Research reportIncrease of glucose transporter densities (Glut1 and Glut3) during chronic administration of nicotine in rat brain
Introduction
Glucose transport proteins mediate the facilitated diffusion of glucose across cell membranes. To date, six functional glucose transporter isoforms (Glut1–5, Glut7) have been identified by molecular cloning techniques. In the brain, mainly two of these isoforms have been found. The glucose transporter Glut1 is localized at the blood–brain barrier endothelium and in perivascular endfeet of astrocytes 4, 11, 14whereas the glucose transporter Glut3 is found in neurons 13, 14, 18. Previous studies have shown an uneven distribution of Glut1 and Glut3 in the brain during normal control conditions 24, 25. Little is known whether local changes in the transporter densities can occur. Since chronic administration of nicotine induces increases of local cerebral glucose utilization (LCGU) in distinct brain areas 6, 12the question arose whether this increase in LCGU is paralleled by increases in the local distribution of Glut1 and/or Glut3 and of capillary density. To this end, rats received osmotic minipumps filled with a nicotine solution. After one week, the local densities of glucose transporters Glut1 and Glut3 were quantified by immunoautoradiographic methods recently developed in our laboratory 24, 25. In the same animals capillaries were made visible by indirect immunofluorescence 5, 21. The results were compared with those of a previous 2-deoxyglucose study of LCGU during chronic nicotine infusion [6].
Section snippets
Materials and methods
Glucose transporters and capillary densities were measured in 12 male Sprague–Dawley rats weighing 240 to 330 g. The animals were anesthetized by a gas mixture of halothane (1–1.5%), N2O (70–80%) and O2 (remainder). Osmotic minipumps (Alzet model 2001, Alza, Palo Alto, CA, USA), filled with l-nicotine (Free base, Sigma, Deisenhofen, Germany), were implanted subcutaneously. The pumps were filled with l-nicotine such as to result in a dosage of 12.5 μg kg−1 min−1 (n=6). Control animals received
Results
Table 1 shows hemodynamic, arterial acid–base and other relevant parameters of both rat groups investigated. In the nicotine group, blood pressure, heart rate, acid base status, hematocrit, body temperature and glucose concentration were unchanged as compared to control rats. Nicotine and cotinine levels were in the targeted range during chronic nicotine infusion. Body weight of the control rats increased continuously from 305±22 g to 349±11 g during the one-week experiment whereas it decreased
Discussion of the methods
The immunoautoradiographic methods developed by our group for the detection of the density of Glut1 and Glut3 have a local resolution of 100–200 μm which is comparable to that of the 2-deoxyglucose method [20]. Whereas the 2-deoxyglucose method allows one to detect the local functional activity of the brain by measuring its glucose utilization, the immunoautoradiographic methods applied in the present study can be used to illustrate the morphological basis of local glucose utilization by
Conclusion
In summary, chronic infusion of nicotine causes an increase in LCGU in distinct brain areas. This increase is paralleled by an upregulation of glucose transporters Glut1 and Glut3 in the same brain areas, whereas capillary density remains unchanged.
Acknowledgements
This study was supported by a grant from VERUM, Stiftung für Verhalten und Umwelt, Munich, Germany. The authors thank PD Dr. G. Scherer, Munich, for the determination of plasma concentrations of nicotine and cotinine.
References (25)
- et al.
Ontogeny and cellular distribution of brain glucose transporter gene expression
Mol. Cell Neurosci.
(1992) - et al.
Immunological analysis of glucose transporters expressed in different regions of the rat brain and central nervous system
Biochem. Biophys. Res. Commun.
(1993) - et al.
Local cerebral glucose utilization of the awake rat during chronic administration of nicotine
Brain Res.
(1988) - et al.
Differential glycosylation of the Glut1 glucose transporter in brain capillaries and choroid plexus
Biochim. Biophys. Acta
(1994) - et al.
Effects of nicotine on cerebral glucose utilization in the rat
Brain Res.
(1990) - et al.
Immunohistochemical localization of the neuron-specific glucose transporter (Glut3) to neuropil in adult rat brain
Brain Res.
(1994) - et al.
Nicotine administration to rats: Methodological considerations
Life Sci.
(1987) - et al.
Glucose transporter expression in the brain: cDNA sequence of mouse Glut3, the brain facilitative glucose transporter isoform, and identification of sites of expression by in situ hybridization
J. Biol. Chem.
(1992) - et al.
Neuron-specific glucose transporter (NSGT): CNS distribution of Glut3 rat glucose transporter (RGT3) in rat central neurons
FEBS Lett.
(1993) - et al.
Glucose transporter immunoreactivity in the hypothalamus and area postrema
Brain Res. Bull.
(1990)
Autoradiographic analysis of the regional distribution of Glut3 glucose transporters in the rat brain
Brain Res.
A rapid gas–liquid chromatographic method for determination of cotinine and nicotine in biological fluids
J. Pharm. Pharmacol.
Cited by (23)
Functional brain imaging of tobacco use and dependence
2006, Journal of Psychiatric ResearchGlucose transporter plasticity during memory processing
2005, NeuroscienceCitation Excerpt :The present study shows for the first time that the hippocampus GLUT1 gene and protein expression are modulated by learning and memory processing. Consistent with previous studies that have shown parallel changes in GLUT expression following neuronal activation (Duelli et al., 1998a,b), we observed that compared with sham-trained animals, training in an operant task induced an increase in GLUT1 immunoreactivity in the hippocampus CA1 pyramidal cell layer that was associated with an increase in GLUT1 mRNA level in the dorsal hippocampus. These results show that the establishment of an association between the bar-pressing action and the consumption of food induced immediate plastic changes in the expression of GLUT1 in the hippocampus.
Nicotine increases in vivo blood-brain barrier permeability and alters cerebral microvascular tight junction protein distribution
2004, Brain ResearchCitation Excerpt :One study found that acute nicotine at non-toxic concentrations had no effect on the permeability of large molecular weight markers at the BBB [49], though this finding did not rule out the possibility that nicotine may disrupt the BBB to passage of smaller molecules [31]. In subsequent chronic studies, non-toxic doses of nicotine altered both the expression and function of ion [2,60] and glucose transporters [9,10] in cerebral microvessels. Additionally, we have reported that nicotine and its major metabolite cotinine increase the permeability of an in vitro model of the BBB, and that this change is associated with diminished expression and altered distribution of the TJ protein ZO-1 mediated by endothelial nicotinic acetylcholine receptors [1].
Nicotine and cotinine modulate cerebral microvascular permeability and protein expression of ZO-1 through nicotinic acetylcholine receptors expressed on brain endothelial cells
2002, Journal of Pharmaceutical SciencesCitation Excerpt :Chen et al.13 have also shown that nicotine raises the influx of permeable solutes across the rat BBB with little or no capillary recruitment. Also, 1 week of nicotine administration results in an increased density of GLUT-1 transporter per brain capillary with no change in capillary density.14 Chronic nicotine infusion was also shown to result in an increase in local cerebral glucose utilization.
The cerebral glucose-fatty acid cycle: Evolutionary roots, regulation, and (patho)physiological importance
2002, International Review of Neurobiology