2 DISTINCT SUBGROUPS OF CHOLECYSTOKININ-IMMUNOREACTIVE CORTICAL INTERNEURONS

Examination of cholecystokinin-immunore active cells in the rat fronta l cortex revealed the presence in layers I-VI of a non-uniform populat ion ranging in size from small to large. All were also immunoreactive for GABA. The most commonly observed dendritic form of the small cells were bipolar or bitufted although some were multipolar and demonstrat ed vasoactive intestinal polypeptide and in a few case calretinin immu noreactivity. The large cells were multipolar or bitufted and lacked e xpression of vasoactive intestinal polypeptide and calretinin immunore activity but occasionally showed calbindin D28k immunoreactivity. Ther efore, the cholecystokinin-immunoreactive cells could be divided into two distinct subpopulations depending on their chemistry and morpholog y. Our previous studies showed that GABAergic cells in the neocortex c ould be classified into at least three chemically different subgroups: (1) parvalbumin-containing cells; (2) somatostatin-containing cells ( most of them also contain calbindin D28k); and (3) vasoactive intestin al polypeptide- and/or calretinin-containing cells. The present result s indicated that the small cholecystokinin-immunoreactive non-pyramida l cells constitute a subset of the vasoactive intestinal polypeptide- and/or calretinin-containing cortical GABAergic cells. The large cells remain to be categorized. (C) 1997 Elsevier Science B.V.