THE EFFECTS OF REPEATED MORPHINE EXPOSURE ON METABOTROPIC GLUTAMATE RECEPTOR ACTIVITY IN ADOLESCENT MICE
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Adolescent mice exhibit marked changes in D2/D3 dopamine receptor activity following administration of certain opioids. Thus, the present study examined whether repeated exposure to morphine would also modulate the activity of metabotropic glutamate receptors (mGluRs) in the dorsal striatum of adolescents. Administration of a group I-specific mGluR agonist, S-3,5-dihydroxyphenylglycine (DHPG), induces face-washing behavior in adolescent mice. Since this behavioral effect has been shown to be mediated by mGluR1, this behavior was used as an indicator of mGluR1 activity in the dorsal striatum. Adolescent mice (n= 9-13 per group) were first examined for their behavioral response to unilateral administration of DHPG directly into the dorsal striatum. Morphine (20 mg/kg, s.c.) was then administered once daily for 6 days. The response to DHPG was re-examined at one of three times, i.e., 2, 4, or 24 hours following administration of the final dose of morphine. At 2 hours following administration of the last morphine dose, mice showed a significant decrease in response to DHPG (i.e. duration of face-washing behavior) relative to their pre-morphine response. At 4 and 24 hours following administration of the last morphine dose, no difference in response to DHPG administration was observed relative to their response prior to morphine administration. This suggests that repeated morphine administration causes a decrease in mGluR1 activity in the dorsal striatum of adolescent mice, which could affect long-term neural activity. Future studies will examine long-term effects of repeated morphine exposure in adolescent mice, as well as the possibility of differential effects by various opioids. Additionally, the effects of repeated morphine exposure on mGluR signaling should be also examined in adults.
Seloff, Katelyn Elizabeth (2013). THE EFFECTS OF REPEATED MORPHINE EXPOSURE ON METABOTROPIC GLUTAMATE RECEPTOR ACTIVITY IN ADOLESCENT MICE. Honors and Undergraduate Research. Available electronically from