Acute hypoxic hypoxia transiently reduces GABA(A) binding site number in developing chick optic lobe
D J Rodríguez Gil1, M S Viapiano, S Fiszer de Plazas
1Instituto de Biología Celular y Neurociencias, Prof. E. De Robertis, Facultad de Medicina, Universidad de Buenos Aires, Paraguay 2155, 1121, Buenos Aires, Argentina.
Insights
Prenatal hypoxic hypoxia significantly reduces GABA binding sites in chick embryos, impacting inhibitory neurotransmission. These effects are age-dependent and reversible upon return to normoxia.
Area of Science:
- Neuroscience
- Developmental Biology
- Biochemistry
Background:
- Prenatal-perinatal hypoxic-ischemic insults critically affect the Central Nervous System (CNS).
- These insults can lead to neural damage, seizures, apoptosis, and excitotoxicity due to neurotransmitter imbalance.
- Understanding the impact on neurotransmitter receptors is crucial for developing interventions.
Purpose of the Study:
- To establish a chick embryo model for normobaric acute hypoxic hypoxia.
- To evaluate changes in the GABA(A) receptor complex in the chick optic lobe following hypoxic injury.
- To assess the reversibility and age-dependency of these modifications.
Main Methods:
- Fertile White Leghorn chicken eggs were incubated and exposed to 8%O(2)/92%N(2) for 1 hour between embryonic days 12-18.
- Following hypoxia, embryos were either allowed recovery in normoxia or immediately processed for biochemical analysis.
- GABA binding assays and pharmacological characterization of the GABA(A) receptor complex were performed.
Main Results:
- Hypoxic treatment caused a significant, age-dependent reduction in GABA binding sites, most pronounced at ED12-16.
- At ED12, a decrease in B(max) but not K(d) for GABA binding was observed post-hypoxia.
- Positive allosteric modulation by a steroid and pentobarbital sodium was enhanced in hypoxic embryos.
- The reduction in [3H]GABA binding reversed after 48 hours of normoxic recovery.
Conclusions:
- Acute prenatal hypoxic hypoxia induces significant, reversible, and age-dependent alterations in CNS inhibitory neurotransmission in chick embryos.
- The GABA(A) receptor complex is a key target of hypoxic injury during development.
- The chick embryo model provides a valuable tool for studying developmental neuroprotection.
Abstract:
The Central Nervous System is known to be critically affected in the prenatal-perinatal period by hypoxic-ischemic insults, which produce several disorders such as loss of neural projections, increased susceptibility to seizures, apoptosis and an imbalance in normal activity of glutamatergic and GABAergic neurones, resulting in acute cell excitotoxicity. The aim of the present work was to establish a chick embryo model of normobaric acute hypoxic hypoxia as well as to evaluate modifications in GABA(A) receptor complex from chick optic lobe, that may result from this injury. Fertile chicken (Gallus gallus domesticus) eggs from White Leghorn were incubated and at embryonic days (ED) 12 to 18, subjected to a stream of 8%O(2)/92%N(2) during1 h, and then were either returned to their shelves in the incubator for recovery, or immediately processed for biochemical studies. Hypoxic treatment produced a significant age dependent reduction in GABA binding sites showing the greatest decrease at the earliest stages studied (ED12-ED16). Saturation curves of GABA binding performed at ED12 showed a decrease in B(max), (control, 5.48+/-0.20, hypoxic, 3.90+/-0.39 pmol/mg protein), but no significant change in K(d). Following 48 h in normoxic atmosphere post-hypoxia reduction in [3H]GABA binding was reversed. Pharmacological properties of GABA(A) receptor at ED12 showed that positive allosteric modulation effects of the steroid 3alpha-hydroxy-5alpha-pregnan-20-one and the barbiturate pentobarbital sodium were enhanced by the treatment. This model of acute prenatal hypoxic hypoxia produced marked alterations in inhibitory CNS neurotransmission that proved reversible and age dependent.
