Elsevier

Neuroscience

Volume 102, Issue 4, 14 February 2001, Pages 715-721
Neuroscience

Letter to Neuroscience
The apical shaft of CA1 pyramidal cells is under GABAergic interneuronal control

https://doi.org/10.1016/S0306-4522(00)00584-4Get rights and content

Abstract

Dendrites of pyramidal cells perform complex amplification and integration (reviewed in 5., 9., 12., 20.). The presence of a large proximal apical dendrite has been shown to have functional implications for neuronal firing patterns13 and under a variety of experimental conditions, the largest increases in intracellular Ca2+ occur in the apical shaft.4., 8., 15., 16., 19., 21., 22., 23. An important step in understanding the functional role of the proximal apical dendrite is to describe the nature of synaptic input to this dendritic region. Using light and electron microscopic methods combined with in vivo labeling of rat hippocampal CA1 pyramidal cells, we examined the total number of GABAergic and non-GABAergic inputs converging onto the first 200 μm of the apical trunk. The number of spines associated with excitatory terminals increased from <0.2 spines/μm adjacent to the soma to 5.5 spines/μm at 200 μm from the soma, whereas the number of GABAergic, symmetric terminals decreased from 0.8/μm to 0.08/μm over the same anatomical region. GABAergic terminals were either parvalbumin-, cholecystokinin- or vasointestinal peptide-immunoreactive. These findings indicate that the apical dendritic trunk mainly receives synaptic input from GABAergic interneurons. GABAergic inhibition during network oscillation may serve to periodically isolate the dendritic compartments from the perisomatic action potential generating sites.

Section snippets

Experimental procedures

The surgical and recording methods have been described in detail previously.17 In short, adult Sprague–Dawley rats (200–300 g; Hilltop Laboratories, Scottsdale, PA) were anesthetized with urethane (1.5 g/kg; Sigma, St. Louis, MO, USA) and placed in a stereotaxic apparatus. A small (1.2×1.2 mm) bone window was drilled above the hippocampus (centered at AP=−3.5 and L=2.5 mm from bregma) for intracellular recordings. The micropipettes were filled with 1 M potassium acetate and 1% biocytin (Sigma). In

Acknowledgements

We thank T. F. Freund for his comments, E. Bonder for technical support, K. G. Baimbridge, T. Gorcs, and P. Somogyi for supplying us CB, PV, VIP, CCK and GABA antibodies, respectively. This work was supported by NIH (NS34994, MH54671), MH12403 (D.A.H.), Human Frontier Science Program (X. L.) and Soros Fellowship (E. P).

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