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Synaptic and intrinsic balancing during postnatal development in rat pups exposed to valproic acid in utero
Elisabeth C Walcott1, Emily A Higgins, Niraj S Desai
1The Neurosciences Institute, San Diego, California 92121, USA.
Insights
Prenatal exposure to valproic acid (VPA) causes neurodevelopmental issues. These abnormalities in young rats improve with age, suggesting a homeostatic response to mitigate teratogenic effects.
Area of Science:
- Neuroscience
- Developmental Neuroscience
- Pharmacology
Background:
- Valproic acid (VPA) is a teratogenic anticonvulsant linked to human birth defects and cognitive impairments.
- Prenatal VPA exposure in rats causes neuroanatomical and behavioral abnormalities.
- Previous studies identified impaired neuronal excitability and increased NMDA currents in young VPA-exposed animals.
Purpose of the Study:
- To investigate the developmental trajectory of VPA-induced neuronal abnormalities in the medial prefrontal cortex.
- To determine if and how these abnormalities resolve during postnatal development.
- To explore the potential homeostatic mechanisms underlying the nervous system's response to teratogenic insult.
Main Methods:
- Whole-cell patch-clamp recordings were performed on layer 2/3 neurons of the medial prefrontal cortex in VPA-exposed and control rats.
- Recordings were conducted across different postnatal developmental stages.
- Computational models were utilized to analyze and interpret physiological data.
Main Results:
- Both impaired intrinsic neuronal excitability and increased NMDA synaptic currents peaked early postnatally in VPA-exposed rats.
- These abnormalities gradually resolved with maturation, with near-normal excitability and NMDA currents observed by early adolescence.
- The developmental correction of these two abnormalities appeared coordinated.
Conclusions:
- The study demonstrates a developmental correction of VPA-induced neuronal abnormalities in the rat medial prefrontal cortex.
- Computational modeling suggests a trade-off between impaired excitability and increased NMDA currents, potentially balancing network activity.
- This coordinated resolution may represent a homeostatic mechanism to maintain nervous system stability following teratogenic exposure.
Abstract:
Valproic acid (VPA) is among the most teratogenic of commonly prescribed anticonvulsants, increasing the risk in humans of major malformations and impaired cognitive development. Likewise, rats exposed prenatally to VPA exhibit a variety of neuroanatomical and behavioral abnormalities. Previous work has shown that pyramidal neuron physiology in young VPA-exposed animals is marked by two strong abnormalities: an impairment in intrinsic neuronal excitability and an increase in NMDA synaptic currents. In this study, we investigated these abnormalities across postnatal development using whole-cell patch recordings from layer 2/3 neurons of medial prefrontal cortex. We found that both abnormalities were at a peak soon after birth but were gradually corrected as animals matured, to the extent that normal excitability and NMDA currents had been restored by early adolescence. The manner in which this correction happened suggested coordination between the two processes. Using computational models fitted to the physiological data, we argue that the two abnormalities trade off against each other, with the effects on network activity of the one balancing the effects of the other. This may constitute part of the nervous system's homeostatic response to teratogenic insult: an attempt to maintain stability despite a strong challenge.
