{"status":"ok","message-type":"work","message-version":"1.0.0","message":{"indexed":{"date-parts":[[2026,4,13]],"date-time":"2026-04-13T11:00:12Z","timestamp":1776078012628,"version":"3.50.1"},"reference-count":43,"publisher":"MDPI AG","issue":"23","license":[{"start":{"date-parts":[[2025,11,25]],"date-time":"2025-11-25T00:00:00Z","timestamp":1764028800000},"content-version":"vor","delay-in-days":0,"URL":"https:\/\/creativecommons.org\/licenses\/by\/4.0\/"}],"funder":[{"name":"Secihti","award":["CF-2023-G-243"],"award-info":[{"award-number":["CF-2023-G-243"]}]}],"content-domain":{"domain":[],"crossmark-restriction":false},"short-container-title":["IJMS"],"abstract":"<jats:p>The calyx of Held is a giant axo-somatic synapse classically confined to the auditory brainstem. We recently identified morphologically similar calyx-like terminals in the extended amygdala (EA) that arise from the ventrolateral parabrachial complex and co-express PACAP, CGRP, VAChT, VGluT1, and VGluT2, targeting PKC\u03b4+\/GluD1+ EA neurons. Here, we asked whether this parabrachial\u2013EA pathway participates in compensation during acute hypotension. In rats given hydralazine (10 mg\/kg, i.p.), we quantified Fos protein during an early phase (60 min) and a late phase (120 min). Early after hypotension, Fos surged in a discrete subpopulation of the parabrachial K\u00f6lliker\u2013Fuse (KF) region and in the EA, whereas magnocellular neurons of the supraoptic and paraventricular nuclei (SON\/PVN) remained largely silent. By 120 min, magnocellular SON\/PVN neurons were robustly Fos-positive. Confocal immunohistochemistry showed that most Fos+ PKC\u03b4+\/GluD1+ EA neurons were encircled by PACAP+ perisomatic terminals (80.8%), of which the majority co-expressed VGluT1 (88.1%). RNAscope in situ hybridization further identified a selective KF population co-expressing Adcyap1 (PACAP) and Slc17a7 (VGluT1) that became fos-positive during the early phase. Together, these data suggest that a KF PACAP+\/VGluT1+ projection forms calyceal terminals around PKC\u03b4+\/GluD1+ EA neurons, providing a high-fidelity route for rapid autonomic rebound to falling blood pressure, while slower endocrine support is subsequently recruited via neurohormone-magnocellular activation. This work links multimodal parabrachial output to temporally layered autonomic\u2013neuroendocrine control.<\/jats:p>","DOI":"10.3390\/ijms262311405","type":"journal-article","created":{"date-parts":[[2025,11,25]],"date-time":"2025-11-25T16:31:54Z","timestamp":1764088314000},"page":"11405","update-policy":"https:\/\/doi.org\/10.3390\/mdpi_crossmark_policy","source":"Crossref","is-referenced-by-count":2,"title":["K\u00f6lliker\u2013Fuse\/Parabrachial Complex PACAP\u2014Glutamate Pathway to the Extended Amygdala Couples Rapid Autonomic and Delayed Endocrine Responses to Acute Hypotension"],"prefix":"10.3390","volume":"26","author":[{"ORCID":"https:\/\/orcid.org\/0000-0002-1486-1659","authenticated-orcid":false,"given":"Vito S.","family":"Hern\u00e1ndez","sequence":"first","affiliation":[{"name":"Department of Physiology, School of Medicine, National Autonomous University of Mexico, Mexico City 04510, Mexico"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"ORCID":"https:\/\/orcid.org\/0000-0002-4210-2772","authenticated-orcid":false,"given":"Pedro","family":"Segura-Chama","sequence":"additional","affiliation":[{"name":"Department of Physiology, School of Medicine, National Autonomous University of Mexico, Mexico City 04510, Mexico"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"ORCID":"https:\/\/orcid.org\/0000-0002-7422-5136","authenticated-orcid":false,"given":"Limei","family":"Zhang","sequence":"additional","affiliation":[{"name":"Department of Physiology, School of Medicine, National Autonomous University of Mexico, Mexico City 04510, Mexico"}],"role":[{"role":"author","vocabulary":"crossref"}]}],"member":"1968","published-online":{"date-parts":[[2025,11,25]]},"reference":[{"key":"ref_1","unstructured":"King, H., Wilfrid, J., and Patterson, M. 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