GLUTAMATE-RECEPTOR TARGETING TO SYNAPTIC POPULATIONS ON PURKINJE-CELLS IS DEVELOPMENTALLY-REGULATED

Selective targeting of neurotransmitter receptors to specific synapse populations occurs in adult neurons, but little is known about the dev elopment of these receptor distribution patterns. In this study, we de monstrate that a specific developmental switch occurs in the targeting of a receptor to an identified synapse population. Localization of de lta and AMPA glutamate receptors at parallel and climbing fiber synaps es on the developing Purkinje cells was studied using postembedding im munogold. Delta receptors were found to be abundant on postsynaptic me mbranes at parallel fiber synapses from postnatal day 10 (P10) to adul t. In contrast, delta receptors were found to be high at climbing fibe r synapses only at P10 and P14. Thus, a major finding of this paper is that high levels of delta receptors are transiently expressed in clim bing fiber synapses in the second postnatal week. Labeling of synapses with anti-delta receptor antibody at P10 was limited to the postsynap tic membrane of excitatory synapses and was absent from GABAergic syna pses. Unlike delta receptor immunolabeling, AMPA receptor immunolabeli ng (GluR2/3 and GluR2 antibodies) was high in the postsynaptic membran es of synapses at early postnatal ages (P2 and P5) and was higher in c limbing fiber synapses than in parallel fiber synapses from P10 to adu lt. The present study shows that synapse-specific targeting of glutama te receptors in Purkinje cells is developmentally regulated, with the postsynaptic receptor composition established during synapse maturatio n. This composition is not dependent on the nature of the initial esta blishment of synaptic connections.