Differential expression of pre- and postsynaptic GABA(B) receptors in rat substantia nigra pars reticulata neurones.
Whole-cell recordings were made from substantia nigra pars reticulata in rat midbrain slices to study the functional expression of pre- and postsynaptic GABA(B) receptors in GABA output neurones. Baclofen (up to 300 microM) dose-dependently activated a weak current which was insensitive to tetrodotoxin and Ca2+-free solution but blocked by Ba2+ and 2-OH-saclofen. The maximum current activated by baclofen (30 microM) was 43.0 +/- 4.5 pA (n = 27), representing only 23% of that in dopamine neurones. Baclofen (1-30 microM) also reduced the frequency of the GABA(A) receptor-mediated miniature inhibitory postsynaptic currents while the distribution of their amplitudes was unaffected. This presynaptic effect of baclofen, prominent at a concentration as low as 1 microM, was sensitive to 2-OH-saclofen and occluded by Cd2+, but was unaffected by Ba2+. The results suggest a predominant role of the presynaptic GABA(B) receptors in substantia nigra pars reticulata. The relative abundance of pre- and postsynaptic GABA(B) receptor subtypes in this brain region may also be important in mediating the anticonvulsant effect of baclofen in rats.
Chan
P K
PK
Department of Physiology, Faculty of Medicine, The Chinese University of Hong Kong, Shatin.
Leung
C K
CK
Yung
W H
WH
D000818:Animals; D001418:Baclofen / Q000494:pharmacology; D008297:Male; D009474:Neurons / Q000187:drug effects / Q000378:metabolism*; D018408:Patch-Clamp Techniques; D051381:Rats; D017207:Rats, Sprague-Dawley; D011954:Receptors, Dopamine / Q000187:drug effects / Q000502:physiology; D018080:Receptors, GABA-B / Q000187:drug effects / Q000378:metabolism*; D017661:Receptors, Presynaptic / Q000187:drug effects / Q000378:metabolism*; D013378:Substantia Nigra / Q000187:drug effects / Q000378:metabolism*
D011954:Receptors, Dopamine; D018080:Receptors, GABA-B; D017661:Receptors, Presynaptic; D001418:Baclofen