LOCAL CIRCUIT NEURONS IMMUNOREACTIVE FOR CALRETININ, CALBINDIN D-28K OR PARVALBUMIN IN MONKEY PREFRONTAL CORTEX - DISTRIBUTION AND MORPHOLOGY

In the cerebral cortex, local circuit neurons provide critical inhibit ory control over the activity of pyramidal neurons, the major class of excitatory efferent cortical cells. The calcium-binding proteins, cal retinin, calbindin, and parvalbumin, are expressed in a variety of cor tical local circuit neurons. However, in the primate prefrontal cortex , relatively little is known, especially with regard to calretinin, ab out the specific classes or distribution of local circuit neurons that contain these calcium-binding proteins. In this study, we used immuno histochemical techniques to characterize and compare the morphological features and distribution in macaque monkey prefrontal cortex of loca l circuit neurons that contain each of these calcium-binding proteins. On the basis of the axonal features of the labeled neurons, and corre lations with previous Golgi studies, calretinin appeared to be present in double-bouquet neurons, calbindin in neurogliaform neurons and Mar tinotti cells, and parvalbumin in chandelier and wide arbor (basket) n eurons. Calretinin was also found in other cell populations, such as a distinctive group of large neurons in the infragranular layers, but i t was not possible to assign these neurons to a known cell class. In a ddition, although the animals studied were adults, immunoreactivity fo r both calretinin and calbindin was found in Cajal-Retzius neurons of layer I. Dual labeling studies confirmed that with the exception of th e Cajal-Retzius neurons, each calcium-binding protein was expressed in separate populations of prefrontal cortical neurons. Comparisons of t he laminar distributions of the labeled neurons also indicated that th ese calcium-binding proteins were segregated into discrete neuronal po pulations. Calretinin-positive neurons were present in greatest densit y in deep layer I and layer II, calbindin-immunoreactive cells were mo st dense in layers II-superficial III, and parvalbumin-containing neur ons were present in greatest density in the middle cortical layers. In addition, the relative density of calretinin-labeled neurons was appr oximately twice that of the calbindin- and parvalbumin-positive neuron s. However, within each group of labeled neurons, their laminar distri bution and relative density did not differ substantially across region s of the prefrontal cortex. These findings demonstrate that calretinin , calbindin, and parvalbumin are markers of separate populations of lo cal circuit neurons in monkey prefrontal cortex, and that they may be useful tools in unraveling the intrinsic inhibitory circuitry of the p rimate prefrontal cortex in both normal and disease states. (C) 1994 W iley-Liss, Inc.