Elsevier

Neuroscience

Volume 123, Issue 3, 2004, Pages 715-724
Neuroscience

Homogenous glycine receptor expression in cortical plate neurons and cajal-retzius cells of neonatal rat cerebral cortex

https://doi.org/10.1016/j.neuroscience.2003.10.014Get rights and content

Abstract

Glycinergic membrane responses have been described in cortical plate neurons (CPn) and Cajal-Retzius cells (CRc) during early neocortical development. In order to elucidate the functional properties and molecular identity of glycine receptors in these two neuronal cell types, we performed whole-cell patch-clamp recordings and subsequent single-cell multiplex reverse transcriptase-polymerase chain reaction (RT-PCR) analyses on visually identified neurons in tangential and coronal slices as well as in situ hybridizations of coronal slices from neonatal rat cerebral cortex (postnatal days 0–4). In both CPn and CRc the glycinergic agonists glycine, β-alanine and taurine induced inward currents with larger current densities in CRc. The functional properties of these currents were similar between CPn and CRc. In both cell types the glycine receptor showed a higher affinity for glycine than for the glycinergic agonists β-alanine and taurine. The glycinergic responses of both cells were blocked by the glycinergic antagonist strychnine and were unaffected by the GABAergic antagonist bicuculline (100 μM), the N-methyl-d-aspartic acid receptor antagonist (±)-2-amino-5-phosphonopentatonic acid (60 μM) and by picrotoxin (30 μM), an antagonist of α homomeric glycine receptors. Single-cell multiplex RT-PCR revealed the expression of glycine receptor α2 and β subunits in CPn and CRc, while no α1 and α3 subunits were observed. In situ hybridization histochemistry showed the expression of mRNAs for α2 and β subunits within the cortical plate and in large neurons of the marginal zone, while there were no signals for α1 and α3 subunits.

In summary, these results suggest that CPn and CRc express glycine receptors with similar functional and pharmacological properties. The correlation of pharmacological properties and mRNA expression suggests that the glycine receptors in both cell types may consist of α2/β heteromeric receptors.

Section snippets

Slice preparation

Tangential and coronal slices were prepared as described previously (Luhmann et al., 2000, Kilb and Luhmann, 2000). Briefly, neonatal (postnatal day [P]0–P4) Wistar rats were deeply anesthetized by hypothermia and decapitated. Animal handling was performed in accordance with international guidelines for the use of animals in research (86/609/EEC) and approved by the local ethical committee (Genehmigungsbehoerde der Landesuntersuchungsanstalt Rheinland-Pfalz). All efforts were made to minimize

Membrane properties

A total of 122 CPn and 207 CRc were used for this investigation. The mean RMP of the CPn was −54.1±1.1 mV (n=122), mean Rinput was 1.3±0.06 GΩ and mean Cinput was 63.0±3.1 nF. In accordance with previous reports (Kriegstein et al., 1987, Luhmann et al., 2000) about 84% of the cells displayed action potentials with an average amplitude of 42.4±1.2 mV (n=102) upon membrane depolarization above a threshold of −40.5±0.5 mV (Fig. 1C1). The action potentials had a width at half-maximal amplitude of

Discussion

The recent study demonstrates for the first time that the functional properties and the molecular expression pattern of glycine receptors are similar between CPn and CRc, in contrast to previous suggestions based on the pharmacological properties of glycine receptors in both cell types (Flint et al., 1998, Kilb et al., 2002). In agreement with previous studies demonstrating the abundance of these subunits in all cortical layers during early corticogenesis (Malosio et al., 1991, Sato et al., 1991

Acknowledgements

This work was supported by DFG grants Lu 375/4-1 and travel grant 446-JAP-111/1/01 to H.J.L. and JSPS-DFG Cooperative Research Grant and Grant-in-Aid 14017041 from the Ministry of Education, Science, Sports, Culture and technology of Japan to A.F. The authors thank B. Hellmuth, B. Krumm and K. Sato for excellent technical assistance.

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    A. Okabe and W. Kilb contributed equally to this work.

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