Structural basis of information capacity changes of sensory-motor cerebral cortex of rat brain during post-resuscitation period.

In a rat model of asphyxial cardiac arrest the volume of the sensory-motor cortex and the number of neurons and synapses were determined 90 min, 6 h, and 1, 3, 7, 14, and 30 days post-resuscitation. The number of synapses was determined from serial fragmental sections, using selective contrast in ethanol solution of phosphorotungsten acid (PTA), and by cytoarchitectonic analysis on medium-thick sections. The sensory-motor cortex (SMC) volume did not change significantly during the subsequent 30 days after resuscitation. The number of neurons decreased from 2.462 +/- 0.082) x 10(6) pre-insult to (1.441 +/- 0.098) x 10(6) 30 days after resuscitation. Damage was most severe in the small neuronal cell complexes of layers III-IV, which serve as an afferent cortical 'entrance'. Damage was least in the large neuronal cell complexes of layer V, which serves as an efferent cortical 'outlet'. The number of SMC synapses decreased from (5.920 +/- 0.51) x 10(9) pre-insult to (3.441 +/- 0.305) x 10(9) 30 days after resuscitation. Damage was most severe in the synaptic pool of the cortical SMC 'entrance'. An increase in the number of high-efficiency hypertrophic synaptic contacts was observed during the post-resuscitation period, which may significantly change interneuronal relationships.