Role of the various groups of afferent fibers of the mesenteric nerves in vasomotor reflexes

The dependence of the magnitude and character of vasomotor reflexes on the amplitude of tetanic stimulation of the mesenteric nerves was investigated in experiments on anesthetized cats. Comparison of the results of analysis of the stimulus amplitude versus reflex magnitude curves with previous data on excitability of the various groups of mesenteric nerve fibers revealed three groups of "vasomotor" afferents with different conduction velocities: fast-conducting Aδ-fibers (conduction velocity over 8 m/sec) evoking depressor or small pressor reflexes; slow-conducting Aδ-fibers (conduction velocity below 8 m/sec), evoking pressor reflexes or, by interaction with impulses of lower-threshold, fast-conducting Aδ-fibers, either reduce the magnitude of the depressor reflexes evoked by those impulses or increase the corresponding pressor reflexes; C-fibers increasing the magnitude of the pressor reflexes evoked by slow-conducting A-fibers.     

On the fibers of the III, IV and VI cranial nerves of the cat.

The fiber content and diameter spectra of the cranial nerves III, IV and VI were analysed in cat. A semi-automatic technique of measuring fiber diameters is presented and compared to the manual method. The number of fibres was counted in the proximal part of the three main nerves and in each of their distal branches before they enter the EOM. Compared to the muscle weight, the branch to the RB had fewer fibers than all the other muscle branches. The diameter spectra of the proximal part of the three main nerves were compared with the diameter spectra of each of their distal branches. Minor differences were found among them. Only the RB had a striking difference in the spectrum which was skewed toward the large diameters.     

Action potential conduction velocity along the caudal and tibial nerves in rat strains selected for excitability of the neuromuscular system

The study was performed on 2 lines of rat selected for high (H) and low (L) excitability threshold of the nervous-muscle apparatus. H-line rats have higher values of spike conduction velocity in caudal and tibial nerves, as compared to those obtained in L-line rats. It is suggested that behavioral differences between these two lines of rat may be connected with changes of neurological characters both of peripheral and central nervous system, as a result of selection.     

Mast cell-mediated long-lasting increases in excitability of vagal C fibers in guinea pig esophagus

Several esophageal pathologies are associated with an increased number of mast cells in the esophageal wall. We addressed the hypothesis that activation of esophageal mast cells leads to an increase in the excitability of local sensory C fibers. Guinea pigs were actively sensitized to ovalbumin. The mast cells in the esophagus were selectively activated ex vivo by superfusion with ovalbumin. Action potential discharge in guinea pig vagal nodose esophageal C-fiber nerve endings was monitored in the isolated (ex vivo) vagally innervated esophagus by extracellular recordings. Ovalbumin activated esophageal mast cells, leading to the rapid release of approximately 20% of the tissue histamine stores. This was associated with a consistent and significant increase in excitability of the nodose C fibers as reflected in a two- to threefold increase in action potential discharge frequency evoked by mechanical (increases in intraluminal pressure) stimulation. The increase in excitability persisted unchanged for at least 90 min (longest time period tested) after ovalbumin was washed from the tissue. This effect could be prevented by the histamine H1 receptor antagonist pyrilamine, but once the increase in excitability occurred, it persisted in the nominal absence of histamine and could not be reversed even with large concentrations of the histamine receptor antagonist. In conclusion, activation of esophageal mast cells leads to a pronounced and long-lived increase in nociceptive C-fiber excitability such that any sensation or reflex evoked via the vagal nociceptors will likely be enhanced. The effect is initiated by histamine acting via H1 receptor activation and maintained in the absence of the initiating stimulus.     

Conduction velocity of the IXth nerve fibers innervating taste organs in the rostral and caudal tongue region in bullfrog

Sensory impulses elicited by electrical, mechanical and chemicalstimulation of the fungiform papillae in the bullfrog tonguewere recorded at two distant points on the glossopharyngealnerve, and the conduction velocities of different types of sensoryunits in the medial branch supplying the caudal two-thirds ofthe tongue were compared with those in the lateral branch innervatingthe rostral third. (1) Rapidly-and slowly-adapting mechanosensitiveunits in the medial branch had the mean conduction velocityof 23 ± 0.4 (S.E.) and 14.8 ± 0.3 m/sec, respectively,the former but not the latter being significantly (P <0.001)slower than the lateral branch units of the same type by 6m/sec.(2) The velocity of gustatory unit impulses was found to rangefrom 14 to 20 m/sec. Statistical examination revealed that themean conduction velocities of the medial branch units can bearranged in the order of water- > sucrose- > acetic acid-= NaCl- >quinine-sensitive units. Similar order had beenfound in the lateral branch units, which were significantly(P <0.001) faster in the mean conduction velocity than themedial branch units of the respective type by 2 m/sec.     

Excitation of cat spinal cord dorsal column fibers during stimulation of different fiber groups of cutaneous and somatic nerves

The effects of electrically stimulating different groups of nerve fibers supplying the skin and muscle on evoked potentials in cat spinal cord dorsal columns were studied. Significant differences in the configuration of dorsal column potentials recorded in response to stimulation of these nerves were found. It was shown that cutaneous nerve unmyelinated fibres were connected to unmyelinated dorsal column fibers. In addition, excitation of cutaneous C-fibers lead to activation of dorsal column fibers with the maximum conduction velocity. The somatic nerve was only connected to myelinated dorsal column fibers, and excitation of its non-myelinated fibers did not cause other types of dorsal column fibers to be activated. It is suggested that the acceleration of cutaneous signal transmission in the dorsal column system may be brought about by the necessity for rapid warning of potentially harmful stimuli.Medical Institute, Russian Federation Ministry of Public Health, Nizhny Novgorod. Translated from Neirofiziologiya, Vol. 24, No. 5, pp. 625–635, September–October, 1992.     

Adenosine modulation of vasoconstrictor responses to stimulation of sympathetic nerves and norepinephrine infusion in the superior mesenteric artery of the cat

Vasoconstriction induced by sympathetic nerve stimulation and by norepinephrine infusion in the superior mesenteric artery of cats anesthetized with pentobarbital was inhibited by adenosine infusions in a dose-related way. The responses to nerve stimulation were not inhibited to a greater extent than the responses to norepinephrine, thus suggesting no presynaptic modulation of sympathetic nerves supplying the resistance vessels of the feline intestinal vascular bed. Blockade of adenosine receptors using 8-phenyltheophylline did not alter the degree of constriction induced by nerve stimulation or norepinephrine infusion, indicating that in the fasted cat, endogenous adenosine co-released or released subsequent to constriction does not affect the peak vasoconstriction reached. Isoproterenol caused similar degrees of vasodilation as adenosine but did not show significant antagonism of the pooled responses to nerve stimulation or norepinephrine infusion; there was no tendency for the degree of dilation induced by isoproterenol to correlate with the inhibition of constrictor responses. Thus, the effect of adenosine on nerve- and norepinephrine-induced constriction is not secondary to nonspecific vasodilation.     

Distribution of myelinated nerves in ascending nerves and myenteric plexus of cat colon

The parts of the colon differ in motor function and in responses to extrinsic and intrinsic nerve stimulation. The distribution of myelinated nerve fibers in the colonic myenteric plexus is not known. Because these fibers might be largely extrinsic in origin, their distribution might indicate the domain of influence of extrinsic nerves and help to explain the different behaviors of the different parts of the colon. Myelinated fibers were examined by electron microscopy in cross sections of the ascending nerves and in myelin-stained whole-mount preparations in the colon. The ascending nerves are much like one another. They have the structure of peripheral nerves, not that of myenteric plexus. The proportion of myelinated fibers in the ascending nerves declines rostrad with no uniform change in total nerve fiber number. Cross-sectional areas of ascending nerves, 3,304 to 7,448 microns 2; total number of nerve fibers per profile, 703-2,651; and mean myelin coat thickness, 0.45 +/- 0.01 micron, do not change uniformly along the ascending nerves. Myelinated fibers are about 2% of total fibers in the extramural colonic nerves, 7-9% in the ascending nerves in the sigmoid colon, and 2-3% at the rostrad ends of the ascending nerves in the transverse colon. Blood vessels lie at the core of each ascending nerve and on the nerve sheath. Myelinated fibers in the ascending nerves degenerate after section of colonic branches of the pelvic plexus and after section of the pudendal nerves, indicating that myelinated nerves reach the colon through both pathways.(ABSTRACT TRUNCATED AT 250 WORDS)     

Conduction of excitation in the cat visual system

Unit responses in area 17 of the visual cortex to stimulation of the lateral geniculate body and optic tract were studied in experiments on unanesthetized cats immobilized with D-tubocurarine. Of the neurons tested, 53.6% responded to stimulation of the lateral geniculate body. In 92% of these cells the responses were orthodromic with latent periods of between 2 and 12.5 msec. Most cells responded with latent periods of 2.0–2.5, 3.0–3.5, and 4.0–4.5 msec, corresponding to latent periods of the components of the electropositive wave of the primary response. Antidromic responses to stimulation of the lateral geniculate body were given by 8% of neurons. The difference between the latent periods of responses of the same visual cortical neurons to stimulation of the optic tract and lateral geniculate body was 0.1–1.8 msec, but for most neurons (55.8%) it was 0.5–1 msec. The histograms of response latencies of visual cortical neurons to stimulation of the above-mentioned formations were found to be similar. It is concluded that the optic radiation contains three principal groups of fibers with conduction velocities of 28.5–16.6, 11.7–8.9, and 7.4–6.0 m/sec, respectively.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 7, No. 6, pp. 589–596, November–December, 1975.