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Postnatal maternal separation elevates the expression of the postsynaptic protein kinase C substrate RC3, but not
Robert K McNamara1, Rebecca L Huot, Robert H Lenox
1Molecular Neuropsychopharmacology Laboratory, Department of Psychiatry, University of Pennsylvania School of Medicine, Philadelphia, Pa, USA.
Insights
Neonatal handling/maternal separation in rats alters hippocampal gene expression. Moderate separation elevates RC3 mRNA, potentially disrupting calcium-calmodulin signaling and mossy fiber synapse development.
Area of Science:
- Neuroscience
- Molecular Biology
- Developmental Biology
Background:
- Neonatal handling/maternal separation in rats causes mossy fiber axon hypoplasia in the hippocampus.
- Understanding the molecular mechanisms underlying this neuroanatomical change is crucial.
Purpose of the Study:
- To investigate the expression of three key protein kinase C substrate mRNAs (GAP-43, RC3, MLP) in the hippocampus following neonatal handling/maternal separation.
- To elucidate the molecular basis of stress-induced alterations in hippocampal development.
Main Methods:
- Quantitative in situ hybridization was used to examine mRNA expression in the hippocampus of Long-Evans hooded rats at various developmental stages (P7, P13, P21, P90).
- Rats were subjected to different maternal separation protocols: normal animal facility (AFR), brief (HMS15), and moderate (HMS180).
Main Results:
- RC3 (neurogranin) mRNA expression was consistently elevated in the hippocampus of moderately separated (HMS180) rats compared to controls and briefly separated rats during postnatal development.
- GAP-43 and MARCKS-like protein (MLP) mRNA levels did not differ significantly across the experimental groups at any time point.
- RC3 mRNA levels in moderately separated rats did not differ from briefly separated rats in adulthood.
Conclusions:
- Elevated RC3 mRNA expression in response to moderate neonatal separation may disrupt calcium-calmodulin signaling pathways.
- This disruption could impair the formation and/or maintenance of mossy fiber-CA3 synapses during critical developmental periods.
- The findings highlight the impact of early life stress on hippocampal molecular development and synaptic plasticity.
Abstract:
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.