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P Levitt

Publications and source records attributed to P Levitt.

At least 19 recordsLinked to original sources
PubMed2006

Bacterial artificial chromosome transgenic analysis of dynamic expression patterns of regulator of G-protein signaling 4 during development. I. Cerebral cortex.

Signaling through G-protein-coupled receptors is modulated by a family of regulator of G protein signaling (RGS) proteins that have been implicated in several neurological and psychiatric disorders. Defining the detailed expression patterns and developmental regulation of RGS proteins has been hampered by an absence of antibodies useful for mapping. We have utilized bacterial artificial chromosome (BAC) methods to create transgenic mice that express GFP under the control of endogenous regulator of G-protein signaling 4 (RGS4) enhancer elements. This report focuses on expression patterns in the developing and mature cerebral cortex. Based on reporter distribution, RGS4 is expressed by birth in neurons across all cortical domains, but in different patterns that suggest region- and layer-specific regulation. Peak expression typically occurs before puberty, with complex down-regulation by adulthood. Deep and superficial neurons, in particular, vary in their patterns across developmental age and region and, in primary sensory cortices, layer IV neurons exhibit low or no expression of the GFP reporter. These data suggest that altering RGS4 function will produce a complex neuronal phenotype with cell- and subdomain-specificity in the cerebral cortex.

Aging↗
PubMed2006

Bacterial artificial chromosome transgenic analysis of dynamic expression patterns of regulator of G-protein signaling 4 during development. II. Subcortical regions.

A large family of regulator of G protein signaling (RGS) proteins modulates signaling through G-protein-coupled receptors. Previous studies have implicated RGS4 as a vulnerability gene in schizophrenia. To begin to understand structure-function relationships, we have utilized bacterial artificial chromosome (BAC) methods to create transgenic mice that express green fluorescent protein (GFP) under the control of endogenous RGS4 enhancer elements, circumventing the lack of suitable antibodies for analysis of dynamic patterns of expression. This report follows from the accompanying mapping paper in cerebral cortex, with a focus on developmental and mature expression patterns in subcortical telencephalic, diencephalic and brainstem areas. Based on reporter distribution, the data suggest that alterations in RGS4 function will engender a complex phenotype of increased and decreased neuronal output, with developmental, regional, and cellular specificity.

Aging↗
PubMed2006

Expression mapping of 5-HT1 serotonin receptor subtypes during fetal and early postnatal mouse forebrain development.

Serotonin (5-HT) is implicated in several aspects of brain development, yet the ontogenetic expression patterns of 5-HT receptors responsible for transducing specific effects have largely not been characterized. Fifteen different 5-HT receptor genes have been cloned; therefore any spatial and/or temporal combination of their developmental expression could mediate a wide array of 5-HT effects. We undertook a detailed analysis of expression mapping of the Gi/o-coupled 5-HT1 (5-HT1A, 1B, 1D and 1F) receptor subtypes in the fetal and early postnatal mouse forebrain. Using receptor subtype-specific riboprobes and in situ hybridization, we observed that all 5-HT1 receptor subtypes are expressed as early as embryonic day (E) 14.5 in the forebrain, typically in gradients within specific structures. Among 5-HT1 receptors, the 5-HT1A receptor transcript is expressed densely in E14.5-16.5 thalamus, in hippocampus, and in a medial to lateral gradient in cortex, whereas the 5-HT1B receptor mRNA is expressed in more lateral parts of the dorsal thalamus and in the striatum at these ages. The 5-HT1D receptor transcript, which also is expressed heavily in E14.5-E16.5 thalamus, appears to be down-regulated at birth. The 5-HT1F receptor transcript is present in proliferative regions such as the cortical ventricular zone, ganglionic eminences, and medial aspects of the thalamus at E14.5-16.5, and otherwise presents similarities to the expression patterns of 5-HT1B and 1D receptor transcripts. Overall, the 5-HT1 subfamily of Gi/o-coupled 5-HT receptors displays specific and dynamic expression patterns during embryonic forebrain development. Moreover, all members of the 5-HT1 receptor class are strongly and transiently expressed in the embryonic dorsal thalamus, which suggests a potential role for serotonin in early thalamic development.

Age Factors↗
PubMed2006

Polymorphic GGC repeat differentially regulates human reelin gene expression levels.

The human gene encoding Reelin (RELN), a pivotal protein in neurodevelopment, includes a polymorphic GGC repeat in its 5' untranslated region (UTR). CHO cells transfected with constructs encompassing the RELN 5'UTR with 4-to-13 GGC repeats upstream of the luciferase reporter gene show declining luciferase activity with increasing GGC repeat number (P < 0.005), as predicted by computer-based simulations. Conversely, RELN 5'UTR sequences boost reporter gene expression above control levels in neuronal SN56 and N2A cell lines, but 12- and 13-repeat alleles still yield 50-60% less luciferase activity compared to the more common 8- and 10-repeat alleles (P < 0.0001). RELN "long" GGC alleles significantly blunt gene expression and may, through this effect, confer vulnerability to human disorders, such as schizophrenia and autism.

5' Untranslated Regions↗
PubMed2005

Sex differences in expression of transforming growth factor-alpha and epidermal growth factor receptor mRNA in Waved-1 and C57Bl6 mice.

A reduction of transforming growth factor-alpha (TGFalpha) expression in the spontaneous Waved-1 (Wa-1) mutant mouse causes specific behavioral and anatomical changes, including reduced fear learning and stress response and enlarged lateral ventricles. These alterations are observed predominantly in male Wa-1 mice after puberty. We hypothesized that regional differences in the expression of TGFalpha and its receptor, epidermal growth factor receptor (EGFR), may regulate the sexual dimorphism of the brain structures and functions during postnatal development. In general, fear learning-associated structures, including hippocampus and amygdala, showed maximum expression before puberty, regardless of genotype. In contrast, an overall temporal delay in the rise of both transcript levels, which peaked around or after puberty onset, was observed for the major stress regulatory hypothalamo-pituitary-adrenal axis. This pattern of expression was reversed for amygdala EGFR and hypothalamus TGFalpha and EGFR transcripts in males. When regional TGFalpha expression was compared between control and Wa-1 mice, far more complex patterns than expected were observed that revealed sex- and structure-dependent differences. In fact, the amygdala, hypothalamus, and pituitary TGFalpha expression pattern in Wa-1 exhibited a clear sex dependency across various age groups. Surprisingly, there was no compensatory up-regulation of the EGFR transcript in Wa-1 mice. The observed expression patterns of the TGFalpha signaling system during normal development and in the Wa-1 mutant mouse suggest complex sex- and age-dependent transcription regulatory mechanisms.

Age Factors↗
PubMed2003

Repeated i.v. cocaine exposure produces long-lasting behavioral sensitization in pregnant adults, but behavioral tolerance in their offspring.

Repeated exposure to cocaine during sensitive periods of forebrain development produces specific, long-lasting changes in the structure and function of maturing neural circuits. Similar regimens of drug exposure in adult animals with mature, homeostatically regulated nervous systems produce neuroadaptations that appear to be quite different in nature and magnitude. We studied the ability of cocaine to induce behavioral sensitization and/or tolerance following repeated administration of i.v. cocaine (3 mg/kg, twice daily) to pregnant rabbits during the period of peak differentiation within the rabbit cerebral cortex (embryonic day [E] 16-E25). Offspring and the adult mothers were behaviorally tested following acute administration of amphetamine 2 months after the litters were born. The offspring, having received cocaine during the prenatal sensitive period, showed profound behavioral tolerance to the amphetamine challenge. In contrast, the mothers of these offspring, who received cocaine at the same dose and duration, and experienced the same period of withdrawal, exhibited robust behavioral sensitization. These data indicate that specific adaptive changes in neural signaling and/or circuitry that occur in response to repeated exposure to psychostimulants are highly dependent upon the maturational state of the brain during which the exposure occurs.

Amphetamine↗
PubMed2001

Regional differences in neurotrophin availability regulate selective expression of VGF in the developing limbic cortex.

Gene and protein expression patterns in the cerebral cortex are complex and often change spatially and temporally through development. The signals that regulate these patterns are primarily unknown. In the present study, we focus on the regulation of VGF expression, which is limited to limbic cortical areas early in development but later expands into sensory and motor areas. We isolated neurons from embryonic day 17 rat cortex and demonstrate that the profile of VGF expression in perirhinal (expressing) and occipital (nonexpressing) populations in vitro is similar to that in the perinatal cortex in vivo. The addition of neutralizing neurotrophin antibodies indicates that endogenous brain-derived neurotrophic factor (BDNF) is necessary for the normal complement of VGF-expressing neurons in the perirhinal cortex, although endogenous neurotrophin-3 (NT-3) regulates the expression of VGF in a subpopulation of cells. ELISA analysis demonstrates that there is significantly more BDNF present in the perirhinal cortex compared with the occipital cortex in the perinatal period. However, the total amount of NT-3 is similar between the two regions and, moreover, there is considerably more NT-3 than BDNF in both areas, a finding seemingly in conflict with regional VGF expression. Quantification of the extracellular levels of neurotrophins in perirhinal and occipital cultures using ELISA in situ analysis indicates that perirhinal neurons release significantly more BDNF than the occipital population. Furthermore, the amount of NT-3 released by the perirhinal neurons is significantly less than the amount of BDNF. Local injection of BDNF in vivo into a normally negative VGF region results in robust ectopic expression of VGF. These data suggest that the local availability of specific neurotrophins for receptor occupation, rather than the total amount of neurotrophin, is a critical parameter in determining the selective expression of VGF in the developing limbic cortex.

Animals↗
PubMed2001

Novel proteoglycan epitope expressed in functionally discrete patterns in primate cortical and subcortical regions.

The molecular diversity of neuronal subpopulations was examined with a new monoclonal antibody, 8B3, that recognizes a condroitin sulfate proteoglycan expressed in anatomically discrete domains of central nervous system regions. In the neocortex, interneurons display 8B3 immunoreactivity in a rostrocaudal gradient, with a distinctive staining pattern that distinguishes known cytoarchitectonic and functional boundaries. The distribution pattern of 8B3 immunoreactivity in subcortical structures is very restricted. In the striatum, 8B3 stains spiny stellate neurons clearly defining a compartment that may correspond to the matrix. Gradients of immunoreactivity are detected in the putamen, globus pallidus, and deep cerebellar nuclei, where the most dense areas of 8B3 immunoreactivity corresponds to zones of polysynaptic projections to association prefrontal cortex. In contrast, the sensorimotor domains express lower levels of immunoreactivity. Only the projection neurons of the ventrolateral nucleus and the GABAergic neurons of the reticular nucleus express significant 8B3 immunoreactivity in the thalamus. In the spinal cord, 8B3 immunoreactivity is primarily associated with a subpopulation of motor neurons in the ventral horn and neurons in Clarke's nucleus. The complex distribution pattern reflects novel aspects of the functional organization of cortical and subcortical systems in the CNS of the primate brain and represents a potentially useful tool to assess subpopulations of neurons and brain areas as putative targets in human disease.

Animals↗
PubMed2001

Analysis of complex brain disorders with gene expression microarrays: schizophrenia as a disease of the synapse.

The level of cellular and molecular complexity of the nervous system creates unique problems for the neuroscientist in the design and implementation of functional genomic studies. Microarray technologies can be powerful, with limitations, when applied to the analysis of human brain disorders. Recently, using cDNA microarrays, altered gene expression patterns between subjects with schizophrenia and controls were shown. Functional data mining led to two novel discoveries: a consistent decrease in the group of transcripts encoding proteins that regulate presynaptic function; and the most changed gene, which has never been previously associated with schizophrenia, regulator of G-protein signaling 4. From these and other findings, a hypothesis has been formulated to suggest that schizophrenia is a disease of the synapse. In the context of a neurodevelopmental model, it is proposed that impaired mechanics of synaptic transmission in specific neural circuits during childhood and adolescence ultimately results in altered synapse formation or pruning, or both, which manifest in the clinical onset of the disease.

Brain Chemistry↗
PubMed2001

Prenatal cocaine exposure produces consistent developmental alterations in dopamine-rich regions of the cerebral cortex.

Administration of cocaine to pregnant rabbits produces robust and long-lasting anatomical alterations in the dopamine-rich anterior cingulate cortex of offspring. These effects include increased length and decreased bundling of layer III and V pyramidal neuron dendrites, increases in parvalbumin expression in the dendrites of interneurons, and increases in detectable GABAergic neurons. We have now examined multiple cortical regions with varying degrees of catecholaminergic innervation to investigate regional variations in the ability of prenatal cocaine exposure to elicit these permanent changes. All regions containing a high density of tyrosine hydroxylase-immunoreactive fibers, indicative of prominent dopaminergic input, exhibited alterations in GABA and parvalbumin expression by interneurons and microtubule-associated protein-2 labeling of apical dendrites of pyramidal neurons. These regions included the medial prefrontal, entorhinal, and piriform cortices. In contrast, primary somatosensory, auditory and motor cortices exhibited little tyrosine hydroxylase staining and no measurable cocaine-induced changes in cortical structure. From these data we suggest that the presence of dopaminergic afferents contributes to the marked specificity of the altered development of excitatory pyramidal neurons and inhibitory interneurons induced by low dose i.v. administration of cocaine in utero.

Animals↗
PubMed2001

Hepatocyte growth factor/scatter factor is a motogen for interneurons migrating from the ventral to dorsal telencephalon.

Cortical interneurons arise from the proliferative zone of the ventral telencephalon, the ganglionic eminence, and migrate into the developing neocortex. The spatial patterns of migratory interneurons reflect the complementary expression of hepatocyte growth factor/scatter factor (HGF/SF) and its receptor, MET, in the forebrain. Scatter assays on forebrain explants demonstrate regionally specific motogenic activity due to HGF/SF. In addition, exogenous ligand disrupts normal cell migration. Mice lacking the urokinase-type plasminogen activator receptor (u-PAR), a key component of HGF/SF activation, exhibit deficient scatter activity in the forebrain, abnormal interneuron migration from the ganglionic eminence, and reduced interneurons in the frontal and parietal cortex. The data suggest that HGF/SF motogenic activity, which is essential for normal development of other organ systems, is a conserved mechanism that regulates trans-telencephalic migration of interneurons.

Animals↗
PubMed2001

Disease-specific changes in regulator of G-protein signaling 4 (RGS4) expression in schizophrenia.

Complex defects in neuronal signaling may underlie the dysfunctions that characterize schizophrenia. Using cDNA microarrays, we discovered that the transcript encoding regulator of G-protein signaling 4 (RGS4) was the most consistently and significantly decreased in the prefrontal cortex of all schizophrenic subjects examined. The expression levels of ten other RGS family members represented on the microarrays were unchanged and hierarchical data analysis revealed that as a group, 274 genes associated with G-protein signaling were unchanged. Quantitative in situ hybridization verified the microarray RGS4 data, and demonstrated highly correlated decreases in RGS4 expression across three cortical areas of ten subjects with schizophrenia. RGS4 expression was not altered in the prefrontal cortex of subjects with major depressive disorder or in monkeys treated chronically with haloperidol. Interestingly, targets for 70 genes mapped to the major schizophrenia susceptibility locus 1q21--22 were present on the microarrays, of which only RGS4 gene expression was consistently altered. The combined data indicate that a decrease in RGS4 expression may be a common and specific feature of schizophrenia, which could be due either to genetic factors or a disease- specific adaptation, both of which could affect neuronal signaling.

Adult↗
PubMed2001

Identification of a sensitive period of prenatal cocaine exposure that alters the development of the anterior cingulate cortex.

Administration of cocaine to pregnant rabbits produces robust and long-lasting anatomical, neurochemical and behavioral alterations in their offspring. For example, exposure to cocaine following implantation [embryonic day (E) 8] through gestation (E29) produces increased length and decreased bundling of layer III and V pyramidal neuron dendrites, increased parvalbumin expression in the dendrites of interneurons, and increased GABA levels in the anterior cingulate cortex (ACC) and other dopamine-rich cortical areas. We have investigated the presence of a sensitive period of in utero exposure during specific developmental epochs prior to and during the onset of cortical development that might be capable of producing such effects. Cocaine (3 mg/kg i.v., twice daily) or saline was administered during embryonic days E16-E25 (onset and peak of corticogenesis), E8-E15 (prior to cortical plate formation), E8-E25 or E8-E29 as in earlier studies. Examination of the ACC in offspring exposed from E8 to E25 and from E16 to E25 were found to induce alterations in the development of pyramidal neurons and interneurons that are nearly identical to those induced by the complete exposure (E8-E29) paradigm. No alterations were observed following the E8-E15 cocaine exposure. These data suggest that exposure to cocaine during E16-E25, the time of peak corticogenesis, appearance of cortical monoamines and onset of D(1) dopamine receptor expression, is necessary and sufficient to produce long-term effects on the organization of excitatory pyramidal neurons and inhibitory interneurons in the ACC.

Animals↗
PubMed2000

In utero cocaine-induced dysfunction of dopamine D1 receptor signaling and abnormal differentiation of cerebral cortical neurons.

Monoamines modulate neuronal differentiation, and alteration of monoamine neurotransmission during development produces specific changes in neuronal structure, function, and pattern formation. We have previously observed that prenatal exposure to cocaine in a clinically relevant animal model produces increased length of pyramidal neuron dendrites in the anterior cingulate cortex (ACC) postnatally. We now report that cocaine administered intravenously to pregnant rabbits at gestational stages preceding and during cortical histogenesis results in the early onset of hypertrophic dendritic outgrowth in the embryonic ACC. Confocal microscopy of DiI-labeled neurons revealed that the atypical, tortuous dendritic profiles seen postnatally in ACC-cocaine neurons already are apparent in utero. No defects in neuronal growth were observed in visual cortex (VC), a region lacking prominent dopamine innervation. In striking correlation with our in vivo results, in vitro experiments revealed a significant enhancement of spontaneous process outgrowth of ACC neurons isolated from cocaine-exposed fetuses but no changes in neurons derived from visual cortex. The onset of modified growth in vivo is paralleled by reduced D(1A) receptor coupling to its G-protein. These data suggest that the dynamic growth of neurons can be regulated by early neurotransmitter signaling in a selective fashion. Prenatal onset of defects in dopamine receptor signaling contributes to abnormal circuit formation and may underlie specific cognitive and behavioral dysfunction.

Aging↗
PubMed2000

Progressive postnatal assembly of limbic-autonomic circuits revealed by central transneuronal transport of pseudorabies virus.

The development of neuronal projections to a target and the establishment of synaptic connections with that target can be temporally distinct events, which typically are distinguished by functional assessments. We have applied a novel neuroanatomical approach to characterize the development of limbic forebrain synaptic inputs to autonomic neurons in neonatal rats. Transneuronal labeling of preautonomic forebrain neurons was achieved by inoculating the ventral stomach wall with pseudorabies virus (PRV) on postnatal day 1 (P1), P4, or P8. In each age group, PRV-positive neurons were present in autonomic and preautonomic regions of the spinal cord and brainstem 62-64 hr after inoculation. Transneuronal forebrain labeling in rats injected on P8 was similar to the transneuronal labeling reported previously in adult rats and included neurons in the medial and lateral hypothalamus, amygdala, bed nucleus of the stria terminalis, and visceral cortices. However, no cortex labeling and only modest amygdala and bed nucleus labeling were observed in rats injected with PRV on P4, and only medial hypothalamic labeling was observed in rats injected on P1. Additional tracing experiments involving central injections of PRV or cholera toxin beta indicated that lateral hypothalamic and telencephalic regions projected to the medullary dorsal vagal complex several days before establishing synaptic connections with gastric-related autonomic neurons. These results demonstrate a novel strategy for evaluating synaptic connectivity in developing neural circuits and show a temporally segregated postnatal emergence of medial hypothalamic, lateral hypothalamic, and telencephalic synaptic inputs to central autonomic neurons.

Aging↗