Opioid Signalling In The Rat Rostral Ventrolateral Medulla

Authors

  • Patrice G Guyenet,

    1. * Department of Pharmacology, University of Virginia School of Medicine, Charlottesville, Virginia, Department of Anatomy and Neurobiology, University of Maryland School of Medicine, Baltimore, Maryland, Neurological Sciences Institute, Oregon Health Sciences University, Portland, Oregon, USA and § Department of Medicine, Flinders University, Bedford Park, South Australia, Australia.
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  • Ruth L Stornetta,

    1. * Department of Pharmacology, University of Virginia School of Medicine, Charlottesville, Virginia, Department of Anatomy and Neurobiology, University of Maryland School of Medicine, Baltimore, Maryland, Neurological Sciences Institute, Oregon Health Sciences University, Portland, Oregon, USA and § Department of Medicine, Flinders University, Bedford Park, South Australia, Australia.
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  • Ann M Schreihofer,

    1. * Department of Pharmacology, University of Virginia School of Medicine, Charlottesville, Virginia, Department of Anatomy and Neurobiology, University of Maryland School of Medicine, Baltimore, Maryland, Neurological Sciences Institute, Oregon Health Sciences University, Portland, Oregon, USA and § Department of Medicine, Flinders University, Bedford Park, South Australia, Australia.
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  • Nicole M Pelaez,

    1. * Department of Pharmacology, University of Virginia School of Medicine, Charlottesville, Virginia, Department of Anatomy and Neurobiology, University of Maryland School of Medicine, Baltimore, Maryland, Neurological Sciences Institute, Oregon Health Sciences University, Portland, Oregon, USA and § Department of Medicine, Flinders University, Bedford Park, South Australia, Australia.
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  • Abdallah Hayar,

    1. * Department of Pharmacology, University of Virginia School of Medicine, Charlottesville, Virginia, Department of Anatomy and Neurobiology, University of Maryland School of Medicine, Baltimore, Maryland, Neurological Sciences Institute, Oregon Health Sciences University, Portland, Oregon, USA and § Department of Medicine, Flinders University, Bedford Park, South Australia, Australia.
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  • Sue Aicher,

    1. * Department of Pharmacology, University of Virginia School of Medicine, Charlottesville, Virginia, Department of Anatomy and Neurobiology, University of Maryland School of Medicine, Baltimore, Maryland, Neurological Sciences Institute, Oregon Health Sciences University, Portland, Oregon, USA and § Department of Medicine, Flinders University, Bedford Park, South Australia, Australia.
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  • Ida J Llewellyn-Smith

    1. * Department of Pharmacology, University of Virginia School of Medicine, Charlottesville, Virginia, Department of Anatomy and Neurobiology, University of Maryland School of Medicine, Baltimore, Maryland, Neurological Sciences Institute, Oregon Health Sciences University, Portland, Oregon, USA and § Department of Medicine, Flinders University, Bedford Park, South Australia, Australia.
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  • Presented at the Experimental Biology Symposium Autonomic and Cardiovascular Regulation: Focus on Nociceptin and Opioid Peptides, Orlando, Florida, USA, March/April 2001.

Dr Patrice G Guyenet, University of Virginia Health System, PO Box 800735, 1300 Jefferson Park Avenue, Charlottesville, VA 22908-0735, USA. Email: pgg@virginia.edu

SUMMARY

1. The present article reviews several aspects of opioid signalling in the rostral ventrolateral medulla (RVLM) and their implications for the neural control of blood pressure.

2. In the RVLM, preproenkephalin (PPE) mRNA is expressed by bulbospinal cells that are strongly barosensitive. These putative presympathetic neurons includes C1 and non-C1 neurons.

3. In the RVLM, PPE mRNA is also present in GABAergic neurons that do not project to the thoracic spinal cord.

4. Rostral ventrolateral medulla presympathetic cells receive enkephalinergic inputs and express μ-opioid receptors (MOR). Some of their synaptic inputs also contain MOR.

5. Pre- and post-synaptic modulation of RVLM presympathetic neurons by MOR agonists has been demonstrated in slices of neonate brain. The post-synaptic effect is inhibitory (increased gK). Presynaptic effects include disfacilitation (reduction of glutamate release) and possibly dishinhibition (reduction of GABA release).

6. In conclusion, opioid signalling plays a pervasive role in the medullospinal network that controls sympathetic tone and arterial pressure. Opioid peptides are made by the presympathetic, presumably excitatory, cells of the RVLM and by local GABAergic inhibitory neurons. In addition, RVLM presympathetic neurons are also controlled by opioid peptides at the pre- and post-synaptic level. μ-Opioid receptors are found post-synaptically, whereas presynaptic receptors probably include both μ and δ subtypes. Conditions that trigger the release of opioid peptides by presympathetic neurons or by inputs to these cells are not fully understood and may include decompensated haemorrhage and certain types of peripheral sensory stimulation related to acupuncture.

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