New brain region that suppresses fear identified.
Post-traumatic stress disorder (PTSD) is a type of anxiety disorder which can develop after a person is involved in or has witnessed traumatic events. The main treatments for people with PTSD are counselling and medication, however, non-specific SSRI antidepressants for PTSD are shown to only benefit 50% of sufferers, with it is still unclear if using medications and counselling together has greater benefit. Now, a study from researchers at Texas A&M University identifies a new area in the brain involved in inhibiting fear, a discovery which holds potential for clinical interventions in patients with psychiatric diseases such as PTSD. The team state they have discovered that a small brain region in the thalamus called the nucleus reuniens plays a role in inhibiting fear in rats. The opensource study is published in the journal Nature Communications.
Previous studies show most drugs that physicians use to treat psychiatric disorders are indiscriminate and target all neurons in the brain. However, behavioral therapies, such as extinction therapy for PTSD, during which patients undergo prolonged, repetitive exposure to their traumas in safe settings, are effective in diminishing fear, however, patients often relapse. The current study provides a specific target for fear suppression by showing that prefrontal cortex inputs to the nucleus reuniens are critically involved in fear extinction.
The current study exposes rats to tones paired initially with mild foot shocks to create the fear response. An extinction procedure is then used, namely exposing the rats to the tones repetitively for prolonged periods, to suppress the fear. Results show that by using a pharmacological approach to inactivate the nucleus reuniens, the rats were unable to suppress fear. The lab then used a targeted pharmacogenetic strategy to silence neurons selectively in the prefrontal cortex projecting to the reuniens. Data findings show that engineered viruses carrying designer receptors activated by designer drugs inhibited these inputs and prevented rats from suppressing fear.
The researchers explain the nucleus reuniens receives projections or inputs from the prefrontal cortex, interconnects the prefrontal cortex and hippocampus, and may serve a pivotal role in regulating emotional learning and memory. They go on to add that the prefrontal cortex plays an emotion regulation role, and identifying this particular projection from the prefrontal cortex to the nucleus reuniens in the thalamus, points to parts of the brain which are important for the inhibitory function of fear, which could be an avenue to new drugs, therapies and interventions for psychiatric disorders.
The team surmise their data shows that the nucleus reuniens and its prefrontal cortex inputs are critical for the extinction of Pavlovian fear memories in rats. For the future, the researchers state that by identifying the involvement of this specific circuit of the brain in fear inhibition, the global medical community can now investigate more targeted treatments for psychiatric disorders that work better and last longer.
Source: Texas A&M University