Stimulation of dog RVLM and A5 area changes sympathetic outflow to vascular beds without effect on the heart.

Studies were conducted in anesthetized, vagotomized dogs while blood pressure; blood flows in femoral, renal, mesenteric, and left circumflex coronary arteries; electrocardiogram; and regional cardiac contractile force were monitored. The ventral surface of the medulla was exposed, and pressor sites in the rostral ventrolateral medulla (RVLM) were mapped by microinjections of L-glutamate. L-Glutamate activation of the RVLM evoked selective effects on different components of the cardiovascular system. Increases of 20-130 mmHg in blood pressure were accompanied by vascular conductance decreases in the femoral (-48 +/- 4%), renal (-30 +/- 4%), and mesenteric (-38 +/- 3%) arterial beds. These effects were without any obvious topography within the RVLM. There were only small or negligible changes in heart rate (HR), cardiac contractile force, and coronary vascular conductance. Thus stimulation of the canine RVLM increased sympathetic tone selectively to structures other than the heart. Stimulation of the ventral medulla in a region that lay rostral to the RVLM and ventromedial to the facial nucleus selectively increased femoral vascular conductance by 103 +/- 33% and decreased vascular conductance in the renal (-20 +/- 5%) and mesenteric (-15 +/- 4%) arterial beds. There was no increase in HR, and the increases in blood pressure were relatively small. Immunohistochemical data led us, tentatively, to identify this rostral area as overlapping part of the A5 area.

Cardiovascular neurons in cat caudal ventrolateral medulla: location and characterization of GABAergic input.

The purposes of the present study were to: (1) characterize the GABAergic input to vasodepressor neurons in the caudal ventrolateral medulla of the cat, and (2) define more precisely the anatomical localization of these neurons in this species. This was done by microinjecting GABA receptor antagonists and agonists, and a negative allosteric modulator of the GABA receptor, namely, ethyl-beta-carboline-3-carboxylate, into the caudal ventrolateral medulla of alpha-chloralose-anesthetized animals while monitoring arterial blood pressure and heart rate. Localization studies where performed relating injection sites in the caudal ventrolateral medulla where cardiovascular responses were elicited, to neurons exhibiting immunoreactivity to tyrosine hydroxylase (TH) and phenethyl-N-methyl-transferase (PNMT). Microinjection of 1 and 10 ng of bicuculline into the caudal ventrolateral medulla produced decreases in mean blood pressure and heart rate of -34 +/- 6.4 and -49 +/- 9.2 mmHg, and -22 +/- 4.3 and -35 +/- 8.2 beats/min, respectively. Hypotension and bradycardia were also observed with picrotoxin microinjection (120 ng). Microinjection of muscimol (100-200 ng) and GABA (12 microgram) had no effect on mean blood pressure and heart rate. Microinjection of ethyl-beta-carboline-3-carboxylate also decreased mean blood pressure (-39 +/- 7.0 mmHg). The location of the micropipette tip after bicuculline microinjection in relation to TH and PNMT immunoreactive cells was as follows: (1) TH-immunoreactive cells of the A1 cell group were visible in the same relative location as the micropipette tip, and (2) no PNMT-positive cells were noted at the sites where bicuculline elicited hypotension. These results indicate that there is a tonic GABAergic input to neurons in the caudal ventrolateral medulla. The location of these neurons overlaps with the A1 cells.

NMDA receptors are involved at the ventrolateral nucleus tractus solitarii for termination of inspiration.

The purpose of the present study was to determine whether blockade of excitatory amino acid receptors at the ventrolateral nucleus of the tractus solitarius would influence respiratory activity. This was done by microinjecting excitatory amino acid receptor antagonists into the ventrolateral nucleus of the tractus solitarius of alpha-chloralose-anesthetized animals while monitoring respiratory activity using a Fleisch pneumotachograph and arterial blood pressure and heart rate. Bilateral microinjection of the NMDA receptor antagonist, 3-[(R)-carboxypiperazin-4-yl]-propyl-1- phosphomic acid (CPP), 5.62 nmol per side, produced an increase in inspiratory duration (+4 +/- 1.6 s, n = 8) which progressed to an apneustic pattern of breathing. Similar results were obtained with CPP microinjected into the ventrolateral nucleus of the tractus solitarius of three vagotomized animals. Bilateral microinjection of a second NMDA receptor antagonist, 2-amino-7-phosphono-heptanoic acid (AP7), 562 nmol per side, produced qualitatively similar effects on respiration as seen with CPP. In contrast, blockade of non-NMDA receptors with 6-cyano-7-nitroquinoxaline-2,3-dione (CNXQ), 0.125 nmol per side, had very little effect on respiration. Activation of NMDA receptors at the ventrolateral nucleus of the tractus solitarius with bilateral microinjection of NMDA, 39 pmol, produced a large increase in expiratory duration (+11 +/- 3 s, n = 8), and apnea during the expiratory phase of the respiratory cycle in half of the animals studied. Similar results were obtained with D,L-alpha-amino-3-hydroxy-5-methyl-4-isoxazol-proprionate (AMPA). These results indicate that an endogenous excitatory amino acid released at the ventrolateral nucleus of the tractus solitarius and acting at the NMDA receptor, plays a significant role in respiratory timing.

Location and completeness of reinnervation by two types of neurons at a single target: the feline muscle spindle.

Muscle spindles from the tenuissimus muscle of the cat were examined microscopically to assess the precision and completeness of reinnervation of intrafusal muscle fibers by efferent and afferent neurons. Positions of motor and sensory nerve terminals were charted relative to the cross-sectional area enclosed by the outer capsule of the spindle. Profiles of nerve endings were measured for normally innervated and reinnervated spindles. The tenuissimus was deprived of innervation by freezing its nerve, sometimes in conjunction with either spinal ganglion removal or ventral rhizotomy. Sensory and motor terminals occupied separate locales along the length of normal muscle spindles. Nerve terminals of efferent and afferent neurons were located in appropriate positions along the length of spindles when axons of both types of neurons regrew together and when either category of axon regenerated alone. Precise reinnervation of muscle spindles occurred in spite of a diminished diameter of intrafusal fibers. Repopulation of the spindle with motor endings was less complete than that by sensory endings, based on the proportion and size of the regenerated terminals. We conclude that under optimal conditions for axonal regrowth, efferent and afferent neurons reinnervate their respective regions along intrafusal muscle fibers but motor lags sensory reinnervation within the spindle. The mechanism by which positional specificity happens during reinnervation of intrafusal fibers requires neither an interaction between terminals of the two types of neurons nor target cells of normal bulk.

Control of lower esophageal sphincter pressure by two sites in dorsal motor nucleus of the vagus.

Our purpose was to determine the central vagal sites for regulating changes in lower esophageal sphincter (LES) pressure in the cat. Injection of the retrograde tracer, horseradish peroxidase, into the LES resulted in labeling of cells in the dorsal motor nucleus of the vagus (DMV), with the largest number of cells appearing in two areas, one area rostral to obex (1.5-4.0 mm) and one area caudal to obex (-0.5 to -1.5 mm). In alpha-chloralose-anesthetized cats, L-glutamic acid was microinjected into these areas and LES pressure, intragastric pressure, and stomach motility were monitored. Microinjection of L-glutamic acid into the rostral area resulted in significant increases in LES pressure (18.6 +/- 4.9 mmHg; P less than 0.05), pyloric motility (baseline minute motility increased from 5.7 +/- 2.2 to 14.5 +/- 3.9 postinjection; P less than 0.05) and stomach pressure (baseline of 16.9 +/- 2.3 mmHg increased to 23.8 +/- 3.7 mmHg postinjection; P less than 0.05). Microinjection of L-glutamic acid into the caudal area resulted in significant decreases in LES pressure (-14.3 +/- 5.8 mmHg; P less than 0.05) and intragastric pressure (-7.5 +/- 2.2 mmHg; P less than 0.05) with no significant changes in pyloric motility. Ipsilateral vagotomy abolished both sets of responses. These data indicate that excitatory and inhibitory control of LES and intragastric pressure are mediated by vagal efferent neurons located in two distinct sites in the DMV.

Stimulation of serotonin2 receptors in the ventrolateral medulla of the cat results in nonuniform increases in sympathetic outflow.

Topical application of the serotonin2 agonist, 1-(2,5-dimethoxy-4-iodophenyl)-2-aminopropane or DOI, in a dose of 30 micrograms/side to the intermediate area of the ventrolateral surface of the medulla produced a significant increase in mean arterial pressure with no significant change in heart rate both in intact animals (n = 8) and in cervically vagotomized animals (n = 3). The pressor response of DOI was blocked by pretreatment of the intermediate area with ketanserin, a serotonin2 antagonist (n = 7). Pretreatment with intravenous phentolamine did not block the pressor response of DOI (n = 3). However, this pressor response could be counteracted by intravenous propranolol (n = 5) or by bilateral stellate ganglionectomy (n = 3). These data suggest that sympathoexcitation by centrally applied DOI selectively increased cardiac inotropy but not chronotropy. Further studies indicate that DOI increased contractile force without increasing heart rate and that the positive inotropic effect of DOI could be counteracted by bilateral stellate ganglionectomy. Bilateral microinjections of DOI into the subretrofacial nucleus in a dose of 100 ng (n = 3) and a dose of 300 ng (n = 3) increased mean arterial blood pressure by 23 +/- 2 and 44 +/- 6 mm Hg, respectively, without producing any changes in heart rate. These data suggest that DOI has a central site of action in the ventrolateral medulla, presumably at the subretrofacial nucleus, which leads to selective sympathoexcitation of the cardiac ventricles.

Medullary raphe: a new site for vagally mediated stimulation of gastric motility in cats.

Thyrotropin-releasing hormone (TRH) is clearly implicated in the control of gastric function via interactions in the dorsal motor nucleus of the vagus (DMV) of the cat. The source of the TRH innervation of the DMV is important to determine because this region could be of importance in control of gastric function. TRH-immunoreactive (ir) neurons are located in the raphe obscurus (Ro), raphe pallidus (Rp), and raphe magnus (Rm). Retrograde tracer applied to the DMV resulted in the most numerous labeled neurons in the caudal Ro and Rp in the same region where TRH-ir neurons are located. To address the question whether DMV-projecting neurons in the raphe subnuclei play a role in control of gastric motility, the following experiments were performed in alpha-chloralose-anesthetized cats while recording pyloric motility and blood pressure. Microinjection of a cell body excitant L-glutamate (44-200 nl, 0.5 M) into the caudal Ro and Rp in 15 experiments produced significant increases in pyloric minute motility index (MMI) of 4.9 +/- 1.5 (from 1.6 +/- 0.7 preinjection to 6.5 +/- 1.8 postinjection, P less than 0.05). Mean blood pressure (MBP) decreased significantly in these animals by 12 +/- 7 mmHg (from 100 +/- 6 to 88 +/- 8 mmHg, P less than 0.05). Saline microinjection in the same sites in seven cases resulted in no significant change in pyloric MMI (-1.0 +/- 0.8) or MBP (-4 +/- 11 mmHg). In five of these experiments, a second microinjection of L-glutamate (132-240 nl) was performed into the caudal Ro and Rp after spinal cord transection. This resulted in a significant increase in pyloric MMI of 3.3 +/- 0.9 (from 1.0 +/- 0.5 preinjection to 4.3 +/- 1.1 postinjection, P less than 0.05) but no change in MBP (+1 +/- 1 mmHg). Bilateral vagotomy resulted in the abrupt cessation of the pyloric response to caudal Ro and Rp stimulation. Microinjection of L-glutamate into the rostral Rp and caudal Rm in nine experiments resulted in no significant changes in pyloric MMI (-0.4 +/- 0.8) or MBP (-10 +/- 11 mmHg). These data indicate that a population of neurons in the caudal raphe nuclei, which may contain TRH, project to the DMV. In addition, excitation of these neurons causes an increase in gastric motility that is not caused by inhibition of sympathetic outflow to the gut but rather by excitation of vagal neurons in the DMV.

TRH: immunocytochemical distribution in vagal nuclei of the cat and physiological effects of microinjection.

In the present study, we have applied antiserum to thyrotropin-releasing hormone (TRH) and avidin-biotin immunocytochemistry to determine the distribution of TRH-like immunoreactivity in the vagal nuclei of the cat. A dense network of TRH-immunoreactive (TRH-IR) fibers and terminals is noted in the dorsal motor nucleus of the vagus (DMV) from 0 to 2.5 mm rostral to the obex. Horseradish peroxidase conjugated wheat germ agglutinin (HRP-WGA)-labeled neurons are noted in this region of the DMV after application of the tracer to the musculature of the pylorus. In dual-stained sections, TRH-IR fibers and terminals appear to terminate in close proximity to HRP-WGA-labeled neurons in the DMV. In contrast, a moderate to low density of TRH-IR fibers and terminals is noted in the nucleus ambiguus (NA), and no HRP-WGA-labeled neurons are noted in this nucleus. To determine the physiological significance of TRH fibers in these vagal nuclei, TRH was microinjected into the DMV and NA while monitoring gastric (antrum and pylorus) and duodenal motility as well as mean blood pressure (MBP) and heart rate. Microinjections of TRH (16-500 ng) into the DMV resulted in increases in pyloric and antral motility (minute motility index increased from 1.28 to 8.70 in the pylorus, P less than 0.05, and from 2.29 to 4.25 in the antrum, P less than 0.05). TRH microinjection also increased the intraluminar pressure in the stomach by 6.1 +/- 1.3 mmHg. No significant changes in duodenal motility, MBP, or heart rate were noted.(ABSTRACT TRUNCATED AT 250 WORDS)

Effect of activation of central nervous system serotonin 1A receptors on cardiorespiratory function.

Previous studies indicate that the new antihypertensive drug, urapidil, acts at the ventral surface of the medulla in cats to produce a fall in blood pressure. In addition, urapidil was found in receptor binding studies to have a relatively high affinity for the serotonin 1A receptor. These results suggest that drugs which bind to the serotonin 1A receptor might exert hypotensive effects at the ventral surface of the medulla (VSM). To test this hypothesis, the effects of 8-hydroxy-2-(di-N-propylamino)tetralin (8-OH-DPAT), the prototype drug for activating serotonin 1A receptors, were evaluated for cardiovascular activity after local application to the VSM. 8-OH-DPAT applied bilaterally to the intermediate area of the VSM in a dose of 1 micrograms/side produced a decrease in mean blood pressure of 60 +/- 7 mm Hg (P less than .05) and a decrease in heart rate of 26 +/- 4 beats/min (P less than .05) (n = 8). Increases in respiratory rate (8 +/- 1 breaths/1 min) and decreases in tidal volume (13 +/- 4 ml) also occurred. These changes were associated with a significant increase in respiratory minute volume (130 +/- 41 ml, P less than .05). Similar cardiorespiratory changes were produced by application of another drug with high affinity for the serotonin 1A receptor, namely B695-40, to the intermediate area of the VSM. Intravenous administration of 8-OH-DPAT in a dose of 100 micrograms/kg mimicked the cardiorespiratory effects of ventral surface application of this agent.(ABSTRACT TRUNCATED AT 250 WORDS)

Medullary parasympathetic projections innervate specific sites in the feline stomach.

The purpose of our study was to determine the site of origin of vagal neurons that innervate specific parts of the stomach (the fundus, corpus, and antrum/pylorus). This was done by injecting the retrograde fluorescent tracer Fast Blue into these parts of the cat stomach and examining the hindbrain for cells labeled with retrograde tracer. We found that vagal preganglionic innervation to the stomach originates from two medullary nuclei, namely, the dorsal motor nucleus of the vagus (bilateral) and the nucleus retroambiguus (left). All parts of the stomach receive innervation from the dorsal motor nucleus of the vagus (primarily from the area ranging from 0.5 to 1.8 mm rostral to the obex), but only the fundus and corpus receive innervation from the nucleus retroambiguus. Injection of tracer into the fundus labeled cells within the lateral half of the dorsal motor nucleus of the vagus and injection of tracer into the antrum/pylorus labeled cells within the medial portion. Finally, injection of tracer into the corpus labeled cells throughout the mediolateral axis of the dorsal motor nucleus of the vagus. The finding of a columnar organization of the dorsal motor nucleus of the vagus implies some type of functional organization of gastrointestinal control. The fact that vagal inputs to the stomach arise from the dorsal motor nucleus of the vagus and nucleus retroambiguus suggests a separation of vagal pathways controlling different gastric functions (e.g., pacemaker activity, motility, and secretion).

Central nervous system site of action for the hypotensive effect of clonidine in the cat.

The purpose of our study was to determine whether clonidine exerts its centrally mediated hypotensive action at three sites that influence arterial pressure located in the medulla, specifically associated with the intermediate area of the ventrolateral medulla. The "intermediate area" lies approximately 1.5 mm caudal to the border of the trapezoid body (caudal border) and 4 mm lateral to the midline. One of the sites that influence arterial pressure lies in the nucleus reticularis rostroventrolateralis. The second site lies in close proximity to the rostral part of the nucleus reticularis lateralis (rLRN) and also near the A1 area. The third site lies in the most rostral area and medial to the nucleus reticularis rostroventrolateralis, that is in the nucleus paragigantocellularis lateralis. Unilateral microinjections of 0.22 and 0.43 nmol of clonidine into the rLRN produced dose-dependent decreases in arterial pressure. The 0.43 nmol dose of clonidine had no effect when unilaterally or bilaterally microinjected into either the nucleus reticularis rostroventrolateralis or into the nucleus paragigantocellularis lateralis. Microinjection of the alpha-2 adrenoceptor antagonist, idazoxan (16.6 nmol), unilaterally into rLRN had no effect per se, but prevented the hypotensive effect of a subsequent microinjection of clonidine. Similarly, bilateral microinjection of idazoxan into rLRN counteracted the hypotensive effect of i.v. administered clonidine. These data indicate that clonidine acts at alpha-2 adrenoceptors in the rLRN to produce hypotension.

Inhibitory control of proximal colonic motility by the sympathetic nervous system.

The purpose of this study is to determine whether or not the sympathetic nervous system provides a tonic inhibitory input to the colon in chloralose-anesthetized cats. Proximal and midcolonic motility were monitored using extraluminal force transducers. An intravenous bolus injection of 5 mg of phentolamine in 14 animals elicited a pronounced increase in proximal colon contractility. The minute motility index changed from 0 +/- 0 to 26 +/- 4 after phentolamine administration. Midcolonic motility also increased in response to phentolamine. Specific blockade of alpha 2-receptors, but not alpha 1-receptors, caused the same response seen with phentolamine. alpha-Adrenergic blockade increased colon contractility after spinal cord transection but not after ganglionic blockade. Blockade of alpha-adrenergic receptors was also performed before vagal and pelvic nerve stimulation and in both cases increased colonic motility. Vagal stimulation alone had no effect on colonic contractility, while pelvic nerve stimulation increased motility at the midcolon. alpha-Receptor blockade did not alter the ineffectiveness of vagal stimulation but did unmask excitatory effects of pelvic nerve stimulation on the proximal colon. All excitatory colonic responses were prevented by blocking muscarinic cholinergic receptors. These data indicate that tonic sympathetic nervous system activity exerts an inhibitory effect on colonic motility. The inhibitory effect is mediated through alpha 2-adrenergic receptors. Based on these findings, we suggest that alterations in sympathetic nervous system activity may be extremely important for the regulation of circular muscle contractions in the colon.

Adrenaline-synthesizing neurons in the medulla of the cat.

In this study, the distribution of neurons containing the adrenaline-synthesizing enzyme phenylethanolamine-N-methyltransferase (PNMT) was mapped in the medulla of the cat. Data from recent studies in the rat suggest that the anatomical structure responsible for cardiorespiratory changes that occur following application of neurotransmitters and drugs to Schlaefke's area on the ventral medullary surface is the nucleus reticularis rostroventrolateralis (RVL), which is distinguished from adjacent regions of the reticular formation, in part, by the presence of adrenaline-synthesizing neurons. To determine whether an equivalent adrenergic population is present in the RVL of the cat, we used antibodies raised against bovine adrenal PNMT to map the distribution of adrenaline-synthesizing neurons in the reticular formation. In the ventrolateral medulla, we found that labeled cells extended from the level of the retrofacial nucleus to the calamus scriptorius. The majority of labeled cells were seen in a nucleus designated RVL at the level of the rostral one-third of the inferior olive. In the dorsomedial medulla, cells were labeled in the caudal aspect of the nucleus tractus solitarii (NTS) and were especially dense in the subnucleus gelatinosus and commissural nucleus of the vagus. A few lightly labeled cells were also present in the rostral pole of the area postrema (AP). In contrast to the rat, few or no immunoreactive cells were found in the rostral NTS, medial longitudinal fasciculus, nucleus paragigantocellularis dorsalis, or periventricular gray. Our results are consistent with the notion that an area of the RVL containing adrenergic perikarya is the anatomical structure responsible for cardiovascular changes that occur when chemicals are applied to Schlaefke's area.

Cardiorespiratory effects produced by microinjecting L-glutamic acid into medullary nuclei associated with the ventral surface of the feline medulla.

The purpose of our study was to use microinjections of L-glutamic acid to better localize the cell bodies in the intermediate area of the ventral medullary surface that exert control over cardiorespiratory activity. L-glutamic acid (200 nl of a 1-M solution) was microinjected into the nucleus paragigantocellularis lateralis, lateral reticular nucleus and into an area which is part of the 'glycine-sensitive area', which lies in the center of the intermediate area. Normally, when L-glutamic acid is applied to the surface of the intermediate area, increases in arterial pressure and tidal volume are observed. Increases in tidal volume were never observed upon microinjection into the 3 sites associated with the intermediate area, suggesting that the tidal volume change elicited from surface application occurs because of L-glutamic acid interacting with cell bodies either on the surface or extremely close to the surface. Pressor responses were elicited with microinjection of L-glutamic acid into the lateral reticular nucleus and the 'glycine-sensitive area', but not the nucleus paragigantocellularis lateralis; indeed, microinjection of L-glutamic acid into the nucleus paragigantocellularis lateralis caused hypotension. Hence, cell bodies responsible for raising arterial pressure may reside in either the lateral reticular nucleus or the 'glycine-sensitive area'.

Effect of electrical and chemical stimulation of the raphe obscurus on phrenic nerve activity in the cat.

The effect of electrical and chemical (L-glutamate) stimulation of the raphe obscurus on phrenic nerve activity was examined in the cat. Phrenic nerve activity was recorded from a C5 nerve root in anesthetized, paralyzed and artificially ventilated cats. Neural discharge was quantitated by integrating the phrenic nerve activity. The respiratory frequency was determined from the integrated nerve signal. Focal electrical stimulation (18-144 microA; 5-40 Hz; 100 microseconds pulse duration) resulted in significant (P less than 0.05) increases in both integrated phrenic nerve (IPN) amplitude and respiratory frequency. These changes were dependent upon current intensity and frequency of stimulation. The largest increases in IPN amplitude and respiratory frequency were 47 +/- 17% and 146 +/- 8%, respectively. To insure that the changes in integrated phrenic nerve activity (IPNA) were the result of stimulation of cell bodies and not axons of passage, L-glutamate (100, 200 nmol) was microinjected (100 nl) into the raphe obscurus. Significant (P less than 0.05) dose-related changes occurred in integrated phrenic nerve amplitude with an increase of 44 +/- 13% at 100 nmol and 80 +/- 13% at 200 nmol L-glutamate. No significant increase in respiratory frequency was observed with L-glutamate microinjection. The results suggest that the raphe obscurus may be involved in respiratory control.

Localization of sites within dorsal motor nucleus of vagus that affect gastric motility.

The purpose of our study was to determine the localization of sites within the dorsal motor nucleus of the vagus (DMV) of the cat that when stimulated would increase gastric motility. To do this, two types of experiments were performed. First, the retrograde tracer fast blue was injected into the antrum and pylorus, and labeled neurons in the DMV were identified. Second, electrical stimulation was performed in areas of the DMV labeled with fast blue as well as in nearby areas with no labeling while monitoring gastric motility, arterial pressure, and heart rate. Results from the first type of studies revealed that peak labeling in the DMV occurred between 0.56 and 1.56 mm rostral to obex. Electrical stimulation in this area using 100 microA, 0.2 ms duration pulses, and 50 Hz resulted in increases in antral and pyloric contractions in 20 animals. The magnitude of pyloric and antral responses elicited by stimulation of the DMV generally correlated to the number of cell bodies labeled with fast blue within the DMV. No changes in arterial pressure occurred, and only a slight (-4%) decrease in heart rate was observed. Maximal increases in motility occurred with 20 Hz (antrum) or 100 Hz (pylorus). These increases in motility were maintained even at 200- and 400-Hz stimulation. Ipsilateral vagotomy or pretreatment with propantheline bromide prevented the increases in gastric motility produced by electrical stimulation of the DMV. Electrical stimulation of more rostral sites in the DMV, the medial nucleus of the solitary tract (NTS), and an area within 1.0 mm medial to the DMV resulted in attenuated or no motility responses. Stimulation of the medial nucleus of the NTS did result in pronounced slowing in heart rate (-61 +/- 21 beats/min). These results suggest that there is a localization of a "stomach area" within the DMV and that electrical stimulation of this area results in gastric motility responses that are mediated by vagal fibers projecting directly to the stomach. In addition, electrical stimulation of the DMV results in selective effects on the gastrointestinal tract in that no pronounced changes in heart rate and arterial pressure occur.

Use of horseradish peroxidase to identify hindbrain sites that influence gastric motility in the cat.

To identify hindbrain sites that influence gastric motility, we administered multiple injections of horseradish peroxidase into the anterior surface of the antrum near the lesser curvature in 3 cats, and used light microscopy to identify horseradish peroxidase-positive neurons in the hindbrain. Retrogradely labeled neurons were found evenly distributed on both sides in the dorsal motor nucleus of the vagus. Labeling extended from 2.5 mm rostral to 2.0 mm caudal to the obex. Labeled neurons were not localized to a specific region of the dorsal motor nucleus of the vagus: no labeling was observed in the nucleus ambiguus or in the nuclei of the solitary tract. Electrical stimulation of the dorsal motor nucleus of the vagus in the area with the greatest number of labeled cell bodies was performed in 4 cats while monitoring antral motility, arterial pressure, and heart rate. Stimulation elicited pronounced antral contractions but no changes in arterial pressure or heart rate. These data demonstrate that the retrograde neuronal tracing technique permits localization of central nervous system sites that specifically influence gastric function.

Evidence for 5-hydroxytryptamine, substance P, and thyrotropin-releasing hormone in neurons innervating the phrenic motor nucleus.

Retrograde tracing with a fluorescent dye (Fast Blue) combined with immunohistochemistry was used to identify putative neurotransmitter(s) at the phrenic motor nucleus in the cat. Fast Blue was injected bilaterally into the diaphragm of five cats, where each phrenic nerve enters the muscle. Seven days later the animals were perfusion fixed and tissue sections from the fourth, fifth, and sixth cervical spinal cord segments were analyzed using a fluorescence microscope. Retrogradely labeled fluorescent phrenic motor neuron cell bodies appeared in all of the segments but primarily in sections from the fifth segment. The same or adjacent transverse sections were then used for the demonstration of the distribution of the neurotransmitters 5-hydroxytryptamine (5-HT), substance P, and thyrotropin-releasing hormone (TRH) in the area of the phrenic motor nucleus using the indirect immunofluorescence technique. The most conspicuous neurotransmitters found at the phrenic motor nucleus were 5-HT and substance P. We observed dense and diffuse fiber networks throughout the ventral horn which contains the phrenic motor nucleus. These fibers contained varicosities in close proximity to phrenic motor neurons. In addition to 5-HT- and substance P-containing nerve endings, some fibers containing TRH were also found in the area of the phrenic motor nucleus. These results are consistent with earlier physiological data suggesting that 5-HT, substance P, and TRH are important neurotransmitters and/or neuromodulators involved in central control of respiration.

Central nervous system site of action of capsaicin-induced cardiovascular changes in the cat.

The purpose of our study was to identify the central nervous system site(s) of action of capsaicin responsible for producing changes in cardiovascular function. To do this, capsaicin was administered into several cerebroventricular regions of chloralose-anesthetized cats while monitoring arterial blood pressure and heart rate. Administration of capsaicin (1, 3, 10, 30, 100 and 300 micrograms) into the forebrain ventricles with restriction of the drug to these ventricles resulted in no significant changes in arterial pressure or heart rate. In contrast, administration of capsaicin into either the 4th ventricle or the cisterna magna resulted in significant increases in arterial pressure and heart rate. Intravenous administration of these doses produced no consistent effects on these indices of cardiovascular function. Bilateral application of capsaicin (3 ng/side) to a ventral medullary site, i.e., Schlaefke's area, known to be a sensitive site for drug-induced cardiovascular responses, resulted in striking increases in pressure and heart rate. Microinjection of this agent into the nucleus tractus solitarius, however, failed to evoke any changes in pressure and heart rate. These results indicate that the area on the ventral surface of the medulla is extraordinarily sensitive to capsaicin and may serve as the site of capsaicin-induced changes in cardiovascular function.

Effects of stimulation of nucleus ambiguus complex on gastroduodenal function.

We investigated the effects of stimulation of the nucleus ambiguus (NA) complex on gastroduodenal motility and gastric secretion in alpha-chloralose-anesthetized cats. Motility was measured by use of extraluminal force transducers sutured to the body, antrum, pylorus, and duodenum. Secretion was measured by determining changes in gastric pH, titratable acidity, and pepsinogen activity. Stimulation of the NA complex (right NA in 11 animals and left NA in 8 animals) elicited contractions of the antrum, pylorus, and duodenum, as well as sinus bradycardia and hypotension using stimulus parameters of 133 microA, 50 Hz, and 0.2-ms pulse duration. Both the motility and cardiovascular responses evoked by electrical stimulation of the NA complex were prevented by ipsilateral vagotomy. The optimum stimulus frequency for eliciting increases in gastroduodenal motility was 50 Hz. Frequencies higher than 50 Hz resulted in attenuated motility responses. This was not true of the heart rate response, as sinus bradycardia was maximal at 10 Hz and was maintained to 100 Hz. Electrical stimulation of the NA complex (8 animals) had no effect on pepsinogen secretion or titratable acidity, but produced a small (0.21 pH units) but significant increase in gastric pH. These results indicate that 1) stimulation of the NA complex results in pronounced increases in motility mediated by the ipsilateral vagus nerve, and 2) the pathways mediating these motility responses appear to involve more synapses than the pathways mediating the motor responses to the heart.