Calcium action potentials restricted to distal apical dendrites of rat neocortical pyramidal neurons

Abstract

Simultaneous whole‐cell voltage and Ca2+ fluorescence measurements were made from the distal apical dendrites and the soma of thick tufted pyramidal neurons in layer 5 of 4‐week‐old (P28–32) rat neocortex slices to investigate whether activation of distal synaptic inputs can initiate regenerative responses in dendrites. Dual whole‐cell voltage recordings from the distal apical trunk and primary tuft branches (540–940 μm distal to the soma) showed that distal synaptic stimulation (upper layer 2) evoking a subthreshold depolarization at the soma could initiate regenerative potentials in distal branches of the apical tuft which were either graded or all‐or‐none. These regenerative potentials did not propagate actively to the soma and axon. Calcium fluorescence measurements along the apical dendrites indicated that the regenerative potentials were associated with a transient increase in the concentration of intracellular free calcium ([Ca2+]i) restricted to distal dendrites. Cadmium added to the bath solution blocked both the all‐or‐none dendritic regenerative potentials and local dendritic [Ca2+]i transients evoked by distal dendritic current injection. Thus, the regenerative potentials in distal dendrites represent local Ca2+ action potentials. Initiation of distal Ca2+ action potentials by a synaptic stimulus required coactivation of AMPA‐ and NMDA‐type glutamate receptor channels. It is concluded that in neocortical layer 5 pyramidal neurons of P28–32 animals glutamatergic synaptic inputs to the distal apical dendrites can be amplified via local Ca2+ action potentials which do not reach threshold for axonal AP initiation. As amplification of distal excitatory synaptic input is associated with a localized increase in [Ca2+]i these Ca2+ action potentials could control the synaptic efficacy of the distal cortico‐cortical inputs to layer 5 pyramidal neurons.

Developing a Neuronal Model for the Pathophysiology of Schizophrenia Based on the Nature of Electrophysiological Actions of Dopamine in the Prefrontal Cortex

“…21 Seamans et al 1997). Under these conditions, multiphasic soma-dendritic high-voltage-activated Ca 2ϩ potentials, activated from Ϫ50 mV, have been recorded from soma and in different regions of the apical dendrites of pyramidal PFC or somatosensory cortical neurons directly (Amitai et al 1993; Kim and Connors 1993;Seamans et al 1997;Schiller et al 1997) (Figure 4)., NO. 2 Prefrontal Dopamine Electrophysiology and Schizophrenia 173 al.…”

Diversity of Gain Modulation by Noise in Neocortical Neurons: Regulation by the Slow Afterhyperpolarization Conductance

“…Spatial factors may affect the gain increase and its modulation by G sAHP . Na ϩ and Ca 2ϩ spikes generated in apical dendrites (Kim and Connors, 1993;Reuveni et al, 1993;Yuste et al, 1994;Schiller et al, 1997;Stuart et al, 1997;Schwindt and Crill, 1999;Larkum et al, 1999) might cause noise to increase gain in some pyramidal neurons. Noisy current injected into the distal apical dendrite of layer 5 pyramidal cells increases gain for 4 stimulus fluctuation to fire, and its gain increases with noise amplitude.…”

Dendritic Control of Spontaneous Bursting in Cerebellar Purkinje Cells

“…The dendrites of Purkinje neurons have a high density of voltage-gated calcium channels (Usowicz et al, 1992) and exhibit prominent dendritic calcium spikes (Llinás and Sugimori, 1980). When evoked, regenerative dendritic potentials can cause bursting in Purkinje cells (Hounsgaard and Yamamoto, 1979;Llinás and Sugimori, 1980;Lev-Ram et al, 1992) as they do in hippocampal and neocortical pyramidal neurons (Wong and Prince, 1978;Schiller et al, 1997;Golding et al, 1999;Larkum et al, 1999). Because the dendrites make a significant contribution to the spontaneous firing of Purkinje neurons (Womack and Khodakhah, 2002a), it is also plausible that they contribute to spontaneous bursting.…”