GW170817: Measurements of Neutron Star Radii and Equation of State

On 17 August 2017, the LIGO and Virgo observatories made the first direct detection of gravitational waves from the coalescence of a neutron star binary system. The detection of this gravitational-wave signal, GW170817, offers a novel opportunity to directly probe the properties of matter at the extreme conditions found in the interior of these stars. The initial, minimal-assumption analysis of the LIGO and Virgo data placed constraints on the tidal effects of the coalescing bodies, which were then translated to constraints on neutron star radii. Here, we expand upon previous analyses by working under the hypothesis that both bodies were neutron stars that are described by the same equation of state and have spins within the range observed in Galactic binary neutron stars. Our analysis employs two methods: the use of equation-of-state-insensitive relations between various macroscopic properties of the neutron stars and the use of an efficient parametrization of the defining function p(ρ) of the equation of state itself. From the LIGO and Virgo data alone and the first method, we measure the two neutron star radii as R_{1}=10.8_{-1.7}^{+2.0}  km for the heavier star and R_{2}=10.7_{-1.5}^{+2.1}  km for the lighter star at the 90% credible level. If we additionally require that the equation of state supports neutron stars with masses larger than 1.97  M_{⊙} as required from electromagnetic observations and employ the equation-of-state parametrization, we further constrain R_{1}=11.9_{-1.4}^{+1.4}  km and R_{2}=11.9_{-1.4}^{+1.4}  km at the 90% credible level. Finally, we obtain constraints on p(ρ) at supranuclear densities, with pressure at twice nuclear saturation density measured at 3.5_{-1.7}^{+2.7}×10^{34}  dyn cm^{-2} at the 90% level.

[Quadrivalent meningococcal conjugate vaccine]

Meningoccocal meningitis is still a severe disease. In Switzerland the predominant serotypes are serotype B and C, but this could change as other groups predominate elsewhere. The indications for immunizing against meningococcal infections as described in the Swiss recommendations will be reviewed. New quadrivalent vaccines conjugated with a protein and efficient against serogroup ACWY will soon be available in our country. They show a number of advantages in term of type of protection and should simplify the current vaccination schedule while giving a better coverage against various serogroups, especially for travellers, but also for children at risk for complications.

[Tuberculosis detection and immunization of long-term travellers]

Reasons why long-term travel (> or =3 months) increases health risks are many, but mainly related to travellers' behaviour. On top of immunizations proposed to all travellers, those against hepatitis B, rabies and typhoid fever should be encouraged, but require time and money. Some vaccines like meningococcal vaccine and japanese encephalitis need to be discussed according to the destination. Tuberculosis is a rare disease in travellers in general but the incidence in health care workers reaches the one of the local population at risk, and therefore tuberculosis detection is recommended.

[Security and travel]

Hijacking, crime, aggression and theaft when people travel abroad are regularly reported by the media. This increases travellers' fears. As there is little research that quantifies risks, subjectivity and preconceived ideas prevail. A survey done among travellers in Geneva, Lausanne and Lyon showed that the risk of incidents was lower in countries located outside of Europe, usually in cities. Most frequently it was baggage stealing, or stealing in the street, during the day. In Europe, stealing by breaking into cars was most frequent. Without becoming paranoid about aggression and burglary, some simple rules can be followed. Keep constant situational awareness, be respectful of the people in countries visited, avoid provocative attitudes and avoid insecure areas.

[Immunization against yellow fever]

Yellow fever is a potentially epidemic arboviral disease, submitted to the international health regulation. The disease is severe but rare in travellers. Immunization protects the individual and prevents transmission to non immune populations. Neurological side effects of the vaccine are rare and already known. More recently severe systemic side effects have been reported, with a seemingly age increasing incidence (1,8/100,000 in the over 60 years old). They seem related to host immunity rather than to an increased virulence of the vaccines. The indication and contra indications to the vaccine must be followed strictly according to the benefit/side effects ratio and to the epidemiology.

[Diarrhea and vaccines: current developments]

Diarrhoea is a main concern for travellers, populations of developing countries and children. Causative pathogens are numerous. An efficient vaccine against cholera is available, also offering a 50% cross-protection against E. Coli enterotoxin (ETEC), however its efficacy is only 23% against all-causes traveller's diarrhoea. Rotavirus can be responsible for severe diarrhoea in infants but rarely causes traveller's diarrhoea. Two new vaccines being under development appear effective and well-tolerated but too expensive for developing countries which most need them. To date, the live oral Ty21a vaccine remains frequently prescribed in Switzerland, with limited indications and suboptimal efficacy. A new oral vaccine is under development.

Evaluation of an Inference‐Based Approach to Treating Obsessive‐Compulsive Disorder

This study evaluated an inference-based approach (IBA) to the treatment of obsessive-compulsive disorder (OCD) by comparing its efficacy with a treatment based on the cognitive appraisal model (CAM) and exposure and response prevention (ERP). IBA considers initial intrusions in OCD (e.g. "Maybe the door is open", "My hands could be dirty") as idiosyncratic inferences about possible states of affairs arrived at through inductive reasoning. In IBA such primary inferences represent the starting point of obsessional doubt, and the reasoning maintaining the doubt forms the focus for therapy. This is unlike CAM, which regards appraisals of intrusions as the maintaining factors in OCD. Fifty-four OCD participants, of whom 44 completed, were randomly allocated to CAM, ERP or IBA. After 20 weeks of treatment all groups showed a significant reduction in scores on the Yale-Brown Obsessive Compulsive Scale (Y-BOCS) and the Padua Inventory. Participants with high levels of obsessional conviction showed greater benefit from IBA than CAM. Appraisals of intrusions changed in all treatment conditions. Strength of primary inference was not correlated with symptom measures except in the case of strong obsessional conviction. Strength of primary inference correlated significantly with the Y-BOCS insight item. Treatment matching for high and low conviction levels to IBA and CAM, respectively, may optimize therapy outcome.

[Neutropenia in a patient treated with clozapine in combination with other psychotropic drugs]

Clozapine is an atypical antipsychotic known for its efficacy in refractory schizophrenia. However, according to different epidemiological studies clozapine can induce neutropenia in less than 3% of patients and may represent a major problem for the management of treatment-resistant patients not responding to conventional or other atypical antipsychotics. Recently, a few case of neutropenia have been reported following the addition of other medications to clozapine, notably paroxetine, risperidone, trimethoprim-sulfamethoxazole and erythromycin. In our report we present the case of Mr A., a 40-year-old Caucasian patient with a 20-year history of paranoid schizophrenia. After numerous trials with conventional antipsychotics, partial remission of psychotic symptoms was obtained with clozapine. Over the past eight years during his treatment with clozapine, the patient presented 2 episodes of neutropenia. The first episode came five years after starting clozapine and was attributed to the addition 6 weeks earlier of haloperidol (2 mg/day) to clozapine (250 mg/day) and divalproex (1,500 mg/day). Recently, one week after the addition of risperidone (2 mg/day) to clozapine (550 mg/day), leukocytes count dropped from 12 100/mm(3) to 5 700/mm(3) and neutrophils from 7 400/mm(3) to 900/mm(3). The patient was also taking haloperidol (4 mg/day), methotrimeprazine (35 mg/day), procyclidine (5 mg/day) and valproic acid (1,500 mg/day). Twelve days after discontinuation of risperidone, leukocytes and neutrophils count increased to 11,100/mm(3) and 6,300/mm(3) respectively while the treatment with clozapine was continued. The first eighteen weeks of treatment represent the period where the risk of neutropenia is the highest. In our patient neutropenia occurred 5 and 7 years after starting clozapine. It is proposed that the two neutropenic episode were precipitated by adding respectively haloperidol and risperidone to clozapine. Also, divalproex can potentially cause a decrease in white blood cell count and may have contributed to the two neutropenic episode. It is suggested that drug interactions may be responsible for neutropenia in clozapine treated patients and that clozapine should not necessarily be discontinued in the presence of neutropenia. Also we propose that hematological surveillance should be done on a weekly basis for 4 to 6 weeks following the addition of psychotropic drugs known for their potential to cause neutropenia when associated with clozapine. Therefore polypharmacy may contribute to cause neutropenia in clozapine treated patients and that discontinuation of an antipsychotic should be done before introducing another one.

Inactivated hepatitis A vaccine booster given >/=24 months after the primary dose

We investigated what happens with the immune response when people come back for their booster dose of inactivated hepatitis A vaccine later than the recommended time of 6-12 months after the primary dose. We recruited a group of 124 travellers who received either the primary doses of Havrix 720 (two doses) or of Havrix 1440 (one dose) >/=24 months before study entry. They received a booster dose of Havrix 1440 and blood was drawn 1 month later. As a control group, we recruited a group of 125 travellers who followed a recommended schedule with a primary dose at month 0 and a booster dose at months 6-12. For both study groups, the GMTs increased dramatically and similarly upon the booster immunisation. Although significantly more late travellers (32%) had lost detectable antibodies than controls (11%) before administration of the booster dose, all these subjects showed an anamnestic response to the booster dose. Delaying the booster dose up to 66 months after primary vaccination did not seem to influence the immunogenicity of the booster dose. However, the recommended 6-12-month interval remains if detectable antibody titers are to be warranted constantly.

Somnambulistic-like behaviour in patients attending a lithium clinic

The prevalence of somnambulistic-like behaviour related to treatment with lithium alone or in combination with other psychotropic medications was evaluated in patients attending a lithium clinic. A written questionnaire on somnambulistic-like behaviour was completed by 389 patients. Information was provided on the time of occurrence, frequency and severity of the episodes, the presence of childhood somnambulism, and the temporal relationship between psychiatric treatment and somnambulistic-like behaviour. Twenty-seven (27) patients (6.9%) presented sleepwalking behaviour related to the onset of treatment with lithium alone or in combination with other psychotropic drugs. Forty-five patients (11.6%) reported childhood somnambulism and 12 of them (27%) had their childhood somnambulism reactivated by the medication. Most patients had a diagnosis of bipolar affective disorder but somnambulistic-like behaviour also occurred in patients with other axis 1 diagnosis. Sleep-related violence was seldomly reported. Therefore, lithium alone or in combination with other psychotropic drugs may induce somnambulistic-like behaviour. A history of childhood somnambulism may increase the risk of developing sleepwalking behaviour while under psychotropic drugs treatment.

[Comparative immunogenicity of 2 antirabies vaccines in a 2-1-1 post-exposure vaccination schedule]

Few trials have compared the Purified Duck Embryo Vaccine (PDEV) and the Human Diploid Cell Vaccine (HDCV) in a post-exposure immunization schedule of 4 shots (2 on day 0 and 1 each on day 7 and 21, or 2-1-1 schedule). A retrospective analysis compared 10 patients with PEDV and 20 with HDCV, who had received the 2-1-1 schedule as well as 20 UI mg/kg of immune globulins on day 0. The median neutralizing antibody titers on day 21 (after 3 doses) and the median of maximum titers until day 90 were higher for HDCV than for PEDV (0.6 IU/ml versus 3.5 IU/ml [p < 0.04] and 2.5 IU/ml versus 5.8 IU/ml [p < 0.03] respectively). Seven patients had not reached the seroconversion titer of 0.5 IU/ml after 3 doses (day 21). These results differ from previous studies showing a 100% seroconversion rate on day 21, and suggest that more studies are required before these 2 vaccines can be used in the 2-1-1 schedule after severe exposure.

[The value of screening serology in anti-hepatitis A vaccination of travelers]

To select the travellers most likely to benefit from anti-hepatitis A (HA) antibody testing, the following criteria have been proposed: (A) being born before 1945, (B) a stay over 1 year in a developing country or (C) a history of jaundice. We present a prospective study to assess the practical use of these criteria. Following a recent survey in the general population of Lausanne showing HA seroprevalence of 52.6% in the age group over 45, we included an A1 criterion (A extended to birth before 1950). Anti-HA IgG testing and a questionnaire were proposed to all travellers presenting one or more criteria.

RESULTS

Out of 1187 consecutive travellers, 176 (14.8%) had one or more criteria (219 [18.5%] when A1 was used). Criteria A applied to 8.5% of all travellers, A1 to 13.8%, B to 6.3% and C to 3.1%. Only 3% of travellers had more than one criterion. Overall seroprevalence among the selected group was 48.3%. Seroprevalence of travellers below 60 years old was under 30%, unless a second criterion was present in which case seroprevalence was 10% higher. Eighty percent of travellers with a history of jaundice were found to be positive. The use of the recommended criteria spared 94 travellers (46.3% of those tested and 7.9% of all travellers) unnecessary immunisation. Among travellers older than 60 years, a 30% economy on the total sum for immunising all of them, without any prior testing was realised.

CONCLUSIONS

Among the population of travelers consulting our travel clinic, the seroprevalence for HA is lower than in the general population. We recommend that testing should be proposed only to travellers aged over 60, or with a history of jaundice, or to those with a combination of 2 out of 3 criteria.

Apoptosis is coordinately regulated with osteoblast formation during bone healing

The ultimate fate of the expanded pool of osteoblasts formed following a typical bone injury is unclear. Since necrosis has not been described in the latter stages of bone healing, there must be some other mechanism by which obsolete osteoblasts are cleared from an injury site. We therefore evaluated the possibility that their removal is pre-programmed, by investigating the occurrence of apoptosis in rats that received a standardized bone injury. Histological evidence identical to that found in tissues known to exhibit apoptosis was obtained, thereby showing that programmed cell death was a normal concomitant of fracture healing. The concentration of apoptotic bodies reached its maximum after the differentiative response had peaked, suggesting that the two processes were coordinated. The same result was found in a second group of rats that received the same bone injury plus a simultaneous standardized soft-tissue injury. The combined injuries resulted in more osteoblasts and more apoptotic bodies, but an identical temporal relationship between the peak responses in the two parameters. The results suggested that osteoblasts were removed from the injury site via apoptosis, and that the process was coordinately regulated with differentiation. Since the number of apoptotic bodies per osteoblast varied during healing, it is likely that apoptosis was associated with healing and not merely with osteoblast concentration.

[Routine cases in intestinal parasitology]

The majority of intestinal parasites isolated in Switzerland is imported by refugees and travellers. Nematodes are more frequently isolated in the first group, whereas Giardia duodenalis and Strongyloides stercoralis predominate in the second. Symptoms are usually mild, but occasionally diarrhea, abdominal pain and weight loss may be encountered. Hypereosinophilia occurs frequently with some parasites. Four cases chosen from the outpatient department of a Swiss medical polyclinic are presented and serve as a basis for discussing persistent and chronic diarrhea, acute traveller's diarrhea, and hypereosinophilia. Differential diagnosis according to type and duration of symptoms, laboratory findings and treatment of the most frequently encountered parasites are reviewed.

Genital Schistosomiasis After a Missed Diagnosis of Katayama Syndrome

Schistosomiasis is increasingly reported in travelers to subSaharan Africa.1,2 Bathing in tropical lakes3 or in other fresh waters2,4 is a recognized risk factor for acquiring it. Most cases present with cercarial dermatitis or, 3 to 6 weeks after infection by Schistosoma mansoni1,2 (occasionnally Schistosoma haematobium), with acute schistosomiasis (Katayama syndrome), when the immune response of the body to the larval maturation and migration elicits fever, sweating, arthralgia, urticaria, and digestive or respiratory symptoms. Late and unusual clinical presentations in travelers include features of spinal cord compression5,6 and ectopic dermal or genital localization,3,7 which can result from a missed diagnosis of the early symptoms of the disease. In the following case, a female traveler developed genital schistosomiasis 1 year after a missed diagnosis of Katayama syndrome.

Somatosensory cortical neurons with an identifiable electrophysiological signature

In both cats and rats, neurons with a distinctively narrow action potential were recognized as a small subset of all neurons isolated in the somatosensory cortex. These cells were characterized by generally having a spontaneous activity, some evidence of an afferent input, a sensitivity to glutamate but a relative resistance to depolarization block induced by glutamate and a marked insensitivity to acetylcholine. Two were filled with horseradish peroxidase (HRP) and recovered. Although others have suggested that such neurons are interneurons, following reconstruction it was apparent that the two cells filled with HRP were pyramidal cells. These observations suggest that there may be more than one class of cortical neurons with thin spikes.

Morphological and electrophysiological characteristics of somatosensory thalamocortical axons studied with intra-axonal staining and recording in the cat

The intracortical arborizations of thalamocortical fibers arising from the ventroposterolateral (VPL) nucleus in the cat were studied following intra-axonal injections of horseradish peroxidase (HRP). The axons were impaled 1.5 to 3 mm below the surface of the cortex, identified electrophysiologically by stimulating the VPL nucleus and functionally by stimulating the somatic receptive field with natural stimuli. Many of the results obtained in a previous study using similar techniques (Landry and Deschênes 1981) were confirmed by the present experiments. Fibers activated by cutaneous stimulation arborized either in area 3b or 1 but some did send branches to both areas. Also, the intracortical arborization of a rapidly adapting cutaneous afferent fiber in area 2 is described. The size and tangential extent of the fiber in area 2 are similar to those arborizing in other areas of the primary somatosensory cortex and consist of multiple patches separated by uninvaded gaps. One fiber activated by stimulation of deep tissue receptors gave rise to two bushes that arborized along a rostrocaudal axis exclusively in area 3b. Terminal boutons and varicosities were found mostly in layers VI, IV, the bottom third of III and the upper portion of V, but some fibers did send a few collateral branches to layer II and the bottom part of layer I. The results suggest that in the forebrain representation, the same modality and submodality can be recorded in more that one cytoarchitectonic area but that areas 3b, 1 and 2 should not be considered as a single functionally homogeneous area. Counts of terminals suggest that a single fiber arborizing in area 1 makes as many as 3 times the number of synapses made in area 2 or 3b. Since fibers appear to be modality and submodality specific, if convergence of modality, submodality and/or body areas occur in the cortex, then this must be preferentially, but not exclusively, done by thalamic fibers of different functions which arborize in the same cytoarchitectonic area and synapse upon a shared postsynaptic target. In the same experiments intra-axonal recordings revealed the presence of two hyperpolarizing after potentials elicited by a preceding action potential. The first after potential was associated with a decrease in excitability of the fiber and an increase in membrane resistance.(ABSTRACT TRUNCATED AT 400 WORDS)

Bicuculline-induced alterations of response properties in functionally identified ventroposterior thalamic neurones

Extracellular recordings of 105 neurones in the cat's somatosensory thalamus were obtained with carbon fibre-containing multibarrel micropipettes. The responses of cells to natural stimulation of cutaneous or deep structures were characterized and the responses to electrical stimulation of primary somatosensory cortex were determined. Receptive fields were mapped and the functional properties were examined before and during the microiontophoretic administration of glutamate, gamma-aminobutyric acid (GABA) and bicuculline methiodide (BMI). Modality and submodality properties of all cells tested apparently remained unchanged qualitatively, despite all pharmacological interventions. BMI lowered the response threshold of a majority of the 48 cells tested for this variable, although almost 25% responded with elevated thresholds. BMI changed the temporal properties of the responses of both thalamocortical relay neurones and of presumed interneurones. Discharges evoked by natural stimuli and by electrical stimulation of the cortex were prolonged and their pattern was altered. Decreases in the frequency of bursts of discharges were often observed with BMI, and these bursts were invariably prolonged and the interspike interval profiles were altered. Receptive field size changes were observed only in 8 of 48 neurones. For two of these, the field size decreased, while for the others there were small increases.

Identification of two populations of corticothalamic neurons in cat primary somatosensory cortex

Extracellular and intracellular recordings of corticothalamic (CT) cells were performed in the primary somatosensory cortex of the cat. CT neurons were antidromically activated by electrically stimulating the ventroposterior lateral (VPL) nucleus of the thalamus and were classified into two types according to their physiological properties. Type 1 had no spontaneous activity and no identifiable somatic receptive field. Type 2 fired action potentials spontaneously and responded to mechanical stimulation of the skin or underlying tissues. Axonal conduction velocities were slower for type 1 cells and their cell bodies were located slightly deeper in the cortex than those of type 2 cells. Both types of CT neurons exhibited inhibitory postsynaptic potentials in response to VPL stimulation but an early synaptic excitation and rebound discharge was observed almost exclusively in type 2 cells. These results suggest that only type 2 CT cells can modify the activity of thalamic neurons through a corticothalamic feedback loop.

Interhemispheric reciprocal interaction between ventroposterolateral thalamic nuclei involving cortical relay neurons

Extracellular and intracellular recordings were performed in the somatosensory cortex of cats anesthetized with sodium pentobarbital. Commissural neurons identified antidromically from the corpus callosum (CC) were activated synaptically at latencies compatible with a monosynaptic delay following stimulation of the thalamic ventroposterolateral (VPL) nucleus. Corticothalamic cells identified antidromically from the VPL nucleus were synaptically driven at latencies compatible with either a mono- or disynaptic delay following CC stimulation. We propose that an interhemispheric reciprocal interaction exists between VPL nuclei via cortical relay cells involving commissural and corticothalamic neurons.

Functional role of GABA in cat primary somatosensory cortex: shaping receptive fields of cortical neurons

Extracellular recordings of 209 neurons were obtained with carbon fiber-containing multibarrel micropipettes. The cells were isolated in the primary somatosensory cortex of cats anesthetized with barbiturate and classified according to the nature of their response to natural stimuli, the nature of the surrounding multiunit responses to the same stimuli, the response to thalamic stimulation, and their depth in the cortex. To study factors controlling the excitability of somatosensory neurons, their receptive fields were examined in the presence of iontophoretically administered gamma-aminobutyric acid (GABA), glutamate, and bicuculline methiodide (BMI). Even when the neurons were depolarized to perithreshold levels with glutamate, or when local inhibitory influences mediated by GABA were antagonized by BMI, the apparent specificity for one class of afferent input was maintained. Neurons responding to stimulation of either cutaneous or deep receptors maintained their modality specificity, and neurons in cutaneous rapidly adapting regions never took on slowly adapting properties. When ejected at currents that did not elicit action potentials, glutamate lowered the threshold for activation by cutaneous stimuli but did not enlarge the receptive field. With larger ejecting currents, the neurons developed an on-going discharge, but even at these higher doses, glutamate did not produce an increase in the receptive-field size. Some neurons in regions of cortex exhibiting slowly adapting multiunit responses were relatively insensitive to glutamate. These cells required four to five times more glutamate to evoke discharges than did most neurons. Other cells, previously unresponsive to somatic stimuli, could be shown to possess distinct cutaneous receptive fields when either glutamate or BMI was ejected in their vicinity. Iontophoretically administered BMI altered the firing pattern of somatosensory neurons, causing them to discharge in bursts of 3-15 impulses. BMI enlarged the receptive-field size of neurons in regions displaying rapidly adapting multiunit background discharges but not in those regions with slowly adapting multiunit discharges. This differential effect of BMI, suggesting that GABA controls receptive-field size in rapidly adapting regions, also indicates that neurons in rapidly adapting regions differ pharmacologically from those in other submodality regions. In all cortical regions, BMI blocked the poststimulus inhibitory period that normally followed thalamic stimulation.(ABSTRACT TRUNCATED AT 400 WORDS)

Morphological and electrophysiological characteristics of pyramidal tract neurons in the rat

Responses evoked in neurons of rat sensorimotor cortex upon stimulation of the pyramidal tract and ipsilateral cerebral peduncle were analysed using intracellular recording. Neurons responding antidromically to pyramidal tract stimulation (PT cells) and neurons failing to respond antidromically but exhibiting orthodromic responses were both stained by intracellular injection of horseradish peroxidase (HRP). Layer V pyramidal neurons, including those responding antidromically, exhibited prominent long lasting membrane hyperpolarizations and inhibitions of action potentials following pyramidal tract or cerebral peduncle stimulation. Upon passage of polarizing intracellular current two components were identified within the hyperpolarizing potential. A short duration initial component readily reversed with hyperpolarizing current. Frequently this earlier component overlapped a period of early excitation consisting of action potentials arising from recurrent EPSPs or large slow depolarizing potentials (SDPs). The second, much longer duration hyperpolarizing component did not reverse with passage of hyperpolarizing current and was often followed by a rebound period of depolarization and action potential generation. Both the excitatory and the inhibitory portions of these responses could be demonstrated in animals with acute thalamic transections severing the ascending lemniscal pathway to cortex. Following intracellular staining with HRP, two types of PT cells were identified by their different intracortical axonal arborizations. Most of the injected neurons had local axonal fields extending widely in layers V and VI, but with few or no collaterals extending radially toward the more superficial layers. A second type of PT cell had axon collaterals limited to a narrow zone around the dendritic field but extending radially as far as layer I. Cells of both types were observed to send axon collaterals into neostriatum. Both types of neurons exhibited morphological and physiological characteristics of slow PT cells, and we could find no cells comparable to the fast conducting PT cells observed in other species.

A reanalysis of the ventrolateral input in slow and fast pyramidal tract neurons of the cat motor cortex

In deeply anesthetized cats the temporal characteristics of ventro-lateral (thalamic) excitatory postsynaptic potentials (EPSPs) induced in pyramidal tract cells were studied with an averaging technique. Stimulation of the ventrolateral thalamus induced EPSPs in all pyramidal tract neurons at latencies of 1-5 ms. It was found that there was a positive relationship between the latency and rise time of stimulation-induced EPSPs and the latency of antidromic invasions of pyramidal tract neurons. In response to two closely spaced shocks the second EPSP had the same latency and amplitude as the first one in both slow and fast pyramidal tract neurons. Moreover, the span of antidromic latencies of ventrolateral thalamic relay cells to motor cortex stimulation showed that these thalamic neurons had the necessary conduction velocities to account for the distribution EPSP latencies recorded in pyramidal tract neurons. From these electrophysiological results, it has been concluded that slow and fast pyramidal tract morphological evidence, obtained at the electron-microscopic level, supporting this conclusion. Terminal degeneration induced by a lesion in the ventrolateral thalamus was found on the apical dendrite of a slow pyramidal tract neurons that had been injected with horseradish peroxidase. It is proposed that the matching between the latencies of EPSPs evoked from the ventrolateral thalamus and the latencies of antidromic invasions of pyramidal tract neurons may reflect a matching between the conduction velocity of thalamocortical and cortico-spinal neurons and/or it may be due to the electrotonic properties of the apical dendrites.

Geometry and orientation of thalamocortical arborizations in the cat somatosensory cortex as revealed by computer reconstruction

The geometry of the intracortical arborization of single neurons from the ventroposterolateral thalamic nucleus in cat was studied with computer reconstruction after intraaxonal injections of horseradish peroxidase in fibers whose receptive field had been identified. The terminal arbors of slowly (SA) and rapidly (RA) adapting thalamocortical neurons were often (60%) composed of two separated bushes of 300-600 microns in diameter separated by a region of about the same size containing much less terminal ramifications. The bushes were aligned mainly along the mediolateral axis of the brain. It is proposed that this structural feature underlies the RA-SA banding already described in the somatosensory areas by physiological experiments.

Intracortical arborizations and receptive fields of identified ventrobasal thalamocortical afferents to the primary somatic sensory cortex in the cat

The intracortical arborizations of neurons from the ventroposterolateral thalamic nucleus (VPL) in the cat were studied by intraaxonal injections of horseradish peroxidase (HRP) following identification of their receptive fields. In the primary somatic sensory cortex (SI) VPL cells terminated in different cytoarchitectonic areas according to their receptive field modality. Fibers excited by deep tissue or joint rotation arborized preferentially in area 3a. Those responding tonically to cutaneous stimuli were located in the anterior part of area 3b; hairdriven cells terminated in area 3b and in the rostral pole of area 1. All fibers had a similar laminar distribution within SI. Axons terminated mostly in layers VI, iV, and the lower part of layer III. None terminated in layers I and II. Most terminal arbors were oriented along the mediolateral axis of the brain. The main arborization of a single VPL cell formed a bush of about 500 micrometers in diameter. some fibers generated two such bushes with an uninvaded region of about 300 micrometer between them. It is proposed that this patchy organization underlies in part the columnar organization of areas SI. Many VPL cells had secondary projection sites in SI. These were issued from smaller-sized collaterals and were located in a different cytoarchitectonic area than that of the main terminal plexuses. A significant number of these collaterals projected to area 4, Insufficient filling of the collaterals by HRP prevented a more complete characterization of the secondary arbors.

Intracortical distribution of axonal collaterals of pyramidal tract cells in the cat motor cortex

Slow and fast pyramidal tract cells (Pt cells) from the cat motor cortex were identified antidromically and injected with horseradish peroxidase (HRP). The axonal collaterals of these cells were mapped following HRP histochemistry with benzidine di-hydrochloride. All cells, slow or fast, show a similar arrangement of their collaterals. A proximal axonal network of 0.5-0.8 mm in diameter delimits a local field of action for collaterals in layers V and VI. The tangential expansion of this local field corresponds to that of the basal dendritic domain of Pt neurons. Much longer collaterals running for millimeters in the lower gray or white matter were observed in all cells. They form at a cortical level a distal field of action for Pt neurons. Many of these long branches were traced to other regions of area 4 or toward other cytoarchitectonic areas. In one case a collateral was seen entering and dividing in area 3a. Due to limitations of the HRP technique most of these long branches could not be followed to their terminals. On the basis of the laminar distribution of Pt cell collaterals (mostly in layers V and VI) synaptic sites where recurrent excitation and inhibition are produced on Pt neurons are discussed.

Morphological characterization of slow and fast pyramidal tract cells in the cat

In adult cats the morphology of slow and fast pyramidal tract (Pt) neurons was studied following intracellular HRP injections and Golgi impregnation. Both types of neurons are pyramidal cells and their soma are all located in the fifth layer of the motor area. As a rule, fast Pt neurons have large somata and their basal and apical dendrites occupy a larger territory in the tangential plane. In layer I, terminal apical dendrites of fast Pt neurons are smooth and divide poorly while those of slow Pt neurons bear a moderate amount of spines and branch profusely. Midway between the pia and layer V, in the third layer, the apical shafts of both types of Pt cells run upward with little branching. These shafts are more numerous in fast Pt cells (7 to 16) and they are almost devoid of spines. Those of slow Pt cells in layer III number between 5 and 9 and are densely covered with spines. Oblique and horizontal branches of slow and fast Pt neurons extend in layer V and some of them invade the lower part of layer III. It is suggested that this zone corresponds to a true fourth layer in the motor area. In both types of cells oblique and lateral branches bear numerous spines. Within the basal dendritic territory of Pt cells, one has to distinguish two dendritic systems: a short and a long one. The former spreads downward obliquely and appears to remain within layer V. The latter is made up of long descending vertical (antiapical) and oblique dendrites (tap root). While both types of cells may have long antiapical dendrites that run down radially to the lower part of layer VI, tap root dendrites which expand laterally below the cell body for considerable distances are a distinctive feature of fast Pt neurons. Though basal dendrites of all Pt cells bear spines, their number, distribution and shape are very variable in fast Pt cells.