GABAA receptor changes in acute allopregnanolone tolerance
Vita Birzniece; Şahruh Türkmen; Charlotte Lindblad; Di Zhu; Inga-Maj Johansson; Torbjörn Bäckström; Göran Wahlström
European Journal of Pharmacology2006
Summary (paraphrased)
This companion mechanistic study links acute allopregnanolone tolerance to concrete GABA-A receptor plasticity: after tolerance induction, α4 subunit abundance and mRNA fall in thalamic relay nuclei, correlating with the dose escalation needed to sustain the neurosteroid's effects. It provides the molecular substrate for the behavioral tolerance seen in the Morris water maze experiments. The message is that chronic neurosteroid elevation rewires inhibitory circuitry — a template for how a persistent excess state could become self-sustaining even after the inducing exposure ends.
Why it’s in the systems review
This paper gives the molecular face of neurosteroid tolerance — downregulated α4 subunits — which is the kind of self-sustaining receptor remodeling Powers' feedback-loop theorizing invokes. If chronic excess remodels GABA-A composition, then removing the drug does not restore the original circuit, offering a persistence mechanism independent of continued exposure. It is the strongest preclinical precedent for "the system does not reset."
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