W. Morishita et Br. Sastry, PRESYNAPTIC ACTIONS OF GABA AND BACLOFEN IN CA1 REGION OF THE GUINEA-PIG HIPPOCAMPUS IN-VITRO, Neuroscience, 61(3), 1994, pp. 447-455
The presynaptic actions of GABA and (+/-)baclofen on the stratum radia
tum in the CA1 region of guinea-pig hippocampal slices were investigat
ed using a modified grease-gap recording technique. D.c. potential shi
fts were recorded in response to varying concentrations of GABA and (/-)baclofen. In Ca2+-free media containing tetrodotoxin, bath applicat
ions of GABA (2.5 mu M to 20 mM) produced depolarizations which were c
oncentration-dependent. Maximum depolarization was attained with 1O mM
GABA. Superfusion of(+/-)baclofen (0.125-500 mu M) produced a concent
ration-dependent hyperpolarization which peaked at a concentration of
250 mu M. The GABA-induced depolarization but not the (+/-)baclofen-in
duced hyperpolarization was depressed by the GABA(A) antagonists bicuc
ulline and picrotoxinin. The(+/-)baclofen-induced hyperpolarization bu
t not the GABA-induced depolarization was suppressed by CGP 35 348, a
GABA(B) antagonist. In the presence of bicuculline, GABA (0.5-5.0 mM)
occasionally caused a hyperpolarization which could be blocked by CGP
35 348. These results indicate that the primary presynaptic action of
GABA on the d.c. potential in the CA1 region of the hippocampus is to
produce a GABA(A) receptor-mediated depolarization, while (+/-)baclofe
n induces a GABA(B) receptor-mediated hyperpolarization. The grease-ga
p d.c. potential recording technique, described in this paper, is expe
cted to be useful in examining changes in the membrane potentials of p
resynaptic terminals.