Morphological change associated with reactive synaptogenesis in the rat dentate gyrus: Insights on the general mechanisms of synaptic plasticity

Research in neuroplasticity has revealed a common ultrastructural cascade across several paradigms, such as development, long-term potentiation (LTP), and adult reactive synaptogenesis (RS). These changes and their functional implications comprise a sequential model, forming a theoretical framework for investigating RS. The density, proportion, and morphology were assessed for several synaptic subtypes. Concave synapses showed an immediate/long-lasting increase in curvature, and retained pre-lesion density despite massive degeneration, suggesting their importance for neural function. Flat synapses showed unique changes in incidence and growth, having implications for development/activation of newly formed synapses. Convex synapses showed opposite changes dependant on proximity from damage, having implications for excitation/inhibition imbalance following lesion induction. These complementary morphological alterations in different synaptic structures support ultrastructural changes as a means for compensation for synaptic loss following denervation. Nearby areas also seem to participate in this response, although with a different strategy than in other paradigms of neuroplasticity.