Regional (14C) 2‐deoxyglucose uptake during forelimb movements evoked by rat motor cortex stimulation: Cortex, diencephalon, midbrain

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Abstract
The caudal forelimb region of right “motor” cortex was repetitively stimulated in normal, conscious rats. Left forelimb movements were produced and (14C) 2-deoxyglucose (2DG) was injected. After sacrifice, regions of increased brain (14C) 2DG uptake were mapped autoradiographically. Uptake of 2DG increased about the stimulating electrode in motor (MI) cortex. Columnar activation of primary (SI) and second (SII) somatosensory neocortex occurred. The rostral or second forelimb (MII) region of motor cortex was activated. Many ipsilateral subcortical structures were also activated during fore-limb MI stimulation (FLMIS). Rostral dorsolateral caudate-putamen (CP), central globus pallidus (GP), posterior entopeduncular nucleus (EPN), sub-thalamic nucleus (STN), zona incerta (ZI), and caudal, ventrolateral substantia nigra pars reticulata (SNr) were activated. Thalamic nuclei that increased (14C) 2DG uptake included anterior dorsolateral reticular (R), ventral and central ventrolateral (VL), lateral ventromedial (VM), ventral ventrobasal (VB), dorsolateral posteromedial (POm), and the parafascicular-centre median (Pf-CM) complex. Activated midbrain regions included ventromedial magnocellular red nucleus (RNm), posterior deep layers of the superior colliculus (SCsgp), lateral deep mesencephalic nucleus (DMN), nucleus tegmenti pedunculopontinus (NTPP), and anterior pretectal nucleus (NCU). Monosynaptic connections from MI or SI to SII, MII, CP, STN, ZI, R, VL, VM, VB, POm, Pf-CM, RNm, SCsgp, SNr, and DMN can account for ipsilateral activation of these structures. GP and EPN must be activated polysynaptically, either from MI stimulation or sensory feedback, since there are no known monosynaptic connections from MI and SI to these structures. Most rat brain motor-sensory structures are somatotopically organized. However, the same regions of R, EPN, CM-Pf, DMN, and ZI are activated during FLMIS compared to VMIS (vibrissae MI stimulation). Since these structures are not somatopically organized, this suggests they are involved in motor-sensory processing independent of which body part is moving. VB, SII, and MII are activated during FLMIS but not during VMIS.