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OBJECTIVES: The mechanism of many neuropsychiatric disorders remains unknown, but the ineffectiveness of the sodium channel blocker lidocaine has been suggested to be a biomarker for Attention Deficit Hyperactivity Disorder (ADHD) and a severe form of Premenstrual Syndrome (PMS) that is considered psychiatric. We conducted single-arm double-blind clinical trials to test whether lidocaine ineffectiveness can be used as a biomarker to identify people with these conditions and provide a clue as to the molecular mechanism and potential psychopharmacological intervention. EXPERIMENTAL DESIGN: We developed a noninvasive taste test for lidocaine ineffectiveness, validated by comparing lidocaine injections to pain testing in 12 subjects, and assessed it in individuals with ADHD and PMS. PRINCIPAL OBSERVATIONS: Lidocaine ineffectiveness had a strong association in women with ADHD + PMS in a sample of 53 subjects and controls (p < 0.001). CONCLUSIONS: These results suggest the possibility of the biological understanding of the combination of ADHD and PMS that is characteristic of the psychiatric disorder Premenstrual Dysphoric Disorder (PMDD). These results and comparison to family pedigrees of a neuromuscular channelopathy with overlapping symptoms suggest the possibility that the clinical phenotype in PMDD is produced by sensory overstimulation, and amenable to molecular understanding and treatment.

The Human Phenotype Ontology (HPO, https://hpo.jax.org) was launched in 2008 to provide a comprehensive logical standard to describe and computationally analyze phenotypic abnormalities found in human disease. The HPO is now a worldwide standard for phenotype exchange. The HPO has grown steadily since its inception due to considerable contributions from clinical experts and researchers from a diverse range of disciplines. Here, we present recent major extensions of the HPO for neurology, nephrology, immunology, pulmonology, newborn screening, and other areas. For example, the seizure subontology now reflects the International League Against Epilepsy (ILAE) guidelines and these enhancements have already shown clinical validity. We present new efforts to harmonize computational definitions of phenotypic abnormalities across the HPO and multiple phenotype ontologies used for animal models of disease. These efforts will benefit software such as Exomiser by improving the accuracy and scope of cross-species phenotype matching. The computational modeling strategy used by the HPO to define disease entities and phenotypic features and distinguish between them is explained in detail.We also report on recent efforts to translate the HPO into indigenous languages. Finally, we summarize recent advances in the use of HPO in electronic health record systems.

Problem: Teaching genetic diagnosis is required in all medical schools and physician assistant programs. However, with thousands of relevant findings and thousands more rare diseases, lectures and narrative resources are inadequate for the task. Whatever information that is taught is easily forgotten and does not carry over into the clinic. Many rare disease patients suffer through “diagnostic odysseys” (3 to 30 years to correct diagnosis). Approach: We used a commercially available diagnostic decision support system (DDSS) that encompasses all Mendelian disorders with known genes, together with other conditions in their differential diagnosis, and a case-based educational approach to teach diagnostic skills in a way that could then be replicated in the clinic. After a lecture, which included a demonstration using the DDSS with a sample case, 74 students were assigned to replicate the sample case at home and then complete 7 other anonymized cases, all with known rare diagnoses. After each case, students saved the “patient summary” that included the findings entered and differential diagnosis list and submitted it as homework. Students also completed a questionnaire about their experience, including satisfaction. Outcomes: Students were effective at diagnosing rare diseases in 483 of the 514 testing instances, a 94% success rate, with success defined as the correct diagnosis being listed in the differential diagnosis. Eighty-five percent of students rated this interactive learning session “highly,” encouraged us to repeat the assignment next year, and 89% reported that they wanted to use the DDSS during their clinical rotations in the coming year. Next Steps: We plan to refine the cases, add more material on findings, and ensure that all the synonyms students might use are in the software tool. We plan to repeat the program next year and recommend its use more widely in medical education.

Deep phenotyping has been defined as the precise and comprehensive analysis of phenotypic abnormalities in which the individual components of the phenotype are observed and described. The three components of the Human Phenotype Ontology (HPO; www.human-phenotype-ontology.org) project are the phenotype vocabulary, disease-phenotype annotations and the algorithms that operate on these. These components are being used for computational deep phenotyping and precision medicine as well as integration of clinical data into translational research. The HPO is being increasingly adopted as a standard for phenotypic abnormalities by diverse groups such as international rare disease organizations, registries, clinical labs, biomedical resources, and clinical software tools and will thereby contribute toward nascent efforts at global data exchange for identifying disease etiologies. This update article reviews the progress of the HPO project since the debut Nucleic Acids Research database article in 2014, including specific areas of expansion such as common (complex) disease, new algorithms for phenotype driven genomic discovery and diagnostics, integration of cross-species mapping efforts with the Mammalian Phenotype Ontology, an improved quality control pipeline, and the addition of patient-friendly terminology. ispartof: Nucleic Acids Research vol:45 issue:D1 pages:D865-D876 ispartof: location:England status: published

National Institutes of Health (NIH), Monarch Initiative [OD #5R24OD011883]; Forums for Integrative Phenomics [U13 CA221044-01]; NCATS Data Translator [1OT3TR002019]; NCATS National Center for Digital Health Informatics Innovation [U24 TR002306];NIH Data Commons [1 OT3 OD02464-01 UNCCH]; Cost Action CA 16118 Neuro-MIG; British Heart Foundation Programme Grant [RG/13/5/30112]; Division of Intramural Research; NIAID; NIH; E-RARE project Hipbi-RD [01GM1608]; European Union's Horizon 2020 Research and Innovation Programme [779257]. Funding for open access charge: NIH; Donald A. Roux Family Fund (to P.N.R.). The Human Phenotype Ontology (HPO) - a standardized vocabulary of phenotypic abnormalities associated with 7000+ diseases - is used by thousands of researchers, clinicians, informaticians and electronic health record systems around the world. Its detailed descriptions of clinical abnormalities and computable disease definitions have made HPO the de facto standard for deep phenotyping in the field of rare disease. The HPO's interoperability with other ontologies has enabled it to be used to improve diagnostic accuracy by incorporating model organism data. It also plays a key role in the popular Exomiser tool, which identifies potential disease-causing variants from whole-exome or whole-genome sequencing data. Since the HPO was first introduced in 2008, its users have become both more numerous and more diverse. To meet these emerging needs, the project has added new content, language translations, mappings and computational tooling, as well as integrations with external community data. The HPO continues to collaborate with clinical adopters to improve specific areas of the ontology and extend standardized disease descriptions. The newly redesigned HPO website (www.human-phenotype-ontology.org) simplifies browsing terms and exploring clinical features, diseases, and human genes.

Introduction: Reducing misdiagnosis has long been a goal of medical informatics. Current thinking has focused on achieving this goal by integrating diagnostic decision support into electronic health records.Methods: A diagnostic decision support system already in clinical use was integrated into electronic health record systems at two large health systems, after clinician input on desired capabilities. The decision support provided three outputs: editable text for use in a clinical note, a summary including the suggested differential diagnosis with a graphical representation of probability, and a list of pertinent positive and pertinent negative findings (with onsets).Results: Structured interviews showed widespread agreement that the tool was useful and that the integration improved workflow. There was disagreement among various specialties over the risks versus benefits of documenting intermediate diagnostic thinking. Benefits were most valued by specialists involved in diagnostic testing, who were able to use the additional clinical context for richer interpretation of test results. Risks were most cited by physicians making clinical diagnoses, who expressed concern that a process that generated diagnostic possibilities exposed them to legal liability.Discussion and Conclusion: Reconciling the preferences of the various groups could include saving only the finding list as a patient-wide resource, saving intermediate diagnostic thinking only temporarily, or adoption of professional guidelines to clarify the role of decision support in diagnosis.

“The objective of this study was to” test the effectiveness of an enhanced genomic report on patient-centered outcome domains including communication, engagement and satisfaction. “Study design utilized” a prospective, randomized, mixed-methods desctiptive study of a whole genome sequencing results report, GenomeCOMPASS™, that was accessed by providers through the electronic health record and by patients through the associated patient portal. “The study was set in” an integrated healthcare delivery system in central Pennsylvania. “Eighty-four” parents of 46 children with undiagnosed Intellectual Disability, Autism Spectrum Disorder and/or multiple congenital anomalies who had participated in a previous study offering whole genome sequencing for their affected child were invited to enroll. Fifty-two parents enrolled. Following a traditional genetics results informing visit, the study coordinator stratified families by diagnostic result and uninformative result and then randomized families within each group to an intervention arm to receive the GenomeCOMPASS™ report or to the usual care arm to receive a summary letter from the medical geneticist. A letter inviting enrollment included a baseline survey, which once returned, constituted enrollment. Surveys were administered at 3 months post-genetics visit. At 6 months, the usual care arm crossed over to receive the intervention and were administered an additional survey at 3 months. Qualitative interviews were conducted following survey completion to augment the survey data regarding the patient centered outcomes of interest. Patient reported outcomes including communication, engagement, empowerment and satisfaction. In the intervention arm, GenomeCOMPASS™ reports were released to 14 families (N = 28 parents) and of those 21 (75%) returned 3 month surveys. In the usual care arm, 12 families (N = 24 parents) received usual care summary letters and of those 20 (83%) returned 3 month surveys. At crossover, GenomeCOMPASS™ reports were released to 20 individuals and 15 (75%) returned 3 month surveys. Qualitative interviews were conducted with 5 individuals. Use of the GenomeCOMPASS™ report was reported by this small group of parents to improve communication with providers and non-health professionals such as educators and therapists and led to increased engagement and high satisfaction. Providers and others involved in the children’s care also endorsed the report’s effectiveness. Reports that addressed negative findings, i.e. uninformative results, were not found to be useful. Although the number of users was small, this study supports that customizable template reports may provide a useful and durable source of information that can support and enhance the information provided by genetics professionals in traditional face-to-face encounters. Trial registration: Clinicaltrials.gov (Record 2013–0594). Electronic supplementary material The online version of this article (10.1007/s10897-017-0176-6) contains supplementary material, which is available to authorized users.

We describe an “integrated genome-phenome analysis” that combines both genomic sequence data and clinical information for genomic diagnosis. It is novel in that it uses robust diagnostic decision support and combines the clinical differential diagnosis and the genomic variants using a “pertinence” metric. This allows the analysis to be hypothesis-independent, not requiring assumptions about mode of inheritance, number of genes involved, or which clinical findings are most relevant. Using 20 genomic trios with neurologic disease, we find that pertinence scores averaging 99.9% identify the causative variant under conditions in which a genomic trio is analyzed and family-aware variant calling is done. The analysis takes seconds, and pertinence scores can be improved by clinicians adding more findings. The core conclusion is that automated genome-phenome analysis can be accurate, rapid, and efficient. We also conclude that an automated process offers a methodology for quality improvement of many components of genomic analysis.

Using vignettes of real cases and the SimulConsult diagnostic decision support software, neurologists listed a differential diagnosis and workup before and after using the decision support. Using the software, there was a significant reduction in error, up to 75% for diagnosis and 56% for workup. This error reduction occurred despite the baseline being one in which testers were allowed to use narrative resources and Web searching. A key factor that improved performance was taking enough time (>2 minutes) to enter clinical findings into the software accurately. Under these conditions and for instances in which the diagnoses changed based on using the software, diagnostic accuracy improved in 96% of instances. There was a 6% decrease in the number of workup items accompanied by a 34% increase in relevance. The authors conclude that decision support for a neurological diagnosis can reduce errors and save on unnecessary testing.

Background The number of trained specialists world-wide is insufficient to serve all children with pediatric rheumatologic disorders, even in the countries with robust medical resources. We evaluated the potential of diagnostic decision support software (DDSS) to alleviate this shortage by assessing the ability of such software to improve the diagnostic accuracy of non-specialists. Methods Using vignettes of actual clinical cases, clinician testers generated a differential diagnosis before and after using diagnostic decision support software. The evaluation used the SimulConsult® DDSS tool, based on Bayesian pattern matching with temporal onset of each finding in each disease. The tool covered 5405 diseases (averaging 22 findings per disease). Rheumatology content in the database was developed using both primary references and textbooks. The frequency, timing, age of onset and age of disappearance of findings, as well as their incidence, treatability, and heritability were taken into account in order to guide diagnostic decision making. These capabilities allowed key information such as pertinent negatives and evolution over time to be used in the computations. Efficacy was measured by comparing whether the correct condition was included in the differential diagnosis generated by clinicians before using the software (“unaided”), versus after use of the DDSS (“aided”). Results The 26 clinicians demonstrated a significant reduction in diagnostic errors following introduction of the software, from 28% errors while unaided to 15% using decision support (p

This study reports on the responses of physicians who reviewed provider and patient versions of a genomic laboratory report designed to communicate results of whole genome sequencing. Semi‐structured interviews addressed concept communication, elements, and format of example genome reports. Analysis of the coded transcripts resulted in recognition of three constructs around communication of genome sequencing results: (1) Providers agreed that whole genomic sequencing results are complex and they welcomed a report that provided supportive interpretation information to accompany sequencing results; (2) Providers strongly endorsed a report that included active clinical guidance, such as reference to practice guidelines, if available; and (3) Providers valued the genomic report as a resource that would serve as the basis to facilitate communication of genome sequencing results with their patients and families. Providers valued both versions of the report, though they affirmed the need for a provider‐oriented report. Critical elements of the report included clear language to explain the result, as well as consolidated yet comprehensive prognostic information with clear guidance over time for the clinical care of the patient. Most importantly, it appears a report with this design has the potential not only to return results but also serves as a communication tool to help providers and patients discuss and coordinate care over time. © 2016 The Authors. American Journal of Medical Genetics Part A published by Wiley Periodicals, Inc.

We examined the vulnerability to excitotoxicity of rat oligodendrocytes in dissociated cell culture at different developmental stages. Mature oligodendrocytes that express myelin basic protein were resistant to excitotoxic injury produced by kainate, whereas earlier stages in the oligodendrocyte lineage were vulnerable to this insult. To test the hypothesis that the sensitivity of immature oligodendrocytes and the resistance of mature oligodendrocytes to kainate toxicity were due to differences in membrane responsiveness to kainate, we used whole-cell patch-clamp recording. Oligodendrocyte precursors in cultures vulnerable to kainate toxicity responded to 500 μM kainate with large inward currents, whereas mature myelin basic protein-expressing oligodendrocytes in cultures resistant to kainate toxicity showed no clear response to application of this agonist. We assayed expression of glutamate receptor subunits (GluR) -2, -4, -6, -7, and KA2 using immunoblot analysis and found that expression of all of these glutamate receptors was significantly down-regulated in mature oligodendrocytes. These results suggest a striking developmental regulation of glutamate receptors in oligodendrocytes and suggest that the vulnerability of oligodendrocytes to non- N-methyl-D-aspartate receptor-mediated excitotoxicity might be much greater in developing oligodendrocytes than after the completion of myelination. © 2002 Wiley-Liss, Inc.

This report describes 2 generations of a family with symptoms of sensory overstimulation that exhibit a potassium sensitivity similar to that seen in hypokalemic periodic paralysis. The sensory overstimulation is characterized by a subjective experience of sensory overload and a relative resistance to lidocaine local anesthesia. The sensory overload is treatable with oral potassium gluconate, with onset of the therapeutic effect in ~20 minutes. The effect of potassium is reminiscent of its effect in the channelopathies underlying hypokalemic periodic paralysis, and the resistance to lidocaine applied peripherally suggests a peripheral sensory localization to the abnormality. The phenotype overlaps with that of attention deficit disorder, raising the possibility of subtypes of attention deficit disorder that have a peripheral sensory cause and novel forms of therapy.

The potential of most N-methyl-D-aspartate antagonists as neuroprotectants is limited by side effects. We previously reported that memantine is an open-channel N-methyl-D-aspartate blocker with a faster off-rate than many uncompetitive N-methyl-D-aspartate antagonists such as dizocilpine maleate. This parameter correlated with memantine's known clinical tolerability in humans with Parkinson's disease. Memantine is the only N-methyl-D-aspartate antagonist that has been used clinically for excitotoxic disorders at neuroprotective doses. Therefore, we wanted to investigate further the basis of its clinical efficacy, safety, and tolerability. Here we show for the first time for any clinically-tolerated N-methyl-D-aspartate antagonist that memantine significantly reduces infarct size when administered up to 2 h after induction of hypoxia/ischemia in immature and adult rats. We found that at neuroprotective concentrations memantine results in few adverse side effects. Compared to dizocilpine maleate, memantine displayed virtually no effects on Morris water maze performance or on neuronal vacuolation. At concentrations similar to those in brain following clinical administration, memantine (6-10 microM) did not attenuate long-term potentiation in hippocampal slices and substantially spared the N-methyl-D-aspartate component of excitatory postsynaptic currents, while dizocilpine maleate (6-10 microM) or D-2-amino-5-phosphovalerate (50 microM) completely blocked these phenomena. We suggest that the favorable kinetics of memantine interaction with N-methyl-D-aspartate channels may be partly responsible for its high index of therapeutic safety, and make memantine a candidate drug for use in many N-methyl-D-aspartate receptor-mediated human CNS disorders.

Cadherins are a family of transmembrane proteins that play a crucial role in cell adhesion and in morphogenesis. Several of the cadherins are expressed in the nervous system, but none is neuron-specific. We characterize a new member of the cadherin family, Br-cadherin, which is present exclusively in the central nervous system. Although the Br-cadherin protein is confined to the central nervous system, its mRNA is present in several additional tissues, suggesting that there is posttranscriptional control of this gene’s expression. Within the central nervous system, Br-cadherin appears to be expressed specifically by neurons. In the mouse, its expression becomes detectable during the first postnatal week, which corresponds temporally to the onset of synaptogenesis and dendrite outgrowth in the brain. This pattern of expression is consistent with a role for Br-cadherin in neuronal development, perhaps specifically with synaptogenesis.

The mechanisms by which activation of excitatory amino acid receptors is coupled to the regulation of gene transcription were studied using cultured hippocampal neurons from neonatal rats. Voltage recording, calcium imaging, specific RNA analysis and immunocytochemistry were carried out on sister cultures. This allowed analysis of the expression of functional glutamate receptor subtypes, examination of their role in controlling intracellular free calcium ([Ca2+]i), and determination of their relative contributions to the transcriptional regulation of six immediate early genes c-fos, fosB, c-jun, junB, zif/268 (also termed Egr-1; NGFI-A; Krox-24) and nur/77 (also termed NGFI-B). Expression of all six immediate early genes was induced in hippocampal neurons by glutamate treatment. Nuclear run-on assays demonstrated that this induction occurred at the transcriptional level. Activation of the N-methyl-D-aspartate subtype of glutamate receptor was necessary and sufficient for the transcriptional response. Non-N-methyl-D-aspartate receptors, while present in cultured hippocampal neurons, contributed relatively little to the regulation of transcription. Calcium imaging showed that glutamate-induced changes in [Ca2+]i were almost entirely mediated by N-methyl-D-aspartate receptors, rather than by L-type voltage-sensitive calcium channels. Previous studies have shown that stimulation with selective agonists of either N-methyl-D-aspartate receptors, non-N-methyl-D-aspartate receptors, or L-type calcium channels can lead to an increase in [Ca2+]i and c-fos expression. Here we demonstrate that in our hippocampal culture system glutamate controls [Ca2+]i and induces immediate early gene transcription primarily by activating N-methyl-D-aspartate receptors.

The irony of predictions such as “attention deficit hyperactivity disorder (ADHD) does not exist” is that once knowledge has advanced enough to settle the question, it is no longer clear what the question meant in the first place. “ADHD Does Not Exist” is the title of a recent book by neurologist Richard Saul,1 which gives a detailed differential diagnosis of attention deficit, with the noble goal of reducing the indiscriminant use of stimulant drugs. Similar questions have also been raised in scientific journals, notably by Warren Weinberg and Roger Brumback in their 1992 article “The myth of attention deficithyperactivity disorder: symptoms resulting from multiple causes”.2 Everyone agrees on the basics. Everyone agrees that there is a finding that we term “attention deficit.” Everyone agrees that many diseases, as well as states such as sleep deprivation, have the finding “attention deficit.” The controversy boils down to whether there is at least one disease entity that we would consider to be primary attention deficit, with no other obvious abnormal findings. I am convinced that this is true, within current definitions. The uncertainty in my mind is what we will decide that “obvious” and “abnormal” mean once we have enough knowledge to answer the question. This perspective comes from the study of families with no obvious findings other than attention deficit, apparently inherited in an autosomal dominant fashion. However, the affected individuals also have a biological marker, one typically not tested, but suggestive of a channelopathy: reduced effectiveness of lidocaine. This is most conveniently demonstrated using lidocaine gel on the tongue, but most convincingly demonstrated by injection of lidocaine in a nondental area and observing negligible loss of sensation.

We examined the electrophysiology of epilepsy in the simplest system that exhibits epileptiform activity: microisland cultures that contain only one neuron. Some of these solitary excitatory hippocampal neurons generate the 'ictal' epileptiform activity characteristic of seizures. These neurons have endogenous (non-transmitter-mediated) bursts of activity that last for many seconds and appear to be driven by a persistent Na+ current. We examined this persistent Na+ current at the single channel level by recording the late openings of Na+ channels using outside-out patch recordings. Phenytoin reduced the probability of these late channel openings, but had less effect on the early channel openings that make up the peak Na+ current. The reduction of late channel openings was larger with pulses to more depolarized voltages. In contrast, the effect on early channel openings was similar at all voltages. There was little effect of phenytoin on the duration of channel openings and no effect on open channel current. This suggests that the persistent Na+ current is crucial in generating seizures. A good strategy for selecting anticonvulsants may be to search for drugs that more selectively block the persistent Na+ current at depolarized voltages. Such drugs could combine effectiveness and reduced side effects.

1. Microcultures were grown containing small numbers of hippocampal neurons. The neurons grew on glial cells attached to patches of either collagen or palladium. A layer of agarose underlying the microcultures prevented connections from forming between nearby microcultures. 2. Neurons formed strong chemical synaptic connections within each microculture, with monosynaptic fast-excitatory, fast-inhibitory, and slow-inhibitory synaptic actions. 3. Small networks with as few as two neurons generated epileptiform activity that closely resembled the epileptiform activity seen in mass cultures containing thousands of neurons. The epileptiform activity was observed when microcultures that were grown for weeks in blockers of synaptic activity (kynurenate and elevated Mg2+) were washed free of these blockers. 4. Such a microculture technique allows study of epileptiform activity in a simplified system and facilitates analysis of the synaptic actions underlying the epileptiform activity.

Medical computing has been split between palm-sized computers optimized for mobility and desktop computers optimized for capability. This split was due to technology too immature to deliver both mobility and capability in the same computer and the lack of medical software that demanded both mobility and capability. Advances in hardware and software are ushering in an era in which fully capable computers will be available ubiquitously. As a result, medical practice, education and publishing will change. Medical practice will be improved by the use of software that not only assists with diagnosis but can do so at the bedside, where the doctor can act immediately upon suggestions such as useful findings to check. Medical education will shift away from a focus on details of unusual diseases and toward a focus on skills of physical examination and using computerized tools. Medical publishing, in contrast, will shift toward greater detail: it will be increasingly important to quantitate the frequency of findings in diseases and their time course since such information can have a major impact clinically when added to decision support software. (J Child Neurol 2006;21:595—599; DOI 10.2310/7010.2006.00155).

In this issue of Neurology® , Wijburg et al.1 introduce a Suspicion Index to be used at the bedside for diagnosing Niemann-Pick disease type C (NP-C). Are such tools likely to be integrated into clinical practice, and if so, how will such integration come about?

We examined the electrophysiology of epilepsy in the simplest system that exhibits epileptiform activity: microisland cultures that contain only one neuron. Some of these solitary excitatory hippocampal neurons generate the 'ictal' epileptiform activity characteristic of seizures. These neurons have endogenous (non-transmitter-mediated) bursts of activity that last for many seconds and appear to be driven by a persistent Na+ current. We examined this persistent Na+ current at the single channel level by recording the late openings of Na+ channels using outside-out patch recordings. Phenytoin reduced the probability of these late channel openings, but had less effect on the early channel openings that make up the peak Na+ current. The reduction of late channel openings was larger with pulses to more depolarized voltages. In contrast, the effect on early channel openings was similar at all voltages. There was little effect of phenytoin on the duration of channel openings and no effect on open channel current. This suggests that the persistent Na+ current is crucial in generating seizures. A good strategy for selecting anticonvulsants may be to search for drugs that more selectively block the persistent Na+ current at depolarized voltages. Such drugs could combine effectiveness and reduced side effects.

• Insulin levels in a 7-year-old boy with hyperphagia and obesity following an episode of meningoencephalitis were studied sequentially during the course of progressive weight gain. High fasting insulin levels (1183 pmol/L) and strikingly high insulin release in response to glucose (7892 pmol/L) were found within weeks of the onset of the illness. The abnormality in insulin secretion occurred prior to the marked weight gain. Hyperinsulinemia was not accompanied by hypoglycemia. Early hyperinsulinemia may be a primary event in the development of hyperphagia and obesity following hypothalamic injury.

Segal, Michael M. and Andrea F. Douglas. Late sodium channel openings underlying epileptiform activity are preferentially diminished by the anticonvulsant phenytoin. J. Neurophysiol. 77: 3021–3034, 1997. Late openings of sodium channels were observed in outside-out patch recordings from hippocampal neurons in culture. In previous studies of such neurons, a persistent sodium current appeared to underlie the ictal epileptiform activity. All the channel currents were blocked by tetrodotoxin. In addition to the transient openings of sodium channels making up the peak sodium current, there were two types of late channel openings: brief late and burst openings. These late channel openings occurred throughout voltage pulses that lasted 750 ms, producing a persistent sodium current. At −30 mV, this current was 0.4% of the peak current. The late channel openings occurred throughout the physiological range of trans-membrane voltages. The anticonvulsant phenytoin reduced the late channel openings more than the peak currents. The effect on the persistent current was greatest at more depolarized voltages, whereas the effect on peak currents was not substantially voltage dependent. In the presence of 60 μM phenytoin, peak sodium currents at −30 mV were 40–41% of control, as calculated using different methods of analysis. Late currents were 22–24% of control. Phenytoin primarily decreased the number of channel openings, with less effect on the duration of channel openings and no effect on open channel current. This set of findings is consistent with models in which phenytoin binds to the inactivated state of the channel. The preferential effect of phenytoin on the persistent sodium current suggests that an important pharmacological mechanism for a sodium channel anticonvulsant is to reduce late openings of sodium channels, rather than reducing all sodium channel openings. We hypothesize that pharmacological interventions that are most selective in reducing late openings of sodium channels, while leaving early channel openings relatively intact, will be those that produce an anticonvulsant effect while interfering minimally with normal function.

1. Paroxysmal depolarizing shifts (PDSs) occur during interictal epileptiform activity. Sustained depolarizations are characteristic of ictal activity, and events resembling PDSs also occur during the sustained depolarizations. To study these elements of epileptiform activity in a simpler context, I used the in vitro chronic-excitatory-block model of epilepsy of Furshpan and Potter and the microculture technique of Segal and Furshpan. 2. Intracellular recordings were made from 93 single-neuron microcultures. Forty of these solitary neurons were excitatory, their action potentials were replaced by PDS-like events or sustained depolarizations as kynurenate was removed from the perfusion solution. PDS-like events were similar to PDSs in intact cortex, mass cultures, and microcultures with more than one neuron. Small voltage fluctuations were also seen in solitary excitatory neurons in the absence of recorded action potentials. Sustained depolarizations developed in 5 of the 40 excitatory neurons. Forty-eight of the 93 solitary neurons were inhibitory, with bicuculline-sensitive hyperpolarizations after the action potential (ascribable to gamma-aminobutyric acid-A autapses). None of the solitary inhibitory neurons displayed sustained depolarizations. Five of the 93 neurons were insensitive to both kynurenate and bicuculline and were not placed in either the excitatory or the inhibitory category. 3. Both N-methyl-D-aspartate (NMDA) and non-NMDA glutamate receptors contributed to the PDS-like events and sustained depolarizations. Only a non-NMDA glutamate receptor component was evident for the small voltage fluctuations. 4. Intracellular recordings were also made from two-neuron microcultures, each containing one excitatory neuron and one inhibitory neuron. Sustained depolarizations developed in five microcultures, in each case only in the excitatory neuron.

A testable model for part of the neuronal specificity problem is proposed here, based on work from several different laboratories. The model suggests that specification of synaptic action is not determined independently for each synapse in a nervous system, but instead is determined by specifying two properties that are suggested to be characteristic of entire neurons - the types of transmitters and synaptic receptors produced by each neuron. The evidence supporting the hypotheses that the transmitters and synaptic receptors used by a neuron are properties that are specified on the level of whole neurons is reviewed here. Also discussed is the current understanding of factors influencing how the transmitters used by a neuron are specified.

We have investigated neurons that receive inputs from more than one cholinergic interneuron, to see whether one cholinergic input can depolarize and the other hyperpolarize by virtue of activating different ACh receptors. We have examined synapses made in the abdominal ganglion of Aplysia californica by 3 cholinergic interneurons. Two of those interneurons have previously been shown to be cholinergic. Using both biochemical and pharmacological tests we have shown a third interneuron to be cholinergic. For 7 postsynaptic cells, we compared 6 new connections that we have identified from cholinergic interneurons, and 12 previously known connections. In each case we found that different cholinergic inputs onto any given cell produced the same synaptic action. This finding held even for L7, a cell known to have two types of ACh receptors. These data are consistent with the hypothesis that a postsynaptic cell does not segregate different types of ACh receptors. If generally true, this lack of segregation may help explain why a nervous system uses more than one neurotransmitter as well as why certain interneurons are needed in neural networks.

Publisher Summary A single neuron can have receptors to more than one neurotransmitter. A single neuron can also have two types of receptor to the same neurotransmitter. For example, on a single neuron there can be acetylcholine (ACh) receptors that produce depolarization by opening Na + channels and ACh receptors that produce hyperpolarization by opening Cl - channels. Several investigators have explored by iontophoresing neurotransmitters onto different regions of neurons that there are different responses to a single neurotransmitter on different regions of the neuron. These experiments suggest that there are indeed instances in which a neuron provides one type of receptor to one input and a different type of receptor to another input that uses the same neurotransmitter. However, several investigators have suggested alternate explanations that could account for the topographic differences in response to iontophoresis, such as different responses to different concentrations of transmitter, or different chloride gradients in different regions of the neuron.