Cholecystokinin Innervation of the Cerebral Cortex in a Reptile, the Lizard Psammodromus algirus

Abstract

We used light and electron microscopic and immunohistochemical methods to map the distribution of cholecystokinin (CCK) in the cerebral cortex of a lizard, Psammodromus algirus. At light microscopy, the CCK immunoreactivity was limited to fibers and terminals densely innervating all cortical regions except for the lateral (pyriform) cortex which was very slightly immunostained. The CCK-positive terminals were almost restricted to the cell layers in every cortical region where they surrounded immunonegative cell bodies and proximal dendrites of neurons within the layer. No CCK-containing neurons were observed within the cerebral cortex. At the electron microscopic level, most positive structures were presynaptic boutons contacting cell bodies and proximal dendrites. All contacts appeared to form symmetric junctions. both the distribution and type of synaptic contacts of CCK fibers in the cerebral cortex of Psammodromus are very similar to the corresponding features in the hippocampus of mammals, although in this lizard the CCK cortical innervation, unlike that in mammals, is probably of extrinsic origin. Double HRP-retrograde labeling and CCK immunohistochemistry show that part of the CCK in the cerebral cortex of Psammodromus arises from the hypothalamic supramammillary nuclei.