Postnatal maternal separation elevates the expression of the postsynaptic protein kinase C substrate RC3, but not presynaptic GAP-43, in the developing rat hippocampus.

We have shown that exposure of rats to neonatal handling/maternal separation results in mossy fiber axon hypoplasia in field CA3 of the hippocampus. To better understand the molecular basis of this neuroanatomical alteration, the present study examined three developmentally regulated protein kinase C substrate mRNAs that are highly expressed in hippocampal granule cells during mossy fiber outgrowth: GAP-43, a presynaptic substrate implicated in axonal outgrowth, RC3 (neurogranin), a postsynaptic substrate implicated in calmodulin signaling, and MARCKS-like protein (MLP), which binds calmodulin and filamentous actin in neurons and glial cells. mRNA expression was examined by quantitative in situ hybridization in the developing [postnatal day 7 (P7), P13, P21, and P90] hippocampus (CA1, CA3, granule cells) in Long-Evans hooded rats: (1) reared under normal animal facility (AFR) conditions, (2) subjected to brief (15 min/day, HMS15), or (3) subjected to moderate (180 min/day) handling/maternal separation (HMS180) on P2-14. RC3 mRNA expression was consistently elevated in all of the hippocampal cell fields in HMS180 rats relative to HMS15 and/or AFR rats over postnatal development, but did not differ from HMS15 rats in adulthood. In contrast, neither GAP-43 mRNA nor MLP mRNA expression differed among AFR, HMS15, or HMS180 rats at any postnatal time point. Elevations in RC3 expression would be predicted to perturb calcium-calmodulin signaling that may, in turn, impair the formation and/or maintenance of mossy fiber-CA3 synapses during postnatal development.