Nociceptive responses in MT 2 receptor knockout mice compared to MT 1 and double MT 1 /MT 2 receptor knockout mice

• Published in: Journal of pineal research p. e12671
• Main Authors: Posa, Luca, Lopez-Canul, Martha, Rullo, Laura, De Gregorio, Danilo, Dominguez-Lopez, Sergio, Aboud, Matthew Kaba, Felicia Caputi, Francesca, Candeletti, Sanzio, Romualdi, Patrizia, Gobbi, Gabriella
• Format: Journal Article
• Language: English
• Published: England 19-05-2020
• Subjects: Pain; knockout mice; MT1 receptor; melatonin; MT2 receptor
• ISSN: 1600-079X

Melatonin, a neurohormone that binds to two G-protein coupled receptors MT
and MT
is involved in pain regulation, but the distinct role of each receptor has yet to be defined. We characterized the nociceptive responses of mice with genetic inactivation of MT
(MT
), or MT
(MT
), or both MT
/MT
(MT
/MT
) receptors in the hot plate test (HPT), and the formalin test (FT). In HPT and FT, MT
display no differences compared to their wildtype littermates (CTL), whereas both MT
and MT
/MT
mice showed a reduced thermal sensitivity as well as a decreased tonic nocifensive behavior during phase 2 of the FT in the light phase. The MT
partial agonist UCM924 induced an antinociceptive effect in MT
but not in MT
and MT
/MT
mice. Also, the competitive opioid antagonist naloxone had no effects in CTL, whereas it induced a decrease of nociceptive thresholds in MT
mice. Our results show that the genetic inactivation of MT
, but not MT
receptors, produces a distinct effect on nociceptive threshold, suggesting that the MT
melatonin receptor subtype is selectively involved in the regulation of pain responses.