Skip to main content

Glycogenolysis in Cerebral Cortex During Sensory Stimulation, Acute Hypoglycemia, and Exercise: Impact on Astrocytic Energetics, Aerobic Glycolysis, and Astrocyte-Neuron Interactions

  • Chapter
  • First Online:
Brain Glycogen Metabolism

Part of the book series: Advances in Neurobiology ((NEUROBIOL,volume 23))

Abstract

Most glycogen in cerebral cortex is located in astrocytes, and the importance of glycogenolysis for critical functions, including neurotransmission and memory consolidation, is strongly supported by many studies. However, specific mechanisms through which glycogen sustains essential functions remain to be established by rigorous, quantitative studies. Cerebral cortical glycogen concentrations are in the range of 10–12 μmol/g in carefully-handled animals, and the calculated rate of glycogenolysis (CMRglycogen) during sensory stimulation is approximately 60% that of glucose utilization (CMRglc) by all cells, with lower rates during acute hypoglycemia and exercise to exhaustion. CMRglycogen is at least fourfold higher when the volume fraction of astrocytes is taken into account. Inclusion of glycogen consumed during sensory stimulation in calculation of the oxygen-glucose index (OGI = CMRO2/CMRglc, which has a theoretical maximum of 6 when no other substrates are metabolized) reduces OGI from 5.0 to 2.8. Thus, at least 53% of the carbohydrate is not oxidized, suggesting that glycogen mobilization supports astrocytic glycolysis, not neuronal oxidation of glycogen-derived lactate that would cause OGI to exceed 6. Failure of glycogenolysis to dilute the specific activity of lactate formed from blood-borne [6-14C]glucose indicates compartmentation of glycolytic metabolism of glucose and glycogen and the rapid release from cerebral cortex of glycogen-derived lactate. Together, these findings invalidate the conclusion by others that glycogen-derived lactate is a major fuel for neurons during neurotransmission, memory consolidation, and exercise to exhaustion. Alternative mechanisms, including glucose sparing for neurons, are presented as testable explanations for data interpreted as lactate shuttling.

This is a preview of subscription content, log in via an institution to check access.

Access this chapter

Chapter
USD 29.95
Price excludes VAT (USA)
  • Available as PDF
  • Read on any device
  • Instant download
  • Own it forever
eBook
USD 149.00
Price excludes VAT (USA)
  • Available as EPUB and PDF
  • Read on any device
  • Instant download
  • Own it forever
Softcover Book
USD 199.99
Price excludes VAT (USA)
  • Compact, lightweight edition
  • Dispatched in 3 to 5 business days
  • Free shipping worldwide - see info
Hardcover Book
USD 199.99
Price excludes VAT (USA)
  • Durable hardcover edition
  • Dispatched in 3 to 5 business days
  • Free shipping worldwide - see info

Tax calculation will be finalised at checkout

Purchases are for personal use only

Institutional subscriptions

Abbreviations

(A-V)substrate:

Arteriovenous difference across the brain for the identified substrate

Asp:

Aspartate

BAY U6751:

4-(2-Chlorophenyl)-l-ethyl-1,4-dihydro-6-methyl-2,3,5-pyridinetricarboxylic acid 5-isopropyl ester disodium salt hydrate

CBF:

Cerebral blood flow rate

CMR:

Cerebral metabolic rate for substrate of interest = CBF(A-V)substrate

CMRglc:

Cerebral metabolic rate for glucose = CBF(A-V)glc

CMRglycogen:

Cerebral metabolic rate for glycogen = Δ[glycogen]/time

CMRO2:

Cerebral metabolic rate for oxygen CBF(A-V)O2

CP-316,819:

[R-R∗,S∗]-5-chloro-N-[2-hydroxy-3-(methoxymethylamino)-3-oxo-l-(phenylmethyl)propyl]-1H-indole-2-carboxamide

DAB:

1,4-Dideoxy-1,4-imino-d-arabinitol

DG:

2-deoxy-d-glucose

DMSO:

Dimethyl sulfoxide

FDG:

2-fluoro-2-deoxy-d-glucose

Glc:

Glucose

Glc-6-P:

Glucose-6-phosphate

Gln:

Glutamine

Glu:

Glutamate

GLUT:

Glucose transporter; GLUT1 in vascular endothelium and astrocytes, and GLUT3 and GLUT4 in neurons

GPR81:

G-protein-coupled lactate receptor81, also known as HCAR1

HCAR1:

Hydroxycarboxylic acid receptor1 also known as GPR81

KO:

Knockout

Lac:

Lactate

LTP:

Long-term potentiation

MCT:

Monocarboxylic acid transporter; MCT1 and MCT4 isoforms are mainly astrocytic, whereas MCT2 is predominantly neuronal

NMDA:

N-Methyl-d-aspartate

OCI:

Oxygen carbohydrate index = CMRO2/[CMRglc + 0.5CMRlac + CMRglycogen] = (A-V)O2/((A-V)glc + 0.5(A-V)lac + Δ[glycogen]), where lactate and [glycogen] are expressed in glucosyl units (2Lac = 1Glc)

OGI:

Oxygen-glucose index = CMRO2/CMRglc = (A-V)O2/(A-V)glc (CBF cancels out). This calculation assumes no other substrates are oxidized

PAPs:

Peripheral astrocytic processes

RSA:

Relative specific activity (SA) = ratio of the SA of a compound of interest to the SA of a reference compound, e.g., SA lactate/SA glucose

SA:

Specific activity (dpm/μmol)

TCA:

Tricarboxylic acid

References

Download references

Acknowledgements

Conflict of interest: The authors declare that they have no conflicts of interest.

Sources of funding: DLR: R01MH109159, R01 NS087568, R01 NS100106.

Author information

Authors and Affiliations

Authors

Corresponding author

Correspondence to Gerald A. Dienel .

Editor information

Editors and Affiliations

Rights and permissions

Reprints and permissions

Copyright information

© 2019 Springer Nature Switzerland AG

About this chapter

Check for updates. Verify currency and authenticity via CrossMark

Cite this chapter

Dienel, G.A., Rothman, D.L. (2019). Glycogenolysis in Cerebral Cortex During Sensory Stimulation, Acute Hypoglycemia, and Exercise: Impact on Astrocytic Energetics, Aerobic Glycolysis, and Astrocyte-Neuron Interactions. In: DiNuzzo, M., Schousboe, A. (eds) Brain Glycogen Metabolism. Advances in Neurobiology, vol 23. Springer, Cham. https://doi.org/10.1007/978-3-030-27480-1_8

Download citation

Publish with us

Policies and ethics