Magnopyramidal neurons in the anterior motor speech region. Dendritic features and interhemispheric comparisons
T. L. Hayes and D. A. Lewis
Department of Neuroscience, University of Pittsburgh, Pa, USA.
OBJECTIVE: To test the hypothesis that the larger somal size of layer III
magnopyramidal neurons in left than in right Brodmann area 45 is associated
with greater measures of dendritic arborization in the left hemisphere
neurons. DESIGN: A case series involving postmortem human brain specimens
was used to compare dendritic parameters of Golgi-impregnated layer III
pyramidal neurons in Brodmann area 45 in the left and right hemispheres.
SUBJECTS: A convenience sample consisting of 9 subjects with no known
neurologic or psychiatric disorders was obtained at autopsy. MAIN OUTCOME
MEASURES: Dendritic parameters of the 10 largest Golgi-impregnated layer
III pyramidal neurons were measured in each hemisphere of each brain using
a eutectic neuron tracing system. The measures examined were somal size,
neuron depth, mean segment length, number of branch points, maximal branch
order, combined dendritic diameter, total dendritic length, horizontal
extent of the dendritic field, and spine density. The Golgi-impregnated
slides were also compared with Nissl-stained slides from adjacent blocks to
determine the laminar location of the sampled neurons. RESULTS: Although
the mean somal size was greater in the left than in the right hemisphere,
none of the dendritic parameters examined was larger for the left
hemisphere neurons. As expected, total dendritic length was positively
correlated to somal size (r = 0.43, P < 001) in the left hemisphere.
However, there was no correlation between these parameters in the right
hemisphere (r = 0.02, P = .76). CONCLUSIONS: The difference between left
and right Brodmann area 45 magnopyramidal neurons in the correlation of
somal size and dendritic length provides additional evidence of anatomical
differences between these 2 populations of neurons. However, the lack of
interhemispheric differences in measures of dendritic arborization suggests
that additional factors contribute significantly to the marked difference
in somal size between the large magnopyramidal neurons in the left and
right hemispheres.