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Modulation of GAP-43 mRNA by GABA and glutamate in cultured cerebellar granule cells
L M Console-Bram1, D H Baird, S G Fitzpatrick-McElligott
1Temple University School of Medicine, Department of Pharmacology, 3420 N. Broad Street, Philadelphia, PA 19140, USA.
Insights
Cerebellar neurotransmitters gamma-amino-butyric acid (GABA) and glutamate regulate GAP-43 mRNA expression in developing and adult rats. GABA decreases GAP-43 mRNA, while glutamate increases it, impacting neuroplasticity.
Area of Science:
- Neuroscience
- Molecular Biology
- Developmental Biology
Background:
- Growth-associated protein 43 (GAP-43) expression is developmentally regulated in the rat cerebellum.
- GAP-43 mRNA is localized in cerebellar granule cells, with higher levels in neonates than adults.
Purpose of the Study:
- To investigate the role of cerebellar neurotransmitters, gamma-amino-butyric acid (GABA) and glutamate, in modulating GAP-43 expression.
- To understand the impact of these neurotransmitters on granule cell maturation and neuroplasticity.
Main Methods:
- Primary cultures of cerebellar granule cells were treated with GABA, glutamate, or their respective receptor agonists/antagonists.
- Quantitative analysis of GAP-43 mRNA levels was performed using in situ hybridization and Northern hybridization.
Main Results:
- GABA exposure significantly decreased GAP-43 mRNA levels, an effect mimicked by GABAA and GABAB receptor agonists.
- Glutamate receptor antagonists (NMDA and non-NMDA) decreased GAP-43 mRNA levels.
- Northern hybridization confirmed that GABA decreased GAP-43 mRNA by 21%, while glutamate increased it by 37%.
Conclusions:
- Cerebellar neurotransmitters GABA and glutamate modulate GAP-43 mRNA expression in granule cells.
- This modulation by excitatory glutamatergic and inhibitory GABAergic inputs may influence cerebellar development and neuroplasticity.
Abstract:
Expression of GAP-43 in the cerebellum and selected regions of the brain has been shown to be developmentally regulated. Localization of GAP-43 mRNA within granule cells of the immature and mature rat cerebellum has been demonstrated by in situ hybridization. Higher levels are detected in the neonate compared to the adult. To determine if the cerebellar neurotransmitters, GABA (gamma-amino-butyric acid) and glutamate are involved in the modulation of GAP-43 expression, cultured cerebellar granule cells were exposed to these transmitters. Cultures were treated with glutamate, GABA, or the agonists/antagonists to their receptors in serum-free media for 5-7 days. Analysis of the levels of GAP-43 mRNA by in situ hybridization indicated that a 7-day exposure to GABA (25 and 50 microM) significantly lowered levels of granule cell GAP-43 mRNA. Specific agonists to the GABAA (muscimol) and GABAB (baclofen) receptors produced a decrease similar to that observed for GABA. Results from these studies also indicated that exposure to non-NMDA (CNQX) and NMDA (CPP, MK-801) glutamate receptor antagonists, and a metabotropic receptor glutamate agonist (ACPD), decreased the level of GAP-43 mRNA. The involvement of GABA and glutamate in the modulation of GAP-43 expression was corroborated by Northern hybridization. These studies revealed that a 5-day exposure to GABA decreased the cellular content of GAP-43 mRNA by 21% whereas exposure to glutamate resulted in a 37% increase. Findings from the studies reported here, using an in vitro cerebellar granule cell model, suggest that levels of GAP-43 mRNA, in vivo, are modulated by input from both excitatory glutamatergic mossy fibers and inhibitory GABAergic Golgi interneurons. Thus, modulation of GAP-43 mRNA by these neurotransmitters may influence granule cell maturation during development in the neonate and neuroplasticity in the adult, possibly at the parallel fiber-Purkinje cell synapse.