NEURONS OF THE MEDIAL CORTEX OUTER PLEXIFORM LAYER OF THE LIZARD PODARCIS-HISPANICA - GOLGI AND IMMUNOCYTOCHEMICAL STUDIES

The study of Golgi-impregnated lizard brains has revealed a scarce but heterogeneous neuronal population in the outer plexiform layer of the medial cortex. Some of the neuronal types detected here resemble the neurons of the dentate molecular layer of the mammalian hippocampus. A ccording to their morphology, five intrinsic neuronal types have been clearly identified: short axon aspinous bipolar neuron (type 1, or sar mentous neuron), short axon aspinous juxtasomatic neuron (type 2, or c oral neuron), short axon sparsely spinous multipolar neuron (type 3, o r stellate neuron), short axon sparsely spinous juxtasomatic multipola r neuron (type 4, or deep stellate neuron), and sparsely spinous juxta somatic horizontal neuron (type 5, or couchant neuron). Most neuronal types were identified as gamma-aminobutyric acid (GABA) and parvalbumi n immunoreactive, and are thus probably involved in medial cortex inhi bition. Moreover, a small fraction of them displayed beta-endorphin im munoreactivity. The distribution of these neuronal types is not unifor m in the laminae of the outer plexiform layer. Type 1 (sarmentous) and type 3 (stellate) neurons overlap the axonal field projection coming from the dorsal cortex and the thalamus, whereas types 4 (deep stellat e) and 5 (couchant) neurons overlap ipsi- and contralateral dorsomedia l projection fields as well as raphe serotoninergic and opioid immunor eactive axonal plexi. Thus, these neuronal types may be involved in th e control of specific inputs to the medial cortex by presumably feed-f orward inhibition; nevertheless, feed-back inhibition may also occur r egarding type 4 (deep stellate) neurons that extend deep dendrites to the zinc-rich bouton field. (C) 1994 Wiley-Liss, Inc.