1. To characterize membrane properties that might be relevant to the f
unction and fate of Cajal-Retzius (CR) cells, the pharmacological and
physiological effects of GABA acting at GABA(A) receptors were studied
in CR cells from embryonic (E18) and postnatal (P11-13) slices of rat
neocortex. 2. From the embryonic to the postnatal stage, GABA-induced
maximum current almost tripled, the EC50 increased from 38 to 74 mu M
, and the Hill number increased from 1.4 to 1.9. Muscimol-elicited cur
rents were qualitatively and quantitatively similar to those produced
by GABA. 3. GABA-induced changes in the amplitude of large-conductance
Ca2+-activated K+ channel current recorded on-cell from E18 CR cells
were consistent with depolarization. 4. GABA-mediated depolarization o
f embryonic and postnatal CR cells was studied directly with perforate
d-patch recording techniques. Ten micromolar and 1 mM GABA, respective
ly, depolarized E18 CR cells to -27 +/- 1 and -25 +/- 3 mV. These same
concentrations of GABA depolarized Pll CR cells to -36 +/- 3 and -23
+/- 3 mV. 5. 5. In postnatal cortex, GABA (100 mu M) increased the fir
ing rate of CR cells 7.3-fold. By contrast, the firing of hippocampal
pyramidal cells from slices of the same age (P12) was totally and reve
rsibly blocked by GABA. 6. These experiments suggest that contrary to
its postnatal inhibitory shift observed in other cells, the depolarizi
ng effect of GABA remains in CR cells from E18 until their virtual dis
appearance.