Critical Study on the Cyto-architecture and Morphological Diversity of the Dorsal Cortex Neurons in the Garden Lizard Calotes versicolor (Daudin)

The cyto-architecture and morphology of the neuronal types of the dorsal cerebral cortex of the lizard,
Calotes versicolor has been studied with the help of Cresyl violet staining and Golgi impregnation
method. The lizard dorsomedial cortex has been considered homologous to the CA3 area of the
mammalian hippocampus because it emits a prominent commissural-contralateral projection, and
because it is the main recipient of the zinc-positive “lizard mossy fibres” coming from the medial
cortex. The dorsal cerebral cortex displayed three neuronal layers. Layer-I contains only few neuronal
somas and also the dendrites ascending from the subjacent layers. Layer-II is characterized by three
to four cell thick densely packed neuronal somas. Layer-III contains loosely packed neuronal somas
and the dendrites and axon descending from layer-I and II. Below the layer-III an ependymal layer is
observed just above the ventricle. Using different characteristics such as criteria of location, dendritic
tree pattern, dendritic spine covering and soma shape seven classes of neurons were distinguished in
the cellular layer of dorsal cortex of Calotes versicolor: multipolar neurons, pyramidal neurons,
monotufted bipolar neurons, monotufted neurons, bitufted neurons, inverted pyramidal neurons and
aspinous bipolar neurons. The dorsal cerebral cortex shows the pyramidal and multipolar neurons to
be dominant type with 38.71% and 30.65% respectively whereas the aspinous bipolar neurons show
only 2.69%. The multipolar neurons have mostly intracortical dendritic branching and connections.
The spine density of dendrites of the dorsal cortex ranges from 22.67±8.18 to 30.76±7.64 spines in
pyramidal, bitufted and multipolar neurons (moderately spinous) whereas it ranges from 10.83±5.64 to
18.18±02.88 spines in monotufted bipolar, monotufted and bitufted bipolar neurons (sparsely spinous)
per 25 μm-length of dendritic segment. The interconnection of neuronal morphology with the behavior
needs more experiments of lesion regeneration.