Bruce I. Turetsky, M.D. - US grants

The proposed studies will investigate regional brain disturbances in schizophrenia by examining event-related potential (ERP) indices of learning and memory in patients and normal controls. The focus on learning and memory is prompted by converging evidence that these functions are disproportionately impaired, and that neuroanatomic structures hypothetically linked to memory are abnormal, in schizophrenia. ERPs will be acquired while subjects engage in verbal and facial learning and recognition memory tasks. This will be done alone and in conjunction with ongoing 15-Oxygen PET Cerebral Blood Flow (CBF) studies, yielding simultaneous electrophysiologic and CBF measures of regional brain activation during the same tasks. Subjects will be 80 patients with schizophrenia and 80 normal controls, recruited and assessed using standard MHCRC procedures, ensuring socio- demographically balanced and well-categorized samples. There will be 40 men and 40 women in each group. The experimental dimensions to be examined are learning versus recognition memory, and verbal versus facial stimulus type. Electrophysiologic data will be recorded from each subject for all four of these cells. PET CBF activation data will be acquired simultaneously with ERPs, from half of the subjects, during the learning and recognition paradigms for one class of stimuli - either verbal or facial - in a counterbalanced design. The hypothesis is that ERP component(s) can be identified which represent physiologic indices of memory retrieval processes, and which differentiate recognition of familiar from unfamiliar stimuli. Verbal and facial stimuli are expected to asymmetrically affect homotopic left and right hemispheric regions, respectively, and to be discernible in topographic asymmetries of the ERP measures. Differences between patients and controls, in both absolute ERP measures and in the laterality of response to verbal and facial stimuli, will be examined. ERP measures will also be examined in relation to regionally-specific measures of activated CBF. It is hypothesized that abnormalities in laterality of the electrophysiologic response, in patients, will parallel abnormalities in laterality of activated CBF. Specifically, an association is expected between abnormal temporal lobe ERPs and reduced CBF activation in medial temporal lobe regions. The relationship of abnormal ERP indices to symptom severity, neuropsychological deficits and structural abnormalities, in patients will also be investigated.

DESCRIPTION: (Verbatim from the Applicant's Abstract) There is growing evidence to suggest that schizophrenia is a neurobehavioral disorder that affects fronto-temporal areas of the brain. A relatively neglected, but in many ways ideal, probe of the fronto-limbic system is olfaction. Olfactory processing is mediated by limbic structures implicated in the pathophysiology of schizophrenia. The olfactory system is unique in that only one synapse lies between peripheral receptors and sensory cortex, providing one of the most direct links between the brain and environment. Patients with schizophrenia have significant olfactory deficits. Unlike the relatively static pattern of cognitive deficits seen over the course of illness, though, olfactory abilities appear to decline in linear fashion, independent of normal aging and gender effects. However, family studies have also demonstrated marked deficits in olfactory identification in unaffected first-degree relatives of schizophrenic probands. It would seem, therefore, that olfactory brain regions are affected by genetically-mediated developmental, as well as neurodegenerative processes. In this project, we will investigate the physiological and anatomical correlates of olfactory dysfunction, longitudinally, in patients, siblings and controls. We will build on prior psychophysical work to include the integrated assessment of psychophysical, psychophysiological and volumetric measures of olfactory structure and function. We will study 40 patients with schizophrenia, 40- otherwise healthy siblings and 40 unrelated controls. Physiological data will be acquired using a unique and previously unavailable assessment tool, unilateral olfactory event-related potentials (ERPs), with high density electrode arrays and current source and dipole localization analytic methods. Psychophysical olfactory test data and volumetric MRI measurements of olfactory cortical regions and the olfactory bulbs and tracts will also be obtained. All testing will be repeated after a two-year interval, to assess any differential decline in olfactory abilities in the patietns, attributed to their disease state. The relationship of these olfactory measures to clinical, cognitive and affective symptoms will be investigated. Given the relevance of the neural substrate, we anticipate that a comprehensive assessment of olfactory integrity will illuminate important aspects of the neuropathology of schizophrenia and could be especially helpful in distinguishing developmental from degenerative aspects of the disorder.

DESCRIPTION: (Verbatim from the Applicant's Abstract) There is growing evidence to suggest that schizophrenia is a neurobehavioral disorder that affects fronto-temporal areas of the brain. A relatively neglected, but in many ways ideal, probe of the fronto-limbic system is olfaction. Olfactory processing is mediated by limbic structures implicated in the pathophysiology of schizophrenia. The olfactory system is unique in that only one synapse lies between peripheral receptors and sensory cortex, providing one of the most direct links between the brain and environment. Patients with schizophrenia have significant olfactory deficits. Unlike the relatively static pattern of cognitive deficits seen over the course of illness, though, olfactory abilities appear to decline in linear fashion, independent of normal aging and gender effects. However, family studies have also demonstrated marked deficits in olfactory identification in unaffected first-degree relatives of schizophrenic probands. It would seem, therefore, that olfactory brain regions are affected by genetically-mediated developmental, as well as neurodegenerative processes. In this project, we will investigate the physiological and anatomical correlates of olfactory dysfunction, longitudinally, in patients, siblings and controls. We will build on prior psychophysical work to include the integrated assessment of psychophysical, psychophysiological and volumetric measures of olfactory structure and function. We will study 40 patients with schizophrenia, 40- otherwise healthy siblings and 40 unrelated controls. Physiological data will be acquired using a unique and previously unavailable assessment tool, unilateral olfactory event-related potentials (ERPs), with high density electrode arrays and current source and dipole localization analytic methods. Psychophysical olfactory test data and volumetric MRI measurements of olfactory cortical regions and the olfactory bulbs and tracts will also be obtained. All testing will be repeated after a two-year interval, to assess any differential decline in olfactory abilities in the patietns, attributed to their disease state. The relationship of these olfactory measures to clinical, cognitive and affective symptoms will be investigated. Given the relevance of the neural substrate, we anticipate that a comprehensive assessment of olfactory integrity will illuminate important aspects of the neuropathology of schizophrenia and could be especially helpful in distinguishing developmental from degenerative aspects of the disorder.

DESCRIPTION (provided by applicant): There is growing evidence that schizophrenia is a neurodevelopmental disorder affecting frontal, temporal, and limbic areas of the brain. A relatively neglected, but in some respects ideal, probe of fronto-temporal limbic system physiology is olfaction. Studies have now demonstrated that patients with schizophrenia are impaired on psychophysical tests of odor identification and detection threshold sensitivity. Unlike their cognitive neuropsychological deficits, which are relatively static, patients' olfactory abilities appear to decline linearly over time. However, family studies have documented odor identification deficits in unaffected first-degree relatives of patients. This suggests that olfactory brain regions are affected by both neurodegenerative and genetically-mediated neurodevelopmental processes. This project represents the only systematic effort to characterize the olfactory deficits of schizophrenia in vivo from a neurobiological, rather than simply behavioral, perspective. Our efforts, to date, have established that 1) specific structural abnormalities exist in the brain regions subserving olfaction; 2) neurophysiological measures of early cortical sensory processing are disturbed; 3) similar structural and physiological deficits exist in first-degree relatives of patients; and 4) abnormalities appear to involve peripheral, as well as central, components of the olfactory system. In this application, we propose a more comprehensive assessment of structural and functional abnormalities of the olfactory system. We will study 40 patients with schizophrenia, 40 otherwise healthy family members, 40 unrelated healthy controls, and 40 bipolar patients with psychotic features as psychiatric controls. New methodologies will be employed to examine peripheral components of olfactory sensory processing, i.e., nasal cavity and associated peripheral olfactory receptor neurons (ORNs), in addition to olfactory cortex, in both patients and family members. Complete multifaceted assessments will be obtained for each individual, to allow us to delineate the inter-relationships among various measures of impairment, and to associate olfactory abnormalities with clinical and behavioral measures. Diagnostic specificity will be determined by comparing patients with schizophrenia (SCH) to patients with bipolar affective disorder with psychotic features (BPD). In a pilot phase, findings from this in vivo study will be integrated with the results of ongoing cellular and molecular studies that use ORN tissue biopsies obtained from these same subjects. Our working model is that olfactory deficits reflect genetically-mediated abnormalities in neuron-to-neuron connectivity, arisen from neurodevelopmentally disturbed processes of neurogenesis and synapse formation.

DESCRIPTION (provided by applicant): There is growing evidence that schizophrenia is a neurodevelopmental disorder affecting frontal, temporal, and limbic areas of the brain. A relatively neglected, but in some respects ideal, probe of fronto-temporal limbic system physiology is olfaction. Studies have now demonstrated that patients with schizophrenia are impaired on psychophysical tests of odor identification and detection threshold sensitivity. Unlike their cognitive neuropsychological deficits, which are relatively static, patients' olfactory abilities appear to decline linearly over time. However, family studies have documented odor identification deficits in unaffected first-degree relatives of patients. This suggests that olfactory brain regions are affected by both neurodegenerative and genetically-mediated neurodevelopmental processes. This project represents the only systematic effort to characterize the olfactory deficits of schizophrenia in vivo from a neurobiological, rather than simply behavioral, perspective. Our efforts, to date, have established that 1) specific structural abnormalities exist in the brain regions subserving olfaction; 2) neurophysiological measures of early cortical sensory processing are disturbed; 3) similar structural and physiological deficits exist in first-degree relatives of patients; and 4) abnormalities appear to involve peripheral, as well as central, components of the olfactory system. In this application, we propose a more comprehensive assessment of structural and functional abnormalities of the olfactory system. We will study 40 patients with schizophrenia, 40 otherwise healthy family members, 40 unrelated healthy controls, and 40 bipolar patients with psychotic features as psychiatric controls. New methodologies will be employed to examine peripheral components of olfactory sensory processing, i.e., nasal cavity and associated peripheral olfactory receptor neurons (ORNs), in addition to olfactory cortex, in both patients and family members. Complete multifaceted assessments will be obtained for each individual, to allow us to delineate the inter-relationships among various measures of impairment, and to associate olfactory abnormalities with clinical and behavioral measures. Diagnostic specificity will be determined by comparing patients with schizophrenia (SCH) to patients with bipolar affective disorder with psychotic features (BPD). In a pilot phase, findings from this in vivo study will be integrated with the results of ongoing cellular and molecular studies that use ORN tissue biopsies obtained from these same subjects. Our working model is that olfactory deficits reflect genetically-mediated abnormalities in neuron-to-neuron connectivity, arisen from neurodevelopmentally disturbed processes of neurogenesis and synapse formation.

[unreadable] DESCRIPTION (provided by applicant): Studies of the neuropathology of schizophrenia have documented a multitude of structural and functional brain abnormalities. The scope of these findings has been vast, and no single set of abnormalities has emerged as being characteristic of, or pathognomonic for, the disorder. However, a few specific themes have received enough empirical support to stand as potential models of the illness, and to offer testable hypotheses of the underlying pathophysiological mechanisms. Among the more robust of these are failures of appropriate neuronal inhibition & excitation and disturbed connectivity across cortical regions. Tests of these mechanisms in patients are limited by the practical constraints of in vivo clinical research and are, therefore, necessarily indirect and inferential. Recent developments in the use of transcranial magnetic stimulation (TMS) as a neurophysiological probe of cortical activity have suggested a means to test the functional integrity and responsivity of neural circuits in a more direct manner. By combining TMS with simultaneous multi-channel evoked potential (EP) recording, we believe that we can assess cortical inhibitory and facilitative mechanisms within localized brain areas, and the neural connectivity across brain regions. This is a novel methodology that has only been applied to a limited extent in the study of healthy individuals. It has been applied even less to the study of clinical populations. Early results, though, have been very promising, and further investigation of its applicability to the study of schizophrenia is clearly warranted. The goal of this project, therefore, is to establish the feasibility and utility of this methodology in the study of schizophrenia. Three experiments will be conducted, each in a sample of 16 schizophrenia patients and 16 healthy subjects. Experiment 1 will characterize the cortical evoked potential response to TMS stimulation, using a broad range of TMS pulse intensities. Experiment 2 will characterize intracortical inhibitory and facilitative mechanisms, using a paired- pulse design in which a suprathreshold TMS pulse is preceded by a subthreshold pulse at various inter-pulse intervals. Experiment 3 will assess regional differences in both the underlying TMS-evoked potential response, and the intracortical facilitation and inhibition of this response through single pulse and paired pulse stimulation of left and right frontal and temporal cortices. Patient-control differences in amplitude, latency and inter-cortical connectivity of the TMS-evoked response will be examined for all three experiments. PUBLIC HEALTH RELEVANCE Despite intensive investigation, the pathophysiology underlying schizophrenia remains unclear. This study will examine the utility of a novel methodology that combines transcranial magnetic stimulation with evoked potential response recording, to investigate the neural mechanisms of cortical inhibition, facilitation and connectivity in schizophrenia patients. This may help to clarify our understanding of the neuropathology of this debilitating disorder. [unreadable] [unreadable] [unreadable]

DESCRIPTION (provided by applicant): Among the sensory modalities, olfaction is most closely associated with the temporo-limbic and frontal regions most commonly implicated in schizophrenia pathology. Olfactory probes may therefore be ideal tools to assess the structural and functional integrity of these neural substrates. To the extent that peripheral sensory afferents are disrupted in schizophrenia, the olfactory system - owing to its strategic anatomic location - may also be especially vulnerable to disruption. So, olfactory dysfunction may be a sensitive indicator of schizophrenia pathology, and may even serve as an "early warning" sign of disease vulnerability or onset. In addition, since neurogenesis and neurodevelopment persist throughout life in the olfactory neuro-epithelium and the olfactory bulb (OB), probes of the olfactory system may provide insight into the neurobiological basis of aberrant neurodevelopment. This project, now in its eleventh year, represents one of the only systematic efforts to characterize schizophrenia olfactory deficits from a neurobiological, rather than a simply behavioral, perspective. Recent studies have identified specific abnormalities implicating abnormal G protein-mediated signal transduction in peripheral olfactory receptor neurons (ORNs) and altered synaptic connectivity between ORNs and olfactory bulb as specific neurodevelopmental mechanisms that may be disrupted. This renewal application proposes a unique in vivo - in vitro translational investigation of these abnormalities. Detailed behavioral and electrophysiological studies of the peripheral olfactory system, including both epithelial and primary sensory cortical responses, will be conducted in 35 adult schizophrenia patients, 35 adolescents with a genetic risk for schizophrenia, 35 clinical-risk adolescents with prodromal symptoms, and appropriate age- matched control groups. Olfactory epithelial biopsy tissue will be acquired from the schizophrenia patients and age-matched controls. As the only accessible source of regenerating neural cells, olfactory epithelial biopsy offers an unparalleled opportunity to directly assess neuronal integrity in a living human. The epithelial biopsy tissue, along with olfactory bulbs obtained from post-mortem material, will used to investigate the cellular and molecular mechanisms that underlie the dysregulations observed in vivo. A particular focus will be G protein- mediated intracellular signal transduction and ORN-OB synaptic connectivity. The overarching hypothesis is that olfactory deficits reflect genetically-mediated abnormalities in intracellular signaling and neuron-to-neuron connectivity, which arise from developmentally disturbed processes of neurogenesis and synapse formation. PUBLIC HEALTH RELEVANCE: Schizophrenia is a complex genetic disorder, with early developmental abnormalities in brain structure and function being important in determining vulnerability to illness. Among the different senses, olfaction is most closely associated with the brain regions implicated in the illness. Smell abnormalities may therefore be an "early warning sign" of disease onset. This study will examine changes in neural responses to odors in schizophrenia patients and adolescents who are at risk for the illness. The molecular causes of these abnormalities will be studied using both olfactory epithelial biopsies and post-mortem olfactory bulb tissue. This may provide important insights into the developmental causes of schizophrenia and facilitate early intervention or prevention.

DESCRIPTION (provided by applicant): Interventions early in the course of the illness could have an enormous impact on the public health costs and functional disability associated with schizophrenia. Early intervention requires a reliable method to identify young people who are at risk for developing psychosis. Youths with sub-psychotic or prodromal symptoms severe enough to prompt a clinical referral have a relatively high rate of conversion to psychosis. They often also exhibit subtle neurobiological and behavioral abnormalities, so-called endophenotypes, that are similar to those found in schizophrenia. These are thought to reflect the abnormal brain development that predisposes towards the illness. A judicious assessment of endophenotypes could, potentially, enhance the identification of individuals who are truly at risk for developing psychosis. To the extent that these developmental markers are evident before the impairment associated with sub-psychotic symptoms becomes obvious, they may also facilitate identification of at-risk youths at an earlier stage in the course of the prodrome. Research focusing on unaffected first-degree relatives of schizophrenia patients has identified many robust endophenotypes that are heritable, trait-like, and independent of overt illness. But these are also extremely poor predictors of future illness. This project will examine a set of neurobiological and behavioral markers that are likely to have more specific utility in predicting schizophrenia risk status. The rationale for this is based on two principles: 1)useful predictive measures should distinguish individuals with sub-psychotic clinical symptoms from unaffected first degree relatives without prodromal symptoms, who are unlikely to develop the illness~ 2) measures that can be mechanistically linked to a dysregulation of embryonic development during the critical late first - early second trimester risk period of fetal development should be more informative than relatively nonspecific indicators of compromised brain structure or function. It is proposed that measures of the neuronal integrity of the olfactory system represent just such specific risk markers. The olfactory system develops during this critical fetal risk perid in close coordination with development of the medial forebrain. It is intimately associated with the limbic brain regions commonly implicated in schizophrenia and is, itself, markedly impaired in schizophrenia. It can therefore illuminate early developmental contributions to heightened disease vulnerability. 35 patients with recent onset schizophrenia, 35 youths with a schizophrenia family member (genetic risk), 35 youths with prodromal symptoms (clinical risk), and 35 healthy comparison youths (low risk) will be studied. Behavioral tests will assess the integrity of olfactory capacity. 3T MR imaging and acoustic rhinometry will assess the structural integrity of the primary olfactory system. 7T 1HMR spectroscopy will assess the neuronal integrity of the primary olfactory system on a molecular level, through measurement of NAA and glutamate. The principal hypothesis is that schizophrenia patients and clinical-risk youths will both exhibit compromised olfactory neuronal integrity that distinguishes them from youths with isolated genetic risk or no risk for the illness.