Analysis and Measurement of the Sympathetic and Sensory Innervation of White and Brown Adipose Tissue

Abstract

Here, we provide a detailed account of how to denervate white and brown adipose tissue (WAT and BAT) and how to measure sympathetic nervous system (SNS) activity to these and other tissues neurochemically. The brain controls many of the functions of WAT and BAT via the SNS innervation of the tissues, especially lipolysis and thermogenesis, respectively. There is no clearly demonstrated parasympathetic innervation of WAT or the major interscapular BAT (IBAT) depot. WAT and BAT communicate with the brain neurally via sensory nerves. We detail the surgical denervation (eliminating both innervations) of several WAT pads and IBAT. We also detail more selective chemical denervation of the SNS innervation via intra-WAT/IBAT 6-hydroxy-dopamine (a catecholaminergic neurotoxin) injections and selective chemical sensory denervation via intra-WAT/IBAT capsaicin (a sensory nerve neurotoxin) injections. Verifications of the denervations are provided (HPLC-EC detection for SNS, ELIA for calcitonin gene-related peptide (proven sensory nerve marker)). Finally, assessment of the SNS drive to WAT/BAT or other tissues is described using the alpha-methyl-para-tyrosine method combined with HPLC-EC, a direct neurochemical measure of SNS activity. These methods have proven useful for us and for other investigators interested in innervation of adipose tissues. The chemical denervation approach has been extended to nonadipose tissues as well.

Neural control of white, beige and brown adipocytes

“…44 In addition, DMH NPY knockdown increased the gene expression of the 'thermogenic program' (that is, PPARγ and Pgc-1α mRNA) in IWAT 44 ; DWAT was not assayed. To demonstrate that this effect was dependent on the SNS innervation of WAT, they used our specific, unilateral sympathetic denervation model, [45][46][47][48] where one IWAT depot received intra-WAT injections of the noradrenergic toxin 6-hydroxy-dopamine (6-OHDA) and its within-animal contralateral IWAT mate received vehicle control injections. [45][46][47][48] In the neurally intact IWAT pads of DMH NPY knockdown rats receiving intra-WAT vehicle injections, NE content (often a surrogate used for sympathetic drive, but not a replacement for NE turnover) was significantly increased compared with that of separate control rats receiving DMH injection of the scrambled shRNA.…”

The Histone Demethylase UTX Promotes Brown Adipocyte Thermogenic Program Via Coordinated Regulation of H3K27 Demethylation and Acetylation

“…Traditional brown adipocytes are located in discrete areas, such as the interscapular BAT; whereas "inducible" beige adipocytes are dispersed in WAT (49 -51), and can be induced by cold exposure or ␤3-adrenergic receptor activation (39,52) through activation of the sympathetic nervous system (SNS) as measured neurochemically by norepinephrine turnover (NETO) (53,54). Therefore, ␤ adrenergic activation via cold or ␤ adrenergic agonists is required for the development of both traditional brown fat and beige adipocytes.…”

Neural innervation of white adipose tissue and the control of lipolysis

“…Therefore, as an important cautionary note, when reading the literature in this and related fields, one cannot surmise that ‘tapping into’ one part of the SNS has any generality to any other part. Moreover, as is discussed below and reviewed recently [292], there are no surrogates for SNS activity – direct measures involve electrophysiological assay of sympathetic nerve activity or neurochemical analysis of sympathetic terminal release of NE ( i.e. , NETO).…”