Effect of portal infusion of hypertonic saline on neurons in the dorsal motor nucleus of the vagus in the rat

Effects of hepatoportal osmo-receptive (or sodium-receptive) afferents on neurons within the dorsal motor nucleus of the vagus (DMV) were investigated electrophysiologically in urethane-chloralose anesthetized rats. Responses of 56 spontaneously active neurons to antidromic stimulation of the ventral trunk of the subdiaphragmatic vagus were recorded in the left DMV. Among them, 35 neurons were inhibited by electrical stimulation of the hepatic branch of the vagus nerve (inhibitory neurons), except two neurons that were slightly excited. Effects of portal infusion of 3.6% NaCl were examined on 26 inhibitory neurons. Sixteen neurons increased their discharge rates and one neuron decreased its discharge rate in response to portal infusion of hypertonic saline. Thirty-five DMV neurons responded to electrical stimulation of the dorsal trunk of the subdiaphragmatic vagus were inhibited by electrical stimulation of the hepatic branch of the vagus. Four neurons were excited by this stimulation. Relatively smaller number of neurons (5 out of 22 inhibitory neurons) increased their discharge rates in response to portal infusion of hypertonic saline. In conclusion, the response of DMV neuron observed in this experiment was characterized by increasing the frequency of spike discharges in response to portal infusion of hypertonic saline. However, these neurons were inhibited by electrical stimulation of the hepatic branch of the vagus nerve. These results suggest that the hepatoportal osmoreceptive afferents may be conveyed to the DMV via inhibitory synapses.     

Chemosensitivity of neurons in the dorsal motor nucleus of the vagus that responded to portal infusion of hypertonic saline in rats

Neural responses in the dorsal motor nucleus of the vagus (DMV) to topical administrations of sodium and portal infusions of hypertonic saline were investigated electrophysiologically by using multibarrel electrodes in anesthetized rats. Of 102 neurons that showed antidromic response to electrical stimulation of the ventral gastric vagus or the accessory celiac vagus, 51 neurons increased and 13 neurons decreased their discharge rates in response to the electrophoretic administration of sodium. The other 38 neurons did not respond to this stimulation. The portal infusion of hypertonic saline elicited neural responses of some DMV neurons whose axons are involved into either the ventral gastric or the accessory celiac vagus. Further, effects of the topical administration and the portal infusion of hypertonic saline were examined on 33 neurons. Typical response was characterized by an increase in discharge rate responding to both of the portal infusion and the topical administration. In conclusion, the DMV neurons receiving the afferent inputs from hepatoportal osmoreceptors may have an enteroceptor function detecting the change in osmotic pressure of their environment.     

Effects of sulphated cholecystokinin octapeptide (CCK-8) on the dorsal motor nucleus of the vagus

Sulphated cholecystokinin octapeptide (CCK-8) was applied by superfusion (2.1 x 10(-7) to 4.2 x 10(-6) M) to neurons of the dorsal motor nucleus of the vagus (DMV) in slice preparations of the rat medulla oblongata. Intracellular recordings show 23 of 54 (43%) neurons to be depolarized and the depolarization to be associated with an increase in membrane input resistance; 6 of 54 (11%) neurons were hyperpolarized and the hyperpolarization was associated with a decrease in membrane input resistance. Both effects were dose-dependent, reversible and persisted after blockade of synaptic transmission by Ca2+ free/high Mg2+ solution. On the other hand, nonsulphated CCK-8, a nonactive analogue of CCK-8, had no effect. These data show that vagal neurons in the DMV have receptors for CCK-8 and that CCK-8 may modulate vagal output mainly by increasing neuronal excitability.     

GABA receptors in the dorsal motor nucleus of the vagus influence feline lower esophageal sphincter and gastric function

Gamma-aminobutyric acid (GABA) antagonist (bicuculline methiodide, BIC; picrotoxin, PIC) or agonist (muscimol, MUS) microinjections were made into the dorsal motor nucleus of the vagus nerve (DMV), and effects on lower esophageal sphincter pressure (LESP), gastric motility, and gastric acid secretion were determined in chloralose-anesthetized cats. Right or left DMV sites were microinjected with BIC, PIC, MUS, or isotonic saline (140 nl) through a glass micropipette having a tip diameter of 15–21 μm. Esophageal body, LESP, and gastric fundic pressures were measured manometrically. Circular smooth muscle contractions of the antrum and pylorus were recorded with strain-gauge force transducers. Gastric acid secretion was measured every 15 min through a gastric cannula and titrated to pH 7.0. DMV microinjection sites were verified histologically. Direct BIC microinjections (0.275 or 0.550 nmol) into the DMV primarily produced a decrease in LESP (71% of all sites tested), with mean LESP changing from 23.2 ± 1.7 mmHg to 3.7 ± 0.7 mmHg (p < 0.01). Tonic LESP increases and phasic LESP contractile activity occurred less frequently. BIC-induced LESP responses were abolished by vagotomy or by microinjections of MUS (0.5 to 10 nmol) into the DMV. Direct PIC microinjection (0.232 nmol) into the DMV produced a pattern of responses similar to those observed with BIC (which were also abolished by vagotomy or by MUS microinjections into the DMV). The antrum and pylorus were also responsive to DMV microinjections of both GABA antagonists. Microinjections of BIC or PIC into the DMV produced increases in gastric circular muscle activity that occurred less frequently than LESP effects, but also were eliminated by vagotomy. The high (0.550 nmol) dose of BIC increased gastric motility significantly more often than the low dose of BIC (p < 0.05). In addition, BIC (0.550 nmol) microinjections into the DMV increased gastric secretary volume (from 0.6 ± 0.2 to 6.0 ± 2.5 ml/15 min; p < 0.01) and total titratible acid (from 34.4 ±8.9 to 86.0 ± 19.1 mEq/15 min; p < 0.01), and decreased gastric pH (from 4.63 ± 0.44 to 3.50 ± 0.49; p < 0.05). Vagotomy also eliminated the gastric secretory effects of DMV BIC. Direct microinjections of MUS into the DMV also blocked BIC- or PIC-induced changes in gastric motility and/or gastric acid secretion. Isotonic saline microinjected into the DMV did not increase basal or decrease stimulated gastric esophageal motility or gastric secretion. These data indicate that LESP, gastric motility, and gastric secretion are influenced by a tonic DMV inhibition mediated by GABA_A receptor stimulation of the DMV. Because disinhibition of these receptors clearly activates the upper gut, future work should focus on identifying the nuclei providing this synaptic input to the DMV that might be involved in the functional regulation of upper gut motor and secretory function.     

Vasopressin-induced pressor response elicited by electrical stimulation of solitary nucleus and dorsal motor nucleus of vagus of rat

Electrical stimulation of the solitary nucleus and dorsal motor nucleus of the vagus elicited a pressor response in vagotomized rat with the spinal cord cut at C₁. The response was entirely accounted for by an increased release of vasopressin upon stimulation as evidenced by absence of response in rats pretreated with a vasopressin antagonist and in Brattleboro rats.     

Direct amygdaloid projections to the dorsal motor nucleus of the vagus nerve: a light and electron microscopic study in the rat

The projections from the central nucleus of the amygdala to the dorsal vagal complex were examined in the rat by means of anterograde and retrograde axonal transport of wheat germ agglutinin-horseradish peroxidase and anterograde degeneration. Light microscopic findings confirmed that the amygdala projects to the dorsal motor nucleus (DMV) and the nucleus of the solitary tract. Electron microscopic experiments demonstrated degenerating axosomatic and axodendritic terminals in the DMV following electrolytic lesions in the central nucleus of the amygdala.     

Prenatal ontogeny of substance P-like immunoreactivity in the nucleus tractus solitarii and dorsal motor nucleus of the vagus nerve of the human fetus: an immunocytochemical study

By using immunocytochemical method, the prenatal ontogeny of substance P-like immunoreactivity (SP-LI) was demonstrated in the dorsal motor nucleus of the vagus nerve (nX) and the nucleus tractus solitarii (nTS) of the human fetus at fetal age (menstruation age) of 11.5 weeks to 40 weeks. The time of initial appearance of SP-LI in the human brainstem nTS was between the fetal age 11.5 weeks and 16 weeks. At fetal age 16 weeks, the nTS showed moderate density of SP-LI fibers and terminals in subnucleus dorsalis of the nTS and nX. While the fetus grew, the density of SP-LI in the human fetus brainstem nTS and nX increased gradually from fetal age 16 weeks to 40 weeks. According to the Nissl staining, at fetal age 23 weeks, the nTS of human fetus can be subdivided into dorsal, medial, dorsolateral, ventrolateral and ventral gelatinosus subnuclei. The cytoarchitectonic subdivisions of human fetus nTS is in good agreement with the results obtained by immunocytochemical staining. These findings indicated that substance P (SP) might play an important role in the development of human brainstem nX, nTS, their related cranial nerves, and in their functional establishment during the pranatal period.     

Induction of apoptosis by thrombin in the cultured neurons of dorsal motor nucleus of the vagus

Background A previous study demonstrated the presence of protease‐activated receptor (PAR) 1 and 2 in the dorsal motor nucleus of vagus (DMV). The aim of this study is to characterize the effect of thrombin on the apoptosis of DMV neurons. Methods The dorsal motor nucleus of vagus neurons were isolated from neonatal rat brainstems using micro‐dissection and enzymatic digestion and cultured. Apoptosis of DMV neurons were examined in cultured neurons. Apoptotic neuron was examined by TUNEL and ELISA. Data were analyzed using anova and Student’s t‐test. Key Results Exposure of cultured DMV neurons to thrombin (0.1 to 10 U mL^?1) for 24 h significantly increased apoptosis. Pretreatment of DMV neurons with hirudin attenuated the apoptotic effect of thrombin. Similar induction of apoptosis was observed for the PAR1 receptor agonist SFLLR, but not for the PAR3 agonist TFRGAP, nor for the PAR4 agonist YAPGKF. Protease‐activated receptors 1 receptor antagonist Mpr(Cha) abolished the apoptotic effect of thrombin, while YPGKF, a specific antagonist for PAR4, demonstrated no effect. After administration of thrombin, phosphorylation of JNK and P38 occurred as early as 15 min, and remained elevated for up to 45 min. Pretreatment of DMV neurons with SP600125, a specific inhibitor for JNK, or SB203580, a specific inhibitor for P38, significantly inhibited apoptosis induced by thrombin. Conclusions & Inferences Thrombin induces apoptosis in DMV neurons through a mechanism involving the JNK and P38 signaling pathways.     

Neurochemical studies of the nucleus of the solitary tract, dorsal motor nucleus of the vagus and the hypoglossal nucleus in rat: Topographical distribution of glutamate uptake, GABA uptake and glutamic acid decarboxylase activity

The topographical distribution of glutamate uptake, GABA uptake, and GAD activity was studied in caudal, intermediate and rostral areas of the nucleus of the solitary tract (NTS), dorsal motor nucleus of the vagus (DMN) and the of the solitary tract (NTS), dorsal motor nucleus of the vagus (DMN) and the hypoglossal nucleus (n.XII). Within the NTS and n.XII, all three neurochemical parameters exhibited increasing activity from caudal to rostral regions. The distribution pattern for glutamate uptake within the DMN was qualitatively similar to the other nuclei studied, whereas GABA uptake and GAD activity were found to be homogeneously distributed within the DMN. The NTS also exhibited a medial-lateral heterogeneity for glutamate and GABA uptake, with the medial aspect of this nucleus containing significantly higher uptake than the lateral aspect.     

Choline acetyltransferase and glutamate uptake in the nucleus tractus solitarius and dorsal motor nucleus of the vagus: effect of nodose ganglionectomy

Unilateral removal of the nodose ganglion resulted in a significant decrease in choline acetyltransferase activity in the ipsilateral dorsal motor nucleus of the vagus but was without effect on enzyme activity in the nucleus of the solitary tract. High affinity glutamate uptake in the dorsal motor nucleus of the vagus and along the rostrocaudal extent of the nucleus of the solitary tract was not affected by nodose ganglionectomy.     

Effect of electrical stimulation of the dorsal nucleus of the vagus nerve on gastric acid secretion in cats.

Electrical stimulation of 3 to 9 V, 100 impules/s 1-ms duration/impulse, applied to the right or left dorsal motor nucleus of the vagus nerve (DNV) produced a significant increase in volume, acidity, and gastric acid output in 14 cats under sodium pentobarbital anesthesia. The increase in acid output occurred during the first 15 min of stimulation or immediately after the stimulation and in some cats lasted for the next 30 min to more than 2 h. In no case did the stimulation within the DNV evoke a decrease in gastric acid secretion. Similar electrical stimulation in sites outside the DNV had no effect on gastric acid secretion. Motor effects such as opening of the mouth, movements of the tongue and whiskers, and salivation were observed to occur randomly during stimulation at sites both inside and outside the DNV zone and were not correlated with changes in gastric acid secretion. After recovery from the acute experiment, two cats were tested under chronic conditions. Electrical stimulation with low voltage applied to the previously effective electrode tips repeatedly produced an increase in the volume of secretion in one cat and an increase in both volume and acidity of secretion in the other cat. This study provided further evidence that the DNV is a secretomotor center.     

Colocalization of GABAA and NMDA receptors within the dorsal motor nucleus of the vagus nerve (DMV) of the rat

Changes in gastric motor activity are observed in response to glutamate and GABA in the DMV. We investigated the expression of GABA_A and NMDA receptors within DMV neurons projecting to the stomach using pseudorabies virus (PRV). PRV immunoreactive (PRV-IR) cells expressing GABA_A α 1-IR, also expressed NMDAR1 suggesting that NMDA and GABA_A receptors are colocalized. These results provide a neuroanatomical basis for these receptors jointly playing a role in gastric motor functions.     

Expression and kinetic properties of Na(+) currents in rat cardiac dorsal root ganglion neurons

The expression and properties of voltage-gated Na(+) currents in cardiac dorsal root ganglion (DRG) neurons were assessed in this study. Cardiac DRG neurons were labelled by injecting the Fast Blue fluorescent tracer into the pericardium. Recordings were performed from 138 cells. Voltage-dependent Na(+) currents were found in 115 neurons. There were 109 neurons in which both tetrodotoxin-sensitive (TTX-S, blocked by 1 microM of TTX) and tetrodotoxin-resistant (TTX-R, insensitive to 1 microM of TTX) Na(+) currents were present. Five cells expressed TTX-R current only and one cell only the TTX-S current. The kinetic properties of Na(+) currents and action potential waveform parameters were measured in neurons with cell membrane capacitance ranging from 15 to 75 pF. The densities of TTX-R (110.0 pA/pF) and TTX-S (126.1 pA/pF) currents were not significantly different. Current threshold was significantly higher for TTX-R (-34 mV) than for TTX-S (-40.4 mV) currents. V(1/2) of activation for TTX-S current (-19.6 mV) was significantly more negative than for TTX-R current (-9.2 mV), but k factors did not differ significantly. V(1/2) and the k constant for inactivation for TTX-S currents were -35.6 and -5.7 mV, respectively. These values were significantly lower than those recorded for TTX-R current for which V(1/2) and k were -62.3 and -7.7 mV, respectively. The action potential threshold was lower, the 10-90% rise time and potential width were shorter before than after the application of TTX. Based on this we drew the conclusion that action potential recorded before adding tetrodotoxin was mainly TTX-S current dependent, while the action potential recorded after the application of toxin was TTX-R current dependent. We also found 23 cells with mean membrane capacitance ranging from 12 to 35 pF (the smallest labelled DRG cells found in this study) that did not express the Na(+) current. The function of these cells is unclear. We conclude that the overwhelming majority of cardiac dorsal root ganglion neurons in which voltage-dependent Na(+) currents were present, exhibited both TTX-S and TTX-R Na(+) currents with remarkably similar expression and kinetic properties.     

Ultrastructure of the dorsal motor nucleus of the vagus nerve in monkey with a comparison of synaptology in monkey and cat

Neurons of the dorsal motor nucleus of the vagus nerve were studied following injections of horseradish peroxidase into the vagus nerve in a monkey (Macaca fascicularis). In frozen sections, the dorsal motor nucleus appeared to be completely filled by labeled medium-sized (20-30 micron in long axis) neurons. Labeled dendrites from these neurons often extended outside the borders of the nucleus into the nucleus of the tractus solitarius. In 1 micron thick plastic sections and ultrathin sections of the dorsal motor nucleus, two distinct types of neurons were observed with the light and electron microscope. Medium-sized neurons with abundant cytoplasm and an oval nucleus were retrogradely labeled with HRP, while small (10-15 micron in long axis) neurons with a paucity of organelles and an invaginated nucleus remained unlabeled. Medium-sized neurons outnumbered the small neurons by approximately five to one. The synaptic organization of the dorsal motor nucleus in monkey was studied and compared with that in cat. The porportions of different types of axosomatic synapses were similar in both species. Terminals containing round vesicles and making symmetrical or asymmetrical contact with the postsynaptic structure were more common than synaptic terminals containing pleomorphic vesicles. In both species, there was a slightly greater synaptic density on the medium-sized neurons than on the small neurons. The synaptic density in the monkey dorsal nucleus was greatest on the smallest dendrites in the neuropil and least on the somata.     

Non-uniform expression of α subunit isoforms of the Na/K pump in rat dorsal root ganglia neurons

Tissue sections and antibodies selectively recognizing isoforms of the α subunit of the Na⁺/K⁺ pump were used to determine the expression of α₁, α₂ and α₃ pump isoforms in the plasma membrane of adult rat dorsal root ganglia (DRG) neurons. There was no detectable membrane signal from DRG neurons that were probed with antibodies to the α₂ isoform of the Na⁺/K⁺ pump. The α₁ isoform of the Na⁺/K⁺ pump was found in most (77±4%) studied DRG neurons, regardless of cell size. Only 16±7% of the neurons expressed a detectable level of the α₃ Na⁺/K⁺ pump and all were apparently from a subpopulation of large DRG neurons. Comparison of cell size distributions and a study of neurons identified in serial sections suggested that of the α₃ positive DRG neurons about 75% coexpressed the α₁ isoform of the Na⁺/K⁺ pump. These data show that the expression of the protein of the α subunit isoforms of the Na⁺/K⁺ pump is not uniform throughout the population of DRG neurons and that α₁ is the predominant isoform in the plasma membrane of these neurons.     

Effects of mammalian brain extracts and chlormadinone acetate on neuronal Na, K-ATPase and electrogenic Na, K-pump activity in vitro

Acid-acetone extracts of brain (from beef and guinea pig) and chlormadinone acetate (CMA) were compared with ouabain for their ability to inhibit the electrogenic Na⁺,K⁺-pump and the Na⁺,K⁺-ATPase of neuronal tissues. The membrane potential of neurones in the paravertebral sympathetic ganglion of the bullfrog was recorded in K⁺-free Ringer's solution by means of the sucrose gap technique. The potassium activated hyperpolarization (K_H⁺), induced by the re-introduction of potassium, was used as an index of electrogenic Na⁺,K⁺-pumping. The K_H⁺ was blocked by 1 μM ouabain. Na⁺,K⁺-ATPase activity was measured in microsomal membrane preparations of frog and beef brain using a continuous spectrophotometric assay. Although ouabain consistently inhibited beef brain Na⁺,K⁺-ATPase (IC₅₀ = 2.2 μM), acid-acetone extracts prepared from guinea pig and beef brain produced only partial inhibition. Neither of the extracts significantly reduced the K_H⁺ of the frog ganglion. CMA inhibited Na⁺,K⁺-ATPase prepared from bullfrog brain and spinal cord with slightly greater potency (IC₅₀ = 4.5 μM) than did ouabain (IC₅₀ = 10 μM). In contrast, electrogenic Na⁺,K⁺-pumping (i.e. the K_H⁺) in the frog ganglion was not affected by this steroid. It is concluded that although both the extracts and CMA inhibited Na⁺,K⁺-ATPase, neither can be considered ouabain-like due to their failure to affect the electrogenic Na⁺,K⁺-pump in situ.     

Na, K-ATPase in the rat olfactory bulb: evidence for a higher enzymatic activity in the glomerular layer

Protein content and ATPase activities have been determined in the superficial and deep layers of the rat olfactory bulb. Protein levels, Mg²⁺-ATPase and Na⁺, K⁺-ATPase activities were significantly higher in the whole homogenate of the superficial layers. These differences were amplified when activity was expressed on a wet weight basis in a crude microsomal preparation isolated by differential centrifugation. Specific activities, however, showed similar values in the microsomal fractions from superficial and deep layers. The results are discussed in terms of differences in the density of neuronal processes and efficiency of K⁺ reuptake mechanisms.     

Effects of perinatal undernourishment on neuronal development of the facial motor nucleus in the rat

The facial nucleus (FN) of the rat is composed of multipolar neurons generated between gestational days G12 and G15. This nucleus is involved in the mechanisms underlying muscle contraction during the sucking reflex. After birth, the neuronal substrate of this reflex is gradually organized to allow the performance of other functions such as gnawing, chewing, swallowing and drinking. Undernourishment is known to produce different degrees of delayed brain development, the greatest of which are similar to the characteristics of the premature syndrome. Neuronal morphological alterations are associated with sucking-reflex deficiencies, which interfere with feeding by the newborn. The current study shows that perinatal undernourishment leads to dendritic arbor hypoplasia and small alterations of soma size in Golgi--Cox impregnated FN neurons of rats. The data suggest that these morphological alterations of FN neurons, may be associated with shifts in the input and integration of signals, and may finally modify the elaboration of motoneuron discharges partly modulating bucolabial muscle contraction during sucking movements and facial expression. Additionally, neonatal nutritional rehabilitation modifies the effects on FN neuronal development, ameliorating the influence of early adverse nutritional conditions.