Delta opioid receptor immunoreactive boutons appose bulbospinal CI neuronsin the rat

Bulbospinal sympathoexcitatory neurons in the rostral ventrolateral medulla are inhibited by activation of delta opioid receptors. However, it is not known whether this opioidergic effect is pre- or post- synaptic. Here, usin g retrograde tracing and immunocytochemistry in adult rats, we provide evid ence that the delta opioid receptor is located on boutons that are presynap tic to both catecholaminergic and non-catecholaminergic neurons that projec t to the spinal cord. We suggest that the sympathoinhibitory action of delt a opioid receptor activation in the rostral ventrolateral medulla is mediat ed presynaptically, resulting in a reduction of excitatory neurotransmitter release from boutons that appose sympathoexcitatory bulbospinal neurons. N euroReport 11:887-891 (C) 2000 Lippincott Williams & Wilkins.