Histopathologic changes in the thalamus of 23 rats after somatosensory cortical infarction produced by middle cerebral artery occlusion were examined using the Fink-Heimer silver staining method, immunohistochemistry with antibodies against glial fibrillary acidic protein and laminin, and conventional stains. Middle cerebral artery occlusion produced cortical infarcts in the lateral parietal region, with variable involvement of the frontoparietal parasagittal sensorimotor cortex. Within 3 days after occlusion, massive terminal degeneration but no neuronal changes were apparent in the ipsilateral thalamus. By 1 week after occlusion, abnormal neurons with darkly stained, shrunken nuclei and atrophic perikarya were present in the ipsilateral thalamic nuclei. These neurons were densely argyrophilic in A xonal lesions cause not only anterograde degen-/ \ eration in distal segments of axons but also A. V . retrograde cell death in some neural centers. 1 -2 Central nervous system lesions thus can damage neural structures remote from the primary lesions. We have reported widespread degeneration of corticofugal axons and their terminals in rat brainstem and spinal cord after cortical infarction produced by middle cerebral artery (MCA) occlusion (MCAO). 3Several anatomic studies have shown retrograde neuronal degeneration in mammalian thalamus after decortication. 1 -2 "* Recent positron emission tomographic studies have revealed hypometabolic states in the ipsilateral thalamus of patients with focal cortical or capsular infarcts after MCAO. 56 We consequently examined the thalamus in rats after unilateral MCAO. Our model consistently produces infarcts in the lateral parietal cortical area, with variable involvement of the parasagittal frontoparietal cortex but little direct ischemic damage to subcortical structures. Received October 18, 1989; accepted January 9, 1990. somatosensory cortex and receive thalamocortical fibers from specific thalamic nuclei, that is, the ventroposteromedial and ventroposterolateral nuclei. 8The ventroposteromedial nucleus is the specific somatosensory relay nucleus for face sensation, while the ventroposterolateral nucleus serves the body, fore limbs, and hind limbs.8 Materials and MethodsWe studied 23 adult male Long-Evans hooded rats weighing 250-350 g. The rats were anesthetized with 40 mg/kg i.p. pentobarbital. The right MCA was exposed via a subtemporal craniotomy preserving the zygomatic arch so that the rats could feed after surgery. 37 The MCA was occluded and divided 1-2 mm below the rhinal fissure. The rats usually showed mild contralateral hemiparesis and a tendency to circle toward the lesioned site after MCA. Such symptoms, however, disappeared within 24 hours. The rats were housed in boxes containing sterile hardwood chips and fed ad libitum. They regained their preoperative weights within a week.The rats were randomly sacrificed 1 (n=4), 2 (n=3), or 3 (n=3) days or 1 (n=6), 3 (n=3), or 6 (n=4) weeks after MCAO by transcardiac perfusion with 4% paraformaldehyde or 10% forma...

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