Reduced Rearing Temperature Augments Responses in Sympathetic Outflow to Brown Adipose Tissue

Abstract

Sympathetic outflow to brown adipose tissue (BAT) contributes to both thermoregulation and energy expenditure in rats through regulation of BAT thermogenesis. Acute cold exposure in mature animals augments BAT thermogenesis; however, the enhanced BAT thermogenic response returns to normal shortly after cessation of the cold exposure. In this study, we sought to determine whether cold exposure in early neonatal life could induce enhanced responses in the sympathetic outflow to BAT and whether this altered sympathetic regulation would be sustained after the cold stimulus was removed. BAT sympathetic nerve activity (SNA) was recorded in urethane-chloraloseanesthetized, artificially ventilated rats that were raised from birth in either 18 or 30°C environments and then, at 8 weeks of age, were maintained in 23°C for at least 4 weeks. An acute hypothermic stimulus, disinhibition of a brainstem thermogenic network in the raphe pallidus, or electrical stimulation in this raphe site produced increases in BAT SNA that were twice as great in rats reared at 18°C as in those reared at 30°C. The norepinephrine content of the interscapular BAT (IBAT) and the number of sympathetic ganglion cells projecting to interscapular BAT were 70% greater in the 18°C-reared rats. We conclude that neonatal exposure to a cold environment induces a permanent developmental alteration in the capacity for sympathetic stimulation of BAT thermogenesis that may be mediated, in part, by a greater number of sympathetic ganglion cells innervating BAT in coldreared animals.

Arousal from hibernation and BAT thermogenesis against cold: central mechanism and molecular basis

“…Recent observations by Shibata and co-workers demonstrate the involvement of neurons in the inferior olive (IO) in the CNS circuit controlling BAT function in anesthetized rats Uno and Shibata, 2001). These workers showed that the increase in BAT temperature induced by removal (Morrison, 1999a;Morrison et al, 1999b;Morrison et al, 2000;Morrison, 2001). …”

Effects of litter size on sympathetic activity in young adult rats

“…The sympathoadrenal system is also susceptible to environmental influences during development. For example, early exposure to a hot environment affects the development of sudomotor function (7), whereas neonatal exposure to cool temperatures induces hyperplasia in sympathetic efferent pathways to brown adipose tissue (16). Moreover, neonatal handling (brief, daily separation of mothers and pups between birth and weaning) leads to diminished sympathetic nervous system (SNS) activity in spleen and heart and to exaggerated adrenal medullary responsiveness to fasting in adult male rats (30).…”

Developmental phenotypic plasticity in a marsupial

“…The reduced RMR values at 16°C T a in CR animals compared with WR animals in our study are most likely due to the improved defense to cold exposure in CR animals because thermoregulatory mechanisms are susceptible to modification by early postnatal experience (Hahn, 1956;Cooper et al, 1980;Young, 1985;Young and Shimano, 1998). It has been demonstrated in rats that continuous early life exposure to a cold environment induces a permanent and irreversible increase in brown adipose tissue (BAT) thermogenesis (Morrison et al, 2000), whereas when adult animals are exposed to cold (cold acclimation) the changes that occur in BAT are reversible when the animals are returned to normal temperatures (Vollmer and Skøtt, 2002). In small placental mammals, BAT is the main source for non-shivering thermogenesis (Andrew, 1978;Himms-Hagen, 1984;Wunder and Gettinger, 1996;Jastroch et al, 2008).…”