This study further investigates the possible connection between postconcussive cognitive impairment and damage to forebrain cholinergic innervation. Moderate parasagittal fluid percussion injury was delivered to adult male rats. Water maze performance and synaptosomal choline uptake was measured at various times following injury. Water maze learning was severely impaired between 1 and 5 weeks, but recovered to normal by 10 weeks. Synaptosomal choline uptake was significantly decreased by 15-27% in the ipsilateral hippocampus and parietal cortex 3 and 7 days following injury, but not by 3 weeks or thereafter. Choline acetyltransferase was also significantly decreased in the ipsilateral cortex at 3 and 7 days with subsequent recovery. This study shows that parasagittal fluid percussion injury causes significant impairment in water maze learning and ipsilateral forebrain cholinergic innervation. Both of these parameters recover spontaneously, but with different time courses.

Clinically, elderly patients have a higher cognitive morbidity from head trauma than young patients. We have modeled injury in aged rats in an effort to elucidate the pathophysiology of this enhanced sensitivity and, in particular, to determine if there are susceptibility differences in forebrain cholinergic innervation in young versus aged rats. Aged (20-23 months) and young (2-3 months) rats were subjected to injury under halothane anesthesia using the Marmarou impact acceleration model. Injury parameters required adjustment downward for the aged rats (323 g at 1.61 m versus 494 g at 2.06 m) to provide equivalent mortality (30% versus 20%) and loss of righting-reflex times (10-12 min average). At 1 week following injury, the aged animals were markedly more impaired in water maze performance than were young rats, and this difference persisted at least up to 5 weeks following injury. The extent of improvement in performance from 1 to 5 weeks was markedly worse for aged animals compared to young animals. Forebrain synaptosomal choline uptake was decreased in aged injured rats by 8-14% at 1, 3, and 5 weeks postinjury, but not decreased in young injured rats. No differences were noted in entorhinal cortex or hippocampal choline uptake. This model effectively demonstrates the markedly increased susceptibility of older animals to head injury and their decreased capacity for recovery. The neurophysiological basis for this difference is presently unknown, but the differences in cognitive dysfunction between young and aged rats appears to be much greater than would seem to be explained by the small differences in forebrain cholinergic innervation.

A patient with a prior left pneumonectomy required surgical drainage of a right upper lobe aspergilloma. A left double-lumen endobronchial tube was placed in the right bronchus intermedius, isolating the right upper lobe while allowing ventilation of the right middle and lower lobes.

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