PARVALBUMIN AND CALBINDIN IN THE RAT CLAUSTRUM - AN IMMUNOCYTOCHEMICAL STUDY COMBINED WITH RETROGRADE TRACING FROM FRONTOPARIETAL CORTEX

The distribution of the calcium binding proteins parvalbumin and calbi ndin D-28k was examined in the claustrum of the rat by means of immuno histochemistry. The two proteins displayed a different and largely com plementary pattern of distribution. Parvalbumin-immunostaining was int ense in the neuropil of the dorsal claustrum and virtually absent in t he neuropil of the ventral claustrum; parvalbumin-immunoreactive neuro nal cell bodies were relatively numerous in the dorsal claustrum and w ere detected only occasionally in the ventral region. On the other han d, calbindin-immunostaining was prevalent in the ventral claustrum; ve ry few calbindin-positive neurons were seen in the dorsal sector of th e nucleus, whereas they were relatively more numerous in the ventral c laustrum. The cell bodies of the majority of the claustral parvalbumin - or calbindin-immunoreactive neurons were oval or round, but immunost ained polymorphous neurons were also observed. The surface of the immu nopositive dendritic branches was smooth, with no evidence of spines. Fluorescent retrograde tracing was combined with immunohistofluorescen ce to determine whether the parvalbumin-containing claustral cells pro ject to the frontoparietal cortex. Neurons labelled after large fluoro gold injections in frontoparietal cortical fields were highly intermin gled in the dorsal claustrum with parvalbumin-immunoreactive cells but the two neuronal populations were separate. These data show that parv albumin-immunoreactive claustral neurons do not project to the frontop arietal cortex. In addition, although these cells may project to other cortical or subcortical targets, the present findings suggest that th ey may represent, at least in part, local circuit claustral neurons, c orresponding to the aspiny intrinsic neurons described in the rat clau strum in studies based on Golgi impregnation.