Seasonal variations in mu opiate receptor signaling in the nervous system of the blue mussel, Mytilus edulis: temperature controls physiological processes
Keywords:nitric oxide, mu opiate receptor, morphine
It is anticipated that invertebrate processes will be subject to seasonal variations because of their poikilothermal characteristics. In the present study we determined if the morphine coupled nitric oxide (NO) release, which is constitutive in nature, exhibits seasonal characteristics, which has previously been shown for catecholamine processes in the marine mollusc Mytilus edulis. In this regard, morphine induced NO release measured on a monthly basis for one year revealed a peak release value (39 ± 4 nM) during the late spring and early summer. The lowest NO release occurred during the months of January (6.0 ± 0.5 nM) through March (6.5 ± 1.1 nM). The lowest sea surface temperatures (1.3 °C) were also recorded in these same three winter months in New York. Relative mu opiate receptor gene expression was assessed by real time PCR during these seasons. The mRNA expression reached a relative peak during the month of June and was at its lowest in February and March, further demonstrating the direct coupling of morphine with this receptor. We conclude that the temperature an animal is chronically exposed to serves to control cellular processes, i.e., opiate signaling.