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.
Department of Physiology, Faculty of Medicine, The Chinese University of Hong Kong, Shatin.
P K
PK
Chan
C K
CK
Leung
W H
WH
Yung
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