Stress potentiation of morphine-induced dopamine efflux in the nucleus accumbens shell is dependent upon stressor uncontrollability and is mediated by the dorsal raphe nucleus.
A single session of uncontrollable (inescapable tailshock, IS), but not controllable (escapable tailshock, ES), stress is known to selectively potentiate subsequent morphine-conditioned place preference in a dorsal raphe nucleus (DRN) serotonin (5-HT) dependent manner. Here, in vivo microdialysis is used to test the hypothesis that prior IS, but not ES, will potentiate morphine-induced dopamine (DA) efflux in the nucleus accumbens (NAc) shell and that this will occur by a pathway involving DRN 5-HT neurons. Male Sprague-Dawley rats were exposed to yoked IS, ES, or no stress. Twenty-four hours later, morphine (3 mg/kg s.c.) or saline was administered during microdialysis. As predicted, prior IS selectively potentiated morphine-induced DA, but not 5-HT, efflux in the NAc. This potentiation was due to morphine's action in the DRN because it was blocked by intra-DRN microinjection of the opioid antagonist naltrexone (10 microg). IS potentiation of morphine-induced DA efflux in the NAc was also dependent upon activation of 5-HT neurons in the DRN because it was blocked by intra-DRN microinjection of the 5-HT1A autoreceptor agonist 8-hydroxy-2-di-n-(propylamino)-tetralin (1 microg). No effect of IS was found on morphine-induced 5-HT or DA efflux in the ventral tegmental area. These results suggest a neural substrate for stress potentiation of morphine reward involving 5-HT neurotransmission in the DRN.
Bland
S T
ST
Department of Psychology and Center for Neuroscience, Campus Box 345, University of Colorado, Boulder, CO 80309-0345, USA. sondra.bland@colorado.edu
Twining
C
C
Schmid
M J
MJ
Der-Avakian
A
A
Watkins
L R
LR
Maier
S F
SF
D000818:Animals; D002851:Chromatography, High Pressure Liquid; D004298:Dopamine / Q000378:metabolism*; D004597:Electroshock; D007276:Injections, Intraventricular; D008297:Male; D017551:Microdialysis; D009020:Morphine / Q000494:pharmacology*; D009270:Naloxone / Q000008:administration & dosage; D009292:Narcotic Antagonists / Q000008:administration & dosage; D009294:Narcotics / Q000494:pharmacology*; D009434:Neural Pathways / Q000187:drug effects / Q000502:physiology; D009714:Nucleus Accumbens / Q000187:drug effects / Q000378:metabolism*; D011903:Raphe Nuclei / Q000187:drug effects / Q000378:metabolism*; D051381:Rats; D017207:Rats, Sprague-Dawley; D012701:Serotonin / Q000378:metabolism; D013315:Stress, Psychological
D009292:Narcotic Antagonists; D009294:Narcotics; D012701:Serotonin; D009270:Naloxone; D009020:Morphine; D004298:Dopamine