Early spread of scrapie from the gastrointestinal tract to the central nervous system involves autonomic fibers of the splanchnic and vagus nerves

Although the ultimate target of infection is the central nervous system (CNS), there is evidence that the enteric nervous system (ENS) and the peripheral nervous system (PNS) are involved in the pathogenesis of orally communicated transmissible spongiform encephalopathies. In several peripherally challenged rodent models of scrapie, spread of infectious agent to the brain and spinal cord shows a pattern consistent with propagation along nerves supplying the viscera. We used immunocytochemistry (ICC) and paraffin-embedded tissue (PET) blotting to identify the location and temporal sequence of pathological accumulation of a host protein, PrP, in the CNS, PNS, and ENS of hamsters orally infected with the 263K scrapie strain. Enteric ganglia and components of splanchnic and vagus nerve circuitry were examined along with the brain and spinal cord. Bioassays were carried out with selected PNS constituents. Deposition of pathological PrP detected by ICC was consistent with immunostaining of a partially protease-resistant form of PrP (PrP(Sc)) in PET blots. PrP(Sc) could be observed from approximately one-third of the way through the incubation period in enteric ganglia and autonomic ganglia of splanchnic or vagus circuitry prior to sensory ganglia. PrP(Sc) accumulated, in a defined temporal sequence, in sites that accurately reflected known autonomic and sensory relays. Scrapie agent infectivity was present in the PNS at low or moderate levels. The data suggest that, in this scrapie model, the infectious agent primarily uses synaptically linked autonomic ganglia and efferent fibers of the vagus and splanchnic nerves to invade initial target sites in the brain and spinal cord.

Increased anterior cingulate and caudate activity in bipolar mania

BACKGROUND

Executive control of cognition, emotion, and behavior are disrupted in the manic state of bipolar disorder. Whereas frontal systems are implicated in such dysfunction, the localization of functional brain abnormalities in the manic state is not well understood.

METHODS

We utilized a high-sensitivity H(2)(15)0 positron emission tomography technique to investigate regions of increased brain activity in mania, compared to euthymia, in bipolar disorder.

RESULTS

The principal findings were manic state-related increased activity in left dorsal anterior cingulate, and left head of caudate.

CONCLUSIONS

The findings suggest that the manic state of bipolar disorder may be associated with heightened activity in a frontal cortical-subcortical neural system that includes the anterior cingulate and caudate.

Detection of PrP in extraneural tissues

Transmissible spongiform encephalopathies (TSEs) or "prion diseases" are a group of unconventional fatal diseases. TSEs are characterised by the accumulation of a modified form of the normal host glycoprotein, PrP (PrP(c)). In the course of infection PrP(c) is converted to an abnormally protease resistant form, PrP(Sc). The exact nature of the infectious agent responsible for these diseases remains controversial. While there is compelling evidence that TSE agents contain an informational molecule, possibly a nucleic acid, some believe that the infectious agent or "prion" is solely composed of PrP(Sc). Nevertheless, PrP is required for TSE pathogenesis, as mice devoid of the PrP gene (PrP(-/-)) remain healthy when challenged with TSE isolates and are unable to replicate infectivity within the central nervous system (CNS) or in other tissues. In recent years immunocytochemistry has been used to pinpoint which cells are associated with abnormal accumulations of PrP, providing important information on the cellular targeting of TSE infection. In uninfected and scrapie-infected mice, PrP protein is found in the CNS and in extraneural tissues such as spleen and lymph nodes. In the peripheral lymphoid system, PrP is associated with follicular dendritic cells that are known to be important for replication of infectivity for at least one TSE strain. This review will focus on current methods for the immunocytochemical detection of PrP in murine extraneural tissues, mainly lymphoid tissues, and will discuss recent findings on the role of the peripheral lymphoid system in TSE pathogenesis.

Early accumulation of pathological PrP in the enteric nervous system and gut-associated lymphoid tissue of hamsters orally infected with scrapie

Infection of the central nervous system (CNS) is a defining feature of scrapie. Several findings suggest that scrapie agent invades the CNS via the splanchnic and vagus nerve after ingestion of infectivity. Here we address the involvement of the enteric nervous system (ENS) and gut-associated lymphoid tissue (GALT) in this pathogenetic process. Immunocytochemistry was used for the detection of pathological PrP in the duodenum and ileum of hamsters fed with 263K scrapie and sacrificed at different stages of incubation. The experiments revealed early infection of various GALT components and of submucosal and myenteric ENS ganglia. These results provide evidence for an important role of the ENS in scrapie neuroinvasion and for centripetal vagal spread of infection from the gut to the brain after oral uptake of agent.

Rostral and orbital prefrontal cortex dysfunction in the manic state of bipolar disorder

OBJECTIVE

This study investigated prefrontal cortex function in the manic state of bipolar disorder.

METHOD

High-sensitivity [15O]H2O positron emission tomography and a word generation activation paradigm were used to study regional cerebral blood flow in five manic and six euthymic individuals with bipolar disorder and in five healthy individuals.

RESULTS

Decreased right rostral and orbital prefrontal cortex activation during word generation and decreased orbitofrontal activity during rest were associated with mania.

CONCLUSIONS

The data support the presence of rostral and orbital prefrontal dysfunction in primary mania. These findings, when seen in the context of the human brain lesion and the behavioral neuroanatomic literatures, may help to explain some of the neurobehavioral abnormalities characteristic of the manic state.

Deposition of disease-associated prion protein involves the peripheral nervous system in experimental scrapie

There is some evidence that the peripheral nervous system (PNS) is involved in the pathogenesis of transmissible spongiform encephalopathies (TSEs). The TSE-specific abnormal prion protein (PrP(sc)) is considered as surrogate marker for infectivity. We traced the deposition of PrP(sc) by immunocytochemistry in sheep and hamsters inoculated intraperitoneally with scrapie. The trigeminal, dorsal root, celiac, thoracic, and nodose ganglia contained ganglion cells and fewer satellite cells with prominent granular PrP(sc) deposition. As a novel deposition pattern, punctate deposits in adaxonal location were seen along nerve fibers of peripheral nerve adjacent to ganglia. Such prominent involvement of the PNS in two different experimental scrapie models emphasizes the need to consider the PNS in natural scrapie and other TSEs including bovine spongiform encephalopathy as potential source of infectivity.

Pathological PrP is abundant in sympathetic and sensory ganglia of hamsters fed with scrapie

Although the ultimate target of infection is the CNS, there is evidence that the peripheral nervous system (PNS) is involved in the pathogenesis of Transmissible Spongiform Encephalopathies (TSEs). We used immunocytochemistry to identify the presence of pathological accumulations of a host protein, PrP, in the CNS and PNS (sensory and autonomic ganglia) of hamsters orally infected with 263K scrapie. All hamsters showed pathological deposition of PrP in most brain areas, along the length of the spinal cord, in nodose (NG) and dorsal root (DRG) ganglia and in the coeliac mesenteric ganglion complex (CMGC). In one case, scant deposition was observed along a few axons of the vagus nerve. This finding suggests that, after oral challenge, TSE infectious agent uses neural pathways and ganglia of the peripheral nervous system to reach target sites in the CNS.

Peripheral serotonin measures in prepubertal psychiatric inpatients and normal children: associations with suicidal behavior and its risk factors

BACKGROUND

This study reports relationships between suicidal behavior and its risk factors in prepubertal children and whole blood and platelet serotonin-related measures.

METHODS

Seventy-five prepubertal psychiatric inpatients including 23 (30.7%) nonsuicidal, 32 (42.7%) with suicidal ideation, and 20 (26.6%) with a suicide attempt were compared to 35 normal prepubertal controls with regard to platelet serotonin content, serotonin-amplified platelet aggregation, and whole blood tryptophan.

RESULTS

Mean whole blood tryptophan content was significantly lower among inpatient children with a recent suicide attempt than among normal controls or inpatients with suicidal ideation (F = 3.94, df = 3.54, p < or = .01). Inpatient children with a mood disorder had significantly higher platelet serotonin content than inpatients without a mood disorder (F = 3.86, df = 2.80, p < or = .03). Racial/ethnic differences were also observed for inpatients and normal controls, with whites having significantly lower levels of platelet serotonin (expressed as ng/mL blood or ng/10(9) platelets) than blacks or Latinos. Blacks had significantly higher levels of whole blood tryptophan than other racial/ethnic groups.

CONCLUSIONS

The results suggest that whole blood tryptophan and platelet serotonin content should be studied for their predictive validity as risk factors for suicidal behavior in youth while controlling for racial/ethnic differences.

Effects of diagnosis, race, and puberty on platelet serotonin levels in autism and mental retardation

OBJECTIVE

To reevaluate platelet serotonin (5-HT) levels in autism, measuring and controlling for effects of race and puberty. The specificity of hyperserotonemia for autism versus cognitive impairment is also assessed.

METHOD

Platelet 5-HT levels were measured in 77 individuals, aged 2 through 37 years, with autistic disorder; 65 normal controls; and 22 mentally retarded or otherwise cognitively impaired (MR/CI) prepubertal children. Effects of diagnosis, race, and pubertal status were evaluated by analysis of variance in separate pre- and postpubertal groups. 5-HT levels were expressed as ng/mL blood and ng/microL platelet volume.

RESULTS

Among prepubertal children, significant effects of diagnosis (ng/mL; F2,109 = 5.9, p = .004) and race (F2,109 = 14.7, p < .0005) were found. Autistic youngsters had significantly higher 5-HT concentrations than controls, although the elevation (25%) was less than typically reported; MR/CI children had levels very similar to those of controls. White children had significantly lower 5-HT levels than black or Latino youngsters, regardless of diagnosis. Diagnosis and race effects were nonsignificant in the postpubertal group. Postpubertal subjects had lower 5-HT concentrations than prepubertal subjects (ng/mL; F1,114 = 28.5, p < .0005).

CONCLUSIONS

The data underscore the importance of matching for race and pubertal status in neuropsychiatric research and suggest that the prevalence of hyperserotonemia in autistic individuals may have been overestimated because of a failure to control for both variables. Hyperserotonemia was not found in MR/CI youngsters without autistic features.

Determination of the frequency and distribution of vascular and parenchymal amyloid with polyclonal and N-terminal-specific PrP antibodies in scrapie-affected sheep and mice

Brains from 17 histopathologically confirmed cases of scrapie, five of which had congophilic vascular amyloid, were stained immunohistochemically for prion protein (PrP) using a polyclonal antibody. Two clinically suspect but pathologically unconfirmed cases of natural sheep scrapie and the brains of four mice infected with the 111A murine scrapie strain were also examined. Selected sections containing amyloid were stained with each of two peptide antibodies which recognise the N-terminal amino acid residues which are lost following protease digestion of the disease-specific isoform of PrP. The mice infected with the 111A murine scrapie strain had large numbers of hypermature plaques. All the amyloid plaques from both natural sheep scrapie brains and experimental murine brains were heavily immunostained by the polyclonal and both peptide antibodies. In addition, disease-specific accumulations of PrP were detected in endothelial cells or in the intima of blood vessels of the cerebral cortex of sheep scrapie brains. The affected blood vessels were located in areas which otherwise lacked typical scrapie pathology. Vascular accumulations of PrP were also found in leptomeningeal and choroid plexus blood vessels. Vascular amyloid was found mainly in the neocortex. Vascular amyloid and disease-specific parenchymal accumulations of PrP were found in two sheep which showed clinical signs of scrapie but lacked its typical vacuolar pathology. These results show that the mature amyloid of scrapie is composed of, or contains a substantial proportion of, whole length PrP protein. Thus truncation of PrP is not essential for the aggregation of PrP into amyloid. The vascular amyloid of natural sheep scrapie originates from the accumulation and release of PrP from endothelial cells presumably following systemic scrapie infection. The topography of vascular amyloid distribution in Great Britain differs from that reported in the Netherlands. As amyloid deposition in mice is largely controlled by the strain of the infecting agent it is possible that the strain of the agent may influence vascular amyloid deposition.

Cerebral targeting indicates vagal spread of infection in hamsters fed with scrapie

The pathogenesis of scrapie and other transmissible spongiform encephalopathies (TSEs) following oral uptake of agent is still poorly understood and can best be studied in mice and hamsters. The experiments described here further extend the understanding of the pathways along which infection spreads from the periphery to the brain after an oral challenge with scrapie. Using TSE-specific amyloid protein (TSE-AP, also called PrP) as a marker for infectivity, immunohistochemical evidence suggested that the first target area in the brain of hamsters orally infected with scrapie is the dorsal motor nucleus of the vagus nerve (DMNV), rapidly followed by the commissural solitary tract nucleus (SN). The cervical spinal cord was affected only after TSE-AP had been deposited in the DMNV, SN and other medullary target areas. For the first time, these results demonstrate conclusively that, in our animal model, initial infection of the brain after oral ingestion of scrapie agent occurs via the vagus nerve, rather than by spread along the spinal cord.

Heparan sulfate proteoglycan is associated with amyloid plaques and neuroanatomically targeted PrP pathology throughout the incubation period of scrapie-infected mice

Heparan sulfate proteoglycan (HSPG) has been found to be associated with amyloid deposits in a number of diseases including the cerebral amyloid plaques of Alzheimer's disease and the transmissible spongiform encephalopathies (TSEs). The role of HSPG in amyloid formation and the neurodegenerative pathology of these diseases have not been established. We have addressed these questions using a scrapie mouse model which exhibits both amyloid and nonamyloid deposition of abnormal PrP protein, the protein marker of TSE infection. The distribution of HSPG was examined throughout the course of the disease in the brains of experimentally infected mice and compared with the distribution of abnormal PrP. Abnormally high levels of HSPG were associated with most types of PrP pathology including all plaque types and diffuse neuroanatomically targeted forms. Scrapie-associated HSPG was present from 70 days after infection, the earliest time-point examined, in the same target areas as abnormal PrP. The association with amyloid plaques may indicate that HSPG is involved in amyloid plaque formation and/or persistence but involvement with early diffuse forms of PrP suggests a more fundamental role in scrapie pathogenesis.

Mice with gene targetted prion protein alterations show that Prnp, Sinc and Prni are congruent

Classical genetic analysis has identified Sinc/Prni as the major gene controlling mouse scrapie incubation time. Sinc/Prni is linked to Prnp, the gene encoding the prion protein (PrP). Prnp alleles express distinct PrP protein variants, PrP A and PrP B, which arise from codon 108L/F and 189 T/V dimorphisms. Prnp genotype segregates with incubation time length which suggests, but does not prove, that incubation time is controlled by PrP dimorphisms, and that the Sinc/Prni and Prnp loci are congruent. We have used gene targetting to construct mice in which the endogenous Prnp allele has been modified to express PrP B instead of PrP A. Challenge with a mouse-adapted BSE strain results in dramatically shortened incubation times and demonstrates that PrP dimorphisms at codon 108 and/or 189 control incubation time, and that Sinc/Prni and Prnp are congruent.

Plasma beta-endorphin, adrenocorticotropin hormone, and cortisol in autism

Plasma levels of the hypothalamo-pituitary-adrenal axis hormones beta-endorphin (BE), adrenocorticotropin hormone (ACTH), and cortisol were measured in autistic (N = 48), mentally retarded/cognitively impaired (MR/CI, N = 16), and normal control (N = 26) individuals. Comparison of log transformed data from the three groups revealed that levels of BE and ACTH were significantly higher (p < .05) in the autistic individuals than in normal controls. The higher means in the autistic group were due to significantly higher plasma levels of BE and ACTH, indices of acute stress response, in the more severely affected individuals. The data support the idea that individuals with severe autism have a heightened response to acute stressors rather than chronic hyperarousal or elevated basal stress response system functioning.

Blunted serotonin response to fenfluramine challenge in premenstrual dysphoric disorder

OBJECTIVE

Indirect evidence suggests that abnormalities in serotonergic function may be involved in the pathogenesis of premenstrual dysphoric disorder. The goal of this study was to test the hypothesis of serotonergic deficiency in premenstrual dysphoric disorder by measuring the prolactin response to fenfluramine.

METHOD

The authors administered the serotonin-releasing drug dl-fenfluramine in a placebo-controlled protocol to nine women with premenstrual dysphoric disorder and 11 healthy female volunteers in the luteal phase of the menstrual cycle.

RESULTS

Compared to the normal subjects, the women with premenstrual dysphoric disorder had a significantly blunted prolactin response to fenfluramine.

CONCLUSIONS

Premenstrual dysphoric disorder appears to be associated with serotonergic deficiency.

In vivo toxicity of prion protein in murine scrapie: ultrastructural and immunogold studies

Prion protein (PrP) is a cell surface, host coded, sialoglycoprotein which accumulates in excess in scrapie, Creutzfeldt-Jakob disease, bovine spongiform encephalopathy and other transmissible spongiform encephalopathies. Infection of mice with the 87 V or ME7 scrapie strains results in distinctive and very different light microscopical patterns of vacuolation and disease specific PrP accumulation. In both of these scrapie strains immunogold electron microscopy was used to locate PrP to the plasmalemma of neurons from where it was released into the neuropil. Initial PrP accumulation around neurons and in early plaques lacking amyloid fibrils was generally not associated with morphological changes either of the neuron or dendrite releasing the PrP or in the adjacent neuropil in which excess PrP accumulated. However, accumulation of pre-amyloid PrP in some brain areas was associated with specific degeneration of dendritic spines and axon terminals. Initial PrP aggregation into fibrils was also associated with tissue damage with both ME7 and 87 V plaques and diffuse accumulations. Tissue damage associated with fibrillogenesis was localized and would not be expected to have clinical significance. We conclude that pre-amyloid PrP release and accumulation is not invariably toxic, either to the neuron releasing PrP or to the neuropil into which it is released. However, axon terminal degeneration and dendritic spine loss in some neuroanatomical areas may be indicative of specific PrP toxicity and may be the main cause of neurological dysfunction in murine scrapie.

Altered circadian activity rhythms and sleep in mice devoid of prion protein

There is a wealth of data supporting a central role for the prion protein (PrP) in the neurodegenerative prion diseases of both humans and other species, yet the normal function of PrP, which is expressed at the cell surface of neurons and glial cells, is unknown. It has been speculated that neuropathology may be due to loss of normal function of PrP. Here we show that in mice devoid of PrP there is an alteration in both circadian activity rhythms and patterns. To our knowledge, this is the first null mutation that has been shown to affect sleep regulation and our results indicate that at least one of the inherited prion diseases, fatal familial insomnia, where there is a profound alteration in sleep and the daily rhythms of many hormones, may be related to the normal function of the prion protein.

Ultrastructural immuno-localization of synthetic prion protein peptide antibodies in 87V murine scrapie

Disease specific forms of a host encoded cell surface sialoglycoprotein called prion protein (PrP) accumulate during this incubation period of the transmissible spongiform encephalopathies. A 33-35 kDa disease specific form of PrP is partially resistant to protease digestion whereas the normal form of PrP can be completely digested. Proteinase K digestion of the murine disease specific form of PrP produces diverse forms of low molecular weight PrP, some of which are N-terminally truncated at amino acid residue 49 or 57 within the octapeptide repeat segment. Amyloid plaques are a pathological feature of many of the transmissible spongiform encephalopathies and are composed of PrP. Using synthetic peptide antibodies to the N-terminus of PrP (which is not present in truncated disease specific PrP) and antibodies to the protease resistant fraction of PrP we have immunostained plaques and pre-amyloid deposits in the brains of mice, experimentally infected with the 87V strain of scrapie, for examination by light and electron microscopy. Classical fibrillar amyloid deposits in plaques as well as pre-amyloid deposits were both immunostained by antibodies to the N-terminus of PrP and to the protease resistant core of the PrP molecule. This suggests that both N-terminal and core amino acid residues are present in disease specific PrP released from scrapie infected cells in vivo. The results also suggest that N-terminal truncation of PrP may not be essential for formation of amyloid fibrils.

Blunted serotonergic responsivity in depressed inpatients

We found a 38% lower maximal prolactin response to an oral challenge dose of 60 mg of dl-fenfluramine relative to placebo in younger (< 30 years) depressed inpatients compared with the response in age-matched healthy controls (p < .03). Severity of depression did not correlate with prolactin response. Prolactin responses in older depressed patients (> or = 30 years) did not differ from older controls. Younger depressed patients differed from older depressed patients in terms of earlier age of onset of first lifetime episode of major depression, greater degree of suicidal intent during a recent suicide attempt, double the level of hopelessness on admission to hospital, and a higher rate of comorbid borderline personality disorder. A blunted prolactin response to fenfluramine may be interpreted as evidence for reduced serotonergic function in younger depressed patients and may underlie their observed greater suicidality and hopelessness.

Plasma androgens in autism

Plasma levels of testosterone and the adrenal androgen dehydroepiandrosterone sulfate (DHEA-S) were measured in male autistic subjects (31 prepubertal, 8 postpubertal), mentally retarded/cognitively impaired subjects (MR, 12 prepubertal), and normal control subjects (NC, 10 prepubertal, 11 postpubertal). Mean levels of plasma testosterone were similar in the postpubertal autistic (4.54 +/- 1.12 ng/ml) and postpubertal NC (5.02 +/- 1.87 ng/ml) groups. Plasma DHEA-S levels in postpubertal autistic (2170 +/- 1020 ng/ml) and postpubertal NC (1850 +/- 777 ng/ml) groups also were not significantly different. Similarly, no significant group differences were seen for testosterone or DHEA-S in the prepubertal autistic, MR, or NC individuals, although prepubertal MR individuals with cerebral palsy did have increased plasma DHEA-S levels compared to age-matched MR or NC individuals. Significant negative correlations were found between testosterone and whole blood serotonin (5-HT) levels in the combined (all subjects, all ages) groups and in the autistic group, suggesting that the effect of puberty on whole blood 5-HT may deserve further study. Data indicate that altered secretion of the androgens is not a common feature of autism. However, abnormalities of adrenal androgen secretion may be present in individuals with cerebral palsy.

Morphogenesis of amyloid plaques in 87V murine scrapie

Amyloid plaques of scrapie-infected mouse brains are composed of fibrillar forms of a host coded, cell surface sialoglycoprotein called PrP (prion protein). Serial ultrastructural immunogold staining was performed on plaques identified by light microscopic immunocytochemistry of brains of VM mice infected with the 87V strain of scrapie. Classical plaques, of a kuru-type morphology, were composed of a central core of bundles of amyloid fibrils. Amyloid fibrils of classical plaques were immunoreactive for PrP. In addition, PrP was also found at the plaque periphery, in the absence of fibrils, at the plasmalemma of cell processes and in the associated extracellular spaces. Frequent microglial cells and occasional astrocytes contained PrP within lysosomes. Other plaques with few or no recognizable amyloid fibrils were frequent and were termed primitive plaques. PrP could be demonstrated in a non-fibrillar form at the plasmalemma and in the extracellular spaces between neurites of such plaques. Many primitive plaques showed little or no sub-cellular pathology associated with the PrP accumulation. PrP was closely associated with the plasmalemma of occasional dendrites passing towards the centre of primitive plaques. These results suggest that plaques are formed around one or more PrP releasing dendrites. PrP accumulates in the extracellular spaces adjacent to such processes prior to its spontaneous aggregation into fibrils. Lysosomal accumulation of PrP in microglia and astrocytes located at the periphery of plaques suggest that these cells are involved in the phagocytosis of excess or abnormal PrP.

PrP gene dosage determines the timing but not the final intensity or distribution of lesions in scrapie pathology

We have produced by gene targeting a mouse line with an inactive PrP gene. In animals heterozygous for this mutation, PrP mRNA is reduced by approximately 50% throughout the brain compared with wild type mice. The steady-state level of PrPc is also significantly reduced in heterozygotes compared to wild type mice. PrP mRNA and protein are not detected in brains of mice homozygous for the mutation. We have infected wild type mice and mice heterozygous and homozygous for the mutation with the ME7 strain of scrapie. A gene dosage effect can be seen in time of disease onset and period over which the disease symptoms develop. In heterozygotes disease onset occurs around 220 days and terminal stages are reached by 280 days. In wild type mice disease onset occurs around 130 days and the terminal stages by 160 days. The PrP-/- mice are resistant to disease up to 475 days. PrP deposition in heterozygous mice starts in the same brain area as wild type mice and can be detected as early as 50 days. The pattern of PrP deposition in the brain of heterozygotes follows an identical course to that observed in wild type mice and by terminal stages of disease the amount deposited is equivalent to wild type mice. Vacuolation is detected later than PrP deposition and distribution and degree in the terminal stages of disease is similar in wild type and heterozygous mice. These results show that signs of disease, vacuolation and PrP deposition are dependent upon PrPc in a rate dependent manner.

Correlative light and electron microscopy studies of PrP localisation in 87V scrapie

The transmissible neurodegenerative diseases, of which scrapie is the archetype, are caused by unconventional infectious agents. Prion protein (PrP), a widespread host coded, cell surface sialoglycoprotein, is thought to be an essential or, controversially, sole component of these agents. During infection, disease specific accumulations of PrP may be observed in immunostained brain sections of mice infected with the 87V scrapie strain as amyloid plaques or as diffuse or granular foci within the neuropil. Using serial light and electron microscopical preparations we determined immunocytochemically that infection specific PrP is present in amyloid fibrils, and accumulates on the plasmalemma of neurites at the periphery of plaques and in the neuropil, irrespective of the morphological form of PrP accumulation when viewed by light microscopy. In some brain areas with dense granular PrP expression complete disruption of neuropil with loss of neurites was associated with fibrils lying free in expanded extracellular space. These results suggest that normal PrP may be converted to its pathological form at the neuronal plasmalemma or in the extracellular space and, furthermore, that amyloid fibrils are formed following the accumulation and aggregation of subunit proteins at these sites.

Infection-specific prion protein (PrP) accumulates on neuronal plasmalemma in scrapie-infected mice

Prion protein (PrP) is an abundant membrane-associated host protein which accumulates in abnormal, relatively protease-resistant forms in the brains of animals with scrapie and related diseases. Using correlative light and electron microscopy we determined the sites of subcellular localization of PrP in mice infected with the 87V strain of scrapie. Disease-specific accumulation of PrP was observed at light microscopy as amyloid plaques or as diffuse or granular staining within the neuropil, often clearly associated with individual neurons. Serial electron microscopical preparations were immunostained for PrP by the immunogold method. Gold particles were located on amyloid fibrils and on the plasmalemma of neurites at the periphery of plaques and in the neuropil, irrespective of the morphological form of PrP accumulation when viewed by light microscopy. This suggests the amyloid fibrils are formed following the accumulation and aggregation of sub-unit proteins at the plasmalemma and, furthermore, that normal PrP may be converted to its pathological form at this site.

Murine scrapie-infected neurons in vivo release excess prion protein into the extracellular space

An originally heretical proposition that the transmissible spongiform encephalopathies are caused by a host-coded protein (the prion hypothesis) is now current dogma. Indeed these disorders are commonly called prion diseases but the prion hypothesis provides no readily acceptable explanation for the source of the informational component of the agent necessary to code for the diversity of strains of scrapie. Ultrastructural immunolocalisation of prion protein (PrP) in murine scrapie shows that PrP accumulates in association with the plasmalemma of neurones, diffusing from the neuronal cell surface into the extracellular space around small neurites prior to aggregation and fibril assembly. These events occur without the involvement of other cell types. The area of neuropil infiltrated with extracellular PrP around infected neurons and neurites indicates that the form of PrP initially produced is not immediately amyloidogenic.

PrP in pathology and pathogenesis in scrapie-infected mice

PrP accumulation in the brains of mice infected with scrapie takes several different forms: amyloid plaques, widespread accumulation in neuropile, and perineuronal deposits. PrP is also sometimes detected within microglia and in or around astrocytes. There are dramatic and reproducible differences between scrapie strains in the relative prominence of these changes and their distribution in the brain. Depending on the scrapie strain, PrP pathology is targeted precisely to particular brain areas, often showing a clear association with identifiable groups of neurons. These results suggest that PrP changes are primarily associated with neurons, and that different scrapie strains recognize and selectively replicate in different populations of neurons. Immunostaining at the ultrastructural level demonstrates an association of PrP with neurite plasmalemma, around amyloid plaques, and in areas of widespread neuropile and perineuronal accumulation. It is probable that PrP is encoded by the Sinc gene, which controls the incubation period of scrapie in mice. Studies using the intraocular infection route show that the Sinc gene controls the onset rather than the rate of replication, suggesting that PrP may be involved in cell-to-cell spread of infection. The accumulation of PrP at the surface of neurons is consistent with such a role.

The relationship of platelet 5-HT2 receptor indices to major depressive disorder, personality traits, and suicidal behavior

Previous research has suggested that major depression and suicidal behavior may be associated with altered serotonin receptor function. In this study, platelet serotonin2 (5-HT2) receptor binding indices were measured in conjunction with serotonin-amplified platelet aggregation, a response mediated by the platelet 5-HT2 receptor complex, in depressed patients and normal controls. The magnitude of serotonin-amplified platelet aggregation was positively correlated with the number of platelet 5-HT2 receptor sites in both groups. Mean values for the receptor binding indices and the receptor-mediated response did not differ significantly between patients and controls, although patients exhibited a wider range of values for each parameter compared with controls. Exploratory analyses were undertaken to determine clinical variables that might contribute to the increased variance in depressed individuals. These analyses failed to reveal a statistically significant relationship between any of the platelet 5-HT2 receptor measures and the subtype or severity of depressive illness, or the presence of comorbid borderline personality disorder. Although the mean number of receptor sites did not differ between patients who had recently attempted suicide and those who had never attempted suicide, a strong positive correlation (p = 0.002) was found between receptor number and the degree of medical damage resulting from the suicidal act. Furthermore, the ratio of the serotonin-amplified platelet aggregation response to platelet 5-HT2 receptor number, an index of the mean responsivity of an individual receptor complex, was lower in suicide attempters versus nonattempters (p = 0.06) and normal controls (p = 0.01). Exploratory analyses also suggested that recent exposure to psychotropic medication may result in a significant increase in platelet 5-HT2 receptor number (p = 0.03). Thus, although the study did not show a consistent alteration in platelet 5-HT2 receptor indices in major depression, the data suggest that specific factors such as suicidality and drug exposure may explain some of the variance in depressed patients.

PrP protein is associated with follicular dendritic cells of spleens and lymph nodes in uninfected and scrapie-infected mice

Abnormal forms of a host protein, PrP, accumulate in the central nervous system in scrapie-affected animals. Here, PrP protein was detected immunocytochemically in tissue sections of spleen, lymph node, Peyer's patches, thymus, and pancreas from uninfected mice and from mice infected with a range of mouse-passaged scrapie strains and bovine spongiform encephalopathy (BSE). In the spleen, lymph node and Peyer's patches, PrP-positive cells were identified as follicular dendritic cells (FDC) by their location, appearance, and immune complex trapping function, whereas in the thymus they appeared to be two types of stromal cells: interdigitating cells (IDC) and cortical epithelial cells. In pancreas, PrP-containing cells were confined to the islets of Langerhans. Although the distribution of PrP immunolabelling was the same in tissues from scrapie-affected and uninfected mice, there was evidence that PrP accumulated in abnormal forms in FDC of infected mice. If, as is likely, PrP is essential for agent replication, our results suggest that FDC are the site of scrapie and BSE replication in the spleen and lymph node.

Infection specific prion protein (PrP) accumulates on neuronal plasmalemma in scrapie infected mice

Prion protein (PrP) is an abundant membrane-associated host protein which accumulates in abnormal, relatively protease-resistant forms in the brains of animals with scrapie and related diseases. Using correlative light and electron microscopy we determined the sites of subcellular localisation of PrP in mice infected with the 87V strain of scrapie. Disease specific accumulation of PrP was observed at light microscopy as amyloid plaques or as diffuse or granular staining within the neuropil, often clearly associated with individual neurons. Serial electron microscopical preparations were immunostained for PrP by the immunogold method. Gold particles were located on amyloid fibrils and on the plasmalemma of neurites at the periphery of plaques and in the neuropil, irrespective of the morphological form of PrP accumulation when viewed by light microscopy. This suggests that amyloid fibrils are formed following the accumulation and aggregation of sub-unit proteins at the plasmalemma and, furthermore, that normal PrP may be converted to its pathological form at this site.

Platelet and whole blood serotonin content in depressed inpatients: correlations with acute and life-time psychopathology

Platelet or whole blood serotonin content did not differ significantly in patients with major depression compared to healthy controls, but within the patient group, platelet serotonin levels correlated negatively with severity of depression (r = -0.49, p = 0.007). Levels were 39% lower in patients who had made a suicide attempt compared to nonattempter patients (47.2 +/- 27.3 versus 77.6 +/- 41.7 ng/10(8) platelets, p = 0.04). Conversely, comorbid borderline personality disorder (85.3 +/- 41.5 ng/10(8) platelets) was associated with 31% greater platelet serotonin content than nonborderline patients (58.9 +/- 31.1 ng/10(8) platelets) and 27% greater than healthy controls (62.4 +/- 19.8 ng/10(8) platelets). A pronounced seasonal variation in whole blood and platelet serotonin content was found in both patients and controls, largely due to lower levels in summer. Excluding cases tested in the summer abolished the statistically significant differences in patients with and without comorbid borderline personality disorder (BPD). Nevertheless, BPD attempters had lower serotonin levels than BPD nonattempters but higher serotonin levels than non-BPD attempters. Current hostility and a life-time history of aggression were positively correlated with platelet serotonin content (r = 0.44, p = 0.04 and r = 0.41, p = 0.06). This study provides evidence for an association between lower platelet serotonin content and depression and suicidal behavior, and association of higher platelet serotonin content and comorbid borderline personality disorder and behavior traits such as aggressivity.

Relationship between central and peripheral serotonin indexes in depressed and suicidal psychiatric inpatients

Serious suicidal behavior, affective disorders, and a variety of other psychopathologic behaviors and syndromes have been found to correlate with measures of the serotonin system. Clinical studies have employed a range of serotonin indexes, including the cerebrospinal fluid level of 5-hydroxyindoleacetic acid, the prolactin response to serotonin agonists, such as fenfluramine hydrochloride, and platelet serotonin-related proteins or serotonin content. Many of these indexes are correlated with suicidal behavior, but the interrelationship of these biologic measures has been uncertain. We studied the relationship of a series of serotonin indexes in patients in whom these measures were correlated with suicidal behavior. A positive correlation was found between cerebrospinal fluid 5-hydroxyindoleacetic acid and the maximal prolactin response to fenfluramine but not with platelet serotonin2 receptor indexes. The fenfluramine-stimulated maximal prolactin response correlated with platelet serotonin2 receptor number, particularly in older patients. We conclude that cerebrospinal fluid 5-hydroxyindoleacetic acid measurements cannot be replaced but can be complemented by less invasive procedures, such as a fenfluramine challenge test or platelet serotonin2 measures, in the study of the relationship of the serotonin system to psychiatric disorders.

Color vision deficits and Rorschach performance in aged persons

Forty-two community residing older adults (M age = 69.28) (32 color normal, 10 color deficient) were administered the Rorschach and measures of both verbal and nonverbal intelligence in order to explore the effect of color vision deficiencies on affective responsivity. Among the sample of older persons screened for both visual and auditory acuity, when controls for intelligence and numbers of responses were made, greater affective constriction was found in the protocols of color vision deficient persons, relative to color normal individuals. These data suggest that Rorschach indicators of affective constriction may be biased in the case of individuals who have experienced color vision decrements. Consequently, first screening for color vision decrements when assessing older persons' personality dynamics may be desirable.

Neuroendocrine and behavioral responses to challenge with the indirect serotonin agonist dl-fenfluramine in adults with obsessive-compulsive disorder

Neuroendocrine and behavioral responses to a single 60-mg oral dose of the indirect serotonin agonist dl-fenfluramine were assessed in unmedicated adults with obsessive-compulsive disorder (OCD) and neuroendocrine results contrasted with those in normal control subjects. Net fenfluramine-induced prolactin release did not differ significantly between OCD patients and normal controls. Prolactin responses in the OCD group were not significantly correlated with baseline Yale-Brown Obsessive Compulsive Scale scores for either obsessions or compulsions, but were positively correlated with the baseline Hamilton Depression Scale score and Hamilton Anxiety Scale score. No clear difference in the severity of patients' obsessions or compulsions was found following challenge with fenfluramine versus placebo. Although the present study does not demonstrate a serotonergic abnormality in OCD, this may be more a reflection of limitations of the test procedures than evidence that central nervous system (CNS) serotonergic function is normal in the disorder.

Cerebral amyloid plaques in Alzheimer's disease but not in scrapie-affected mice are closely associated with a local inflammatory process

Complement proteins of the classical pathway can be immunohistochemically identified in cerebral amyloid plaques in Alzheimer's disease. Microglial cells in and around amyloid plaques express class II major histocompatibility (MHC) antigens and complement receptors CR3 and CR4. Negative immunostaining for immunoglobulins and for T-cell subsets in the brain parenchyma demonstrates a lack of evidence for the involvement of specific immune responses (such as an immune complex-mediated complement activation or a cell-mediated immune response) in cerebral amyloid deposits in Alzheimer's disease. Cerebral amyloid plaques in scrapie-affected mice (slow-virus induced encephalopathy) do not contain complement factors C1q and C3c and are not clustered with microglial cells expressing MHC class II molecules or complement receptor CR3. The data presented suggest the induction of a reactive inflammatory process by beta/A4 amyloid in the human brain, but not by scrapie-induced PrP amyloid in mice. Our findings do not support the hypothesis that the immune system is involved in the generation of amyloid plaques in Alzheimer's disease.

Effects of age and gender on CNS serotonergic responsivity in normal adults

The effects of age and gender on central nervous system (CNS) serotonergic responsivity were assessed with a neuroendocrine challenge test in 30 normal adults. Subjects greater than or equal to 30 years of age, compared with younger subjects, exhibited decreased prolactin secretion in response to a 60-mg oral dose of dl-fenfluramine hydrochloride, an indirect serotonin agonist. Furthermore, women had greater prolactin responses than men. As prolactin secretory capacity appears to be stable through midlife, the age-associated decrease in fenfluramine-induced prolactin release suggests a decline in CNS serotonergic responsivity. In contrast, the finding of greater prolactin release in women than in men probably reflects the effects of nonserotonergic modulatory influences at the level of the lactotroph. Age and gender effects must be considered in studies of the CNS serotonergic system.

Inhibition of serotonin-amplified human platelet aggregation by ketanserin, ritanserin, and the ergoline 5HT2 receptor antagonists-LY53857, sergolexole, and LY237733

Human platelets are known to possess 5HT2 receptors which, when activated, amplify the aggregation response produced by other aggregating agents. Several 5HT2 receptor antagonists, including ketanserin and ritanserin, are known to antagonize serotonin-mediated aggregation of human platelets. In the present study, we document the ability of three ergoline 5HT2 receptor antagonists, LY53857, sergolexole, and LY237733, to antagonize the serotonergic component of the human platelet aggregation response. Potencies of the ergoline esters (LY53857 and sergolexole) and the ergoline amide (LY237733) to inhibit serotonin-amplified platelet aggregation responses were similar to the potencies of ketanserin and ritanserin under the conditions of our study. Furthermore, all five 5HT2 receptor antagonists were capable of fully inhibiting the serotonergic component of the platelet aggregation response. In contrast to these potent ergoline esters and amides, 1-isopropyl dihydrolysergic acid (up to 10(-5)M), a putative metabolite of the ergoline esters, was ineffective under these in vitro conditions. These data are consistent with the high potency of these ergolines as antagonists of 5HT2 receptors and further support the involvement of 5HT2 receptors on human platelets in the amplifying response to serotonin.

Precise targeting of the pathology of the sialoglycoprotein, PrP, and vacuolar degeneration in mouse scrapie

Widespread immunostaining of PrP protein was demonstrated in scrapie mouse brain, distributed diffusely in the neuropil and focally in amyloid plaques, microglia and 2-5 microns structures resembling neuronal processes. With the 87V scrapie strain, which produces focal vacuolation in particular areas, PrP pathology was precisely targeted to these same areas, predating vacuolar degeneration by at least several weeks. On the other hand, both vacuolar and PrP changes were widely distributed throughout the brain with the ME7 scrapie strain. It is likely that the precise targeting of PrP pathology, followed by vacuolar degeneration, reflects an underlying targeting and localised replication of infectious agent.

Serotonergic responsivity in male young adults with autistic disorder. Results of a pilot study

Altered serotonergic function has been postulated to exist in autistic disorder. Central serotonergic responsivity was assessed with a neuroendocrine challenge test in seven male young adults with autistic disorder and in seven age- and gender-matched healthy controls. Binding indexes and physiologic responsivity of the platelet serotonin-2 (5-HT2) receptor complex were also measured, as was whole-blood serotonin content. Compared with controls, autistic subjects had substantially blunted prolactin release in response to a 60-mg oral dose of fenfluramine hydrochloride, an indirect serotonin agonist [corrected]. Furthermore, the magnitude of serotonin-amplified platelet aggregation, mediated by the platelet 5-HT2 receptor complex, was reduced in the autistic group, as was the mean number of platelet 5-HT2 receptor sites. Among autistic subjects, fenfluramine-induced prolactin release correlated positively with the serotonin-amplified platelet aggregation response and negatively with whole-blood serotonin content. The results of the present study are compatible with the hypothesis that central serotonergic responsivity is decreased in male autistic young adults. Correlations between central and peripheral serotonergic measures in autistic subjects suggest that systemic alterations in serotonergic function may occur in autism.

Immunostaining of scrapie cerebral amyloid plaques with antisera raised to scrapie-associated fibrils (SAF)

Brain sections from 16 different mouse scrapie models were immunostained with antisera to scrapie-associated fibrils (SAF) from three experimental scrapie sources (hamster 263K, mouse ME7 and mouse 22L). These models involved seven strains of scrapie injected intracerebrally or intraperitoneally into a range of inbred mouse strains, producing a wide variety of neuropathological changes. The only brain structures which were positively immunostained were amyloid plaque cores in those models in which plaques could be readily identified using traditional amyloid stains. The intensity of immunostaining correlated with the density of amyloid in the cores, as detected by Congo red and thioflavine S staining. No differences in immunostaining specificity were found between antisera or between plaques in different combinations of scrapie strain and mouse genotype. There were also no differences in immunoreactivity between plaques in different parts of the brain. These results strongly suggest that SAF and histologically detectable amyloid in scrapie mice are derived from the same precursor protein. Scrapie-associated cerebrovascular amyloid and plaques in sheep and goats also gave positive immunostaining with SAF antisera, although the lesions in the natural disease could only be stained after formic acid pretreatment. Senile plaques in Alzheimer's disease and Down's syndrome, although structurally similar to scrapie amyloid plaques, were found to be completely negative for SAF, in agreement with previous biochemical and immunocytochemical findings.

No evidence for involvement of plasma proteins or blood-borne cells in amyloid plaque formation in scrapie-affected mice. An immunohistoperoxidase study

The present study was designed to investigate blood-brain permeability and the possible involvement of plasma proteins and blood-borne cells in amyloid plaque formation in scrapie-affected mice. No abnormal extravasation of intravenously injected horseradish peroxidase (HRP) was found and with immunocytochemical techniques no plasma proteins were detected in neuropil from scrapie-affected mice. In contrast to an earlier report, these findings suggest that the blood-brain barrier is essentially intact in scrapie-affected mice. Using immunohistochemical and enzyme histochemical methods no cells belonging to the monocyte-macrophage lineage were detected in association with amyloid plaques. Thus, by these methods there was no evidence that plasma proteins or blood-borne cells are involved in amyloid plaque formation in scrapie-affected mice. However, astrocytes were consistently found to be associated with amyloid plaques at all stages of their development.

The association between spontaneous pyelonephritis and maturity-onset diabetes mellitus in male MM mice

Blood glucose and glucose tolerance tests demonstrated that many male MM mice are diabetic. Serial urine sampling showed that the diabetes occurred only in mature MM males and consisted of a single self-limiting episode. Histological examination of the pancreas, together with measurements of body weight, glycosylated haemoglobin and plasma insulin, revealed that the diabetes was of the maturity-onset insulin-resistant type. Bacteriological examination of the urine samples showed that urinary tract infection, a known feature of male MM mice, occurred in the diabetics but only after the onset of hyperglucosuria. It was concluded that the high urinary glucose levels of diabetic MM males are of prime importance in the aetiology of the renal infection which occurs rarely in non-diabetic MM males or in other strains in the colony. An infectious aetiology for the diabetes per se was excluded by the existence of diabetes in germfree MM males.

Assessment of binding indices and physiological responsiveness of the 5-HT2 receptor on human platelets

This is the first report of parallel studies of binding indices and physiological responsiveness of the "Serotonin-two" (5-HT2) receptor on the human platelet membrane. Binding indices were measured by a microassay employing [125I]ILSD as radioligand and ketanserin to define specific binding. A single receptor population was found, characterized by a KD of 1.69 +/- 0.45 nM and Bmax of 14.5 +/- 6.0 pmol/g protein in healthy subjects. Functional responsiveness of the platelet 5-HT2 receptor complex was assessed by measurement of the extent to which serotonin (10uM) augmented platelet aggregation induced by threshold concentrations of adenosine diphosphate (ADP). A statistically significant positive correlation was found between the number of platelet 5-HT2 receptor sites (Bmax) and the magnitude of the serotonin-amplified aggregation response (r = .70, n = 38, p less than 0.001). Assessment of binding indices and physiological responsiveness of the platelet 5-HT2 receptor complex should facilitate study of age, hormonal, disease, and drug effects on 5-HT2 receptor function in human subjects.

Autoclaved, formol-fixed scrapie mouse brain is suitable for histopathological examination, but may still be infective

Autoclaving Creutzfeldt-Jakob disease (CJD)-infected brain after fixation has been proposed previously as a means of making it safe for handling in the laboratory, while preserving its microscopic integrity. However, the practice which was recommended (126 degrees C for 30 min) would be unlikely to achieve complete decontamination. Autoclaving scrapie mouse brain (an analogue for CJD) to the higher, recommended standard of 134-138 degrees C for 18 min was found to lead to some tissue damage but not sufficient to prevent meaningful qualitative and quantitative study of the histopathological lesions.

Increased serotonin2 and beta-adrenergic receptor binding in the frontal cortices of suicide victims

A statistically significant 28% increase in the mean (+/- SD) number of serotonin2 receptors (127.8 +/- 13.4 vs 99.6 +/- 11.1 fmol/mg of protein) and a 73% increase in beta-adrenergic receptor binding (14.5 +/- 1.5 vs 8.4 +/- 1.5 fmol/mg) was found in the frontal cortices of violent suicide victims compared with matched controls. No significant differences were found in the number of serotonin1 binding sites (109.5 +/- 13.4 vs 99.9 +/- 8.8 fmol/mg). We have previously reported a reduced density of presynaptic tritiated imipramine binding sites on serotonergic nerve terminals in the frontal cortices of suicide victims. These data support the hypothesis that suicide completed by violent methods is associated with reduced presynaptic serotonergic activity that has generated compensatory upregulation of the postsynaptic serotonin2 receptor sites. The increase observed in beta-adrenergic binding suggests that there may also be a concomitant reduction in presynaptic noradrenergic activity associated with suicide. If antidepressant pharmacotherapies specifically downregulate cortical beta-adrenergic and/or serotonin2 receptors in depressed subjects, as has been demonstrated in animal studies, and since these effects would be in the opposite direction of the receptor changes found in suicide victims, they may account for the therapeutic action of antidepressants on suicidal behavior and depressive disorders.