CALBINDIN D28K AND PARVALBUMIN GENE-EXPRESSION IN RAT EMBRYONIC VENTRAL FOREBRAIN GRAFTS

The present study characterizes expression of calbindin D28 K (CB-D28 K) and parvalbumin (PV) in ventral forebrain (VFB) grafts placed in th e neocortex of adult rats bearing quisqualic acid lesions to the nucle us basalis magnocellularis. Three to nine months after transplantation surgery, rats were killed for in situ hybridization with probes to CB -D28K or PV and for immunohistochemistry with antibodies to CB-D28K or PV. In addition, an antibody to choline acetyltransferase (ChAT) was used to characterize the cholinergic component in the graft and an ant ibody to tyrosine hydroxylase (TH) to explore catecholaminergic innerv ation of the graft. Quantitative analysis of CB-D28K and PV messenger ribonucleic acid (mRNA) was based on counts of silver grains generated by emulsion autoradiography. Cells expressing CB-D28K mRNA were signi ficantly larger than such cells in the adult VFB and the mean number o f silver grains per cell was significantly greater than to such cells in the adult VFB. The level of CB-D28K mRNA expression as calculated b y ratio of silver grains per unit area was also significantly increase d. Quantification of PV mRNA showed no significant differences between the cells in the graft and in the adult VFB. In order to begin to int erpret these findings, a comparison was made with such cells in the VF B of developing rats. Brain sections were sampled from embryonic day 1 7 and postnatal days 1, 5, 12, 19 and adult (6-12 months of age). Cell s expressing CB-D28K mRNA were detected in ventral forebrain from post natal day 5 and cells expressing PV mRNA were detected in ventral fore brain from postnatal day 19. In the course of normal development of th e ventral forebrain, no CB-D28K cells were found that were as large or expressed such high levels of CB-D28K mRNA as observed in the grafts. We conclude that changes in grafted cells expressing CB-D28K do not r eflect an arrest of developmental processes. TH immunohistochemistry r evealed lack of catecholaminergic innervation of the graft, whereas ad ult mediolateral septal cells that express CB-D28K receive such innerv ation in addition to other neurotransmitter inputs. Imbalance in neuro transmitter inputs to grafted cells expressing CB-D28K is discussed as a possible factor in their increased size and gene expression.