Changes in some ultrastructural parameters of cortical synapses in the initial phases of kindling

Repeated electrical stimulation of the sensorimotor region of rat cerebral cortex at 10 min intervals led to the development and progressive prolongation of self-sustained after-discharges (SSAD). One minute after the third SSAD ended, an electronoptic morphological analysis of type I synapses after Gray from the second cortical layer of the homotopic area of the unstimulated hemisphere was carried out. In the experimental animals, an 11.7% increase in the area of the presynaptic bag and a 5.5% increase in its perimeter were demonstrated. The number of agranular synaptic vesicles per constant unit area fell by 70.8%. The area of the mitochondria in the presynaptic ending increased by 49.8% and their perimeter by 16.1%. The area of the postsynaptic element increased by 34.1% and its perimeter by 15.7%. Changes in the synapses are evaluated as manifestations of exhaustion and primarily as a manifestation of ion shifts during the epileptic seizure. The findings nevertheless also testify to incipient activation of restitution mechanisms in the structures of the synaptic apparatus within a very short time after termination of the seizure.