Elsevier

Brain Research

Volume 927, Issue 2, 15 February 2002, Pages 111-121
Brain Research

Research report
PSA-NCAM expression in the piriform cortex of the adult rat. Modulation by NMDA receptor antagonist administration

https://doi.org/10.1016/S0006-8993(01)03241-3Get rights and content

Abstract

Administration of NMDA receptor antagonists upregulates the expression of the polysialylated form of the neural cell adhesion molecule (PSA-NCAM) in the adult hippocampus. Since the piriform cortex is also populated by PSA-NCAM immunoreactive neurons during adulthood, we sought to characterize them in detail and to test whether NMDA receptor antagonists also modulate PSA-NCAM in this cortical region. PSA-NCAM immunoreactivity is located mainly in layer II, where many neurogliaform and some pyramidal–semilunar transitional neurons are labeled. Many large neurons in layer III and endopiriform nucleus also express PSA-NCAM. Interestingly, some small labeled cells resembling migratory neuroblasts appear in these layers and in the ventral end of the corpus callosum subjacent to the piriform cortex. These putative migratory cells and some neurogliaform neurons in layer II do not express NeuN, a marker of differentiated neurons. Many of these PSA-NCAM immunoreactive cells also express doublecortin, a molecule involved in neuronal migration. The number of PSA-NCAM immunoreactive neurogliaform neurons increases significantly 7 days after the administration of an NMDA receptor antagonist. Moreover, 21 days after the treatment we observe a significant increase in the number of doublecortin expressing cells in the deep layers of the piriform cortex. These results expand the current knowledge of the neuronal populations expressing PSA-NCAM in the piriform cortex, suggesting that some of these cells could be involved in structural plastic events such as axonal outgrowth, synaptogenesis or even neuronal migration. Similar to the hippocampus, NMDA receptors appear to play a critical role in these processes in the adult piriform cortex.

Introduction

The neural cell adhesion molecule (NCAM) is a membrane bound glycoprotein that mediates cell to cell and cell to extracellular matrix interactions [12], [42]. This protein is capable of incorporating long chains of α2,8 polysialic acid (PSA) [14]. The presence of this carbohydrate confers anti-adhesive properties to NCAM [41] and consequently it has been implicated in several developmental events such as neuronal migration [35], synaptogenesis [27], [47] or axonal outgrowth and fasciculation [13], [52]. Consequently, PSA-NCAM is expressed in some regions of the adult brain that retain the capability to undergo structural changes, such as the hypothalamus [1], the hippocampus [43] or the piriform cortex [44].

It has been shown that there is a significant increase in the number of PSA-NCAM expressing neurons in the adult rat medial temporal cortex, which contains the piriform cortex, after spatial learning [16], [33] and a similar effect has been found in the dentate gyrus [15]. Furthermore, we have recently shown that the number of PSA-NCAM immunoreactive granule neurons in the hippocampus is significantly increased 7 days after the administration of an NMDA receptor antagonist [31]. NMDA antagonist treatment also increases neurogenesis in the adult dentate gyrus [10], which may contribute to the increase in PSA-NCAM expression, since newly generated granule neurons express PSA-NCAM [45]. Nevertheless, part of the increase in the number of PSA-NCAM immunoreactive neurons is also likely to be due to an upregulation of the expression of this molecule in preexisting neurons.

NMDA receptors play a key role in several events in the central nervous system, such as neuronal birth and migration [23]. Antagonists to these glutamate receptors have been also shown to interfere with targeting and pruning of axons and regulation of synaptogenesis during development [9], [11], [48]. NMDA receptor antagonists also induce axonal sprouting during adulthood [25], [49] and appear to be critical for some processes related to learning such as LTP [3].

The main objectives of this study were to perform a detailed anatomical characterization of PSA-NCAM expression in the piriform cortex, and determine whether NMDA receptor antagonist treatment can influence its expression in this region. The piriform cortex is an area characterized by the presence of axonal outgrowth and synaptic reorganization in response to physiological or experimental manipulations [18]. Consequently, several molecules related to neural plasticity such as GAP-43 [4], MAP1-B [32], rCRMP-4/Tuc4 [30] or PSA-NCAM [44] have been found in the piriform cortex of the adult rat. PSA-NCAM immunoreactivity appears highly down-regulated after development, although it is still expressed in certain neuronal populations of layers II and III of the adult piriform cortex. Previous reports have described PSA-NCAM immunoreactivity in small- and medium-sized neurons. Some of these immunoreactive cells in layer II resembled semilunar or fusiform neurons [44]. In a recent study we have found that PSA-NCAM is expressed in the piriform cortex by many other populations than those described previously, such as neurogliaform neurons [30], thus one of the objectives of this study is to characterize in detail the cellular populations expressing the polysialylated form of NCAM in the adult piriform cortex.

Our results demonstrate that, apart from semilunar and fusiform neurons, some other cell types in the piriform cortex express PSA-NCAM, such as neurogliaform cells in layer II and big interneuron-like cells in layer III. Moreover, we have found PSA-NCAM-expressing cells resembling migratory neuroblasts in layer III and endopiriform nucleus. These cells do not show immunoreactivity for NeuN, a marker of differentiated neurons and they co-express doublecortin (DCX), a protein involved in neuronal migration and differentiation. Administration of an NMDA receptor antagonist induces a significant increase in the number of cells expressing PSA-NCAM in the piriform cortex layer II 7 days after the treatment and also increases the number of DCX-expressing cells in the deep layers of the piriform cortex in animals surviving for 21 days.

Section snippets

Animals and treatments

Twenty-five young adult male Sprague–Dawley rats (200–250 g; Charles River Laboratory) were used in this study. All animal experimentation was conducted in accordance with the National Institutes of Health (NIH) Guide for the Care and use of Laboratory Animals (NIH Publication 85-23, revised 1985) and was approved by the Committee on Animal research of the Rockefeller University. The rats were injected with the competitive NMDA receptor antagonist CGP43487 (5 mg/kg i.p.) in saline. The animals

Results

The piriform or olfactory cortex is a three-layered paleocortical region in which fiber systems and neuronal cell types are highly segregated within layers. Afferent fibers coming from the lateral olfactory tract and other cortical regions make synapses in layer I, an area almost devoid of neuronal somata [38], [51]. Layer II is formed by densely packed neurons with semilunar, pyramidal and fusiform morphology. Many small neurons (neurogliaform cells) with irregular axonal trajectories also

Discussion

Our study describes in detail the neuronal populations expressing PSA-NCAM in the piriform cortex of the adult rat. The presence of this molecule in many neurons of layer II and its co-existence with molecules implicated in axonal outgrowth suggests that these neurons are undergoing structural plasticity during adulthood. Administration of an NMDA receptor antagonist significantly increases the number of PSA-NCAM immunoreactive cells in the piriform cortex layer II, suggesting that PSA-NCAM

Acknowledgements

This study was supported by a P50 MH58911-01A1 grant to BMc and a PM97-0104 Spanish DGESIC grant. Juan Nacher was recipient of a postdoctoral fellowship from the Valencian Conselleria de Cultura Educacio i Ciencia and a short term fellowship from the Human Frontier Science Program. The authors wish to thank Drs. G. Rougon and C. Walsh for the generous gift of anti PSA and anti DCX antibodies, respectively.

References (52)

  • T. Seki et al.

    Distribution and possible roles of the highly polysialylated neural cell adhesion molecule (NCAM-H) in the developing and adult central nervous system

    Neurosci. Res.

    (1993)
  • C.J. Shatz

    TI-Impulse activity and the patterning of connections during CNS development

    Neuron

    (1990)
  • M.J. West

    New stereological methods for counting neurons

    Neurobiol. Aging

    (1993)
  • G. Alonso et al.

    PSA-NCAM and B-50/GAP-43 are coexpressed by specific neuronal systems of the adult rat mediobasal hypothalamus that exhibit remarkable capacities for morphological plasticity

    J. Comp. Neurol.

    (1997)
  • J. Altman

    Autoradiographic and histological studies of postnatal neurogenesis. IV. Cell proliferation and migration in the anterior forebrain, with special reference to persisting neurogenesis in the olfactory bulb

    J. Comp. Neurol.

    (1969)
  • C.H. Bailey et al.

    Toward a molecular definition of long-term memory storage

    Proc. Natl. Acad. Sci. USA

    (1996)
  • L.I. Benowitz et al.

    Anatomical distribution of the growth-associated protein GAP-43/B-50 in the adult rat brain

    J. Neurosci.

    (1988)
  • P.J. Bernier et al.

    Bcl-2 protein as a marker of neuronal immaturity in postnatal primate brain

    J. Neurosci.

    (1998)
  • A.K. Butler et al.

    A role for N-methyl-d-aspartate receptors in the regulation of synaptogenesis and expression of the polysialylated form of the neural cell adhesion molecule in the developing striatum

    Dev. Neurosci.

    (1998)
  • H.A. Cameron et al.

    Regulation of adult neurogenesis by excitatory input and NMDA receptor activation in the dentate gyrus

    J. Neurosci.

    (1995)
  • H.T. Cline et al.

    TI-NMDA receptor agonist and antagonists alter retinal ganglion cell arbor structure in the developing frog retinotectal projection

    J. Neurosci.

    (1990)
  • B.A. Cunningham et al.

    Neural cell adhesion molecule: structure, immunoglobulin-like domains, cell surface modulation, and alternative RNA splicing

    Science

    (1987)
  • P. Doherty et al.

    A threshold effect of the major isoforms of NCAM on neurite outgrowth

    Nature

    (1990)
  • G.B. Fox et al.

    Memory consolidation induces a transient and time-dependent increase in the frequency of neural cell adhesion molecule polysialylated cells in the adult rat hippocampus

    J. Neurochem.

    (1995)
  • G.B. Fox et al.

    Consolidation of passive avoidance learning is associated with transient increases of polysialylated neurons in layer II of the rat medial temporal cortex

    J. Neurobiol.

    (2000)
  • B. Friedman et al.

    Plasticity in the olfactory cortex: age-dependent effects of deafferentation

    J. Comp. Neurol.

    (1986)
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