Address for correspondence: Dr. Asla Pitkänen, A.I. Virtanen Institute for Molecular Sciences, University of Kuopio, P.O. Box 1627, FIN-70 211 Kuopio, Finland. Voice: 358-17-16 3296; fax: 358-17-16 3025.
asla.pitkanen{at}uku.fi
Ann. N.Y. Acad. Sci. 985: 34-49 (2003).
The present study is part of an ongoing project aimed at understanding
the electrophysiologic properties of single amygdaloid neurons
and their correlations with the morphology of the somata as
well as axonal and dendritic trees. The axonal morphology of
14 three-dimensional, reconstructed spiny neurons (4 in the
lateral and 10 in the basal nucleus) that were filled
in vivo with intracellular injections of biocytin is described. Three-dimensional
reconstruction was performed using Neurolucida software (MicroBrightField).
Sholl analysis was used to assess the axonal length as well
as the number of axonal varicosities and endings within concentric
spherical shells placed at 50-µm intervals from the soma.
These data indicate that the same neuron can innervate several
amygdaloid nuclear divisions or nuclei and extra-amygdaloid
regions. This finding suggests that the same neuron can modulate
various brain areas in parallel. Both the presumed intra-amygdaloid
(all axonal branches within the amygdala) and extra-amygdaloid
(axons also outside the amygdala) projection neurons have dense
perisomatic axonal arborizations, and consequently, the intra-amygdaloid
and extra-amygdaloid projection neurons are difficult to differentiate
based on the analysis of perisomatic axonal morphology. Furthermore,
the same extra-amygdaloid neuron can drive many neurons both
locally as well as at extra-amygdaloid projection areas within
a relatively short time. Finally, the axonal morphology of spiny
neurons located in the lateral or basal nuclei was similar.
These data provide baseline quantitative information about the
axonal dimensions of amygdaloid neurons and can form the anatomic
basis for modeling amygdaloid neuronal circuits when more quantitative
data regarding neuronal numbers, size, and dendritic morphology
become available.
