The Journal of Neurophysiology Vol. 82 No. 4 October 1999, pp. 1993-1999
Copyright ©1999 by the American Physiological Society

RAPID COMMUNICATION

Action Potential-Induced Dendritic Calcium Dynamics Correlated With Synaptic Plasticity in Developing Hippocampal Pyramidal Cells

 ¹Department of Integrative Brain Science, Graduate School of Medicine, Kyoto University, Kyoto 606-8501; and  ²Japan Science and Technology Corporation, Saitama 332-0012, Japan

Isomura, Yoshikazu and Nobuo Kato. Action Potential-Induced Dendritic Calcium Dynamics Correlated With Synaptic Plasticity in Developing Hippocampal Pyramidal Cells. J. Neurophysiol. 82: 1993-1999, 1999. In hippocampal CA1 pyramidal cells, intracellular calcium increases are required for induction of long-term potentiation (LTP), an activity-dependent synaptic plasticity. LTP is known to develop in magnitude during the second and third postnatal weeks in the rats. Little is known, however, about development of intracellular calcium dynamics during the same postnatal weeks. We investigated postnatal development of intracellular calcium dynamics in the proximal apical dendrites of CA1 pyramidal cells by whole cell patch-clamp recordings and calcium imaging with the Ca²⁺ indicator fura-2. Dendritic calcium increases induced by intrasomatically evoked action potentials were slight during the first postnatal week but gradually became robust 3 to 6-fold during the second and third postnatal weeks. These calcium increases were blocked by application of 250 µM CdCl₂, a nonspecific blocker for high-threshold voltage-dependent calcium channels (VDCCs). Under the voltage-clamp condition, both calcium currents and dendritic calcium accumulations induced by depolarization were larger at the late developmental stage (P15-18) than the early stage (P4-7), indicating developmental enhancement of calcium influx mediated by high-threshold VDCCs. Moreover, theta-burst stimulation (TBS), a protocol for LTP induction, induced large intracellular calcium increases at the late developmental stage, in synchrony with maturation of TBS-induced LTP. These results suggest that developmental enhancement of intracellular calcium increases induced by action potentials may underlie maturation of calcium-dependent functions such as synaptic plasticity in hippocampal neurons.