BRANCHING OF ACTIVE DENDRITIC SPINES AS A MECHANISM FOR CONTROLLING SYNAPTIC EFFICACY

Recent experimental findings (Yuste R, and Denk W. (1995) Nature 375, 652-654) suggest that dendritic spines possess excitable membranes. Th eoretically, it was shown earlier that the shape of active spines can significantly affect somatopetal synaptic signal transfer. Studies of long-term potentiation in the hippocampus have related the increased s ynaptic efficacy to a number of structural modifications of spines, in cluding an increased number of branched spines [Trommald M. el al. (19 90) In Neurotoxicity of Excitatory Amino Acids, pp. 163-174. Raven Pre ss, New York] and a strengthened capability for spines to alter their spatial positions [Hosokawa T. et al. (1995) J. Neurosci. 15, 5560-557 33. In the present simulation study, the potential physiological impac t of several types of spine changes was examined in a compartmental ne uron model built using the neuromodelling software NEURON [Hines M. (1 993) In Neural Systems. Analysis and Modeling, pp. 127-136. Kluwer Aca demic, Norwell, MA]. The model included 30 complex spines, with dual c omponent synaptic currents and mechanisms of Ca2+ uptake, diffusion, b inding and extrusion within spine heads. The results show that local c lustering properties of spine distributions along dendrites are unlike ly to affect synaptic efficacy. However, partial fusion of active spin es, which results in formation of spine branches, or subtle changes in spine branch positions, could alone significantly increase synaptic s ignal transfer. These data illustrate possible mechanisms whereby subt le morphological changes in dendritic spines (compatible with changes reported in the literature) may be linked to the cellular mechanisms o f learning and memory. Copyright (C) 1996 IBRO.