SUPPRESSION OF THE GLUTAMATE-RECEPTOR DELTA-2 SUBUNIT PRODUCES A SPECIFIC IMPAIRMENT IN CEREBELLAR LONG-TERM DEPRESSION

1. The role of the glutamate receptor subunit delta 2 in the induction of cerebellar long-term depression (LTD) was investigated by applicat ion of antisense oligonucleotides. The delta 2 subunit is selectively localized to Purkinje cells (PCs), with the highest levels being in th e PC dendritic spines, where parallel fibers are received and where ce rebellar LTD is expressed. 2. Immunocytochemical analysis of calbindin -positive PCs revealed that both the dendritic and somatic expression of delta 2 was reduced in antisense- but not in sense-treated cultures . An antisense oligonucleotide directed against the related subunit de lta 1 did not affect the expression of delta 2 in PCs. 3. Cerebellar L TD may be reliably induced in a preparation of cultured embryonic cere bellar neurons from the mouse when parallel and climbing fiber stimula tion are replaced by brief glutamate pulses and strong, direct depolar ization of the PC, respectively, Application of an antisense oligonucl eotide directed against delta 2 completely blocked the induction of LT D produced by glutamate/depolarization conjunctive stimulation. A delt a 2 sense oligonucleotide or an antisense oligonucleotide directed aga inst the related delta 1 subunit had no effect. 4. The effect of the d elta 2 antisense oligonucleotide was not related to attenuation of cal cium influx via voltage-gated channels or calcium mobilization via met abotropic glutamate receptors, as assessed with fura-2 microfluorimetr y. Current flow through lpha-amino-3-hydroxy-5-methyl-4-isoxazolepropi onic acid-receptor-associated ion channels also appeared unaltered. Al l three of these processes have previously been shown to be required f or cerebellar LTD induction. The observation that delta 2 is involved in a metabotropic-glutamate-receptor-independent signaling pathway tha t is required for LTD induction supports the view that delta 2 partici pates in the formation of a novel postsynaptic receptor complex.