title: Parabrachial complex links pain transmission to descending pain modulation.
abstract: The rostral ventromedial medulla (RVM) has a well-documented role in pain modulation and exerts antinociceptive and pronociceptive influences mediated by 2 distinct classes of neurons, OFF-cells and ON-cells. OFF-cells are defined by a sudden pause in firing in response to nociceptive inputs, whereas ON-cells are characterized by a "burst" of activity. Although these reflex-related changes in ON- and OFF-cell firing are critical to their pain-modulating function, the pathways mediating these responses have not been identified. The present experiments were designed to test the hypothesis that nociceptive input to the RVM is relayed through the parabrachial complex (PB). In electrophysiological studies, ON- and OFF-cells were recorded in the RVM of lightly anesthetized male rats before and after an infusion of lidocaine or muscimol into PB. The ON-cell burst and OFF-cell pause evoked by noxious heat or mechanical probing were substantially attenuated by inactivation of the lateral, but not medial, parabrachial area. Retrograde tracing studies showed that neurons projecting to the RVM were scattered throughout PB. Few of these neurons expressed calcitonin gene-related peptide, suggesting that the RVM projection from PB is distinct from that to the amygdala. These data show that a substantial component of "bottom-up" nociceptive drive to RVM pain-modulating neurons is relayed through the PB. While the PB is well known as an important relay for ascending nociceptive information, its functional connection with the RVM allows the spinoparabrachial pathway to access descending control systems as part of a recurrent circuit.
authors.affiliation: Departments of Neurological Surgery and.
authors.forename: Zachary
authors.initials: Z
authors.lastname: Roeder
authors.affiliation: Departments of Neurological Surgery and.
authors.forename: QiLiang
authors.initials: Q
authors.lastname: Chen
authors.affiliation: Departments of Neurological Surgery and.
authors.forename: Sophia
authors.initials: S
authors.lastname: Davis
authors.affiliation: Departments of Neurological Surgery and.
authors.forename: Jonathan D
authors.initials: JD
authors.lastname: Carlson
authors.affiliation: Departments of Neurological Surgery and.
authors.forename: Domenico
authors.initials: D
authors.lastname: Tupone
authors.affiliation: Departments of Neurological Surgery and.|Behavioral Neuroscience, Oregon Health & Science University, Portland, OR, USA.
authors.forename: Mary M
authors.initials: MM
authors.lastname: Heinricher
mesh_terms: D000200:Action Potentials / Q000187:drug effects; D000779:Anesthetics, Local / Q000627:therapeutic use; D000818:Animals; D015740:Calcitonin Gene-Related Peptide / Q000378:metabolism; D058785:GABA-A Receptor Agonists / Q000494:pharmacology; D006358:Hot Temperature / Q000009:adverse effects; D008012:Lidocaine / Q000494:pharmacology; D008297:Male; D008526:Medulla Oblongata / Q000166:cytology* / Q000378:metabolism; D008845:Microinjections; D009118:Muscimol / Q000494:pharmacology; D009434:Neural Pathways / Q000187:drug effects / Q000502:physiology*; D009619:Nociceptors / Q000145:classification / Q000187:drug effects / Q000502:physiology*; D010146:Pain / Q000188:drug therapy / Q000209:etiology / Q000473:pathology*; D010147:Pain Measurement; D065823:Parabrachial Nucleus / Q000502:physiology*; D010812:Physical Stimulation / Q000009:adverse effects; D051381:Rats; D017207:Rats, Sprague-Dawley; D017208:Rats, Wistar
chemical_list: D000779:Anesthetics, Local; D058785:GABA-A Receptor Agonists; D009118:Muscimol; D008012:Lidocaine; D015740:Calcitonin Gene-Related Peptide