Elizabeth Scarr

Studies on [3H]CP-55940 binding in the human central nervous system: regional specific changes in density of cannabinoid-1 receptors associated with schizophrenia and cannabis use.

A number of studies suggested that cannabis use can cause or exacerbate psychoses and may increase the risk of developing schizophrenia. These findings suggest that changes in the cannabinoid system of the brain may be involved in the pathology of schizophrenia. To determine whether changes in the cannabinoid system were present in the brains of subjects with schizophrenia, we used in situ radioligand binding and autoradiography to measure the binding of [3H]CP-55940 to the cannabinoid-1 receptor in the dorsolateral prefrontal cortex (Brodmanns area 9), caudate-putamen and areas of the temporal lobe from schizophrenic and control subjects, some of whom had ingested cannabis close to death. There was an increase in the density of [3H]CP-55940 binding to cannabinoid-1 receptors in the dorsolateral prefrontal cortex from subjects with schizophrenia (mean+/-S.E.M.: 142+/-9.9 vs 119+/-6.6fmol/mg estimated tissue equivalents; P<0.05) that was independent of recent cannabis ingestion. There was an increase in the density of cannabinoid-1 receptors in the caudate-putamen from subjects who had recently ingested cannabis (151+/-9.0 vs 123+/-7.2fmol/mg estimated tissue equivalents; P<0.05) that was independent of diagnoses. These data indicate that there are changes in cannabinoid-1 receptors in the dorsolateral prefrontal cortex that may prove to be associated with the pathology of schizophrenia. By contrast, changes in the density of cannabinoid-1 receptors may occur in the caudate-putamen in response to cannabis ingestion.

Decreased muscarinic1 receptors in the dorsolateral prefrontal cortex of subjects with schizophrenia.

To test the hypothesis that muscarinic receptors are involved in the pathology of schizophrenia, we measured muscarinic1 (M1R) and muscarinic4(M4R) protein and mRNA as well as [3H]pirenzepine binding in Brodmanns areas (BA) 9 and 40 obtained postmortem from 20 schizophrenic and 20 age/sex-matched control subjects. There was a significant decrease in [3H]pirenzepine binding to BA 9 (mean ± SEM: 151 ± 15 vs 195 ± 10 fmol mg−1 ETE; P< 0.02), but not BA 40 (143 ± 13 vs 166 ± 11 fmol mg−1 ETE), from subjects with schizophrenia. The level of M1R protein (0.11 ± 0.007 vs 0.15 ± 0.008 OD; P < 0.01), but not M4R protein, was decreased in BA9 from schizophrenic subjects with neither receptor protein being altered in BA 40. The level of M1R mRNA was decreased in BA 9 (30 ± 7.0 vs 79 ± 14 dpm × 103 mg−1ETE, P < 0.01) and BA 40 (28 ± 5.9 vs 99 ± 14, P < 0.01) with schizophrenia but M4R mRNA was only decreased in BA 40 (48 ± 6.6 vs 89 ± 9.9, P < 0.005). These data suggest that the M1R, at least in the dorsolateral prefrontal cortex, may have a role in the pathology of schizophrenia.

Changes in Serotonin2A and GABAA receptors in schizophrenia : Studies on the human dorsolateral prefrontal cortex

Abstract: Having shown a decrease in serotonin2A receptors in the dorsolateral prefrontal cortex (DLPFC) from schizophrenic subjects, we have now determined if this change was reflective of widespread changes in neurochemical markers in DLPFC in schizophrenia. In Brodmann’s area (BA) 9 from 19 schizophrenic and 19 control subjects, we confirmed a decrease in the density of [3H]ketanserin binding to serotonin2A receptors in tissue from the schizophrenic subjects [39 ± 3.3 vs. 60 ± 3.6 fmol/mg estimated tissue equivalents (ETE); p < 0.005]. In addition, the density of [3H]muscimol binding to GABAA receptors was increased in the schizophrenic subjects (526 ± 19 vs. 444 ± 28 fmol/mg ETE; p < 0.02). [3H]YM‐09151‐2, N‐[1‐(2‐thienyl)cyclohexyl]‐3,4‐[3H]piperidine, [3H]SCH 23390, [3H]mazindol, and NG‐nitro‐L‐[3H]arginine binding to BA 9 did not differ between groups, and there was no specific binding of [3H]raclopride or 7‐hydroxy‐2‐(di‐n‐[3H]propylamino)tetralin to BA 9 from either cohort of subjects. This suggests the density of dopamine D1‐like and NMDA receptors, the dopamine transporter, and nitric oxide synthase activity are not altered in BA 9 from schizophrenic subjects. The selective nature of the changes in serotonin2A and GABAA receptors in DLPFC could indicate that these changes are involved in the pathology of schizophrenia.

Decreased NR1, NR2A, and SAP102 transcript expression in the hippocampus in bipolar disorder.

OBJECTIVES Schizophrenia is associated with dysfunction of glutamatergic neurotransmission, and several studies have suggested glutamatergic abnormalities in bipolar disorder. Recent data suggest involvement of the NMDA receptor signaling complex, which includes NMDA receptor subunits as well as associated intracellular interacting proteins critical for NMDA receptor assembly, trafficking, and activation; the most well-characterized being PSD93, PSD95, SAP102, and NF-L. Previously, studies from our laboratories have described changes in glutamate receptor subunit transcript and binding site expression in schizophrenia and changes in NMDA receptor binding site expression in bipolar disorder in postmortem brain tissue. In the present work, we focus on the expression of these molecules in hippocampus in schizophrenia and bipolar affective disorder I. METHODS We performed in situ hybridization to assess hippocampal expression of the transcripts encoding NMDA receptor subunits NR1, 2A, 2B, 2C and 2D, and the transcripts for the NMDA receptor associated PSD proteins PSD95, PSD93, NF-L, and SAP102 in subjects with schizophrenia, bipolar affective disorder I, and a comparison group. We also measured [(3)H]CGP39653 and [(3)H]MK-801 binding site expression in the hippocampus in schizophrenia. RESULTS There was a significant decrease in the expression of transcripts for NR1 and NR2A subunits and SAP102 in bipolar disorder. We did not detect any changes in these transcripts or in binding site expression in the hippocampus in schizophrenia. CONCLUSIONS We propose that the NMDA receptor signaling complex, including the intracellular machinery that is coupled to the NMDA receptor subunits, is abnormal in the hippocampus in bipolar disorder. These data suggest that bipolar disorder might be associated with abnormalities of glutamate-linked intracellular signaling and trafficking processes.

Phospholipase C-β1 knockout mice exhibit endophenotypes modeling schizophrenia which are rescued by environmental enrichment and clozapine administration

Phospholipase C-β1 (PLC-β1) is a rate-limiting enzyme implicated in postnatal-cortical development and neuronal plasticity. PLC-β1 transduces intracellular signals from specific muscarinic, glutamate and serotonin receptors, all of which have been implicated in the pathogenesis of schizophrenia. Here, we present data to show that PLC-β1 knockout mice display locomotor hyperactivity, sensorimotor gating deficits as well as cognitive impairment. These changes in behavior are regarded as endophenotypes homologous to schizophrenia-like symptoms in rodents. Importantly, the locomotor hyperactivity and sensorimotor gating deficits in PLC-β1 knockout mice are subject to beneficial modulation by environmental enrichment. Furthermore, clozapine but not haloperidol (atypical and typical antipsychotics, respectively) rescues the sensorimotor gating deficit in these animals, suggesting selective predictive validity. We also demonstrate a relationship between the beneficial effects of environmental enrichment and levels of M1/M4 muscarinic acetylcholine receptor binding in the neocortex and hippocampus. Thus we have demonstrated a novel mouse model, displaying disruption of multiple postsynaptic signals implicated in the pathogenesis of schizophrenia, a relevant behavioral phenotype and associated gene–environment interactions.

Clozapine reverses schizophrenia-related behaviours in the metabotropic glutamate receptor 5 knockout mouse: association with N-methyl-d-aspartic acid receptor up-regulation

Abnormalities in glutamatergic signalling are proposed in schizophrenia in light of the schizophreniform psychosis elicited by NMDA antagonists. The metabotropic glutamate receptor 5 (mGluR5) interacts closely with the NMDA receptor and is implicated in several behavioural endophenotypes of schizophrenia. We have demonstrated that mice lacking mGluR5 have increased sensitivity to the hyperlocomotive effects of the NMDA antagonist MK-801. Mice lacking mGluR5 also show abnormal locomotor patterns, reduced prepulse inhibition (PPI), and deficits on performance of a short-term spatial memory task on the Y-maze. Chronic administration of the antipsychotic drug clozapine ameliorated the locomotor disruption and reversed the PPI deficit, but did not improve Y-maze performance. Chronic clozapine increased NMDA receptor binding ([3H]MK-801) but did not alter dopamine D2 ([3H]YM-09151), 5-HT2A ([3H]ketanserin), or muscarinic M1/M4 receptor ([3H]pirenzepine), binding in these mice. These results demonstrate behavioural abnormalities that are relevant to schizophrenia in the mGluR5 knockout mouse and a reversal of behaviours with clozapine treatment. These results highlight both the interactions between mGluR5 and NMDA receptors in the determination of schizophreniform behaviours and the potential for the effects of clozapine to be mediated by NMDA receptor regulation.

Decreased cortical muscarinic receptors define a subgroup of subjects with schizophrenia

Schizophrenia is widely acknowledged as being a syndrome, consisting of an undefined number of diseases probably with differing pathologies. Although studying a syndrome makes the identification of an underlying pathology more difficult; neuroimaging, neuropsychopharmacological and post-mortem brain studies all implicate muscarinic acetylcholine receptors (CHRM) in the pathology of the disorder. We have established that the CHRM1 is selectively decreased in the dorsolateral prefrontal cortex of subjects with schizophrenia. To expand this finding, we wanted to ascertain whether decreased cortical CHRMs might (1) define a subgroup of schizophrenia and/or (2) be related to CHRM1 genotype. We assessed cortical [3H]pirenzepine binding and sequenced the CHRM1 in 80 subjects with schizophrenia and 74 age sex-matched control subjects. Kernel density estimation showed that [3H]pirenzepine binding in BA9 divided the schizophrenia, but not control, cohort into two distinct populations. One of the schizophrenia cohorts, comprising 26% of all subjects with the disorder, had a 74% reduction in mean cortical [3H]pirenzepine binding compared to controls. We suggest that these individuals make up ‘muscarinic receptor-deficit schizophrenia’ (MRDS). The MRDS could not be separated from other subjects with schizophrenia by CHRM1 sequence, gender, age, suicide, duration of illness or any particular drug treatment. Being able to define a subgroup within schizophrenia using a central biological parameter is a pivotal step towards understanding the biochemistry underlying at least one form of the disorder and may represent a biomarker that can be used in neuroimaging.

The effect of estrogen on dopamine and serotonin receptor and transporter levels in the brain: An autoradiography study

The aim of the present study was to elucidate the effect of estrogen on dopaminergic and serotonergic regulation of prepulse inhibition (PPI) by measuring its effects on the density of dopamine transporters (DAT), dopamine D(1) and D(2) receptors, serotonin transporters (SERT), serotonin-1A (5-HT(1A)) and 5-HT(2A) receptors using radioligand binding autoradiography. Three groups of female Sprague-Dawley rats were compared: sham-operated controls, untreated ovariectomized (OVX) rats and OVX rats with a 17beta-estradiol implant (OVX+E). These groups were identical to our previous prepulse inhibition (PPI) studies, allowing comparison of the results. Results showed that in the nucleus accumbens, DAT levels were 44% lower in OVX rats than in intact controls. Estrogen treatment completely reversed the effect of OVX in this brain region to levels similar to those in intact controls. Dopamine D(2) receptor density was increased in OVX rats by 28% in the nucleus accumbens and 25% in the caudate nucleus compared to intact controls. Estrogen treatment reversed this increase and, in addition, reduced dopamine D(2) receptor levels by a further 25% and 20%, respectively, compared to intact control rats. There were no differences between the groups with respect to the densities of dopamine D(1) receptors, SERT, 5-HT(1A) receptors or 5-HT(2A) receptors. These results show effects of estrogen treatment on central indices of dopaminergic, but not serotonergic function. The observed changes do not provide a direct overlap with the effects of these estrogen treatment protocols on drug-induced disruptions of PPI, but it is possible that a combination of effects, i.e. on both DAT and dopamine D(2) receptor density, is involved. These data could also be relevant for our understanding of the potential protective effect of estrogen treatment in schizophrenia.

Autophagy has a key role in the pathophysiology of schizophrenia

Autophagy is a process preserving the balance between synthesis, degradation and recycling of cellular components and is therefore essential for neuronal survival and function. Several key proteins govern the autophagy pathway including beclin1 and microtubule associated protein 1 light chain 3 (LC3). Here, we show a brain-specific reduction in beclin1 expression in postmortem hippocampus of schizophrenia patients, not detected in peripheral lymphocytes. This is in contrast with activity-dependent neuroprotective protein (ADNP) and ADNP2, which we have previously found to be deregulated in postmortem hippocampal samples from schizophrenia patients, but that now showed a significantly increased expression in lymphocytes from related patients, similar to increases in the anti-apoptotic, beclin1-interacting, Bcl2. The increase in ADNP was associated with the initial stages of the disease, possibly reflecting a compensatory effect. The increase in ADNP2 might be a consequence of neuroleptic treatment, as seen in rats subjected to clozapine treatment. ADNP haploinsufficiency in mice, which results in age-related neuronal death, cognitive and social dysfunction, exhibited reduced hippocampal beclin1 and increased Bcl2 expression (mimicking schizophrenia and normal human aging). At the protein level, ADNP co-immunoprecipitated with LC3B suggesting a direct association with the autophagy process and paving the path to novel targets for drug design.

Muscarinic receptors: do they have a role in the pathology and treatment of schizophrenia?

The high affinity of antipsychotic drugs for the dopamine D2 receptor focused attention onto the role of these receptors in the genesis of psychoses and the pathology of schizophrenia. However, psychotic symptoms are only one aspect of the complex symptom profile associated with schizophrenia. Therefore, research continues into other neurochemical systems and their potential roles in key features associated with schizophrenia. Modulating the cholinergic system in attempts to treat schizophrenia predates specific neurochemical hypotheses of the disorder. Cholinergic modulation has progressed from the use of coma therapy, through the use of anti‐cholinergic drugs to control side‐effects of older (typical) antipsychotic medications, to the development of drugs designed to specifically activate selected muscarinic receptors. This review presents data implicating a decrease in muscarinic receptors, particularly the M1 receptor, in the pathology of schizophrenia and explores the potential physiological consequences of such a change, drawing on data available from muscarinic receptor knockout mice as well as clinical and pre‐clinical pharmacology. The body of evidence presented suggests that deficits in muscarinic receptors are associated with some forms of schizophrenia and that targeting these receptors could prove to be of therapeutic benefit to patients with the disorder.