Dual influence of temperature on compound nerve action potential

The permeability of the blood-brain barrier has been measured using a technique which is independent of blood flow and is sufficiently accurate to monitor the penetration of weakly permeant substances.The permeability of the blood-brain barrier to [¹⁴C]sucrose has been measured in rats anaesthetised with either urethane or pentobarbitone (Nembutal). The values obtained from urethane-anaesthetised untreated rats were slightly lower, thus demonstrating the suitability of urethane as an anaesthetic for blood-brain barrier experiments.The permeability of the barrier has been measured in rats which had been drinking 7.5% ethanol for 6 months, or had been administered an anaesthetic dose of ethanol, or both. No statistically significant difference was found between the permeability measurements in rats subjected to any of these treatments. Positive controls in which 0.3 ml of a 30% ethanol solution was injected into the internal carotid artery demonstrated the sensitivity of the employed technique. Thus it was found that the blood-brain barrier does not weaken with respect to sucrose when the blood ethanol concentration reaches an anaesthetic level.     

Epileptogenesis and the Immature Brain

Summary: Epidemiological studies indicate that the incidence of seizures is highest early in life. This report discusses the experimental data derived from studies of focal epileptogenesis of the immature brain in tandem with ongoing maturational changes. During development, neurons have characteristic neurophysiological properties. Local interictal discharges are long in duration, lack a stereotypic morphology, and have limited fields. Yet the immature brain is very susceptible to the development of bilateral, although asynchronous, seizures and status epilepticus induced by amygdala kindling or by convul-sant drugs. This increased seizure susceptibility may be due to a functional immaturity of a substantia nigra, GABA-sensitive output system. The morbidity of convulsions occurring early in life may not be as grave as previously thought in terms of subsequent acquisition of "normal" developmental milestones. The propensity to develop recurrent convulsions in adulthood is not related to the severity of a single seizure in infancy. Although multiple severe seizures may predispose animals to the development of seizures later in life, this is not a unique feature of the immature brain, since it also occurs in the adult brain. Finally, there is evidence that the immature brain may respond to anticonvulsant drugs differently from its mature counterpart; these findings emphasize the need to develop new antiepileptic therapies that take into account the maturational state of the brain.     

Simple spike firing in the posterior lateral cerebellar cortex of Macaque Mulatta was correlated with success–failure during a visually guided reaching task

Evidence has been accumulating which supports a role for the cerebellum in motor learning. Motor learning is though to be mediated by complex spikes acting as an error signal, which when firing in conjunction with simple spike activity modify synapses between parallel fibers and Purkinje cells. We studied the activity of neurons in the posterior lateral cerebellar cortex of macaques that were performing reaches to visual targets. We found that simple spike firing in many of these neurons was modulated by whether the monkey successfully hit the target or not. The success–failure modulation was present for reaches using either arm and could persist for several hundred milliseconds into a period when the monkey was constrained from moving its arms. This temporally extended success–failure activity could interact with complex spike firing in order to enhance learning, particularly when the motor command is temporally separated from sensory feedback.     

Relative reward processing in primate striatum

Rewards are often not only valued according to their physical characteristics but also relative to other available rewards. The striatum (caudate nucleus, putamen, ventral striatum including nucleus accumbens) is involved in the organization of movement and the processing of reward information. We studied the activity of single striatal neurons in macaques that were presented with different combinations of two rewards. We found in nearly half of the investigated neurons that the processing for one reward shifted, relative to the other rewards that were available in a given trial block. The relative reward processing concerned all forms of striatal activity related to reward-predicting visual stimuli, arm movements and reception of rewards. The observed changes may provide a neural basis for the known shifts in valuation of rewarding outcomes relative to known references.     

Applicability of NeuroTrend as a bedside monitor in the neuro ICU

Objective

To assess whether ICU caregivers can correctly read and interpret continuous EEG (cEEG) data displayed with the computer algorithm NeuroTrend (NT) with the main attention on seizure detection and determination of sedation depth.

Physiologic studies in the human brain in movement disorders

Physiologic studies are useful in identifying brain targets during functional neurosurgical procedures for the treatment of Parkinson's disease and other movement disorders. These studies also open a window into the function and dysfunction in the basal ganglia. Recording of the activity of single neurons in the motor thalamus, the globus pallidus or the subthalamic nucleus with microelectrodes is providing important insights into the pathophysiology of parkinsonism and the mechanism of action of medical therapy and surgical interventions.     

Arthritis induced in cat by sodium urate: a possible animal model for tonic pain

An attempt has been made to determine whether cats rendered arthritic by the injection of monosodium urate (MSU) crystals (rod-shaped 40-130 micrometers length) into one knee joint capsule can be used as animal model of tonic (chronic) pain. A limp and a decrease in body weight supported by the injected hind leg's paw occurred approximately 1 h after the MSU (20 mg) injection, reached a maximum at 2-3 h, and lasted for more than 6 h before a gradual return to pre-injection levels. They were diminished by systemic administration and local (the dorsal part of the nucleus raphe dorsalis) application of morphine, this effect being blocked by naloxone. This suggests that the limping and the paw pressure decrease are the reflexion of pain. It is suggested that the animal model of the MSU-induced arthritis is useful for the study of tonic pain.     

Effects of hemodialytic treatment on uremic polyneuropathy

Summary The involvement of the peripheral motor and sensory nerve, at least on a subclinical level, is a nearly constant event with chronic renal failure. The study of the motor and sensory propagation velocity indicates that a widespread functional lesion of the axon with a peripheral point of attack and secondary demyelination, may be the basic pathogenetic event of uremic polyneuropathy. Prolonged hemodialytic treatment is substantially unable to influence the evolution of uremic polyneuropathy. The electrophysiological follow-up study of the peripheral nerve does not seem to be an index of adequate dialysis.

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Zusammenfassung Die Beteiligung des peripheren motorischen und sensiblen Nerven, zumindest subklinisch, ist bei chronischer Niereninsuffizienz Regel. Die Untersuchung der motorischen und sensorischen Erregungsleitungsgeschwindigkeit spricht dafür, daß bei der urämischen Polyneuropathie als wesentliches pathologisches Geschehen das Axon besonders distal ausgedehnt betroffen ist mit einer sekundären Demyelinisation. Auch langdauernde Hämodialyse scheint nicht in der Lage zu sein, die Entwicklung der urämischen Polyneuropathie zu beeinflussen. Die elektrophysiologische fortlaufende Kontrolle des peripheren Nerven scheint nicht ein brauchbarer Parameter für eine wirksame Dialyse zu sein.

     

Normal and abnormal face selectivity of the M170 response in developmental prosopagnosics

Developmental prosopagnosia is a lifelong impairment in face recognition despite normal low-level visual processing. Here we used magnetoencephalography (MEG) to examine the M170 response, a component occurring approximately 170 ms after stimulus onset, in a group of five developmental prosopagnosics. In normal subjects, the M170 is “face-selective”, with a consistently higher amplitude to faces than to a wide variety of other visual stimulus categories; the N170, a component recorded using event-related potentials (ERP) and thought to be analogous to the M170, also shows this “face selectivity”. Two previous ERP studies with developmental prosopagnosics have found attenuation or absence of face selectivity in the N170 response of these subjects [Bentin, S., Deouell, L. Y., & Soroker, N. (1999). Selective visual streaming in face recognition: Evidence from developmental prosopagnosia. Neuroreport, 10, 823–827; Kress, T., & Daum, I. (2003). Event-related potentials reflect impaired face recognition in patients with congenital prosopagnosia. Neuroscience Letters, 352, 133–136]. Three of our developmental prosopagnosic group showed this non-selective pattern at the M170 while the remaining two prosopagnosics were indistinguishable from normal controls. Thus, impaired face recognition is not necessarily correlated with an absence of the “face-selective” M170. Furthermore, ERP recordings collected simultaneously in the two developmental prosopagnosics with seemingly selective M170s also showed N170s within the same normal selective range, demonstrating that the face-selective signals found with MEG are not due to differences between MEG and ERP. While the presence of face selectivity at these neurophysiological markers is insufficient for predicting normal behavioral performance with faces, it could help to distinguish different classes of face recognition deficits.     

Neurophysiology of micturition and continence in women

Micturition and continence involve the coordination of complex neural events between the central and peripheral nervous systems. An understanding of these events provides a foundation for the treatment of voiding disorders in women such as stress urinary incontinence, urge incontinence and interstitial cystitis. The purpose of this paper is to comprehensively review the neuroanatomy, enurophysiology and neuropharmacology of micturition and continence. However, a brief section discussing clinical correlations will follow each of these topics to help integrate the basic science with clinical obervations.