Differential regulation of brown adipose and splanchnic sympathetic outflows in rat: Roles of raphe and rostral ventrolateral medulla neurons

Shaun F. Morrison

Research output: Contribution to journalArticlepeer-review

33 Scopus citations


1. The medullary premotor neurons determining the sympathetic outflow regulating cardiac function and vasoconstriction are located in the rostral ventrolateral medulla (RVLM). The present study sought evidence for an alternative location for the sympathetic premotor neurons determining the sympathetic nerve activity (SNA) controlling brown adipose tissue (BAT) metabolism and thermogenesis. 2. The tonic discharge on sympathetic nerves is determined by the inputs to functionally specific sympathetic preganglionic neurons from supraspinal populations of premotor neurons. Under normothermic conditions, BAT SNA was nearly silent, while splanchnic (SPL) SNA, controlling mesenteric vasoconstriction, exhibited sustained large-amplitude bursts. 3. The rostral raphe pallidus (RPa) contains potential sympathetic premotor neurons that project to the region of sympathetic preganglionic neurons in the thoracic spinal cord. Disinhibition of neurons in RPa elicited a dramatic increase in BAT SNA, with only a small rise in SPL SNA. 4. Splanchnic SNA was strongly influenced by the baro-receptor reflex, as indicated by a high coherence with the arterial pressure wave, a significant amplitude modulation over the time-course of the cardiac cycle and a marked inhibition of SPL SNA during a sustained increase in arterial pressure. When acti- vated, the bursts in BAT SNA exhibited no correlation with arte- rial pressure and were not affected by increases in arterial pressure. 5. Because these characteristics and reflex responses in sympathetic outflow have been shown to arise from the on-going or altered discharge of sympathetic premotor neurons, the marked differences between SPL and BAT SNA provide strong evidence supporting the hypothesis that vasoconstriction and thermogenesis (metabolism) are controlled by distinct populations of sympathetic premotor neurons, the former in the RVLM and the latter, potentially, in the RPa.

Original languageEnglish (US)
Pages (from-to)138-143
Number of pages6
JournalClinical and Experimental Pharmacology and Physiology
Issue number1-2
StatePublished - 2001
Externally publishedYes


  • Baroreceptor reflex
  • Brown adipose tissue
  • Frequency domain
  • GABA inhibition
  • Hypothermia
  • Raphe pallidus
  • Rostral ventrolateral medulla
  • Sympathetic nerve activity
  • Thermogenesis
  • Vasoconstriction

ASJC Scopus subject areas

  • Physiology
  • Pharmacology
  • Physiology (medical)


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