title: Activity correlations between on-like and off-like cells of the rostral ventromedial medulla and simultaneously recorded wide-dynamic-range neurons of the spinal dorsal horn in rats.
abstract: Considerable evidence supports the notion that on- and off-cells of the rostral ventromedial medulla (RVM) facilitate and depress, respectively, spinal nociceptive transmission. This notion stems from a covariation of on- or off-cell activities and spinal nocifensive reflexes. Such covariation could theoretically be due to their independently responding to a common source, or to an RVM-derived modulation of ventral horn neurons. Here, we tested whether on- and off-cells indeed modulate spinal nociceptive neurons. In deeply anesthetized rats, unitary recordings were simultaneously made from an RVM on-like or off-like cell and a spinal nociceptive neuron that shared a receptive field (RF) at a hind paw. Action potential firing in RVM/spinal neuron pairs was highly correlated, positively for on-like cells and negatively for off-like cells, both during ongoing activity and during application of calibrated noxious pressure to the RF. Microinjection of morphine into RVM induced a correlated decrease in on-like cell/spinal neuron ongoing activity and response to noxious stimulation. RVM morphine induced changes in off-like cell activity that were not correlated with spinal neuronal activity. These results suggest that on-cells exert a positive modulation upon spinal nociceptive neurons, upstream to ventral horn circuits and plausibly at the origin of nociceptive information that eventually reaches the cerebral cortex. On-cells may in this manner contribute to inflammation- and neuropathy-induced increases in withdrawal reflexes. Most significantly, on-cell modulation of nociceptive neurons may be a key factor in clinical pain conditions such as hyperalgesia and allodynia.
authors.affiliation: Catedra de Fisiologia, Escuela de Bioanalisis, Facultad de Medicina, Universidad Central de Venezuela, Apartado 9995, Caracas 1050, Venezuela. Electronic address: rafaelsalas_47@yahoo.com.
authors.forename: Rafael
authors.initials: R
authors.lastname: Salas
authors.affiliation: Laboratorio de Neurofisiologia, Centro de Biofisica y Bioquimica, Instituto Venezolano de Investigaciones Cientificas (IVIC), Apartado 20632, Caracas 1020-A, Venezuela. Electronic address: karlaramirez15@gmail.com.
authors.forename: Karla
authors.initials: K
authors.lastname: Ramirez
authors.affiliation: Laboratorio de Neurofisiologia, Centro de Biofisica y Bioquimica, Instituto Venezolano de Investigaciones Cientificas (IVIC), Apartado 20632, Caracas 1020-A, Venezuela. Electronic address: horaciovan@gmail.com.
authors.forename: Horacio
authors.initials: H
authors.lastname: Vanegas
authors.affiliation: Laboratorio de Neurofisiologia, Centro de Biofisica y Bioquimica, Instituto Venezolano de Investigaciones Cientificas (IVIC), Apartado 20632, Caracas 1020-A, Venezuela. Electronic address: enriquevr@yahoo.com.
authors.forename: Enrique
authors.initials: E
authors.lastname: Vazquez
mesh_terms: D000200:Action Potentials; D000701:Analgesics, Opioid / Q000494:pharmacology; D000758:Anesthesia; D000818:Animals; D006614:Hindlimb / Q000502:physiology; D008159:Lumbar Vertebrae; D008297:Male; D008526:Medulla Oblongata / Q000187:drug effects / Q000502:physiology*; D008839:Microelectrodes; D008845:Microinjections; D009020:Morphine / Q000494:pharmacology; D009434:Neural Pathways / Q000187:drug effects / Q000502:physiology; D059225:Nociception / Q000187:drug effects / Q000502:physiology; D009619:Nociceptors / Q000502:physiology*; D020671:Posterior Horn Cells / Q000502:physiology*; D011312:Pressure; D017207:Rats, Sprague-Dawley; D013997:Time Factors
chemical_list: D000701:Analgesics, Opioid; D009020:Morphine
keywords: Descending pain facilitation; RVM off-cell; RVM on-cell; Spinal nociceptive neuron