Florey Department of Neuroscience and Mental Health - Research Publications

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An investigation into "two hit" effects of BDNF deficiency and young adult cannabinoid receptor stimulation on prepulse inhibition regulation and memory in mice

Klug, M ; van den Buuse, M (FRONTIERS RESEARCH FOUNDATION, 2013-10-21)

Reduced brain-derived neurotrophic factor (BDNF) signaling has been shown in the frontal cortex and hippocampus in schizophrenia. The aim of the present study was to investigate whether a BDNF deficit would modulate effects of chronic cannabis intake, a well-described risk factor for schizophrenia development. BDNF heterozygous mice (HET) and wild-type controls were chronically treated during weeks 6, 7, and 8 of life with the cannabinoid receptor agonist, CP55,940 (CP). After a 2-week delay, there were no CP-induced deficits in any of the groups in short-term spatial memory in a Y-maze task or novel object recognition memory. Baseline prepulse inhibition (PPI) was lower but average startle was increased in BDNF HET compared to wild-type controls. Acute CP administration before the PPI session caused a marked increase in PPI in male HET mice pre-treated with CP but not in any of the other male groups. In females, there were small increases of PPI in all groups upon acute CP administration. Acute CP administration furthermore reduced startle and this effect was greater in HET mice irrespective of chronic CP pre-treatment. Analysis of the levels of [(3)H]CP55,940 binding by autoradiography revealed a significant increase in the nucleus accumbens of male BDNF HET mice previously treated with CP but not in any of the other groups or in the caudate nucleus. These results show that BDNF deficiency and chronic young-adult cannabinoid receptor stimulation do not interact in this model on learning and memory later in life. In contrast, male "two hit" mice, but not females, were hypersensitive to the effect of acute CP on sensorimotor gating. These effects may be related to a selective increase of [(3)H]CP55,940 binding in the nucleus accumbens, reflecting up-regulation of CB1 receptor density in this region. These data could be of relevance to our understanding of differential "two hit" neurodevelopmental mechanisms in schizophrenia.
Locomotor hyperactivity in 14-3-3ζ KO mice is associated with dopamine transporter dysfunction

Ramshaw, H ; Xu, X ; Jaehne, EJ ; McCarthy, P ; Greenberg, Z ; Saleh, E ; McClure, B ; Woodcock, J ; Kabbara, S ; Wiszniak, S ; Wang, T-Y ; Parish, C ; van den Buuse, M ; Baune, BT ; Lopez, A ; Schwarz, Q (NATURE PUBLISHING GROUP, 2013-12)

Dopamine (DA) neurotransmission requires a complex series of enzymatic reactions that are tightly linked to catecholamine exocytosis and receptor interactions on pre- and postsynaptic neurons. Regulation of dopaminergic signalling is primarily achieved through reuptake of extracellular DA by the DA transporter (DAT) on presynaptic neurons. Aberrant regulation of DA signalling, and in particular hyperactivation, has been proposed as a key insult in the presentation of schizophrenia and related neuropsychiatric disorders. We recently identified 14-3-3ζ as an essential component of neurodevelopment and a central risk factor in the schizophrenia protein interaction network. Our analysis of 14-3-3ζ-deficient mice now shows that baseline hyperactivity of knockout (KO) mice is rescued by the antipsychotic drug clozapine. 14-3-3ζ KO mice displayed enhanced locomotor hyperactivity induced by the DA releaser amphetamine. Consistent with 14-3-3ζ having a role in DA signalling, we found increased levels of DA in the striatum of 14-3-3ζ KO mice. Although 14-3-3ζ is proposed to modulate activity of the rate-limiting DA biosynthesis enzyme, tyrosine hydroxylase (TH), we were unable to identify any differences in total TH levels, TH localization or TH activation in 14-3-3ζ KO mice. Rather, our analysis identified significantly reduced levels of DAT in the absence of notable differences in RNA or protein levels of DA receptors D1-D5. Providing insight into the mechanisms by which 14-3-3ζ controls DAT stability, we found a physical association between 14-3-3ζ and DAT by co-immunoprecipitation. Taken together, our results identify a novel role for 14-3-3ζ in DA neurotransmission and provide support to the hyperdopaminergic basis of pathologies associated with schizophrenia and related disorders.
SEX DIFFERENCES AND THE ROLE OF ESTROGEN IN ANIMAL MODELS OF SCHIZOPHRENIA: INTERACTION WITH BDNF

Wu, YC ; Hill, RA ; Gogos, A ; Van Den Buuse, M (PERGAMON-ELSEVIER SCIENCE LTD, 2013-06-03)

Schizophrenia is a severe psychiatric disorder with a complex and variable set of symptoms. Both genetic and environmental mechanisms are involved in the development of the illness and lead to structural and neurochemical abnormalities in the brain. An intriguing facet of schizophrenia is sex differences, which have been described for nearly all features of the illness, including the peak age of onset, symptoms and treatment response. The ovarian hormone, estrogen, may be protective against schizophrenia and evidence is accumulating that estrogen may exert this effect via an interaction with brain-derived neurotrophic factor (BDNF). Both estrogen and BDNF have trophic effects on the developing brain and promote synaptic plasticity and maintain neurons well into adulthood. Major neurotransmitter systems including dopaminergic, serotonergic and glutamatergic pathways are modulated and supported by estrogen and BDNF. Despite their commonalities, estrogen and BDNF have mostly been examined independently but increasing evidence suggests an interaction between the two in brain regions pertinent to schizophrenia. This review will focus on the role of estrogen and BDNF in clinical and animal studies of schizophrenia. We include animal models of neurotransmitter dysfunction and genetic manipulation to show how estrogen may provide a protective effect in schizophrenia, including through mediating BDNF expression and activity. This posited estrogen-BDNF interaction could play a key role in modulating sex-dependent results reported in animal work as well as sex differences in clinical aspects of schizophrenia.
Schizophrenia-like disruptions of sensory gating by serotonin receptor stimulation in rats: Effect of MDMA, DOI and 8-OH-DPAT

Thwaites, SJ ; Gogos, A ; Van den Buuse, M (PERGAMON-ELSEVIER SCIENCE LTD, 2013-11-01)

Schizophrenia pathophysiology is associated with alterations in several neurotransmitter systems, particularly dopamine, glutamate and serotonin (5-HT). Schizophrenia patients also have disruptions in sensory gating, a brain information filtering mechanism in response to repeated sensory stimuli. Dopamine and glutamate have been implicated in sensory gating; however, little is known about the contribution of serotonin. We therefore investigated the effects of several psychoactive compounds that alter serotonergic neuronal activity on event-related potentials (ERP) to paired auditory pulses. Male Sprague-Dawley rats were implanted with cortical surface electrodes to measure ERPs to 150 presentations of two 85 dB bursts of white noise, 500 ms apart (S1 and S2). Saline-treated animals suppressed the response to S2 to less than 50% of S1. In contrast, treatment with the serotonin releaser, MDMA (ecstasy; 2.0mg/kg), the 5-HT2A/2C receptor agonist, DOI (0.5mg/kg), or the 5-HT1A/7 receptor agonist, 8-OH-DPAT (0.5mg/kg), caused an increase in S2/S1 ratios. Analysis of waveform components suggested that the S2/S1 ratio disruption by MDMA was due to subtle effects on the ERPs to S1 and S2; DOI caused the disruption primarily by reducing the ERP to S1; 8-OH-DPAT-induced disruptions were due to an increase in the ERP to S2. These results show that 5-HT receptor stimulation alters S2/S1 ERP ratios in rats. These results may help to elucidate the sensory gating deficits observed in schizophrenia patients.
Modafinil disrupts prepulse inhibition in mice: Strain differences and involvement of dopaminergic and serotonergic activation

Kwek, P ; van den Buuse, M (ELSEVIER SCIENCE BV, 2013-01-15)

Modafinil is a wakefulness-promoting agent with possible beneficial effects for the management of addiction and in psychiatric conditions, but also with abuse potential of its own. The mechanism of action of modafinil remains unclear. We studied pharmacological mechanisms in the effect of modafinil on prepulse inhibition (PPI), a model of sensorimotor gating. Mice were tested in automated startle boxes after administration of modafinil and antagonist drugs. Oral administration of 100mg/kg of modafinil, but not lower doses, caused a significant reduction of PPI in C57Bl/6 mice, but not Balb/c mice. This effect of modafinil could be blocked by co-treatment with the dopamine D(2) receptor antagonist, haloperidol, and the serotonin (5-HT) 2A receptor antagonist, ketanserin, but not the 5-HT(1A) receptor antagonist, WAY100,635. At 30mg/kg, which did not influence PPI, modafinil inhibited PPI disruption caused by the dopamine transporter inhibitor, GBR12909. There was no interaction between modafinil and the serotonin transporter inhibitor, fluoxetine. There were no consistent effects of modafinil on startle amplitude. These results show that oral modafinil treatment may cause disruption of PPI in mice. This effect was strain-dependent, involving dopamine D(2) and 5-HT(2A) receptor activation, and was likely mediated by an interaction with the dopamine transporter. These results extend our insight into the behavioral effects of modafinil and could be of importance for the clinical use of this agent as they may indicate an increased risk of side-effects in conditions where PPI is already reduced, such as in schizophrenia and bipolar disorder.
Sex-dependent alterations in BDNF-TrkB signaling in the hippocampus of reelin heterozygous mice: a role for sex steroid hormones

Hill, RA ; Wu, Y-WC ; Gogos, A ; van den Buuse, M (WILEY, 2013-08)

Neurodevelopmental psychiatric disorders such as schizophrenia may be caused by a combination of gene × environment, gene × gene, and/or gene × sex interactions. Reduced expression of both Reelin and Brain-Derived Neurotrophic factor (BDNF) has been associated with schizophrenia in human post-mortem studies. However, it remains unclear how Reelin and BDNF interact (gene × gene) and whether this is sex-specific (gene × sex). This study investigated BDNF-TrkB signaling in the hippocampus of male and female Reelin heterozygous (Rln(+/-) ) mice. We found significantly increased levels of BDNF in the ventral hippocampus (VHP) of female, but not male Rln(+/-) compared to wild-type (WT) controls. While levels of TrkB were not significantly altered, phosphorylated TrkB (pTrkB) levels were significantly lower, again only in female Rln(+/-) compared to WT. This translated to downstream effects with a significant decrease in phosphorylated ERK1 (pERK1). No changes in BDNF, TrkB, pTrkB or pERK1/2 were observed in the dorsal hippocampus of Rln(+/-) mice. Ovariectomy (OVX) had no effect in WT controls, but caused a significant decrease in BDNF expression in the VHP of Rln(+/-) mice to the levels of intact WT controls. The high expression of BDNF was restored in OVX Rln(+/-) mice by 17β-estradiol treatment, suggesting that Rln(+/-) mice respond differently to an altered estradiol state than WT controls. In addition, while OVX had no significant effect on TrkB or ERK expression/phosphorylation, OVX + estradiol treatment markedly increased TrkB and ERK1 phosphorylation in Rln(+/-) and, to a lesser extent in WT controls, compared to intact genotype-matched controls. These data may provide a better understanding of the interaction of Reelin and BDNF in the hippocampus, which may be involved in schizophrenia.
BDNF deficiency and young-adult methamphetamine induce sex-specific effects on prepulse inhibition regulation

Manning, EE ; van den Buuse, M (FRONTIERS RESEARCH FOUNDATION, 2013-06-12)

Brain-derived neurotrophic factor (BDNF) has been implicated in the pathophysiology of schizophrenia, yet its role in the development of specific symptoms is unclear. Methamphetamine (METH) users have an increased risk of psychosis and schizophrenia, and METH-treated animals have been used extensively as a model to study the positive symptoms of schizophrenia. We investigated whether METH treatment in BDNF heterozygous (HET) mutant mice has cumulative effects on sensorimotor gating, including the disruptive effects of psychotropic drugs. BDNF HETs and wildtype (WT) littermates were treated during young adulthood with METH and, following a 2-week break, prepulse inhibition (PPI) was examined. At baseline, BDNF HETs showed reduced PPI compared to WT mice irrespective of METH pre-treatment. An acute challenge with amphetamine (AMPH) disrupted PPI but male BDNF HETs were more sensitive to this effect, irrespective of METH pre-treatment. In contrast, female mice treated with METH were less sensitive to the disruptive effects of AMPH, and there were no effects of BDNF genotype. Similar changes were not observed in the response to an acute apomorphine (APO) or MK-801 challenge. These results show that genetically-induced reduction of BDNF caused changes in a behavioral endophenotype relevant to the positive symptoms of schizophrenia. However, major sex differences were observed in the effects of a psychotropic drug challenge on this behavior. These findings suggest sex differences in the effects of BDNF depletion and METH treatment on the monoamine signaling pathways that regulate PPI. Given that these same pathways are thought to contribute to the expression of positive symptoms in schizophrenia, this work suggests that there may be significant sex differences in the pathophysiology underlying these symptoms. Elucidating these sex differences may be important for our understanding of the neurobiology of schizophrenia and developing better treatments strategies for the disorder.