EMBRYONIC CORTICAL-NEURONS DIFFERENTIATE INTO VARIOUS TYPES OF INTERNEURONS WHEN HETEROTOPICALLY TRANSPLANTED INTO THE ADULT-RAT BRAIN

The adult cortex represents a heterogeneous mixture of different class es of pyramidal neurons and non-pyramidal interneurons. After grafting embryonic cortical anlage into the adult striatum, the present study investigated whether the development of different populations of inter neurons in heterotopic cortical grafts is similar to the adult cortex. The presence of specific subpopulations of interneurons in grafts was assessed by immunocytochemistry using various antibodies against mark er molecules for interneurons such as neuropeptides and calcium-bindin g proteins. These molecules are expressed to a different extent in spe cific subpopulations of cortical interneurons. Cortical primordia obta ined on embryonic day 14 (E14) were stereotactically grafted into the center of the left striatum of adult recipient rats. After an 8-week d ifferentiation period, host rats were perfusion fixed and immunocytoch emistry was performed using antibodies against neuropeptide Y (NPY), v asoactive intestinal polypeptide (VIP), somatostatin, parvalbumin and calbindin D-28k. Within the grafts, the number of immunopositive inter neurons as well as the intensity of immunostaining for different marke r molecules corresponded well with those of the adult cortex. In contr ast, the expression pattern in the graft demonstrated clear difference s when compared with the surrounding host striatum. The present study demonstrates, that at E14 at least some cells of the cortical anlage a re primed to develop into different classes of interneurons independen t of their normal environment and their regular synaptic connections. Thus, different interneuron progenitor cells survive transplantation a nd develop cell-specific morphological and cytochemical characteristic s. Differentiation into various subpopulations of neurons may be a pre requisite for potential therapeutic approaches in humans.