Elsevier

Neuroscience

Volume 120, Issue 4, 15 September 2003, Pages 923-939
Neuroscience

Postnatal development and migration of cholecystokinin-immunoreactive interneurons in rat hippocampus

https://doi.org/10.1016/S0306-4522(03)00409-3Get rights and content

Abstract

The development of cholecystokinin-immunoreactive (CCK-IR) interneurons in the rat hippocampus was studied using immunocytochemical methods at the light and electron microscopic levels from early (P0–P8) to later postnatal (P12–P20) periods. The laminar distribution of CCK-IR cell bodies changed considerably during the studied period, which is suggested to be due to migration. CCK-IR cells appear to move from the molecular layer of the dentate gyrus to their final destination at the stratum granulosum/hilus border, and tend to concentrate in the distal third of stratum radiatum in CA1-3. The density of CCK-IR cells is rapidly decreasing during the first 4 postnatal days without any apparent reduction in their total number, therefore it is due to the pronounced growth of hippocampal volume in this period.

Axons of CCK-IR interneurons formed symmetrical synapses already at P0, and by far the predominant targets were dendrites of presumed principal cells in all subfields of the hippocampus. These axon arbors began to concentrate around pyramidal cell bodies only at P8, at earlier ages CCK-IR axons crossed stratum pyramidale at right angles, and gave rise to varicose collaterals only outside this layer. The dendrites and somata of CCK-IR cells received synapses already at P0, but those were mostly symmetrical, apart from a few immature asymmetrical synapses. At P4, mature asymmetrical synapses with considerable amounts of synaptic vesicles were already commonly encountered. Thus, the innervation of CCK-IR interneurons apparently develops later than their output synapses, suggesting that they may be able to release transmitter before receiving any considerable excitatory drive.

We conclude that CCK-IR cells represent one, if not the major, interneuron type that assists in the maturation of glutamatergic synapses (activation of N-methyl-d-aspartate receptors) via GABAergic depolarization of principal cell dendrites, and may contribute to the generation of giant depolarizing potentials. CCK-IR cells will change their function to perisomatic hyperpolarizing inhibition, as glutamatergic transmission in the network becomes operational.

Section snippets

Immunocytochemistry

The studies were conducted in accordance with the principles and procedures outlined in the NIH Guide for the Care and Use of Laboratory Animals. All efforts were made to minimize both the suffering and the number of animals used.

Newborn (P0, n=4), 2 (P2, n=4), 4 (P4, n=3), 8 (P8, n=3), 12 (P12, n=3) and 20 (P20, n=3) day old male Wistar rats were used for the present study. Perfusion and immunostaining was performed according to the protocols described in detail earlier (Katona et al., 1999).

Results

At all ages investigated in the present study, CCK-IR cell bodies and fibers were readily seen in the strata oriens, pyramidale, radiatum, granulosum, moleculare and the hilus. In the stratum lacunosum-moleculare labeled cells were only rarely seen (Fig. 1, Fig. 2). The density of labeled cells in the hippocampus as well as their selective frequency in the different layers changed considerably during the period of postnatal development. CCK-IR processes were heavily stained and could be

Changes in the laminar distribution of CCK-IR cell bodies

The rapid decrease in the density of CCK-IR cells between P0 and P4 can be explained in several possible ways. According to published data, cells may stop synthesizing certain proteins or peptides during development, as happens with some calretinin-immunoreactive and calbindin D28k-immunoreactive cells in rat cerebral cortex. However, disappearance of these proteins from the cells in both cases takes several weeks Fonseca et al., 1995, Alcantara et al., 1996. The disappearance of neuropeptide

Acknowledgements

This work was supported by the Howard Hughes Medical Institute, the National Institutes of Health (NIH, NS 30549), and OTKA Hungary (T032251) to T.F.F. The visit of Dr. Morozov to Budapest was supported by IBRO. Monoclonal antibody 9303 raised against CCK was kindly provided by CURE/Gastroenteric Biology Center, Antibody/RIA Core, NIH grant DK 41301. The authors are grateful for the excellent technical assistance of Dr. Gábor Nyíri, Ms Katalin Lengyel and Mr. Gy Goda. Dr. Yezekiel Ben-Ari is

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