Phrenic nerve afferents elicited cord dorsum potential in the cat cervical spinal cord

Background  

The diaphragm has sensory innervation from mechanoreceptors with myelinated axons entering the spinal cord via the phrenic nerve that project to the thalamus and somatosensory cortex. It was hypothesized that phrenic nerve afferent (PnA) projection to the central nervous system is via the spinal dorsal column pathway.     

Interactions of human cord dorsum potential.

The slow positive wave (P2 wave) of the evoked spinal electrogram was recorded from the posterior epidural space in wakeful man, and studied by applying several modes of peripheral nerve stimulation. With graded stimulation the P2 wave amplitude rapidly reached the maximum at weaker stimulation than that required for the initially positive spikes (P1) and the preceding negative (N1) wave. The "second" component of the P2 appeared during stronger stimulation or during excitemenpt of the subjects. With prolonged repetitive stimulation the P2 wave increased its duration with several summits on the decaying phase. Two interactions were observed between the P2 waves produced by conditioning and testing stimulations in the same or different nerves: inhibition or occlusion by strong stimulation and faciliation by weak stimulation. Thus, the characteristic of the P2 wave in man was similar in part to that of the positive wave observed in decerebrate animals, and differnt in other ways presumably due to influences from supraspinal structures or species differences.     

Anatomical specificity of regenerated muscle sensory afferents in the spinal cord of the bullfrog

The specificity of central projections made by regenerated muscle sensory fibers in the brachial spinal cord was studied with anatomical tracing methods. Sensory fibers were interrupted by freezing dorsal roots in postmetamorphic bullfrogs. After several months, regenerated sensory fibers were labeled with horseradish peroxidase applied to the triceps brachii muscle nerve, and their arborizations within the spinal cord were reconstructed from serial cross sections. Most of the regenerated projections from triceps muscle sensory afferents ended in or near their normal terminal field. A few branched and appeared to terminate more dorsally than normal, however, sometimes within the region where cutaneous afferents normally terminate. In contrast to the normal pathway followed by muscle afferents within the spinal cord, many regenerated afferents grew along the circumference of the spinal cord, just under the pial surface, and then turned abruptly toward the midline and into their appropriate terminal region. This suggests that regenerating afferents may actively seek out their appropriate targets and are not simply passively guided to them.     

Modulation of upper airway muscle activities by bronchopulmonary afferents.

Here we review the influence of bronchopulmonary receptors (slowly and rapidly adapting pulmonary stretch receptors, and pulmonary/bronchial C-fiber receptors) on respiratory-related motor output to upper airway muscles acting on the larynx, tongue, and hyoid arch. Review of the literature shows that all muscles in all three regions are profoundly inhibited by lung inflation, which excites slowly adapting pulmonary stretch receptors. This widespread coactivation includes the recruitment of muscles that have opposing mechanical actions, suggesting that the stiffness of upper airway muscles is highly regulated. A profound lack of information on the modulation of upper airway muscles by rapidly adapting receptors and bronchopulmonary C-fiber receptors prohibits formulation of a conclusive opinion as to their actions and underscores an urgent need for new studies in this area. The preponderance of the data support the view that discharge arising in slowly adapting pulmonary stretch receptors plays an important role in the initiation of the widespread and highly coordinated recruitment of laryngeal, tongue, and hyoid muscles during airway obstruction.     

Comment: unresolved questions concerning muscle afferents

Some current questions regarding muscle afferent receptors are discussed. These include the significance of variable distribution patterns of muscle spindles in different muscles and of differences in intrinsic spindle morphology. The significance of the very large and variable population of small myelinated afferent fibres in muscle is also discussed.     

Conformational difference between diastereomers of Dnp-Val-Aib-Gly-Leu-pNA studied by x-ray crystal analyses

In order to investigate the Conformational change of the α-aminoisobutyric acid (Aib) containing peptide by the D /L replacement of an amino acid residue, single crystals of two diastereomers, Dnp-L -Val-Aib-Gly-L -Leu-pNA (L -L isomer) and Dnp-D -Val-Aib-Gly-L -Leu-pNA (D -L isomer), were prepared from aqueous methanol solutions as CH₃OH and CH₃OH · H₂O solvates, respectively, and were analyzed by the x-ray diffraction method. Molecular conformation of L -L isomer adopts consecutive two different types of β-turns, a type II′ β-turn bent at Aib-Gly, and a type III β-turn bent at Gly-Leu, stabilized by two intramolecular (Leu) NH …? O?C (Val) and (pNA) NH …? O?C(Aib) hydrogen bonds. In contrast, these two intramolecular hydrogen bonds lead the D -L isomer to a distorted 3₁₀-helix conformation consisting of consecutive two type-III β-turn of Aib-Gly-Leu sequence. The most significant structural difference between these diastereomers is the mutual orientation between the Dnp and pNA chromophores. While the extensive stacking of both the chromophores is intramolecularly formed for the folded conformation of L -L isomer, they are oriented toward an opposite direction in the open conformation of D -L isomer and are intermolecularly stacked with each other. The large separation between these diastereomers observed in the chromatography is discussed in the relation with their Conformational differences. © 1993 John Wiley & Sons, Inc.     

Sympathetic action in skeletal muscle studied by recording mitogenetic radiation

The reaction of sarcoplasmic molecular organization on the irritation of the sympathetic system was studied in tired frog muscles. The molecular changes have been determined by registration of mitogenic irradiation. The intensive irradiation recorded at the phase of highest sympathetic effect indicated the reinforcement of the regulation process it is suggested that structural and energetic substrate changes associated with irradiation are directly involved in the modulating influences of the sympathetic system.     

Peculiarities of the synaptic adaptation of the intermediate neurons of the thoracic segments of the spinal cord by cutaneous,muscle, and visceral afferents

The responses of the interneurons of the thoracic segments of the spinal cord to stimulation of the intercostal and splanchnic nerves were studied on decerebrated and narcotized cats. It was established that the neurons of different layers of the gray matter (according to Rexed) differ substantially in type of afferent inputs. Cells in laminae I–III and IV are activated chiefly by somatic afferents: primarily high-threshold in laminae I–III and low-threshold in lamina IV. The neurons of lamina V and most of the neurons of laminae VII and VIII respond to stimulation of high-threshold somatic afferents (cutaneous fibers of the A group and muscle afferents of groups II and III), as well as visceral afferents of group A, conducting impulses at a rate of 9–35 m/sec. Cells of laminae VII and VIII, monosynaptically activated by muscle afferents of group I, do not respond to stimulation of the visceral afferents. The peculiarities of the "functional" laminar organization of the thoracic segments of the spinal cord are discussed.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 2, No. 6, pp. 563–572, November–December, 1970.     

Activation of thin-fiber muscle afferents by a P2X agonist in cats.

The responses of group III and IV triceps surae muscle afferents to intra-arterial injection of alpha,beta-methylene ATP (50 microg/kg) was examined in decerebrate cats. We found that this P2X(3) agonist stimulated only three of 18 group III afferents but 7 of 9 group IV afferents (P < 0.004). The three group III afferents stimulated by alpha,beta-methylene ATP conducted impulses below 4 m/s. Pyridoxal phosphate-6-azophenyl-2',4'-disulfonic acid, a P2-receptor antagonist, prevented the stimulation of these afferents by alpha,beta-methylene ATP. We conclude that P2X(3) agonists stimulate only the slowest conducting group III muscle afferents as well as group IV afferents.     

NO formation in nucleus tractus solitarii attenuates pressor response evoked by skeletal muscle afferents

We have previously shown that static muscle contraction induces the expression of c-Fos protein in neurons of the nucleus tractus solitarii (NTS) and that some of these cells were codistributed with neuronal NADPH-diaphorase [nitric oxide (NO) synthase]-positive fibers. In the present study, we sought to determine the role of NO in the NTS in mediating the cardiovascular responses elicited by skeletal muscle afferent fibers. Static contraction of the triceps surae muscle was induced by electrical stimulation of the L7 and S1 ventral roots in anesthetized cats. Muscle contraction during microdialysis of artificial extracellular fluid increased mean arterial pressure (MAP) and heart rate (HR) 51 +/- 9 mmHg and 18 +/- 3 beats/min, respectively. Microdialysis of L-arginine (10 mM) into the NTS to locally increase NO formation attenuated the increases in MAP (30 +/- 7 mmHg, P < 0.05) and HR (14 +/- 2 beats/min, P > 0.05) during contraction. Microdialysis of D-arginine (10 mM) did not alter the cardiovascular responses evoked by muscle contraction. Microdialysis of N(G)-nitro-L-arginine methyl ester (2 mM) during contraction attenuated the effects of L-arginine on the reflex cardiovascular responses. These findings demonstrate that an increase in NO formation in the NTS attenuates the pressor response to static muscle contraction, indicating that the NO system plays a role in mediating the cardiovascular responses to static muscle contraction in the NTS.     

The action potential in the smooth muscle of the guinea pig taenia coli and ureter studied by the double sucrose-gap method

The configuration of the electrotonic potential and the action potential observed by the double sucrose-gap method was similar to that observed with a microelectrode inserted into a cell in the center pool between the gaps. In the taenia and the ureter, the evoked spike was larger in low Na or in Na-free (sucrose substitute) solution than in normal solution. However, the plateau component in the ureter was suppressed in the absence of Na. In Ca-free solution containing Mg (3–5 mM) and Na (137 mM), the membrane potential and membrane resistance were normal, but no spike could be elicited in both the taenia and ureter. Replacement of Ca with Sr did not affect the spike in the taenia, nor the spike component of the ureter but prolonged the plateau component. The prolonged plateau disappeared on removal of Na, while repetitive spikes could still be evoked. It was concluded that the spike activity in the taenia and in the ureter of the guinea pig is due to Ca entry, that the plateau component in the ureter is due to an increase in the Na conductance of the membrane, and that both mechanisms, for the spike and for the plateau, are separately controlled by Ca bound in the membrane.     

The state of water in muscle as studied by pulsed NMR

Spin-lattice relaxation times for the water protons in rat gastronemius muscle are reported over the temperature range +37 to −70°C at six resonance frequencies ranging from 4.5 to 60.0 MHz. From −8 to −70°C, the bulk of the muscle water is frozen. The unfrozen part is termed the hydrated layer and amounts to 7–12% of the total water content. Its correlation time takes teh form of a log-Gaussaian distribution function. From +37 to −8°C, the spin-lattice relaxation time is explained by the exchange of water between the hydration layer and the rest of the water, which behaves like ordinary liquid water. The fact that the observed T₂ values are smaller than the calculated values is attributed to the inner field inhomogeneity of the heterogenous system and/or the modification of T₂ due to non-zero dipolar interaction.In the presence of perdeuterated dimethylsulfoxide, the freezing point of water decreases and the amount of non-freezable water increases. T₁ of water protons for muscle containing 10, 20, and 40% dimethylsulfoxide was calculated.     

Drug-induced zeta potential changes in liposomes studied by laser Doppler spectroscopy

The technique of laser Doppler spectroscopy is used to measure the electrophoretic mobility of liposomes under the influence of one beta-blocking agent and three local anesthetics. All four drugs decrease the mobility (i.e., the zeta potential) of negatively charged phospholipids (soybean lipids, phosphatidylserine and cardiolipin). The mobility of electrostatically neutral pure phosphatidylcholine (zero mobility under control conditions at pH 7 and 4) is increased linearly with the logarithm of drug concentration, indicating binding and incorporation of positively charged drug molecules. The sequence of strength of activity, measured by zeta-potential changes, corresponds to that found in biological tissues: propranolol greater than tetracaine greater than lidocaine greater than procaine. For purely negatively charged lipids (phosphatidylserine, cardiolipin) the activity of the drug is higher at acidic pH, (pH 4), while for electrostatically neutral (phosphatidylcholine) or partly neutral (soybean) lipid liposomes drug activity is about the same at pH 9, 7 and 4. A Hill plot of the data reveals noncooperative drug binding. From the line width of the scattering power spectrum the mean particle radius and the average interparticle distance in the samples are determined.     

Superimposing noise linearizes the responses of primary muscle spindle afferents to sinusoidal muscle stretch

Experiments were conducted in anaesthetized and spinalized cats to measure the extent to which the non-linear response of Ia afferent fibers to sinusoidal muscle stretch as expressed by the peristimulus-time-histograms, PSTHs, can be transformed into a linear one by means of the superposition of random stretch ("mechanical noise"). The gastrocnemius muscles of one hind leg were stretched and the response to sinewave muscle stretch (amplitudes between 0.01 and 4.0 mm, frequencies between 0.1 and 20 Hz) were investigated while band-limited mechanical noise was superimposed on the sinewave stretch. The random stretch upper cut-off frequency was varied between 60 and 300 Hz; the displacements were normally distributed. The noise amplitude sigma, i.e. the standard deviation of the displacement distributions, was varied systematically between 0.002 and 0.4 mm. Mechanical noise was very effective in raising the mean discharge rate. Added to the sinusoidal stretch it prevented the cessation of firing during the release phase of the stretch cycle, or at least reduced the duration of discharge pauses, i.e., a linearization occurred. In general, the larger the noise amplitude, the more the amplitude of the fundamental harmonic component was attenuated and the phase lead reduced. Apart from this rule the particular combination of superimposing small noise (sigma less than 0.02 mm) on small sinewave stretch (A less than 0.02 mm) could enhance the depth of sinusoidal modulation of cycle histograms (compared with responses to pure sinusoids). Linearizing the sinewave response by additional noise allowed the estimation of frequency response characteristics in the otherwise non-linear range of amplitudes (sinewave amplitude 0.5-1.0 mm).(ABSTRACT TRUNCATED AT 250 WORDS)