POSTSYNAPTIC CURRENTS AND SHORT-TERM SYNAPTIC PLASTICITY IN PURKINJE-CELLS GRAFTED ONTO AN UNINJURED ADULT CEREBELLAR CORTEX

It has been shown recently that embryonic Purkinje cells grafted extra parenchymally into an intact cerebellum, in the absence of any sign of damage, are able to migrate into the host molecular layer where they receive a climbing fibre innervation. Using the same technique, we inv estigated the development of the electrophysiological properties of th e synapses between the grafted cells and their main afferents. Purkinj e cells either in the graft or having migrated into the molecular laye r of the host were recorded using the whole-cell patch-clamp method in acutely prepared slices 17-112 days after grafting. Spontaneous posts ynaptic currents with a single-exponential decay and mediated by GABA( A) receptors were very similar to those described in normal Purkinje c ells. Excitatory postsynaptic currents (EPSCs) evoked by climbing fibr e and by parallel fibre stimulation were blocked by an pha-amino-3-hyd roxy-5-methyl-4-isoxazole-propionic acid (AMPA)/kainate antagonist, an d displayed the linear current-voltage relation typical of postnatal P urkinje cells. The attainment of normal functional properties by the a dult axons at the newly formed synaptic sites was shown by the express ion of short-term facilitation of parallel fibre EPSCs and of short-te rm depression of climbing fibre EPSCs. The grafted Purkinje cells show ed climbing fibre polyinnervation 17-20 days after grafting which evol ved to monoinnervation at 23-45 days, confirming the completion of the developmental programme up to maturation. Our experiments support the view that the adult intact brain is able to accept and integrate an a dditional number of neurons which show fully mature electrophysiologic al properties which are electrophysiologically indistinguishable from those of the host neurons.