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Biomedical subjects

D G Ferrington

Publications and source records attributed to D G Ferrington.

24 records · Page 2Linked to original sources
PubMed1980

A simple, accurate method for reproducing details of histological sections using a microfiche printer.

A rapid, inexpensive method is described for achieving accurate reproduction of histological sections. The method uses a microfiche reader-printer (for library use) which produces A4 size prints. Interchangeable lenses on the microfiche printer permit the magnification of the section to be varied over the range 6.6-72 times. Where large numbers of sections are involved the speed and low cost of the method offers considerable advantages over traditional hand tracing or photomicrography.

Histological Techniques↗
PubMed1980

Functional capacities of tactile afferent fibres in neonatal kittens.

1. Responses were recorded from individual tactile afferent fibres isolated by microdissection from the median nerve of pentobarbitone-anaesthetized neonatal kittens (1-5 days post-natal age). Experiments were also conducted on adult cats to permit precise comparisons between neonatal and adult fibres.2. Neonatal fibres with receptive fields on the glabrous skin of the foot pads were classified into two broad groups, a slowly adapting class (40%) which responded throughout a 1 sec period of steady indentation and a rapidly adapting or dynamically sensitive class comprising 60% of units. Fibres in these two groups had overlapping conduction velocities in the range 4.3 to 7.5 m/sec and were believed to be the developing Group II afferents of the adult.3. Neonatal slowly adapting fibres qualitatively resembled their adult counter-parts. They displayed graded stimulus-response relations which, over the steepest segment of the curves, had mean slopes of 15.7 impulses/100 mum of indentation. Plateau levels of response were often reached at amplitudes of skin indentation of < 0.5-0.7 mm.4. Dynamically sensitive fibres with receptive fields on the glabrous skin were studied using sinusoidal cutaneous vibration which in the adult enables them to be divided into two distinct classes. However, in the neonate, they formed a continuum whether criteria of sensitivity or responsiveness were used.5. In response to vibration neonatal fibres differed from adult ones according to the following quantitative indices: (i) sensitivity as measured by both absolute thresholds and thresholds for a 1: 1 pattern of response, both of which were higher in the neonate than in the adult at all frequencies > 50 Hz and differed by an order of magnitude at frequencies >/= 200 Hz; (ii) responsiveness based on the mean impulse rate evoked at a fixed amplitude of cutaneous vibration; (iii) band width of vibratory sensitivity which in the neonate was confined to approximately 5-300 Hz whereas in the two classes of adult units it covered the range 5-800 Hz; (iv) capacity for coding information about vibration frequency. Impulse activity of neonatal fibres was less tightly phase-locked to the vibratory stimulus and showed a poorer reflection of the periodic nature of the vibratory stimulus than impulse patterns of adult units.6. The results reveal that tactile receptors and afferent fibres in the neonate are functionally immature. Their restricted coding capacities suggest that peripheral tactile sensory mechanisms impose limits on the ability of the new-born animal to derive information about its tactile environment.

Animals↗
PubMed1978

Coding of information about tactile stimuli by neurones of the cuneate nucleus.

1. The responses of cuneate neurones to controlled tactile stimulation of the foot pads were examined in unanaesthetized, decerebrate cats. The neurones were divided into three functional classes; one sensitive to steady tactile stimuli, and two dynamically sensitive classes which could be readily differentiated by their responsiveness to cutaneous vibration. Each class appeared to receive an exclusive input from only one of the three known groups of tactile receptors associated with the foot pads, namely the Pacinian corpuscles, the Merkel endings and the intradermal, encapsulated endings known as Krause or Meissner corpuscles. 2. Cuneate neurones responsive to steady indentation of the skin displayed approximately linear or sigmoidal stimulus-response relations over indentation ranges up to approximately 1.5--2 mm. Response variability at a fixed stimulus intensity was relatively low and showed little systematic change over the full range of the stimulus-response curves. 3. One class of dynamically sensitive cuneate neurones responded to cutaneous vibration over a range of approximately 5-80 Hz with maximal responsiveness around 30 Hz. The other class, the Pacinian neurones, responded over a range of approximately 80- greater than 600 Hz with maximal responsiveness at 200-400 Hz. The thresholds and combined band width of vibratory sensitivity of these populations were comparable with known subjective thresholds and range of cutaneous vibratory sensibility. 4. Responses of cuneate neurones were phase-locked to the vibratory stimulus suggesting that information about vibration frequency could be coded by the patterns of impulse activity. Quantitative measures indicated that maximal phase-locking occurred in responses to vibration frequencies of 10-50 Hz with a progressive decline at higher frequencies. Above 400 Hz, impulse activity occurred almost randomly throughout the vibratory stimulus cycle and therefore carried little further signal of vibratory frequency. The decline, with increasing frequency, in the ability of cuneate neurones to signal information about vibratory frequency parallels the known subjective capacities for frequency discrimination. 5. A switch-over occurred at approximately 80 Hz in the population of cuneate neurones able to provide the more reliable signal of vibratory frequency; above 80 Hz, the Pacinian neurones; below 80 Hz, the neurones receiving intradermal, rapidly adapting receptor input from the pads. 6. The observed properties of cuneate neurones are compatible with a role in signalling information which could contribute to subjective tactile abilities.

Action Potentials↗
PubMed1977

Human tactile detection thresholds: modification by inputs from specific tactile receptor classes.

1. Human detection thresholds for a vibratory stimulus applied to the volar surface of the index finger were examined under conditions where afferents from specific tactile receptor classes were simultaneously activated from the thenar eminence. The experiments were designed to test whether stimuli which have been shown previously to induce afferent inhibition of ;tactile' neurones in the cuneate nucleus of the cat could modify human subjective performance in a tactile detection task. Conditioning stimuli to the thenar eminence were usually of three forms; steady indentation to engage slowly adapting tactile receptors; 300 Hz vibration to engage Pacinian corpuscles; and 30 Hz vibration to engage the intradermal, rapidly adapting tactile receptors which are thought to be Meissner's corpuscles.2. In ten subjects the mean detection threshold for a 30 Hz test stimulus in the absence of conditioning stimulation was 8.6 +/- 1.0 mum (S.E.). Detection thresholds were increased substantially in the presence of a 300 Hz, 100 mum conditioning stimulus (mean increase 11.1 +/- 2.0 mum), whereas minor or insignificant effects were seen with conditioning stimuli consisting of (a) 30 Hz, 100 mum (mean increase 1.4 +/- 0.8 mum), (b) steady indentation, 1.5 mm in amplitude (mean increase 1.3 +/- 0.7 mum) or (c) 300 Hz, 100 mum to the contralateral thenar eminence (mean increase 0.4 +/- 0.5 mum).3. The 300 Hz conditioning stimulus to the ipsilateral thenar eminence caused a marked increase in detection thresholds at all test stimulus frequencies over the range 10-450 Hz. The effects of the conditioning stimulation therefore operated on inputs from Pacinian corpuscles, which are responsible for vibration detection at 80-450 Hz, and on inputs from the intradermal, rapidly adapting receptors which are responsible for vibration detection at 10-80 Hz.4. The band width of conditioning vibratory frequencies which was effective at amplitudes of 100 mum in bringing about increases in detection threshold extended from 50-80 Hz to 300 Hz, the maximum tested.5. Whereas amplitudes of 1-2 mum produced clear increases in detection thresholds with conditioning stimuli of 300 Hz, amplitudes of > 200 mum were needed at 30 Hz.6. The observed elevations in detection threshold are consistent with an afferent-induced inhibitory action exerted at synaptic relays of the sensory pathway by tactile inputs arising exclusively or predominantly from Pacinian corpuscles.

Adult↗