Volume 17, Number 16,
Issue of August 15, 1997
pp. 6352-6364
Copyright ©1997 Society for Neuroscience
Massive Autaptic Self-Innervation of GABAergic Neurons in Cat
Visual Cortex
Received April 2, 1997; revised June 3, 1997; accepted June 6, 1997.
Gábor Tamás1, 2,
Eberhard H. Buhl1, and
Peter Somogyi1
1 Medical Research Council, Anatomical
Neuropharmacology Unit, Department of Pharmacology, University of
Oxford, Oxford OX1 3TH, United Kingdom, and 2 Department of
Comparative Physiology, József Attila University, Szeged, Hungary
H-6726
Autapses are transmitter release sites made by the axon of a neuron
on its own dendrites. We determined the numbers and precise subcellular
position of autapses on different spiny and smooth dendritic cell types
using intracellular biocytin filling in slices of adult neocortex.
Potential self-innervation was light microscopically assessed on
10 pyramidal cells, 7 spiny stellate cells, and 41 smooth dendritic
neurons from cortical layers II-V. Putative autapses occurred on each
smooth dendritic neuron and on seven pyramids, but not on spiny
stellate cells. However, electron microscopic examination of all light
microscopically predicted sites on pyramids (n = 28) showed only one case of self-innervation with two autapses on
dendritic spines. Interneurons were classified by postsynaptic target
distribution () and all putative autapses of
seven basket, three dendrite-targeting, and three double bouquet cells
were scrutinized. All basket and dendrite-targeting cells established
self-innervation, the number of autapses being 12 ± 7 and 22 ± 12 (mean ± SD), respectively; only one of the double bouquet cells
formed autapses (n = 3). Basket cell autapses
(n = 74) were closer to the soma (12.2 ± 22.3 µm) than autapses established by dendrite-targeting cells (51.8 ± 49.9 µm; n = 66).
The degree of self-innervation is cell type-specific. Unlike on spiny
cells, autapses are abundant on GABAergic basket and dendrite-targeting
interneurons, with subcellular location similar to that of synapses
formed by the parent cell on other neurons. The extensive
self-innervation may modulate integrative properties and/or the firing
rhythm of the neuron in a manner temporally correlated with its own
activity.
Key words:
autapse;
interneuron;
neocortex;
inhibition;
pyramidal
cell;
feedback