title: "On-" and "off-" cells in the rostral ventromedial medulla of rats held in thermoneutral conditions: are they involved in thermoregulation?
abstract: In thermal neutral condition, rats display cyclic variations of the vasomotion of the tail and paws, synchronized with fluctuations of blood pressure, heart rate, and core body temperature. "On-" and "off-" cells located in the rostral ventromedial medulla, a cerebral structure implicated in somatic sympathetic drive, 1) exhibit similar spontaneous cyclic activities in antiphase and 2) are activated and inhibited by thermal nociceptive stimuli, respectively. We aimed at evaluating the implication of such neurons in autonomic regulation by establishing correlations between their firing and blood pressure, heart rate, and skin and core body temperature variations. When, during a cycle, a relative high core body temperature was reached, the on-cells were activated and within half a minute, the off-cells and blood pressure were depressed, followed by heart rate depression within a further minute; vasodilatation of the tail followed invariably within ∼3 min, often completed with vasodilatation of hind paws. The outcome was an increased heat loss that lessened the core body temperature. When the decrease of core body temperature achieved a few tenths of degrees, sympathetic activation switches off and converse variations occurred, providing cycles of three to seven periods/h. On- and off-cell activities were correlated with inhibition and activation of the sympathetic system, respectively. The temporal sequence of events was as follows: core body temperature → on-cell → off-cell ∼ blood pressure → heart rate → skin temperature → core body temperature. The function of on- and off-cells in nociception should be reexamined, taking into account their correlation with autonomic regulations.
authors.affiliation: Sorbonne Universités, Université Pierre et Marie Curie, Université Paris 06, Faculté de Médecine, Paris, France; and Neurosciences Paris-Seine, Institut National de la Santé et de la Recherche Médicale UMRS-1130, Centre National de la Recherche Scientifique UMR-8246, Paris, France.
authors.forename: Nabil
authors.initials: N
authors.lastname: El Bitar
authors.affiliation: Sorbonne Universités, Université Pierre et Marie Curie, Université Paris 06, Faculté de Médecine, Paris, France; and Neurosciences Paris-Seine, Institut National de la Santé et de la Recherche Médicale UMRS-1130, Centre National de la Recherche Scientifique UMR-8246, Paris, France.
authors.forename: Bernard
authors.initials: B
authors.lastname: Pollin
authors.affiliation: Sorbonne Universités, Université Pierre et Marie Curie, Université Paris 06, Faculté de Médecine, Paris, France; and Neurosciences Paris-Seine, Institut National de la Santé et de la Recherche Médicale UMRS-1130, Centre National de la Recherche Scientifique UMR-8246, Paris, France daniel.le_bars@upmc.fr.
authors.forename: Daniel
authors.initials: D
authors.lastname: Le Bars
mesh_terms: D000818:Animals; D001794:Blood Pressure; D001833:Body Temperature Regulation; D006339:Heart Rate; D008297:Male; D008526:Medulla Oblongata / Q000166:cytology / Q000502:physiology*; D009474:Neurons / Q000502:physiology*; D051381:Rats; D017207:Rats, Sprague-Dawley; D013564:Sympathetic Nervous System / Q000502:physiology; D014666:Vasomotor System / Q000502:physiology
keywords: blood pressure variability; pain modulation; rostral medullary raphe; rostral ventromedial medulla; thermoregulation