Learned interaction of visual and idiothetic cues in the control of place field orientation.

In a symmetrical environment (like a square box) hippocampal place cells use a mixture of visual and idiothetic (movement) information to tell them which way the environment is oriented. The present experiment tested the hypothesis that if the visual landmarks were mobile, place cells would learn to disregard these and rely on idiothetic cues instead. Place cells were recorded in a square box surrounded by circular black curtains.

Genetic control and dynamics of the cellular immune response to the human T-cell leukaemia virus, HTLV-I.

About 1% of people infected with the human T-cell leukaemia virus, type 1 (HTLV-I) develop a disabling chronic inflammatory disease of the central nervous system known as HTLV-I-associated myelopathy/tropical spastic paraparesis (HAM/TSP). Patients with HAM/TSP have a vigorous immune response to HTLV-I, and it has been widely suggested that this immune response, particularly the HTLV-I-specific cytotoxic T-lymphocyte (CTL) response, causes the tissue damage that is seen in HAM/TSP. In this paper we summarize recent evidence that a strong CTL response to HTLV-I does in fact protect against HAM/TSP by reducing the proviral load of HTLV-I.

HLA alleles determine human T-lymphotropic virus-I (HTLV-I) proviral load and the risk of HTLV-I-associated myelopathy.

The risk of disease associated with persistent virus infections such as HIV-I, hepatitis B and C, and human T-lymphotropic virus-I (HTLV-I) is strongly determined by the virus load. However, it is not known whether a persistent class I HLA-restricted antiviral cytotoxic T lymphocyte (CTL) response reduces viral load and is therefore beneficial or causes tissue damage and contributes to disease pathogenesis. HTLV-I-associated myelopathy (HAM/TSP) patients have a high virus load compared with asymptomatic HTLV-I carriers.

Place cells, navigational accuracy, and the human hippocampus.

The hippocampal formation in both rats and humans is involved in spatial navigation. In the rat, cells coding for places, directions, and speed of movement have been recorded from the hippocampus proper and/or the neighbouring subicular complex. Place fields of a group of the hippocampal pyramidal cells cover the surface of an environment but do not appear to do so in any systematic fashion.

Learning of landmark stability and instability by hippocampal place cells.

Place cells in the rat hippocampus fire whenever the animal is in a particular location. In a symmetrical environment, their receptive fields (place fields) are oriented by visual cues, and if these are unavailable they are oriented by movement-generated (idiothetic) cues. The present study tested the hypothesis that the cells would learn not to 'trust' a visual cue if the rat experienced it to be unstable (Knierim et al.

Directional control of hippocampal place fields.

Pyramidal cells in the rat hippocampus fire whenever the animal is in a particular place, suggesting that the hippocampus maintains a representation of the environment. Receptive fields of place cells (place fields) are largely determined by the distance of the rat from environmental walls. Because these walls are sometimes distinguishable only by their orientation with respect to the outside room, it has been hypothesised that a polarising directional input enables the cells to locate their fields off-centre in an otherwise symmetrical environment.

Robotic and neuronal simulation of the hippocampus and rat navigation.

The properties of hippocampal place cells are reviewed, with particular attention to the nature of the internal and external signals that support their firing. A neuronal simulation of the firing of place cells in open-field environments of varying shape is presented. This simulation is coupled with an existing model of how place-cell firing can be used to drive navigation, and is tested by implementation as a miniature mobile robot.

Aseptic meningitis and encephalitis: the role of PCR in the diagnostic laboratory.

In this study we have devised a simple and robust PCR strategy to detect a wide range of viruses, bacteria, and parasites, all of which are capable of causing aseptic meningitis and encephalitis. The techniques developed have been used in a routine diagnostic virology laboratory to test prospectively 2,233 cerebrospinal fluid specimens. A virus was detected in 147 specimens of cerebrospinal fluid from 143 patients.

Diagnosis of viral infections of the central nervous system: clinical interpretation of PCR results.

Background: Standard laboratory techniques, such as viral culture and serology, provide only circumstantial or retrospective evidence of viral infections of the central nervous system (CNS). We assessed the diagnostic accuracy of PCR of cerebrospinal fluid (CSF) in the diagnosis of viral infections of the CNS.

Methods: We examined all the CSF samples that were received at our diagnostic virology laboratory between May, 1994, and May, 1996, by nested PCR for viruses associated with CNS infections in the UK.

Modifiable neuronal connections: an overview for psychiatrists.

Synaptic plasticity is currently the target of much neurobiological research, because it is thought to play an important role in brain function (particularly memory formation). However, it has attracted little attention from psychiatrists to date despite accumulating evidence that links it to various clinical syndromes, including amnesia and possibly psychosis. The purpose of this article is to present an overview of the two major arms of synaptic plasticity research-theoretical (the field of neural network modeling) and neurobiological (long-term potentiation).

LTP and spatial learning--where to next?

Hebb suggested, in 1949, that memories could be stored by forming associative connections between neurons if the criterion for increasing the connection strength between them be that they were active simultaneously. Much attention has been devoted towards trying to determine a) if there is a physiological substrate of such a rule, and b) if so, whether the phenomenon participates in real-life memory formation. The discovery of the electrically induced increase in synaptic strength known as long-term potentiation (LTP), in the early 1970s, demonstrated that a neural version of the Hebb rule could be observed under laboratory conditions in the hippocampus, a structure important for some types of learning.

The clear liquid diet is no longer a necessity in the routine postoperative management of surgical patients.

The reinstitution of oral intake in patients who have undergone intra-abdominal surgery has traditionally progressed in a stepwise fashion. Various retrospective studies and anecdotal reports have suggested that a "regular" diet as the first postoperative meal is well tolerated. Although clear liquids are accepted as the standard first postoperative meal, there appears to be little scientific data to support their use.

Medial septal control of theta-correlated unit firing in the entorhinal cortex of awake rats.

The present study investigated whether the medial septal nucleus controls theta-correlated unit activity in the entorhinal cortex (EC), as it does in the hippocampus. Single neurones were recorded from the medial EC of rats as they ran on a linear track or chased food pellets on a small platform. The most prominent pattern of cell activity observed was burst firing occurring near the peaks of the ongoing dentate gyrus theta rhythm.

Two cases of infected atherosclerotic aneurysms and a comparison with infective endocarditis.

Two cases of infected atherosclerotic aneurysms thought to have arisen following haematogenous seeding of atheromatous lesions are described. Although infective endocarditis also arises by the haematogenous route, there are striking contrasts in both the range and therefore likely source of organisms, together with a perceived difference in the rate of blood-culture positivity. This case report provides a focus for discussion of these observations.

Non-convulsive status epilepticus as a complication of Mycoplasma pneumoniae infection.

Described is a confirmed case of non-convulsive status epilepticus, an unusual presentation of M. pneumoniae infection. The postulated pathological mechanisms in this infection are reviewed.

Paradoxical enhancement of long-term potentiation in poor-learning rats at low test stimulus intensities.

Much empirical evidence and numerous theoretical models point to modification of synaptic efficacy as a mechanism for memory formation. To evaluate theoretical models, it is necessary to obtain quantitative experimental data relating learning to experimentally induced synaptic efficacy changes (such as long-term potentiation, LTP). An important problem in this type of experiment is how to quantify the LTP induced by a given stimulation protocol.

LTP-like synaptic efficacy changes following electroconvulsive stimulation.

Synaptic plasticity is thought to represent a mechanism for memory formation. Memory disturbances commonly follow electroconvulsive therapy (ECT) for depression. Accordingly, we examined the development and duration of the effects of electroconvulsive stimulation (ECS) on hippocampal synaptic plasticity in rats.

Cumulative long-term potentiation in the rat dentate gyrus correlates with, but does not modify, performance in the water maze.

The electrically induced increase in hippocampal synaptic strength known as long-term potentiation (LTP) is thought to involve some of the same mechanisms as those mediating information storage during spatial learning. Physiological saturation of synaptic weights might therefore be expected to occlude spatial learning. In support of this, Castro et al.

Induction of Fos-like immunoreactivity and the maintenance of long-term potentiation in the dentate gyrus of unanesthetized rats.

Memory formation in the mammalian central nervous system may require long-lasting alterations in gene expression. However, it is not yet known whether the candidate memory mechanism long-term potentiation (LTP) requires alterations in gene expression for its maintenance, nor the extent to which the time course of LTP can be manipulated at the time of induction. In this study we influenced the time course of LTP decay for the perforant path input to the dentate gyrus in awake rats by manipulating conditions at the time of induction, and correlated the outcome with the induction of c-fos protein(s) (Fos), as measured immunohistochemically in the dentate gyrus of separate animals 2 h post-tetanization.

Changes in cell surface antigens during stem cell ontogeny.

A panel of monoclonal antibodies that bind to the murine pluripotential stem cell CFU-s was used to examine the antigenic profile of the stem cell during ontogeny. The results show that the stem cell surface changes dramatically during development. One group of three independently derived monoclonal antibodies binds to subpopulations (50%-70%) of stem cells at plateau values, and these populations increase marginally during development.

Response of the diaphragm muscle to electrical stimulation of the phrenic nerve. A histochemical and ultrastructural study.

The histological, histochemical, and ultrastructural features of canine diaphragms subjected to pacing by high-frequency electrical stimulation (27 to 33 Hz) of the phrenic nerve are compared with unstimulated diaphragms and with diaphragms subjected to pacing by low-frequency stimulation (11 to 13 Hz). The high-frequency group showed a reduced tidal volume (fatigue) after long-term stimulation, and myopathic changes which included enlarged internal and sarcolemmal nuclei, ring fibers, moth-eaten fibers with irregular histochemical staining, core/targetoid fibers, and smearing and aggregation of Z-band material with electron microscopy. The low-frequency group did not develop a significant degree of fatigue or pathological changes, and showed histochemical evidence of transformation to fast-twitch (type II) fibers.

Recombination analysis of naturally diploid Candida albicans.

A multiply auxotrophic strain, hOG45, was derived from Candida albicans ATCC 10261. Prototrophic revertants of this multiple auxotroph were selected after mutagenesis. These prototrophic revertants were distinguishable from the original prototroph, ATCC 10261, because of their mitotic instability.