Developmental Changes in Spontaneous GABA_A‐mediated Synaptic Events in Rat Hippocampal CA3 Neurons

Abstract

Ongoing spontaneous postsynaptic potentials (SPSPs) were intracellularly recorded at 34-36 degrees C from hippocampal CA3 neurons in slices obtained from postnatal days (P) 0-6 and 7-31. SPSPs occurred randomly, and their frequency distribution was fitted by a single exponential function. They were little affected by kynurenic acid, but were reversibly blocked by bicuculline, implying that they were mediated by GABAA receptors. The mean amplitude was 4.53 +/- 0.89 mV in control conditions and 4.07 +/- 0.79 mV in kynurenic acid. In kynurenic acid (with CsCl-filled microelectrodes), SPSPs reversed polarity at 2.4 +/- 2 mV. When tetrodotoxin (1 microM) was added to kynurenic acid solution, GABAA-mediated miniature postsynaptic potentials (MPSPs) were recorded. Under these conditions large events disappeared. The mean amplitude of MPSPs was 2.51 +/- 0.43 mV. The mean frequency decreased from 2.96 +/- 1.04 Hz in kynurenic acid to 0.4 +/- 0.15 Hz in kynurenic acid plus tetrodotoxin. In contrast with P0-P6, at P7-P31 SPSPs were significantly affected by kynurenic acid. The mean amplitude of SPSPs shifted from 4.71 +/- 0.82 mV in control conditions to 3.79 +/- 0.76 mV in kynurenic acid. At this developmental stage, the reversal potential of GABAA-mediated SPSPs shifted towards more negative values (-23.7 +/- 1.3 mV). Addition of tetrodotoxin to kynurenic acid solution abolished larger events and revealed GABAergic MPSPs. The mean amplitude of MPSPs was 2.72 +/- 0.5 mV, a value very close to that observed at P0-P6. Synaptic currents were recorded at 22-24 degrees C from voltage-clamped CA3 pyramidal neurons (at P6) using the tight-seal whole-cell recording technique.(ABSTRACT TRUNCATED AT 250 WORDS)

Nicotine activates immature “silent” connections in the developing hippocampus

“…Spontaneous miniature AMPA-mediated EPSCs were recorded in the presence of tetrodotoxin (1 M) from P2-P5 CA1 pyramidal cells at 24°C (n ϭ 7) and 33°C (n ϭ 7). In agreement with previous work (26,27), in some neurons (6͞14) spontaneous glutamatergic activity was not detected (four silent cells were recorded at 24°C and two at 33°C). Bath application of 1 M nicotine, a concentration close to that present in the smoker's blood immediately after smoking a cigarette (28), caused the appearance of mEPSCs ( Fig.…”

Novel and Transient Populations of Corticotropin-Releasing Hormone-Expressing Neurons in Developing Hippocampus Suggest Unique Functional Roles: A Quantitative Spatiotemporal Analysis

“…Quantitative data were derived from eight sections per rat (see Materials and Methods) and two animals per age group. fects, and functional excitatory glutamatergic synaptic transmission is established (Ben-Ari et al, 1989;Hosokawa et al, 1994;Durand et al, 1996;Ben-Ari et al, 1997). This "switch" is accompanied by transient hyperexcitability of the hippocampal network (Gomez-Di Cesare et al, 1997).…”

Slow Kinetics of Miniature IPSCs during Early Postnatal Development in Granule Cells of the Dentate Gyrus

“…Previous studies have shown that GABAergic neurons are born prenatally (Schlessinger et al, 1978;Amaral and Kurz, 1985;Lubbers et al, 1985), and by the end of the first postnatal week, they make synaptic contacts on granule cell dendrites as well as somata (Lubbers and Frotscher, 1988;Ribak, 1988, 1990). Although GABAergic responses have been shown to occur in developing hippocampal and cortical pyramidal cells (Mueller et al, 1984;Kriegstein et al, 1987;Janigro and Schwartzkroin, 1988;Ben-Ari et al, 1989;Gaiarsa et al, 1990;Blanton and Kriegstein, 1991;Luhmann and Prince, 1991;Zhang et al, 1991;Hosokawa et al, 1994;Fleidervish and Gutnick, 1995), the functional properties of the early GABA A receptormediated synaptic transmission in the late-developing dentate granule cells are not well understood. The data presented here demonstrate that the overwhelming majority of dentate granule cells of the early postnatal rat possess functionally active GABAergic synaptic inputs [interestingly, no glutamatergic synaptic events can be observed at this time in granule cells (our unpublished observations)], similar to CA1 and CA3 pyramidal cells (Ben-Ari et al, 1989;Hosokawa et al, 1994;Gaiarsa et al, 1995).…”