A new study has found that cannabidiol (CBD) can prevent stress-induced impairments in the brain’s ability to suppress learned fear, identifying several biological mechanisms that could have implications for treating post-traumatic stress disorder (PTSD).
The study, published November 6 in the journal Neuropharmacology, was conducted by researchers at the University of São Paulo in Brazil. It found that repeated CBD treatment protected rats from difficulties extinguishing fear memories following exposure to intense stress, while also influencing serotonin, cannabinoid and nitric oxide signaling in the brain.
Researchers used male Wistar rats subjected to a single prolonged stress procedure, an established experimental model designed to reproduce certain behavioral and physiological features associated with PTSD. The stressful experience increased conditioned fear, impaired the animals’ ability to recall that a previously threatening stimulus was no longer dangerous, and heightened cardiovascular responses to trauma-related cues.
These impairments involve a process known as fear extinction, in which the brain learns that a stimulus previously associated with danger no longer represents a threat. Difficulties with this process are considered an important feature of PTSD, particularly when traumatic memories continue triggering fear responses despite the absence of immediate danger.
Following stress exposure, researchers administered CBD at doses of 5 or 10 milligrams per kilogram of body weight over seven days. Both doses prevented impairments in fear extinction memory, indicating that repeated treatment helped preserve the animals’ ability to recall newly learned safety information.
The researchers also examined whether a single CBD treatment could produce similar benefits. A higher one-time dose of 30 milligrams per kilogram was effective, while single doses of 5 or 10 milligrams per kilogram were not, suggesting that both dosage and treatment duration influenced the results.
For comparison, the researchers tested paroxetine, a selective serotonin reuptake inhibitor (SSRI) commonly prescribed for PTSD and other psychiatric conditions. Repeated paroxetine treatment also prevented the stress-induced behavioral impairments.
Further experiments investigated how CBD produced its protective effects. When researchers administered compounds that blocked serotonin 5-HT1A receptors or cannabinoid CB1 receptors, CBD’s benefits were weakened, indicating that both signaling systems contribute to its effects on fear extinction.
The study also identified changes involving neuronal nitric oxide synthase (nNOS), an enzyme involved in nitric oxide production and neuronal signaling. Stress increased activation-related phosphorylation of this enzyme in the prelimbic region of the medial prefrontal cortex, an area involved in regulating emotional responses and learned fear.
Repeated CBD treatment normalized this increased phosphorylation, while blocking serotonin or cannabinoid signaling prevented or weakened that effect. Researchers also found that administering an experimental nNOS inhibitor prevented heightened fear responses and extinction impairments, providing additional evidence that nitric oxide-related signaling plays a role in the observed benefits.
The protective effects of CBD and the nNOS inhibitor also persisted in an experimental procedure involving renewed exposure to a stress-related reminder. This suggests that the effects were not limited to the initial fear-extinction testing conditions.
Notably, the treatments did not change overall levels of CB1 receptors, 5-HT1A receptors or nNOS following the initial stress procedure. Instead, the findings point toward changes in receptor signaling and enzyme activation as important mechanisms underlying CBD’s effects.
The researchers concluded that CBD’s ability to prevent stress-related fear extinction deficits involves interactions between serotonin and cannabinoid receptors, with neuronal nitric oxide synthase serving as a potential downstream target.
The findings provide new preclinical evidence that CBD may help regulate the persistence of traumatic fear responses through multiple biological pathways, supporting further investigation of its potential applications in PTSD treatment.
