A population-based study of the incidence of delusional infestation in Olmsted County, Minnesota, 1976-2010.

BACKGROUND: Delusional infestation (DI) is a well-recognized clinical entity but there is a paucity of reliable data concerning its epidemiology. Knowledge of the epidemiology is fundamental to an understanding of any disease and its implications. Epidemiology is most accurately assessed using population-based studies, which are most generalizable to the wider population in the U.S. and worldwide. To our knowledge, no population-based study of the epidemiology (particularly incidence) of DI has been reported to date. OBJECTIVES: To determine the incidence of delusional infestation (DI) using a population-based study. METHODS: Medical records of Olmsted County residents were reviewed using the resources of the Rochester Epidemiology Project to confirm the patient's status as a true incident case of DI and to gather demographic information. Patients with a first-time diagnosis of DI or synonymous conditions between 1 January 1976 and 31 December 2010 were considered incident cases. RESULTS: Of 470 identified possible diagnoses, 64 were true incident cases of DI in this population-based study. The age- and sex-adjusted incidence was 1·9 [95% confidence interval (CI) 1·5-2·4] per 100 000 person-years. Mean age at diagnosis was 61·4 years (range 9-92 years). The incidence of DI increased over the four decades from 1·6 (95% CI 0·6-2·6) per 100 000 person-years in 1976-1985 to 2·6 (95% CI 1·4-3·8) per 100 000 person-years in 2006-2010. CONCLUSIONS: Our data indicate that DI is a rare disease, with incidence increasing across the life span, especially after the age of 40 years.

A novel function for serotonin-mediated short-term facilitation in aplysia: conversion of a transient, cell-wide homosynaptic hebbian plasticity into a persistent, protein synthesis-independent synapse-specific enhancement.

Studies of sensitization and classical conditioning of the gill-withdrawal reflex in Aplysia have shown that the synaptic connections between identified glutamatergic sensory neurons and motor neurons can be enhanced in one of two ways: by a heterosynaptic (modulatory input-dependent) mechanism that gives rise with repetition to long-term facilitation and by a homosynaptic (activity-dependent) mechanism that gives rise with repetition to a facilitation that is partially blocked by 2-amino-5-phosphonovaleric acid and by injection of 1,2-bis(2-aminophenoxy)ethane-N,N,N', N'-tetraacetate (BAPTA) into the postsynaptic cell and is similar to long-term potentiation in the hippocampus. We here have examined how these two forms of facilitation interact at the level of an individual synaptic connection by using a culture preparation consisting of a single bifurcated sensory neuron that forms independent synaptic contacts with each of two spatially separated motor neurons. We find that the homosynaptic facilitation produced by a train of action potentials is cell wide and is evident at all of the terminals of the sensory neuron. By contrast, the heterosynaptic facilitation mediated by the modulatory transmitter serotonin (5-HT) can operate at the level of a single synapse. Homosynaptic activation gives rise to only a transient facilitation lasting a few hours, even when repeated in a spaced manner. The heterosynaptic facilitation produced by a single pulse of 5-HT, applied to one terminal of the sensory neuron, also lasts only minutes. However, when one or more homosynaptic trains of spike activity are paired with even a single pulse of 5-HT applied to one of the two branches of the sensory neuron, the combined actions lead to a selective enhancement in synaptic strength only at the 5-HT-treated branch that now lasts more than a day, and thus amplifies, by more than 20-fold, the duration of the individually produced homo- and heterosynaptic facilitation. This form of synapse-specific facilitation has unusual long-term properties. It does not require protein synthesis, nor is it accompanied by synaptic growth.

Is heterosynaptic modulation essential for stabilizing Hebbian plasticity and memory?

In 1894, Ramón y Cajal first proposed that memory is stored as an anatomical change in the strength of neuronal connections. For the following 60 years, little evidence was recruited in support of this idea. This situation changed in the middle of the twentieth century with the development of cellular techniques for the study of synaptic connections and the emergence of new formulations of synaptic plasticity that redefined Ramón y Cajal's idea, making it more suitable for testing. These formulations defined two categories of plasticity, referred to as homosynaptic or Hebbian activity-dependent, and heterosynaptic or modulatory input-dependent. Here we suggest that Hebbian mechanisms are used primarily for learning and for short-term memory but often cannot, by themselves, recruit the events required to maintain a long-term memory. In contrast, heterosynaptic plasticity commonly recruits long-term memory mechanisms that lead to transcription and to synpatic growth. When jointly recruited, homosynaptic mechanisms assure that learning is effectively established and heterosynaptic mechanisms ensure that memory is maintained.

Structural changes and the storage of long-term memory in Aplysia.

Long-term memory for sensitization of the gill-withdrawal reflex in Aplysia is associated with the growth of new synaptic connections between sensory and motor neurons. The duration of this structural change parallels the behavioral retention of the memory. Such changes can be reconstituted in dissociated cell culture by repeated presentations of the modulatory neurotransmitter serotonin (5HT) and are associated with an activity-dependent downregulation of NCAM-related cell adhesion molecules thought to contribute to cell recognition and axonal outgrowth during development. Thus, aspects of the mechanisms utilized for learning-related synaptic growth initiated by experience in the adult may eventually be understood in the context of the molecular logic that shapes synaptic circuitry during the later stages of neuronal development.

A transient, neuron-wide form of CREB-mediated long-term facilitation can be stabilized at specific synapses by local protein synthesis.

In a culture system where a bifurcated Aplysia sensory neuron makes synapses with two motor neurons, repeated application of serotonin (5-HT) to one synapse produces a CREB-mediated, synapse-specific, long-term facilitation, which can be captured at the opposite synapse by a single pulse of 5-HT. Repeated pulses of 5-HT applied to the cell body of the sensory neuron produce a CREB-dependent, cell-wide facilitation, which, unlike synapse-specific facilitation, is not associated with growth and does not persist beyond 48 hr. Persistent facilitation and synapse-specific growth can be induced by a single pulse of 5-HT applied to a peripheral synapse. Thus, the short-term process initiated by a single pulse of 5-HT serves not only to produce transient facilitation, but also to mark and stabilize any synapse of the neuron for long-term facilitation by means of a covalent mark and rapamycin-sensitive local protein synthesis.

Tissue plasminogen activator contributes to the late phase of LTP and to synaptic growth in the hippocampal mossy fiber pathway.

The expression of tissue plasminogen activator (tPA) is increased during activity-dependent forms of synaptic plasticity. We have found that inhibitors of tPA inhibit the late phase of long-term potentiation (L-LTP) induced by either forskolin or tetanic stimulation in the hippocampal mossy fiber and Schaffer collateral pathways. Moreover, application of tPA enhances L-LTP induced by a single tetanus. Exposure of granule cells in culture to forskolin results in secretion of tPA, elongation of mossy fiber axons, and formation of new, active presynaptic varicosities contiguous to dendritic clusters of the glutamate receptor R1. These structural changes are blocked by tPA inhibitors and induced by application of tPA. Thus, tPA may be critically involved in the production of L-LTP and specifically in synaptic growth.

Mutation in the phosphorylation sites of MAP kinase blocks learning-related internalization of apCAM in Aplysia sensory neurons.

The synaptic growth that accompanies 5-HT-induced long-term facilitation of the sensory to motor neuron connection in Aplysia is associated with the internalization of apCAM at the surface membrane of the sensory neuron. We have now used epitope tags to examine the fate of each of the two apCAM isoforms (membrane bound and GPI-linked) and find that only the transmembrane form is internalized. This internalization can be blocked by overexpression of transmembrane constructs with a single point mutation in the two MAPK consensus sites, as well as by injection of a specific MAPK antagonist into sensory neurons. These data suggest MAPK phosphorylation at the membrane is important for the internalization of apCAMs and, thus, may represent an early regulatory step in the growth of new synaptic connections that accompanies long-term facilitation.

Synapse-specific, long-term facilitation of aplysia sensory to motor synapses: a function for local protein synthesis in memory storage.

The requirement for transcription during long-lasting synaptic plasticity has raised the question of whether the cellular unit of synaptic plasticity is the soma and its nucleus or the synapse. To address this question, we cultured a single bifurcated Aplysia sensory neuron making synapses with two spatially separated motor neurons. By perfusing serotonin onto the synapses made onto one motor neuron, we found that a single axonal branch can undergo long-term branch-specific facilitation. This branch-specific facilitation depends on CREB-mediated transcription and involves the growth of new synaptic connections exclusively at the treated branch. Branch-specific long-term facilitation requires local protein synthesis in the presynaptic but not the postsynaptic cell. In fact, presynaptic sensory neuron axons deprived of their cell bodies are capable of protein synthesis, and this protein synthesis is stimulated 3-fold by exposure to serotonin.

Toward a molecular definition of long-term memory storage.

The storage of long-term memory is associated with a cellular program of gene expression, altered protein synthesis, and the growth of new synaptic connections. Recent studies of a variety of memory processes, ranging in complexity from those produced by simple forms of implicit learning in invertebrates to those produced by more complex forms of explicit learning in mammals, suggest that part of the molecular switch required for consolidation of long-term memory is the activation of a cAMP-inducible cascade of genes and the recruitment of cAMP response element binding protein-related transcription factors. This conservation of steps in the mechanisms for learning-related synaptic plasticity suggests the possibility of a molecular biology of cognition.

Reconstitution of the hippocampal mossy fiber and associational-commissural pathways in a novel dissociated cell culture system.

Synapses of the hippocampal mossy fiber pathway exhibit several characteristic features, including a unique form of long-term potentiation that does not require activation of the N-methyl-D-aspartate receptor by glutamate, a complex postsynaptic architecture, and sprouting in response to seizures. However, these connections have proven difficult to study in hippocampal slices because of their relative paucity (<0.4%) compared to commissural-collateral synapses. To overcome this problem, we have developed a novel dissociated cell culture system in which we have enriched mossy fiber synapses by increasing the ratio of granule-to-pyramidal cells. As in vivo, mossy fiber connections are composed of large dynorphin A-positive varicosities contacting complex spines (but without a restricted localization). The elementary synaptic connections are glutamatergic, inhibited by dynorphin A, and exhibit N-methyl-D-aspartate-independent long-term potentiation. Thus, the simplicity and experimental accessibility of this enriched in vitro mossy fiber pathway provides a new perspective for studying nonassociative plasticity in the mammalian central nervous system.

Aplysia CREB2 represses long-term facilitation: relief of repression converts transient facilitation into long-term functional and structural change.

The switch from short- to long-term facilitation induced by behavioral sensitization in Aplysia involves CREB-like proteins, as well as the immediate-early gene ApC/EBP. Using the bZIP domain of ApC/EBP in a two-hybrid system, we have cloned ApCREB2, a transcription factor constitutively expressed in sensory neurons that resembles human CREB2 and mouse ATF4. ApCREB2 represses ApCREB1-mediated transcription in F9 cells. Injection of anti-ApCREB2 antibodies into Aplysia sensory neurons causes a single pulse of serotonin (5-HT), which induces only short-term facilitation lasting minutes, to evoke facilitation lasting more than 1 day. This facilitation has the properties of long-term facilitation: it requires transcription and translation, induces the growth of new synaptic connections, and occludes further facilitation by five pulses of 5-HT.

5-HT and cAMP induce the formation of coated pits and vesicles and increase the expression of clathrin light chain in sensory neurons of aplysia.

In the course of studying proteins involved in long-term facilitation in Aplysia, we found that 5-HT and cAMP, a second messenger activated by 5-HT, lead to the removal of a set of N-CAM-related cell adhesion molecules (apCAMs) from the surface membrane of sensory neurons by means of receptor-mediated endocytosis. Here we describe that, as part of this coordinated program for endocytosis, 5-HT and cAMP also induce in the sensory neurons an increase in the density of coated pits and coated vesicles and an increase in the expression of the light chain of Aplysia clathrin (apClathrin). The clathrin-related endocytosis seems designed to internalize and redistribute apCAMs and other surface membrane proteins in the sensory neurons, and thus it appears to constitute one of the initial steps in the growth of new synaptic connections that accompanies long-term facilitation.

Inhibitors of protein and RNA synthesis block structural changes that accompany long-term heterosynaptic plasticity in Aplysia.

Synaptic connections between the sensory and motor neurons of Aplysia in culture undergo long-term facilitation in response to serotonin (5-HT) and long-term depression in response to FMRFamide. These long-term functional changes are dependent on the synthesis of macromolecules during the period in which the transmitter is applied and are accompanied by structural changes. There is an increase and a decrease, respectively, in the number of sensory neuron varicosities in response to 5-HT and FMRFamide. To determine whether macromolecular synthesis is also required for the structural changes, we examined in parallel the effects of inhibitors of protein (anisomycin) or RNA (actinomycin D) synthesis on the structural and functional changes. We have found that anisomycin and actinomycin D block both the enduring alterations in varicosity number and the long-lasting changes in synaptic potential. These results indicate that macromolecular synthesis is required for expression of the long-lasting structural changes in the sensory cells and that this synthesis is correlated with the long-term functional modulation of sensorimotor synapses.

Serotonin-mediated endocytosis of apCAM: an early step of learning-related synaptic growth in Aplysia.

The long-term facilitation of synaptic efficacy that is induced by serotonin in dissociated cell cultures of sensory and motor neurons of Aplysia is accompanied by the growth of new synaptic connections. This growth is associated with a down-regulation in the sensory neuron of Aplysia cell adhesion molecules (apCAMs). To examine the mechanisms of this down-regulation, thin-section electron microscopy was combined with immunolabeling by gold-conjugated monoclonal antibodies specific to apCAM. Within 1 hour, serotonin led to a 50% decrease in the density of gold-labeled complexes at the surface membrane of the sensory neuron. This down-regulation was achieved by a heterologous, protein synthesis-dependent activation of the endosomal pathway, which leads to internalization and apparent degradation of apCAM. The internalization is particularly prominent at sites where the processes of the sensory neurons contact one another and may act there to destabilize process-to-process contacts that normally inhibit growth. In turn, the endocytic activation may lead to a redistribution of membrane components to sites where new synapses form.

Morphological aspects of synaptic plasticity in Aplysia. An anatomical substrate for long-term memory.

The morphological basis of long-term sensitization of the gill-and-siphon withdrawal reflex in Aplysia was explored by examining the structure of identified sensory neuron synapses in control and behaviorally modified animals. Following long-term training, sensitized animals displayed an increase in the number of sensory neuron synapses compared to control animals. The relative permanence of these structural changes and their similarity in time course to the behavioral duration of sensitization suggest a role for synapse number changes during long-term memory.

Structural plasticity at identified synapses during long-term memory in Aplysia.

We have used the gill- and siphon-withdrawal reflex of Aplysia californica to determine the morphological basis of the prolonged changes in synaptic effectiveness that underlie long-term habituation and sensitization. We have found that clear structural changes accompany behavioral modification and have demonstrated that these can be detected at the level of identified sensory neuron synapses, a critical site of plasticity for the short-term forms of both types of learning. These alterations occur at two different levels of synaptic organization and include (1) changes in focal regions of synaptic membrane specialization--the number, size and vesicle complement of sensory neuron active zones are larger in sensitized animals and smaller in habituated animals compared with controls--and (2) a parallel but more dramatic and global trend involving modulation of the total number of presynaptic varicosities per sensory neuron. Quantitative analysis of the time course over which these structural alterations occur during sensitization has further demonstrated that changes in the number of varicosities and active zones persist in parallel with the behavioral retention of the memory. This increase in the number of sensory neuron synapses during long-term sensitization in Aplysia is similar to changes in the number of synapses in the mammalian brain following various forms of environmental manipulations and learning (Greenough, 1984). Therefore learning may involve a form of neuronal growth across a broad segment of the animal kingdom, thereby suggesting a role for structural synaptic plasticity during long-term behavioral modifications.

Innervation of vascular and cardiac muscle of Aplysia by multimodal motoneuron L7.

1. The cardiovascular system of Aplysia has proven to be a useful preparation for study of the neural control of circulation. To better understand the neural integration of function in this system, we have attempted to gain a more complete picture of its morphology and innervation patterns, with particular emphasis on the abdominal aorta and heart. 2. The vasoconstrictor muscle fibers of the abdominal aorta were found by dye injection to be extensively branched, with many processes that are less than 1 micron in diameter. Because of the wide spacing between individual muscle fibers, these fine processes, which have relatively few contractile filaments, may be required to mediate the electrical coupling that is observed between muscle cells. 3. L7, an identified cell in the abdominal ganglion, had been shown by others to be an excitatory motoneuron for the gill, the siphon, and the sheath-contracting muscles of the pleuroabdominal connectives, and also to excite the gill motoneurons in the branchial ganglion (5, 43, 56). We have found that this multimodal motoneuron also directly excites the auricle of the heart and the vasoconstrictor muscle of the abdominal aorta. 4. The excitatory effect of L7 on the abdominal aorta interacts synergistically with that produced by the other known excitatory inputs to that structure, the LBVc vasoconstrictor motoneurons. 5. The abdominal aorta is also richly innervated by axons immunoreactive for serotonin and for the neuropeptide FMRFamide. Serotonin inhibits the contractions of the aorta elicited by firing either L7 or the LBVC cells. In contrast, FMRFamide selectively inhibits the contractions elicited by the LBVC cells. 6. Our results suggest that a significant amount of the functional integration of the cardiovascular and respiratory systems is achieved by the use of a motoneuron common to both systems, and that there is likely to be extensive peripheral inhibitory modulation of the vasoconstrictor inputs to the abdominal aorta.

Time course of structural changes at identified sensory neuron synapses during long-term sensitization in Aplysia.

We have used the gill- and siphon-withdrawal reflex of Aplysia californica to explore the morphological basis of the synaptic plasticity that underlies long-term sensitization. In earlier studies (Bailey and Chen, 1983, 1988a), we described 2 classes of structural changes at identified sensory neuron synapses that occur following long-term sensitization: (1) increases in the number, size, and vesicle complement of active zones and (2) an overall increase in the total number of synaptic varicosities per sensory neuron. In the present study, we have begun to examine which of these anatomical changes might be necessary for the maintenance of long-term sensitization by exploring the time course over which they occur and, in particular, their duration relative to the persistence of the memory assessed behaviorally. Toward this end we have quantitated changes in both the total number of varicosities and their active zone morphology in single HRP-labeled sensory neurons taken from long-term sensitized and control animals at different intervals (1-2 d, 1 week, and 3 weeks) following training. We have found that long-term sensitized animals examined within 48 hr after the completion of training demonstrate an increase in the total number of varicosities per sensory neuron as well as an increase in the incidence, size, and vesicle complement of their synaptic active zones compared with control animals. The increase in the number of varicosities and active zones persists unchanged for at least 1 week, and the increase in active zone number is only partially reversed at the end of 3 weeks.(ABSTRACT TRUNCATED AT 250 WORDS)