Neurochemical and morphological evidence of an antinociceptive neural pathway from nucleus raphe dorsalis to nucleus accumbens in the rabbit.
Previous studies using a pharmacological approach suggested a neural pathway emanating from the periaqueductal gray (PAG) to the nucleus accumbens relevant to antinociception. This was investigated with neurochemical and histochemical methods in the present study. Push-pull perfusion and radioimmunoassay were used to measure the release of immunoreactive-(ir) enkephalin (ir-ENK) and ir-beta-endorphin (ir-beta-EP) in the nucleus accumbens after microinjection of morphine into the PAG and the nucleus raphe dorsalis (NRD) of the rabbit. Morphine administration elicited an increase in ir-ENK and ir-beta-EP in the nucleus accumbens. Horseradish peroxidase (HRP) retrograde tracing in combination with 5-hydroxytryptamine (5-HT) immunocytochemistry revealed a serotonergic projection from the NRD and ventral PAG to the nucleus accumbens in the rabbit. About 7% of the serotonin-positive cells in the NRD and ventral PAG send fibers directly to the nucleus accumbens, with an ipsilateral dominance. These results indicate the existence of a serotonergic pathway from the NRD to the N. accumbens involved in opioid analgesia.
Ma
Q P
QP
Department of Physiology, Beijing Medical University, China.
Han
J S
JS
D000818:Animals; D001923:Brain Chemistry / Q000187:drug effects*; D004745:Enkephalins / Q000378:metabolism; D006735:Horseradish Peroxidase; D007150:Immunohistochemistry; D007267:Injections; D008297:Male; D009020:Morphine / Q000008:administration & dosage / Q000494:pharmacology; D009434:Neural Pathways / Q000166:cytology / Q000502:physiology*; D009619:Nociceptors / Q000502:physiology*; D009714:Nucleus Accumbens / Q000033:anatomy & histology / Q000166:cytology / Q000502:physiology*; D010487:Periaqueductal Gray; D011817:Rabbits; D011863:Radioimmunoassay; D011903:Raphe Nuclei / Q000033:anatomy & histology / Q000166:cytology / Q000502:physiology*; D012701:Serotonin / Q000502:physiology; D001615:beta-Endorphin / Q000378:metabolism
D004745:Enkephalins; D012701:Serotonin; D001615:beta-Endorphin; D009020:Morphine; D006735:Horseradish Peroxidase