The absence of a major Ca2+ signaling pathway in GABAergic neurons of the hippocampus - PubMed (original) (raw)

The absence of a major Ca2+ signaling pathway in GABAergic neurons of the hippocampus

A Sík et al. Proc Natl Acad Sci U S A. 1998.

Abstract

The Ca2+/calmodulin-dependent protein phosphatase 2B or calcineurin (CN) participates in several Ca2+-dependent signal transduction cascades and, thus, contributes to the short and long term regulation of neuronal excitability. By using a specific antibody to CN, we demonstrate its absence from hippocampal interneurons and illustrate a physiological consequence of such CN deficiency. Consistent with the lack of CN in interneurons as detected by immunocytochemistry, the CN inhibitors FK-506 or okadaic acid significantly prolonged N-methyl-D-aspartate channel openings recorded in the cell-attached mode in hippocampal principal cells but not those recorded in interneurons. Interneurons were also devoid of Ca2+/calmodulin-dependent protein kinase IIalpha, yet many of their nuclei contained the cyclic AMP-responsive element binding protein. On the basis of the CN and Ca2+/calmodulin-dependent protein kinase IIalpha deficiency of interneurons, entirely different biochemical mechanisms are expected to govern Ca2+-dependent neuronal plasticity in interneurons versus principal cells.

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Figures

Figure 1

Figure 1

CN immunoreactivity is present in principal cells but not in GABAergic interneurons of the hippocampus. (A) High-magnification light micrograph of the stratum pyramidale from the CA1 region. The presence of the reaction product in the perinuclear cytoplasm, proximal and distal dendrites, and its absence from the nuclei of pyramidal cells is clearly visible. Both the nuclei and the cytoplasm of large neurons (showing the characteristics of interneurons) are devoid of immunoreactivity (arrows). (B) In addition to conventional pyramidal cells, a large CA1 stratum radiatum cell is also immunoreactive for CN (arrow). Note the thick bifurcated apical dendrite (small arrows) characteristic of this type of an ectopic pyramidal cell in the CA1 region. (C and D) Matching surfaces of adjacent sections, one stained for CN (C) and the other stained for GABA (D). Identification of cell bodies cut in half shows the lack of CN immunoreacivity in GABA-positive interneurons (arrows) in CA1 stratum pyramidale and oriens. Stratum oriens, o; stratum pyramidale, p; stratum radiatum, r. [Bars = 25 μm (A and B) and 50 μm (C and D).]

Figure 2

Figure 2

Subcellular localization of CN immunoreactivity using the preembedding immunogold method with silver intensification (A, C–E) or with the conventional immunoperoxidase technique with DAB as a chromogen (B). (A) CN immunoreactivity (black dots of irregular size) is present in the perinuclear cytoplasm of a pyramidal cell (s) and in dendrites (d) but not in glial cells (gl). (B) CN immunoreactivity, as indicated by the diffusible DAB reaction product, is present in dendrites and dendritic spines but is absent from axon terminals. Arrows indicate asymmetric synaptic contacts formed by CN-negative boutons (asterisks) on CN-positive dendritic spines. (C and D) Silver-intensified colloidal gold particles show the subcellular localization of CN in dendrites. Particles were often seen attached to small membrane-limited structures (arrowheads) that resembled saccules of smooth endoplasmic reticulum or spine apparatus fragments. Note the asymmetric synapses terminating on labeled pyramidal cell dendritic spines (arrow). (E) An axon initial segment is shown to be CN immunoreactive. [Bars = 1 μm (A, D, and E) and 0.5 μm (B and C).]

Figure 3

Figure 3

(A and B) Light micrographs of adjacent sections (mirror technique) showing the absence of CaMKIIα (A and C, at high magnification) in GABAergic (B and D, at high magnification) interneurons (arrows) in the hilar region. Capillaries (asterisks) are used as landmarks (C and D). Granule cells are positive for CaMKIIα. (E) Black DAB–Ni2+ reaction product indicates the presence of CREB immunoreactivity in the nuclei of pyramidal cells and in parvalbumin (PV)-immunoreactive GABAergic interneurons (black arrows) in the CA3 region of the hippocampus. White arrows mark the CREB-positive nuclei of PV-immunoreactive neurons. g, Granule cell layer; h, hilus. [Bars = 20 μm (A and B), 10 μm (C and D), and 25 μm (E).]

Figure 4

Figure 4

FK-506, a potent and specific CN inhibitor, prolongs NMDA channel openings in a CA1 pyramidal cell but not in an interneuron. Representative traces (Left), with openings depicted as downward deflections, and open time histograms (Right) calculated from the same patches before and after application of FK-506 (50–100 nM). Scale bars denote 10 ms and 2 pA. Within 6–8 min after bath application of the drug, the mean open time increased from 1.45 ms to 2.96 ms in this pyramidal cell. In contrast to hippocampal principal cells (also see Table 1), the mean NMDA channel open time in the interneuron did not change during the same experimental conditions. The logarithmic binned open time distributions plotted on a square root ordinate were best fitted with the sum of two exponentials and yielded mean open times of 0.69 ms under control conditions and 0.71 ms in FK-506. The individual open time components (τ1 and τ2) are indicated on the graphs with their respective amplitude components in parentheses.

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References

    1. Levitan I B. Annu Rev Physiol. 1994;56:193–212. - PubMed
    1. Braun A P, Schulman H. Annu Rev Physiol. 1995;57:417–445. - PubMed
    1. Ghosh A, Greenberg M E. Science. 1995;268:239–247. - PubMed
    1. Soderling T R. Adv Second Messenger Phosphoprotein Res. 1995;30:175–189. - PubMed
    1. Nairn A C, Shenolikar S. Curr Opin Neurobiol. 1992;2:296–301. - PubMed

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