Energetic responses to cold temperatures in rats lacking forebrain-caudal brain stem connections

Abstract

Hypothalamic neurons are regarded as essential for integrating thermal afferent information from skin and core and issuing commands to autonomic and behavioral effectors that maintain core temperature (T(c)) during cold exposure and for the control of energy expenditure more generally. Caudal brain stem neurons are necessary elements of the hypothalamic effector pathway and also are directly driven by skin and brain cooling. To assess whether caudal brain stem processing of thermal afferent signals is sufficient to drive endemic effectors for thermogenesis, heart rate (HR), T(c), and activity responses of chronic decerebrate (CD) and control rats adapted to 23 degrees C were compared during cold exposure (4, 8, or 12 degrees C) for 6 h. Other CDs and controls were exposed to 4 or 23 degrees C for 2 h, and tissues were processed for norepinephrine turnover (NETO), a neurochemical measure of sympathetic drive. Controls maintained T(c) for all temperatures. CDs maintained T(c) for the 8 and 12 degrees C exposures, but T(c) declined 2 degrees C during the 4 degrees C exposure. Cold exposure elevated HR in CDs and controls alike. Tachycardia magnitude correlated with decreases in environmental temperature for controls, but not CDs. Cold increased NETO in brown adipose tissue, heart, and some white adipose tissue pads in CDs and controls compared with their respective room temperature controls. These data demonstrate that, in neural isolation from the hypothalamus, cold exposure drives caudal brain stem neuronal activity and engages local effectors that trigger sympathetic energetic and cardiac responses that are comparable in many, but not in all, respects to those seen in neurologically intact rats.

Decreasing temperature shifts hippocampal function from memory formation to modulation of hibernation bout duration in Syrian hamsters

“…Thus, control of nonshivering thermogenesis is depicted by the sequence of brain regions labeled 1-5 (30). [Although decerebration would delete regions 1, 6, and 10, some degree of thermoregulation would still be possible, consistent with the work of Grill and colleagues (31).] Moreover, regions on one level of the neuroaxis (e.g., 2, 7, 11 in the midbrain, pons) have distinctively different nuclei (33).…”

“…Each of these thermoeffector pathways receives and processes afferent signals from central (6) and peripheral thermosensors (33). The fact that decerebrate rats, lacking hypothalamic to caudal brain stem communication, retain some ability to regulate body temperature (31) confirms that both midbrain and hindbrain portions of a pathway receive and process afferent information from thermosensory neurons and that control is distributed all along the pathway, rather than being localized to the hypothalamus or to any other single structure or brain level.…”

Multiple thermoregulatory effectors with independent central controls

“…Alternatively or additionally, they might receive signals from cold skin by more direct pathways that are contained within the midbrain and brain stem. This possibility should be considered because in decerebrate rats, cold exposure is still able to increase BAT norepinephrine turnover (indicating sympathetic activation) (Nautiyal et al 2008) and neurons responding to skin temperature may still be recorded in the medullary raphé (Dickenson 1977).…”

The adipose organ of obesity-prone C57BL/6J mice is composed of mixed white and brown adipocytes

“…However, cold exposure seems to activate primarily the central nervous system ( 52 ), making the browning phenomenon more likely to be secondary, also in relation to the scarce number of brown adipocytes detected at 28°C and to the high reactivity of TH-positive parenchymal fi bers after cold exposure in C57BL/6J mice. Branching of TH-positive parenchymal fi ber is found in both strains but is greater in C57BL/6J mice, suggesting that mammals with a limited BAT could also be selected for browning therapeutic strategies.…”