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Subcellular membrane fractions were isolated from the circular muscle of the corpus of canine stomach by differential and isopycnic sucrose density gradient centrifugation. Differential centrifugation gave a mitochondrial fraction enriched (fourfold) in cytochrome c oxidase and a microsomal fraction enriched (fourfold) in 5'-nucleotidase and NADPH-cytochrome c reductase over postnuclear supernatant. On the basis of a study using continuous gradient, a discontinuous sucrose density gradient was prepared to yield F1 to F5 fractions. The F3 fraction at the interface of 18-32% (w/w) sucrose was maximally enriched (13-fold) in 5'-nucleotidase. The fraction contained very low levels of cytochrome c oxidase but did contain NADPH-cytochrome c reductase (eightfold enrichment). The F4 fraction, at the interface of 32-40% (w/w) sucrose, was maximally enriched in NADPH-cytochrome c reductase (12-fold) and cytochrome c oxidase (6-fold). The distribution of the azide-insensitive. ATP-dependent Ca2+ uptake correlated very well with that of 5'-nucleotidase but less well with NADPH-cytochrome c reductase and not at all with cytochrome c oxidase. Sodium azide and ruthenium red inhibited the ATP-dependent Ca2+ uptake by the mitochondrial fraction and postnuclear supernatant, but not by the F3 fraction. ATP-dependent Ca2+ uptake by the F3 fraction was inhibited by calcium ionophores A23187 and ionomycin, but not by the sodium ionophore, monensin. These results are consistent with the hypothesis that the plasma membrane plays a major role ih regulating intracellular Ca2+ concentration in canine corpus circular muscle.

The effect of myosin light chain phosphorylation on the association of myosin with the cytoskeletal structures of platelets was quantitated. In unstimulated platelets, little myosin light chain was phosphorylated and myosin remained in solution when cytoskeletons from Triton X-100 lysates of platelets were sedimented by centrifugation. In platelets activated by thrombin, the calcium ionophore A23187, or collagen, the rate and extent of myosin light chain phosphorylation paralleled the association of myosin with platelet cytoskeletal structures. Dephosphorylation of myosin light chain and myosin dissociation from the cytoskeleton occurred at comparable rates at longer times after addition of the stimulating agents to platelets. Quantitation of radioactive phosphate in the cytoskeleton-associated myosin and in the soluble myosin showed that the phosphorylated myosin light chain was selectively isolated with the Triton-insoluble cytoskeletons, whereas nonphosphorylated myosin was not associated. Inhibition of the light chain kinase with the calmodulin antagonist trifluoperazine inhibited myosin light chain phosphorylation and incorporation of myosin into the platelet cytoskeletons. Inhibition of light chain phosphorylation by prostaglandin E1 and prostacyclin produced similar effects. Thus, phosphorylation of the myosin light chain stabilizes the association of myosin with the contractile structures within platelets.

The study was conducted to develop self-report measures of cognitive and somatic trait and state anxiety for children and to evaluate the utility of distinguishing between cognitive and somatic anxiety. Sixty-seven fourth grade children anticipated and then performed a mathematics task either in a high- or low-stress condition. While the children anticipated performing the task, measures of seven cognitive behaviors were obtained by means of both a think aloud procedure and a questionnaire. The results of the study indicated that reliable trait and state measures of cognitive and somatic anxiety were successfully developed. Further, the trait measures of cognitive and somatic anxiety were found to be relatively impervious to induced anxiety states. As expected, cognitive trait anxiety but not somatic trait or state anxiety was found to be related to task performance. High cognitive state and/or trait anxiety was found to be associated with more preoccupation and performance denigration as well as taking less of an analytic attitude toward the situation. Somatic trait and state anxiety were found to be associated with preoccupation. In general, the results support the construct validity of the measures developed and the utility of distinguishing between cognitive and somatic anxiety in children.

Glucose and water transport is depressed in the hamster jejunum in vivo by ethanol (4.8%) which also produced fluid-filled blebs at the tips of the villi. The epithelial cells over the blebs appeared stretched and cuboidal, the lateral intercellular spaces (LIS) were no longer recognizable, and the lacteals were closed. Forty-five minutes after discontinuation of the ethanol, water transport returned to normal while glucose transport remained depressed. At this time the villus structure had returned to normal. The blebs had disappeared, the LIS were again recognizable, and their appearance and number were similar to those in the control animals. Thus, the depression of water transport correlated with the obvious structural changes caused by ethanol; however, the depression of glucose absorption is associated with some effect of ethanol not evident by routine light microscopy.

The quiescent canine gastrointestinal tract responsed to close intraarterial acetylcholine with an atropine-sensitive, hexamethonium, and tetrodotoxin-insensitive contraction, thus suggesting acetylcholine interacts with a muscarinic receptor located on the muscle. When the gut is actively contracting (spontaneously, in response to field stimulation or to motilin), acetylcholine caused a contraction followed by prolonged inhibition of contractions. No such inhibition was apparent after tetrodotoxin; therefore, the receptor for acetylcholine-induced inhibition was apparently on nerves. Neither the acetylcholine-induced excitation nor the inhibition was altered by hexamethonium or reserpine treatment. Both inhibitory and excitatory responses were greatly reduced by atropine, suggesting that both receptors were muscarinic in nature. McNeil A343 produced inhibition but no excitation. Tetrodotoxin, hexamethonium, reserpine, and pirenzepine all increased the concentration of McNeil A343 required for production of 50% inhibition, suggesting it acts via multiple mechanisms. Furthermore, pirenzepine reduced both the inhibitory and excitatory response to acetylcholine, suggesting that it is nonselective in its action on the neural inhibitory or muscular excitatory receptors. We suggest that the presynaptic muscarinic receptor responsible for inhibitory effects of acetylcholine is on the postganglionic cholinergic neuron itself and constitutes an important negative-feedback loop to reduce excessive cholinergic output. Although such a mechanism has been found in vitro previously, this is the first report in vivo in canine small intestine.

The glycoprotein Ib.IX complex is a major component of the platelet membrane. It mediates the adhesion of platelets to exposed subendothelium and provides an attachment site for the membrane skeleton on the plasma membrane. The present study was designed to characterize the structure of the glycoprotein Ib.IX complex. Electron microscopy of purified glycoprotein Ib.IX complex in detergent showed that each complex existed as a flexible rod with a globular domain on either end. The overall length of the complex was approximately 59.5 nm. The smaller globular domain had a diameter of approximately 8.9 nm; the larger, a diameter of approximately 15.9 nm. In the absence of detergent, the glycoprotein Ib.IX complexes tended to self-associate through the larger globular domain, suggesting that this domain contained the hydrophobic region that inserts into the membrane. Proteases known to cleave glycoprotein Ib alpha close to its membrane-insertion site released the larger globular domain. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis showed that this domain was composed of glycoprotein Ib beta, glycoprotein IX, and a Mr = 25,000 fragment of glycoprotein Ib alpha. Proteolysis at the external end of glycoprotein Ib alpha reduced the size of the smaller globular domain. This study shows that the glycoprotein Ib.IX complex has an elongated shape, with a globular domain on the end that inserts into the membrane and a smaller globular domain on the end of glycoprotein Ib alpha that is oriented external to the plasma membrane.

EMGs have been performed on patients suffering from organic torticollis, hysterical torticollis and on normal control subjects. The EMG activity of the sternomastoid muscles during head rotation in control subjects and those with hysterical torticollis showed similar characteristics and neither group showed a response to body tilt. Subjects suffering from organic torticollis, however, did show a response to tilt. The results suggest that the response to backward tilt might aid in distinguishing the organic and hysterical forms of torticollis.

In order to study the morphological effects of exposure of the jejunum to low ethanol concentrations, we perfused hamster jejunum with 2.1-4.8% ethanol. Following 45 min exposure, many of the villi developed fluid-filled blisters. To compare these findings to the effect of an inert solute at similar concentrations, we perfused hamster jejuna with mannitol. This caused necrosis of the villus tips but no blister formation. Therefore the blisters were the result of the action of ethanol. The rat jejunum was less resistant to ethanol than that of the hamster. We suggest that the initial insult of the freely permeant ethanol is deep to the epithelium, resulting in accumulation of edema under the epithelium.

Close intraarterial injections of motilin to the small intestine of the anaesthetized dog produce prolonged phasic contractions. Tetrodotoxin infused intraarterially blocked field stimulated contractions and abolished the response to motilin as did treatment with a combination of hexamethonium and atropine. Atropine alone increased the dose of motilin required to induce responses. Hexamethonium alone similarly increased the dose of motilin required in the jejunum, but not for the ileum. These results suggest that motilin acts to contract small intestine by stimulation of intrinsic excitatory nerves, some of which are post-ganglionic cholinergic and some of which are not, but are activated by a pathway with a nicotinic synapse. The ED50 for ileal contractions was greater than that for the jejunum and the time to reach maximum contractions longer suggesting a decreased responsiveness of the lower small intestine to motilin as compared to the upper gastrointestinal tract. These results and the lesser quantity of immunoreactive motilin in the ileum than in the jejunum may explain the lack of relationship of the activity front of the migrating motor complex in the lower small intestine to venous motilin concentrations.

Ouabain-sensitive Rb+ uptake and [3H]ouabain binding were used to measure rates of Na+ pumping and the number of pump sites, respectively, in thoracic aortae from opossums. From the number of Rb+ ions pumped per site per minute, estimates of pump turnover have been made. Values obtained are comparable to those of other species (see Table 1).

The structural relationship of nerve, muscle, and interstitial cells of Cajal in circular muscle of the lesser curvature of the dog stomach (corpus) has been studied. This muscle has also been characterized functionally. Muscle cells are arranged in bundles and are interconnected by numerous gap junctions averaging 30 per 100 cross-sectioned muscle cells, and leading to an estimate that each cell has about 200 gap junctions. No other smooth muscle studied to date has such a high density of gap junctions. Nerve varicosities, mostly containing a predominance of small agranular vesicles with some containing a predominance of large granular vesicles, are located outside muscle bundles, usually in small- to medium-sized bundles. Very few nerves containing small granular vesicles, presumably adrenergic, were found in agreement with functional studies. A substantial number of damaged nerve profiles was also found, perhaps contributing to the loss of nerve-dependent responses present in vivo, but absent in vitro. Interstitial cells of Cajal were rare in this tissue, about 1 per 1000 cross-sectioned muscle cells. When present, they often made gap junction contact with smooth muscle and were closely innervated. The findings of a structural basis for very tight coupling between cells, the absence of a structural basis for direct neural control over motor function, and other findings have implications for the control of contractions in this muscle.

The relationship of immunoreactive (IR) motilin release from the duodenum to duodenal motility changes was investigated in anaesthetized dogs. Stimulation of one or both vagi at 5 or 15 Hz or field stimulation of intrinsic duodenal nerves produced significant increases in duodenal vein IR motilin concentrations and accompanying increases in duodenal motility. However, only stimulation of both vagi at 15 Hz produced significant changes in peripheral venous concentrations of IR motilin. These occurred after a delay at a time when both the duodenum and the antrum were quiescent. Either hexamethonium or atropine blocked IR motilin release induced by stimulation of intrinsic or extrinsic nerves while only atropine inhibited the release induced by intraarterial carbachol. The response stimulated by carbachol and blocked by atropine was tetrodotoxin insensitive and the muscarinic receptor involved was presumably located on a nonneural structure. The site sensitive to hexamethonium was presumably the neural pathway which terminated at the muscarinic receptor. Concomitant studies of duodenal motility responses to vagal and field stimulation suggested a conventional neural pathway with preganglionic cholinergic nerves in the vagus, postganglionic cholinergic nerves in the duodenum (activated by field stimulation) and a smooth muscle muscarinic receptor. Activation of antral motility by stimulation of the abdominal vagus or intraarterial carbachol injections to the antrum increased duodenal IR motilin release in the absence of duodenal motility. Thus activation of the intrinsic nerves which cross the pylorus initiated IR motilin release as well as inhibited duodenal motility.(ABSTRACT TRUNCATED AT 250 WORDS)

Integrated EMG recordings have been used to study the eyeblink component of the human startle reflex. They have shown that the response, to either an auditory or a painful stimulus, consists of an initial excitation followed by a more prolonged period during which a second stimulus, of the same or different sensory modality, fails to evoke a response, or evokes one which is reduced in amplitude. The period of reduced responsiveness does not follow voluntary or spontaneous eyeblinks. Increasing the duration of the startle evoking stimulus has little effect on the excitatory component of the response, but prolongs the subsequent period of reduced responsiveness. When stimuli of one modality are presented repetitively to the subject, the eyeblink response is habituated; the response to a subsequent testing stimulus, of a different sensory modality, is then smaller than that evoked by the testing stimulus alone, but greater than that evoked by the testing stimulus when it follows a single conditioning stimulus. It is concluded that the excitatory and inhibitory components of the startle reflex are at least partially separable and that stimulus novelty has some significance in eliciting a response.

This study evaluates the structural organization of the cytoskeleton within unactivated, discoid platelets. Previously, such studies have been difficult to interpret because of the ease with which platelets are stimulated, the sensitivity of actin filaments to cell extraction buffers, and the general problem of preserving actin filaments with conventional fixatives, compounded by the density of the cytoplasm in the platelet. In this study we have employed a new fixative containing lysine, which protects actin filaments against damage during fixation and thin-section processing. We used thick (0.25-micron) sections and conventional thin sections of extracted cells (fixed and lysed simultaneously by the addition of 1% Triton X-100 to the initial fixative) as well as thin sections of whole cells to examine three preparations of human platelets: discoid platelets washed by sedimentation; discoid platelets isolated by gel filtration; and circulating platelets collected by dripping blood directly from a vein into fixative. In all of these preparations, long, interwoven actin filaments were observed within the platelet and were particularly concentrated beneath the plasma membrane. These filaments appeared to be linked at irregular intervals to the membrane and to each other via short, approximately 20- to 50-nm-long cross-links of variable width. Although most filaments were outside the circumferential band of microtubules and the cisternae of the open canalicular system, individual filaments dipped down into the cytoplasm and were found between the microtubules and in association with other membranes. The ease with which single actin filaments can be seen in the dense cytoplasm of the human platelet after lysine/aldehyde fixation suggests the great potential of this new fixative for other cells.

Motilin, pentagastrin and substance P (SP), injected intra-arterially into the canine gastric corpus in vivo increased the amplitude of contractions by an action dependent on activation of cholinergic nerves; i.e. atropine or tetrodotoxin (TTX) completely blocked the responses to motilin and pentagastrin and increased the ED50 of SP. TTX and atropine were not equally effective in increasing the ED50 for SP in vivo and the effect of combining them depended on the order of their addition. Both were much more effective than the SP analog D-Pro2, D-Trp7,9 SP (DSP) which appeared to be a weak antagonist of actions dependent on neural activity. In strips from the same region in vitro no receptors dependent on cholinergic nerve activation could be demonstrated for any peptide; i.e., all were atropine- and TTX-insensitive. Motilin, as expected in the absence of such receptors caused no contractile response in vitro. SP, also as predicted, caused contractions suggesting that a smooth muscle receptor, independent of nerve activation was present. However contrary to expectation pentagastrin induced an atropine and TTX-insensitive increase in the amplitude and frequency of contractions. These results show that 1) the most sensitive sites of action of a number of excitatory peptides depend on cholinergic nerve function in vivo; 2) such sites or the nerve activity on which they depend cannot be demonstrated in vitro; 3) SP has an additional site of action on smooth muscle demonstrable in vivo and in vitro, but motilin does not; 4) pentagastrin has only an action dependent on nerve function in vivo, but manifests an action independent of nerve function in vitro. We conclude that sites and mechanisms of action of peptides cannot be assumed to be identical in vivo and in vitro. Actions dependent on nerves are often lost in vitro and not all smooth muscle actions can be demonstrated in vivo.

Contractions of canine pylorus and adjacent muscles were recorded with antral and duodenal strain gauges and a Dent sleeve manometric assembly with additional side holes in the pylorus. In vivo, vasoactive intestinal polypeptide (VIP) and peptide histamine isoleucine (PHI) given through the gastroepiploic artery inhibited both spontaneous and acetylcholine-induced pyloric contractions, before and after neural blockade with tetrodotoxin. Galanin inhibited only nerve-stimulated contractions. VIP greater than PHI much greater than galanin inhibited pyloric motor activity initiated by field stimulation of duodenal intramural nerves or intraduodenal infusion of 0.1 N HCl. In vitro, forskolin or field stimulation of nerves inhibited contractions of the pyloric muscle induced by various agonists but VIP-PHI failed to inhibit these contractions on two-thirds of the strips. The in vivo results suggest that VIP (or PHI) may be an inhibitory mediator in the pylorus acting directly on smooth muscle. Galanin may inhibit neural excitatory pathways in the pylorus. However, the structures on which VIP and PHI act in vivo may have become nonfunctional in vitro and other mediators account for the neural inhibition observed in isolated strips.

Twenty Holstein steers subclinically infected with coccidia were allotted to 2 groups of 10 steers each. One group received a diet containing 0.5 mg of decoquinate/kg of body weight. After 25 days on the diet, there was no difference between the groups in lymphocyte blastogenic responsiveness to mitogens; however, there were differences in neutrophil function. Lymphocytes from steers of the decoquinate-fed group had decreased random migration under agarose, enhanced cytochrome C reduction, and enhanced iodination activity. Other measures of neutrophil function evaluated (chemotactic index, Staphylococcus aureus ingestion, and antibody-dependent and -independent cell-mediated cytotoxicity) were not affected. After 30 days of decoquinate feeding, half of the cattle in each group received 5 daily IM injections of dexamethasone (0.04 mg/kg of body weight). The dexamethasone-treated steers from the group that did not have decoquinate in the diet developed clinical coccidiosis, whereas the decoquinate-treated steers remained clinically normal. Lymphocyte and neutrophil function were again evaluated for a 3-day period beginning 4 days after dexamethasone treatment was halted. Neutrophils from the steers that developed clinical coccidiosis after dexamethasone administration had significantly (P less than 0.05) inhibited random migration under agarose, cytochrome C reduction, and iodination activity, but significantly (P less than 0.01) enhanced S aureus ingestion. The feeding of decoquinate prevented the inhibition of neutrophil cytochrome C reduction and lessened the inhibition of neutrophil iodination in the dexamethasone-treated group. Dexamethasone treatment was associated with an inhibition of lymphocyte blastogenic responsiveness to phytohemagglutinin in principals as well as controls.

Inhibition of adenylate cyclase in intact platelets by addition of compounds such as 2', 5' - dideoxyadenosine prevented the inhibition of platelet aggregation by PGE1 but did not affect the responses of platelets to aggregating agents in the absence of PGE1. This confirms that cyclic AMP mediates the effects of PGE1 but indicates that the level of cyclic AMP in unstimulated platelets is too low to affect the actions of aggregating agents. Studies on the phosphorylation of proteins in intact 32P-labelled platelets showed that PGE1 increased the phosphorylation of a membrane-bound polypeptide (P24) and prevented the increased phosphorylation of other polypeptides (P47 and P20) that occurred on addition of inducers of the release reaction. It is suggested that the cyclic AMP-dependent phosphorylation of P24 stimulates the active transport of Ca(2+) out of the platelet cytosol, so preventing phosphorylation of P47 and P20, reactions which may be involved in the release mechanism. As increases in platelet cyclic GMP could be dissociated from both platelet aggregation and the release reaction, it is proposed that the bidirectional regulation of platelet function is achieved primarily by the opposing actions of increases in the concentrations of Ca(2+) and cyclic AMP.

A 34-week stillborn infant had omphalocele, agenesis of the sternum and anterior rib cage, membranous diaphragms with eventration of the viscera, ectopia cordis with absence of the pericardium, and congenital heart defect. These findings are consistent with a diagnosis of Cantrell pentalogy. The presence of bilateral clubfeet, spina bifida, hydrocephalus, abnormal ears, and horseshoe kidneys suggested a chromosome abnormality. Chromosome analysis showed trisomy 18. Individuals with manifestations of Cantrell pentalogy deserve cytogenetic evaluation.

Decoquinate (Deccox: Hess & Clark) has been demonstrated in in-house and university studies to be an active coccidiostat when fed daily at 0.5 mg/kg body weight during periods of oocyst exposure, or when experience indicates coccidiosis is likely to be a hazard. For prevention, feeding should be continued for at least 28 days. In 6 feedlot trials with 1993 cattle in 5 geographic areas, decoquinate fed at this level for 90-120 days had no adverse effects. In 5 of these trials, treated cattle had equal or slightly improved average daily gains and feed conversion by comparison with controls.

In opossum esophagus the highest density of varicose substance P-like immunoreactive deposits was in the muscularis mucosa, and this muscle layer, which is thick and prominent, was the most sensitive in contracting to exogenous substance P. On field stimulation, a tetrodotoxin-sensitive biphasic contraction was produced; an initial phasic component was followed after cessation of stimulation by a prolonged tonic component. This contractile response was unaffected by guanethidine or antagonists to several nerve mediators and to histamine and serotonin antagonists. Each component showed a different frequency dependence. The phasic component was abolished by atropine and potentiated by physostigmine; the tonic component was reduced or abolished after carbachol or physostigmine and potentiated by atropine. The tonic component was inhibited after substance P tachyphylaxis or by the substance P antagonist [D-Pro2, D-Trp7,9]substance P. On electron microscopic examination, the majority of nerve varicosities contained a mixture of small agranular and large granular vesicles. We postulate that acetylcholine and substance P may coexist in and be coreleased from nerves of this muscle and that the acetylcholine release occurs first, causing an initial phasic response and delaying and diminishing the release of substance P. The two mediators cause muscle contraction by actions on independent receptors.

We have utilized the Southern blotting technique to analyse genomic DNA from males with ornithine transcarbamylase (OTC) deficiency and their families. Using a nearly full-length human cDNA probe, we have identified 3 patients with deletions at this locus and have characterized 4 different restriction fragment length polymorphisms that can be used as linkage markers for the OTC mutation. These polymorphisms occur at sufficiently high frequencies so as to enable us to distinguish the two X-chromosomes in approximately 80% of OTC carriers. As a direct consequence of these findings, prenatal diagnosis and carrier assessment can be offered to a large fraction of families at risk for OTC deficiency.

Basal release of vasoactive intestinal polypeptide (VIP) was 100-fold higher than substance P (SP) release from the vascularly perfused, neurally isolated canine small intestine. High-frequency field stimulation increased SP release but decreased VIP release. VIP release was markedly reduced by tetrodotoxin, perfusion with Ca-free medium, or by hexamethonium but not by atropine. Acetylcholine increased VIP output by an atropine-sensitive mechanism. Methionine-enkephalin or dynorphin (at 10-fold higher concentrations) markedly reduced VIP output; the actions of both these were abolished by naloxone. BHT-920, an alpha 2-adrenoceptor agonist, reduced VIP output markedly by a rauwolscine-sensitive mechanism. Isoproterenol and phenylephrine were without effect. Motilin produced persistent inhibition of VIP output. Thus VIP neurons of isolated canine small intestine were continuously active, driven by intrinsic cholinergic nerves, and subject to presynaptic inhibition by opioid agonists, alpha 2-adrenoceptor agonists, and motilin. This intrinsic neural system may provide tonic inhibitory control to the small intestinal circular muscle and provide a mechanism by which agents may modulate intestinal motor function.

The distribution of nerves containing galanin-immunoreactive (GAL-IR) material was compared to the distribution of neurons containing vasoactive intestinal polypeptide (VIP) immunoreactivity in the canine gastrointestinal tract. The actions of intra-arterially administered galanin and VIP on motility in the gastric antrum and corpus and the intestines were also studied. All sphincter muscles contained galanin- and VIP-immunoreactive nerve profiles. VIP-immunoreactive nerve profiles were present in all layers of the stomach, small intestine, and colon. GAL-IR nerve somata were common in the submucous plexus of ileum and colon and in the myenteric plexus of the terminal antrum, as were nerve processes in various layers. In the small intestine, galanin inhibited contractile responses to field stimulation of intrinsic nerves and also reduced the contractions after nerve blockade with tetrodotoxin (TTX). VIP often enhanced field-stimulated contractions at low doses but inhibited these and the contractions after TTX at higher doses. In the stomach and colon, both peptides inhibited responses to field stimulation; whether these effects were due to actions on smooth muscle was not tested. The distribution and actions of galanin in gut are consistent with the hypothesis that it acts at smooth muscle sites and possibly at prejunctional sites.

The responses of the circular muscle of canine colon to stimulation of intrinsic nerves and to the probable mediators of these nerves were studied in vivo. In vivo studies were carried out using close intra-arterial injections and local field stimulation of proximal, mid-, and distal colon while recording circumferential contractions. Our results suggest that acetylcholine is the major excitatory mediator, but another excitatory mediator could be released by high frequency field stimulation after atropine. Norepinephrine had mixed inhibitory and excitatory effects, but no evidence was obtained that it was released by field stimulation. Substance P had mainly excitatory effects partly by a mechanism involving nerves and partly by a direct effect on muscle; it in addition to norepinephrine deserves further evaluation as the mediator of noncholinergic excitation to high frequency field stimulation. There is no explanation of the inhibition it produced after initial excitation during field stimulation. Vasoactive intestinal peptide had inhibitory effects but these were incomplete and inconsistent. This may be related to our inability to demonstrate relaxation or inhibition to field stimulation after atropine. Further evaluation of the possible role of vasoactive intestinal peptide and other agents as nonadrenergic, noncholinergic inhibitory mediators is required.