Development of cortical spreading depression and of its transition to the caudate nucleus in rats.

The development of Leão's spreading depression (SD) of electroencephalographic activity was studied in young rats by recording the accompanying slow potential changes (SPC). The propagation rate of cortical SD increased from 1.65 mm/min on Day 15 to 2.6 mm/min on Day 20; the increase of SPC amplitude and the decrease of SPC duration were less evident over the same period. The SD elicited in the caudate nucleus by microinjections of KCl did not spread to neocortex in 20- and 30-day-old rats and transition occurred in only 5% of KCl applications in 40-day-old rats. Application of a pyrrolopyrimidine derivative (BW 57-271; 5 mg/kg) increased the cortico-caudate SD transition of 100% in rats aged 20 days or older and increased the SPC amplitude in both structures. The development of SD parameters can be ascribed to dendritic growth and to the decrease of extracellular space; the cortico-caudate propagation block can be ascribed to morphological immaturity of the transitional zone.