Opioid receptors and peptides are expressed to varying degrees throughout the amygdala2021. In particular, the intercalated cells (ITCs) are one possible site where enkephalin could regulate fear and anxiety behaviours. ITCs are small clusters of densely packed GABAergic neurons that en-sheath the basolateral amygdala (BLA). Coronal sections give rise to three separate clusters: the smaller lateral (lpc) and medial (mpc) paracapsular ITC clusters are located within the external and intermediate capsules respectively and the larger main island (Im), is located ventromedial to the BLA22 (Fig. 1a). While the lpc provides feedforward inhibition to the BLA23, the mpc acts as an inhibitory interface between the BLA and CeA and thus regulates fear learning24. In particular the mpcs are required for fear extinction25. Less is known about the functional role of the main island although it is possible the Im plays a similar role to the mpc. Indeed, Im neurons also receive sensory information from both the BLA2426 and the thalamus27 along with more complex information from the medial pre-frontal cortex (mPFC), a region highly implicated in fear extinction2829. Like the mpcs, the Im sends inhibitory GABAergic projections to the medial central nucleus (CeM)212630 and thus could gate expression of the conditioned fear response31. The Im may be particularly important during fear extinction as extinction activates Im neurons2232, their ablation (along with the mpc) reduces extinction25 and treatments that reverse the extinction deficit in anxious mice elevate Im neuron activity32.