Tn. Ricciardi et At. Malouf, DIFFERENTIAL-EFFECTS OF ZINC ON HYPERPOLARIZING AND DEPOLARIZING GABA(A) SYNAPTIC POTENTIALS IN HIPPOCAMPAL SLICE CULTURES, Brain research, 680(1-2), 1995, pp. 80-87
We have examined the changes in GABA(A)-mediated synaptic potentials r
ecorded from CA3 pyramidal neurons in hippocampal slice cultures follo
wing application of zinc (Zn2+). Unlike 4-AP, Zn2+ did not enhance fas
t hyperpolarizing potentials but primarily enhanced depolarizing GABA(
A) potentials. Zn2+ did not alter the postsynaptic response of pyramid
al neurons to pressure applied GABA, consistent with previous reports
that Zn2+ enhances the release of GABA from presynaptic terminals. To
examine the role of local circuitry in the production of Zn2+ response
s, we recorded from cultures maintained for 7-10 days following remova
l of the dentate and hilus to allow complete degeneration of the messy
fibers (DGX cultures). Zn2+ produced giant depolarizing potentials (G
DPs) in DGX cultures that were identical to those in intact cultures.
In contrast, the 4-AP response was dramatically altered in DGX culture
s. In DGX cultures, Zn2+ co-applied with 4-AP appeared to inhibit the
production of fast hyperpolarizing GABAA synaptic potentials produced
by 4-AP alone. This inhibition of fast hyperpolarizing potentials sugg
ests that Zn2+ may reduce the release of GABA onto pyramidal cell soma
ta. These observations suggest that Zn2+ enhances GABA release from lo
cal circuit neurons that synapse onto pyramidal cell dendrites, and in
hibits GABA release onto pyramidal cell somata.