RT Journal Article
SR Electronic
T1 Seasonal Variation in the Brain μ-Opioid Receptor Availability
JF The Journal of Neuroscience
JO J. Neurosci.
FD Society for Neuroscience
SP 1265
OP 1273
DO 10.1523/JNEUROSCI.2380-20.2020
VO 41
IS 6
A1 Lihua Sun
A1 Jing Tang
A1 Heidi Liljenbäck
A1 Aake Honkaniemi
A1 Jenni Virta
A1 Janne Isojärvi
A1 Tomi Karjalainen
A1 Tatu Kantonen
A1 Pirjo Nuutila
A1 Jarmo Hietala
A1 Valtteri Kaasinen
A1 Kari Kalliokoski
A1 Jussi Hirvonen
A1 Harry Scheinin
A1 Semi Helin
A1 Kim Eerola
A1 Eriika Savontaus
A1 Emrah Yatkin
A1 Juha O. Rinne
A1 Anne Roivainen
A1 Lauri Nummenmaa
YR 2021
UL http://www.jneurosci.org/content/41/6/1265.abstract
AB Seasonal rhythms influence mood and sociability. The brain μ-opioid receptor (MOR) system modulates a multitude of seasonally varying socioemotional functions, but its seasonal variation remains elusive with no previously reported in vivo evidence. Here, we first conducted a cross-sectional study with previously acquired human [11C]carfentanil PET imaging data (132 male and 72 female healthy subjects) to test whether there is seasonal variation in MOR availability. We then investigated experimentally whether seasonal variation in daylength causally influences brain MOR availability in rats. Rats (six male and three female rats) underwent daylength cycle simulating seasonal changes; control animals (two male and one female rats) were kept under constant daylength. Animals were scanned repeatedly with [11C]carfentanil PET imaging. Seasonally varying daylength had an inverted U-shaped functional relationship with brain MOR availability in humans. Brain regions sensitive to daylength spanned the socioemotional brain circuits, where MOR availability peaked during spring. In rats, MOR availabilities in the brain neocortex, thalamus, and striatum peaked at intermediate daylength. Varying daylength also affected the weight gain and stress hormone levels. We conclude that cerebral MOR availability in humans and rats shows significant seasonal variation, which is predominately associated with seasonal photoperiodic variation. Given the intimate links between MOR signaling and socioemotional behavior, these results suggest that the MOR system might underlie seasonal variation in human mood and social behavior.SIGNIFICANCE STATEMENT Seasonal rhythms influence emotion and sociability. The central μ-opioid receptor (MOR) system modulates numerous seasonally varying socioemotional functions, but its seasonal variation remains elusive. Here we used positron emission tomography to show that MOR levels in both human and rat brains show daylength-dependent seasonal variation. The highest MOR availability was observed at intermediate daylengths. Given the intimate links between MOR signaling and socioemotional behavior, these results suggest that the MOR system might underlie seasonal variation in human mood and social behavior.