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Biomedical subjects

M D Craggs

Publications and source records attributed to M D Craggs.

At least 37 records · Page 2Linked to original sources
PubMed1986

A putative non-cholinergic mechanism in urinary bladders of New but not Old World primates.

The effects of atropine on bladder contractions evoked by sacral ventral root stimulation were investigated in two species of New World monkey (marmoset and cebus) and in paraplegic man. The findings were then compared to those previously obtained for the cat and two species of Old World monkey (rhesus and baboon). The results show the marmoset and cebus to represent a transitional stage between the complete sensitivity of the bladders of Old World monkeys to atropine and the relative insensitivity of the cat bladder. The bladder response is shown to comprise two components, an atropine sensitive component which is slow in onset and an atropine resistant component which is easily fatigued. The experiments in paraplegic people confirm that the parasympathetic innervation of the bladder of man is, like that of Old World monkeys, exclusively cholinergic. A behavioural interpretation is tentatively offered to explain the two types of innervation.

Animals↗
PubMed1985

Bladder electromyograms and function in monkeys after atropine.

Voiding induced in conscious monkeys by infusion of sterile saline into the bladder via a chronically implanted bladder catheter was stable over many months. Artefact-free recordings of electrical activity were obtained from the bladder neck and dome of these animals during bladder filling and voiding. Characteristic voiding electromyograms were recorded from both sites but were seen first in the record from the neck. Small doses of methyl-atropine abolished both voiding and the electromyograms; evoked responses to sacral ventral root stimulation were similarly prevented. Therefore the bladders of both man and monkey are very sensitive to atropine, unlike the bladders of most other animals.

Anesthesia↗
PubMed1982

The effects of parasympathetic blocking agents on bladder electromyograms and function in conscious and anaesthetized cats.

Voiding induced in conscious cats by infusion of sterile saline into the bladder via a chronically implanted bladder catheter was stable over many months. Artefact-free recordings of electrical activity obtained from the bladder neck and dome of these preparations during bladder filling and voiding showed characteristic voiding electromyograms but did not permit a functional differentiation. Both voiding and the associated electromyogram were abolished by the ganglion blocking agent, pentolinium. Hyoscine or methyl atropine did not affect the electromyogram but impaired the ability of cats to empty their bladders completely. In anaesthetized cats, ganglion blocking agents prevented a rise in bladder pressure during sacral ventral root stimulation but a hyoscine-sensitive bladder contraction was seen following the period of stimulation. Further stimulation during this post-stimulus rise in intravesical pressure revealed a hyoscine-sensitive stimulus-bound relaxation. Sacral ventral root stimulation relaxed the bladder neck/proximal urethra particularly in the presence of sympathetic tone.

Anesthesia↗
PubMed1981

Gating of somatosensory evoked potentials during different kinds of movement in man.

1. Somatosensory evoked potentials from electrical stimulation of the digital nerves of the right thumb have been recorded during the performance of various motor tasks in eight normal subjects. 2. The N20-P30 primary cortical response is only moderately affected by task context, while the P45-N55 secondary response is markedly 'gated' by movement of the stimulated digit. The late N140 vertex is variable. 3. In most subjects, active and passive movements are about equally effective in suppressing the secondary complex; but in one, passive movement has come to be rather less effective than active. 4. Secondary response suppression occurs in proportion to the velocity of the movement of the thumb, up to a velocity of 20 deg/s. 5. Secondary response suppression is unrelated to load in the range 0 to 0.16 Nm. 6. When the stimulus is timed to occur at various points in movement, secondary complex suppression occurs at all stages; but there is little or no suppression when stimulation is timed at 200 ms before the start of or 500 ms after the end of a movement. 7. Secondary response suppression is maximal when the same digit is both moving and shocked. When the right index or little finger are moved instead, the right thumb being stimulated, suppression is less; when the left thumb moves, no suppression is seen. 8. Secondary response suppression is reduced but not lost if the skin and interphalangeal joint of the thumb are anaesthetized distal to the stimulating electrodes. 9. Secondary response suppression is unimpaired when the radial nerve is anaesthetized, paralysing the finger extensors. 10. In an attempt to identify the course taken by the afferent volley between the primary and secondary responses, and to identify the gating site, we recorded the responses in six patients with Parkinson's disease who had undergone thalamotomy. Their secondary responses were present, and gated in the normal way. 11. We are unable to confirm whether the secondary response represents the re-arrival at cortical level of a volley that has traversed the cerebrocerebellar loop. 12. We confirm that the secondary complex is located a little anterior to the primary cerebral response. 13. We conclude that a gating action is exerted in the brain on somatosensory afferent activity, after it first reaches the cortex, and that this gating action associated with movement is controlled by other afferent signals from the stimulated limb, and particularly from the stimulated digit.

Adult↗
PubMed1980

A pilot study of the effects of methylphenidate on the vigilance-related EEG in hyperactivity.

Seven hyperactive children underwent a reaction time (RT) test requiring prolonged (15 min) vigilance, once while receiving methylphenidate and once without medication. EEG samples taken immediately before each RT measurement were subjected to power-spectral analysis. Compared to the off-medication condition, methylphenidate reduced the RT whilst paradoxically increasing EEG alpha power relative to higher and lower frequencies in 5 out of the 7 children. On this medication, the RT increased during the course of the task, and the relative EEG alpha power increased compared to other frequencies. Off medication, RTs showed an even greater increase with prolonged vigilance, but the accompanying EEG changes were the reverse of those seen on medication. The altered EEG power spectrum on methylphenidate appears closer to that of a normal EEG, and may be related to the improvement in specific attention produced by this drug in hyperactivity.

Alpha Rhythm↗
PubMed1980

A technique for anodally blocking large nerve fibres through chronically implanted electrodes.

If a spinal root of a baboon or rhesus monkey is trapped in an initially loose-fitting silicone rubber channel containing two or more platinum electrodes, electrical pulses sent through these electrodes can stimulate nerve fibres close to the cathode and block the resulting impulses close to the anode. We show (1) how anodal break excitation and excitation of fibres outside the silicone rubber channel can be avoided; (2) that an implant 26 months old behaves like a recent one; (3) that in a root containing somatic motor fibres and parasympathetic fibres, all somatic motor fibres can be blocked and most or all parasympathetic fibres excited but not blocked; (4) that provided that the electrodes pass no net direct current, prolonged stimulation with block can be harmless; (5) how block can be achieved in one direction only along a root; (6) that a peripheral nerve can be blocked by the same techniques.

Animals↗
PubMed1976

The stability of the electrical stimulation map of the motor cortex of the anesthetized baboon.

We have made repeated maps of the movements obtained by threshold electrical stimulation, with surface cathodal trains of pulses, of the motor cortex of 4 baboons, using chronically implanted arrays of electrodes. The electrode arrays were judged to remain in a constant relationship with the cortex because they did not move relative to the skull, and the arm/leg border obtained remained stable. There was evidence of a stability of response over a period of weeks. In 3 of the 4 animals, there was stability of the responding digit(s) regardless of the movement made by the digit(s), and of the digital movements performed (regardless of the digits involved). The stability of the map from minute was almost complete. Those variations that occur do so mainly by confusion within the motor homunculus, rather than by its movement as a whole across the cortex. Reasons for the imperfect long-term stability of the map are discussed in terms of variations in the physiological 'set' of the presumed polysynaptic pathways that are stimulated.

Animals↗
PubMed1976

The real bladder electromyogram.

The nature of bladder electrical activity was investigated in anaesthetised cats and 1 baboon. A time-locked muscle response to sacral ventral root stimulation was most clearly detected within a 10-40 Hz frequency band, the response preceding the rise in intravesical pressure. During reflex voiding only activity in the 10-40 Hz band was consistently related to reflex voiding and to the small contractions leading up to voiding. It is concluded that only a very limited part of the wide band electrical activity recorded from the bladder can be considered genuine electromyogram and that the 10-40 Hz frequency band probably excludes the worst of the artefact. Possible sources of artefact and their relation to changes in intravesical pressure are presented in Table I.

Animals↗