Qi Pei

Changes in mRNA abundance of microtubule-associated proteins in the rat brain following electroconvulsive shock.

MICROTUBULE-ASSOCIATED proteins (MAPs) are involved in the maintenance of mature neuronal morphology, neurite outgrowth and neuronal plasticity. Alteration in MAP expression may underlie neuronal structural changes in response to seizure activity. The aim of the present study was to investigate whether electroconvulsive shock (ECS), an animal model of electroconvulsive therapy (ECT) in clinical treatment of depression, affected gene expression of MAPs in the rat brain. Using in situ hybridization, we studied the expression of encoding mRNA for MAPs in the brains of rats treated with ECS 5 times over 10 days. The abundance of mRNA encoding microtubule-associated protein 2 (MAP2), a dendritic MAP, was significantly increased (142% compared with controls) in the dentate gyrus 6 and 24 h after the last shock, and had returned to baseline levels within 48 h. These changes were confined to the dentate gyrus no significant changes were observed in CA1 and CA3 of the hippocampus. The increase in MAP2 expression was accompanied by an increase in MAP2 immunoreactivity in the molecular layer of the dentate gyrus. The abundance of mRNA encoding for tau, an axon-specific MAP, and MAP1B, an embryonic MAP, was unaffected by ECS. These data demonstrate that ECS specifically altered the mRNA and protein expression of MAP2 but had no effect on tau or MAP1B, and suggest that changes in MAP2 expression may be related to morphological changes in the dentate gyrus, particularly in the dendrites.

Use of Arc expression as a molecular marker of increased postsynaptic 5-HT function after SSRI/5-HT1A receptor antagonist co-administration.

An increase in central postsynaptic 5‐hydroxytryptamine (5‐HT) function activates expression of activity‐related cytoskeletal protein (Arc). Here, Arc expression was used to test whether, in rats, co‐administration of a 5‐HT re‐uptake inhibitor (paroxetine) and a 5‐HT1A receptor antagonist (WAY 100635) increases postsynaptic 5‐HT function. After pre‐treatment with WAY 100635 (0.3u2003mg/kg s.c.), paroxetine (5u2003mg/kg s.c.) caused a threefold increase in 5‐HT in prefrontal cortex microdialysates. In situ hybridization studies found that neither paroxetine (5u2003mg/kg s.c.) nor WAY 1000635 (0.3u2003mg/kg s.c.) altered Arc mRNA abundance in any region examined. In contrast, paroxetine (5u2003mg/kg s.c.) increased Arc mRNA after pre‐treatment with WAY 100635 (0.3u2003mg/kg s.c.). This increase was apparent in cortical regions (frontal, parietal and cingulate) and caudate nucleus but was absent in hippocampus (CA1). Increases in Arc mRNA were accompanied by an increase in c‐fos mRNA. The increase in Arc expression induced by paroxetine/WAY 100635 was abolished by the 5‐HT synthesis inhibitor, p‐chlorophenylalanine (300u2003mg/kg i.p., daily for two days). In conclusion, paroxetine and WAY 100635 injected in combination (but not alone) caused a region‐specific, 5‐HT‐mediated increase in Arc expression. These data provide molecular evidence that co‐administration of a 5‐HT re‐uptake inhibitor and 5‐HT1A receptor antagonist increases 5‐HT function at the postsynaptic level.

5-HT efflux from rat hippocampus in vivo produced by 4-aminopyridine is increased by chronic lithium administration

Effects of lithium on central 5-HT function have been shown using electrophysiological, behavioural and neurochemical approaches. Chronic lithium administration, for example, enhances both electrophysiological and behavioural responses mediated by postsynaptic 5-HT1A receptors as well as increasing potassium-evoked and electrically evoked release of 5-HT from the hippocampus in in vitro slices and in vivo. Our studies have shown that potassium-channel blocking drugs increase 5-HT release in vivo, and others have shown that lithium suppresses potassium currents in some cell types. We therefore investigated in the rat the effect of short-term (3 days) and long-term (21 days) lithium on 5-HT release evoked by potassium-channel blockade, using in vivo microdialysis. Long-term lithium treatment enhanced 5-HT efflux in rat hippocampus produced by 4-aminopyridine (4-AP) perfused in microdialysis fluid by as much as 100% within 40 min, compared with non-lithium-treated control rats. Short-term lithium treatment did not enhance 4-AP-induced 5-HT efflux. The effect of local tetraethylammonium chloride (TEA) on hippocampal 5-HT release was unaltered by long-term lithium treatment. In addition, neither the effect of local perfusion with 4-AP on efflux of striatal 5-HT, or dopamine in nucleus accumbens, was altered by chronic lithium treatment. These results show that long-term lithium treatment enhances 4-AP-stimulated efflux of 5-HT in the hippocampus, but not in the striatum, nor dopamine output in the nucleus accumbens.(ABSTRACT TRUNCATED AT 250 WORDS)

Effect of 5-HT depletion by MDMA on hyperthermia and Arc mRNA induction in rat brain

Rationale3,4-Methylenedioxymethamphetamine (MDMA) administration to rats produces an acute hyperthermic response and induces localised neuronal activation, which can be visualised via expression of immediate-early genes. The pharmacological and anatomical basis of these effects are unclear. At high doses, MDMA also causes selective neurotoxicity at serotonergic nerve terminals.ObjectiveWe investigated the effect of 5-hydroxytryptamine (5-HT) depletion on the acute hyperthermic response to MDMA and the pattern of neuronal excitation indicated by Arc (activity-regulated cytoskeleton associated gene) in naive rats and following administration of MDMA at a neurotoxic dose.MethodsExpression of Arc mRNA was investigated by in situ hybridisation histochemistry using 35S-labelled oligonucleotide probe.ResultsMDMA induced a significant hyperthermia together with increased Arc mRNA expression in cortical regions, caudate-putamen and CA1 hippocampus but not hypothalamus. At 21xa0days after a neurotoxic dose of MDMA, brain 5-HT and 5-HIAA levels were significantly reduced by 21–32%. In these animals, both the hyperthermic response and the pattern and extent of Arc mRNA expression induced by a subsequent dose of MDMA were unaltered. However, basal Arc expression was significantly increased in cortical regions and CA1 hippocampus.ConclusionWe conclude that the acute hyperthermic response induced by MDMA is not attenuated by moderate depletion of 5-HT, further questioning mediation via a serotonergic mechanism. Arc mRNA induction by MDMA exhibits highly localised expression, which is not altered following 5-HT depletion. However, following a neurotoxic dose of MDMA, basal expression of Arc is increased, particularly in cortex and CA1, suggesting that mechanisms underlying synaptic plasticity might also be modified.

Evidence for the differential co-localization of neurokinin-1 receptors with 5-HT receptor subtypes in rat forebrain

Studies suggest that like selective 5-hydroxytryptamine (5-HT; serotonin) reuptake inhibitors, antagonists at neurokinin-1 receptors (NK1Rs) may have antidepressant and anxiolytic properties. NK1Rs are present in 5-HT innervated forebrain regions which may provide a common point of interaction between these two transmitter systems. This study aimed to investigate for cellular co-localization between NK1Rs and 5-HT receptor subtypes in mood-related brain regions in the rat forebrain. With experiments using fluorescence immunocytochemistry, double-labelling methods demonstrated a high degree of co-localization between NK1Rs and 5-HT1A receptors in most regions examined. Co-localization was highest in the medial septum (88% NK1R expressing cells were 5-HT1A receptor-positive) and hippocampal regions (e.g. dentate gyrus, 65%), followed by the lateral/basolateral amygdala (35%) and medial prefrontal cortex (31%). In contrast, co-localization between NK1Rs and 5-HT2A receptors was infrequent (< 8%) in most areas examined except for the hippocampus (e.g. CA3, 43%). Overall co-localization between NK1Rs and 5-HT1A receptors was much greater than that between NK1Rs and 5-HT2A receptors. Thus, these experiments demonstrate a high degree of co-localization between NK1Rs and 5-HT1A receptors in cortical and limbic regions of the rat forebrain. These findings suggest a novel site of interaction between NK1R antagonists and the 5-HT system.