Journal of Neuroscience, Vol 6, 448-462, Copyright © 1986 by Society for Neuroscience
Functional metabolic mapping during forelimb movement in rat. I. Stimulation of motor cortex
RC Collins, EM Santori, T Der, AW Toga and EW Lothman
The quantitative 14C-deoxyglucose (DG) autoradiographic technique has been
used to study changes in cerebral metabolism during forelimb movements
induced by graded stimulation of motor cortex. Experiments were directed at
studying basic physiologic and anatomic aspects of the metabolic changes.
Single shocks caused movement without metabolic change, whereas
low-frequency trains caused seizures. Repetitive high- frequency train
stimuli of short duration (500 Hz for 20 msec) caused jerk movements
coupled with DG uptake in pathways. With stimulation of the forelimb motor
zone at frequencies of 15-30/min there was prominent activation of cortical
columns and strips in ipsilateral SI, SII, and MII, and contralateral MI
and SI. Higher frequencies (120/min) were required to cause significant
changes in DG in subcortical circuits. The most prominent changes occurred
within a longitudinal corridor in dorsal thalamus and a ventral corridor in
second-order sites in basal ganglia. Metabolic activation also occurred in
contralateral cerebellum, the cuneate nucleus, and dorsal horn of the
cervical spinal cord. Changes in these latter two sites were largely
eliminated by removing feedback sensory activity. Stimulation of the
forelimb sensory zone activated different sites in caudatoputamen and
thalamus but similar zones in midbrain and cerebellum. The magnitude of the
metabolic response in distant sites depended on the frequency of cortical
stimulation. Different frequency-response relationships in different sites
seemed to reflect the nature of the cortical input as well as differential
effects of anesthesia. The pattern of the metabolic response was studied by
comparing sites of activation with sites of the anatomic projections from
motor and sensory cortical zones. 3H- and 14C-labeled amino acids were used
to map the site and relative strength of pathways. Results revealed good
correlation between the site of anatomic projection and the site of DG
uptake but no consistent relationship between the relative strength of a
projection and the magnitude of metabolic change within its field. Changes
in glucose utilization with metabolic mapping experiments depend on the
nature, strength, and frequency of stimulation; the site and nature of
anatomic projection; the effects of anesthesia; and the strength of sensory
feedback associated with the induced behavior.