Developmental changes in the localisation of the mGluR1 alpha subtype of metabotropic glutamate receptors in purkinje cells

The regulation of neurotransmitter receptors during synapse formation has b een studied extensively at the neuromuscular junction, but little is known about the development of excitatory neurotransmitter receptors during synap togenesis in central synapses. In this study we show qualitatively and quan titatively that a receptor undergoes changes in localisation on the surface of rat Purkinje cells during development in association with its excitator y synapses. The presence of mGluR1 alpha at parallel and climbing fibre syn apses on developing Purkinje cells was studied using high-resolution immuno electron microscopy. Immunoreactivity for mGluR1 alpha was detected from em bryonic day 18 in Purkinje cells, and showed dramatic changes in its locali sation with age. At early postnatal ages (P0 and P3), mGluR1 alpha was foun d both in somata and stem dendrites but was not usually associated with syn aptic contacts. At P7, mGluR1 alpha became concentrated in somatic spines a ssociated with climbing fibres and in the growing dendritic arborisation ev en before innervation by parallel fibres. During the second and third postn atal week, when spines and parallel fibre synapses were generated, mGluR1 a lpha became progressively concentrated in the molecular layer, particularly in the synaptic specialisations. As a result, during the fourth postnatal week, the pattern and level of mGluR1 alpha expression became similar to th e adult and mGluR1 alpha appeared in high density in perisynaptic sites. Our results indicate that mGluR1 alpha is present in the developing Purkinj e cells prior to their innervation by climbing and parallel fibres and demo nstrate that this receptor undergoes a dynamic and specific regulation duri ng postnatal development in association with the establishment of synaptic inputs to Purkinje cell. (C) 2001 IBRO. Published by Elsevier Science Ltd. All rights reserved.