Disruption of NMDA receptor-mediated regulation of PPI in the maternal immune activation model of schizophrenia is restored by 17ß-estradiol and raloxifene.

Maternal immune activation (MIA) during pregnancy is known to increase the risk of development of schizophrenia in the offspring. Sex steroid hormone analogues have been proposed as potential antipsychotic treatments but the mechanisms of action involved remain unclear. Estrogen has been shown to alter N-methyl-d-aspartate (NMDA) receptor binding in the brain. We therefore studied the effect of chronic treatment with 17ß-estradiol, its isomer, 17α-estradiol, and the selective estrogen receptor modulator, raloxifene, on MIA-induced psychosis-like behaviour and the effect of the NMDA receptor antagonist, MK-801. Pregnant rats were treated with saline or the viral mimetic, poly(I:C), on gestational day 15. Adult female offspring were tested for changes in baseline prepulse inhibition (PPI) and the effects of acute treatment with MK-801 on PPI and locomotor activity. Poly(I:C) offspring had significantly lower baseline PPI compared to control offspring, and this effect was prevented by 17ß-estradiol and raloxifene, but not 17α-estradiol. MK-801 reduced PPI in control offspring but had no effect in poly(I:C) offspring treated with vehicle. Chronic treatment with 17ß-estradiol and raloxifene restored the effect of MK-801 on PPI. There were no effects of MIA or estrogenic treatment on MK-801 induced locomotor hyperactivity. These results show that MIA affects baseline PPI as well as NMDA receptor-mediated regulation of PPI in female rats, and strengthen the view that estrogenic treatment may have antipsychotic effects.

The effect of estradiol add-back: a longitudinal MRI study in prostate cancer patients.

We investigated the effect of estradiol add-back therapy (EAT) on brain activation related to cognitive function and affect in addition to putative changes in gray and white matter volume in testosterone depleted participants with prostate cancer. We conducted a randomized controlled, double-blinded trial in which 40 patients received 0.9 mg of transdermal estradiol per day for 6 months or matched placebo. Anatomical MRI and three functional MRI (fMRI) scans were obtained for the emotion recognition task, verbal memory task, and visuospatial memory task. Activation in corresponding cognitive and affective brain networks was demonstrated for all tasks. Longitudinally, there was no difference in brain activation, reaction time, or accuracy in response to the fMRI tasks between the EAT group and placebo group at 6 months. In addition, there was no detectable change in whole-brain gray or white matter volume or in hippocampal volume between the two groups after 6 months. This study supports earlier findings that EAT does not improve verbal memory or affect and has no immediate effect on hippocampal volume in testosterone depleted patients with prostate cancer.

Cocaine and amphetamine regulated transcript (CART) mediates sex differences in binge drinking through central taste circuits.

The neuropeptide cocaine- and amphetamine-regulated transcript (CART) has been implicated in alcohol consumption and reward behaviours, yet mechanisms mediating these effects have yet to be identified. Using a transgenic CART knockout (KO) mouse line we uncovered a sexually dimorphic effect of CART in binge drinking, with male CART KO mice increasing intake, whilst female CART KO mice decreased their alcohol intake compared to controls. Female CART KO mice show greater sensitivity to bitter solutions that can be overshadowed through addition of a sweetener, implicating taste as a factor. Further we identify that this is not driven through peripherally circulating sex hormones, but the central nucleus of the amygdala (CeA) is a locus where CART contributes to the regulation of alcohol consumption, with CeA CART neutralisation specifically reducing plain alcohol, but not sweetened alcohol consumption in female mice. These findings may have implications for the development of sex-specific treatment options for alcohol use disorders through targeting the CART system.

Sex Differences in Psychosis: Focus on Animal Models.

Most psychiatric illnesses, such as schizophrenia, show profound sex differences in incidence, clinical presentation, course, and outcome. Fortunately, more recently the literature on sex differences and (to a lesser extent) effects of sex steroid hormones is expanding, and in this review we have focused on such studies in psychosis, both from a clinical/epidemiological and preclinical/animal model perspective. We begin by briefly describing the clinical evidence for sex differences in schizophrenia epidemiology, symptomatology, and pathophysiology. We then detail sex differences and sex hormone effects in behavioral animal models of psychosis, specifically psychotropic drug-induced locomotor hyperactivity and disruption of prepulse inhibition. We expand on the preclinical data to include developmental and genetic models of psychosis, such as the maternal immune activation model and neuregulin transgenic animals, respectively. Finally, we suggest several recommendations for future studies, in order to facilitate a better understanding of sex differences in the development of psychosis.

Characterisation of Deficits and Sex Differences in Verbal and Visual Memory/Learning in Bipolar Disorder.

OBJECTIVE: Cognitive impairment is consistently reported in bipolar disorder (BD), but few studies have characterised which memory component processes are affected. Further, it is unknown whether the component processes underlying memory impairment are moderated by sex. The present study examined diagnosis and sex differences in both verbal and visual memory/learning domains in patients with BD and psychiatrically healthy controls. METHOD: Verbal and visual memory/learning were measured using the Hopkins Verbal Learning Test-Revised (HVLT-R) and Brief Visuospatial Memory Test-Revised (BVMT-R). 114 patients with BD (n = 50 males, n = 64 females), were compared to 105 psychiatrically healthy controls (n = 42 males, n = 63 females). RESULTS: Patients with BD had worse performance in verbal and visual immediate and total recall, verbal and visual delayed free recall, and verbal recognition discrimination scores, but there were no group differences in learning slopes and cumulative learning index scores. There were trends for BD females to outperform BD males in visual memory/learning free recall and cumulative learning, but these results did not survive multiple testing correction. These findings did not change in a secondary sensitivity analysis comparing only strictly euthymic BD patients to controls (n = 64). CONCLUSION: The present study found trait-like verbal and visual memory/learning impairment in BD that was attributable to deficient encoding and/or consolidation processes rather than deficits in learning. We did not find marked sex differences in either visual or verbal memory/learning measures, although some trend level effects were apparent and deserve exploration in future studies.

Reassessment of amphetamine- and phencyclidine-induced locomotor hyperactivity as a model of psychosis-like behavior in rats.

Locomotor hyperactivity induced by psychotomimetic drugs, such as amphetamine and phencyclidine, is widely used as an animal model of psychosis-like behaviour and is commonly attributed to an interaction with dopamine release and N-methyl-D-aspartate (NMDA) receptors, respectively. However, what is often not sufficiently taken into account is that the pharmacological profile of these drugs is complex and may involve other neurotransmitter/receptor systems. Therefore, this study aimed to assess the effect of three antagonists targeting different monoamine pathways on amphetamine- and phencyclidine-induced locomotor hyperactivity. A total of 32 rats were pre-treated with antagonists affecting dopaminergic, noradrenergic and serotonergic transmission: haloperidol (0.05 mg/kg), prazosin (2 mg/kg) and ritanserin (1 mg/kg), respectively. After 30 min of spontaneous activity, rats were injected with amphetamine (0.5 mg/kg) or phencyclidine (2.5 mg/kg) and distance travelled, stereotypy and rearing recorded in photocell cages over 90 min. Pre-treatment with haloperidol or prazosin both reduced amphetamine-induced hyperactivity although pre-treatment with ritanserin had only a partial effect. None of the pre-treatments significantly altered the hyperlocomotion effects of phencyclidine. These findings suggest that noradrenergic as well as dopaminergic neurotransmission is critical for amphetamine-induced locomotor hyperactivity. Hyperlocomotion effects of phencyclidine are dependent on other factors, most likely NMDA receptor antagonism. These results help to interpret psychotomimetic drug-induced locomotor hyperactivity as an experimental model of psychosis.

TrkB agonist 7,8-dihydroxyflavone reverses an induced prepulse inhibition deficit selectively in maternal immune activation offspring: implications for schizophrenia.

Reduced brain-derived neurotrophic factor (BDNF) signalling has been implicated in schizophrenia endophenotypes, including deficits in prepulse inhibition (PPI). Maternal immune activation (MIA) is a widely used neurodevelopmental animal model for schizophrenia but it is unclear if BDNF and its receptor, tropomyosin receptor kinase B (TrkB), are involved in PPI regulation in this model. Pregnant Long Evans rats were treated with the viral mimetic, polyinosinic-polycytidylic acid (poly I:C; 4 mg/kg i.v.), and nine male offspring from these dams were compared in adulthood to 11 male Long Evans controls. Offspring underwent PPI testing following injection with the TrkB agonist, 7,8-dihydroxyflavone (7,8-DHF) (10 mg/kg i.p.), with or without the dopamine receptor agonist, apomorphine (APO; 1 mg/kg s.c.), or the dopamine releasing drug, methamphetamine (METH; 2 mg/kg s.c.). Acute administration of APO and METH caused the expected significant reduction of PPI. Acute administration of 7,8-DHF did not alter PPI on its own; however, it significantly reversed the effect of APO on PPI in poly I:C rats, but not in controls. A similar trend was observed in combination with METH. Western blot analysis of frontal cortex revealed significantly increased levels of BDNF protein, but not TrkB or phosphorylated TrkB/TrkB levels, in poly I:C rats. These findings suggest that, selectively in MIA offspring, 7,8-DHF has the ability to reverse PPI deficits caused by dopaminergic stimulation. This effect could be associated with increased BDNF expression in the frontal cortex. These data suggest that targeting BDNF signalling may have therapeutic potential for the treatment of certain symptoms of schizophrenia.

An investigation into nicotinic receptor involvement in mood disorders uncovers novel depression candidate genes.

BACKGROUND: We have previously reported reduced expression of the cholinergic autoreceptor CHRM2 in Brodmann's Area (BA) 24 of the anterior cingulate cortex from subjects with major depressive disorder (MDD) and bipolar disorder (BD), consistent with a hypercholinergic state. This led us to investigate whether levels of the high affinity nicotinic acetylcholine receptors are also altered in BA 24. METHODS: We measured the binding levels of a high-affinity nicotinic receptor-selective radioligand, [3H]epibatidine, in BA 24 from subjects with MDD (n = 20), BD (n = 18) and age- and sex-matched controls (n = 20). We used qPCR to measure mRNA expression of the high affinity nicotinic acetylcholine receptor subunit CHRNB2 in these subjects. RESULTS: [3H]Epibatidine binding density and CHRNB2 mRNA expression were not significantly altered in either MDD or BD compared to control levels. While validating reference genes for our qPCR experiments, we found that the mRNA levels of 3 putative reference genes, TFB1M, PPIA and SNCA, were increased in MDD but not BD compared to controls. Further investigations in other cortical regions showed that these changes were specific to BA24. LIMITATIONS: Cohort size and available patient data were limited due to standard constraints associated with post-mortem studies. CONCLUSION: Our data suggest that decreased CHRM2 in BA24 in mood disorders is not associated with a corresponding change in high affinity nicotinic acetylcholine receptor expression. Our findings of increased TFB1M, PPIA and SNCA expression in MDD point to a broader derangement of several homeostatic pathways in MDD that are distinct from BD.

The impact of ovariectomy and chronic estrogen treatment on gene expression in the rat cortex: Implications for psychiatric disorders.

Estrogens, via estrogen-mediated changes in CNS function, have been suggested to be beneficial in the treatment of several psychiatric disorders. Few studies have used transcriptomic technologies to determine the effect of estrogen on gene expression in the CNS. Thus, we aimed to examine the impact of ovariectomy (the removal of all ovarian hormones) and estrogen replacement on rat frontal cortical gene expression. We used the Agilent SurePrint G3 Gene Expression Rat Array to measure levels of RNA in intact (cycling) female rats and in ovariectomized rats that were, or were not, given 17ß-estradiol in implants for 4 weeks. Compared to untreated ovariectomized rats, intact rats (effect of ovarian hormones; comparison 1) and rats receiving 17ß-estradiol replacement (estrogen-specific effects; comparison 2) showed significant changes in cortical gene expression (58 and 36 genes, respectively). These changes in gene expression would be expected to affect pathways that regulate neurotransmitters, glutathione and sphingolipids; pathways known to be implicated in the pathophysiologies of psychiatric disorders. When we compared the levels of gene expression in the two comparisons that had a significance of p < 0.01 independent of magnitude of change, there was a strong correlation between fold changes in gene expression for 127 genes. We posit that this correlation is due to the level of expression of these genes being strongly influenced by both cycling and replacement estrogen. Further exploration of ovarian hormone- and estrogen-sensitive gene expression may provide new insight into the aetiology of aspects of psychiatric disorders that show sex differences.

Long-term effects of young-adult methamphetamine on dorsal raphe serotonin systems in mice: Role of brain-derived neurotrophic factor.

To assess the long-term effects of chronic adolescent methamphetamine (METH) treatment on the serotonin system in the brain, we used serotonin-1A receptor (5-HT1A) and serotonin transporter (SERT) autoradiography, and quantitative tryptophan-hydroxylase 2 (TPH2) immunohistochemistry in the raphe nuclei of mice. Because of the modulatory role of brain-derived neurotrophic factor (BDNF) on the serotonin system and the effects of METH, we included both BDNF heterozygous (HET) mice and wildtype (WT) controls. Male and female mice of both genotypes were treated with an escalating METH dose regimen from the age of 6-9 weeks. At least two weeks later, acute locomotor hyperactivity induced by a 5 mg/kg D-amphetamine challenge was significantly enhanced in METH-pretreated mice, showing long-term sensitisation. METH pretreatment caused a small, but significant decrease of 5-HT1A receptor binding in the dorsal raphe nucleus (DRN) of males independent of genotype, but there were no changes in the median raphe nucleus (MRN) or in SERT binding density. METH treatment reduced the number of TPH2 positive cells in ventral subregions of the rostral and medial DRN independent of genotype. METH treatment selectively reduced DRN cell counts in BDNF HET mice compared to wildtype mice in medial and caudal ventrolateral subregions previously associated with panic-like behaviour. The data increase our understanding of the long-term and selective effects of METH on brain serotonin systems. These findings could be relevant for some of the psychosis-like symptoms associated with long-term METH use.

Orexins (hypocretins): The intersection between homeostatic and hedonic feeding.

Orexins are hypothalamic neuropeptides originally discovered to play a role in the regulation of feeding behaviour. The broad connections of orexin neurons to mesocorticolimbic circuitry suggest they may play a role in mediating reward-related behaviour beyond homeostatic feeding. Here, we review the role of orexin in a variety of eating-related behaviour, with a focus on reward and motivation, and the neural circuits driving these effects. One emerging finding is the involvement of orexins in hedonic and appetitive behaviour towards palatable food, in addition to their role in homeostatic feeding. This review discusses the brain circuitry and possible mechanisms underlying the role of orexins in these behaviours. Overall, there is a marked bias in the literature towards studies involving male subjects. As such, future work needs to be done to involve female subjects. In summary, orexins play an important role in driving motivation for high salient rewards such as highly palatable food and may serve as the intersection between homeostatic and hedonic feeding.

Cortical expression of the RAPGEF1 gene in schizophrenia: investigating regional differences and suicide.

Rap guanine nucleotide exchange factor 1 (RAPGEF1) is involved in cell adhesion and neuronal migration. Previously we found lower RAPGEF1 mRNA levels in Brodmann's area (BA) 9 in subjects with schizophrenia compared to controls. This study aimed to determine whether RAPGEF1 expression was altered in other brain regions implicated in schizophrenia and whether this was associated with suicide. Using qPCR, we measured the levels of RAPGEF1 in post-mortem BA 8 and 44 from 27 subjects with schizophrenia and 26 non-psychiatric control subjects. To address the effect of antipsychotic treatments, Rapgef1 mRNA levels were measured in the cortex from rats treated with typical antipsychotic drugs. There was no difference in RAPGEF1 normalised relative expression levels in BA 8 or 44. However, in BA 8, schizophrenia subjects had higher raw Ct RAPGEF1 levels compared to controls. There were higher RAPGEF1 levels in suicide completers compared to non-suicide schizophrenia subjects in BA 8. Rapgef1 expression levels in the rat cortex did not vary with antipsychotic treatment. Our findings suggest changes in RAPGEF1 expression may be limited to the dorsolateral prefrontal cortex from subjects with schizophrenia. Further investigation of the function of RAPGEF1 may lead to a greater understanding of the pathophysiology of schizophrenia.

The effect of 17ß-estradiol on maternal immune activation-induced changes in prepulse inhibition and dopamine receptor and transporter binding in female rats.

Maternal immune activation (MIA) during pregnancy is associated with an increased risk of development of schizophrenia in later life. 17ß-estradiol treatment may improve schizophrenia symptoms, but little is known about its efficacy on MIA-induced psychosis-like behavioural deficits in animals. Therefore, in this study we used the poly(I:C) neurodevelopmental model of schizophrenia to examine whether MIA-induced psychosis-like behavioural and neurochemical changes can be attenuated by chronic treatment (2-6 weeks) with 17ß-estradiol. Pregnant rats were treated with saline or the viral mimetic, poly(I:C), on gestational day 15 and adult female offspring were tested for changes in prepulse inhibition (PPI) and density of dopamine D1 and D2 receptors and dopamine transporters in the forebrain compared to control offspring. Poly(I:C)-treated offspring exhibited significantly disrupted PPI, an effect which was reversed by chronic treatment with 17ß-estradiol. In control offspring, but not poly(I:C) offspring, PPI was significantly reduced by acute treatment with either the dopamine D1/D2 receptor agonist, apomorphine, or dopamine releaser, methamphetamine. 17ß-estradiol restored the effect of apomorphine, but not methamphetamine, on PPI in poly(I:C) offspring. There was a strong trend for a dopamine D2 receptor binding density increase in the nucleus accumbens core region in poly(I:C) offspring, and this was reversed by chronic 17ß-estradiol treatment. No changes were found in the nucleus accumbens shell, caudate putamen or frontal cortex or in the density of dopamine D1 receptors or transporters. These findings suggest that 17ß-estradiol may improve some symptoms of schizophrenia, an effect that may be mediated by selective changes in dopamine D2 receptor density.

The Impact of Removal of Ovarian Hormones on Cholinergic Muscarinic Receptors: Examining Prepulse Inhibition and Receptor Binding.

Ovarian hormones, such as estrogens and progesterone, are known to exert beneficial effects on cognition and some psychiatric disorders. The basis of these effects is not fully understood, but may involve altered cholinergic neurotransmission. This study aimed to investigate how a lack of ovarian hormones would impact muscarinic receptor-induced deficits in prepulse inhibition (PPI) and muscarinic receptor density in several brain regions. Adult female rats were either ovariectomized, to remove the source of ovarian hormones, or left intact (sham-operated). PPI is a measure of sensorimotor gating that is typically impaired in schizophrenia patients, and similar deficits can be induced in rats by administering scopolamine, a muscarinic receptor antagonist. Our results revealed no significant effects of ovariectomy on PPI after saline or scopolamine treatment. Autoradiography was performed to measure cholinergic muscarinic receptor binding density using [3H]-pirenzepine, [3H]-AF-DX, and [3H]-4-DAMP, to label M1, M2/M4, and M3 receptors, respectively. We examined the amygdala, caudate putamen, dorsal hippocampus, motor cortex, retrosplenial cortex, and ventromedial hypothalamus. There were no significant group differences in any region for any muscarinic receptor type. These results suggest that removing peripheral ovarian hormones does not influence the cholinergic muscarinic receptor system in the context of PPI or receptor binding density.

Pharmacological Mechanisms Involved in Sensory Gating Disruption Induced by (±)-3,4-Methylene- Dioxymethamphetamine (MDMA): Relevance to Schizophrenia.

Sensory gating deficits have been demonstrated in schizophrenia, but the mechanisms involved remain unclear. In the present study, we used disruption of paired-pulse gating of evoked potentials in rats by the administration of (±)-3,4-methylene-dioxymethamphetamine (MDMA) to study serotonergic and dopaminergic mechanisms involved in auditory sensory gating deficits. Male Sprague-Dawley rats were instrumented with cortical surface electrodes to record evoked potential changes in response to pairs of 85dB tones (S1 and S2), 500msec apart. Administration of MDMA eliminated the normal reduction in the amplitude of S2 compared to S1, representing disruption of auditory sensory gating. Pretreatment of the animals with the dopamine D1 receptor antagonist, SCH23390, the dopamine D2 receptor antagonist, haloperidol, the serotonin (5-HT)1A receptor antagonist, WAY100635, or the 5-HT2A receptor antagonist, ketanserin, all blocked the effect of MDMA, although the drugs differentially affected the individual S1 and S2 amplitudes. These data show involvement of both dopaminergic and serotonergic mechanisms in disruption of auditory sensory gating by MDMA. These and previous results suggest that MDMA targets serotonergic pathways, involving both 5-HT1A and 5-HT2A receptors, leading to dopaminergic activation, involving both D1 and D2 receptors, and ultimately sensory gating deficits. It is speculated that similar interactive mechanisms are affected in schizophrenia.

Sex differences in the effect of maternal immune activation on cognitive and psychosis-like behaviour in Long Evans rats.

Maternal immune activation during pregnancy is associated with increased risk of development of schizophrenia in later life. There are sex differences in schizophrenia, particularly in terms of age of onset, course of illness and severity of symptoms. However, there is limited and inconsistent literature on sex differences in the effects of maternal immune activation on behaviour with relevance to schizophrenia. The aim of this study was therefore to investigate sex differences in the effects of maternal immune activation by treating Long Evans rats with poly(I:C) on gestational day 15. We compared adult male and female offspring on spatial working memory in the touchscreen trial-unique nonmatching-to-location task, pairwise discrimination and reversal learning, as well as on prepulse inhibition and psychotropic drug-induced locomotor hyperactivity. Male, but not female poly(I:C) offspring displayed a deficit in spatial working memory, particularly at the longer delay. Neither pairwise discrimination nor reversal learning showed an effect of poly(I:C), but female controls outperformed male controls in the reversal learning task. Significant reduction of prepulse inhibition and enhancement of acute methamphetamine-induced locomotor hyperactivity was found similarly in male and female poly(I:C) offspring. These results show that maternal immune activation induces a range of behavioural effects in the offspring, with sex specificity in the effects of maternal immune activation on some aspects of cognition, but not psychosis-like behaviour.

A model of emotional stress-induced binge eating in female mice with no history of food restriction.

Overeating is a major contributing factor to obesity and related health complications. For women, in particular, negative emotions such as stress strongly influence eating behavior and bingeing episodes. Modeling this type of binge eating in rodents presents challenges: firstly, stress-induced anorexia is commonly observed in rodents therefore a mild stressor is required in order to observe an orexigenic effect. Second, many studies report using calorie restriction to observe the required behavior; yet this does not necessarily reflect the human condition. Thus, the aim of this study was to develop a model of emotional stress-induced bingeing independent of caloric restriction. Female and male C57BL/6J mice were divided into ad libitum (n = 20 per sex) and food-restricted (n = 20 per sex) groups which were both further split into a control group and a group exposed to frustration stress (n = 10 per group). All mice were provided intermittent access to a highly palatable food in 2 cycles. At the end of each cycle the stress group was subjected to a 15-minute frustration episode where highly palatable food was within the home cage but inaccessible. Both groups were then given free access for 15 minutes. Frustrated female mice from the ad libitum displayed binge-like behavior compared with controls (P = .0001). Notably, this behavior was absent in males. Ovariectomy had no impact on binge-like behavior. Collectively, these data validate a novel model of emotional stress-induced binge eating specific to female mice which does not require caloric restriction and is not driven by ovarian hormones.

The importance of sex differences in pharmacology research.

This article is part of a themed section on The Importance of Sex Differences in Pharmacology Research. To view the other articles in this section visit http://onlinelibrary.wiley.com/doi/10.1111/bph.v176.21/issuetoc.

An alternative theory for hormone effects on sex differences in PTSD: The role of heightened sex hormones during trauma.

Women are at least twice as susceptible to developing post-traumatic stress disorder (PTSD) compared to men. Although most research seeking to explain this discrepancy has focussed on the role of oestradiol during fear extinction learning, the role of progesterone has been overlooked, despite relatively consistent findings being reported concerning the role of progesterone during consolidation of emotional and intrusive memories. In this review article, we outline literature supporting the role of progesterone on memory formation, with particular emphasis on potential memory-enhancing properties of progesterone when subjects are placed under stress. It is possible that progesterone directly and indirectly exerts memory-enhancing effects at the time of trauma, which is an effect that may not be necessarily captured during non-stressful paradigms. We propose a model whereby progesterone's steroidogenic relationship to cortisol and brain-derived neurotrophic factor in combination with elevated oestradiol may enhance emotional memory consolidation during trauma and therefore present a specific vulnerability to PTSD formation in women, particularly during the mid-luteal phase of the menstrual cycle.

Widespread Changes in Positive Allosteric Modulation of the Muscarinic M1 Receptor in Some Participants With Schizophrenia.

BACKGROUND: Preclinical and some human data suggest allosteric modulation of the muscarinic M1 receptor (CHRM1) is a promising approach for the treatment of schizophrenia. However, it is suggested there is a subgroup of participants with schizophrenia who have profound loss of cortical CHRM1 (MRDS). This raises the possibility that some participants with schizophrenia may not respond optimally to CHRM1 allosteric modulation. Here we describe a novel methodology to measure positive allosteric modulation of CHRM1 in human CNS and the measurement of that response in the cortex, hippocampus, and striatum from participants with MRDS, non-MRDS and controls. METHODS: The cortex (Brodmann's area 6), hippocampus, and striatum from 40 participants with schizophrenia (20 MRDS and 20 non-MRDS) and 20 controls were used to measure benzyl quinolone carboxylic acid-mediated shift in acetylcholine displacement of [3H]N-methylscopolamine using a novel in situ radioligand binding with autoradiography methodology. RESULTS: Compared with controls, participants with schizophrenia had lower levels of specific [3H]N-methylscopolamine binding in all CNS regions, whilst benzyl quinolone carboxylic acid-modulated binding was less in the striatum, Brodmann's area 6, dentate gyrus, and subiculum. When divided by subgroup, only in MRDS was there lower specific [3H]N-methylscopolamine binding and less benzyl quinolone carboxylic acid-modulated binding in all cortical and subcortical regions studied. CONCLUSIONS: In a subgroup of participants with schizophrenia, there is a widespread decreased responsiveness to a positive allosteric modulator at the CHRM1. This finding may have ramifications it positive allosteric modulators of the CHRM1 are used in clinical trials to treat schizophrenia as some participants may not have an optimal response.