Harmonizing data on correlates of sleep in children within and across neurodevelopmental disorders: lessons learned from an Ontario Brain Institute cross-program collaboration.

There is an increasing desire to study neurodevelopmental disorders (NDDs) together to understand commonalities to develop generic health promotion strategies and improve clinical treatment. Common data elements (CDEs) collected across studies involving children with NDDs afford an opportunity to answer clinically meaningful questions. We undertook a retrospective, secondary analysis of data pertaining to sleep in children with different NDDs collected through various research studies. The objective of this paper is to share lessons learned for data management, collation, and harmonization from a sleep study in children within and across NDDs from large, collaborative research networks in the Ontario Brain Institute (OBI). Three collaborative research networks contributed demographic data and data pertaining to sleep, internalizing symptoms, health-related quality of life, and severity of disorder for children with six different NDDs: autism spectrum disorder; attention deficit/hyperactivity disorder; obsessive compulsive disorder; intellectual disability; cerebral palsy; and epilepsy. Procedures for data harmonization, derivations, and merging were shared and examples pertaining to severity of disorder and sleep disturbances were described in detail. Important lessons emerged from data harmonizing procedures: prioritizing the collection of CDEs to ensure data completeness; ensuring unprocessed data are uploaded for harmonization in order to facilitate timely analytic procedures; the value of maintaining variable naming that is consistent with data dictionaries at time of project validation; and the value of regular meetings with the research networks to discuss and overcome challenges with data harmonization. Buy-in from all research networks involved at study inception and oversight from a centralized infrastructure (OBI) identified the importance of collaboration to collect CDEs and facilitate data harmonization to improve outcomes for children with NDDs.

FAIR in action: Brain-CODE - A neuroscience data sharing platform to accelerate brain research.

The effective sharing of health research data within the healthcare ecosystem can have tremendous impact on the advancement of disease understanding, prevention, treatment, and monitoring. By combining and reusing health research data, increasingly rich insights can be made about patients and populations that feed back into the health system resulting in more effective best practices and better patient outcomes. To achieve the promise of a learning health system, data needs to meet the FAIR principles of findability, accessibility, interoperability, and reusability. Since the inception of the Brain-CODE platform and services in 2012, the Ontario Brain Institute (OBI) has pioneered data sharing activities aligned with FAIR principles in neuroscience. Here, we describe how Brain-CODE has operationalized data sharing according to the FAIR principles. Findable-Brain-CODE offers an interactive and itemized approach for requesters to generate data cuts of interest that align with their research questions. Accessible-Brain-CODE offers multiple data access mechanisms. These mechanisms-that distinguish between metadata access, data access within a secure computing environment on Brain-CODE and data access via export will be discussed. Interoperable-Standardization happens at the data capture level and the data release stage to allow integration with similar data elements. Reusable - Brain-CODE implements several quality assurances measures and controls to maximize data value for reusability. We will highlight the successes and challenges of a FAIR-focused neuroinformatics platform that facilitates the widespread collection and sharing of neuroscience research data for learning health systems.

Validating a novel deterministic privacy-preserving record linkage between administrative & clinical data: applications in stroke research.

Introduction: Research data combined with administrative data provides a robust resource capable of answering unique research questions. However, in cases where personal health data are encrypted, due to ethics requirements or institutional restrictions, traditional methods of deterministic and probabilistic record linkages are not feasible. Instead, privacy-preserving record linkages must be used to protect patients' personal data during data linkage. Objectives: To determine the feasibility and validity of a deterministic privacy preserving data linkage protocol using homomorphically encrypted data. Methods: Feasibility was measured by the number of records that successfully matched via direct identifiers. Validity was measured by the number of records that matched with multiple indirect identifiers. The threshold for feasibility and validity were both set at 95%. The datasets shared a single, direct identifier (health card number) and multiple indirect identifiers (sex and date of birth). Direct identifiers were encrypted in both datasets and then transferred to a third-party server capable of linking the encrypted identifiers without decrypting individual records. Once linked, the study team used indirect identifiers to verify the accuracy of the linkage in the final dataset. Results: With a combination of manual and automated data transfer in a sample of 8,128 individuals, the privacy-preserving data linkage took 36 days to match to a population sample of over 3.2 million records. 99.9% of the records were successfully matched with direct identifiers, and 99.8% successfully matched with multiple indirect identifiers. We deemed the linkage both feasible and valid. Conclusions: As combining administrative and research data becomes increasingly common, it is imperative to understand options for linking data when direct linkage is not feasible. The current linkage process ensured the privacy and security of patient data and improved data quality. While the initial implementations required significant computational and human resources, increased automation keeps the requirements within feasible bounds.

Assessing the validity of administrative health data for the identification of children and youth with autism spectrum disorder in Ontario.

Population-level identification of children and youth with ASD is essential for surveillance and planning for required services. The objective of this study was to develop and validate an algorithm for the identification of children and youth with ASD using administrative health data. In this retrospective validation study, we linked an electronic medical record (EMR)-based reference standard, consisting 10,000 individuals aged 1-24 years, including 112 confirmed ASD cases to Ontario administrative health data, for the testing of multiple case-finding algorithms. Sensitivity, specificity, positive predictive value (PPV), negative predictive value (NPV), and corresponding 95% confidence intervals (CI) were calculated for each algorithm. The optimal algorithm was validated in three external cohorts representing family practice, education, and specialized clinical settings. The optimal algorithm included an ASD diagnostic code for a single hospital discharge or emergency department visit or outpatient surgery, or three ASD physician billing codes in 3 years. This algorithm's sensitivity was 50.0% (95%CI 40.7-88.7%), specificity 99.6% (99.4-99.7), PPV 56.6% (46.8-66.3), and NPV 99.4% (99.3-99.6). The results of this study illustrate limitations and need for cautious interpretation when using administrative health data alone for the identification of children and youth with ASD. LAY SUMMARY: We tested algorithms (set of rules) to identify young people with ASD using routinely collected administrative health data. Even the best algorithm misses more than half of those in Ontario with ASD. To understand this better, we tested how well the algorithm worked in different settings (family practice, education, and specialized clinics). The identification of individuals with ASD at a population level is essential for planning for support services and the allocation of resources. Autism Res 2021, 14: 1037-1045. © 2021 The Authors. Autism Research published by International Society for Autism Research published by Wiley Periodicals LLC.

Identifying Children and Youth With Autism Spectrum Disorder in Electronic Medical Records: Examining Health System Utilization and Comorbidities.

Autism spectrum disorder (ASD) is a neurodevelopmental disorder requiring significant health and educational resources for affected individuals. A reference standard for ASD was generated from an existing population-based cohort of 10,000 children and youth aged 1-24 years who were randomly selected for chart abstraction from 29,256 patients from 119 family physicians. We developed and validated an algorithm to identify children and youth with ASD within an electronic medical record system (N = 80,237, aged 1-24 years) in order to examine the prevalence of comorbidities and quantify health system utilization within the cohort. We identified 1,062 children and youth with ASD representing a prevalence of 1.32%. Compared to individuals without ASD, those with ASD had a higher prevalence of asthma, were more likely to visit a specialist, undergo surgery, and be hospitalized for psychiatric reasons. Children and youth with ASD in Ontario have complex health system needs, illustrated through a significant burden of comorbidities and increased health system utilization. LAY SUMMARY: Our paper generates population-based estimates of health system use by children and youth with ASD, who have a higher burden of comorbidities than the general population. We developed a case-finding algorithm and applied it in electronic medical records to create a cohort of children and youth with ASD, thereby generating an important resource to further study the health care needs of individuals with ASD.

The theory of change of the evaluation support program: Enhancing the role of community organizations in providing an ecology of care for neurological disorders.

This paper discusses the Ontario Brain Institute's theory of change for the Evaluation Support Program, a program designed to enhance the role of community organizations in providing care and services for people living with a brain disorder. This is done by helping community organizations build evaluation capacity and foster the use of evidence to inform their activities and services. Helping organizations to build capacities to track the 'key ingredients' of their successes will help ensure that successes are replicated and services can be improved to maximize the benefit that people receive from them. This paper describes the hypothesized outcomes and early impacts of the Evaluation Support Program, as well as how the program will contribute to the field of evaluation capacity building.

Experiments in evaluation capacity building: Enhancing brain disorders research impact in Ontario.

This paper is the introductory paper on a forum on evaluation capacity building for enhancing impacts of research on brain disorders. It describes challenges and opportunities of building evaluation capacity among community-based organizations in Ontario involved in enhancing brain health and supporting people living with a brain disorder. Using an example of a capacity building program called the "Evaluation Support Program", which is run by the Ontario Brain Institute, this forum discusses multiple themes including evaluation capacity building, evaluation culture and evaluation methodologies appropriate for evaluating complex community interventions. The goal of the Evaluation Support Program is to help community-based organizations build the capacity to demonstrate the value that they offer in order to improve, sustain, and spread their programs and activities. One of the features of this forum is that perspectives on the Evaluation Support Program are provided by multiple stakeholders, including the community-based organizations, evaluation team members involved in capacity building, thought leaders in the fields of evaluation capacity building and evaluation culture, and the funders.

Formulation of evidence-based messages to promote the use of physical activity to prevent and manage Alzheimer's disease.

BACKGROUND: The impending public health impact of Alzheimer's disease is tremendous. Physical activity is a promising intervention for preventing and managing Alzheimer's disease. However, there is a lack of evidence-based public health messaging to support this position. This paper describes the application of the Appraisal of Guidelines Research and Evaluation II (AGREE-II) principles to formulate an evidence-based message to promote physical activity for the purposes of preventing and managing Alzheimer's disease. METHODS: A messaging statement was developed using the AGREE-II instrument as guidance. Methods included (a) conducting a systematic review of reviews summarizing research on physical activity to prevent and manage Alzheimer's disease, and (b) engaging stakeholders to deliberate the evidence and formulate the messaging statement. RESULTS: The evidence base consisted of seven systematic reviews focused on Alzheimer's disease prevention and 20 reviews focused on symptom management. Virtually all of the reviews of symptom management conflated patients with Alzheimer's disease and patients with other dementias, and this limitation was reflected in the second part of the messaging statement. After deliberating the evidence base, an expert panel achieved consensus on the following statement: "Regular participation in physical activity is associated with a reduced risk of developing Alzheimer's disease. Among older adults with Alzheimer's disease and other dementias, regular physical activity can improve performance of activities of daily living and mobility, and may improve general cognition and balance." The statement was rated favourably by a sample of older adults and physicians who treat Alzheimer's disease patients in terms of its appropriateness, utility, and clarity. CONCLUSION: Public health and other organizations that promote physical activity, health and well-being to older adults are encouraged to use the evidence-based statement in their programs and resources. Researchers, clinicians, people with Alzheimer's disease and caregivers are encouraged to adopt the messaging statement and the recommendations in the companion informational resource.

The ketogenic diet: proposed mechanisms of action.

The ketogenic diet is a high-fat, low-carbohydrate diet used to treat drug-resistant seizures, especially in children. A number of possible mechanisms of action have been proposed to explain the anticonvulsant effects of the diet. Four of these hypothetical mechanisms are discussed in the present article: the pH hypothesis, the metabolic hypotheses, the amino acid hypothesis, and the ketone hypothesis.

The effects of a ketogenic diet on ATP concentrations and the number of hippocampal mitochondria in Aldh5a1(-/-) mice.

BACKGROUND: Succinic semialdehyde dehydrogenase (SSADH) deficiency is an inborn error of GABA metabolism characterized clinically by ataxia, psychomotor retardation and seizures. A mouse model of SSADH deficiency, the Aldh5a1(-/-) mouse, has been used to study the pathophysiology and treatment of this disorder. Recent work from our group has shown that the ketogenic diet (KD) is effective in normalizing the Aldh5a1(-/-) phenotype, although the mechanism of the effect remains unclear. METHODS: Here, we examine the effects of a KD on the number of hippocampal mitochondria as well as on ATP levels in hippocampus. Electron microscopy was performed to determine the number of mitochondria in the hippocampus of Aldh5a1(-/-) mice. Adenosine triphosphate (ATP) levels were measured in hippocampal extracts. RESULTS: Our results show that the KD increases the number of mitochondria in Aldh5a1(-/-) mice. We also show that Aldh5a1(-/-) mice have significant reductions in hippocampal ATP levels as compared to controls, and that the KD restores ATP in mutant mice to normal levels. GENERAL SIGNIFICANCE: Taken together, our data suggest that the KD's actions on brain mitochondria may play a role in the diet's ability to treat murine SSADH deficiency.

Acetone as an anticonvulsant.

Recent interest in the anticonvulsant effects of acetone has stemmed from studies related to the ketogenic diet (KD). The KD, a high-fat diet used to treat drug-resistant seizures, raises blood and brain levels of three ketones: beta-hydroxybutyrate, acetoacetate, and acetone. An obvious question is whether these ketones have anticonvulsant properties. We found that neither beta-hydroxybutyrate nor acetoacetate has proven to be anticonvulsant. Acetone, however, is clearly anticonvulsant at physiological, and near-physiological, nontoxic concentrations. Despite knowledge of acetone's anticonvulsant properties since the 1930's, acetone had never been characterized using the standard animal seizure tests. In our recent experiments, acetone was found to be active in animal models of tonic-clonic seizures, typical absence seizures, complex partial seizures, and atypical absence seizures associated with Lennox-Gastaut syndrome. Therapeutic indices are either comparable or better than that of valproate, a standard broad-spectrum anticonvulsant. A number of acetone-like molecules have also been tested, and these also show good potency up to a "cutoff" point of nine carbons contained in the side chain. Above this number, potency disappears, suggesting the possibility of a receptor for acetone and its analogs.

Circadian distribution of generalized tonic-clonic seizures associated with murine succinic semialdehyde dehydrogenase deficiency, a disorder of GABA metabolism.

Human succinic semialdehyde dehydrogenase (SSADH) deficiency is an autosomal recessive disorder of GABA metabolism associated with motor impairment and epileptic seizures. Similarly, mice with targeted deletion of the Aldh5a1 gene (Aldh5a1(-/-)) exhibit SSADH deficiency and seizures early in life. These seizures begin as absence seizures the second week of life, but evolve into generalized convulsive seizures that increase in severity and become lethal during the fourth postnatal week. The seizures are alleviated and survival is prolonged when the mutant animals are weaned onto a ketogenic diet (KD). The persistence of spontaneous, recurrent, generalized tonic-clonic seizures in KD-treated adult Aldh5a1(-/-) mice allowed us to quantify their daily (circadian) distribution using a novel behavioral method based on the detection of changes in movement velocity. Adult KD-treated Aldh5a1(-/-) mice exhibited a seizure phenotype characterized by fits of wild running clonus accompanied by jumping and bouncing. These hypermotor seizures were largely spontaneous and occurred daily in a nonrandom pattern. The seizure rhythm showed a peak shortly after dark phase onset (2008 hours) with near-24-hour periodicity. Age-matched wild-type littermates showed no evidence of abnormal motor behavior. These new data suggest that generalized tonic-clonic seizures in Aldh5a1(-/-) mice are more frequent during a specific time of day and will provide useful information to clinicians for the treatment of seizures associated with human SSADH deficiency.

A ketogenic diet rescues the murine succinic semialdehyde dehydrogenase deficient phenotype.

Succinic semialdehyde dehydrogenase (SSADH) deficiency is a heritable disorder of GABA degradation characterized by ataxia, psychomotor retardation and seizures. To date, there is no effective treatment for SSADH deficiency. We tested the hypothesis that a ketogenic diet (KD) would improve outcome in an animal model of SSADH deficiency, the SSADH knockout mouse (Aldh5a1-/-). Using a 4:1 ratio of fat to combined carbohydrate and protein KD we set out to compare the general phenotype, in vivo and in vitro electrophysiology and [35S]TBPS binding in both Aldh5a1-/- mice and control (Aldh5a1+/+) mice. We found that the KD prolonged the lifespan of mutant mice by >300% with normalization of ataxia, weight gain and EEG compared to mutants fed a control diet. Aldh5a1-/- mice showed significantly reduced mIPSC frequency in CA1 hippocampal neurons as well as significantly decreased [35S]TBPS binding in all brain areas examined. In KD fed mutants, mIPSC activity normalized and [35S]TBPS binding was restored in the cortex and hippocampus. The KD appears to reverse toward normal the perturbations seen in Aldh5a1-/- mice. Our data suggest that the KD may work in this model by restoring GABAergic inhibition. These data demonstrate a successful experimental treatment for murine SSADH deficiency using a KD, giving promise to the idea that the KD may be successful in the clinical treatment of SSADH deficiency.

The anticonvulsant effects of progesterone and its metabolites on amygdala-kindled seizures in male rats.

Progesterone is a neurosteroid that modulates neuronal excitability. The anticonvulsant effects of progesterone are largely mediated by the actions of its metabolites. The purpose of this study was to measure the anticonvulsant effects of progesterone, 5alpha-dihydroprogesterone, and allopregnanolone against amygdala-kindled seizures in male rats. The amygdala kindling model is a model of human complex partial seizures with secondary generalization. A bipolar electrode was chronically implanted in the right amygdala of male Wistar rats. All subjects were kindled to 30 stage 5 seizures and stability tested. Multiple doses of progesterone, 5alpha-dihydroprogesterone, or allopregnanolone were administered in separate dose-response studies. The antiseizure effects of each compound were determined. A progesterone time-response study was also conducted. At 30 min after injection, progesterone had an ED50 of 65.3 mg/kg against the secondarily generalized seizure and an ED50 of 114 mg/kg against the focal seizure. 5alpha-dihydroprogesterone had a low ED50 of 6.2 mg/kg against both the generalized component of the amygdala-kindled seizure and the focal seizure. Allopregnanolone had an ED50 of 15.2 mg/kg against the secondarily generalized seizure and was not effective against the focal seizure. Progesterone is an effective anticonvulsant against the secondarily generalized component of amygdala-kindled seizures in male rats. Progesterone is only effective against the focal seizure at high ataxic doses. 5alpha-dihydroprogesterone is a potent anticonvulsant against both the kindled amygdala focal discharge and the secondarily generalized seizure. Allopregnanolone is an effective anticonvulsant against the secondarily generalized component of the seizure, but not against the amygdala focal discharge.

A ketogenic diet and diallyl sulfide do not elevate afterdischarge thresholds in adult kindled rats.

INTRODUCTION: Acetone has been shown to have broad-spectrum anticonvulsant actions in animal seizure models and has been hypothesized to play a role in the anticonvulsant mechanism of the ketogenic diet (KD). The present study examined the ability of a KD to elevate amygdaloid afterdischarge thresholds (ADT) in fully kindled rats. The effects of the KD were studied in the presence and absence of diallyl sulfide (DAS), an inhibitor of acetone metabolism. METHODS: Twenty-four adult male rats were kindled to 30 stage 5 seizures. Afterdischarge thresholds (ADT) were determined. Subjects were then administered one of the following diets: (1) KD+V (vehicle; KD+V); (2) KD+DAS; (3) control diet+V (CD+V); (4) CD+DAS. They were stimulated every second day. Blood sampling was performed every second day--on non-stimulating days--to determine levels of glucose, beta-hydroxybutyrate, acetoacetate, and acetone. After 20 days, ADTs were re-determined. RESULTS: Blood acetone concentrations were significantly higher in the KD+DAS group as compared to the other groups, although they did not reach "therapeutic levels". None of the treatments, however, elevated ADTs. CONCLUSIONS: The KD was unable to elevate amygdaloid ADTs in fully kindled rats. Although subjects in the KD+DAS group achieved significant elevations of blood acetone, these concentrations (e.g. 0.2 mM) were much lower than those (>2.0 mM) previously shown to confer anticonvulsant activity. There appears to be large difference between humans and rats in their ability to produce elevated blood acetone levels on the KD. These data suggest that adult rats are not ideal subjects for modeling the anticonvulsant actions of the KD.

Lack of benefit of linoleic and alpha-linolenic polyunsaturated fatty acids on seizure latency, duration, severity or incidence in rats.

BACKGROUND: Polyunsaturated fatty acids have been reported to increase seizure threshold and to reduce seizure duration and severity in rats. OBJECTIVE: The purpose of the present study was to test the anticonvulsant effects of an essential fatty acid mixture containing linoleic and alpha-linolenic acids at a 4:1 ratio (SR-3 compound), using the pentylenetetrazol seizure model in Long-Evans hooded rats. RESULTS: There were no significant effects of SR-3 on seizure latency, duration or severity (P>0.05). There were also no significant differences in the incidence of myoclonic jerks, forelimb and hindlimb clonus, forelimb and hindlimb tonus or running fits in rats that received SR-3, as compared to control rats (P>0.05). CONCLUSION: Linoleic and alpha-linolenic polyunsaturated fatty acids have no beneficial effects on seizure latency, duration, average severity or incidence.

A comparison of the ability of a 4:1 ketogenic diet and a 6.3:1 ketogenic diet to elevate seizure thresholds in adult and young rats.

PURPOSE: The pentylenetetrazol (PTZ) infusion test was used to compare seizure thresholds in adult and young rats fed either a 4:1 ketogenic diet (KD) or a 6.3:1 KD. We hypothesized that both KDs would significantly elevate seizure thresholds and that the 4:1 KD would serve as a better model of the KD used clinically. METHODS: Ninety adult rats and 75 young rats were placed on one of five experimental diets: (a) a 4:1 KD, (b) a control diet balanced to the 4:1 KD, (c) a 6.3:1 KD, (d) a standard control diet, or (e) an ad libitum standard control diet. All subjects were seizure tested by using the PTZ infusion test. Blood glucose and beta-hydroxybutyrate (beta-OHB) levels were measured. RESULTS: Neither KD elevated absolute "latencies to seizure" in young or adult rats. Similarly, neither KD elevated "threshold doses" in adult rats. In young rats, the 6.3:1 KD, but not the 4:1 KD, significantly elevated threshold doses. The 6.3:1 KD group showed poorer weight gain than the 4:1 KD group when compared with respective controls. The most dramatic discrepancies were seen in young rats. CONCLUSIONS: "Threshold doses" and "latency to seizure" data provided conflicting measures of seizure threshold. This was likely due to the inflation of threshold doses calculated by using the much smaller body weights found in the 6.3:1 KD group. Ultimately, the PTZ infusion test in rats may not be a good preparation to model the anticonvulsant effects of the KD seen clinically, especially when dietary treatments lead to significantly mismatched body weights between the groups.

The antidepressant properties of the ketogenic diet.

BACKGROUND: The ketogenic diet is used to treat epilepsy refractory to anticonvulsant medication. Individuals with epilepsy often have behavioral problems and deficits in attention and cognitive functioning. The ketogenic diet has been found to effect improvements in these domains. It has also been suggested that the ketogenic diet may act as a mood stabilizer. METHODS: The present research used the Porsolt test, an animal model of depression, to determine whether the ketogenic diet has antidepressant properties. Porsolt test scores of rats on the ketogenic diet were compared with those of rats on a control diet. RESULTS: The rats on the ketogenic diet spent less time immobile, suggesting that rats on the ketogenic diet, like rats treated with antidepressants, are less likely to exhibit "behavioral despair." CONCLUSIONS: It is concluded that the ketogenic diet may have antidepressant properties.

Female advantage in speeded colour naming: a special naming factor or superior motor sequencing?

Women name colours more quickly than men do, and our recent research suggests that the female advantage for colour naming extends to speeded naming of shapes. The female advantage could reflect a superiority in producing and execuring the motor sequences underlying the required vocal response. Or, women could have faster access to or retrieval of colour labels. The present study tested these two possibilities by administering 3 speeded colour-naming tasks. In the first task, participants named a patch of colour as quickly as possible after it was presented. In the second task, participants made manual (instead of vocal) responses. In the third task, vocal responses were required but a randomly varying delay period was introduced between the presentation of the colour patch and the required response. Females reponded more quickly on the first task but there was no such advantage in the manual or delayed conditions. Taken together, these results suggest that the female advantage for speeded naming tasks reflects an advantage for sequencing movements rather than a special naming ability.

Differential regulation of hippocampal BDNF mRNA by typical and atypical antipsychotic administration.

Apart from their differential propensities to block dopamine D2 and serotonin 5-HT2 receptors, the molecular mechanisms underlying the clinical efficacy of typical and atypical antipsychotics in schizophrenia are largely unknown. Given recent interest in the effects of antipsychotics on neurotrophic and other growth related factors, the effects of antipsychotics on brain-derived neurotrophic factor (BDNF), a neurotrophin crucial to the structural integrity of adult neurons, were investigated in male Wistar rats. Chronic (19 day) but not acute (45 min) antipsychotic administration significantly altered levels of hippocampal BDNF mRNA. In addition, whereas chronic treatment with the strong D2 receptor-blocker haloperidol significantly downregulated hippocampal BDNF mRNA, the selective 5-HT2 receptor-blocker ritanserin significantly upregulated CA1 hippocampal BDNF mRNA in comparison to controls. Since high doses of risperidone and clozapine produce potent inhibition of both 5-HT2 and D2 receptors, while lower doses produce significantly greater 5-HT2 vs. D2 receptor blockade, a dose-response study was employed to determine whether low doses of these atypical antipsychotics would also upregulate hippocampal BDNF mRNA in the absence of significant D2 receptor blockade. Whereas chronic haloperidol and high-dose risperidone significantly downregulated hippocampal BDNF mRNA, intermediate and lower doses of risperidone and clozapine were, unlike ritanserin, without effect when compared to controls. Thus, although the long-term downregulation of hippocampal BDNF mRNA may underlie the different clinical profiles of certain antipsychotics, this effect seems to be associated with antipsychotic doses that not only cause significant D2 receptor inhibition, but are usually associated with side effects rather than therapeutic efficacies.