Efferent projection from the preoptic area for the control of non‐shivering thermogenesis in rats

Abstract

To investigate the characteristics of efferent projections from the preoptic area for the control of non‐shivering thermogenesis, we tested the effects of thermal or chemical stimulation, and transections of the preoptic area on the activity of interscapular brown adipose tissue in cold‐acclimated and non‐acclimated anaesthetized rats. Electrical stimulation of the ventromedial hypothalamic nucleus (VMH) elicited non‐shivering thermogenesis in the brown adipose tissue (BAT); warming the preoptic area to 41.5 °C completely suppressed the thermogenic response. Injections of d,l‐homocysteic acid (DLH; 0.5 mm, 0.3 μl) into the preoptic area also significantly attenuated BAT thermogenesis, whereas injections of control vehicle had no effect. Transections of the whole hypothalamus in the coronal plane at the level of the paraventricular nucleus induced rapid and large rises in BAT and rectal temperatures. This response was not blocked by pretreatment with indomethacin. The high rectal and BAT temperatures were sustained more than 1 h, till the end of the experiment. Bilateral knife cuts that included the medial forebrain bundle but not the paraventricular nuclei elicited similar rises in BAT and rectal temperatures. Medial knife cuts had no effect. These results suggest that warm‐sensitive neurones in the preoptic area contribute a larger efferent signal for non‐shivering thermogenesis than do cold‐sensitive neurones, and that the preoptic area contributes a tonic inhibitory input to loci involved with non‐shivering thermogenesis. This efferent inhibitory signal passes via lateral, but not medial, hypothalamic pathways.

Identification of Sympathetic Premotor Neurons in Medullary Raphe Regions Mediating Fever and Other Thermoregulatory Functions

“…In addition, another pathway through the dorsomedial hypothalamic nucleus was also proposed to transmit POA-derived pyrogenic PGE 2 signals . Other reports showed that warming of the POA abolished BAT thermogenesis evoked by stimulation of a hypothalamic region (Chen et al, 1998) and that this inhibitory effect by POA warming was antagonized by bicuculline injection into the raphe pallidus nucleus (Taniguchi et al, 2003). These findings suggest that the pyrogenic and heat-gain signals from the POA are conveyed to rostral medullary raphe regions and activate VGLUT3-expressing neurons therein.…”

“…Thus, PGE 2 is considered to act on the EP3 receptor of POA neurons and trigger fever. The POA is also known as one of the major central thermosensitive sites to monitor deep body temperature: cooling of this region causes nonshivering thermogenesis (Banet et al, 1978;Imai-Matsumura et al, 1984), possibly as a result of suppression of warmsensitive neurons (Chen et al, 1998).…”

Preoptic–Raphé Connections for Thermoregulatory Vasomotor Control

“…The currently accepted model of thermoregulation is that both heat production and heat loss are under tonic inhibitory control by warm-sensitive preoptic neurons (Zhang et al, 1995;Chen et al, 1998;Nagashima et al, 2000;Osaka, 2004;Rathner et al, 2008;Tanaka et al, 2009), with those regulating heat production projecting to the DMH and those regulating heat dissipation projecting directly to the medullary raphé (Nakamura and Morrison, 2007;Morrison et al, 2008;Rathner et al, 2008). No significant output from the preoptic region has been attributed to coldsensitive cells.…”

Sympathetic nervous system control of triglyceride metabolism: novel concepts derived from recent studies

“…Cooling of this area activates BAT ( 62,63 ), whereas warming suppresses its activity ( 64 ). The signal is mediated through the VMH and medulla oblongata and then passes through the spinal cord until it reaches the relevant IML neurons ( 65 ).…”