DARPP-32, A DOPAMINE AND CYCLIC AMP-REGULATED PHOSPHOPROTEIN, IS PRESENT IN CORTICOTHALAMIC NEURONS OF THE RAT CINGULATE CORTEX

DARPP-32 immunocytochemistry and retrograde axonal labeling were combined to determine whether DARPP-32-containing neurons of the rat anterior cingulate cortex project to thalamus. Following injections of fluorescent latex microspheres into the mediodorsal thalamic nuclei, a large proportion of the DARPP-32 immunostained neurons in layer VI were also retrogradely labeled. In area 24a, these neurons were mostly found in layer VIb, whereas in area 24b, they were visible throughout layer VI. The presence of DARPP-32 in certain corticothalamic neurons suggests that these cells may be modulated by dopamine, which increases DAR-PP-32 phosphorylation, and possibly by glutamate, which antagonizes DARPP-32 phosphorylation via the N-methyl-D-aspartate (NMDA) receptor.