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Biomedical subjects

R J Porter

Publications and source records attributed to R J Porter.

At least 19 recordsLinked to original sources
PubMed1992

New antiepileptic drugs: from serendipity to rational discovery.

Antiepileptic drug discovery has made enormous progress from the serendipity and screening processes of earlier days to the rational drug development of today. The modern era of research began with the recognition that enhancement of inhibitory processes in the brain might favorably influence the propensity for seizures, gamma-aminobutyric acid (GABA) being the main inhibitory transmitter. Work in this field led to the development of vigabatrin, which inhibits the enzyme responsible for the degradation of GABA. More recently, research has focused on the therapeutic potential of blocking excitatory amino acids--in particular glutamate. Of the three receptors for glutamate, the N-methyl-D-aspartate (NMDA) receptor is considered the one of most interest in epilepsy, and research on a series of competitive NMDA receptor antagonists--especially those that are orally active--is in the forefront of antiepileptic drug development today. A further alternative for diminishing neuronal excitability is to modulate sodium, potassium, or calcium channels. The latter are especially implicated in absence seizures.

Animals↗
PubMed1992

Current medical therapy of epilepsy.

The treatment of epilepsy firstly depends upon the correct diagnosis, with emphasis on considerations of etiology, seizure type, and epilepsy syndrome. Following an appropriate diagnostic conclusion, the patient may be started on the medication matched to the seizure type. A full understanding of the pharmacology of antiepileptic drugs will enable the physician to obtain maximum benefit from the available pharmaceutical armamentarium.

Anticonvulsants↗
PubMed1991

A case of mosaicism involving an unstable 13/14 Robertsonian translocation.

Prenatal diagnosis of mosaicism involving an apparently unstable 13/14 Robertsonian translocation is reported. This illustrates the difficulties encountered in counselling when mosaicism is ascertained prenatally. Other reported examples of apparently unstable Robertsonian translocations are discussed.

Adult↗
PubMed1991

Disorders of consciousness and associated complex behaviors.

Behavioral events during epileptic seizures, while varied, comprise only a portion of the total spectrum of human behavior. Studies using intensive video monitoring have permitted insight into the common and uncommon events in epileptic seizures. Comparison of data from these studies with data from other disorders, notably psychiatric disease, allows a more complete understanding of the nature of these disorders and of the differential diagnosis of each. Disorders in which consciousness is altered are common and heterogeneous; it is now possible to differentiate these various disorders. The information presented here provides a framework for the physician confronted with these diagnostic dilemmas.

Behavior↗
PubMed1991

Different phase-stable relationships of the upper lip and jaw for production of vowels and diphthongs.

Relational invariants have been reported in the timing of articulatory gestures across suprasegmental changes, such as rate and stress. In the current study, the relative timing of the upper lip and jaw was investigated across changes in both suprasegmental and segmental characteristics of speech. The onset of upper lip movement relative to the vowel-to-vowel jaw cycle during intervocalic bilabial production was represented as a phase angle, and analyzed across changes in stress, vowel height, and vowel/diphthong identity. Results indicated that the relative timing of the upper lip and jaw varied systematically with changes in stress and vowel/diphthong identity, while remaining constant across changes in vowel height. It appears that modifications in relative timing may be due to adjustments in the jaw cycle as a result of the compound nature of jaw movement for diphthongs as compared to vowels, with further modifications due to the effect of stress on these compound movements.

Adult↗
PubMed1991

Discrimination of formant transition onset frequency: psychoacoustic cues at short, moderate, and long durations.

Two experiments determined the just noticeable difference (jnd) in onset frequency for speech formant transitions followed by a 1800-Hz steady state. Influences of transition duration (30, 45, 60, and 120 ms), transition-onset region (above or below 1800 Hz), and the rate of transition were examined. An overall improvement in discrimination with duration was observed suggesting better frequency resolution and, consequently, better use of pitch/timbre cues with longer transitions. In addition, falling transitions (with onsets above 1800 Hz) were better discriminated than rising, and changing onset to produce increments in transition rate-of-change in frequency yielded smaller jnd's than changing onset to produce decrements. The shortest transitions displayed additional rate-related effects. This last observation may be due to differences in the degree of dispersion of activity in the cochlea when high-rate transitions are effectively treated as non-time-varying, wideband events. The other results may reflect mechanisms that extract the temporal envelopes of signals: Envelope slope and magnitude differences are proposed to provide discriminative cues that supplement or supplant weaker spectrally based pitch/timbre cues for transitions in the short-to-moderate duration range. It is speculated that these cues may also support some speech perceptual decisions.

Attention↗
PubMed1990

General assay for phosphoproteins in cerebrospinal fluid: a candidate marker for paraneoplastic cerebellar degeneration.

The components of protein phosphorylation systems (protein kinases, protein phosphatases, and their phosphoprotein substrates) are highly enriched in neuronal cells compared with other cell types. We exploited this relative neuronal enrichment of protein phosphorylation system components to develop a general assay technique for putative protein kinase substrates (phosphoproteins) in human cerebrospinal fluid. Using this cerebrospinal fluid phosphoprotein assay, we have detected a putative protein kinase C substrate protein of apparent Mr 60 kd in 6 of 14 patients with paraneoplastic cerebellar degeneration but not in any of 55 patients with a variety of other neurological diseases. Phosphoproteins in cerebrospinal fluid may provide novel and unique markers for the diagnosis or staging of neuronal diseases as well as offer potential insights into the biochemical characterization of affected neuronal populations.

Adult↗
PubMed1989

Mechanisms of action of new antiepileptic drugs.

Our understanding of how new antiepileptic drugs work mirrors what we know about how currently marketed antiepileptic compounds exert their action--that information is scarce and elusive. The mechanism of action of antiepileptic drugs is nevertheless inextricably linked to epileptogenesis itself, and investigations of several promising new compounds are underway to establish the levels at which these drugs act. Compounds act on synapses and membranes as well as affecting receptors, neurotransmitters, and peptides. The most extensive data are available on drugs that inhibit the action of GABA or its receptors, including new benzodiazepine-like agents and barbituric-acid derivatives. The few drugs that act by inhibiting the effects of excitatory amino acids are reviewed. Finally, the maximal electroshock test is an empirical method to determine the antiepileptic properties of a drug; several agents under development have been effective in this screening technique.

Acetamides↗
PubMed1989

New antiepileptic drugs.

In contrast with the situation only a decade ago, a profusion of new potential AEDs has been introduced for world-wide clinical testing. Which, if any, of these compounds will be added to the physician's armamentarium against epileptic seizures is unknown, but the continuing flow of testable compounds augurs well for the future.

Anticonvulsants↗
PubMed1979

Early insulin release following suckling in neonatal lambs and rabbits.

Developmental changes in the plasma insulin response to milk ingestion have been determined in neonatal lambs fed by bottle and in naturally suckled infant rabbits. In lambs at 4 days of age and older plasma insulin increased within 5 min of suckling and declined again before increasing to a second peak 60 to 120 min after the feed. The early insulin peak was not associated with any change in plasma glucose and was absent in lambs at 1 day of age. When the early insulin peak was absent the increase in plasma glucose following the meal was greater. The early, apparently reflex, release of insulin also occurred in some 'sham-fed' lambs. Atropine administration before feeding abolished the early peak in insulin. A marked early peak of insulin release, not accompanied by any consistent change in plasma glucose, was also observed in naturally-suckled infant rabbits at 1, 5, 10 and 15 days after birth.

Animal Population Groups↗
PubMed1979

Ear dominance in perception of dichotic chords: pure tones versus tone glides.

Pitch judgments for dichotic chords composed of two pure tones often show a bias in favor of the chord-component going to one ear. This "ear-advantage for pitch" (EAP) varies between subjects, but is very stable within subject and is thought to reflect differences in spectral "sensitivity" of the two auditory pathways. The present study explored this hypothesis by examining pitch judgments of complexes composed of tones dichotically paired with frequency-varying signals. The direction and strength of EAP was first established using pure tones, then rising tone glides were introduced into the channel going to thenondominant ear. Since a glide possesses less energy at a given frequency than a pure tone of equal duration, an increase in EAP was expected. An increase in EAP was consistently observed for only one subject; three subjects showed small, variable effects; and six subjects displayed a decrease in EAP. The results suggested that factors other than relative spectral sensitivity affect observed EAP.

Acoustic Stimulation↗