Glutamate-operated channels: developmentally early and mature forms arise by alternative splicing.

The expression of two alternative splice variants, Flip and Flop, in mRNAs encoding the four AMPA-selective glutamate receptors (GluR-A, -B, -C, and -D) was studied in the developing brain by in situ hybridization. These receptors are expressed prominently before birth, and patterns of distribution for Flip versions remain largely invariant during postnatal brain development. In contrast, the Flop versions are expressed at low levels prior to postnatal day 8. Around this time, the expression of Flop mRNAs increases throughout the brain, reaching adult levels by postnatal day 14. Thus, receptors carrying the Flop module appear to participate in mature receptor forms.