Neurosteroid Agonist at GABAA receptor induces persistent neuroplasticity in VTA dopamine neurons.
The main fast-acting inhibitory receptors in the mammalian brain are γ-aminobutyric acid type-A (GABAA) receptors for which neurosteroids, a subclass of steroids synthesized de novo in the brain, constitute a group of endogenous ligands with the most potent positive modulatory actions known. Neurosteroids can act on all subtypes of GABAA receptors, with a preference for δ-subunit-containing receptors that mediate extrasynaptic tonic inhibition. Pathological conditions characterized by emotional and motivational disturbances are often associated with perturbation in the levels of endogenous neurosteroids. We studied the effects of ganaxolone (GAN)-a synthetic analog of endogenous allopregnanolone that lacks activity on nuclear steroid receptors-on the mesolimbic dopamine (DA) system involved in emotions and motivation. A single dose of GAN in young mice induced a dose-dependent, long-lasting neuroplasticity of glutamate synapses of DA neurons ex vivo in the ventral tegmental area (VTA). Increased α-amino-3-hydroxy-5-methyl-4-isoxazole propionic acid (AMPA)/N-methyl-D-aspartate ratio and rectification of AMPA receptor responses even at 6 days after GAN administration suggested persistent synaptic targeting of GluA2-lacking AMPA receptors. This glutamate neuroplasticity was not observed in GABAA receptor δ-subunit-knockout (δ-KO) mice. GAN (500 nM) applied locally to VTA selectively increased tonic inhibition of GABA interneurons and triggered potentiation of DA neurons within 4 h in vitro. Place-conditioning experiments in adult wild-type C57BL/6J and δ-KO mice revealed aversive properties of repeated GAN administration that were dependent on the δ-subunits. Prolonged neuroadaptation to neurosteroids in the VTA might contribute to both the physiology and pathophysiology underlying processes and changes in motivation, mood, cognition, and drug addiction.
Institute of Biomedicine, Pharmacology, University of Helsinki, Helsinki, Finland.
Elena
E
Vashchinkina
Institute of Biomedicine, Pharmacology, University of Helsinki, Helsinki, Finland.
Aino K
AK
Manner
Institute of Biomedicine, Pharmacology, University of Helsinki, Helsinki, Finland.
Olga
O
Vekovischeva
Institute of Biomedicine, Pharmacology, University of Helsinki, Helsinki, Finland.
Bjørnar
B
den Hollander
Department of Pharmacology, Drug Development and Therapeutics, University of Turku, Turku, Finland.
Mikko
M
Uusi-Oukari
Institute of Biomedicine, Pharmacology, University of Helsinki, Helsinki, Finland.
Teemu
T
Aitta-Aho
Institute of Biomedicine, Pharmacology, University of Helsinki, Helsinki, Finland.
Esa R
ER
Korpi
D000200:Action Potentials / Q000187:drug effects / Q000235:genetics; D000818:Animals; D004298:Dopamine / Q000378:metabolism; D059290:Dopaminergic Neurons / Q000187:drug effects*; D018683:Excitatory Amino Acid Agents / Q000494:pharmacology; D005260:Female; D018682:GABA Agents / Q000494:pharmacology; D005968:Glutamate Decarboxylase / Q000235:genetics; D049452:Green Fluorescent Proteins / Q000235:genetics / Q000378:metabolism; D066298:In Vitro Techniques; D008297:Male; D051379:Mice; D008810:Mice, Inbred C57BL; D008822:Mice, Transgenic; D009473:Neuronal Plasticity / Q000187:drug effects*; D018377:Neurotransmitter Agents / Q000494:pharmacology*; D010852:Picrotoxin / Q000494:pharmacology; D011280:Pregnanolone / Q000031:analogs & derivatives / Q000494:pharmacology; D011963:Receptors, GABA-A / Q000235:genetics / Q000378:metabolism*; D017557:Ventral Tegmental Area / Q000166:cytology*; D005680:gamma-Aminobutyric Acid / Q000494:pharmacology
D004298:Dopamine; D018683:Excitatory Amino Acid Agents; D018682:GABA Agents; D005968:Glutamate Decarboxylase; D049452:Green Fluorescent Proteins; D018377:Neurotransmitter Agents; D010852:Picrotoxin; D011280:Pregnanolone; D011963:Receptors, GABA-A; D005680:gamma-Aminobutyric Acid; C105051:ganaxolone; C402565:glutamate decarboxylase 1