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, using retrograde tracing and immunocytochemistry in adult rats, we provide evidence that the delta opioid receptor is located on boutons that are presynaptic to both catecholaminergic and non-catecholaminergic neurons that project to the spinal cord. We suggest that the sympathoinhibitory action of delta opioid receptor activation in the rostral ventrolateral medulla is mediated presynaptically, resulting in a reduction of excitatory neurotransmitter release from boutons that appose sympathoexcitatory bulbospinal neurons. (C) 2000 Lippincott Williams and Wilkins.
- Opioid receptor
- Phenylethanolamine- N-methyltransferase
- Presympathetic neurons
- Retrograde tracing
- Rostral ventrolateral medulla