Abstract:
Pyramidal cells are characterised by markedly different sized dendritic trees, branching
patterns and spine density across the cortical mantle. Moreover, pyramidal cells have
been shown to differ in structure among homologous cortical areas in different species;
however, most of these studies have been conducted in primates. Whilst pyramidal cells
have been quantified in a few cortical areas in some other species there are, as yet, no
uniform comparative data on pyramidal cell structure in a homologous cortical area
among species in different Orders. Here we studied layer III pyramidal cells in V1 of
three species of rodents, the greater cane rat, highveld gerbil and four-striped mouse, by
the same methodology used to sample data from layer III pyramidal cells in primates.
The data reveal markedly different trends between rodents and primates: there is an
appreciable increase in the size, branching complexity and number of spines in the
dendritic trees of pyramidal cells with increasing size of V1 in the brain in rodents,
whereas there is relatively little difference in primates. Moreover, pyramidal cells in
rodents are larger, more branched and more spinous than those in primates. For example,
the dendritic trees of pyramidal cells in V1 of the adult cane rat are nearly three times
larger, and have more than ten times the number of spines in their basal dendritic trees,
than those in V1 of the adult macaque (7900 and 600, respectively), which has a V1 40
times the size that of the cane rat. It remains to be determined to what extent these
differences may result from development or reflect evolutionary and/or processing
specializations.
