Slow kinetics of miniature IPSCs during early postnatal development in granule cells of the dentate gyrus - PubMed (original) (raw)
Slow kinetics of miniature IPSCs during early postnatal development in granule cells of the dentate gyrus
G S Hollrigel et al. J Neurosci. 1997.
Abstract
Whole-cell patch-clamp recordings were used to investigate the properties of GABAA receptor-mediated postsynaptic currents during development in dentate gyrus granule cells from neonatal [postnatal day 0 (P0)] to adult rats in brain slices. The frequency of miniature IPSCs (mIPSCs) was low at birth and increased progressively with age. The mIPSCs of all ages could be satisfactorily fitted with the sum of a single exponential rise and single exponential decay. From P0 to P14, both the rise time and the decay time constants were significantly longer than in the adult. The mIPSC rise and decay kinetics did not change during the first 2 postnatal weeks, but during the third week the kinetics sped up and by P21 attained adult values. In contrast, the amplitude of the mIPSCs did not change during development. The synaptic GABAA receptors in immature and adult cells showed differential sensitivity to modulators. The subunit-specific benzodiazepine agonist zolpidem increased the decay time constant of the IPSCs of immature granule cells with a reduced potency compared with the adult. Furthermore, zinc decreased the amplitude and decay time constant of mIPSCs from developing granule cells, whereas it had no effect on mIPSCs in adult neurons. The results reveal for the first time that until the end of the second postnatal week the synaptic GABAA receptor-mediated currents in dentate granule cells display slower rise and decay kinetics but similar amplitudes compared with adult, resulting in a net decrease in synaptic charge transfer during development.
Figures
Fig. 1.
mIPSC frequency increases with age in dentate granule cells. Top traces are representative recordings of mIPSCs recorded in voltage-clamp at −60mV with CsCl-filled pipettes. The GABA-mediated Cl− currents reversed at −0.5 ± 2.1 mV and were blocked by 20 μ
m
bicuculline (not shown). The bar graph is the summary of the frequency of mIPSCs as a function of age. The frequency continued to increase throughout the ages examined. P0–P4: 0.8 ± 0.2 Hz; P5–P9: 1.7 ± 0.5 Hz; P10–P14: 2.3 ± 0.5 Hz; P21: 6.7 ± 0.6 Hz; adult: 11.0 ± 2.1 Hz. The number of cells is indicated in parentheses.
Fig. 2.
The kinetics of mIPSCs is slower in P0–P4 granule cells compared with adult granule cells, and kinetics of mIPSCs from P5–P9 neurons remains slower than that of adult neurons.A, Averages of 489 mIPSCs (P0–P4) and 478 mIPSCs (adult) recorded at −60mV. Both the rise and decay are qualitatively slower than the adult current. The mIPSCs in the adult as well as in the young cells were fit by the sum of a single exponential rise and single exponential decay. The values for the equations were as follows: adult, A = −92.5 pA; τr = 0.15 msec; τD = 4.3 msec; young: A = −99.2 pA; τr = 0.36 msec; τD = 9.5 msec. B, C, D, Cumulative probability plots of the amplitude, rise time (10–90%), and single exponential decay time of the mIPSCs in_A_. The median amplitudes were P0–P4, 74.41 pA; P5–P9, 69.9 pA; adult: 76.37 pA. The median rise times were P0–P4, 0.91 msec; P5–P9, 1.03 msec; adult: 0.29 msec. The median decay time constants were P0–P4, 9.2 msec; P5–P9, 7.7 msec; adult, 4.5 msec. Significant differences of the distributions were found for the rise times and decay time constants for the P0–P4/P5–P9 versus adult groups, whereas there was no significant difference between P0–P4 and P5–P9 (Kolmogorov–Smirnov test).
Fig. 4.
GABAA receptor-mediated synaptic currents of granule cells at different stages of development have similar kinetics. A, B, Two examples of granule cells recorded and stained with biocytin. The dashed lines_indicate the borders of the granule cell layer. Note that both cells were located within the granule cell layer, each had an axon projecting through the hilus, and the majority of the dendrites were oriented toward the molecular layer. C, D, The averages of the IPSCs recorded from A and B, respectively. Open circles are the raw data points; the_solid line is the best-fit function describing the currents. Each cell, despite different stages of maturation, had similar IPSC kinetics. The values for the equations were (C) A = −194.3 pA; τr = 0.43 msec; τD = 11.1 msec; (D) A = −243.3 pA; τr = 0.37 msec; τD = 13.5 msec. Note that the currents were accurately described by the sum of a single exponential rise and a single exponential decay.
Fig. 3.
mIPSC kinetics is developmentally regulated.A–C, Summary data of the rise time constants, decay time constants, and amplitudes of the mIPSCs as a function of age. Bars of the same color are not statistically different (_t_test). Both the rise time constants and decay time constants significantly decreased at P21 and were not different from adult values. The amplitude of the mIPSCs did not change with age.D, Bar graph of the synaptic charge transfer (measured as the area under the best-fit curve describing the IPSCs) versus age. Consistent with the developmental change in kinetics, the synaptic charge transfer was larger in young neurons (242.3 ± 22.2% of the adult) and decreased to adult values by P21 (100.5 ± 3.0%).Numbers in parentheses are the number of cells.
Fig. 5.
Synaptic GABAA receptors of young granule cells are less sensitive to modulation by zolpidem. In both the young and adult granule cells, 0.05 μ
m
zolpidem did not significantly increase the decay time constant of the IPSCs (P0–P4, 8.8 ± 8.5% increase; adult, 9.8 ± 5.9% increase); however, 0.5 μ
m
zolpidem increased the decay time constant of P0–P4 IPSCs by 27.3 ± 9.0% and of adult IPSCs by 80.5 ± 8.6%. The difference in the relative increase caused by 0.5 μ
m
zolpidem was significant between the P0–P4 values and adult values. Zolpidem (5.0 μ
m
) increased P0–P4 IPSC decay times by 82.0 ± 30.3% and adult IPSC decay times by 97.2 ± 5.1%. These effects were not significantly different (t test). Number of cells indicated within the bars.
Fig. 6.
Zinc inhibits mIPSCs of young granule cells.A–C, Bar graphs comparing the effects of ZnCl2 (300 μ
m
) on mIPSC amplitude, decay time constant, and rise time constant. Zinc significantly decreased the amplitude (control, 74.0 ± 3.8 pA; zinc, 54.0 ± 3.9 pA) and decay time constant (control, 9.6 ± 0.7 msec; zinc, 6.9 ± 0.8 msec) of P0–P4 mIPSCs. Zinc did not change the rise time constant of P0–P4 mIPSCs (control, 0.41 ± 0.05 msec; zinc, 0.41 ± 0.04 msec). In addition, zinc did not change the parameters of adult mIPSCs: amplitude (control, 72.4 ± 4.2 pA; zinc, 66.6 ± 8.9 pA), decay time constant (control, 4.5 ± 0.2 msec; zinc, 4.2 ± 0.3 msec), rise time constant (control, 0.19 ± 0.02 msec; zinc, 0.18 ± 0.00 msec). Number of cells indicated within the bars.
References
- Amaral DG, Kurz J. The time of origin of cells demonstrating glutamic acid decarboxylase-like immunoreactivity in the hippocampal formation of the rat. Neurosci Lett. 1985;59:33–39. - PubMed
- Bayer SA. Development of the hippocampal region in the rat. I. Neurogenesis examined with 3H-thymidine autoradiography. J Comp Neurol. 1980;190:87–114. - PubMed
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