PubMed · 7951481
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M O Carruba, E Nisoli. 1994. A weighty problem.. https://pubmed.ncbi.nlm.nih.gov/7951481/
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Leptin is an adipocyte hormone that functions as an afferent signal in a negative feedback loop regulating body weight, and acts by interacting with a receptor in the hypothalamus and other tissues. Leptin treatment has potent effects on lipid metabolism, and leads to a large, specific reduction of adipose tissue mass after several days. Here we show that leptin also acts acutely to increase glucose metabolism, although studies of leptin's effect on glucose metabolism have typically been confounded by the weight-reducing actions of leptin treatment, which by itself could affect glucose homoeostasis. We have demonstrated acute in vivo effects of intravenous and intracerebroventricular administrations of leptin on glucose metabolism. A five-hour intravenous infusion of leptin into wild-type mice increased glucose turnover and glucose uptake, but decreased hepatic glycogen content. The plasma levels of insulin and glucose did not change. Similar effects were observed after both intravenous and intracerebroventricular infusion of leptin, suggesting that effects of leptin on glucose metabolism are mediated by the central nervous system (CNS). These data indicate that leptin induces a complex metabolic response with effects on glucose as well as lipid metabolism. This response is unique to leptin, which suggests that new efferent signals emanate from the CNS after leptin treatment.
Neurons performing the same function can be identified immunohistochemically because they often share the same neurochemistry. The distribution of calcium-binding proteins, like calbindin, has been used previously to identify functional subpopulations of neurons in many parts of the nervous system. In this study we have investigated the distribution of calbindin D28K-immunoreactivity in subpopulations of sympathetic preganglionic neurons in the intermediolateral nucleus of the rat spinal cord. The majority of calbindin D28K-immunoreactive preganglionic neurons also had co-localised nitric oxide synthase, although a population of preganglionic neurons in the mid- to low thoracic intermediolateral nucleus expressed only calbindin D28K-immunoreactivity. Retrograde-tracing studies showed that calbindin D28K-immunoreactive neurons projected to the superior cervical and stellate ganglia, with smaller numbers of cells projecting to the lumbar sympathetic chain and superior mesenteric ganglia. Very few calbindin D28K-immunoreactive neurons projected to the inferior mesenteric ganglion, and none projected to the adrenal medulla. The distribution of calbindin D28K-immunoreactive terminals and postganglionic neurons in the superior cervical and stellate ganglia was also investigated. Many postganglionic neurons were calbindin D28K-immunoreactive, and most of these lacked neuropeptide Y-immunoreactivity. Calbindin D28K-immunoreactive nerve terminals were common and formed dense pericellular baskets around many postganglionic neurons, including some of those that were calbindin D28K-immunoreactive, but only rarely formed pericellular baskets around neuropeptide Y-immunoreactive neurons. The function of some of the classes of postganglionic neurons that were the target of calbindin D28K-immunoreactive preganglionic terminals was determined by combining immunohistochemistry with retrograde-tracer injections into a range of peripheral tissues. Calbindin D28K-immunoreactive nerve terminals, with co-localised nitric oxide synthase-immunoreactivity, surrounded secretomotor neurons projecting to the submandibular salivary gland and pilomotor neurons projecting to skin, but did not surround neurons projecting to brown fat or vasomotor neurons projecting to the skin, muscle, or salivary glands.
We have undertaken a study of the role of coenzyme Q (CoQ) in glycerol-3-phosphate oxidation in mitochondrial membranes from hamster brown adipose tissue, using either quinone homologs, as CoQ1 and CoQ2, or the analogs duroquinone and decylubiquinone as artificial electron acceptors. We have found that the most suitable electron acceptor for glycerol-3-phosphate:CoQ reductase activity in situ in the mitochondrial membrane is the homolog CoQ1 yielding the highest rate of enzyme activity (225 +/- 41 nmol x min(-1) x mg(-1) protein). With all acceptors tested the quinone reduction rates were completely insensitive to Complex III inhibitors, indicating that all acceptors were easily accessible to the quinone-binding site of the dehydrogenase preferentially with respect to the endogenous CoQ pool, in such a way that Complex III was kept in the oxidized state. We have also experimentally investigated the saturation kinetics of endogenous CoQ (1.35 nmol/mg protein of a mixture of 70% CoQ9 and 30% CoQ10) by stepwise pentane extraction of brown adipose tissue mitochondria and found a K(m) of the integrated activity of glycerol-3-phosphate cytochrome c reductase for endogenous CoQ of 0.22 nmol/mg protein, indicating that glycerol-3-phosphate-supported respiration is over 80% of V(max) with respect to the CoQ pool. A similar K(m) of 0.19 nmol CoQ/mg protein was found in glycerol-3-phosphate cytochrome c reductase in cockroach flight muscle mitochondria.