Acute Thrombotic Infarction Suppresses Metabolic Activation of Ipsilateral Somatosensory Cortex: Evidence for Functional Diaschisis

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Abstract
To study the effects of focal infarction on the capacity for functional activation of an ipsilateral somatosensory system remote from the lesion, we produced a small thrombotic infarct in the left frontal pole of male Wistar rats by a photochemical method. Five days later, the awake, restrained rats received tactile stimulation of the large whiskers (vibrissae) of the right side of the face, while a double-label 14C-autoradiographic study of local CMRglc (lCMRglc) and local CBF (lCBF) was performed. Unlesioned and unstimulated animals served as controls. In rats without frontal infarct, vibrissae stimulation led to activation of lCMRglc in the three synaptic relay stations of the barrel-field pathway (ipsilateral trigeminal medullary nucleus, contralateral ventrobasal thalamus, and contralateral barrel-field cortex). The mean increment in lCMRglc was 42% in lamina IV of barrel-field cortex and 49% in ventrobasal thalamus. Normalized lCBF tended to increase in superficial cortical laminae. In unstimulated animals with frontal infarct, lCMRglc was reduced by 20–30% throughout the ipsilateral barrel-field cortex as well as other ipsilateral cortical regions, but not in ventrobasal thalamus or other subcortical areas. In animals with frontal infarct subjected to contralateral vibrissae stimulation, a remarkable suppression of activation was observed throughout the barrel-field cortex so that left-less-than-right hemispheral lCMRglc asymmetry persisted despite stimulation. The ventrobasal thalamus, similarly, failed to increment its lCMRglc with vibrissae stimulation, whereas activation of the trigeminal nucleus was not suppressed. Similar trends were observed in the normalized lCBF data. These observations, which establish that a small frontal infarct is capable of suppressing normal physiological activation in remote ipsilateral brain structures, may have important implications with respect to suppression and recovery of function in human ischemic stroke.