Principal cell spiking, postsynaptic excitation, and oxygen consumption in the rat cerebellar cortex.
One contention within the field of neuroimaging concerns the character of the depicted activity: Does it represent neuronal action potential generation (i.e., spiking) or postsynaptic excitation? This question is related to the metabolic costs of different aspects of neurosignaling. The cerebellar cortex is well suited for addressing this problem because synaptic input to and spiking of the principal cell, the Purkinje cell (PC), are spatially segregated. Also, PCs are pacemakers, able to generate spikes endogenously. We examined the contributions to cerebellar cortical oxygen consumption (CMRO2) of postsynaptic excitation and PC spiking during evoked and ongoing neuronal activity in the rat. By inhibiting excitatory synaptic input using ionotropic glutamate receptor blockers, we found that the increase in CMRO2 evoked by parallel fiber (PF) stimulation depended entirely on postsynaptic excitation. In contrast, PC spiking was largely responsible for the increase in CMRO2 when ongoing neuronal activity was increased by gamma-aminobutyric acid type A receptor blockade. In this case, CMRO2 increased equally during PC spiking with excitatory synaptic activity as during PC pacemaker spiking without excitatory synaptic input. Subsequent inhibition of action potential propagation and neurotransmission by blocking voltage-gated Na+-channels eliminated the increases in CMRO2 due to PF stimulation and increased PC spiking, but left a large fraction of CMRO2, i.e., basal CMRO2, intact. In conclusion, whereas basal CMRO2 in anesthetized animals did not seem to be related to neurosignaling, increases in CMRO2 could be induced by all aspects of neurosignaling. Our findings imply that CMRO2 responses cannot a priori be assigned to specific neuronal activities.
Thomsen
Kirsten
K
Institute of Neuroscience and Pharmacology, University of Copenhagen, and Department of Clinical Neurophysiology, Glostrup Hospital, Panum Institute 12.5, Blegdamsvej 3, DK-2200 Copenhagen N, Denmark. kthomsen@sund.ku.dk
Piilgaard
Henning
H
Gjedde
Albert
A
Bonvento
Gilles
G
Lauritzen
Martin
M
D018750:6-Cyano-7-nitroquinoxaline-2,3-dione / Q000494:pharmacology; D000200:Action Potentials / Q000502:physiology*; D000704:Analysis of Variance; D000818:Animals; D001640:Bicuculline / Q000494:pharmacology; D001703:Biophysics; D002247:Carbon Isotopes / Q000378:metabolism; D002525:Cerebellar Cortex / Q000098:blood supply / Q000166:cytology*; D003847:Deoxyglucose / Q000378:metabolism; D016291:Dizocilpine Maleate / Q000494:pharmacology; D004558:Electric Stimulation / Q000379:methods; D018691:Excitatory Amino Acid Antagonists / Q000494:pharmacology; D019706:Excitatory Postsynaptic Potentials / Q000187:drug effects / Q000502:physiology*; D018756:GABA Antagonists / Q000494:pharmacology; D017078:Laser-Doppler Flowmetry / Q000379:methods; D008297:Male; D009412:Nerve Fibers / Q000502:physiology; D009434:Neural Pathways / Q000502:physiology; D010101:Oxygen Consumption / Q000187:drug effects / Q000502:physiology*; D011689:Purkinje Cells / Q000502:physiology*; D051381:Rats; D017208:Rats, Wistar; D012039:Regional Blood Flow / Q000187:drug effects; D026941:Sodium Channel Blockers / Q000494:pharmacology; D013779:Tetrodotoxin / Q000494:pharmacology
D002247:Carbon Isotopes; D018691:Excitatory Amino Acid Antagonists; D018756:GABA Antagonists; D026941:Sodium Channel Blockers; D013779:Tetrodotoxin; D016291:Dizocilpine Maleate; D018750:6-Cyano-7-nitroquinoxaline-2,3-dione; D003847:Deoxyglucose; D001640:Bicuculline