Actions of 3 alpha,5 alpha-tetrahydrodeoxycorticosterone on single neurones of the mesencephalic reticular formation in the rat.
The effects of microinjections of 3 alpha,5 alpha-tetrahydrodeoxycorticosterone (3 alpha-THDOC) on single neurones of the mesencephalic reticular formation (MRF) were investigated in rats anaesthetized with urethan. Microinjections of approximately 100 nl of 0.5-2 microM 3 alpha-THDOC inhibited firing of 105 of 112 neurones (94%). Microinjections of approximately 100 nl of 100-250 nM of 3 alpha-THDOC did not alter neuronal activity, but in 52 of 68 cases (76%) it potentiated the inhibitory action of microiontophoretically applied gamma-aminobutyric acid (GABA). The 3 beta-isomer of tetrahydrodeoxycorticosterone did not elicit any changes in neuronal firing. The effects of 3 alpha-THDOC were reversibly antagonized by microiontophoretically applied bicuculline. This 'in vivo' study supports the hypothesis that 3 alpha-THDOC may function as endogenous modulator of GABAA-mediated inhibition in various physiopathological conditions.
Ermirio
R
R
Istituto di Fisiologia Umana, Università degli Studi, Genova, Italy.
Blanchi
D
D
Ruggeri
P
P
Cogo
C E
CE
Molinari
C
C
D000200:Action Potentials / Q000187:drug effects; D000818:Animals; D001640:Bicuculline / Q000494:pharmacology; D003345:Corticosterone / Q000031:analogs & derivatives* / Q000037:antagonists & inhibitors / Q000494:pharmacology; D007478:Iontophoresis; D008297:Male; D009474:Neurons / Q000187:drug effects / Q000502:physiology*; D051381:Rats; D011919:Rats, Inbred Strains; D012154:Reticular Formation / Q000166:cytology / Q000187:drug effects / Q000502:physiology*; D005680:gamma-Aminobutyric Acid / Q000494:pharmacology
D005680:gamma-Aminobutyric Acid; C003676:tetrahydrocorticosterone; D003345:Corticosterone; D001640:Bicuculline