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T Bartsch

Publications and source records attributed to T Bartsch.

27 records · Page 2Linked to original sources
PubMed2000

Reflex patterns in preganglionic sympathetic neurons projecting to the superior cervical ganglion in the rat.

Reflex patterns in preganglionic neurons projecting in the cervical sympathetic trunk (CST) were analyzed in response to stimulation of various afferent systems. We focused on the question whether these preganglionic neurons can be classified into functionally distinct subpopulations. Reflex responses were elicited by stimulation of trigeminal and spinal nociceptive, thermoreceptive as well as baroreceptor and chemoreceptor afferents. Multi- and single fiber preparations were studied in baroreceptor intact and sino-aortically denervated animals. Spontaneous activity of 36 preganglionic single neurons ranged from 0.2 to 3.5 imp/s (median= 1.11 imp/s). The degree of cardiac rhythmicity (CR) in the activity of sympathetic neurons was 69.5+/-13% (mean+/-S.D.; N=52; range=39-95%). Noxious stimulation of acral skin activated the majority (67%) of sympathetic preparations by 37+/-25% (N=35) above pre-stimulus activity; 15% were inhibited. In these neurons the response to noxious stimulation of acral skin was significantly correlated with the degree of CR (P<0.001, N=52) in that neurons showing the strongest excitation to noxious stimulation displayed the strongest CR. Noxious mechanical stimulation of body trunk skin (N=60) inhibited the majority (80%) of fiber preparations tested (by 34+/-18% of pre-stimulus activity, N=48); an activation was not observed. Cold stimulation of acral (N=9) and body trunk skin (N=42) activated most fiber preparations. Trigeminal stimulation evoked a uniform reflex activation of preganglionic neurons (+79+/-73% of pre-stimulus activity, N=32). Chemoreceptor stimulation by systemic hypercapnia elicited inhibitory (-31+/-19%, N=8) as well as excitatory (+59+/-5%, N=4) responses. These results show that preganglionic sympathetic neurons projecting to target organs in the head exhibit distinct reflex patterns to stimulation of various afferent systems; however, a clear classification into different functional subgroups did not emerge. Furthermore, reflex patterns showed a segmental organization to noxious cutaneous stimulation of acral parts and body trunk reflecting a differential central integration of spinal afferent input. Compared with the cat the reflex organization of sympathetic neurons projecting to the head seems to be less differentiated in the anesthetized rat.

Action Potentials↗
PubMed2000

Influence of magnetic fields on electron-Ion recombination at very low energies

Radiative recombination (inverse photoionization) is believed to be well understood since the beginning of quantum mechanics. Still, modern experiments consistently reveal excess recombination rates at very low electron-ion center-of-mass energies. In a detailed study on recombination of F6+ and C6+ ions with magnetically guided electrons we explored the yet unexplained rate enhancement, its dependence on the magnetic field B, the electron density n(e), and the beam temperatures T( perpendicular) and T( ||). The excess scales as T(-1/2)( perpendicular) and, surprisingly, as T(-1/2)( ||), increases strongly with B, and is insensitive to n(e). This puts strong constraints on explanations of the enhancement.

Journal Article↗
PubMed1999

Hypoventilation recruits preganglionic sympathetic fibers with inspiration-related activity in the superior cervical trunk of the rat.

Activity in preganglionic sympathetic neurons projecting in the cervical sympathetic trunk (CST) of rats was analysed with respect to changes in the pattern of the respiratory modulation during a long lasting hypoventilation. Under normal acid-base status (pH: 7.36+/-0.04, pCO2: 42.1+/-6.1 mm Hg, pO2: 135.8+/-43 mm Hg) a maximum of activity during expiration (expiration-related activity) was observed in all nerve recordings (n = 27). No other pattern of respiratory modulation was observed under this condition. Under a hypoventilation a dissociation between the duration of phrenic nerve activity and that of the inspiratory inhibition in neurons with expiration-related activity was observed as the inhibition was significantly prolonged by 49+/-24.9% and outlasted inspiration in 5/7 multifibers. When acid-base status was systematically changed (pH: 7.15+/-0.05, pCO2: 80.4+/-11.8 mm Hg, pO2: 62.8+/-17.5 mm Hg [n = 7]) by a hypoventilation lasting for several hours activity with a maximum peak during central inspiration (inspiration-related activity) emerged and disappeared when control conditions were reestablished. Neurons with expiration-related activity showed a cardiac rhythmicity (CR) of 62.5+/-14.6% (n = 27) and were inhibited to baroreceptor stimulation whereas neurons with inspiration-related activity showed no discernible CR (23.1+/-5.1%; n = 7) and were not inhibited to baroreceptor stimulation. Furthermore, expiration-related neurons were inhibited by 32.5+/-18.3% (n = 27) during noxious cutaneous stimulation while neurons with inspiration-related activity were activated by 21.5+/-12.1% (n = 7). These findings suggest that the respiratory modulation of preganglionic sympathetic activity in the CST consists of expiration-related activity in normal acid-base status. During hypoventilation neurons with inspiration-related activity are recruited. These neurons show reflex patterns distinct from expiration-related neurons and probably constitute a subgroup of sympathetic neurons which is activated under increased respiratory drive.

Adrenergic Fibers↗
PubMed1999

Rhythmicity in single fiber postganglionic activity supplying the rat tail.

Rhythmicity in single fiber postganglionic activity supplying the rat tail. The temporal pattern of ongoing sympathetic vasoconstrictor activity may play an important role for neurovascular transmission. Here we analyzed the activity of postganglionic fibers projecting into the ventral collector nerve of anesthetized and artificially ventilated vagotomized Wistar rats with respect to the presence of rhythmic firing under normocapnic conditions. Most of the fibers studied were likely vasoconstrictor and involved in thermoregulation. Accumulated histograms of sympathetic activity were produced synchronized with the electrocardiogram to detect cardiac rhythmicity, with phrenic nerve activity to detect modulation with the central respiratory cycle, and with tracheal pressure to uncover a reflex modulation associated with artificial ventilation. Sympathetic activity, phrenic activity, and tracheal pressure also were examined by spectral analysis and autocorrelation to detect rhythmicities distinct from respiration. Twenty-seven filaments containing two to seven fibers with spontaneous activity and 51 single fibers were analyzed. Ongoing activity was 1.12 +/- 0.65 imp/s (mean +/- SD, n = 51); conduction velocity was 0.62 +/- 0.06 m/s (n = 30). Cardiac rhythmicity in sympathetic activity was weak (46.2 +/- 16.4%). The dominant rhythm in the activity of 19/27 few-fiber preparations and 37/51 single fibers corresponded to the central respiratory cycle. The pattern consisted of an inhibition during inspiration and an activation in expiration. In 10/19 few-fiber preparations and 21/37 single fibers of this group, there was also a concomitant, less prominent rhythm related to artificial ventilation. By contrast, 8/27 few-fiber preparations and 11/51 single fibers exhibited a dominant pump-related modulation, whereas phrenic-related rhythmicity was subordinate. The dominant rhythm in the activity of two single fibers was related to neither central respiration nor artificial ventilation. We conclude that the ongoing activity of most postganglionic neurons supplying the rat tail is modulated by the central respiratory rhythm generator, suggesting that changes in respiratory drive may alter perfusion of the tail and therefore heat dissipation. Reflex modulation in parallel with artificial ventilation, independent of vagal afferents and possibly due to ventilatory changes of baroreceptor activity, is also an important source of rhythmicity in these neurons.

Animals↗
PubMed1997

Responses of rat postganglionic sympathetic vasoconstrictor neurons following blockade of nitric oxide synthesis in vivo.

The hypothesis was tested that the activation of postganglionic sympathetic neurons contributes to the peripheral vasoconstriction and the blood pressure increase which are observed in rats after systemic blockade of nitric oxide synthase by substituted L-arginine analogues. Single and multifiber postganglionic sympathetic activity supplying hindlimb hairy skin and the activity in the caudal lumbar sympathetic trunk supplying mainly hindlimb skeletal muscle were recorded in anaesthetized, paralysed and artificially ventilated Wistar rats before, during and up to 1 h after intravenous injection of a supramaximal dose (10 or 35 mg/kg) of N(G)-nitro-L-arginine methyl ester. This elicited a sustained rise of arterial blood pressure, a long-lasting decrease in heart rate and vasoconstriction in hindlimb skin and skeletal muscle as measured by laser Doppler flowmetry. With intact buffer nerves all sympathetic neurons analysed responded with a decrease in their ongoing activity in parallel with the vasoconstriction and the increased blood pressure, except for one neuron which was unresponsive. These responses were probably mediated by the arterial baroreceptors. since it was shown that N(G)-nitro-L-arginine methyl ester did not impair the function of both the afferent and the efferent limb of the reflex. Furthermore, baroreceptor denervation almost abolished the inhibitory responses in sympathetic neurons. In baroreceptor denervated animals, with a latency of about 15 min after N(G)-nitro-L-arginine methyl ester there was an increase in sympathetic activity without a further increase in blood pressure. It was concluded that sympathetic vasoconstrictor neurons which supply the rat hindlimb do not contribute by neurogenic means to the vasoconstriction and the blood pressure increase occurring after blockade of the nitric oxide synthase. Instead, the results suggest that sympathetic vasoconstrictor neurons, via the baroreceptor loop, counteract the vasoconstriction caused by the blockade of endothelium-derived nitric oxide. Therefore nitric oxide does not seem to play a role in the central regulation of activity in the sympathetic vasoconstrictor pathways studied here. The long latency increase in sympathetic activity observed after N(G)-nitro-L-arginine methyl ester in baroreceptor-denervated animals may be due to an impairment of blood flow in the brainstem.

Animals↗
PubMed1996

Two distinct mechanisms generate the respiratory modulation in fibre activity of the rat cervical sympathetic trunk.

Preganglionic multifibre activity was recorded in the cervical sympathetic trunk of vagotomized Wistar rats and analysed for its respiratory modulation. The aim of the study was to investigate whether both a central and a reflex component of respiratory modulation are observed in sympathetic activity of rats as was previously demonstrated in cats. For this purpose, sympathetic activity was summed over several hundred cycles (i) with respect to phrenic nerve discharge as an indicator for central respiration and (ii) with respect to tracheal pressure as an indicator for artificial ventilation. As a consequence of vagotomy both cycles were desynchronized. Sympathetic activity which was analysed exhibited a central respiratory modulation with a minimum during inspiration and a broad peak during expiration. Additionally, in the activity of 44/49 filaments a ventilation-related modulation was seen in parallel with the falling phase of the blood pressure waves accompanying artificial ventilation. The analysis of the latter rhythm during central apnoea and after complete sino-aortic denervation proved its reflex origin and its independence of the central respiratory modulation. We conclude that in rats respiratory modulation of sympathetic activity is caused by two distinct mechanisms, one being of central and one being of reflex, probably baroreceptor, origin.

Adrenergic Fibers↗
PubMed1996

p53-dependent cell cycle arrest induced by N-acetyl-L-leucinyl-L-leucinyl-L-norleucinal in platelet-derived growth factor-stimulated human fibroblasts.

Proteases are known to play important roles in cell growth control, although the underlying mechanisms are still poorly understood. Here we show that the protease inhibitor N-acetyl-L-leucinyl-L-leucinyl-L-norleucinal induced cell cycle arrest in platelet-derived growth factor-stimulated human fibroblasts at the G1/S boundary of the cell cycle by inhibiting the proteasome. Inhibition of the proteasome resulted in accumulation of the tumor suppressor p53, which was followed by an increase in the amount of the cyclin-dependent kinase-inhibitor p21. As a consequence, both phosphorylation and activity of the cyclin-dependent kinase 2/cyclin E complex were inhibited. We further observed that the retinoblastoma gene product, pRb, remained in the hypophosphorylated state, thus preventing cells from progression into the S-phase. These studies strongly support the hypothesis that the proteasome is a key regulator in the G1-phase of cell cycle progression.

Calpain↗
PubMed1996

Functional properties of postganglionic sympathetic neurones supplying the submandibular gland in the anaesthetized rat.

Sympathetic neurones supplying the submandibular salivary gland innervate blood vessels, secretory and myoepithelial cells. Here we examined whether these functionally different sympathetic neurones show distinct reflex response patterns. In anaesthetized rats, single unit activity was recorded from postganglionic axons projecting to the gland. Neurones were tested for their responses to stimulation of baroreceptors, cutaneous nociceptors and cold receptors and to gustatory stimuli applied to the tongue. Respiratory modulation was also analysed. Only a few postganglionic neurones identified electrically (5-10%) were spontaneously active. They were excited by noxious and cold stimuli, inhibited by baroreceptor stimulation and exhibited respiratory modulation. None of the units responded to gustatory stimuli. Thus, in anaesthetized rats spontaneously active sympathetic neurones supplying the submandibular gland behave like vasoconstrictor neurones. Sympathetic neurones with other functions are probably silent.

Anesthesia, General↗