Elsevier

Schizophrenia Research

Volume 113, Issues 2–3, September 2009, Pages 298-307
Schizophrenia Research

Developmental changes in the mRNA expression of neuropeptides and dopamine and glutamate receptors in neonates and adult rats after ventral hippocampal lesion

https://doi.org/10.1016/j.schres.2009.05.009Get rights and content

Abstract

Background

The neurodevelopment of hippocampus and prefrontal cortex are known to influence different functions in normal and pathological conditions including cognition and sensorimotor functions. The neonatal lesion of the ventral hippocampus (VH) in rats has been established as an animal model of schizophrenia and is used to study postpubertal changes in behavior and neurobiology. In order to investigate whether early VH lesion in rats alters the expression of genes implicated in schizophrenia pre- and post-puberty, we studied the mRNA expression of neuropeptides (substance P, dynorphin and enkephalin), dopamine D1, dopamine D2, and NMDA (subunits NR1 and NR2A) receptors in this animal model.

Methods

Rat pups were lesioned at postnatal day 7 by injecting ibotenic acid into the VH bilaterally, and then sacrificed at age 35 (pre-puberty) and 65 (post-puberty) days. Another group of adult rats had the same lesion in the VH, to independently assess the effects of the lesion on the expression of genes, and then sacrificed at week 4 and 8 post lesion. Sham groups were injected with cerebrospinal fluid using the same procedure. Brains were removed and sectioned to study the mRNA expression using in situ hybridization (ISH).

Results

The main results are the postpubertal onset of increased NR1 mRNA expression in all cortical regions and decreased dopamine D2 receptor, substance P and enkephalin mRNA expression in the striatum only in rats lesioned as neonates. These changes were not observed in the adult group with VH lesion.

Conclusions

Our results demonstrate that the postpubertal behavioral changes in this animal model (and possibly schizophrenia) are related to postpubertal onset of changes in the development of functions and interactions of the dopamine and glutamate receptors in the mesocortical system.

Introduction

Abnormal cortical neurodevelopment has been suggested to play a major role in the pathophysiology of schizophrenia. Neonatal excitotoxic lesions of the ventral hippocampus (VH) in rats result in the post-pubertal onset of abnormal dopamine (DA)-dependent behaviors such as exacerbated hyperlocomotion in a novel environment and enhanced stereotypy after apomorphine (for review see Lipska and Weinberger, 2002), enhanced sensitivity to the N-Methyl-d-Aspartate (NMDA) antagonist MK-801 (Al-Amin et al., 2000) and deficits in working memory (Lipska et al., 2002), sensorimotor gating (Grecksch et al., 1999) and social interaction (Becker et al., 1999) similar to those seen in schizophrenia. The postpubertal behavioral abnormalities are mostly secondary to alteration of the neurodevelopment of prefrontal cortex (PFC) (Wood et al., 2003) as lesions in the PFC can abolish these abnormalities (Flores et al., 2005, Lipska et al., 1998).

Preclinical, clinical, neuroimaging and post-mortem studies have supported the role of the dopamine system in the pathophysiology of schizophrenia (see recent reviews by Meisenzahl et al., 2007, Toda and Abi-Dargham, 2007). However the exact abnormalities of this system in the different brain regions involved in schizophrenia are still not very clear. Data from animal models and postmortem neurochemical studies have also implicated the NMDA receptors and the glutamate system in the neurobiology of schizophrenia (Coyle, 2006, Kristiansen et al., 2007, Morris et al., 2005, Mouri et al., 2007, Shim et al., 2008). Several clinical studies support the use of NMDA/glycine site agonists as potential new treatments for persistent negative symptoms of schizophrenia (Javitt, 2006). Furthermore, recent data have demonstrated the postpubertal emergence of disruption of the PFC dopamine–glutamate interaction in rats with neonatal ventral hippocampus lesion (Tseng et al., 2007).

The neuropeptides in the brain have also been shown to alter the function of the dopamine and glutamate systems and to play a major role in many neuropsychiatric disorders (see review by Holsboer, 2003). In patients with schizophrenia, postmortem measures showed that nigral pro-enkephalin (ENK)-derived peptide in D2 receptor-containing neurons was significantly elevated while substance P (SP) and dynorphin (DYN) which are expressed in D1 receptor-containing neurons were unchanged (Iadarola et al., 1991). Horger and Roth (1996) proposed that neuropeptides can uniquely modulate the mesoprefrontal DA neurons and contribute to their activation following exposure to mild stress. Both typical and atypical antipsychotics have been shown to activate the dynorphinergic gamma amino butyric acid (GABA) neurons in the nucleus accumbens (NAC) (Ma et al., 2003).

This study investigates the possibility that postpubertal emergence of behavioral and cognitive abnormalities seen in the neonatal VH lesion animal model might involve alteration of the neurodevelopment of dopamine, glutamate and neuropeptides functions in the striatum and cortical regions. We studied the effects of neonatal VH lesion in rats on the mRNA expression of DA D1 and D2, NMDA (subunits NR1 and NR2A) receptors I and IIA and neuropeptides (ENK, DYN and SP) at two stages of development (prepuberty and postpuberty) and compared the results to sham controls. The brain regions studied are the caudate putamen (CPu), NAC core and shell (NAC-c and NAC-s respectively), cingulum, frontal and parietal cortices (Fig. 1B). To assure that the findings are related to changes in neurodevelopment and not secondary to VH lesion per se we evaluated the effects of VH lesion in adult rats on the same parameters. To the extent that this animal model reproduces some aspects of schizophrenia, identifying molecular substrates of the disease process can provide better understanding of the pathophysiology of schizophrenia.

Section snippets

Subjects and surgery

In the experiments with neonatal VH-lesioned rats, female Sprague–Dawley rats were brought pregnant at 14 days of gestation and housed individually in breeding cages. Litters of four to six male pups were formed. Surgery was performed as previously described by Al-Amin et al. (2004) with minor modifications. Sprague–Dawley male pups (age 7 days and weight 12–16 g) were anesthetized by hypothermia (placed on wet ice for 10–20 min) and then placed on a stereotaxic instrument (Stoelting, Wood

Verification of lesion

Coronal sections (40 µm) through the hippocampus of lesioned rats were colored with cresyl violet in order to identify the extension of the lesion. As previously demonstrated (Al-Amin et al., 2004), the damage was restricted to the VH in the majority of rats. The damage as seen by cell loss, cavitations, and gliosis was evident in all the cytoarchitectural subdivisions (CA1–CA3) of the hippocampal formation. The dorsal hippocampus was spared and the lateral ventricles were enlarged (Fig. 1).

Discussion

The main findings in our experiments showed that neonates and adult rats had similar decreases in D1 mRNA expression after 8 weeks in both sham and lesion groups. D2 mRNA expression was differentially affected by this lesion where in adults it was increased in CPu at 8 weeks post lesion but in neonates it decreased significantly at age 65 days in the lesion group (Fig. 3A). In regards to NMDA receptors, the expression of NR1 mRNA tends to decrease with age in both adults and neonates. However,

Conclusions

The study demonstrates clearly that the neurodevelopmental alterations of dopamine, NMDA and neuropeptides in the neonatal VH lesion animal model of schizophrenia occur mainly at postpuberty. This similarity with the reported postpubertal onset of abnormal behaviors in the same animal model and in schizophrenia provides further opportunities to understand the neurobiology of schizophrenia.

Role of the funding source

The sponsors had no role in the study design; in the collection, analysis and interpretation of data; in the writing of the report; and in the decision to submit the paper for publication.

Contributors

Hassen Al-Amin, Mohamed Jaber, Nayef Saadé and Samir Atweh designed the study and obtained the funding. Hassen Al-Amin and Nayef Saade did the animal surgery. Rana El-Rawas, Mohamed Jaber and Nathalie Thiriet designed and finished the ISH experiments. Hassen Al-Amin finished the statistical analysis. All authors contributed to and approved the final manuscript.

Conflict of interest

The authors declare no conflict of interest.

Acknowledgements

This research was supported by grants from the Franco-Lebanese CEDRE project (2007–2008), CNRS-France (PICS: 2005–2006) and LNCSR-Lebanon. R El Rawas is a recipient of a CNRS PhD fellowship (BDI-PED, 2005–2008).

References (50)

  • LipskaB.K. et al.

    Excitotoxic lesions of the rat medial prefrontal cortex. Effects on abnormal behaviors associated with neonatal hippocampal damage

    Neuropsychopharmacology

    (1998)
  • LipskaB.K. et al.

    Neonatal damage of the ventral hippocampus impairs working memory in the rat

    Neuropsychopharmacology

    (2002)
  • MaJ. et al.

    Dynorphinergic GABA neurons are a target of both typical and atypical antipsychotic drugs in the nucleus accumbens shell, central amygdaloid nucleus and thalamic central medial nucleus

    Neuroscience

    (2003)
  • MorrisB.J. et al.

    PCP: from pharmacology to modelling schizophrenia

    Curr. Opin. Pharmacol.

    (2005)
  • MouriA. et al.

    Phencyclidine animal models of schizophrenia: approaches from abnormality of glutamatergic neurotransmission and neurodevelopment

    Neurochem. Int.

    (2007)
  • PezziS. et al.

    The vulnerability of striatal projection neurons and interneurons to excitotoxicity is differentially regulated by dopamine during development

    Int. J. Dev. Neurosci.

    (2005)
  • SchmaussC. et al.

    Dopamine and the action of opiates: a reevaluation of the dopamine hypothesis of schizophrenia. With special consideration of the role of endogenous opioids in the pathogenesis of schizophrenia

    Biol. Psychiatry

    (1985)
  • TakahashiH. et al.

    The role of extrastriatal dopamine D2 receptors in schizophrenia

    Biol. Psychiatry

    (2006)
  • TooneyP.A. et al.

    Increased tachykinin NK(1) receptor immunoreactivity in the prefrontal cortex in schizophrenia

    Biol. Psychiatry

    (2001)
  • TsengK.Y. et al.

    Post-pubertal disruption of medial prefrontal cortical dopamine–glutamate interactions in a developmental animal model of schizophrenia

    Biol. Psychiatry

    (2007)
  • WanR.Q. et al.

    Enhancement of postsynaptic sensitivity to dopaminergic agonists induced by neonatal hippocampal lesions

    Neuropsychopharmacology

    (1997)
  • WangZ.P. et al.

    Age-related changes in the contents of neuropeptides in the rat brain and pituitary

    Neurobiol. Aging

    (1993)
  • ZavitsanouK. et al.

    Selective alterations in ionotropic glutamate receptors in the anterior cingulate cortex in schizophrenia

    Neuropsychopharmacology

    (2002)
  • Al-AminH.A. et al.

    Exaggerated MK-801-induced motor hyperactivity in rats with the neonatal lesion of the ventral hippocampus

    Behav. Pharmacol.

    (2000)
  • Al AminH.A. et al.

    Effects of ventral hippocampal lesion on thermal and mechanical nociception in neonates and adult rats

    Eur. J. Neurosci.

    (2004)
  • Cited by (14)

    • Coupling of gene expression in medial prefrontal cortex and nucleus accumbens after neonatal ventral hippocampal lesions accompanies deficits in sensorimotor gating and auditory processing in rats

      2013, Neuropharmacology
      Citation Excerpt :

      Evidence exists for abnormal function in medial prefrontal cortex (mPFC) and ventral forebrain dopamine systems after NVHLs, and for abnormalities in gene expression in frontal and temporal cortex and striatum (e.g. El-Rawas et al., 2009; Flores et al., 2005; Marquis et al., 2006, 2008; Mitchell et al., 2005; Wong et al., 2005; Yabuki et al., 2013). These findings have come from both “agnostic” large microarray analyses (Wong et al., 2005) and from more focused, hypothesis-driven studies in which genes were selected based on specific biological models of schizophrenia (El-Rawas et al., 2009; Mitchell et al., 2005). Interestingly, the largest empirical survey of gene transcription profiles using over 5000 rat and 25,000 human cDNA's identified no significant effects of NVHLs on the expression of numerous genes that have been associated with schizophrenia risk via genomic analyses in humans (Wong et al., 2005), including catechol-O-methyltransferase (COMT) and neuregulin-1 (NRG1).

    • Differential role of NR2A and NR2B subunits in N-methyl-D-aspartate receptor antagonist-induced aberrant cortical gamma oscillations

      2012, Biological Psychiatry
      Citation Excerpt :

      Accumulating evidence indicates that both chronic and acute damage due to NMDA-R antagonists may depend on the same type of the receptor containing the NR2A subunit. NR2A receptors were implicated in delayed behavioral deficits in several chronic animal models, such as in rats reared in isolation (30) or subjected to neonatal treatment with phencyclidine (14) or ventral hippocampal lesion (31), and now the results of this study show their preferential involvement in acute aberrant gamma activation after NMDA-R blockade as well. It should be noted that pharmacologic manipulation of a very complex receptor is not without limitations because of the imperfect selectivity of the available compounds.

    • Intact neurobehavioral development and dramatic impairments of procedural-like memory following neonatal ventral hippocampal lesion in rats

      2012, Neuroscience
      Citation Excerpt :

      Although there are no studies to date showing a striatal dysfunction in NVHL, related or not with procedural memory deficits, there are a few studies suggesting that NVHL-induced striatal dysfunctions might rely on glutamatergic and/or cholinergic alterations. El-Rawas et al. (2009) reported increased striatal NR1 mRNA expression, considered concurrent to the hypofunction of NMDA receptors. Laplante et al. (2005) showed an increase of M1 and M2 muscarinic receptor binding in the striatum, which would compensate for sensitized striatal dopaminergic activity.

    • Cortical disinhibition in the neonatal ventral hippocampal lesion model of schizophrenia: New vistas on possible therapeutic approaches

      2012, Pharmacology and Therapeutics
      Citation Excerpt :

      When a younger cohort was included, the deficits were observed in adult, not juvenile NVHL rats (Al-Amin et al., 2001; Goto & O'Donnell, 2002). Also, a similar lesion performed in adult rats did not yield the same array of anomalies (El-Rawas et al., 2009). Therefore, this model seems to imply two distinct and critical developmental periods: an early one, when the lesion is made and likely affecting the establishment of synaptic architecture, and a late one during adolescence in which these circuits would normally mature.

    View all citing articles on Scopus
    1

    Tel.: +961 1 350000x5650; fax: +961 1 749209.

    View full text