Consolidation of altered associability information by amygdala central nucleus

The Recruitment of a Neuronal Ensemble in the Central Nucleus of the Amygdala During the First Extinction Episode Has Persistent Effects on Extinction Expression

BACKGROUND

Adaptive behavior depends on the delicate and dynamic balance between acquisition and extinction memories. Disruption of this balance, particularly when the extinction of memory loses control over behavior, is the root of treatment failure of maladaptive behaviors such as substance abuse or anxiety disorders. Understanding this balance requires a better understanding of the underlying neurobiology and its contribution to behavioral regulation.

METHODS

We microinjected Daun02 in Fos-lacZ transgenic rats following a single extinction training episode to delete extinction-recruited neuronal ensembles in the basolateral amygdala (BLA) and central nucleus of the amygdala (CN) and examined their contribution to behavior in an appetitive Pavlovian task. In addition, we used immunohistochemistry and neuronal staining methods to identify the molecular markers of activated neurons in the BLA and CN during extinction learning or retrieval.

RESULTS

CN neurons were preferentially engaged following extinction, and deletion of these extinction-activated ensembles in the CN but not the BLA impaired the retrieval of extinction despite additional extinction training and promoted greater levels of behavioral restoration in spontaneous recovery and reinstatement. Disrupting extinction processing in the CN in turn increased activity in the BLA. Our results also show a specific role for CN PKCδ+ neurons in behavioral inhibition but not during initial extinction learning.

CONCLUSIONS

We showed that the initial extinction-recruited CN ensemble is critical to the acquisition-extinction balance and that greater behavioral restoration does not mean weaker extinction contribution. These findings provide a novel avenue for thinking about the neural mechanisms of extinction and for developing treatments for cue-triggered appetitive behaviors.

Anatomic alterations across amygdala subnuclei in medication-free patients with obsessive-compulsive disorder

BACKGROUND

The amygdala has been implicated in obsessive-compulsive disorder (OCD), a common, disabling illness. However, the regional distribution of anatomic alterations in this structure and their association with the symptoms of OCD remains to be established.

METHODS

We collected high-resolution 3D T1-weighted images from 81 untreated patients with OCD and no lifetime history of comorbid psychotic, affective or anxiety disorders, and from 95 age- and sex-matched healthy controls. We extracted the volume of the central nucleus of the amygdala (CeA) and the basolateral complex of the amygdala (BLA) and compared them across groups using FreeSurfer 6.0. In exploratory analyses, we evaluated other subnuclei, including the cortical medial nuclei, the anterior amygdaloid area, and the corticoamygdaloid transition area.

RESULTS

Patients with OCD had reduced amygdala volume bilaterally compared with healthy controls (left, p = 0.034; right, p = 0.002). Volume reductions were greater in the CeA (left: -11.9%, p = 0.002; right: -13.3%, p < 0.001) than in the BLA (left lateral nucleus: -3.3%, p = 0.029; right lateral nucleus: -3.9%, p = 0.018; right basal nucleus: -4.1%, p = 0.017; left accessory basal nucleus: -6.5%, p = 0.001; right accessory basal nucleus: -9.3%, p < 0.001). Volume reductions in the CeA were associated with illness duration. Exploratory analysis revealed smaller medial (left: -15.4%, p < 0.001, η2 = 0.101) and cortical (left: -9.1%, p = 0.001, η2 = 0.058; right: -15.4%, p < 0.001, η2 = 0.175) nuclei in patients with OCD compared with healthy controls.

LIMITATIONS

Although the strict exclusion criteria used in the study helped us to identify OCD-specific alterations, they may have limited generalizability to the broader OCD population.

CONCLUSION

Our results provide a comprehensive anatomic profile of alterations in the amygdala subnuclei in untreated patients with OCD and highlight a distinctive pattern of volume reductions across subnuclei in OCD. Based on the functional properties of the amygdala subnuclei established from preclinical research, CeA impairment may contribute to behavioural inflexibility, and BLA disruption may be responsible for altered fear conditioning and the affective components of OCD.