PARVALBUMIN-CONTAINING NEURONS IN THE CEREBRAL-CORTEX OF THE LIZARD PODARCIS-HISPANICA - MORPHOLOGY, ULTRASTRUCTURE, AND COEXISTENCE WITH GABA, SOMATOSTATIN, AND NEUROPEPTIDE-Y

The morphology, fine structure, and degree of colocalization with GABA , somatostatin, and neuropeptide Y of parvalbumin-containing cells wer e studied with immunocytochemistry in the cerebral cortex of the lizar d Podarcis hispanica. Parvalbumin-containing cells make up a morpholog ically heterogeneous population of spine-free neurons, displaying the morphological features of nonprincipal cells previously described in G olgi studies. Electron microscopically, parvalbumin-immunoreactive cel l bodies are similar in all cortical areas and layers. The perisomatic input is moderate in number, and boutons with either round clear vesi cles or flattened vesicles were observed making asymmetric or symmetri c synaptic contacts, respectively. Parvalbumin-immunoreactive dendrite s are smooth and almost completely covered with synaptic boutons of di fferent types, most of which establish asymmetric contacts. Parvalbumi n-immunoreactive boutons are concentrated around cell bodies of princi pal cells. They are large, containing abundant mitochondria and small pleomorphic vesicles, and establishing symmetric synaptic contacts wit h somata, proximal dendritic shafts, and axon initial segments of prin cipal cells. Colocalization studies revealed that all the parvalbumin- containing cells are GABA-immunoreactive, representing only a fraction of the GABA-immunopositive cell population, and that parvalbumin- and peptide- (somatostatin and neuropeptide Y) containing cells show a ne gligible overlap. These results demonstrate that in the cerebral corte x of the lizard Podarcis hispanica, parvalbumin-containing cells repre sent a subset of nonprincipal GABAergic neurons largely involved in pe risomatic inhibition, which are different from the peptide-containing cells, and suggest that they may include both axosomatic and axoaxonic cells. (C) 1993 Wiley-Liss, Inc.