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A Reverse Genetic Approach to Test Functional Redundancy During Embryogenesis
Published on: August 11, 2010
Effect of early embryonic exposure to morphine on defects in the GABAergic system of day-old chicks
Dongmei Wang1, Juan Jiang1, Wen Shang1
1CAS Key Laboratory of Mental Health, Institute of Psychology, Beijing, China; Department of Psychology, University of Chinese Academy of Sciences, Beijing, China.
Insights
Early embryonic exposure to morphine in chicks impairs the GABA system, affecting brain development and increasing susceptibility to addiction in offspring. This highlights critical developmental windows for drug exposure effects.
Area of Science:
- Neuroscience
- Developmental Biology
- Pharmacology
Background:
- Embryonic drug exposure can cause lasting neurodevelopmental and behavioral issues in offspring.
- The GABAergic system plays a crucial role in brain development and function.
- Understanding the impact of gestational drug exposure on offspring addiction susceptibility is vital.
Purpose of the Study:
- To investigate the effects of embryonic morphine exposure on the GABA system in developing chicks.
- To determine if early embryonic morphine exposure alters GABAergic function and subsequent drug responses.
- To identify critical developmental periods for morphine's impact on the GABA system.
Main Methods:
- Administered morphine to chicken embryos during specific developmental stages (days 5-8 and 13-16).
- Utilized neuroelectrophysiology, immunohistochemistry, and behavioral assays to assess GABAergic function.
- Examined spontaneous and evoked inhibitory postsynaptic potentials (IPSPs), GABAergic receptor function, synaptic density, and behavioral responses to morphine.
Main Results:
- Morphine exposure during embryonic days 5-8 (MorphineE5-8) significantly reduced IPSP incidence and induction.
- MorphineE5-8 decreased GABAergic responses to muscimol and reduced GAD-expressing synaptic density in the IMM region.
- MorphineE5-8 increased GABAA receptor γ2 subunit expression and de-inhibited morphine-induced psychomotor responses in chicks.
Conclusions:
- Early embryonic morphine exposure (days 5-8) disrupts GABAergic function in the intermediate medial interstitial (IMM) region.
- These GABAergic deficits alter the responsiveness of postnatal chicks to addictive drugs, potentially increasing addiction susceptibility.
- The findings underscore the critical vulnerability of early embryonic development to addictive drug exposure and its long-term consequences on the GABA system.
Abstract:
Embryonic morphine exposure (EME) leads to abnormal brain development and behavior in the offspring, and the functional alteration of γ-aminobutyric acid (GABA) system is considered to be one of the important mechanisms. To mimic the problem of susceptibility of human gestational drug abuse on addictive drugs in offspring, we administered morphine exposure on days 5-8 and 13-16 of chicken embryo development and examined the functions of GABA neurons and their receptors in postnatal chicks by neuroelectrophysiology, immunohistochemistry and behavioral methods. We found that morphine exposure during embryonic stages 5-8 (MorphineE5-8) significantly reduced the incidence of spontaneous inhibitory postsynaptic potentiation (IPSP) and the induction of evoked IPSP and the mean amplitude of GABAA agonist muscimol-induced response in the intermediate medial interstitial (IMM) region, compared to naïve controls or saline-exposed chicks. The results of immunocytochemistry further suggest that MorphineE5-8 decreased the synaptic density of GAD-expressing sites in the IMM, while increased the expression of the GABAA receptor subtype γ2 isoform. Behavioral results found that Morphine5-8 treatment de-inhibited morphine-induced psychomotor responses in postnatal chicks. Morphine exposure at embryonic stages 13-16 (MorphineE13-16) showed no significant changes in the above indicators compared to the saline group. Evidence suggests that early embryonic morphine exposure leads to defects in GABAergic function in the IMM, which in turn alters the responsiveness of postnatal chicks to addictive drugs. These results will help to understand the GABA mechanisms by which embryonic addictive drug exposure contributes to offspring susceptibility to addiction.
