Identification of sympathetic premotor neurons mediating fever and thermoregulation in the rostral ventromedial medulla

Abstract

The rostral ventromedial medulla (RVMM) sympathetically regulates thermogenesis in brown adipose tissue (BAT) and constriction of skin blood vessels. However, the sympathetic-related neurons in the RVMM remain to be identified. First, we found that vesicular glutamate transporter 3 (VGLUT3) -immunoreactive neurons in the rostral raphe pallidus nucleus and raphe magnus nucleus expressed Fos in response to both fever-inducing stimulus (central injection of prostaglandin E₂) and cold-exposure (4°C, 4 hours) in rats. Most of the VGLUT3-expressing neurons were negative for serotonin immunoreactivity, and many of them were labeled trans-synaptically with pseudorabies virus inoculated into rat interscapular BAT or tail. Furthermore, we found that the VGLUT3-positive neurons directly project onto sympathetic preganglionic neurons in the intermediolateral cell column (IML) of the spinal cord; and that VGLUT3-positive axon terminals in the IML formed asymmetric synapses, suggesting the excitatory characteristics of the synapses. These results suggest that the rostral medullary raphe regions contain glutamatergic neurons that could be categorized as a novel group of sympathetic premotor neurons involved in fever induction and thermoregulation. [Jpn J Physiol 54 Suppl:S196 (2004)]