Steroid hormone fluctuations and GABA(A)R plasticity.

Area of Science:

• Neuroscience
• Endocrinology
• Neuropharmacology

Background:

• Fluctuating steroid hormone levels create vulnerability for neurological disorders such as catamenial epilepsy, premenstrual syndrome, and postpartum depression.
• Neurosteroids significantly impact neuronal excitability by altering GABAA receptor (GABAAR) function.
• Changes in neurosteroid levels during stress, the ovarian cycle, and pregnancy profoundly affect GABAAR structure and function.

Purpose of the Study:

• To investigate the relationship between changing neurosteroid levels and alterations in GABAAR subunit composition.
• To understand how these GABAAR changes influence neuronal excitability and susceptibility to neurological disorders.
• To explore the potential homeostatic mechanisms involving GABAAR reorganization in response to neurosteroid fluctuations.

Main Methods:

• Analysis of GABAAR subunit expression (gamma2 and delta) in response to varying neurosteroid levels.
• Assessment of neuronal excitability through seizure susceptibility and anxiety-like behavior in mice.
• Examination of the input-output relationship to determine changes in neuronal excitability.

Main Results:

• Moderate, brief increases in neurosteroids decreased GABAAR gamma2 and increased delta subunit expression, reducing seizure susceptibility and anxiety.
• Robust increases in neurosteroids during pregnancy decreased both GABAAR gamma2 and delta subunit expression, increasing neuronal excitability.
• These findings demonstrate a direct link between neurosteroid-induced GABAAR alterations and changes in neuronal excitability.

Conclusions:

• Alterations in GABAAR subunit composition serve as a homeostatic mechanism to maintain neuronal inhibition amidst fluctuating neurosteroid levels.
• Receptor reorganization is crucial for preventing sedation or hyperexcitability under varying neurosteroid conditions.
• Dysregulation of GABAARs in response to steroid hormone changes may contribute to the pathophysiology of steroid hormone-associated neurological disorders.