ABSTRACT
Apolipoprotein D (ApoD) has many actions critical to maintaining mammalian CNS function. It is therefore significant that levels of ApoD have been shown to be altered in the CNS of subjects with schizophrenia, suggesting a role for ApoD in the pathophysiology of the disorder. There is also a large body of evidence that cortical and hippocampal glutamatergic, serotonergic and cholinergic systems are affected by the pathophysiology of schizophrenia. Thus, we decided to use in vitro radioligand binding and autoradiography to measure levels of ionotropic glutamate, some muscarinic and serotonin 2A receptors in the CNS of ApoD(-/-) and isogenic wild-type mice. These studies revealed a 20% decrease (mean+/-SEM: 104+/-10.2 vs. 130+/-10.4 fmol/mg ETE) in the density of kainate receptors in the CA 2-3 of the ApoD(-/-) mice. In addition there was a global decrease in AMPA receptors (F(1,214)=4.67, p<0.05) and a global increase in muscarinic M2/M4 receptors (F(1,208)=22.77, p<0.0001) in the ApoD(-/-) mice that did not reach significance in any single cytoarchitectural region. We conclude that glutamatergic pathways seem to be particularly affected in ApoD(-/-) mice and this may contribute to the changes in learning and memory, motor tasks and orientation-based tasks observed in these animals, all of which involve glutamatergic neurotransmission.
Subject(s)
Gene Expression Regulation/genetics , Hippocampus/metabolism , Receptors, Kainic Acid/metabolism , Animals , Apolipoproteins D/deficiency , Autoradiography/methods , Dizocilpine Maleate/metabolism , Dizocilpine Maleate/pharmacology , Excitatory Amino Acid Agonists/metabolism , Excitatory Amino Acid Agonists/pharmacology , Excitatory Amino Acid Antagonists/metabolism , Excitatory Amino Acid Antagonists/pharmacokinetics , Female , Gene Expression Regulation/drug effects , Hippocampus/diagnostic imaging , Hippocampus/drug effects , Ketanserin/metabolism , Ketanserin/pharmacokinetics , Mice , Mice, Inbred C57BL , Mice, Knockout , Muscarinic Antagonists/metabolism , Muscarinic Antagonists/pharmacokinetics , Pirenzepine/analogs & derivatives , Pirenzepine/metabolism , Pirenzepine/pharmacokinetics , Protein Binding/drug effects , Protein Binding/genetics , Radioligand Assay/methods , Radionuclide Imaging , Tissue Distribution/drug effects , Tritium/metabolism , alpha-Amino-3-hydroxy-5-methyl-4-isoxazolepropionic Acid/metabolism , alpha-Amino-3-hydroxy-5-methyl-4-isoxazolepropionic Acid/pharmacokineticsABSTRACT
To date, treatment of organophosphate (OP) poisoning shows several shortcomings, and OP-victims might suffer from lasting cognitive deficits and sleep-wake disturbances. In the present study, long-term effects of soman poisoning on learning ability, memory and neurogenesis were investigated in rats, treated with the anticholinergic atropine and the oxime HI-6 for reactivation of soman-inhibited acetylcholinesterase. We also investigated whether sub-chronic treatment with the reported neurogenesis enhancer olanzapine would stimulate neurogenesis and possibly normalize the anticipated long-term deleterious effects of soman intoxication. Animals were treated with HI-6 (125 mg/kg i.p.), followed after 30 min by soman (200 microg/kg s.c.) and atropine sulphate (16 mg/kg i.m.) 1 min thereafter. Soman poisoning led to an elevation of extracellular acetylcholine levels to 1500% over baseline values as assessed by striatal microdialysis. Brain acetylcholinesterase was inhibited over 95%. This was accompanied by short recurrent seizures lasting for 40 min. Osmotic minipumps releasing olanzapine (7.5 mg/kg/day) or vehicle were subcutaneously implanted 24 h post-intoxication. After drug delivery for 4 weeks, newborn cells were BrdU labeled. Learning and memory performance were assessed 8 weeks after soman poisoning, followed by analysis of surviving newborn cells (BrdU) and neurogenesis (doublecortin, DCX). Eight weeks after soman-intoxication a significantly impaired learning ability was found that was paralleled by significantly lower numbers of DCX-positive cells but no changes in the number of BrdU-labeled cells. Apparently, the present Olanzapine regime was ineffective. We conclude that soman poisoning has long lasting effects on learning ability, a finding that was accompanied by impaired neurogenesis. Although we confirm a correlation between impaired neurogenesis and cognitive deficits, establishing the true causal relationship between these processes in OP exposed animals awaits future research.
