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C Vahle-Hinz

Publications and source records attributed to C Vahle-Hinz.

16 recordsLinked to original sources
PubMed2007

Corresponding minimum alveolar concentrations of isoflurane and isoflurane/nitrous oxide have divergent effects on thalamic nociceptive signalling.

BACKGROUND: Suppression of nociceptive signalling in the thalamus is considered to contribute significantly to the anaesthetic state. Assuming additivity of anaesthetic mixtures, our study assessed the effects of corresponding minimum alveolar concentrations (MACs) of isoflurane and isoflurane/nitrous oxide on thalamic nociceptive signalling. METHODS: Nociceptive response activity (elicited by controlled radiant heat stimuli applied to cutaneous receptive fields) of single thalamic neurons was compared in rats anaesthetized at approximately 1.1 and approximately 1.4 MAC isoflurane with that at approximately 1.1 and approximately 1.4 MAC isoflurane/nitrous oxide. RESULTS: Under baseline anaesthesia ( approximately 0.9 MAC isoflurane), noxious stimulation elicited excitatory responses in all neurons (n = 19). These responses were uniformly suppressed at approximately 1.1 and approximately 1.4 MAC isoflurane. In contrast, at approximately 1.1 and approximately 1.4 MAC isoflurane/nitrous oxide, excitatory responses no different to baseline were still present in 64 and 37% of the neurons, respectively. CONCLUSIONS: These data demonstrate a pronounced nitrous oxide-induced response variability. It appears that, with respect to thalamic transfer of nociceptive information, the interaction of isoflurane and nitrous oxide may not be compatible with the concept of additivity and that the antinociceptive potency of nitrous oxide is considerably less than previously reported.

Anesthetics, Combined↗
PubMed2002

Differential effects of isoflurane on excitatory and inhibitory synaptic inputs to thalamic neurones in vivo.

BACKGROUND: Mechanosensory thalamocortical relay neurones (TCNs) receive glutamatergic excitatory input and are subjected to gamma-aminobutyric acid (GABA)Aergic inhibitory input. This study assessed the effects of an increase in concentration of isoflurane on thalamic excitatory and inhibitory mechanisms. METHODS: TCNs (n = 15) of the thalamic ventral posteromedial nucleus responding to mechanical stimulation of whiskers were investigated in rats anaesthetized with end-tidal concentrations of isoflurane of approximately 0.9% (ISOlow, baseline) and approximately 1.9% (ISOhigh). Response activity induced by controlled vibratory movement of single whiskers was recorded before, during and after iontophoretic administration of the GABAA receptor antagonist bicuculline to the vicinity of the recorded neurone. RESULTS: The increase in concentration of isoflurane induced a suppression of vibratory responses to 14 (4)% [mean (SEM)] of baseline activity. Blockade of GABAA receptors by bicuculline during ISOlow and ISOhigh caused increases in response activity to 259 (32)% and 116 (25)% of baseline activity, respectively. The increase in isoflurane concentration enhanced overall inhibitory inputs by 102 (38)%, whilst overall excitatory inputs were reduced by 54 (7)%. CONCLUSIONS: These data suggest that doubling the concentration of isoflurane doubles the strength of GABAAergic inhibition and decreases the excitatory drive of TCNs by approximately 50%. The isoflurane-induced enhancement of GABAAergic inhibition led to a blockade of thalamocortical information transfer which was not accomplished by the effects of isoflurane on glutamatergic synaptic transmission alone. Thus, it appears that, with respect to transmission of information in the thalamus, the most prominent action of isoflurane is an enhancement of GABAAergic synpatic inhibition, and that effects on glutamatergic neurotransmission may contribute to a lesser extent.

Anesthetics, Inhalation↗
PubMed2001

Local GABA(A) receptor blockade reverses isoflurane's suppressive effects on thalamic neurons in vivo.

Many in vitro effects of volatile anesthetics are known, but the mechanisms of action are still under debate. Because suppression of sensory perception is one of the major goals of general anesthesia, we studied the effects of isoflurane on the processing of somatosensory information in anesthetized rats. Local iontophoretic administration of the gamma-aminobutyric acid-A (GABA(A)) receptor antagonist bicuculline in the thalamic ventral posteromedial nucleus reversed suppressive effects of isoflurane on thalamocortical relay neurons (TCNs). The action potential discharges of TCNs (n = 23) in response to defined mechanical stimulation of receptive fields seen with small concentrations of isoflurane (0.79% +/- 0.01%, mean +/- SEM) were suppressed under large concentrations (1.44% +/- 0.04%). In addition, the tonic response pattern was lost, which initially encoded the information about the stimulus features. In 70% of TCNs, bicuculline administration reestablished the initially present tonic response pattern under large isoflurane concentrations. These results indicate that isoflurane suppresses somatosensory information transfer at the thalamic level in vivo, apparently by enhancing thalamic GABA(A) receptor-mediated inhibition.

Anesthetics, Inhalation↗
PubMed1999

Responses of neurons in the lateral thalamus of the cat to stimulation of urinary bladder, colon, esophagus, and skin.

In seven female alpha-chloralose-anesthetized cats, 52 lateral thalamic neurons were tested with noxious distension of the urinary bladder, the distal colon and the lower esophagus. In addition, the neurons were characterized with innocuous and noxious mechanical stimulation of the skin and deep structures. Of the 52 neurons tested, 32 (62%) were visceroceptive. Of these visceroceptive neurons, 20 (63%) were located in the periphery of the ventral posterolateral nucleus (VPLp), 10 (31%) in the adjacent posterior complex (PO), and two (6%) in the ventrolateral nucleus (VL). No differences were found with respect to location between neurons responsive or unresponsive to visceral stimulation. Ten neurons (31%) received input from more than one viscus and, therefore, showed viscerovisceral convergence. Excitatory or "inhibitory" responses were elicited by stimulation of the esophagus in 21 neurons, of the colon in 13, and of the urinary bladder in 11 neurons. No indications were found for a segregation of neurons responsive to a certain viscus and their location in VPLp or PO. Of 51 neurons, for which a somatic receptive field was determined, 44 (86%) exhibited low threshold type (LT), and seven (14%) wide dynamic range type (WDR) responses. The data indicate that there might exist a somatovisceral coregistration, because many neurons (69%) had homosegmental receptive fields, and bladder stimulation was the most successful stimulus. It is concluded that VPLp and the adjacent PO in the cat play a role in the perception and localization of painful events originating from thoracic and pelvic organs.

Animals↗
PubMed1999

Isoflurane induces dose-dependent changes of thalamic somatosensory information transfer.

In spite of several reports about suppressive effects of volatile anesthetics on somatosensation, their neuronal mechanisms are largely unknown. The present study investigates somatosensory impulse transmission at the thalamic level in rats under varied concentrations of isoflurane by recordings of neuronal responses to mechanical stimulation of the body surface. Single-unit recordings of thalamo-cortical relay neurons (TCNs, third order neurons; n=28) and presumed trigemino-thalamic fibers (TTFs, second order neurons; n=7) were performed in the ventral posteromedial nucleus. Functional response characteristics were quantified following defined tactile stimulation (trapezoidal or vibratory deflection of sinus hairs or fur) applied to the neuronal receptive fields. End-tidal isoflurane concentration was increased in steps of 0.2% between 0.6% (baseline) and 2.0%. The response activity in all TCNs studied was suppressed in a dose-dependent manner (2.0% isoflurane decreased responses to 3. 5+/-1.1% of baseline; mean+/-S.E.M.); the response activity in TTFs was much less affected (decrease to 55.0+/-8.2%). Suppression of ongoing activity, however, was similar for both, TCNs and TTFs. Furthermore, in TCNs, the response characteristics changed with increasing isoflurane between 1.0% and 1.8%: tonic and sustained responses were converted to phasic on-responses. In contrast, the tonic and sustained response characteristics of TTFs were preserved even at higher isoflurane concentrations. The results indicate that isoflurane attenuates the output of somatosensory signals in the specific nucleus of the rat's thalamus, while its input is only marginally affected. The observed changes of thalamic neuronal response characteristics, at least in part, may cause the loss in sensory discrimination observed during general anesthesia.

Anesthetics, Inhalation↗
PubMed1997

Projections from the renal nerve to the cat's lateral somatosensory thalamus.

The representation of the kidney in the lateral somatosensory thalamus was mapped using electrical stimulation of the renal nerve in pentobarbitone-anesthetized cats. Ninety-five of 197 thalamic neurons studied responded to renal nerve stimulation. The responsive neurons were located in the periphery of the ventral posterolateral nucleus (42%; VPLp) and the neighboring dorsal and lateral aspects of the posterior complex (58%; POd and POl). No visceroceptive neurons were found within VPL proper. The mean response latency of the thalamic neurons to electrical nerve stimulation was 9.5 +/- 2.6 ms (mean +/- S.D.), suggesting an involvement of A delta, and possibly A beta fibers in the primary afferent pathway. The visceroceptive neurons were further characterized with innocuous mechanical stimulation of the body surface, and for 94 of the 95 neurons a somatic receptive field could be determined. Of these, 35% were located on the lower back and belly, i.e., the dermatomes of the lower thoracic and upper lumbar spinal projection areas of the renal nerve. 52% of the somatic receptive fields were located on the contralateral foot, thigh, tail, or hind leg (lower lumbar, sacral and coccygeal dermatomes) and 13% covered the arm and upper body (upper thoracic and lower cervical dermatomes). Comparison between the thalamic representations of the renal and pelvic nerves showed that both covered comparable areas adjacent and around, but not within VPL proper. It is concluded that VPLp, POd and POl play a role in processing visceral, possibly including nociceptive, information from the kidney of the cat.

Animals↗
PubMed1994

Amino acids modify thalamo-cortical response transformation expressed by neurons of the ventrobasal complex.

The hypothesis has been tested that inhibitory mechanisms, active spatially and temporally between the input and the output of thalamic neurons, determine the nature of the information transmitted to the cerebral cortex. To enable this assessment, in barbiturate-anesthetized cats and urethane-anesthetized rats juxtacellular recordings were performed together with microiontophoretic ejection of transmitter agonists and antagonists. The effects of these drugs were studied on responses evoked by mechanical stimulation of cutaneous receptive fields (RFs) of neurons in the thalamic ventrobasal complex (VB). Neurons from different parts of the VB were investigated: 29 units were located medially, in the ventral posteromedial nucleus (VPM; facial RFs), and 11 units were located laterally, in the ventral posterolateral nucleus (VPL; forepaw and body RFs). A further eleven VB units had no detectable RF. Twenty-six neurons were tested with electrical stimulation of the somatosensory cortex (SI), 17 of these being identified as thalamo-cortical relay neurons and 5 being classified as presumed interneurons; the remaining 4 could not be activated. Four additional recordings were from trigemino-thalamic or thalamo-cortical fibers. For the quantitative assessment of the neurons' input and output, neuronal activity was induced by feedback-controlled, mechanical trapezoidal and/or sinusoidal stimuli applied to sinus hairs, fur or skin and the numbers of prepotentials and soma spikes were compared in peristimulus time histograms (PSTHs) generated simultaneously for both types of signal from 'DC' recordings. Iontophoretic administration of excitatory amino acids (EAAs) or bicuculline methiodide (BMI) increased output-input ratios in 87% of the cases tested, due to a higher rate of conversion of prepotentials into soma spikes taking place. In cases of neurons exhibiting a sustained-to-transient response pattern, changes to sustained-to-sustained patterns were demonstrated. Tests with gamma-aminobutyric acid (GABA) produced decreased output-input ratios in 90% of the neurons, due to a lower conversion rate of prepotentials into soma spikes taking place. In cases of neurons exhibiting high output-input ratios (sustained-to-sustained type), the responses changed to the sustained-to-transient pattern. For cortically evoked antidromic spikes of VB neurons, GABA produced a failure of the initial segment (IS-) spike to invade the soma, whereas BMI and glutamate (Glu) facilitated soma depolarization. When ejected with relatively higher currents than those needed to alter output-input ratios, EAAs decreased prepotential amplitudes while GABA produced increases in 16 of 18 neurons.(ABSTRACT TRUNCATED AT 400 WORDS)

Amino Acids↗
PubMed1994

Projections from the pelvic nerve to the periphery of the cat's thalamic ventral posterolateral nucleus and adjacent regions of the posterior complex.

1. Mapping experiments were performed in the region of the ventral posterolateral nucleus of the lateral thalamus in pentobarbitone-anesthetized cats with the aim to locate foci with input from the electrically stimulated pelvic nerve. The locations of the recording sites were verified in Nissl-stained histological sections with reference to electrolytic lesions. 2. Of the 68 visceroceptive thalamic neurons identified, 63% were located in the periphery of the ventral posterolateral nucleus (VPLp) and 34% in the dorsal, lateral, and medial aspects of the posterior complex (POd, POl, and POm, respectively) directly adjacent to VPLp. The region surrounding the middle and caudal part of the ventral posterolateral nucleus (VPL) received a much denser input from the pelvic nerve than that around the rostral pole of VPL. 3. The response latencies of the thalamic neurons to pelvic nerve stimulation ranged from 10 to 65 ms (median: 16 ms; interquartile distance: 12-20 ms) indicating a transmission of information from the pelvic space via small and large diameter myelinated fibers. 4. Seventy-nine percent of the visceroceptive neurons tested (n = 58), in addition, had low threshold somatic receptive fields that were located in 67% of the cases in regions of the lower back, the thigh, the tail and/or the heel and in 26% of the cases on the hindfoot. None of the 40 visceroceptive neurons tested with noxious mechanical stimulation of the skin responded to this kind of stimulus.(ABSTRACT TRUNCATED AT 250 WORDS)

Afferent Pathways↗
PubMed1993

Representation of the urinary bladder in the lateral thalamus of the cat.

1. In alpha-chloralose-anesthetized cats the region surrounding the ventral posterolateral nucleus (VPL) of the thalamus was investigated to locate foci with input from the urinary bladder stimulated by application of intravesical pressure. The locations of the recording sites were verified in Nissl-stained histological sections with reference to electrolytic lesions. 2. Of the 23 visceroceptive thalamic neurons identified, 4 (17%) were located in the periphery of the VPL (VPLp) and 19 (83%) in the lateral and dorsal aspects of the posterior complex (POl and POd, respectively) adjoining VPLp. 3. The neurons responded to noxious intensities of intravesical pressure in the range of 50-100 mmHg. Excitatory responses were elicited in 8 (35%) neurons, "inhibitory" responses in 13 (57%) neurons, and 2 (9%) neurons responded with an increase and a decrease of their discharge to subsequent stimuli. 4. Of the 22 visceroceptive thalamic neurons tested for this parameter, 73% had low-threshold cutaneous receptive fields (RFs). These were located in the region of the lower back, the hip, the thigh, and the proximal tail (12 PO neurons), or covered the entire postcranial contralateral part of the body (3 PO neurons). For only one of the VPLp neurons, a somatic RF was found and this was located on the distal tail. The neurons responded to tap stimuli applied at a low repetition rate. None of the 11 neurons tested with noxious pinching of the skin was activated by this kind of stimulus. 5. It is concluded that the cat's lateral thalamic region, around but not within VPL proper, contains neurons that play a role in the processing of information about noxious events in the urinary bladder. A comparison with results from experiments in the monkey indicates differences in the organization of the visceroceptive systems between both species, regarding the thalamic localization of visceroceptive neurons, the occurrence of convergent low-threshold somatic RFs, and the association of excitatory and inhibitory effects of urinary bladder stimulation with the location of somatic RFs.

Afferent Pathways↗
PubMed1988

A combined recording and microiontophoresis technique for input-output analysis of single neurons in the mammalian CNS.

A method is described for producing electrolytically sharpened and lacquer-insulated steel microelectrodes and for their attachment to a multibarrel micropipet assembly by light-curing bonding compound. This electrode complex is specially designed for recordings from deep brain structures. It permits the analysis of the input signals to and the output signals from a single neuron recorded simultaneously from an extracellular electrode position, termed juxtacellular recording. Furthermore it provides the ability to manipulate pharmacologically the input-output ratio expressed by the neuron under varying sequences of natural stimulation.

Action Potentials↗
PubMed1986

Electrical stimulation reveals relatively ineffective sural nerve projections to dorsal horn neurons in the cat.

Electrical stimulation of the sural nerve (SN) revealed input from sural nerve afferents to L6 and L7 dorsal horn neurons that were not apparent using natural mechanical stimuli, especially in cells with variable latency responses to SN stimulation. Nearly all (31/32) cells that had reliable, fixed latency responses to SN stimulation also had an excitatory receptive field (RF) in the region of skin innervated by the sural nerve (SN region). About one-third (20/57) of the cells with variable latency responses to SN stimulation, however, had an RF outside the SN region. Most (130/146) cells with no response to SN stimulation had RFs outside the SN region. There were no obvious differences between variable latency cells with RFs in the SN region vs those with RFs outside it in latency of response to SN stimulation, recording depth, RF sizes or modality properties. In a subsample of 31 postsynaptic dorsal column neurons all cells responding to SN stimulation also had an RF in the SN region. Strengthening of relatively ineffective projections from the sural nerve by lesions might be expected to lead to an increase in the proportion of cells responding with impulses to natural stimulation of the skin innervated by the sural nerve, and, hence, to an increase in average RF size.

Animals↗
PubMed1985

The structure of the terminal arborizations of physiologically identified retinal ganglion cell Y axons in the kitten.

Retinal ganglion cell (r.g.c.) axons (n = 17) in the optic tract of 4-5 week-old kittens and adult cats (n = 4, this study, n = 27 from other reports) were studied both physiologically and morphologically. Axons were initially classified during extracellular recording with a battery of physiological tests that included Fourier analysis of the response to a sinusoidally counterphased sine-wave grating. Y axons had a significant second harmonic response component (greater than twice the fundamental) present independent of the spatial phase position of the grating. These axons were then recorded from intracellularly and subsequently filled ionophoretically with horseradish peroxidase (HRP). The HRP filled the axons' terminal arborizations in the dorsal lateral geniculate nucleus (l.g.n.). The innervation pattern and and structure of the terminal arborizations of the kitten r.g.c. Y axons were compared to those of the adult. The kitten Y axons innervated the l.g.n. in a pattern similar to that of the adult (individual branches from a single axon always innervated lamina A or A1 and may also have innervated lamina C, the medial interlaminar nucleus (m.i.n.) and/or sent branches that coursed medial to the l.g.n.). Fourteen of seventeen of these Y axons in the kitten innervated either of the A-laminae heavily (greater than 200 terminal boutons per axon). The remaining three r.g.c. Y axons in the kitten had only small arborizations within lamina A (less than fifty terminal boutons per axon) but heavily innervated lamina C. The structure of the terminal boutons on the kitten r.g.c. Y axons was highly variable when compared to axons of adult cats. Some of the boutons were spherical or crenulated as in the adult. Many others had filopodia and growth cone-like terminals with fine extensions. This variable maturation of terminal boutons was seen both between axons and on individual axons. The number of boutons on the kitten r.g.c. Y axons in the A-laminae was significantly less than that of adult Y axons. The mean numbers of boutons per axon were 476 and 1553 in the kittens and adult cats, respectively (P less than 0.001, Mann-Whitney U test). The width of the terminal arborization of individual Y axons in the A-laminae of the kittens was considerably smaller than in adult cats (mean widths of the terminal arborizations are 192 and 293 micron in the kittens and adult cats, respectively).(ABSTRACT TRUNCATED AT 400 WORDS)

Action Potentials↗
PubMed1982

Evidence against transmitter function of met-enkephalin and chemosynaptic impulse generation in "Merkel cell" mechanoreceptors.

Using the mechanoreceptors in the cat's sinus hair follicles as a model system the recent hypothesis (Hartschuh and Weihe 1980) was tested that Merkel cells are mechanoreceptive sensory cells releasing met-enkephalin as a neurotransmitter to initiate action potentials in the terminals of type I afferent fibres. Since the met-enkephalin antagonist naloxone, even in high doses, did not affect responses in any type I mechanosensitive afferent it is unlikely that a synaptic mechanism with the release of met-enkephalin underlies impulse generation in Merkel cell-axon complexes, nor did naloxone influence the responses from other types of mechanoreceptors.

Afferent Pathways↗
PubMed1981

Merkel cell receptors: structure and transducer function.

An electron microscopic and electrophysiological investigation was made of Merkel cell-neurite complexes in the sinus hair follicles of the cat. These mechanoreceptors respond with very precise phase locking to heavy-frequency vibratory stimuli as well as to static hair displacements. The mechanoelectric transduction process is faster than that known for any other somatic mechanoreceptor. These data show that the nerve endings themselves and not the Merkel cells are the mechanoelectric transducer elements in these receptors.

Action Potentials↗