Synaptic correlates of fear and extinction learning in the amygdala

ore 11.00
Sala Convegni - Palazzo Fedrigotti, Corso Bettini n. 31 - Rovereto

Relatore:
Taiju Amano - Unit for Affiliative Social Behavior, RIKEN Brain Science Institute, Japan

Abstract:
Accumulating data suggest that the amygdala plays a critical role in the acquisition and expression of conditioned fear responses. The lateral nucleus (LA) is the input station of the amygdala for information about conditioned stimuli (CS), whereas the medial sector of the central nucleus (CeM) is the main output region that projects to brainstem fear effectors. However, there are no direct projections from LA to CeM. We hypothesized that the basal nuclei of the amygdala (including BA; basolateral; BL and basomedial; BM) bridge the gap between LA and CeM. We examined the effects of local BL and/or BM inactivations with muscimol 15 min prior to testing fear recall. Independent inactivation of either BL or BM did not reduce conditioned freezing even though an extinction recall deficit was seen the next day. In contrast, combined BL-BM inactivation blocked fear expression. These results suggest that BL and BM nuclei are both involved in fear expression but that there is functional redundancy between them. Furthermore, the extinction deficit caused by BL and/or BM inactivation suggests that these nuclei normally drive extinction related plasticity in one or more of their targets. Likely candidates include infralimbic and GABAergic intercalated (ITC) neurons. We tested the BL-mediated responses of CeM and ITC neurons by whole-cell patch-clamp recording. We observed that extinction training causes a potentiation of BL inputs to ITC neurons, an effect that required infralimbic activity during or shortly after extinction training and caused increased feed-forward inhibition in CeM. Enhancement of BL inputs to ITC neurons involved an altered expression profile of ionotropic glutamate receptors. Therefore, we propose that the expression of conditioned fear responses is determined by the balance between excitatory BA inputs and feed-forward inhibition mediated by ITC neurons in CeM fear output neurons.