Biomedical subjects

H Dickhaus

Publications and source records attributed to H Dickhaus.

23 records · Page 2Linked to original sources

PubMed1985

Tonic descending inhibition affects intensity coding of nociceptive responses of spinal dorsal horn neurones in the cat.

The supraspinal inhibitory control of lumbar spinal dorsal horn neurones was investigated in N2O-anaesthetized cats by reversibly blocking conduction in the spinal cord. Dorsal horn neurones selected for this study had convergent input from myelinated (A-) and unmyelinated (C-) fibres in the posterior tibial and/or superficial peroneal nerves of the hind limb. Virtually all of them could also be excited by noxious heating of the skin of the footpad region and by low intensity mechanical stimulation of the foot. Variation of the temperature of noxious radiant skin heating (40-56 degrees C, 10 sec in duration) resulted in graded responses of the neurones. The stimulus-response functions (SRF) were monotonic; in the majority of 32 cases they were linear. Neurones could be classified according to their maximum discharge frequency in response to skin heating into 22 weakly sensitive units (responses below 100 Hz at 50 degrees C) and 10 highly sensitive units (above 100 Hz). Responses outlasted the period of skin heating by seconds to minutes. A reversible conduction block of spinal axons by cooling a 15 mm cord segment (L1) with a thermode at 0 degrees C affected the responsiveness of the dorsal horn neurones in 12 of 15 cases. The maximum discharge frequency to a certain temperature of skin heating was increased during the spinal block. The duration of heat-evoked discharges was either not changed or increased during the spinal block. The SRF were reversibly displaced during the spinal blockade to higher discharge frequencies and lower threshold temperatures of skin heating. In 8 of 12 cases the change in the SRF was a nearly parallel shift, whereas in 4 units the increase of responsiveness had a complex effect upon the SRF. The decrease in the threshold to skin heating ranged up to 4.5 degrees C; the mean decrease was 2 degrees C. It is confirmed that in anaesthetized cats, nociceptive spinal neurones are subject to a tonically active descending inhibition, which is interrupted by local spinal cooling. The effect of the spinal block on the SRF of the neurones suggests that this tonic inhibition is similar to that produced by electrical stimulation in the lateral reticular formation of the brain-stem.

Animals↗

PubMed1984

Evidence for a monosynaptic connection between slowly adapting pulmonary stretch receptor afferents and inspiratory beta neurones.

The synaptic connection between slowly adapting pulmonary stretch receptor afferents and inspiratory neurones within a region ventral to the tractus solitarius was determined using intracellular recording and spike triggered averaging techniques. When the vagus nerve was stimulated at intensities eliciting a Hering-Breuer reflex, the difference in mean latency between centrally recorded action potentials of slowly adapting pulmonary stretch receptor afferents and e.p.s.p.s of inspiratory beta neurones was 0.2 ms. This difference is indicative of a monosynaptic connection. Extracellular single unit spikes of slowly adapting pulmonary stretch receptors recorded from the nodose ganglion were used to trigger the averaging of synaptic noise recorded from inspiratory neurones. A prominent wave of synaptic depolarization was observed in all inspiratory beta neurones even when a small number of sweeps were averaged. This depolarization was absent from inspiratory alpha neurones. The shape indices of these depolarizations are consistent with a monosynaptic connection between slowly adapting pulmonary stretch receptor afferents and inspiratory beta neurones. In addition, the data raise the possibility that this connection is multiple and distributed.

Animals↗

PubMed1978

[Inhibition in the spinal cord: a neuronal mechanism of hypalgesia produced by acupuncture (author's transl)].

Central nervous system mechanisms of nociception and pain were studied electrophysiologically in the spinal cord of cats. A great proportion of dorsal horn neurons respond to noxious skin stimuli, for instance to heating to 50 degrees C; such stimuli predominantly activate afferent C fibres. These spinal neurons participate in the transmission of nociceptive information to the brain. The heat-evoked discharges of dorsal horn neurons are effectively inhibited by repetitive electrical stimulation of large;, low-threshold cutaneous A fibres. The inhibition reaches its maximum effect after several minutes of nerve stimulation, and declines at a slow rate after the end of stimulation. This long-term suppression is considered to be a neuronal mechanism underlying hypalgesia produced in man e.g. by acupuncture and by transcutaneous nerve stimulation.

Acupuncture Therapy↗

PubMed1978

External nucleus of inferior colliculus: auditory and spinal somatosensory afferents and their interactions.

1. The discharges of 129 units were studied in the external nucleus of the inferior colliculus of 11 anesthetised and paralyzed cats. This region is known to receive fibers from auditory nuclei and the dorsal column nuclei. 2. Stimuli used were pure tone bursts, monaural or binaural, tactile stimulation of the body surface, and electrical stimulation of the dorsal columns (DC) at a low cervical level and of the contralateral and ipsilateral tibial nerves. 3. Forty-six percent of units were only influenced by one type of stimulation (26% auditory, 20% DC). Of the remaining bimodally influenced units, the majority was excited by pure tone stimuli and inhibited by DC stimulation. 4. A small proportion of the total population (18%) was excited by both DC and auditory input, and units sensitive to both tones and tactile stimulation of the skin were rare (4%). 5. Auditory tuning curves were generally very broad compared with those of units in the central nucleus of the inferior colliculus. Similarly, somatic receptive fields were large and usually extended over a whole limb. 6. The majority of tone-responsive units were influenced binaurally (70%); most somatic receptive fields were located on the contralateral fore- or hindlimb (16/18). 7. The results indicate that both auditory and somatosensory information is contained in the discharges of units in the external nucleus of the inferior colliculus. 8. Speculations are made about the role of this nucleus in descending auditory input to the spinal cord and in the comparison of auditory and cutaneous information during sound-evoked coordinated body movements.

Acoustic Stimulation↗

PubMedDate not supplied

Representations of ECG--late potentials in the time frequency plane.

It is shown that time frequency signal analysis could be a useful technique in detecting late potentials (LP). In particular, the spectrogram, the Wigner distribution and the wavelet transform have been applied to ECG signals from patients with sustained ventricular tachycardia. Comparisons of the three algorithms reveals that much better time localization is achieved by the wavelet transform. Moreover, it is concluded that a separation between healthy subjects and patients could be obtained based upon time frequency analysis.

Action Potentials↗