Developmental regulation of SNAP-25 isoform expression in GABAergic neurons. Panels A and B show a pair of graphs comparing cell populations prepared from acutely dissociated adult cortex of GAD67-GFP (ΔNeo) and nontransgenic wild type mice, respectively, after fluorescence-activated cell sorting (FACS). The selectivity of the fractionation is demonstrated by the distinct population of GFP-positive cells (dashed oval, panel A) that was readily distinguished in cells derived from GAD67-GFP (ΔNeo) mice, but was absent in preparations from wild type animals (panel B). The arrows in A indicate the two sorted cell populations, GFP-positive (green arrow) and -negative (black arrow), used for molecular analysis. Panel C shows the relative levels of SNAP-25a (solid bar) and SNAP-25b (white bar) RNA transcripts in adult neurons from GFP-positive (GFPpos, n = 4) and -negative (GFPneg, n = 2) populations. Panel D, SNAP-25 isoform RNA transcript expression in sorted immature neurons obtained from cortex of P7 neonates (GFPpos, n = 7; GFPneg, n = 4). Note that in contrast to the earlier developmental time point where comparable levels of the two isoform transcripts are expressed in both GFPpos and GFPneg cell populations, mature neurons of both populations express predominantly the SNAP-25b transcript.