Effect of iontophoretically applied 5-hydroxytryptamine on the excitability of single primary afferent C- and A-fibers in the cat spinal cord

Excitability testing of single sural afferent C- and A-fibers was employed to study possible presynaptic effects of 5-hydroxytryptamine (5-HT) applied iontophoretically at the intraspinal point of lowest threshold for their antidromic activation in anesthetized or decerebrate spinalized cats. Threshold for single fibers recorded in the sural nerve was measured prior to and during iontophoretic application of 5-HT through a micropipette positioned in close proximity to the intraspinal stimulating electrode. 5-HT produced dose-related increases in threshold for antidromic activation in 21 or 30 C-fibers. Six of 9 A delta, and 4 of 7 A beta-fibers were similarly affected.

Serotonergic mediation of descending inhibition from midbrain periaqueductal gray, but not reticular formation, or spinal nociceptive transmission in the cat

Electrical stimulation in the midbrain periaqueductal gray (PAG) and lateral midbrain reticular formation (LRF) strongly suppresses the responses of spinal dorsal horn neurons to noxious heating of the skin. The possible role of serotonin (5-hydroxytryptamine, 5-HT) was investigated by quantitatively comparing certain parameters of descending inhibition from PAG and LRF in normal cats [14,15] and cats whose central 5-HT levels had been reduced by pretreatment with p-chlorophenylalanine (PCPA, 300 or 500 mg/kg i.p., 72 h prior to acute experiment). Single lumbar dorsal horn neuronal responses to noxious radiant heating of glabrous footpad skin(50 degrees C, 10 sec, 1/3 min) were recorded in normal and PCPA-pretreated cats anesthetized with sodium pentobarbital and N2O. Inhibition of neuronal heat-evoked responses during midbrain stimulation (mean frequency 30 Hz, up to 800 microA current intensity) was expressed as percent of the unit's control response in the absence of midbrain stimulation. Inhibition by PAG stimulation of units from cats pretreated with 300 mg/kg PCPA (mean inhibition at 450 microA to 60% of control in 12 units) was not detectably different from that in control (non-pretreated) cats. However, inhibition by PAG stimulation was significantly weaker in units from cats pretreated with 500 mg/kg PCPA (mean to 83.4% of control in 9 units). In the latter group, mean current threshold for inhibition was higher, and slope of current-intensity plots lower, than in the control and 300 mg/kg PCPA pretreatment groups. In contrast, mean inhibition by LRF stimulation was enhanced in the 300 and 500 mg/kg PCPA treatment groups in a dose-related manner. In normal (non-pretreated) cats, systemic administration of the putative 5-HT antagonist methysergide (0.07--1 mg/kg) reduced or abolished inhibition by PAG stimulation in each of 8 units. Low doses of methysergide had little or no effect on inhibition produced by LRF stimulation in 6 units. The results suggest pharmacologically distinct mechanisms of inhibition produced by stimulation in PAG and LRF.

The opiate antagonist naloxone does not consistently block inhibition of spinal nociceptive transmission produced by stimulation in lateral midbrain reticular formation of the cat

Electrical stimulation in the lateral midbrain reticular formation (LRF) inhibited the responses of spinal dorsal horn neurons to noxious (50 degrees C) skin heating. Systemic administration of naloxone (0.1-2 mg/kg) had no effect on inhibition produced by LRF stimulation in 10 units, while this inhibition was partially blocked in 3 units. The results indicate that endogenous opiates are not primarily involved in mediating descending inhibition from LRF stimulation.

Time course and effective sites for inhibition from midbrain periaqueductal gray of spinal dorsal horn neuronal responses to cutaneous stimuli in the cat

Inhibition of spinal dorsal horn neuronal responses to noxious (50 degrees C) skin heating by stimulation of the midbrain periaqueductal gray (PAG) was quantitatively investigated in cats anesthetized with sodium pentobarbital and nitrous oxide. Systematic variation of the interval between onset of PAG stimulation (PAGS) and onset of noxious skin heating revealed that a marked reduction of spinal unit heat-evoked discharges occured immediately upon onset of PAGS, and ceased immediately at offset of PAGS with a post-stimulation excitatory rebound. Stimulation at sites in both ventral and dorsal PAG produced inhibition, the strength of which increased sometimes in a linear manner with increasing strength of PAGS. Thresholds for the generation of descending inhibition were higher in dorsal than ventral PAG. PAGS also inhibited spinal unit responses to non-noxious skin stimulation (brushing of hairs). Descending inhibition from PAG is considered as a possible mechanism for analgesia produced by stimulation of PAG and other brainstem structures.

Differential inhibitory effects of medial and lateral midbrain stimulation on spinal neuronal discharges to noxious skin heating in the cat

1. The inhibitory effects of electrical stimulation in midbrain periaqueductal gray (PAG) and lateral reticular formation (LRF) on spinal dorsal horn neuronal responses to noxious skin heating were investigated in cats anesthetized with Nembutal and N2O. 2. Thirty-one dorsal horn units driven by electrical stimulation of the posterior tibial and/or superficial peroneal nerves at A- and C-fiber strength responded to noxious radiant heating (e.g., 50 degrees C) of the skin of the hindpaw. All units tested were inhibited by electrical stimulation (100-Hz trains, 3/s) of both PAG and LRF. 3. Systematic tracking with the stimulating electrode revealed that descending inhibition is generated at sites throughout the mediolateral extent of the midbrain. Particularly effective sites were in LRF and PAG. 4. More powerful descending inhibition was generated from LRF than from PAG sites, based on quantitative comparison in the same unit of a) degree of inhibition of spinal unit heat-evoked discharges by PAG and LRF stimulation at the same current intensity, b) current threshold for inhibition by PAG and LRF stimulation, and c) slope of curves plotting degree of inhibition in relation to intensity of PAG and LRF stimulation. 5. Dorsal horn neurons show a linear relationship between response magnitude and temperature of skin heating during a series of heat stimuli (42-50 degrees C) applied at 3-min intervals. When the series is repeated during PAG stimulation, the slope of the linear temperature-response curve is reduced without a change in the response threshold. In contrast, repetition of the heating series during LRF stimulation produced a parallel rightward shift in the linear temperature-response curve, with commensurate increase in response threshold. 6. The results indicate that functionally separate descending inhibitory systems are activated by stimulation of PAG and LRF. Possible inhibitory mechanisms and the functional significance of descending inhibition from PAG and LRF are discussed.

Calendar life span versus budding life span of Saccharomyces cerevisiae

This investigation is concerned with the internal factors governing the life span of individual yeast cells. The life span may be limited either by the number of buds a cell can produce or by internal measurement of metabolic time. The natural relationship between the number of cells a single cell can produce and the passage of time was modified by three different kinds of treatment: (1) by cooling the cells for several hours each day; (2) by preculturing the cells in media which inhibit cell division before allowing logarithmic growth; and (3) by culturing the cells in a medium which reduces the rate of budding. All these methods led to a prolongation of chronological life span, but the life span measured by the number of buddings remained remarkably constant. We therefore conclude that there is some kind of factor involved in the budding process which determines life span.

Irreverisble differential block of A- and C-fibres following local nerve heating in the cat

1. Local heating of a nerve was used to block conduction in the myelinated or A-fibres while preserving normal function in most of the non-myelinated or C-fibres. Compound action potentials of A- and C-fibres, and impulses in single C-fibres were recorded to measure the block. 2. Most experiments were done on the posterior tibial nerve of the cat's hind limb. Conducted heat was applied in successive periods of about 2 min each to 15 mm of the exposed nerve. 3. The range of temperatures used was between 45 and 52 degrees C. Below 46 degrees C no conduction block was obtained. With increasing temperature the cumulative time of heating required to produce a block in at least 99% of A-fibres decreased from around 110 min at 46.5 degrees C to 10 min at 51 degrees C. 4. In the posterior tibial nerve the C-fibre compound action potential was reduced to 0.66 of control (mean of twenty-two experiments) when the A-fibre action potential was less than 1% of control. The corresponding value of this selectivity coefficient was 0.20 in seven superficial peroneal and sural nerves. 5. Once a conduction block of A-fibres was reached the remaining C-fibres showed normal functioning, including conduction of repetitive impulses at up to 30 Hz evoked by electrical nerve and adequate skin stimulation. C-fibre conduction persisted for at least 33 h, but not longer than 3 days. 6. This pure C-fibre nerve might be useful for studying central nervous system effects of C-fibres.

Encoding of graded noxious skin heating by neurons in posterior thalamus and adjacent areas in the cat

Impulse discharges were recorded from 62 single units in the posterior thalamic and adjacent nuclei of the cat which received input from hindlimb cutaneous nerves. Noxious radiant heating (e.g., 50 degrees C for 10 sec) of the hindpaw excited 32% of the units. The magnitude of heat-evoked unit discharges was graded with the intensity of noxious heating. Such units had large cutaneous receptive fields spanning 2 or more limbs, and responded to strong mechanical stimuli (pressure, pinch). About half of the units responded also to light stimuli such as hair bending or touch.

[Hydroxyethyl starch (HAS 450/0.7) in human plasma and liver. Course of concentration and histological changes]

In 12 patients 1,000 ml hydroxyethyl starch (Mw 450,000, degree of substitution 0.7) was infused intravenously. A liver biopsy was performed in 10 patients undergoing abdominal surgery 30 minutes to 28 days after the infusion. The liver tissue was investigated by light and electron microscopy. The plasma level of hydroxyethyl starch decreased to 4.8% of the initial concentration 28 days after the infusion (Anthron method). Single intracellular vacuoles were shown by electron microscopy 30 minutes after the end of infusion in Kupffer's cells only. However, 6 to 28 days after infusion intracellular vacuoles were demonstrated in parenchymal liver cells, Kupffer's cells, interstitial histiocytes and to a lesser degree in the cells of the small bile ducts. The pathogenic importance of the portracted elimination from the plasma and the liver storage is unknown.

Presynaptic excitability changes induced by morphine in single cutaneous afferent C- and A-fibers

Intraspinal microstimulation was used to test the excitability of single cutaneous (sural) A- and C-fibers at their central terminals in the cat. Systemic morphine (1.0-2.6 mg/kg) increased the antidromic threshold to 110% (mean value) of control in C-fibers. In some of the C-fibers this effect was reversed by naloxone. A-fibers were not consistently affected by mophine.

Inhibition of spinal neuronal responses to noxious skin heating by stimulation of mesencephalic periaqueductal gray in the cat

1. Discharges of lumbar dorsal horn neurons were evoked by noxious radiant skin heating, and inhibition of the heat-evoked responses by stimulation of the mesencephalic periaqueductal gray was investigated in N2O-anesthetized cats. 2. Thirty-seven units selected on the basis of receiving afferent C-fiber input from the posterior tibial and/or superficial peroneal nerves responded vigorously to 50 degrees C heating of the plantar surface of the ipsilateral hindpaw. All discharges were inhibited by periaqueductal gray stimulation (PAGS) at current strengths of 300--900 microA; the mean threshold for inhibition was 167 microamperemeter. The mean frequency of the inhibited discharge was 39% of the control response. 3. Effective PAGS sites were distributed throughout the ventral PAG bilaterally. Stimulus current-distance estimates indicate that small (0.5--1.2 mm diameter) volumes of tissue within the PAG were stimulated. 4. A monotonic relationship between temperature and unitary discharge was found for skin heating from threshold to about 50 degrees C. PAGS resulted in a decrease in the slope of the curve plotting discharge against temperature, without altering the threshold. 5. Inhibition of the heat-evoked discharges rarely outlasted the PAGS. 6. Possible neural substrates for descending inhibition and correlates with neural mechanisms of analgesia are discussed.

The opiate antagonist, naloxone, does not affect descending inhibition from midbrain of nociceptive spinal neuronal discharges in the cat

Discharges were recorded from spinal dorsal horn neurons in response to noxious skin heating (e.g. 50 degrees C). Repetitive electrical stimulation of the mesencephalic periaqueductal gray (PAG) inhibited these nociceptive discharges. In each of 9 experiments systemic administration of naloxone (1-3 mg/kg) did not affect this descending inhibition, arguing against involvement of endogenous opiates.

[Incomplete lead fracture as a cause of bradyarrhythmia in patients with artificial pacemakers (author's transl)]

The fracture of a permanent cardiac pacing lead may be complete or incomplete. In the first case, the function of the pacemaker system will completely cease. An incomplete fracture, however, is defined as a capillary interruption of the wire and will lead to a loose connexion between both parts of the electrode. This, in turn, may result in sudden changes of the electrical resistance of the lead and, therefore, in alterations of the electrode voltage during the second part of the biphasic current wave delivered by the pacemaker; this voltage change--in the 10-mV-range--will inhibit a blocking demand pacemaker with an intermittent, irregular increase of the pacemaker escape interval as the corresponding ECG finding. Usually, this "oversensing" phenomenon can be eliminated by turning the pacemaker function to the fixed rate mode with a test magnet applied. -- Although this malfunction is more often seen with bipolar pacemaker systems and with epicardial wires, it may also occur in a unipolar, transvenous system. -- Among 2100 patients, we have seen this malfunction in 6 cases in whom other, even more rare causes--such as a defect of the electronic circuit of the pulse generator, muscle potentials, etc.--could be ruled out. The x-ray findings revealed no evidence of a lead fracture in any case. The diagnosis was established on the ECG, the examination of the surgically removed electrode in 2 cases, and the finding, that only the implantation of a new lead abolished the malfunction, whereas the implantation of a new pacemaker alone ws ineffective.

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.

[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.

Radio diagnosis using 125I-fibrinogen and 203Hg-thymidine

A comparative study of 125I-fibrinogen and 203Hg-thymidine using 144 Ehrlich carcinoma-bearing mice, indicates that tumor affinity of carrier substances with covalent labeling could be better used for scintigraphic tumor diagnosis. Halogenated or possibly metallo-organic compounds offer an alternative to the metal complexes in general use up to now.

[Neurophysiological basis of pain and pain therapy (author's transl)]

Painful stimuli are encoded by specialized nociceptors. In the spinal cord the afferent nerves transmit them at the synapse to dorsal horn neurons, which are considered here as models for neuronal mechanisms in nociception. In particular, inhibitory effects of spinal and of supraspinal origin are shown to modulate the nociceptive messages ascending to the brain. These inhibitions are activated by various methods of electrostimulation (of the peripheral nerves, dorsal columns, electroacupuncture) that are used clinically for the management of pain.

[Distribution study using 57Co-, 51Cr-, 111In- and 99mTc-bleomycin in mice with a solid Ehrlich carcinoma]

From the comparative studies of 57Co-, 51Cr-, 111In- and 99mTc-Bleomycin using 282 solid Ehrlich-carcinoma-bearing mice, 57Co was found to be the most suitable bleomycin preparation for tumorscintigraphy. The results obtained by 111In-Bleomycin of linear tumor cell absorption indicates a possible use of 111In-Bleomycin as an agent for objective histological differentiation also in cells previously treated with therapeutic agents.

Verteilungsstudie mit 57Co-, 51Cr-, 111In- und 99mTc-Bleomycin in Mäusen mit einem soliden Ehrlich-Karzinom

Anhand der Verteilungsstudie von 57Co-, 51Cr-, 111In-und 99mTc-Bleomycin an 282 Mäusen mit einem soliden Ehrlich-Karzinom ist 57Co-Bleomycin am besten zur allgemeinen Tumorszintigraphie geeignet. Die Beobachtung über einen nahezu linearen 111In-Einbau in das Tumorgewebe (8—48 Std. post in-jektionem) stellt möglicherweise ein Hilfsmittel zur Objektivierung histologischer Differenzen und therapeutischer Maßnahmen im malignen Gewebe dar.

Dorsal root potentials produced by afferent volleys in cutaneous group 3 fibers

1. Dorsal root potentials (DRP) were recorded in the lumbosacral spinal cord of decerebrated unanaesthetized cats, following afferent volleys restricted to the thin myelinated (Group III) cutaneous afferents of the hind limb. The thick myelinated fibres (Group II) were blocked by a depolarizing current.2. A pure Group III volley produced a DRP of negative polarity, called the III-DRP, signalling a depolarization of the intraspinal terminals of afferent fibres. The longer latency of the III-DRP when compared to that of the DRP after a Group II volley was accounted for quantitatively by the lower conduction velocity of the Group III fibres.3. Special attention was given to the presence of III-DRPs having a predominantly positive polarity thus signalling a presynaptic hyperpolarization. Such ;positive III-DRPs' were, however, never observed in this investigation.4. Both after transection of the spinal cord at various levels and after administration of pentobarbitone the III-DRP persisted at normal polarity. The duration of the DRPs was increased by these experimental procedures.5. The implications of these findings are discussed in relation to the prominent role postulated for the Group III fibres in the context of the gate control theory of pain.

Characteristics of spinal neurones responding to cutaneous myelinated and unmyelinated fibres

1. Spike discharges were recorded from neurones in the lumbar spinal cord in cats anaesthetized by barbiturate.2. The neurones were examined systematically for various physiological parameters and for their location. Especially the neurones situated in the dorsal horn were classified for the following parameters: mono- or polysynaptic linkage to myelinated afferents; type of natural stimuli which excited the neurones; depth from the cord surface; number of impulses discharged upon a cutaneous A fibre stimulus; steady-state discharge in the absence of intentional stimulation.3. All neurones were also tested as to whether or not they responded to volleys in cutaneous C fibres. Of 111 units which were activated by the A fibres in nerves from the hairy skin, 57 (= 51%) responded to C volleys in those nerves too.4. By blocking conduction in the A fibres using polarizing currents it was shown that the responses to C fibre volleys were partially or totally suppressed by a preceding discharge of the neurone in response to an A volley. Using search stimuli which were suprathreshold for C fibres one cell out of 36 could be found which responded only to afferent volleys in C fibres.5. About half of all neurones were shown to be connected monosynaptically to cutaneous A fibres, as was judged from the synaptic delay. The other half were polysynaptically linked to the A fibres. Both mono- and polysynaptic neurones were found in all layers of the dorsal horn. About 15% of the cells had additional input from muscle Group II and/or III fibres via polysynaptic pathways.6. Subdividing the A and A+C responsive neurones according to their mono- (M) or polysynaptic (P) connexions yielded the following sub-samples: MC, 39%; PC, 15%; MA, 13%; PA, 33%. Most MC neurones had, and most PA units had not, a spontaneous discharge. About half of the PA cells could not be driven by natural skin stimulation. The majority of MC units responded specifically to movement of hairs.7. A model was proposed hypothesizing two pathways in the dorsal horn, one showing convergence of A and C fibres and the other not. Some relations concerning other observations on C fibre effects were discussed.

Presynaptic depolarization of myelinated afferent fibres evoked by stimulation of cutaneous C fibres

1. The origin of the dorsal root potential observed following a volley in cutaneous unmyelinated or C fibres (C-DRP) has been investigated by several assays.2. Measurements of the spatial decrement of the C-DRP along the dorsal roots indicate that mainly the thick myelinated primary afferent fibres contribute to this C-DRP.3. The spatial configuration of the intraspinal potential field during the course of the C-DRP is similar to that of the field correlated to the A-DRP, i.e. the DRP evoked by a volley in the A fibres of the same cutaneous nerve. It is concluded therefrom that both A- and C-DRPs signal presynaptic depolarizations of afferent fibres in the same regions of the dorsal horn.4. Intrafibre recordings reveal that C input produces primary afferent depolarization (C-PAD) mainly in cutaneous and articular afferents, but not in muscle Group Ia afferents.5. These findings and direct measurements of the interactions between A- and C-DRPs indicate that the pathways involved in A- and C-PAD exhibit convergence.6. C-DRPs were also recorded from contralateral rootlets.7. Some functional aspects of the PAD produced by an afferent volley in C fibres are discussed.