{"status":"ok","message-type":"work","message-version":"1.0.0","message":{"indexed":{"date-parts":[[2026,7,29]],"date-time":"2026-07-29T18:59:17Z","timestamp":1785351557146,"version":"3.55.0"},"reference-count":49,"publisher":"MDPI AG","issue":"4","license":[{"start":{"date-parts":[[2026,2,12]],"date-time":"2026-02-12T00:00:00Z","timestamp":1770854400000},"content-version":"vor","delay-in-days":0,"URL":"https:\/\/creativecommons.org\/licenses\/by\/4.0\/"}],"funder":[{"name":"Ministry of Education and Science of Bulgaria","award":["DO-1 277\/2025"],"award-info":[{"award-number":["DO-1 277\/2025"]}]}],"content-domain":{"domain":[],"crossmark-restriction":false},"short-container-title":["IJMS"],"abstract":"<jats:p>This study aims to assess the rate and duration of rat brain retention after a single intranasal administration of indocyanine green (ICG) as an aqueous solution or encapsulated in poly(D,L-lactide-co-glycolide) (PLGA) nanoparticles. Near-infrared fluorescence emission of ICG from the brain and visceral organs was measured at 1, 4, and 24 h, as well as at 1 and 2 weeks after administration. It was observed that both ICG formulations stained the olfactory bulbs and brainstem, the latter mainly in the basolateral region of the pons. Reduced staining was observed on day 7 after treatment, and the signal remains detectable on day 14. Additionally, while emission from ICG-labeled brains in water decreased after two weeks compared to day 7, in ICG-loaded nanoparticles, the emission was significantly higher on day 14. It is concluded that ICG is transported into the brain via both nose-to-brain delivery pathways\u2014through and along olfactory or trigeminal nerves\u2014and that ICG is a useful dye for in vivo studies due to its long-lasting emission and low toxicity. Furthermore, the suggested penetration of ICG-encapsulated PLGA nanoparticles via these transport mechanisms makes them a useful carrier for brain delivery of substances that are rapidly eliminated from circulation or do not cross the blood\u2013brain barrier.<\/jats:p>","DOI":"10.3390\/ijms27041782","type":"journal-article","created":{"date-parts":[[2026,2,12]],"date-time":"2026-02-12T15:28:11Z","timestamp":1770910091000},"page":"1782","update-policy":"https:\/\/doi.org\/10.3390\/mdpi_crossmark_policy","source":"Crossref","is-referenced-by-count":1,"title":["Indocyanine Green as a Marker for Nose-to-Brain Delivery Pathways, Brain Distribution, and PLGA Nanoparticle Efficiency"],"prefix":"10.3390","volume":"27","author":[{"given":"Milena","family":"Mishonova","sequence":"first","affiliation":[{"name":"Department of Animal and Human Physiology, Faculty of Biology, Sofia University \u201cSt. Kliment Ohridski\u201d, 8 Dragan Tsankov Blvd., 1164 Sofia, Bulgaria"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Lea","family":"Koceva","sequence":"additional","affiliation":[{"name":"Department of Animal and Human Physiology, Faculty of Biology, Sofia University \u201cSt. Kliment Ohridski\u201d, 8 Dragan Tsankov Blvd., 1164 Sofia, Bulgaria"},{"name":"Institute of Neurobiology, Bulgarian Academy of Sciences, Acad. G. Bonchev Str., Bl. 23, 1113 Sofia, Bulgaria"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"ORCID":"https:\/\/orcid.org\/0000-0002-5737-536X","authenticated-orcid":false,"given":"Bissera","family":"Pilicheva","sequence":"additional","affiliation":[{"name":"Faculty of Pharmacy, Medical University of Pleven, 1 St. Kliment Ohridski Str., 5800 Pleven, Bulgaria"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"ORCID":"https:\/\/orcid.org\/0000-0001-9780-0538","authenticated-orcid":false,"given":"Plamen","family":"Zagorchev","sequence":"additional","affiliation":[{"name":"Faculty of Pharmacy, Medical University of Pleven, 1 St. Kliment Ohridski Str., 5800 Pleven, Bulgaria"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Neli","family":"Raikova","sequence":"additional","affiliation":[{"name":"Department of Animal and Human Physiology, Faculty of Biology, Sofia University \u201cSt. Kliment Ohridski\u201d, 8 Dragan Tsankov Blvd., 1164 Sofia, Bulgaria"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"ORCID":"https:\/\/orcid.org\/0000-0003-3475-2131","authenticated-orcid":false,"given":"Mitko","family":"Mladenov","sequence":"additional","affiliation":[{"name":"Institute of Biology, Faculty of Natural Sciences and Mathematics, Ss. Cyril and Methodius University, 1000 Skopje, North Macedonia"},{"name":"Department of Fundamental and Applied Physiology, Russian State Medical University, 117997 Moscow, Russia"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"ORCID":"https:\/\/orcid.org\/0000-0001-7981-4506","authenticated-orcid":false,"given":"Rossitza","family":"Konakchieva","sequence":"additional","affiliation":[{"name":"Department of Cell and Developmental Biology, Faculty of Biology, Sofia University \u201cSt. Kliment Ohridski\u201d, 1164 Sofia, Bulgaria"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"ORCID":"https:\/\/orcid.org\/0000-0002-2759-7981","authenticated-orcid":false,"given":"Hristo","family":"Gagov","sequence":"additional","affiliation":[{"name":"Department of Animal and Human Physiology, Faculty of Biology, Sofia University \u201cSt. Kliment Ohridski\u201d, 8 Dragan Tsankov Blvd., 1164 Sofia, Bulgaria"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"ORCID":"https:\/\/orcid.org\/0000-0002-6848-5513","authenticated-orcid":false,"given":"Iliyana","family":"Sazdova","sequence":"additional","affiliation":[{"name":"Department of Animal and Human Physiology, Faculty of Biology, Sofia University \u201cSt. Kliment Ohridski\u201d, 8 Dragan Tsankov Blvd., 1164 Sofia, Bulgaria"}],"role":[{"vocabulary":"crossref","role":"author"}]}],"member":"1968","published-online":{"date-parts":[[2026,2,12]]},"reference":[{"key":"ref_1","unstructured":"Frey, W.H. 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