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A new model for prenatal brain damage. I. GABAA receptor activation induces cell death in developing rat hippocampus
Joseph L Nuñez1, Jesse J Alt, Margaret M McCarthy
1Physiology Department, University of Maryland School of Medicine, Baltimore 21201, USA. jnune001@umaryland.edu
Insights
Activating GABA(A) receptors with muscimol in newborn rats increases hippocampal cell death, particularly in males. This damage, mediated by calcium channels, offers a new model for hypoxic-ischemic brain injury in premature infants.
Area of Science:
- Neuroscience
- Developmental Neuroscience
- Perinatal Medicine
Background:
- Premature infants face high risks of hypoxic-ischemic brain damage.
- Current models inadequately replicate these events in immature brains.
- Immature neurons' primary excitatory drive involves GABA(A) receptor activation, leading to calcium influx.
Purpose of the Study:
- To investigate the role of GABA(A) receptor activation in neonatal brain injury.
- To establish a novel animal model for hypoxic-ischemic brain damage in premature infants.
Main Methods:
- Administered muscimol (a GABA(A) receptor activator) to newborn rats and hippocampal cultures.
- Utilized diltiazem (an L-type calcium channel blocker) as a preventative measure.
- Compared findings in vivo with results from hippocampal cultures.
Main Results:
- Exogenous GABA(A) receptor activation by muscimol significantly increased hippocampal cell death in newborn rats.
- The observed effects were region-specific, persistent, and more pronounced in males.
- Muscimol-induced damage was abolished by pretreatment with diltiazem, implicating L-type calcium channels.
- In vitro results corroborated in vivo findings, confirming direct hippocampal mediation.
Conclusions:
- GABA(A) receptor activation contributes to excitotoxicity and cell death in the immature brain.
- This model using muscimol in newborn rats effectively mimics hypoxic-ischemic brain damage seen in premature infants.
- Targeting GABA(A) receptor-mediated calcium influx may offer therapeutic strategies for neonatal brain injury.
Abstract:
Premature infants are at exceptionally high risk for hypoxic-ischemic insults and other traumatic events that result in permanent brain damage. However, no current models adequately mimic these events. An emerging concept is that the major excitatory drive in immature neurons is derived from depolarizing responses following activation of the gamma-aminobutyric acid (GABA)(A) receptor, resulting in the opening of voltage-sensitive calcium channels. While calcium-mediated signal transduction is trophic in developing neurons, excessive calcium entry is a major mediator of excitotoxicity. We report that exogenous activation of GABA(A) receptors by muscimol in newborn rats increases cell death in the hippocampus. The effects are region specific, persistent, and greater in males. Muscimol-induced damage is prevented by pretreatment with diltiazem, an L-type voltage-sensitive calcium channel blocker. Results using hippocampal cultures parallel those observed in vivo, indicating that the effects are mediated directly in the hippocampus. Existing models of pediatric hypoxic-ischemic brain damage focus on the effects of glutamate in the postnatal day 7 rat, because it is considered analogous to the newborn human. This makes the newborn rat analogous to the late gestational human. Ischemia in newborn rats induces GABA release and we propose that treatment with muscimol mimics the cell death cascade induced by hypoxia-ischemia in premature human infants.