Behaviorally-induced ultrastructural plasticity in the hippocampal region after cerebral ischemia

Behavioral training has been shown to induce synaptic plasticity in both intact and injured animals. Because of the possibility that the adaptive changes after ischemic damage may make the brain more malleable to behavioral training, we examined the effects of complex environment (EC) housing and exercise (EX) after global cerebral ischemia on synaptic structural alterations. Forty-two adult male Wistar rats were included in the study and assigned to either ischemia or sham group. Following ischemic or sham surgery, rats were randomized to either EC, EX, or social condition (SC, paired housing) group. CA1 was processed for electron microscopy and unbiased stereological techniques were used to evaluate plasticity. Significantly decreased neuron density was seen in anterior and medial CA1 in ischemic animals regardless of behavioral training. Neuron density in anterior CA1 was 31% less than the medial area. Synaptogenesis was influenced by cerebral ischemia and behavioral training in that all ischemic groups and sham EC animals showed greater number of synapses per neuron compared to the sham EX and SC groups. Analysis of synapse configuration showed that the synaptogenesis in ischemia EX and SC rats was formed mainly by synapses with single synaptic boutons, whereas in the ischemia EC and sham EC rats synaptogenesis was formed mainly by synapses with multiple synaptic boutons. Furthermore, housing of sham and ischemia rats in EC resulted in increased number of synapses with perforated postsynaptic density. Together, these data suggest that behavioral experience in EC after insult may be able to enhance synaptic plasticity.