The Journal of Neuroscience, December 1992, fZ(12): 4923-4931 Vasoactive Intestinal Peptide and Noradrenaline Exert Long-Term Control on Glycogen Levels in Astrocytes: Blockade by Protein Synthesis Inhibition Olivier Sorg and Pierre J. Magistretti lnstitut de Physiologie, Universitk de Lausanne, CH-1005 Lausanne. Switzerland Vasoactive intestinal peptide (VIP) and noradrenaline (NA) increases in brain glycogen content, particularly in astro- have been previously shown to promote glycogenolysis in cytes, that are observed in experimental neurodegeneration mouse cerebral cortex (Magistretti, 1990). This action, which induced by brain trauma or x-irradiation (Shimizu and Ha- is fully expressed within a few minutes, is exerted on astro- muro, 1958; Lundgren and Miquel, 1970). In both conditions, cytes (Sorg and Magistretti, 1991). In the present article, we the increase in glycogen occurs in reactive astrocytes that report a second, temporally delayed, action of VIP or NA in have been partially or totally deprived of their neuronal en- primary cultures of mouse cerebral cortical astrocytes; thus, vironment. following glycogenolysis, an induction of glycogen resyn- thesis is observed, resulting, within 9 hr, in glycogen levels The glycogen content of the rodent brain rangesbetween 20 and that are 6-10 times higher than those measured before the 60 nmol/mg protein, dependingon the region (Passonneauand application of either neurotransmitter. This effect of VIP or Lauderdale, 1974; Sagar et al., 1987). In the cerebral cortex, NA is concentration dependent and, for NA, is mediated by glycogen levels are approximately 30 nmol/mg protein (Sagar adrenergic receptors of the B subtype. The continued pres- et al., 1987). Glycogen is localized in astrocytes,to suchan extent ence of the neurotransmitter is not necessary for this long- that this cell type can be positively identified at the ultrastruc- term effect, since pulses as short as 1 min result in the tural level by the presenceof glycogen granulesin the cytoplasm doubling of glycogen levels 9 hr later. The induction of gly- (Peters et al., 1991). This astrocytic glycogen pool is metabol- cogen resynthesis triggered by VIP or NA is dependent on ically very active, as indicated by its rapid turnover rate (Wa- protein synthesis, since both cycloheximide and actinomy- tanabe and Passonneau,1973; Ibrahim, 1975; Siesjo, 1978) and tin D abolish it entirely. The ability to elicit glycogenolysis by the fact that it is under the control of multiple regulatory is not sufficient per se to trigger the induction of glycogen mechanisms(Magistretti, 1988). Thus, decreasedsynaptic ac- resynthesis. Thus, two glycogenolytic agents such as meth- tivity, achieved for example by anesthesia(Nelson et al., 1968; oxamine, an a,-adrenergic agonist, and phorbol 12,13-di- Brunner et al., 1971; Passonneauet al., 1971), markedly in- butyrate, both acting via protein kinase C activation, are creasesthe glycogen content of the brain, particularly in astro- unable to induce glycogen resynthesis. This observation, cytes (Phelps, 1972).Administration ofthe glutamine synthetase taken together with the fact that dibutyryl-CAMP application inhibitor methionine sulfoximine has similar effects (Phelps, also results in enhanced glycogen resynthesis, strongly sug- 1975).Glycogen levels are also increasedduring slow-wave sleep gests that the long-term effect of VIP or NA is mediated by (Kamovsky et al., 1983). Under normal conditions, glycogen is the CAMP second-messenger pathway. These results indi- hardly visible at the light microscopic level using standard stain- cate that the same neurotransmitter, for example, VIP or NA, ing procedures(Shimizu and Hamuro, 1958). However, a com- can elicit two actions with different time courses: (1) gly- mon finding reported following lesionsof the brain parenchyma cogenolysis, occurring within minutes, and (2) glycogen re- either of traumatic origin, for example, stab wound (Shimizu synthesis, fully expressed after several hours. The two ac- and Hamuro, 1958; Hager et al., 1967; Haymaker et al., 1970; tions are mechanistically coordinated since the long-term Watanabe and Passonneau,1974; Al-Ali and Robinson, 1982) one, that is, glycogen resynthesis, ensures that sufficient or by x-ray irradiation (Wolfe et al., 1962; Lundgren and Miquel, substrate is available for the expression of the short-term 1970) is a massive deposition of glycogen granules, predomi- effect, that is, glycogenolysis. These results also indicate nantly in glial cells at the periphery of the lesioned area. These that the glycogen content of astrocytes in primary culture, histochemical observations have been confirmed by biochem- a condition in which neurons are absent, can increase con- ical measurementsof glycogen levels following brain trauma, siderably; a parallel could therefore be drawn with the marked which indicate an early (i.e., within 10 min) decreasefollowed by a delayed increasein glycogen after 2.5-24 hr (Watanabe and Passonneau, 1974). Another neurodegenerative condition in Received Apr. 24, 1992; revised July 6, 1992; accepted July 16, 1992. which glycogen accumulations are observed, particularly in the We thank Dr Jean-Luc Martin for his comments and for helpful discussions. This work was supported by a grant from Fonds National Suisse de la Recherche cerebral cortex, is Alzheimer’s disease(Mann et al., 1987). Brain Scientifique (31-26427.89) to P.J.M. glycogen levels are also under the tight control of numerous Correspondence should be addressed to Pierre J. Magistretti, M.D., Ph.D., Institut de Physiologic, Universite de Lausanne, 7 rue du Bugnon, CH-1005 Lau- neurohumoral factors (Magistretti, 1988). Thus, the monoam- sanne, Switzerland. inesnoradrenaline (NA), histamine,and serotonin(5-HT) (Quach Copyright 0 1992 Society for Neuroscience 0270-6474/92/124923-09$05.00/O et al., 1978, 1980, 1982), as well as adenosineand the peptide 4924 Sorg and Magistretti l Bidirectional Effects of VIP and NA on Glycogen in Astrocytes Table 1. Induction of glycogen resynthesis elicited by VIP as a function of pulse duration Glycogen levels Pulse duration (nmoVmg protein) Experiment 1 0 35 iz 7 10 min 149 & 18 30 min 396 t- 29 1 hr 382 + 25 2 hr 381 + 13 9 hr 507 * 12 Experiment 2 0 27 k 5 1 min 60 k 4 Time (hours) 5 min 69 k 4 15 min 106 + 7 Figure I. Time course of the effects of VIP on glycogen levels. VIP (1 30 min 135 -t 4 PM) was applied for various periods of time. The inset shows in detail 9 hr 365 k 16 the curve for short periods of VIP application. Results are the mean f SEM of quadruplicate determinations from one experiment, repeated VIP (1 PM) was added for various periods of time. The medium was replaced with once with similar results. one not containing the neurotransmitter, and glycogen levels were assayed 9 hr after the beginning of VIP application. Results are the mean 2 SEM of quadru- plicate determinations for each separate experiment. vasoactive intestinal peptide (VIP), exert a potent glycogenolytic action in slices of the cerebral cortex (Magistretti et al., 1981, cultures in which 85-90% of cells are immunoreactive for glial fibrillary 1986; Hof et al., 1988). More recently, most of these neuro- acidic protein (Stoyanov et al., 1988). transmitters have been shown to promote glycogenolysisin pri- Glycogen assay. After 14-2 1 d in culture, the cells reached confluence mary cultures of astrocytes (Sorg and Magistretti, 1991). In con- and were used for the glycogen assay, as previously described (Sorg and trast, in this cellularly homogeneous preparation, insulin (Dringen Magistretti, 1991). Culture medium was replaced with a serum-free and Hamprecht, 1992), glutamate, and methionine sulfoximine DMEM containing 5 mM glucose (instead of 25 mM for the culture medium). Four hours after having replaced the medium, pharmacolog- but not phenobarbital (Swanson et al., 1989, 1990) increase in ical agents were added for various periods of time, during which cultures a time- and concentration-dependent manner the glycogen con- were maintained in the incubator.-The reaction was stopped by washing tent. These observations led us to propose that the primary the cells with ice-cold PBS (phosphate-buffered saline), and by adding action of certain neurotransmitters such as VIP or NA may be 2 ml of 30 mM HCl. The cells were son&ted and the susuension was used to measure glycogen as described by Nahorski and Rogers (1972). to regulate local energy homeostasiswithin the CNS by acting Briefly, three 100 pl aliquots were sampled. In the first aliquot, 300 ~1 on non-neuronalcells such as astrocytes(Magistretti, 1990,199 1). of acetate buffer were added. In the second, 300 ~1 of a solution con- From the foregoing set of observations, it is clear that the me- taining 10% of amyloglucosidase (10 mg/ml) in acetate buffer (0.1 M, tabolism of brain glycogen occurs predominantly in astrocytes pH 4.65) were added, and the mixture was incubated at room temper- and that it is more dynamically regulatedthan previously thought. ature for 30 min. After incubation with amyloglucosidase, 2 ml ofTris HCl buffer (0.1 M, pH 8.1) containing MgCl, (3.3 mM), ATP (0.2 mM), As a further indication of the plasticity of brain glycogen NADP (25 &ml), hexokinase (4 &ml), and glucose-6-phosphate de- metabolism, we report in the present article on a study con- hydrogenase (2 &ml) were added, and the mixture was incubated at ducted in primary cultures of mousecerebral cortical astrocytes, room temperature for 30 min. The first aliquot was treated identically. in which two opposed and temporally regulated actions of a The fluorescence of the NADPH formed was then read on a fluorometer (excitation, 340 nm; emission, 450 nm). The first aliquot gives the sum single neurotransmitter on glycogen levels are demonstrated. of glucose and glucose-6-phosphate, while the second gives the sum of Thus, in addition to promoting glycogenolysiswithin a few min- glycogen, glucose, and glucose-6-phosphate; the amount of glycogen is utes (Sorg and Magistretti, 1991), VIP or NA markedly stim- then determined by the difference between the first two aliquots.