Acute brown adipose tissue temperature response to cold in monosodium glutamate-treated Siberian hamsters

Abstract

Neonatal monosodium glutamate (MSG) administration increases adiposity, decreases energy expenditure and is associated with arcuate nucleus (Arc) destruction. Disrupted brown adipose tissue (BAT) thermogenesis underlies some of these effects, although, interscapular BAT temperature (T IBAT ) has not been measured. Therefore, we tested the effects of neonatal MSG or vehicle administration in Siberian hamsters and, when they were adults, measured T IBAT during acute cold exposure. The Arc and its projection to the hypothalamic paraventricular nucleus (PVH) are both components of the CNS outflow circuits to IBAT, with the latter implicated in BAT thermogenesis that could be compromised by MSG treatment. Using a viral transneuronal tract tracer, pseudorabies virus (PRV), we also tested whether the components of these circuits were intact. As adults, MSG-treated hamsters had significantly increased body mass and some white fat pad masses, markedly reduced Arc Nissl and neuropeptide staining, and PVH neuropeptide fiber staining. Cold-exposed (18 h at 5 °C) MSG-and vehicle-treated hamsters initially maintained T IBAT , but the ability of the former waned after 2 h being significantly decreased by 18 h. PRV immunoreactive fibers/cells were not altered by neonatal MSG treatment despite substantial Arc and PVH destruction. MSG-and vehicle-treated hamsters given an exogenous norepinephrine challenge showed identical increases in the duration and peak of T IBAT . Thus, the inability of MSG-treated animals to sustain T IBAT in the cold is not due to any obvious MSG-induced deletions of central sympathetic outflow circuits to IBAT, but appears to be extrinsic to the tissue nevertheless.

Brown Adipose Tissue Has Sympathetic-Sensory Feedback Circuits

“…This greater SNS outflow from the MPA than SS inflow supports our previous finding of relatively sparse MPA H129-infected neurons from IBAT compared with many other areas (Vaughan and Bartness, 2012), but impressive PRV152-infected neurons (Bamshad et al, 1999;Song et al, 2008;Leitner and Bartness, 2009). Despite the relatively small number of MPA-MPO-MnPO SS circuit neurons, this by no means necessarily lessens its contribution to thermoregulatory signaling from the skin (Nakamura and Morrison, 2008a,b) as the MPA-SS innervation in the present study mainly reflects the SS pathway originating from the IBAT.…”

“…The ventromedial hypothalamic nucleus (VMH) was scarcely represented only by a few PRV152-IR neurons by comparison with other forebrain regions (Table 1; Fig. 1G,I ) as we have seen previously (Bamshad et al, 1999;Song et al, 2008;Leitner and Bartness, 2009). The overall percentage of PRV152-and H129-IR posterior hypothalamus and thalamus double-labeled neurons was ϳ9.0% (Fig.…”

“…Finally, we have not noticed left-right pad differences in brain infections with injections of either PRV152 or H129. Note that pilot studies indicated no left-right IBAT differences (C. H. Vaughan and T. J. Bartness; and C. K. Song and T. J. Bartness, unpublished observations) nor in our published work (Bamshad et al, 1999;Song et al, 2008;Leitner and Bartness, 2009;Vaughan and Bartness, 2012).…”

“…For CL316,243 administration, two electronic transponders (Bio Medic Data Systems) each with a built-in temperature sensor were gently implanted under each IBAT pad, the output of which was read with a handheld DAS-7007R scanner (Bio Medic Data Systems) for IBAT temperature (T IBAT ) acquisition as we have used successfully previously Nautiyal et al, 2008;Song et al, 2008;Leitner and Bartness, 2009;Vaughan et al, 2011;Vaughan and Bartness, 2012). This system provides an opportunity to program the transponder with a unique identification code to distinguish between left and right IBAT pad temperatures.…”

Anterograde transneuronal viral tract tracing reveals central sensory circuits from brown fat and sensory denervation alters its thermogenic responses

“…After the capsaicin injections, a temperature transponder [Implantable Programmable Temperature Transponder (IPTT) 300, BioMedic Data Systems, Seaford, DE] that was gas sterilized was tied to sterile silk sutures and then secured under the left IBAT pad as we described previously (8,35,56). The dorsum was closed with sterile wound clips (Stoelting, Wood Dale, IL), and then a ventral incision was made through the skin and peritoneal cavity for iButton implantation.…”