain that are primarily dopaminergic (>50%) and contribute to the mesocortical and mesolimbic dopamine pathways.
Mesolimbic dopamine system	A dopaminergic pathway in the brain that projects from A10 dopamine neurons in the VTA to limbic structures including the nucleus accumbens, amygdala, hippocampus, and medial prefrontal cortex.