{"id":9,"date":"2025-06-03T23:10:19","date_gmt":"2025-06-03T20:10:19","guid":{"rendered":"https:\/\/sun.utu.fi\/?page_id=9"},"modified":"2025-08-18T23:57:41","modified_gmt":"2025-08-18T20:57:41","slug":"sad","status":"publish","type":"page","link":"https:\/\/sun.utu.fi\/?page_id=9","title":{"rendered":"SAD"},"content":{"rendered":"\n<p><strong>Summary of our contributions:<\/strong><\/p>\n\n\n\n<ul class=\"wp-block-list\">\n<li>Identified seasonal variation in brain \u03bc-opioid receptor (MOR) signalling (<em>J Neurosci<\/em>, 2021), awarded\u00a0<em>Publication of the Year<\/em>.<\/li>\n\n\n\n<li>Discovered MOR signalling in brown adipose tissue and its seasonal modulation (<em>EJNMMI<\/em>, 2023).<\/li>\n\n\n\n<li>Revealed brain\u2013BAT interaction mechanisms via MOR signalling (<em>EJNMMI<\/em>, 2025).<\/li>\n\n\n\n<li>Proposed a novel MOR-mediated mechanism for seasonal affective disorder (book chapter, 2025).\u00a0<\/li>\n\n\n\n<li>Demonstrated seasonal dopamine D2\/3 receptor changes (<em>EJNMMI<\/em>, 2024).<\/li>\n\n\n\n<li>Revealed reduced glucose metabolism in social brain regions during dark seasons <em>(J. Biol. Rhythms, 2025).<\/em><\/li>\n<\/ul>\n\n\n\n<p><strong>Seasonal affective disorder (SAD)<\/strong>&nbsp;affects a substantial proportion of people living in Finland. Our work has contributed to understanding the underlying neurotransmission mechanisms of SAD, particularly by revealing seasonal patterns in&nbsp;<strong>mu-opioid receptor (MOR)<\/strong>&nbsp;signaling.<\/p>\n\n\n\n<p>Using a large PET imaging dataset of brain MOR availability in healthy individuals, we discovered an&nbsp;<strong>inverted-U shaped relationship<\/strong>&nbsp;between MOR levels and local daylength variation (Sun L. et al.,&nbsp;<em>Journal of Neuroscience<\/em>, 2021). This finding was validated in animal models, where rats were exposed to photoperiodic cycles mimicking natural daylength changes (Sun L. et al., 2021).<\/p>\n\n\n\n<p>Subsequently, Sun and colleagues demonstrated that&nbsp;<strong>brown adipose tissue (BAT)<\/strong>&nbsp;expresses MOR and exhibits seasonal fluctuations in MOR signaling (Sun L. et al.,&nbsp;<em>EJNMMI<\/em>, 2022). As BAT plays a central role in energy homeostasis, the presence of MOR signaling in BAT suggests a potential&nbsp;<strong>cross-talk between the central nervous system and peripheral metabolic regulation<\/strong>. Indeed, our further study (Sun L. et al.,&nbsp;<em>EJNMMI<\/em>, 2025) showed that this brain-BAT interaction is modulated by season, with enhanced coupling observed during the darker months.<\/p>\n\n\n\n<p>In summary, our research has advanced the understanding of brain\u2013body mechanisms underlying SAD, highlighting a pivotal role for MOR signaling. Given MOR\u2019s central role in&nbsp;<strong>social cognition<\/strong>&nbsp;and&nbsp;<strong>reward processing<\/strong>, its seasonal fluctuations in both the brain and peripheral energy systems may contribute to seasonal mood changes.&nbsp;<strong>Dysregulation of this seasonal MOR signaling dynamic may underlie the pathophysiology of SAD<\/strong>.<\/p>\n\n\n\n<p>Dr. Sun has been interviewed by <strong><a href=\"https:\/\/yle.fi\/a\/74-20001599\" data-type=\"link\" data-id=\"https:\/\/yle.fi\/a\/74-20001599\" target=\"_blank\" rel=\"noreferrer noopener\">Yle<\/a>, <a href=\"https:\/\/www.ts.fi\/tiede\/5234569\" data-type=\"link\" data-id=\"https:\/\/www.ts.fi\/tiede\/5234569\" target=\"_blank\" rel=\"noreferrer noopener\">Turun Sanomat<\/a>, <\/strong>and<strong> <a href=\"https:\/\/www.forbes.com\/sites\/carolineseydel\/2021\/03\/29\/a-key-brain-chemical-fluctuates-with-the-seasons-new-study-finds\/\" data-type=\"link\" data-id=\"https:\/\/www.forbes.com\/sites\/carolineseydel\/2021\/03\/29\/a-key-brain-chemical-fluctuates-with-the-seasons-new-study-finds\/\" target=\"_blank\" rel=\"noreferrer noopener\">Forbes<\/a><\/strong> due to relevant scientific findings. <\/p>\n\n\n\n<p><strong>Key Publications:<\/strong><\/p>\n\n\n\n<ul class=\"wp-block-list\">\n<li><strong>Lihua Sun<\/strong>&nbsp;(2025), The endogenous opioid neurotransmission and seasonal affective disorders, Book chapter of \u201cHandbook of the Biology and Pathology of Mental Disorders\u201d,&nbsp;<em>Springer<\/em><\/li>\n\n\n\n<li><strong>Lihua Sun<\/strong>, &#8230;, Anne Roivainen (2025).&nbsp;Dark seasons enhance brain and brown adipose tissue interactions related to mu-opioid receptor signaling. European Journal of Nuclear Medicine and Molecular Imaging.&nbsp;<\/li>\n\n\n\n<li><strong>Lihua Sun<\/strong>, &#8230;, Lauri Nummenmaa (2024).&nbsp;Seasonal variation in D2\/3 dopamine receptor availability in the human brain,&nbsp;<em>European Journal of Nuclear Medicine and Molecular Imaging<\/em><\/li>\n\n\n\n<li><strong>Lihua Sun<\/strong>, &#8230;, Anne Roivainen (2022).&nbsp;[11C]carfentanil PET imaging for studying the peripheral opioid system in vivo: effect of photoperiod on mu-opioid receptor availability in brown adipose tissue.&nbsp;<em>European Journal of Nuclear Medicine and Molecular Imaging<\/em>.&nbsp;<\/li>\n\n\n\n<li><strong>Lihua Sun<\/strong>, &#8230;, Lauri Nummenmaa (2021).&nbsp;<em>Journal of Neuroscience<\/em>, 41(6), 1265\u20131273.<\/li>\n\n\n\n<li>Kyoungjune Pak, &#8230;,&nbsp;<strong>Lihua Sun<\/strong> (2025). Impact of Day Length on Brain Glucose Metabolism in Men: A Large-Scale Repeated Measures PET Study. Journal of Biological Rhythms.&nbsp;<\/li>\n\n\n\n<li><strong>Lihua Sun<\/strong>, &#8230;, Kaisa M Hartikainen (2016).&nbsp;Human brain reacts to transcranial extraocular light.&nbsp;<em>PLoS ONE<\/em>.<\/li>\n<\/ul>\n","protected":false},"excerpt":{"rendered":"<p>Summary of our contributions: Seasonal affective disorder (SAD)&nbsp;affects a substantial proportion of people living in Finland. Our work has contributed to understanding the underlying neurotransmission mechanisms of SAD, particularly by revealing seasonal patterns in&nbsp;mu-opioid receptor (MOR)&nbsp;signaling. Using a large PET imaging dataset of brain MOR availability in healthy individuals, we discovered an&nbsp;inverted-U shaped relationship&nbsp;between MOR [&hellip;]<\/p>\n","protected":false},"author":2,"featured_media":0,"parent":0,"menu_order":0,"comment_status":"closed","ping_status":"closed","template":"","meta":{"footnotes":""},"class_list":["post-9","page","type-page","status-publish","hentry"],"jetpack_sharing_enabled":true,"_links":{"self":[{"href":"https:\/\/sun.utu.fi\/index.php?rest_route=\/wp\/v2\/pages\/9","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/sun.utu.fi\/index.php?rest_route=\/wp\/v2\/pages"}],"about":[{"href":"https:\/\/sun.utu.fi\/index.php?rest_route=\/wp\/v2\/types\/page"}],"author":[{"embeddable":true,"href":"https:\/\/sun.utu.fi\/index.php?rest_route=\/wp\/v2\/users\/2"}],"replies":[{"embeddable":true,"href":"https:\/\/sun.utu.fi\/index.php?rest_route=%2Fwp%2Fv2%2Fcomments&post=9"}],"version-history":[{"count":17,"href":"https:\/\/sun.utu.fi\/index.php?rest_route=\/wp\/v2\/pages\/9\/revisions"}],"predecessor-version":[{"id":255,"href":"https:\/\/sun.utu.fi\/index.php?rest_route=\/wp\/v2\/pages\/9\/revisions\/255"}],"wp:attachment":[{"href":"https:\/\/sun.utu.fi\/index.php?rest_route=%2Fwp%2Fv2%2Fmedia&parent=9"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}