DIFFERENTIAL EXPRESSION OF KAINATE RECEPTORS IN THE BASAL GANGLIA OF THE DEVELOPING AND ADULT-RAT BRAIN

Glutamate is the principal excitatory transmitter of the mammalian bra in and plays a particularly important role in the physiology of the ba sal ganglia structures responsible for movement regulation. Using in s itu hybridization with oligonucleotide probes, we examined the express ion patterns of the five known kainate type glutamate receptor subunit genes, KA1, KA2 and GluR5-7, in the basal ganglia of adult and develo ping rat brain. In the adult rat, a highly organized and selective pat tern of expression of the kainate subunits was observed in the basal g anglia and associated structures as well as in other regions of the br ain. KA2 mRNA was abundant in the striatum, nucleus accumbens, subthal amic nucleus and substantia nigra pars compacta, and was present at lo wer levels in the globus pallidus and substantia nigra pars reticulata . Neither KA1 nor GluR5 expression was observed in the basal ganglia o f adult rats, although these messages were present in other regions. G luR6 was highly expressed in the striatum and subthalamic nucleus and to a lesser extent in the substantia nigra pars reticulata, while no h ybridization signal was detectable in the large, presumably dopaminerg ic neurons of the substantia nigra pars compacta. In contrast, GluR7 w as strongly expressed in the substantia nigra pars compacta, was prese nt at lower levels in the striatum, globus pallidus and substantia nig ra pars reticulata, and was not detectable in the subthalamic nucleus. During postnatal development, expression of the kainate receptor subu nits was characteristically highest on postnatal day 1 and declined to adult levels by day 20; however, in the globus pallidus we did observ e the transient expression of KA1 and GluR5 between day 1 and day 10. These results demonstrate that the neuronal structures comprising the basal ganglia express a distinct combination of kainate receptor subun it genes, suggesting that the pharmacological properties of the result ant glutamate receptors are likely to be regionally specific. The orga nization of expression of these genes is established early in Life, wh ich is consistent with the important role they may play in establishin g the functions of the motor system. (C) 1997 Elsevier Science B.V.