Raphe obscurus neurons participate in thermoregulation in rats

Abstract

The thermoregulatory mechanism constitutes a complex and integrated system. The "main controller" is the hypothalamus, which comprises many different sub-areas; it receives inputs either from temperature sensitive neurons within the hypothalamus itself to monitor core temperature or from receptors in the skin which monitor the changes in external temperature. Nevertheless, the final drive or command to the vascular smooth muscle is not controlled by the hypothalamus but by a complex neuronal circuitry that comprises brainstem and spinal cord nuclei 1 .In rats, non-evaporative heat loss occurs mainly through the tail 2 , the blood vessels vasodilate when the hypothalamic preoptic area is warmed 3 . The efferent signals for this response originate in heat-sensitive neurons, and the descending pathway passes through the medial forebrain bundle 4 . Blood flow to the rat tail is determined by the level of activity in its sympathetic postganglionic vasoconstrictor fibers 5 . These are supplied by preganglionic sympathetic neurons situated mainly in the intermediolateral cell column of the first and second lumbar segments 6,7 . ABSTRACTIn mammalian, several evidences suggest that central serotonin participates in thermoregulation. Nucleus raphe obscurus (NRO), a serotonergic nucleus, has been recognized to be the source of generation of various hemodynamic patterns in different behavioral conditions, but its involvement in thermoregulation is unclear. In the present study, extracellular action potentials of NRO neurons were recorded in anesthetized rats, which were submitted to cold and warm stimuli in the tail. The firing rate of the neurons was compared before and after each stimulation. It was found that 59% of the neurons submitted to a cold stimulus trial had a significant increase in their firing frequency, while 48% of the neurons submitted to warm stimulation trial were inhibited. The opposite responses in neuronal activity of NRO units to cooling or heating suggest that these cells are involved in producing the homoeothermic vascular adaptations secondary to changes in cutaneous temperature in the rat tail.Key words: nucleus raphe obscurus, serotonin, serotonergic neurons. RESUMOA termorregulação em mamíferos envolve a participação da serotonina. O núcleo obscuro da rafe (NRO), que é serotoninérgico, participa do controle autonômico, mas seu envolvimento na termorregulação é incerto. Neste estudo, registramos potenciais de ação extracelulares de neurônios do NRO em ratos anestesiados nos quais a cauda foi submetida a estímulos de calor ou frio. A frequência de disparo dos neurônios foi comparada antes e depois dos estímulos. O grupo controle não apresentou modificação da frequência de disparo, enquanto que 59% dos neurônios registrados em animais submetidos a estímulo de frio tiveram sua frequência aumentada. Por outro lado, 48% dos animais submetidos a estímulo de calor tiveram sua frequência de disparo diminuída. As respostas opostas da frequência de disparo em neurônios de animais submetidos à estimulação...

Separate and shared sympathetic outflow to white and brown fat coordinately regulates thermoregulation and beige adipocyte recruitment

“…RPa neurons are necessary for adaptive thermoregulation during cold exposure including populations of thyrotropin-releasing hormone neurons, which have been shown to be activated during 24-h cold exposure (13,15,47,52). The ROb contains serotonergic neurons that increase firing with a cold stimulus, but are inhibited by a warm one (66). The thermoregulatory role of the A5 region has not been fully tested as the raphe, but it contains noradrenergic neurons that have frequently been labeled in tract tracing studies from fat (2,3,44,50,58,59,63,64).…”

5-HT Receptors and Temperature Homeostasis

“…This is indirectly evidenced by electrophysiological studies of brain neurons. Thus, it was found that the majority of raphe obscurus thermosensitive 5-HT neurons decrease the frequency of their discharges upon exposure to heat and increase it upon cooling (2/3 and 3/4 of neurons, respectively) [ 133 ]. Nason and Mason [ 134 ] in the medullary raphe also observed increased discharge of the cells, which they identified as 5-HT ones, in response to cold.…”