In other brain regions, detecting the actions of endogenously released opioids requires intense stimulation12131415161718. Consistent with this, in the hypothalamus, where dense core vesicle release has been most thoroughly studied, optimal release is elicited by intense stimulation (at least 5–10 Hz)37. However, less intense stimulation (1 Hz) can elicit small but significant peptide release37. In light of this, we tested whether we could stimulate endogenous opioid peptide release using less intense stimulation. We initially tested whether the standard paired-pulse stimulation (‘low stimulus', Fig. 3a) was sufficient to produce an endogenous opioid effect. To determine the actions of endogenously released opioids, we examined whether the opioid antagonist naloxone (10 μM) increased the eEPSC amplitude, with an increase taken to indicate a reversal of endogenous opioid inhibition (Fig. 3a). However, naloxone did not increase eEPSC amplitude at the BLA-Im synapse in response to the low-stimulus protocol (Fig. 3b,i).