A Basomedial Amygdala to Intercalated Cells Microcircuit Expressing PACAP and Its Receptor PAC1 Regulates Contextual Fear

BMA (Basomedial amygdalar nucleus) MBA:319 projects to IA (Intercalated amygdalar nucleus) MBA:1105 · Mouse

In PACAP-EGFP reporter mice, PACAP-expressing cell bodies were concentrated in the lateral and basomedial amygdala and GFP-labelled fibres densely occupied both dorsal and ventral medial intercalated cell clusters. With an intersectional strategy (retrograde Cre-dependent HSV-FLP in mICCs plus FLP-dependent ChR2-eYFP in BMA), labelled axon terminals from BMA were seen in the mICCs, overlapping FoxP2-positive mICC tissue.

Fig. 1A,B,D–G; Results, first section

Made by an AI model reading the paper (claude-opus-5, extract@0.3.0); a second AI model (claude-opus-5) agrees.

BMA (Basomedial amygdalar nucleus) MBA:319 projects to CEA (Central amygdalar nucleus) MBA:536 · Mouse

In the same PACAP-EGFP reporter sections in which labelled fibres filled the mICCs, essentially no GFP-labelled terminals from amygdalar PACAP neurons were found in the central amygdala.

Fig. 1A,B; Results, first section

Made by an AI model reading the paper (claude-opus-5, extract@0.3.0); a second AI model (claude-opus-5) disagrees. “The paper only reports little/no PACAP-EGFP fiber labeling in CN from reporter mice, which does not test a BMA-specific projection with an anterograde tracer.”

BMA (Basomedial amygdalar nucleus) MBA:319 projects to IA (Intercalated amygdalar nucleus) MBA:1105 · Mouse

A retrogradely transported, Cre-dependent HSV carrying mCherry and FLP was injected into the dorsal mICCs of PACAP-Cre mice; mCherry-labelled somata appeared in the BMA, showing that PACAP-expressing BMA neurons send axons to the mICCs.

Fig. 1D–G; Results, first section

Made by an AI model reading the paper (claude-opus-5, extract@0.3.0); a second AI model (claude-opus-5) agrees.

BMA (Basomedial amygdalar nucleus) MBA:319 functionally connects to IA (Intercalated amygdalar nucleus) MBA:1105 · Mouse

Unilateral in vivo blue-light stimulation of ChR2-expressing PACAP BMA neurons that project to the mICCs raised the number of cfos-positive cells in the ipsilateral mICCs relative to the unstimulated hemisphere. In slices, single light flashes over ChR2-expressing BMA PACAPergic fibres evoked EPSCs in most recorded mICC neurons; these were abolished by TTX, restored/increased by TTX plus 4-AP (consistent with a monosynaptic connection), and blocked by CNQX, showing glutamate release from BMA terminals. The PAC1 antagonist PACAP 6-38 increased EPSC amplitude without changing the paired-pulse ratio.

Figs. 3A–D, 4C–I

Made by an AI model reading the paper (claude-opus-5, extract@0.3.0); a second AI model (claude-opus-5) agrees.