Recovery from impaired working memory performance during chronic Δ-9-tetrahydrocannabinol administration to adolescent rhesus monkeys

BACKGROUND

The relationship between adolescent cannabis use and susceptibility to persistent cognitive impairments is poorly understood.

AIMS

We examined the effects of repeated exposure to Δ-9-tetrahydrocannabinol (THC) on reinforcement-related learning and performance of spatial working memory (WM) tasks of varying difficulty in adolescent monkeys.

METHODS

Seven pairs of male adolescent rhesus monkeys, matched for baseline cognitive performance, received vehicle or THC intravenously 5 days/week for 12 months. Performance on 4-item spatial WM trials was assessed throughout the 12-month study period. At the 6-month time point, more difficult novel and distractor 8-item spatial WM trials were added. Residual effects on performance were determined 23 or 71 h after THC or vehicle administration throughout the study.

RESULTS/OUTCOMES

Relative to vehicle-exposed animals, repeated THC exposure was initially associated with significantly slower improvement in performance accuracy on 4-item spatial WM trials; however, this performance difference gradually diminished such that by month 12, accuracy did not significantly differ between vehicle and THC groups. Similarly, for the novel and distractor 8-item trials introduced at month 6, performance accuracy improved more slowly in the THC than in the vehicle group, despite comparable performance between groups on the 4-item task during this same period.

CONCLUSIONS/INTERPRETATION

These findings suggest that compared to vehicle exposure, THC exposure during adolescence impairs the reinforcement-related learning process required for improved performance on spatial WM tasks, but this impairment might be overcome with continued training, even in the face of ongoing THC exposure.

Covariate adjusted classification trees

In studies that compare several diagnostic groups, subjects can be measured on certain features and classification trees can be used to identify which of them best characterize the differences among groups. However, subjects may also be measured on additional covariates whose ability to characterize group differences is not meaningful or of interest, but may still have an impact on the examined features. Therefore, it is important to adjust for the effects of covariates on these features. We present a new semi-parametric approach to adjust for covariate effects when constructing classification trees based on the features of interest that is readily implementable. An application is given for postmortem brain tissue data to compare the neurobiological characteristics of subjects with schizophrenia to those of normal controls. We also evaluate the performance of our approach using a simulation study.

Cortical GABA markers identify a molecular subtype of psychotic and bipolar disorders

BACKGROUND

Deficits in gamma aminobutyric acid (GABA) neuron-related markers, including the GABA-synthesizing enzyme GAD67, the calcium-binding protein parvalbumin, the neuropeptide somatostatin, and the transcription factor Lhx6, are most pronounced in a subset of schizophrenia subjects identified as having a 'low GABA marker' (LGM) molecular phenotype. Furthermore, schizophrenia shares degrees of genetic liability, clinical features and cortical circuitry abnormalities with schizoaffective disorder and bipolar disorder. Therefore, we determined the extent to which a similar LGM molecular phenotype may also exist in subjects with these disorders.

METHOD

Transcript levels for GAD67, parvalbumin, somatostatin, and Lhx6 were quantified using quantitative PCR in prefrontal cortex area 9 of 184 subjects with a diagnosis of schizophrenia (n = 39), schizoaffective disorder (n = 23) or bipolar disorder (n = 35), or with a confirmed absence of any psychiatric diagnoses (n = 87). A blinded clustering approach was employed to determine the presence of a LGM molecular phenotype across all subjects.

RESULTS

Approximately 49% of the subjects with schizophrenia, 48% of the subjects with schizoaffective disorder, and 29% of the subjects with bipolar disorder, but only 5% of unaffected subjects, clustered in the cortical LGM molecular phenotype.

CONCLUSIONS

These findings support the characterization of psychotic and bipolar disorders by cortical molecular phenotype which may help elucidate more pathophysiologically informed and personalized medications.

Optimal second-order product probability bounds

Let P(c) = P(X1 ≦ c1, · ··, Xp ≦ cp) for a random vector (X1, · ··, Xp). Bounds are considered of the form where T is a spanning tree corresponding to the bivariate probability structure and di is the degree of the vertex i in T. An optimized version of this inequality is obtained. The main result is that alwayṡ dominates certain second-order Bonferroni bounds. Conditions on the covariance matrix of a N(0,Σ) distribution are given so that this bound applies, and various applications are given.

A simultaneous characterization of the Poisson and bernoulli distributions

Let N, X1, X2, · ·· be non-constant independent random variables with X1, X2, · ·· being identically distributed and N being non-negative and integer-valued. It is shown that the independence of and implies that the Xi's have a Bernoulli distribution and N has a Poisson distribution. Other related characterization results are considered.

Dysregulated ErbB4 Splicing in Schizophrenia: Selective Effects on Parvalbumin Expression

OBJECTIVE

Alternative splicing of ErbB4 transcripts is dysregulated in the dorsolateral prefrontal cortex in schizophrenia. ErbB4 regulates the activity of parvalbumin interneurons, and therefore dysregulated ErbB4 splicing could contribute to lower parvalbumin interneuron activity and consequently lower parvalbumin levels in schizophrenia. However, ErbB4 is also present in calretinin interneurons, which are not affected in schizophrenia. Therefore, the authors hypothesized that dysregulated ErbB4 splicing occurs selectively in parvalbumin interneurons and is associated with lower parvalbumin levels in schizophrenia.

METHOD

Tissue samples enriched in calretinin and parvalbumin interneurons were laser microdissected from dorsolateral prefrontal cortex layers 2 and 4, respectively, from matched pairs of schizophrenia and comparison subjects. Transcript levels for pan-ErbB4, four ErbB4 splicing variants (JM-a, JM-b, CYT-1, CYT-2), parvalbumin, and calretinin were quantified by quantitative polymerase chain reaction (qPCR) in each layer. Transcript levels for myocardial infarction associated transcript (MIAT), which regulates ErbB4 splicing, were quantified in gray matter by qPCR and in parvalbumin interneurons by microarray.

RESULTS

Calretinin and parvalbumin mRNAs were preferentially expressed in layers 2 and 4, respectively. In schizophrenia subjects, lower parvalbumin levels, higher CYT-1 and JM-a levels, and lower CYT-2 and JM-b levels were detected selectively in layer 4. In layer 4, the JM-a/JM-b ratio was inversely correlated with parvalbumin levels in schizophrenia subjects. MIAT levels were preferentially higher in parvalbumin interneurons in schizophrenia subjects.

CONCLUSIONS

These findings suggest that elevated MIAT expression alters ErbB4 splicing selectively in parvalbumin interneurons in schizophrenia. Dysregulated ErbB4 splicing in schizophrenia may contribute to lower activity of parvalbumin interneurons and an activity-dependent down-regulation of parvalbumin expression.

Altered cortical expression of GABA-related genes in schizophrenia: illness progression vs developmental disturbance

BACKGROUND

Schizophrenia is a neurodevelopmental disorder with altered expression of GABA-related genes in the prefrontal cortex (PFC). However, whether these gene expression abnormalities reflect disturbances in postnatal developmental processes before clinical onset or arise as a consequence of clinical illness remains unclear.

METHODS

Expression levels for 7 GABA-related transcripts (vesicular GABA transporter [vGAT], GABA membrane transporter [GAT1], GABAA receptor subunit α1 [GABRA1] [novel in human and monkey cohorts], glutamic acid decarboxylase 67 [GAD67], parvalbumin, calretinin, and somatostatin [previously reported in human cohort, but not in monkey cohort]) were quantified in the PFC from 42 matched pairs of schizophrenia and comparison subjects and from 49 rhesus monkeys ranging in age from 1 week postnatal to adulthood.

RESULTS

Levels of vGAT and GABRA1, but not of GAT1, messenger RNAs (mRNAs) were lower in the PFC of the schizophrenia subjects. As previously reported, levels of GAD67, parvalbumin, and somatostatin, but not of calretinin, mRNAs were also lower in these subjects. Neither illness duration nor age accounted for the levels of the transcripts with altered expression in schizophrenia. In monkey PFC, developmental changes in expression levels of many of these transcripts were in the opposite direction of the changes observed in schizophrenia. For example, mRNA levels for vGAT, GABRA1, GAD67, and parvalbumin all increased with age.

CONCLUSIONS

Together with published reports, these findings support the interpretation that the altered expression of GABA-related transcripts in schizophrenia reflects a blunting of normal postnatal development changes, but they cannot exclude a decline during the early stages of clinical illness.

EM Estimation for Finite Mixture Models with Known Mixture Component Size

We consider the use of an EM algorithm for fitting finite mixture models when mixture component size is known. This situation can occur in a number of settings, where individual membership is unknown but aggregate membership is known. When the mixture component size, i.e., the aggregate mixture component membership, is known, it is common practice to treat only the mixing probability as known. This approach does not, however, entirely account for the fact that the number of observations within each mixture component is known, which may result in artificially incorrect estimates of parameters. By fully capitalizing on the available information, the proposed EM algorithm shows robustness to the choice of starting values and exhibits numerically stable convergence properties.

Functional Maturation of GABA Synapses During Postnatal Development of the Monkey Dorsolateral Prefrontal Cortex

Development of inhibition onto pyramidal cells may be crucial for the emergence of cortical network activity, including gamma oscillations. In primate dorsolateral prefrontal cortex (DLPFC), inhibitory synaptogenesis starts in utero and inhibitory synapse density reaches adult levels before birth. However, in DLPFC, the expression levels of γ-aminobutyric acid (GABA) synapse-related gene products changes markedly during development until young adult age, suggesting a highly protracted maturation of GABA synapse function. Therefore, we examined the development of GABA synapses by recording GABAAR-mediated inhibitory postsynaptic currents (GABAAR-IPSCs) from pyramidal cells in the DLPFC of neonatal, prepubertal, peripubertal, and adult macaque monkeys. We found that the decay of GABAAR-IPSCs, possibly including those from parvalbumin-positive GABA neurons, shortened by prepubertal age, while their amplitude increased until the peripubertal period. Interestingly, both GABAAR-mediated quantal response size, estimated by miniature GABAAR-IPSCs, and the density of GABAAR synaptic appositions, measured with immunofluorescence microscopy, were stable with age. Simulations in a computational model network with constant GABA synapse density showed that the developmental changes in GABAAR-IPSC properties had a significant impact on oscillatory activity and predicted that, whereas DLPFC circuits can generate gamma frequency oscillations by prepubertal age, mature levels of gamma band power are attained at late stages of development.

Repeated Δ9-tetrahydrocannabinol exposure in adolescent monkeys: persistent effects selective for spatial working memory

OBJECTIVE

Epidemiological findings suggest that, relative to adults, adolescents are more vulnerable to the adverse persistent effects of cannabis on working memory. However, the potential confounds inherent in human studies preclude direct determination of a cause-and-effect relationship between adolescent cannabis use and heightened susceptibility to persistent working memory impairments. Consequently, the authors examined the effects of repeated exposure to Δ9-tetrahydrocannabinol (THC) on performance of spatial and object working memory tasks in adolescent monkeys.

METHOD

Seven pairs of male adolescent rhesus monkeys, matched for baseline cognitive performance, received vehicle or THC intravenously 5 days/week for 6 months. Performance on spatial and object memory tasks was assessed 23 or 71 hours after drug administration throughout the study. In addition, acute effects on working memory were also assessed at the beginning and end of the 6-month period.

RESULTS

Relative to the vehicle-exposed control animals, those with repeated THC exposure had a blunted trajectory of accuracy improvements on the spatial working memory task in a delay-dependent manner. Accuracy improvements on the object working memory task did not differ between groups. Relative to the acute effects of THC on working memory at the beginning of the study, neither sensitivity nor tolerance was evident after 6 months of THC exposure.

CONCLUSIONS

Because maturation of performance is later for spatial than for object working memory, these findings suggest that persistent effects of THC on cognitive abilities are more evident when exposure coincides with the developmental stage during which the underlying neural circuits are actively maturing.

An adaptive two-stage dose-response design method for establishing proof of concept

We propose an adaptive two-stage dose-response design where a prespecified adaptation rule is used to add and/or drop treatment arms between the stages. We extend the multiple comparison procedures-modeling (MCP-Mod) approach into a two-stage design. In each stage, we use the same set of candidate dose-response models and test for a dose-response relationship or proof of concept (PoC) via model-associated statistics. The stage-wise test results are then combined to establish "global" PoC using a conditional error function. Our simulation studies showed good and more robust power in our design method compared to conventional and fixed designs.

A model for repeated clustered data with informative cluster sizes

Many chronic diseases or health conditions manifest with recurring episodes, each of which can be characterized by a measure of intensity or severity. Both the number of episodes and the severity of each episode can depend on the latent severity of an individual's underlying condition. Data such as this are commonly gathered repeatedly at fixed follow-up intervals. An example is a study of the association between stressful life events and the onset of depression. Stress exposure is assessed through the frequency and intensity of stressful life events occurring each month. Both the number of events and the intensity of each event at each measurement occasion are informative about the underlying severity of stress over time. One might hypothesize that people that approach the onset of a depressive episode have worse stress profiles than the controls, reflected by both more frequent and more intense stressors. We propose models to analyze data collected repeatedly on both the frequency of an event and its severity when both of these are informative about the underlying latent severity. Maximum likelihood estimators are developed, and simulations with small to moderate sample sizes show that the estimators also have good finite sample properties, and they are robust against misspecification of the model. This method is applied to a psychiatric data set.

Intracortical excitatory and thalamocortical boutons are intact in primary auditory cortex in schizophrenia

Schizophrenia is associated with auditory processing impairments that could arise as a result of primary auditory cortex excitatory circuit pathology. We have previously reported a deficit in dendritic spine density in deep layer 3 of primary auditory cortex in subjects with schizophrenia. As boutons and spines can be structurally and functionally co-regulated, we asked whether the densities of intracortical excitatory or thalamocortical presynaptic boutons are also reduced. We studied 2 cohorts of subjects with schizophrenia and matched controls, comprising 27 subject pairs, and assessed the density, number, and within-bouton vesicular glutamate transporter (VGluT) protein level of intracortical excitatory (VGluT1-immunoreactive) and thalamocortical (VGluT2-immunoreactive) boutons in deep layer 3 of primary auditory cortex using quantitative confocal microscopy and stereologic sampling methods. We found that VGluT1- and VGluT2-immunoreactive puncta densities and numbers were not altered in deep layer 3 of primary auditory cortex of subjects with schizophrenia. Our results indicate that reduced dendritic spine density in primary auditory cortex of subjects with schizophrenia is not matched by a corresponding reduction in excitatory bouton density. This suggests excitatory boutons in primary auditory cortex in schizophrenia may synapse with structures other than spines, such as dendritic shafts, with greater frequency. The discrepancy between dendritic spine reduction and excitatory bouton preservation may contribute to functional impairments of the primary auditory cortex in subjects with schizophrenia.

Adjusting for matching and covariates in linear discriminant analysis

In studies that compare several diagnostic or treatment groups, subjects may not only be measured on a certain set of feature variables, but also be matched on a number of demographic characteristics and measured on additional covariates. Linear discriminant analysis (LDA) is sometimes used to identify which feature variables best discriminate among groups, while accounting for the dependencies among the feature variables. We present a new approach to LDA for multivariate normal data that accounts for the subject matching used in a particular study design, as well as covariates not used in the matching. Applications are given for post-mortem tissue data with the aim of comparing neurobiological characteristics of subjects with schizophrenia with those of normal controls, and for a post-mortem tissue primate study comparing brain biomarker measurements across three treatment groups. We also investigate the performance of our approach using a simulation study.

Delay- and dose-dependent effects of Δ⁹-tetrahydrocannabinol administration on spatial and object working memory tasks in adolescent rhesus monkeys

Among adolescents, the perception that cannabis can cause harm has decreased and use has increased. However, in rodents, cannabinoid administration during adolescence induces working memory (WM) deficits that are more severe than if the same exposure occurs during adulthood. As both object and spatial WM mature in a protracted manner, although apparently along different trajectories, adolescent cannabis users may be more susceptible to impairments in one type of WM. Here, we evaluate the acute effects of a range of doses (30-240 μg/kg) of intravenous Δ⁹-tetrahydrocannabinol (THC) administration on the performance of spatial and object WM tasks in adolescent rhesus monkeys. Accuracy on the object WM task was not significantly affected by any dose of THC. In contrast, THC administration impaired accuracy on the spatial WM task in a delay- and dose-dependent manner. Importantly, the THC-induced spatial WM deficits were not because of motor or motivational impairments. These data support the idea that immature cognitive functions are more sensitive to the acute effects of THC.

Expected loss functions as additional measures to assess performance of multiple testing procedures for combination drug dose finding

There are several measures that are commonly used to assess performance of a multiple testing procedure (MTP). These measures include power, overall error rate (family-wise error rate), and lack of power. In settings where the MTP is used to estimate a parameter, for example, the minimum effective dose, bias is of interest. In some studies, the parameter has a set-like structure, and thus, bias is not well defined. Nevertheless, the accuracy of estimation is one of the essential features of an MTP in such a context. In this paper, we propose several measures based on the expected values of loss functions that resemble bias. These measures are constructed to be useful in combination drug dose response studies when the target is to identify all minimum efficacious drug combinations. One of the proposed measures allows for assigning different penalties for incorrectly overestimating and underestimating a true minimum efficacious combination. Several simple examples are considered to illustrate the proposed loss functions. Then, the expected values of these loss functions are used in a simulation study to identify the best procedure among several methods used to select the minimum efficacious combinations, where the measures take into account the investigator's preferences about possibly overestimating and/or underestimating a true minimum efficacious combination. The ideas presented in this paper can be generalized to construct measures that resemble bias in other settings. These measures can serve as an essential tool to assess performance of several methods for identifying set-like parameters in terms of accuracy of estimation.

Simultaneous confidence bands for comparisons to placebo, with application to detecting the minimum effective dose

In this article we consider a max-min approach to construct two-sided and one-sided simultaneous confidence bands in a dose-response study for the contrast in mean responses of each ascending dose versus placebo. The method utilizes the assumption of monotone non-decreasing dose-response curve. Also discussed is a step-down testing procedure that utilizes the lower bands to estimate the minimum effective dose (MED). The performance of our proposed step-down procedure is assessed by simulations and is shown to be superior to competitors when the MED is the lowest dose in a dose-response study.

Increased expression of Kalirin-9 in the auditory cortex of schizophrenia subjects: its role in dendritic pathology

Reductions in dendritic arbor length and complexity are among the most consistently replicated changes in neuronal structure in post mortem studies of cerebral cortical samples from subjects with schizophrenia, however, the underlying molecular mechanisms have not been identified. This study is the first to identify an alteration in a regulatory protein which is known to promote both dendritic length and arborization in developing neurons, Kalirin-9. We found Kalirin-9 expression to be paradoxically increased in schizophrenia. We followed up this observation by overexpressing Kalirin-9 in mature primary neuronal cultures, causing reduced dendritic length and complexity. Kalirin-9 overexpression represents a potential mechanism for dendritic changes seen in schizophrenia.

Cortical deficits of glutamic acid decarboxylase 67 expression in schizophrenia: clinical, protein, and cell type-specific features

OBJECTIVE

Cognitive deficits in schizophrenia are associated with altered activity of the dorsolateral prefrontal cortex, which has been attributed to lower expression of the 67 kDa isoform of glutamic acid decarboxylase (GAD67), the major γ-aminobutyric acid (GABA)-synthesizing enzyme. However, little is known about the relationship of prefrontal GAD67 mRNA levels and illness severity, translation of the transcript into protein, and protein levels in axon terminals, the key site of GABA production and function.

METHOD

Quantitative polymerase chain reaction was used to measure GAD67 mRNA levels in postmortem specimens of dorsolateral prefrontal cortex from subjects with schizophrenia and matched comparison subjects with no known history of psychiatric or neurological disorders (N=42 pairs). In a subset of this cohort in which potential confounds of protein measures were controlled (N=19 pairs), Western blotting was used to quantify tissue levels of GAD67 protein in tissue. In five of these pairs, multilabel confocal immunofluorescence was used to quantify GAD67 protein levels in the axon terminals of parvalbumin-containing GABA neurons, which are known to have low levels of GAD67 mRNA in schizophrenia.

RESULTS

GAD67 mRNA levels were significantly lower in schizophrenia subjects (by 15%), but transcript levels were not associated with predictors or measures of illness severity or chronicity. In schizophrenia subjects, GAD67 protein levels were significantly lower in total gray matter (by 10%) and in parvalbumin axon terminals (by 49%).

CONCLUSIONS

The findings that lower GAD67 mRNA expression is common in schizophrenia, that it is not a consequence of having the illness, and that it leads to less translation of the protein, especially in the axon terminals of parvalbumin-containing neurons, support the hypothesis that lower GABA synthesis in parvalbumin neurons contributes to dorsolateral prefrontal cortex dysfunction and impaired cognition in schizophrenia.

Acquisition and baseline performance of working memory tasks by adolescent rhesus monkeys

Adolescence is a transitional stage of development characterized by protracted refinements in the neural circuits required for adult level proficiency of working memory. Because impaired working memory is a hallmark feature of several psychiatric disorders that have their onset during adolescence, model systems that can be used to assess the maturation of working memory function, and of disease-related risk factors that disrupt its development, are of particular importance. However, few studies have investigated the maturation of working memory in nonhuman primates. Thus in the present study, we adapted two working memory tests that are among the most widely used in human and adult nonhuman primates, for adolescent rhesus monkeys. Using a touch-screen apparatus, monkeys were trained on a spatial delayed-response task to assess spatial working memory and a delayed match-to-sample task to assess object working memory. The results indicate that adolescent rhesus monkeys readily and efficiently acquire the ability to perform touch-screen based, complex tests of working memory. These data establish that distinct components of adult prefrontal cortex-dependent cognitive functions can be effectively modeled and evaluated in adolescent monkeys. As such, this approach should be useful for assessing the influence of environmental risk factors on the protracted maturation of working memory in adolescent macaques.

Ultrastructural localization of high-affinity choline transporter in the rat anteroventral thalamus and ventral tegmental area: differences in axon morphology and transporter distribution

The high-affinity choline transporter (CHT) is a protein integral to the function of cholinergic neurons in the central nervous system (CNS). We examined the ultrastructural distribution of CHT in axonal arborizations of the mesopontine tegmental cholinergic neurons, a cell group in which CHT expression has yet to be characterized at the electron microscopic level. By using silver-enhanced immunogold detection, we compared the morphological characteristics of CHT-immunoreactive axon varicosities specifically within the anteroventral thalamus (AVN) and the ventral tegmental area (VTA). We found that CHT-immunoreactive axon varicosities in the AVN displayed a smaller cross-sectional area and a lower frequency of synapse formation and dense-cored vesicle content than CHT-labeled profiles in the VTA. We further examined the subcellular distribution of CHT and observed that immunoreactivity for this protein was predominantly localized to synaptic vesicles and minimally to the plasma membrane of axons in both regions. This pattern is consistent with the subcellular distribution of CHT displayed in other cholinergic systems. Axons in the AVN showed significantly higher levels of CHT immunoreactivity than those in the VTA and correspondingly displayed a higher level of membrane CHT labeling. These novel findings have important implications for elucidating regional differences in cholinergic signaling within the thalamic and brainstem targets of the mesopontine cholinergic system.

On Identifying Minimum Efficacious Doses in Combination Drug Trials

To determine that a combination drug is effective, the FDA requires demonstration that the combination itself is effective and that each component makes a contribution to the claimed effect. In a study with at least one component known to be effective at the considered doses, these regulatory requirements can be satisfied by showing that the combination is superior to each component. We term such a combination an efficacious combination. In a dose-response study involving combination drugs, one of which is known to be effective, we are interested in detecting those combinations which are efficacious, and for which no lower dose combination is also efficacious. We term these combinations the minimum efficacious dose set and our goal is to estimate this set. Our procedure requires first identifying all possible minimum efficacious dose sets and the corresponding hypotheses for a given design. Next, the proper testing order based on a graph representation is established and the hypotheses are tested using the "average" test under the closed testing principle. This procedure is shown to have strong control of overall error rate. The power of this procedure is studied by simulation.

Mixture modeling with applications in schizophrenia research

Finite mixture modeling, together with the EM algorithm, have been widely used in clustering analysis. Under such methods, the unknown group membership is usually treated as missing data. When the "complete data" (log-)likelihood function does not have an explicit solution, the simplicity of the EM algorithm breaks down. Authors, including Rai and Matthews (1993), Lange (1995a) and Titterington (1984), developed modified algorithms therefore. As motivated by research in a large neurobiological project, we propose in this paper a new variant of such modifications and show that it is self-consistent. Moreover, simulations are conducted to demonstrate that the new variant converges faster than its predecessors.

Volume and neuron number of the lateral geniculate nucleus in schizophrenia and mood disorders

Subjects with schizophrenia show deficits in visual perception that suggest changes predominantly in the magnocellular pathway and/or the dorsal visual stream important for visiospatial perception. We previously found a substantial 25% reduction in neuron number of the primary visual cortex (Brodmann's area 17, BA17) in postmortem tissue from subjects with schizophrenia. Also, many studies have found reduced volume and neuron number of the pulvinar--the large thalamic association nucleus involved in higher-order visual processing. Here, we investigate if the lateral geniculate nucleus (LGN), the visual relay nucleus of the thalamus, has structural changes in schizophrenia. We used stereological methods based on unbiased principles of sampling (Cavalieri's principle and the optical fractionator) to estimate the total volume and neuron number of the magno- and parovocellular parts of the left LGN in postmortem brains from nine subjects with schizophrenia, seven matched normal comparison subjects and 13 subjects with mood disorders. No significant schizophrenia-related structural differences in volume or neuron number of the left LGN or its major subregions were found, but we did observe a significantly increased total volume of the LGN, and of the parvocellular lamina and interlaminar regions, in the mood group. These findings do not support the hypothesis that subjects with schizophrenia have structural changes in the LGN. Therefore, our previous observation of a schizophrenia-related reduction of the primary visual cortex is probably not secondary to a reduction in the LGN.

Fully automated common carotid artery and internal jugular vein identification and tracking using B-mode ultrasound

We describe a fully automated ultrasound analysis system that tracks and identifies the common carotid artery (CCA) and the internal jugular vein (IJV). Our goal is to prevent inadvertent damage to the CCA when targeting the IJV for catheterization. The automated system starts by identifying and fitting ellipses to all the regions that look like major arteries or veins throughout each B-mode ultrasound image frame. The spokes ellipse algorithm described in this paper tracks these putative vessels and calculates their characteristics, which are then weighted and summed to identify the vessels. The optimum subset of characteristics and their weights were determined from a training set of 38 subjects, whose necks were scanned with a portable 10 MHz ultrasound system at 10 frames per second. Stepwise linear discriminant analysis (LDA) narrowed the characteristics to the five that best distinguish between the CCA and IJV. A paired version of Fisher's LDA was used to calculate the weights for each of the five parameters. Leave-one-out validation studies showed that the system could track and identify the CCA and IJV with 100% accuracy in this dataset.

Drop-the-Losers Design: Binomial Case

Drop-the-losers designs were introduced for normal distributions as a method of combining phase II and III clinical trials together under a single protocol with the purpose of more rapidly evaluating drugs by eliminating as much as possible the delays that typically occur between the two phases of clinical development. In the design, the sponsor would administer k treatments along with a control in the first stage. During a brief interim period, efficacy data would be used to select the best treatment (with a rule to deal with ties) for further evaluation against the control in a second stage. At the end of the study, data from both stages would be used to draw inferences about the selected treatment relative to the control with adjustments made for selection in between the two stages. Because the inferences are model based, exact confidence intervals can be determined for the parameter of interest. In the present case, the parameter of concern is the probability of a beneficial response that is dichotomous in nature.

Reduced dendritic spine density in auditory cortex of subjects with schizophrenia

We have previously identified reductions in mean pyramidal cell somal volume in deep layer 3 of BA 41 and 42 and reduced axon terminal density in deep layer 3 of BA 41. In other brain regions demonstrating similar deficits, reduced dendritic spine density has also been identified, leading us to hypothesize that dendritic spine density would also be reduced in BA 41 and 42. Because dendritic spines and their excitatory inputs are regulated in tandem, we further hypothesized that spine density would be correlated with axon terminal density. We used stereologic methods to quantify a marker of dendritic spines, spinophilin-immunoreactive (SP-IR) puncta, in deep layer 3 of BA 41 and 42 of 15 subjects with schizophrenia, each matched to a normal comparison subject. The effect of long-term haloperidol exposure on SP-IR puncta density was evaluated in nonhuman primates. SP-IR puncta density was significantly lower by 27.2% in deep layer 3 of BA 41 in the schizophrenia subjects, and by 22.2% in deep layer 3 of BA 42. In both BA 41 and 42, SP-IR puncta density was correlated with a marker of axon terminal density, but not with pyramidal cell somal volume. SP-IR puncta density did not differ between haloperidol-exposed and control monkeys. Lower SP-IR puncta density in deep layer 3 of BA 41 and 42 of subjects with schizophrenia may reflect concurrent reductions in excitatory afferent input. This may contribute to impairments in auditory sensory processing that are present in subjects with schizophrenia.

Effect of chronic antipsychotic exposure on astrocyte and oligodendrocyte numbers in macaque monkeys

BACKGROUND

Both in vivo and postmortem studies suggest that oligodendrocyte and myelination alterations are present in individuals with schizophrenia. However, it is unclear whether prolonged treatment with antipsychotic medications contributes to these disturbances. We recently reported that chronic exposure of macaque monkeys to haloperidol or olanzapine was associated with a 10%-18% lower glial cell number in the parietal grey matter. Consequently, in this study we sought to determine whether the lower glial cell number was due to fewer oligodendrocytes as opposed to lower numbers of astrocytes.

METHODS

With fluorescent immunocytochemical techniques, we optimized the visualization of each cell type throughout the entire thickness of tissue sections, while minimizing final tissue shrinkage. As a result, we were able to obtain robust stereological estimates of total oligodendrocyte and astrocyte numbers in the parietal grey matter with the optical fractionator method.

RESULTS

We found a significant 20.5% lower astrocyte number with a non-significant 12.9% lower oligodendrocyte number in the antipsychotic-exposed monkeys. Similar effects were seen in both the haloperidol and olanzapine groups.

CONCLUSIONS

These findings suggest that studies investigating glial cell alterations in schizophrenia must take into account the effect of antipsychotic treatment.

Conserved regional patterns of GABA-related transcript expression in the neocortex of subjects with schizophrenia

OBJECTIVE

Individuals with schizophrenia exhibit disturbances in a number of cognitive, affective, sensory, and motor functions that depend on the circuitry of different cortical areas. The cognitive deficits associated with dysfunction of the dorsolateral prefrontal cortex result, at least in part, from abnormalities in GABA neurotransmission, as reflected in a specific pattern of altered expression of GABA-related genes. Consequently, the authors sought to determine whether this pattern of altered gene expression is restricted to the dorsolateral prefrontal cortex or could also contribute to the dysfunction of other cortical areas in subjects with schizophrenia.

METHOD

Real-time quantitative polymerase chain reaction was used to assess the levels of eight GABA-related transcripts in four cortical areas (dorsolateral prefrontal cortex, anterior cingulate cortex, and primary motor and primary visual cortices) of subjects (N=12) with schizophrenia and matched normal comparison subjects.

RESULTS

Expression levels of seven transcripts were lower in subjects with schizophrenia, with the magnitude of reduction for each transcript comparable across the four areas. The largest reductions were detected for mRNA encoding somatostatin and parvalbumin, followed by moderate decreases in mRNA expression for the 67-kilodalton isoform of glutamic acid decarboxylase, the GABA membrane transporter GAT-1, and the alpha 1 and delta subunits of GABA(A) receptors. In contrast, the expression of calretinin mRNA did not differ between the subject groups in any of the four areas.

CONCLUSIONS

Because the areas examined represent the major functional domains (e.g., association, limbic, motor, and sensory) of the cerebral cortex, our findings suggest that a conserved set of molecular alterations affecting GABA neurotransmission contribute to the pathophysiology of different clinical features of schizophrenia.

Evidence of temporal cortical dysfunction in rhesus monkeys following chronic cocaine self-administration

Cocaine abusers show impaired performance on cognitive tasks that engage prefrontal cortex. These deficits may contribute to impaired control and relapse in abusers. Understanding the neuronal substrates that lead to these deficits requires animal models that are relevant to the human condition. However, to date, models have mostly focused on behaviors mediated by subcortical systems. Here we evaluated the impact of long-term self-administration of cocaine in the rhesus monkey on cognitive performance. Tests included stimulus discrimination (SD)/reversal and delayed alternation tasks. The chronic cocaine animals showed marked deficits in ability to organize their behavior for maximal reward. This was demonstrated by an increased time needed to acquire SDs. Deficits were also indicated by an increased time to initially learn the delayed alternation task, and to adapt strategies for bypassing a reliance on working memory to respond accurately. Working memory per se (delay dependent performance) was not affected by chronic self-administration. This pattern of cognitive deficits suggests dysfunction that extends beyond localized prefrontal cortical areas. In particular, it appears that temporal cortical function is also compromised. This agrees with other recent clinical and preclinical findings, and suggests further study into addiction related dysfunction across more widespread cortical networks is warranted.

Multivariate bernoulli mixture models with application to postmortem tissue studies in schizophrenia

A novel mixture model is presented for repeated measurements in which correlation among repeated observations on the same subject is induced via correlated unobservable component indicators. The mixture components in our model are linear regressions, and the mixing proportions are logits with random effects. Inference is facilitated by sampling from the posterior distribution of the parameters via Markov chain Monte Carlo methods. The model is applied to a neuronal postmortem brain tissue study to examine the differences in neuron volumes between schizophrenic and control subjects.

Effect of chronic exposure to antipsychotic medication on cell numbers in the parietal cortex of macaque monkeys

Both in vivo and post-mortem investigations have demonstrated smaller volumes of the whole brain and of certain brain regions in individuals with schizophrenia. It is unclear to what degree such smaller volumes are due to the illness or to the effects of antipsychotic medication treatment. Indeed, we recently reported that chronic exposure of macaque monkeys to haloperidol or olanzapine, at doses producing plasma levels in the therapeutic range in schizophrenia subjects, was associated with significantly smaller total brain weight and volume, including an 11.8-15.2% smaller gray matter volume in the left parietal lobe. Consequently, in this study we sought to determine whether these smaller volumes were associated with lower numbers of the gray matter's constituent cellular elements. The use of point counting and Cavalieri's principle on Nissl-stained sections confirmed a 14.6% smaller gray matter volume in the left parietal lobe from antipsychotic-exposed monkeys. Use of the optical fractionator method to estimate the number of each cell type in the gray matter revealed a significant 14.2% lower glial cell number with a concomitant 10.2% higher neuron density. The numbers of neurons and endothelial cells did not differ between groups. Together, the findings of smaller gray matter volume, lower glial cell number, and higher neuron density without a difference in total neuron number in antipsychotic-exposed monkeys parallel the results of post-mortem schizophrenia studies, and raise the possibility that such observations in schizophrenia subjects might be due, at least in part, to antipsychotic medication effects.

Anatomical evidence of impaired feedforward auditory processing in schizophrenia

BACKGROUND

Somal volumes of pyramidal cells are reduced within feedforward but not feedback circuits in areas 41 and 42 of the auditory cortex of subjects with schizophrenia. Because neuronal somal volume depends on both the number of axonal terminations onto and furnished by the neuron, we hypothesized that axon terminal densities are reduced in feedforward but not feedback auditory pathways in subjects with schizophrenia.

METHODS

We used stereologic methods to quantify the density of a marker of axon terminals, synaptophysin-immunoreactive (SY-IR) puncta, in areas 41 and 42 of 15 subjects with schizophrenia and matched normal comparison subjects. The effect of long-term haloperidol exposure on density of SY-IR puncta was similarly evaluated in nonhuman primates.

RESULTS

Synaptophysin-immunoreactive puncta density was 13.6% lower in deep layer 3 of area 41 in the schizophrenia subjects but was not changed in layer 1 of area 41 or in deep layer 3 of area 42. Density of SY-IR puncta did not differ between haloperidol-exposed and control monkeys.

CONCLUSIONS

Reduction of SY-IR puncta density is selective for feedforward circuits within primary auditory cortex of subjects with schizophrenia. This deficit may contribute to impairments in auditory sensory processing in this disorder.

Primary visual cortex volume and total neuron number are reduced in schizophrenia

A number of studies that assessed the visual system in subjects with schizophrenia found impairments in early visual processing. Furthermore, functional imaging studies suggested changes in primary visual cortex activity in subjects with schizophrenia. Interestingly, postmortem studies of subjects with schizophrenia reported an increased density of neurons in the primary visual cortex (Brodmann's area 17, BA17). The observed changes in visual processing may thus be reflected in structural changes in the circuitry of BA17. To characterize the structural changes further we used stereological methods based on unbiased principles of sampling (Cavalieri's principle and the optical fractionator) to estimate the total volume and neuron number of BA17 in postmortem brains from 10 subjects with schizophrenia and 10 matched normal comparison subjects. In addition, we assessed cortical thickness. We found a marked and significant reduction in total neuron number (25%) and volume (22%) of BA17 in the schizophrenia group relative to the normal comparison subjects. In contrast, we found no changes in neuronal density or cortical thickness between the two groups. Subjects with schizophrenia therefore have a smaller cortical area allocated to primary visual perception. This finding suggests the existence of a schizophrenia-related change in cortical parcellation.

Somal size of immunolabeled pyramidal cells in the prefrontal cortex of subjects with schizophrenia

BACKGROUND

Although the somal volume of Nissl-stained deep layer 3 pyramidal cells is reduced in prefrontal cortex area 9 of subjects with schizophrenia, the subset of large pyramidal cells immunoreactive (IR) for nonphosphorylated neurofilament protein (NNFP) is not. Consequently, we hypothesized that the somal volume of another subset of pyramidal cells immunoreactive for neuronal calcium binding protein-1 (Necab-1) is significantly reduced in schizophrenia.

METHODS

We labeled Necab-1-IR pyramidal neurons using immunoperoxidase techniques and estimated the mean somal volume in deep layer 3 of area 9 in 13 matched pairs of control and schizophrenic subjects. Identical studies were conducted for pyramidal neurons immunoreactive for neuronal nuclear protein (Neu-N), which is present in all neurons.

RESULTS

In subjects with schizophrenia, neither the mean somal volume of Necab-1-IR pyramidal neurons nor of Neu-N-IR pyramidal neurons was significantly different from control subjects. In addition, the mean somal volume of Neu-N-IR cells was larger than that of Nissl-stained cells in both subject groups, and the magnitude of this difference was greater for the subjects with schizophrenia.

CONCLUSIONS

These findings suggest that immunoperoxidase techniques are associated with an overestimation of the volume of labeled neurons. This confound appears to interact with disease state, and thus obscures differences between diagnostic groups.

Selective elimination of glutamatergic synapses on striatopallidal neurons in Parkinson disease models

Parkinson disease is a common neurodegenerative disorder that leads to difficulty in effectively translating thought into action. Although it is known that dopaminergic neurons that innervate the striatum die in Parkinson disease, it is not clear how this loss leads to symptoms. Recent work has implicated striatopallidal medium spiny neurons (MSNs) in this process, but how and precisely why these neurons change is not clear. Using multiphoton imaging, we show that dopamine depletion leads to a rapid and profound loss of spines and glutamatergic synapses on striatopallidal MSNs but not on neighboring striatonigral MSNs. This loss of connectivity is triggered by a new mechanism-dysregulation of intraspine Cav1.3 L-type Ca(2+) channels. The disconnection of striatopallidal neurons from motor command structures is likely to be a key step in the emergence of pathological activity that is responsible for symptoms in Parkinson disease.

The influence of chronic exposure to antipsychotic medications on brain size before and after tissue fixation: a comparison of haloperidol and olanzapine in macaque monkeys

It is unclear to what degree antipsychotic therapy confounds longitudinal imaging studies and post-mortem studies of subjects with schizophrenia. To investigate this problem, we developed a non-human primate model of chronic antipsychotic exposure. Three groups of six macaque monkeys each were exposed to oral haloperidol, olanzapine or sham for a 17-27 month period. The resulting plasma drug levels were comparable to those seen in subjects with schizophrenia treated with these medications. After the exposure, we observed an 8-11% reduction in mean fresh brain weights as well as left cerebrum fresh weights and volumes in both drug-treated groups compared to sham animals. The differences were observed across all major brain regions (frontal, parietal, temporal, occipital, and cerebellum), but appeared most robust in the frontal and parietal regions. Stereological analysis of the parietal region using Cavalieri's principle revealed similar volume reductions in both gray and white matter. In addition, we assessed the subsequent tissue shrinkage due to standard histological processing and found no evidence of differential shrinkage due to drug exposure. However, we observed a pronounced general shrinkage effect of approximately 20% and a highly significant variation in shrinkage across brain regions. In conclusion, chronic exposure of non-human primates to antipsychotics was associated with reduced brain volume. Antipsychotic medication may confound post-mortem studies and longitudinal imaging studies of subjects with schizophrenia that depend upon volumetric measures.

Relationship of brain-derived neurotrophic factor and its receptor TrkB to altered inhibitory prefrontal circuitry in schizophrenia

Dysfunction of inhibitory neurons in the prefrontal cortex (PFC), represented by decreased expression of GABA-related genes such as the 67 kDa isoform of glutamate decarboxylase (GAD67) and parvalbumin (PV), appears to contribute to cognitive deficits in subjects with schizophrenia. We investigated the involvement of signaling mediated by brain-derived neurotrophic factor (BDNF) and its receptor tyrosine kinase TrkB in producing the altered GABA-related gene expression in schizophrenia. In 15 pairs of subjects with schizophrenia and matched control subjects, both BDNF and TrkB mRNA levels, as assessed by in situ hybridization, were significantly decreased in the PFC of the subjects with schizophrenia, whereas the levels of mRNA encoding the receptor tyrosine kinase for neurotrophin-3, TrkC, were unchanged. In this cohort, within-pair changes in TrkB mRNA levels were significantly correlated with those in both GAD67 and PV mRNA levels. Decreased BDNF, TrkB, and GAD67 mRNA levels were replicated in a second cohort of 12 subject pairs. In the combined cohorts, the correlation between within-pair changes in TrkB and GAD67 mRNA levels was significantly stronger than the correlation between the changes in BDNF and GAD67 mRNA levels. Neither BDNF nor TrkB mRNA levels were changed in the PFC of monkeys after a long-term exposure to haloperidol. Genetically introduced decreases in TrkB expression, but not in BDNF expression, also resulted in decreased GAD67 and PV mRNA levels in the PFC of adult mice; in addition, the cellular pattern of altered GAD67 mRNA expression paralleled that present in schizophrenia. Decreased TrkB signaling appears to underlie the dysfunction of inhibitory neurons in the PFC of subjects with schizophrenia.

Drop-the-Losers Design: Normal Case

Drop-the-losers designs are statistical designs which have two stages of a trial separated by a data based decision. In the first stage k experimental treatments and a control are administered. During a transition period, the empirically best experimental treatment is selected for continuation into the second phase, along with the control. At the study's end, inference focuses on the comparison of the selected treatment with the control using both stages' data. Traditional methods used to make inferences based on both stages' data can yield tests with higher than advertised levels of significance and confidence intervals with lower than advertised confidence. For normally distributed data, methods are provided to correct these deficiencies, providing confidence intervals with accurate levels of confidence. Drop-the-losers designs are particularly applicable to biopharmaceutical clinical trials where they can allow Phase II and Phase III clinical trials to be conducted under a single protocol with the use of all available data.

Lamina-specific reductions in dendritic spine density in the prefrontal cortex of subjects with schizophrenia

OBJECTIVE

In a previous study the authors found that dendritic spine density was reduced on prefrontal pyramidal neurons in layer 3 of subjects with schizophrenia. From a neural circuitry perspective, understanding the pathophysiological significance of this finding requires knowledge of whether pyramidal neurons in other cortical layers are similarly affected. The authors' goal was to determine whether their finding in layer 3 was also present in other cortical layers in the same group of subjects with schizophrenia.

METHOD

Spine density and other dendritic measures were made for pyramidal neurons in layers 5 and 6 of prefrontal area 46 in the brains of deceased subjects with schizophrenia, subjects with other psychiatric disorders, and normal comparison subjects.

RESULTS

None of the dendritic measures for layer 5 or 6 pyramidal neurons differed across the subject groups, but the within-subject differences in spine density between deep layer 3 and layer 5 or 6 pyramidal neurons were significantly greater in the patients with schizophrenia than in the comparison subjects.

CONCLUSIONS

These findings are consistent with the idea that prefrontal pyramidal neurons involved in corticocortical and/or thalamocortical connections are preferentially affected in schizophrenia.

Analysis of pyramidal neuron morphology in an inducible knockout of brain-derived neurotrophic factor

BACKGROUND

The messenger ribonucleic acid (mRNA) for brain-derived neurotrophic factor (BDNF), a regulator of pyramidal neuron dendritic spine density during development, is decreased in the prefrontal cortex of subjects with schizophrenia, and the level of BDNF mRNA expression is positively correlated with dendritic spine density in the same subjects.

METHODS

To determine whether reduced BDNF mRNA expression might account for decreased spine density in schizophrenia, a knockout of the BDNF gene was induced in mice during embryogenesis or at 12 weeks of age. Quantitative assessments were made of the dendritic arbor of Golgi-impregnated pyramidal neurons in the prelimbic and anterior cingulate cortices in adulthood.

RESULTS

Despite an 80% reduction in BDNF mRNA levels in both knockouts, neither spine density nor other dendritic or somal measures were decreased compared with wild-type animals.

CONCLUSIONS

A reduction in BDNF expression alone does not seem to be sufficient to alter pyramidal neuron morphology in mice. This finding suggests that other molecular abnormalities are also required to produce the pyramidal neuron dendritic spine abnormalities observed in schizophrenia.