Differences between Somatic and Dendritic Inhibition in the Hippocampus

Abstract

Hippocampal synaptic inhibition is mediated by distinct groups of inhibitory cells. Some contact pyramidal cells perisomatically, while others terminate exclusively on their dendrites. We examined perisomatic and dendritic inhibition by recording from CA3 inhibitory and pyramidal cells and injecting biocytin to visualize both cells in light and electron microscopy. Single perisomatic inhibitory cells made 2-6 terminals clustered around the soma and proximal pyramidal cell processes. Dendritic cells established 5-17 terminals, usually on different dendrites of a pyramidal cells. Perisomatic terminals were larger than those facing dendritic membrane. Perisomatic inhibitory cells initiated the majority of simultaneous IPSPs seen in nearby pyramidal cells. Single IPSPs initiated by perisomatic sodium-dependent action potentials. Activation of inhibitory fibers terminating on dendrites could suppress calcium-dependent spikes. Thus, distinct inhibitory cells may differentially control dendritic electrogenesis and axonal output of hippocampal pyramidal cells.

GABAergic interneurons are the targets of cannabinoid actions in the human hippocampus

“…In the tissue derived from tumor-induced epileptic tissue (in which the GABA release experiments have been done), we found that almost one-third of the CB1-positive cells were negative for CCK. In contrast, the absolute number and size of the boutons may vary widely across different interneuron types, 12,16,30 which likely correlates with the amount of released GABA, and may also explain the discrepancy between the quantitative data of the anatomical and pharmacological experiments.…”

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

“…Recently, GABA has also been shown to exert a compartmental modulation of soma and dendrites in single hippocampal pyramidal neurons (Buhl et al 1994; Kim et al 1995;Miles et al 1996). In the dendrites, GABAergic inhibitory postsynaptic potentials (IPSPs) may serve the following functions.…”

“…The pyramdial neuron receives functionally segregated inputs in its apical dendrites and basal dendrites from diverse cortical and subcortical regions (see Table 1). The GABAergic interneuron exerts tonic hyperpolarizing action in the apical dendrites, as well as in the somatic region of the pyramidal cell (Soltesz et al 1995;Miles et al 1996;Kim et al 1995). The modulatory inputs to the pyramidal dendrite by the GABAergic interneurons can, in turn, be regulated by mesocortical dopamine inputs to these interneurons.…”

“…GABAergic hyperpolarzation may serve this very important role in controlling neuronal excitability. Second, they may alter the timing of onset and kinetics of activation of the dendritic high-voltageactivated Ca 2ϩ channels that can be activated by synaptic inputs or by backpropagated spikes (Callaway et al 1995;Miles et al 1996;Tsubokawa and Ross 1996;Miura et al 1997). Third, they may hyperpolarize dendritic membranes and shunt strong depolarizing inputs.…”

GABAergic Interneurons Implications for Understanding Schizophrenia and Bipolar Disorder

“…Each of these inhibitory cells forms multiple synaptic contacts that are distributed along various branches of a single pyramidal neuron. This distribution implies that each contact may have only a very weak effect on the postsynaptic neuron, suggesting that the activity of dendritic inhibitory cells may have to be synchronized in order to effectively modulate the membrane potential of pyramidal neurons (Freund and Buzsaki 1996;Miles et al 1996). Another common factor is that the dendritic arborization of these neurons tends to be restricted to only one or two layers so that their influence is limited to selective intrinsic or extrinsic afferents (for a review see Freund and Buzsaki 1996).…”