Kristian Gundersen

• Cramer, Alyssa A. W.; Prasad, Vikram; Eftestøl, Einar; Song, Taejeong; Hansson, Kenth-Arne; Dugdale, Hannah F.; Sadayappan, Sakthivel; Ochala, Julien; Gundersen, Kristian & Millay, Douglas P. (2020). Nuclear numbers in syncytial muscle fibers promote size but limit the development of larger myonuclear domains. Nature Communications.  ISSN 2041-1723.  11, s 1- 14 . doi: 10.1038/s41467-020-20058-7 Full text in Research Archive.
• Hansson, Kenth-Arne; Eftestøl, Einar; Bruusgaard, Jo C.; Juvkam, Inga; Cramer, Alyssa W.; Malthe-Sørenssen, Anders; Millay, Douglas P. & Gundersen, Kristian (2020). Myonuclear content regulates cell size with similar scaling properties in mice and humans. Nature Communications.  ISSN 2041-1723.  11(1) . doi: 10.1038/s41467-020-20057-8 Full text in Research Archive.
• Hansson, Kenth-Arne; Solbrå, Andreas Våvang; Gundersen, Kristian & Bruusgaard, Jo C. (2020). Computational assessment of transport distances in living skeletal muscle fibers studied in situ. Biophysical Journal.  ISSN 0006-3495.  119(11), s 2166- 2178 . doi: 10.1016/j.bpj.2020.10.016
• Psilander, Niklas; Eftestøl, Einar; Cumming, Kristoffer Toldnes; Solgård, Inga Juvkam; Ekblom, Maria M.; Sunding, Kerstin; Wernbom, Mathias; Holmberg, Hans-Christer; Ekblom, Björn; Bruusgaard, Jo C.; Raastad, Truls & Gundersen, Kristian (2019). Effects of training, detraining, and retraining on strength, hypertrophy, and myonuclear number in human skeletal muscle. Journal of applied physiology.  ISSN 8750-7587.  126(6), s 1636- 1645 . doi: 10.1152/japplphysiol.00917.2018 Full text in Research Archive. Show summary

  Previously trained mouse muscles acquire strength and volume faster than naïve muscles; it has been suggested that this is related to increased myonuclear density. The present study aimed to determine whether a previously strength-trained leg (mem-leg) would respond better to a period of strength training than a previously untrained leg (con-leg). Nine men and 10 women performed unilateral strength training (T1) for 10 wk, followed by 20 wk of detraining (DT) and a 5-wk bilateral retraining period (T2). Muscle biopsies were taken before and after each training period and analyzed for myonuclear number, fiber volume, and cross-sectional area (CSA). Ultrasound and one repetition of maximum leg extension were performed to determine muscle thickness (MT) and strength. CSA (~17%), MT (~10%), and strength (~20%) increased during T1 in the mem-leg. However, the myonuclear number and fiber volume did not change. MT and CSA returned to baseline values during DT, but strength remained elevated (~60%), supporting previous findings of a long-lasting motor learning effect. MT and strength increased similarly in the mem-leg and con-leg during T2, whereas CSA, fiber volume, and myonuclear number remained unaffected. In conclusion, training response during T2 did not differ between the mem-leg and con-leg. However, this does not discount the existence of human muscle memory, since no increase in the number of myonuclei was detected during T1 and no clear detraining effect was observed for cell size during DT; thus, the present data did not allow for a rigorous test of the muscle memory hypothesis.

• Gundersen, Kristian; Bruusgaard, Jo C.; Egner, Ingrid Marie; Eftestøl, Einar & Bengtsen, Mads (2018). Muscle memory: virtues of your youth?. Journal of Physiology.  ISSN 0022-3751.  596(18), s 4289- 4290 . doi: 10.1113/JP276354
• Winje, Ivan; Bengtsen, Mads; Eftestøl, Einar; Juvkam, Inga; Bruusgaard, Jo C. & Gundersen, Kristian (2018). Specific labelling of myonuclei by an antibody against pericentriolar material 1 on skeletal muscle tissue sections. Acta Physiologica.  ISSN 1748-1708.  223(4), s 1- 9 . doi: 10.1111/apha.13034 Full text in Research Archive.
• Winje, Ivan; Sheng, Xia; Hansson, Kenth-Arne; Solbrå, Andreas Våvang; Tennøe, Simen; Saatcioglu, Fahri; Bruusgaard, Jo C. & Gundersen, Kristian (2018). Cachexia does not induce loss of myonuclei or muscle fibres during xenografted prostate cancer in mice. Acta Physiologica.  ISSN 1748-1708.  s 1- 9 . doi: 10.1111/apha.13204
• Eftestøl, Einar; Egner, Ingrid Marie; Lunde, Ida Gjervold; Ellefsen, Stian; Andersen, Tom; Sjåland, Cecilie; Gundersen, Kristian & Bruusgaard, Jo C. (2016). Increased hypertrophic response with increased mechanical load in skeletal muscles receiving identical activity patterns. American Journal of Physiology - Cell Physiology.  ISSN 0363-6143.  311(4), s C616- C629 . doi: 10.1152/ajpcell.00016.2016
• Egner, Ingrid Marie; Bruusgaard, Jo C. & Gundersen, Kristian (2016). Satellite cell depletion prevents fiber hypertrophy in skeletal muscle. Development.  ISSN 0950-1991.  143(16), s 2898- 2906 . doi: 10.1242/dev.134411
• Gundersen, Kristian (2016). Muscle memory and a new cellular model for muscle atrophy and hypertrophy. Journal of Experimental Biology.  ISSN 0022-0949.  219(2), s 235- 242 . doi: 10.1242/jeb.124495
• Eftestøl, Einar; Alver, Tine Norman; Gundersen, Kristian & Bruusgaard, Jo C. (2014). Overexpression of SMPX in adult skeletal muscle does not change skeletal muscle fiber type or size. PLOS ONE.  ISSN 1932-6203.  9(6) . doi: 10.1371/journal.pone.0099232 Full text in Research Archive.
• Løvås, Tom-Ole; Bruusgaard, Jo C.; Øynebråten, Inger; Gundersen, Kristian & Bogen, Bjarne (2014). DNA vaccines: MHC II-targeted vaccine protein produced by transfected muscle fibres induces a local inflammatory cell infiltrate in mice. PLOS ONE.  ISSN 1932-6203.  9(10) . doi: 10.1371/journal.pone.0108069 Full text in Research Archive.
• Egner, Ingrid Marie; Bruusgaard, Jo C.; Eftestøl, Einar & Gundersen, Kristian (2013). A cellular memory mechanism aids overload hypertrophy in muscle long after an episodic exposure to anabolic steroids. Journal of Physiology.  ISSN 0022-3751.  591(24), s 6221- 6230 . doi: 10.1113/jphysiol.2013.264457
• Bruusgaard, Jo C.; Egner, Ingrid Marie; Klungervik, Tove; Dupre-Aucouturier, S; Desplanches, D & Gundersen, Kristian (2012). No change in myonuclear number during muscle unloading and reloading. Journal of applied physiology.  ISSN 8750-7587.  113(2), s 290- 296 . doi: 10.1152/japplphysiol.00436.2012
• Vikne, Harald; Gundersen, Kristian; Liestøl, Knut; Mæhlen, Jan & Vøllestad, Nina Køpke (2012). Intermuscular relationship of human muscle fiber type proportions: Slow leg muscles predict slow neck muscles. Muscle and Nerve.  ISSN 0148-639X.  45(4), s 527- 535 . doi: 10.1002/mus.22315
• Gundersen, Kristian (2011). Excitation-transcription coupling in skeletal muscle: the molecular pathways of exercise. Biological Reviews.  ISSN 1464-7931.  86(3), s 564- 600 . doi: 10.1111/j.1469-185X.2010.00161.x
• Lunde, Ida Gjervold; Anton, Siobhan Lisa; Bruusgaard, Jo C.; Rana, Zaheer Ahmad; Ellefsen, Stian & Gundersen, Kristian (2011). Hypoxia inducible factor 1α links fast-patterned muscle activity and fast muscle phenotype in rats. Journal of Physiology.  ISSN 0022-3751.  589(6), s 1443- 1454 . doi: 10.1113/jphysiol.2010.202762
• Bruusgaard, Jo C.; Johansen, Ida Beitnes; Egner, Ingrid Marie; Rana, Zaheer Ahmad & Gundersen, Kristian (2010). Myonuclei acquired by overload exercise precede hypertrophy and are not lost on detraining. Proceedings of the National Academy of Sciences of the United States of America.  ISSN 0027-8424.  107(34), s 15111- 15116 . doi: 10.1073/pnas.0913935107
• Rana, Zaheer Ahmad; Gundersen, Kristian & Buonanno, Andres (2010). The ups and downs of gene regulation by electrical activity in skeletal muscles. Journal of Muscle Research and Cell Motility.  ISSN 0142-4319.  30, s 255- 260 . doi: 10.1007/s10974-010-9200-2
• Rana, Zaheer Ahmad; Gundersen, Kristian & Buonanno, Andres (2009). The ups and downs of gene regulation by electrical activity in skeletal muscles. Journal of Muscle Research and Cell Motility.  ISSN 0142-4319.  30(7-8), s 255- 260 . doi: 10.1007/s10974-010-9200-2
• Bruusgaard, Jo C. & Gundersen, Kristian (2008). In vivo time-lapse microscopy reveals no loss of murine myonuclei during weeks of muscle atrophy. Journal of Clinical Investigation.  ISSN 0021-9738.  118 . doi: 10.1172/JCI34022
• Gundersen, Kristian & Bruusgaard, Jo C. (2008). Nuclear domains during muscle atrophy: nuclei lost or paradigm lost?. Journal of Physiology.  ISSN 0022-3751.  586 . doi: 10.1113/jphysiol.2008.154369
• Rana, Zaheer Ahmad; Gundersen, Kristian & Buonanno, Andres (2008). Activity-dependent repression of muscle genes by NFAT. Proceedings of the National Academy of Sciences of the United States of America.  ISSN 0027-8424.  105, s 5921- 5926 . doi: 10.1073/pnas.0801330105
• Ekmark, Merete; Rana, Zaheer Ahmad; Stewart, G; Hardie, DG & Gundersen, Kristian (2007). De-phosphorylation of MyoD is linking nerve-evoked activity to fast myosin heavy chain expression in rodent adult skeletal muscle. Journal of Physiology.  ISSN 0022-3751.  584, s 637- 650
• Lunde, Ida Gjervold; Ekmark, Merete; Rana, Zaheer Ahmad; Buonanno, Andres & Gundersen, Kristian (2007). PPARdelta expression is influenced by muscle activity and induces slow muscle properties in adult rat muscles after somatic gene transfer. Journal of Physiology.  ISSN 0022-3751.  582(3), s 1277- 1287 . doi: 10.1113/jphysiol.2007.133025 Show summary

  The effects of exercise on skeletal muscle are mediated by a coupling between muscle electrical activity and gene expression. Several activity correlates, such as intracellular Ca(2+), hypoxia and metabolites like free fatty acids (FFAs), might initiate signalling pathways regulating fibre-type-specific genes. FFAs can be sensed by lipid-dependent transcription factors of the peroxisome proliferator-activated receptor (PPAR) family. We found that the mRNA for the predominant muscle isoform, PPARdelta, was three-fold higher in the slow/oxidative soleus compared to the fast/glycolytic extensor digitorum longus (EDL) muscle. In histological sections of the soleus, the most oxidative fibres display the highest levels of PPARdelta protein. When the soleus muscle was stimulated electrically by a pattern mimicking fast/glycolytic IIb motor units, the mRNA level of PPARdelta was reduced to less than half within 24 h. In the EDL, a three-fold increase was observed after slow type I-like electrical stimulation. When a constitutively active form of PPARdelta was overexpressed for 14 days in normally active adult fibres after somatic gene transfer, the number of I/IIa hybrids in the EDL more than tripled, IIa fibres increased from 14% to 25%, and IIb fibres decreased from 55% to 45%. The level of succinate dehydrogenase activity increased and size decreased, also when compared to normal fibres of the same type. Thus PPARdelta can change myosin heavy chain, oxidative enzymes and size locally in muscle cells in the absence of general exercise. Previous studies on PPARdelta in muscle have been performed in transgenic animals where the transgene has been present during muscle development. Our data suggest that PPARdelta can mediate activity effects acutely in pre-existing adult fibres, and thus is an important link in excitation-transcription coupling.

• Vikne, Harald; Refsnes, PE; Ekmark, Merete; Medbø, Jon Ingulf; Gundersen, Vidar & Gundersen, Kristian (2006). Muscular performance after concentric and eccentric exercise in trained men. Medicine & Science in Sports & Exercise.  ISSN 0195-9131.  38(10), s 1770- 1781
• Bruusgaard, Jo C.; Liestøl, Knut & Gundersen, Kristian (2006). Distribution of myonuclei and microtubules in live muscle fibers of young, middle-aged, and old mice. Journal of applied physiology.  ISSN 8750-7587.  100, s 2024- 2030
• Gundersen, Kristian (2005). Genteknologi og idrettsprestasjoner. Tidsskrift for Den norske legeforening.  ISSN 0029-2001.  125, s 16- 16
• Bruusgaard, Jo C.; Brack, AS; Hughes, SM & Gundersen, Kristian (2005). Muscle hypertrophy induced by the Ski protein: cyto-architecture and ultrastructure. Acta Physiologica Scandinavica.  ISSN 0001-6772.  185(2), s 141- 149
• Rana, Zaheer Ahmad; Gundersen, Kristian; Buonanno, A & Vullhorst, D (2005). Imaging transcription in vivo: distinct regulatory effects of fast and slow activity patterns on promoter elements from vertebrate troponin I isoform genes. Journal of Physiology.  ISSN 0022-3751.  562
• Rana, Zaheer A; Ekmark, Merete & Gundersen, Kristian (2004). Coexpression after electroporation of plasmid mixtures into muscles in vivo. Acta Physiologica Scandinavica.  ISSN 0001-6772.  181, s 233- 238
• Bruusgaard, Jo C.; Liestøl, Knut; Ekmark, Merete; Kollstad, K & Gundersen, Kristian (2003). Number and spatial distribution of nuclei in the muscle fibres of normal mice studied in vivo. Journal of Physiology.  ISSN 0022-3751.  551(2), s 467- 478
• Ekmark, Merete; Grøvevik, Eirik; Schjerling, Peter & Gundersen, Kristian (2003). Myogenin induces higher oxidative capacity in pre-existing mouse muscle fibres after somatic DNA transfer. Journal of Physiology.  ISSN 0022-3751.  548, s 259- 269
• Sollid, Jørund; de Angelis, Paula; Gundersen, Kristian & Nilsson, Gøran Erik (2003). Hypoxia induces adaptive and reversible gross morphological changes in crucian carp gills. Journal of Experimental Biology.  ISSN 0022-0949.  206, s 3667- 3673 Show summary

  We show that crucian carp (Carassius carassius) living in normoxic (aerated) water have gills that lack protruding lamellae, the primary site of O2 uptake in fish. Such an unusual trait leads to a very small respiratory surface area. Histological examination showed that the lamellae (secondary lamellae) of these fish were embedded in a cell mass (denoted embedded lamellae). When the fish were kept in hypoxic water, a large reduction in this cell mass occurred, making the lamellae protrude and increasing the respiratory surface area by 7.5-fold. This morphological change was found to be reversible and was caused by increased apoptosis combined with reduced cell proliferation. Carp with protruding lamellae had a higher capacity for oxygen uptake at low oxygen levels than fish with embedded lamellae, but water and ion fluxes appeared to be increased, which indicates increased osmoregulatory costs. This is, to our knowledge, the first demonstration of an adaptive and reversible gross morphological change in the respiratory organ of an adult vertebrate in response to changes in the availability of oxygen.

• Carlsen, Harald & Gundersen, Kristian (2000). Helix-loop-helx transcription factors in electrically active and inactive skeletal muscles. Muscle and Nerve.  ISSN 0148-639X.  23, s 1374- 1380
• Hughes, S.M.; Chi, M.M.Y.; Lowry, O.H. & Gundersen, Kristian (1999). Myogenin induces a shift of enzyme activity from glycolytic to oxidative metabolism in muscles of transgenic mice. Journal of Cell Biology.  ISSN 0021-9525.  145(3), s 633- 642
• Utvik, Jo Kristian; Njå, Arild & Gundersen, Kristian (1999). DNA injection into single cells of intact mice. Human Gene Therapy.  ISSN 1043-0342.  10, s 291- 300 Show summary

  We describe a technique wherein single muscle fibers of intact mice are made transgenic by intracellular injection of DNA expression vectors for the reporter genes lacZ and green fluorescent protein (GFP). Application of in vivo imaging techniques allowed identification of single cells during the injections, and of the same single cells when the muscle was reexposed days or weeks later. DNA concentration by itself had little effect on fiber survival or expression efficacy, but it seemed crucial to exceed a threshold of about 10(6) injected plasmid molecules in order to obtain expression. On the other hand, experiments with coinjection of two different plasmids suggested that relatively few individual molecules were eventually transcribed in expressing cells. Plasmid DNA remained localized to the injection site, and expression was confined to nuclei in the vicinity. Expression was stable, as reporter was detected 2-61 days after injection.

• Gundersen, Kristian (1998). Determination of muscle contractile properties: the importance of the nerve. Acta Physiologica Scandinavica.  ISSN 0001-6772.  162, s 333- 341
• Windisch, A.; Gundersen, Kristian; Szabolcs, M.J.; Gruber, H. & Lømo, Terje (1998). Fast to slow transformation of denervated and electrically stimulated rat muscle. Journal of Physiology.  ISSN 0022-3751.  510(2), s 623- 632
• Jóhannsson, E.; Jensen, K.; Gundersen, Kristian; Dahl, Hans A. & Bonen, A. (1996). Effect of electrical stimulation patterns on glucose transport in rat muscles. American Journal of Physiology. Regulatory Integrative and Comparative Physiology.  ISSN 0363-6119.  40, s R426- R431

View all works in Cristin

• Bengtsen, Mads; Winje, Ivan; Eftestøl, Einar; Domanska, Diana Ewa; Landskron, Johannes & Gundersen, Kristian (2019). The Epigenetic landscape of two phenotypic extreme skeletal muscles - soleus and EDL. Acta Physiologica.  ISSN 1748-1708. . doi: 10.1111/apha.13414
• Bengtsen, Mads; Winje, Ivan; Landskron, Johannes; Meza-Zepeda, Leonardi A & Gundersen, Kristian (2019). The Epigenetic landscape of two phenotypic extreme skeletal muscles.
• Bengtsen, Mads; Winje, Ivan; Landskron, Johannes; Meza-Zepeda, Leonardo A. & Gundersen, Kristian (2019). The Epigenetic landscape of two phenotypic extreme skeletal muscles.
• Eftestøl, Einar; Psilander, Niklas; Cumming, Kristoffer Toldnes; Juvkam, Inga; Ekblom, Maria M.; Sunding, Kerstin; Wernbom, Mathias; Holmberg, Hans-Christer; Ekblom, Björn; Bruusgaard, Jo C.; Raastad, Truls & Gundersen, Kristian (2019). Muscle memory: Are myonuclei ever lost?. Journal of applied physiology.  ISSN 8750-7587.  128(2), s 456- 457 . doi: 10.1152/japplphysiol.00761.2019
• Nygård, Kamilla; Juvkam, Inga; Bengtsen, Mads & Gundersen, Kristian (2019). NFATs regulatory potential and role in skeletal muscle during voluntary exercise. Acta Physiologica.  ISSN 1748-1708. . doi: 10.1111/apha.13414
• Bengtsen, Mads; Winje, Ivan; Landskron, Johannes; Meza-Zepeda, Leonardo A. & Gundersen, Kristian (2018). The Epigenetic landscape of two phenotypic extreme skeletal muscles.
• Hansson, Kenth-Arne; Gundersen, Kristian & Bruusgaard, Jo C. (2018). In vivo confocal imaging and 3D rendering of the neuromuscular end plate and its synaptic myonuclei. Acta Physiologica.  ISSN 1748-1708.
• Egner, Ingrid Marie; Bruusgaard, Jo C. & Gundersen, Kristian (2017). An apparent lack of effect of satellite cell depletion on hypertrophy could be due to methodological limitations. Response to `Methodological issues limit interpretation of negative effects of satellite cell depletion on adult muscle hypertrophy?. Development.  ISSN 0950-1991.  144(8), s 1365- 1367 . doi: 10.1242/dev.148163
• Eftestøl, Einar; Egner, Ingrid Marie; Ellefsen, Stian; Andersen, Tom; Gundersen, Kristian & Bruusgaard, Jo C. (2016). The importance of mechanosensation in skeletal muscle hypertrophy.
• Bruusgaard, Jo C. & Gundersen, Kristian (2014). Musklene dine kan huske. Aftenposten (morgenutg. : trykt utg.).  ISSN 0804-3116.
• Eftestøl, Einar; Bruusgaard, Jo C. & Gundersen, Kristian (2012). The contraction duration is not important for hypertrophy in strength trained rats.
• Egner, Ingrid Marie; Bruusgaard, Jo C.; Eftestøl, Einar & Gundersen, Kristian (2012). Effects of anabolic steroid on nuclear number and muscle mass.
• Anton, Siobhan Lisa; Bruusgaard, Jo C. & Gundersen, Kristian (2011). In Vivo Knockdown of Myogenin Leads to a Faster Muscle Phenotype.
• Anton, Siobhan Lisa; Bruusgaard, Jo C. & Gundersen, Kristian (2011). In vivo knockdown of myogenin leads to a faster muscle phenotype. Journal of Muscle Research and Cell Motility.  ISSN 0142-4319.  32, s 345- 346 . doi: 10.1007/s10974-011-9265-6
• Gundersen, Kristian; Eftestøl, Einar; Egner, Ingrid Marie & Bruusgaard, Jo C. (2011). The effect of testosterone propionate on overloaded skeletal muscle.
• Aarebrot, Frank; Waage, Hilde Henriksen; Gundersen, Kristian; Matlary, Janne Haaland; Hessen, Dag Olav; Brochmann, Grete; Eriksen, Trond Berg; Lomheim, Sylfest; Hurum, Jørn Harald; Hellesøy, Cathrine & Endresen, Kristoffer Hatteland (2010, 26. juni). Vi er ikke blitt redde!.  Aftenposten.
• Anton, Siobhan Lisa; Lunde, Ida Gjervold; Bruusgaard, Jo C. & Gundersen, Kristian (2010). HIF-1a regulates the oxidative capacity of adult rat skeletal muscle. Journal of Muscle Research and Cell Motility.  ISSN 0142-4319.  32, s 136- 136 . doi: 10.1007/s10974-011-9257-6
• Anton, Siobhan Lisa; Lunde, Ida Gjervold; Bruusgaard, Jo C. & Gundersen, Kristian (2010). HIF-1a regulates the oxidative capacity of adult rat skeletal muscle.
• Brandtzæg, Per; Bruusgaard, Jo C. & Gundersen, Kristian (2009). Djevelens advokat i Snåsa. Morgenbladet.  ISSN 0805-3847.
• Brandtzæg, Per; Bruusgaard, Jo C. & Gundersen, Kristian (2009). Lemfeldig observasjon. Morgenbladet.  ISSN 0805-3847.
• Bruusgaard, Jo C.; Johansen, Ida Beitnes; Egner, Ingrid Marie & Gundersen, Kristian (2009). Are myonuclei forever?. Journal of Muscle Research and Cell Motility.  ISSN 0142-4319.  30(1), s 307
• Gundersen, Kristian (2009). Myter om formidling. Morgenbladet.  ISSN 0805-3847.
• Gundersen, Kristian (2009). Snåsakoden. Dagbladet.  ISSN 0805-3766.
• Gundersen, Kristian (2009). Vivant professores?. Universitas.  ISSN 0805-1798.
• Hansen, Einar Eftestøl Holm; Bruusgaard, Jo C. & Gundersen, Kristian (2009). What is the role of SMPX in skeletal muscle?. Journal of Muscle Research and Cell Motility.  ISSN 0142-4319.  129(1), s 329
• Lunde, Ida Gjervold; Bruusgaard, Jo C. & Gundersen, Kristian (2009). HIF-1a regulates fast MyHC expression in skeletal muscle of normally active adult rats. Journal of Muscle Research and Cell Motility.  ISSN 0142-4319.  129(1), s 328
• Brandtzæg, Per; Bruusgaard, Jo C. & Gundersen, Kristian (2008). Tvilsom bevisvurdering. Morgenbladet.  ISSN 0805-3847.
• Gundersen, Kristian (2008). Fra akademisk drift til akademisk flom. Morgenbladet.  ISSN 0805-3847.
• Bruusgaard, Jo C. & Gundersen, Kristian (2007). No loss of myonuclei after inactivity-induced skeletal muscle atrophy. Acta Physiologica Scandinavica.  ISSN 0001-6772. Show summary

  OBJECTIVE: The skeletal muscle cells are the largest cells in the mammalian body, and are one of few syncytia in mammals. Both in man and in animals it has been widely accepted that muscle cell size is correlated, and perhaps even causally related, to the number of myonuclei. Thus, it is assumed that hypertrophy involves incorporation of new nuclei from satellite cells, and that atrophy involves loss of nuclei by apoptosis. METHODS: Mice were denervated or neural transmission was blocked using TTX for up to 24 days, and stained in vivo using either intracellular injection of fluorescent oligonucleotides, or transfection with a plasmid encoding EGFP with a nuclear localization signal. Apoptotic nuclei were detected using TdT-labeling of fragmented DNA. RESULTS: After denervation up to 24 days there was no loss of myonuclei in neither the EDL nor solei muscles. We found the number of myonuclei per mm to be 52.95±1.7 (before denervation), vs. 54.31±2,8 (after denervation) in the EDL, and in the soleus 71.94±2.9 vs. 74.56±3.9, in spite of a reduction in cross sectional area of more than 50%. TTX block of the sciatic nerve yielded similar results. Apoptotic nuclei were found in the atrophying muscle tissue, but none of these were identified as belonging to muscle fibers. CONCLUSION: The classical idea of a constant karyoplasmatic ratio cannot be maintained for denervation atrophy. We confirm that in the first period after denervation, muscle tissue is undergoing atrophy and an active period of apoptosis, but the loss of cell nuclei by apoptosis seems to be confined to stroma and satellite cells.

• Ekmark, Merete & Gundersen, Kristian (2007). Transcription factors linking muscle activity to muscle phenotype. -A study of myogenin, MyoD and PPARd.
• Gundersen, Kristian (2007). Etter kunnskapsfallet: Hva nå?. Morgenbladet.  ISSN 0805-3847.  31/8
• Gundersen, Kristian (2007). Frihet under press. Dagbladet.  ISSN 0805-3766.  9/6
• Lunde, Ida Gjervold; Ekmark, Merete; Rana, Zaheer Ahmad; Buonanno, Andres & Gundersen, Kristian (2007). PPARdelta expression differs in slow and fast skeletal muscle and is influenced by muscle activity. Journal of Muscle Research & Cell Motility.  28(7-8), s 475- 475
• Lunde, Ida Gjervold; Ekmark, Merete; Rana, Zaheer Ahmad; Buonanno, Andres & Gundersen, Kristian (2007). PPARdelta is a link between muscle activity and a slow/oxidative muscle phenotype. Acta Physiologica.  ISSN 1748-1708.  190, s 65- 65
• Welde, Boye; Svebak, Sven; Gundersen, Kristian & Ekmark, Merete (2007). Effects of resistance training on muscle histology and cross-country ski performance. Show summary

  Previous research has demonstrated that heavy resistance exercise can increase the endurance performance in runners (Paavolainen et al., 1999) and that upper body training can induce the same effect in cross-country skiers (Hoff et al., 2002, 1999; Østerås et al., 2002; Terzis et al., 2005). It has also been demonstrated that such training improves work economy in runners (Johnston et al., 1997; Paavolainen et al., 1999) and in cross-country skiers (Hoff et al., 2002, 1999; Østerås et al., 2002). Although some previous studies have pointed out the effects of strength and upper body training upon endurance per¬formance, others have found no effect (Bishop et al., 1999; Bastiaans et al., 2001). Moreover, Hoff and co-workers (1999, 2002) and Østerås et al. (2002) studied the effect of maximal resistance exercise in a modified cable pulley specifically designed to simulate the movement pattern of the arms in ski double poling, whereas training outcomes were tested in double poling on a ski-ergometer in the laboratory. Thus, it remains to examine to what extent the findings reported by Hoff and co-workers (1999, 2002) and Østerås et al. (2002) apply to cross-country ski performance. Human skeletal muscles are composed of functionally diverse fibre types and show consider¬able plasticity. They can alter their phenotypic profile as well as significantly in¬crease muscle strength and size in response to specific training stimuli (Pette & Staron, 2001). Although histological and histochemical alterations are well documented in sedentary or moderately trained individuals subjected to concurrent strength and endurance training (Campos et al., 2002; Häkkinen et al., 2003; Putman et al., 2004), less is known about the consequences of adding strength training to already well trained elite endurance athletes. This study aimed at evaluating effects of two intensive resistance exercise programs and to relate these effects to cross-country ski race performance, roller- ski test performance and adaptations of the vastus lateralis muscle in male and female elite junior cross-country skiers. Generally, improvements in roller board test performance positively predicted enhanced roller-ski time-trial test performance (P = 0.04), whereas enhanced performance in push- ups (P = 0.004) and increased cross- sectional area of the type IIAX muscle fibres (P = 0.03) positively predicted cross- country ski race performance. Gender differences in predictions of cross-country ski race performance were observed: Training by 3∙30 reps predicted performance improvement among females (P = 0.05), whereas training by 3∙6 reps predicted performance improvement among males (P = 0.03). Effects of upper body resistance training generally appeared to be important for cross-country ski race performance. Strength test performance rose from pre-to- post training measurements in all subjects. Minor changes were found in vastus lateralis muscle fibre type composition.

• Bruusgaard, Jo C. & Gundersen, Kristian (2006). Muscle atrophy is not accompanied by loss of myonuclei. Journal of Muscle Research and Cell Motility.  ISSN 0142-4319.  27(5-7), s 533
• Ekmark, Merete & Gundersen, Kristian (2006). MyoD is activity dependent and can change muscle phenotype in the fast direction. Journal of Muscle Research and Cell Motility.  ISSN 0142-4319.  27(5-7), s 515- 515
• Lunde, Ida Gjervold; Ekmark, Merete & Gundersen, Kristian (2006). Regulation of adult muscle phenotype by PPARδ. Journal of Muscle Research and Cell Motility.  ISSN 0142-4319.  27(5-7), s 520- 520
• Gundersen, Kristian (2006). Motstandere av akademisk frihet. Universitas.  ISSN 0805-1798.
• Bruusgaard, Jo C. & Gundersen, Kristian (2005). Number and spatial distribution of myonuclei studied in vivo.
• Gundersen, Kristian (2005). Forskeren og revisoren. Dagbladet.  ISSN 0805-3766.
• Gundersen, Kristian (2005). UiOs rolle i Norge: Elitisme på Norsk. Dagbladet.  ISSN 0805-3766.
• Bruusgaard, Jo C.; Brack, Andrew; Hughes, Simon & Gundersen, Kristian (2004). Ultrastrucural changes in young mice expressing the MSVski proto-oncogene. Journal of Muscle Research and Cell Motility.  ISSN 0142-4319.  25, s 268 Show summary

  Mice carrying the MSVski proto-oncogene undergo muscle hypertrophy. This effect has been attributed to decreased protein breakdown possibly as a result of TGF-b signaling. The muscle fibers of these animals exhibit a reduced specific force (N/mm2) when compared to normal animals. This led us to investigate the ultrastructure of young ski mice using electron microscopy, in order to expose whether there might be a reduction in the relative amount of contractile apparatus. We also used in vivo injections of myonuclear dyes to investigate nuclear number. The study revealed enlarged mitochondria with disintegrated or damaged cristae, disrupted z-discs and a significantly larger amount of non-contractile area. The increase in nuclear number accompanying hypertrophy seen in normal mice was also absent. These findings could explain the lower specific force, as well as indicating a non-myosin related effect of the ski protein.

• Ekmark, Merete & Gundersen, Kristian (2004). Myogenin and MyoD as regulators of muscle phenotype in the adult. Journal of Muscle Research and Cell Motility.  ISSN 0142-4319.  25(3), s 272
• Bruusgaard, Jo C.; Liestøl, Knut; Ekmark, Merete; Kollstad, Kjetil & Gundersen, Kristian (2003). Number and spatial distribution of nuclei in muscle fibers of normal mice studied in vivo. Journal of Muscle Research and Cell Motility.  ISSN 0142-4319.  24, s 326
• Ekmark, Merete & Gundersen, Kristian (2003). MyoD -A regulator of fast myosin heavy chains?. Journal of Muscle Research and Cell Motility.  ISSN 0142-4319.  24(4-6), s 326- 326
• Gundersen, Kristian (2003). Fristilte universiteter betyr ikke økt akademisk frihet. Aftenposten (morgenutg. : trykt utg.).  ISSN 0804-3116.
• Ekmark, Merete & Gundersen, Kristian (2002). Effekter av myogenin på skjelettmuskelfibre hos voksne mus.
• Gundersen, Kristian (2000). En ny forskningspolitikk for Norge?. Aftenposten (morgenutg. : trykt utg.).  ISSN 0804-3116.
• Gundersen, Kristian (1998). Typisk norsk å være dum?. Aftenposten (morgenutg. : trykt utg.).  ISSN 0804-3116.
• Gundersen, Kristian; Utvik, Jo Kristian & Njå, Arild (1998). DNA injection in single cells of intact mice.
• Gundersen, Kristian & Bremer, Jon (1998). Forskningens nye herrer?. Forskningspolitikk.  ISSN 0333-0273.  4, s 22- 23
• Gundersen, Kristian & Røttingen, John-Arne (1998). Universitetet kastet ut med badevannet. Aftenposten (morgenutg. : trykt utg.).  ISSN 0804-3116.
• Gundersen, Kristian; Utvik, Jo Kristian & Njå, Arild (1998). Single transgenic muscle fibers in intact mice.
• Utvik, Jo Kristian; Ashtari, Ohmid; Bruusgaard, Jo C.; Bezakova, Gabriela; Mathiesen, Iacob; Lømo, Terje; Njå, Arild & Gundersen, Kristian (1997). Injection and expression of foreign DNA in single skeletal muscle fibers in vivo.

View all works in Cristin