Dijet imbalance measurements in Au+Au and pp collisions at sqrt[s_{NN}]=200 GeV at STAR

We report the first dijet transverse momentum asymmetry measurements from Au+Au and pp collisions at RHIC. The two highest-energy back-to-back jets reconstructed from fragments with transverse momenta above 2  GeV/c display a significantly higher momentum imbalance in heavy-ion collisions than in the pp reference. When reexamined with correlated soft particles included, we observe that these dijets then exhibit a unique new feature-momentum balance is restored to that observed in pp for a jet resolution parameter of R=0.4, while rebalancing is not attained with a smaller value of R=0.2.

Charge-Dependent Directed Flow in Cu+Au Collisions at sqrt[s_{NN}]=200 GeV

We present the first measurement of charge-dependent directed flow in Cu+Au collisions at sqrt[s_{NN}]=200  GeV. The results are presented as a function of the particle transverse momentum and pseudorapidity for different centralities. A finite difference between the directed flow of positive and negative charged particles is observed that qualitatively agrees with the expectations from the effects of the initial strong electric field between two colliding ions with different nuclear charges. The measured difference in directed flow is much smaller than that obtained from the parton-hadron-string-dynamics model, which suggests that most of the electric charges, i.e., quarks and antiquarks, have not yet been created during the lifetime of the strong electric field, which is of the order of, or less than, 1  fm/c.

Beam Energy Dependence of the Third Harmonic of Azimuthal Correlations in Au+Au Collisions at RHIC

We present results from a harmonic decomposition of two-particle azimuthal correlations measured with the STAR detector in Au+Au collisions for energies ranging from sqrt[s_{NN}]=7.7 to 200 GeV. The third harmonic v_{3}^{2}{2}=⟨cos3(ϕ_{1}-ϕ_{2})⟩, where ϕ_{1}-ϕ_{2} is the angular difference in azimuth, is studied as a function of the pseudorapidity difference between particle pairs Δη=η_{1}-η_{2}. Nonzero v_{3}^{2}{2} is directly related to the previously observed large-Δη narrow-Δϕ ridge correlations and has been shown in models to be sensitive to the existence of a low viscosity quark gluon plasma phase. For sufficiently central collisions, v_{3}^{2}{2} persist down to an energy of 7.7 GeV, suggesting that quark gluon plasma may be created even in these low energy collisions. In peripheral collisions at these low energies, however, v_{3}^{2}{2} is consistent with zero. When scaled by the pseudorapidity density of charged-particle multiplicity per participating nucleon pair, v_{3}^{2}{2} for central collisions shows a minimum near sqrt[s_{NN}]=20  GeV.

The effects of methylnaltrexone alone and in combination with acutely administered codeine on gastrointestinal and colonic transit in health

BACKGROUND

The short-term effects of methylnaltrexone (MNTX), a peripherally acting mu-opioid receptor antagonist, on gastrointestinal and colonic transit remain unclear.

AIM

To compare the effects of placebo, codeine, subcutaneous (s.c.) MNTX and codeine with s.c. MNTX on gastrointestinal and colonic transit of solids in healthy humans.

METHODS

In a randomized, parallel-group, double-blind, placebo-controlled trial of 48 healthy volunteers, effects of 6 consecutive days of placebo [s.c. and p.o. (orally), n = 8], codeine (p.o. 30 mg q.d.s., n = 8), MNTX (s.c. 0.30 mg/kg, n = 16) and combined MNTX and codeine (same doses and routes, n = 16) on gastrointestinal and colonic transit were assessed. A validated scintigraphic method was used to measure transit during the last 48 h of treatment. Bowel function was estimated during treatment as well as 1 week preceding treatment using standard diaries. Analysis of covariance was used to assess treatment effects.

RESULTS

Codeine delayed colonic transit [geometric centre at 24 h (P = 0.04) and ascending colon t(1/2) (P = 0.02)] and reduced stool frequency (P = 0.002), but had no effect on stool form. MNTX did not affect transit, stool frequency or stool form, either alone or with codeine (P > 0.3). No drug interaction effects were detected (P > 0.15).

CONCLUSION

Methylnaltrexone does not alter gastrointestinal or colonic transit and does not reverse acute codeine-associated delayed gut transit in health.

Pharmacogenetics of low dose clonidine in irritable bowel syndrome

Adrenergic and serotonergic (ADR-SER) mechanisms alter gut (gastrointestinal, GI) sensorimotor functions. We aimed to determine whether candidate ADR-SER genes affect GI responses to low dose clonidine (CLO) in humans. Forty healthy and 120 irritable bowel syndrome (IBS) participants received CLO, 0.1 mg or 0.15 mg b.i.d., for 6 days. At baseline and post-CLO, we measured: gastric volume (GV); satiation volume; rectal compliance, sensation thresholds and ratings with distensions. Genetic variations tested were: alpha2A (C-1291G), alpha2C (Del 322-325), GNbeta3 (C825T) and solute carrier family 6 (neurotransmitter transporter, serotonin), member 4 (SLC6A4) (serotonin transporter linked polymorphic region). CLO reduced volume to satiation (P = 0.002), postprandial GV (P < 0.001), sensation threshold for pain (<0.001); CLO increased rectal compliance (P = 0.024). There were significant associations between post-CLO responses and gene variations for DeltaGV (alpha2A and SLC6A4), rectal sensation of gas (alpha2A, GNbeta3), urgency (alpha2A); and pain (GNbeta3 and SLC6A4); and rectal compliance (SLC6A4). alpha2A, GNbeta3 and SLC6A4 genotypes significantly modify responses to CLO on sensory and motor GI functions in health and IBS.

Does co-administration of a non-selective opiate antagonist enhance acceleration of transit by a 5-HT4 agonist in constipation-predominant irritable bowel syndrome? A randomized controlled trial

Opioid neurons exhibit tonic restraint on intestinal motility; opioid antagonists stimulate peristalsis and increase transit. In vitro, 5-hydroxytryptamine (5-HT4) agonists combined with selective opioid antagonists significantly increased colonic propulsion relative to a 5-HT4 agonist alone. We hypothesized that the combination of 5-HT4 agonist and non-selective opioid antagonist enhances intestinal transit more than either treatment alone in female constipation-predominant irritable bowel syndrome (C-IBS) patients. Our aim was to examine the effect of tegaserod 6 mg b.i.d. alone and combined with naltrexone 50 mg on intestinal transit and stool characteristics in females with C-IBS. Forty-eight patients were randomized to tegaserod alone, naltrexone alone or in combination with tegaserod or placebo for 6 days. Small bowel, ascending colon half-life (in pharmacokinetics) (t1/2), and colonic geometric centre (8, 24, 48 h) were assessed by scintigraphy. Tegaserod increased small bowel (P < 0.01) and colon transit (P < 0.01). Naltrexone did not accelerate colonic transit relative to placebo. Combination treatment did not significantly accelerate transit relative to tegaserod alone. Tegaserod and tegaserod with naltrexone resulted in looser stool form (P < 0.01). In female C-IBS patients, tegaserod accelerates small bowel and colon transit and contributed to looser stool consistency. Use of naltrexone, 50 mg, does not support the hypothesis that combination of 5-HT4 agonist and non-selective opioid antagonist enhances intestinal transit.

Pharmacodynamic effects of a novel prokinetic 5-HT receptor agonist, ATI-7505, in humans

ATI-7505, an investigational 5-HT(4) receptor agonist, was designed to have similar activity as cisapride without the cardiac adverse effects, i.e. without QT prolongation. In addition, ATI-7505 is not metabolized by CYP450. The aim of the study was to assess the effect of ATI-7505 on gastrointestinal (GI) and colonic transit in healthy humans. A randomized, parallel-group, double-blind, placebo-controlled study evaluated effects of 9-day treatment with ATI-7505 (3, 10 or 20 mg t.i.d.) on scintigraphic GI and colonic transit in healthy volunteers (12 per group). Primary endpoints were gastric-emptying (GE) T(1/2), colonic geometric centre (GC) at 24 h and ascending colon (AC) emptying T(1/2). Daily stool diaries were kept. Analysis of covariance assessed overall treatment group differences, followed by post hoc unadjusted pairwise comparisons. There were borderline overall treatment effects (decrease) on GE T(1/2) (P = 0.154); the 20 mg t.i.d. of ATI-7505-accelerated GE vs placebo (P = 0.038). ATI-7505 increased colonic transit (GC24, P = 0.031) with fastest transit at 10 mg t.i.d. vs placebo (P = 0.065). ATI-7505 accelerated AC emptying T(1/2) (overall P = 0.075) with 10 mg dose vs placebo (P = 0.042). There was looser stool (Bristol stool form scale, overall P = 0.056) with the 10 and 20 mg t.i.d. doses. No safety issues were identified. ATI-7505 accelerates overall colonic transit and tends to accelerate GE and AC emptying and loosen stool consistency.

Association of distinct alpha(2) adrenoceptor and serotonin transporter polymorphisms with constipation and somatic symptoms in functional gastrointestinal disorders

BACKGROUND

The role of genetics in the phenotypic manifestations of irritable bowel syndrome (IBS) is unclear. Our aims were: (1) to compare the prevalence of polymorphisms of alpha 2 (alpha(2)) adrenoceptors, norepinephrine transporter, and serotonin transporter protein (soluble carrier protein member 4 (SLC6A4)) promoter in patients with lower functional gastrointestinal disorders (FGID) and in healthy controls; and (2) to test associations of these genetic variations with symptoms of IBS and high somatic symptom scores.

METHODS

Validated bowel and somatic symptom questionnaires characterised the phenotype: 90 with IBS constipation (IBS-C), 128 IBS diarrhoea, 38 IBS alternating bowel function, and 20 chronic abdominal pain. Logistic regression analyses assessed associations of different polymorphisms for alpha(2) adrenoceptor and SLC6A4 with IBS or chronic abdominal pain phenotypes and high somatic score.

RESULTS

Two distinct polymorphisms independently appeared to be associated with the phenotype IBS-C: alpha(2C) Del 322-325 (odds ratio (OR) 2.48 (95% confidence interval (CI) 0.98, 6.28); p = 0.05) and alpha(2A) -1291 (C-->G) (OR 1.66 (95% CI 0.94, 2.92); p = 0.08) relative to wild-type. Overall, the alpha(2C) Del 322-325 polymorphism (alone or combined with other polymorphisms) was also significantly associated with a high somatic symptom score (OR 2.2 (95% CI 1.06, 4.64); p = 0.03). Combinations of polymorphisms were also associated with high somatic scores.

CONCLUSION

Functionally distinct alpha(2A) and alpha(2C) adrenoceptor and serotonin transporter polymorphisms are associated with constipation and high somatic symptoms in patients with lower functional gastrointestinal disorders, although the strength of the genetic contribution to the phenotype is unclear.

Effects of asimadoline, a kappa-opioid agonist, on satiation and postprandial symptoms in health

AIM

To evaluate the effect of single administrations of asimadoline, a kappa-opioid agonist, on satiation volume, postprandial symptoms and gastric volumes.

METHODS

Healthy subjects received oral placebo, or 0.5 or 1.5 mg asimadoline in a randomized, double-blind fashion 1 h prior to testing. We assessed effects on the volume of Ensure to achieve full satiation and postprandial symptoms 30 min after meal, and on gastric volume (fasting and postprandial) measured by 99mTc-single photon emission tomography (SPECT) imaging.

RESULTS

Thirteen healthy subjects were studied in each treatment arm. Compared to placebo, asimadoline 0.5 mg decreased postprandial fullness (P = 0.027) without affecting the volume ingested at full satiation (P = 0.6). Asimadoline 1.5 mg decreased satiation during meal, allowing increased satiation volumes (P = 0.008) and tended to decrease postprandial fullness (P = 0.067), despite higher volumes ingested. There was a significant treatment-gender interaction in the effect of asimadoline on gastric volumes (P < 0.05). Asimadoline 0.5 mg (not 1.5 mg) increased fasting (P = 0.047) and postprandial (P = 0.009) gastric volumes in females but decreased fasting volumes in males (P = 0.008). The effect of asimadoline on gastric volume did not explain the effect observed on satiation volume (P = 0.371) or postprandial fullness (P = 0.399).

CONCLUSION

A single oral administration of asimadoline decreases satiation and postprandial fullness in humans independently of its effects on gastric volume.

A randomized controlled trial of a probiotic, VSL#3, on gut transit and symptoms in diarrhoea-predominant irritable bowel syndrome

AIM

To investigate the effects of a probiotic formulation, VSL#3, on gastrointestinal transit and symptoms of patients with Rome II irritable bowel syndrome with predominant diarrhoea.

METHODS

Twenty-five patients with diarrhoea-predominant irritable bowel syndrome were randomly assigned to receive VSL#3 powder (450 billion lyophilized bacteria/day) or matching placebo twice daily for 8 weeks after a 2-week run-in period. Pre- and post-treatment gastrointestinal transit measurements were performed in all patients. Patients recorded their bowel function and symptoms daily in a diary during the 10-week study, which was powered to detect a 50% change in the primary colonic transit end-point.

RESULTS

There were no significant differences in mean gastrointestinal transit measurements, bowel function scores or satisfactory global symptom relief between the two treatment groups, pre- or post-therapy. Differences in abdominal bloating scores between treatments were borderline significant (P = 0.09, analysis of covariance). Further analysis revealed that abdominal bloating was reduced (P = 0.046) with VSL#3 [mean post- minus pre-treatment score, - 13.7; 95% confidence interval (CI), - 2.5 to - 24.9], but not with placebo (P = 0.54) (mean post- minus pre-treatment score, - 1.7; 95% CI, 7.1 to - 10.4). With the exception of changes in abdominal bloating, VSL#3 had no effect on other individual symptoms: abdominal pain, gas and urgency. All patients tolerated VSL#3 well.

CONCLUSION

VSL#3 appears to be promising in the relief of abdominal bloating in patients with diarrhoea-predominant irritable bowel syndrome. This is unrelated to an alteration in gastrointestinal or colonic transit.

Effects of 5-HT(3) antagonism on postprandial gastric volume and symptoms in humans

BACKGROUND

Alosetron reduces symptoms of dyspepsia, but the physiological basis for the symptomatic benefit is unclear.

AIM

To assess 5-HT3 antagonism on postprandial gastric volume and symptoms after ingestion of maximum tolerable volume of a liquid meal.

METHODS

In 36 healthy volunteers, we assessed effects of placebo, 0.5 and 1 mg b.d. alosetron on fasting and postprandial gastric volumes (using single photon emission computed tomography) and symptoms based on 100 mm VAS, 30 min after maximum volume ingested.

RESULTS

The 5-HT3 antagonist reduced postprandial symptoms (aggregate score: P < 0.05), nausea (P < 0.001), and tended to reduce bloating (P=0.08). Both 0.5 and 1 mg alosetron reduced nausea (P < 0.025); 1 mg alosetron reduced aggregate symptoms (P < 0.05) and bloating (P < 0.05). Effects on pain (P=0.19) and fullness (P=0.14) were not statistically significant. There were no significant effects of the 5-HT3 antagonist on volume of meal tolerated or on SPECT-measured fasting or postprandial gastric volumes.

CONCLUSION

5-HT3 antagonism reduces aggregate symptoms, nausea and bloating after a liquid meal without increase in gastric volumes, suggesting a role for 5-HT3 in afferent functions in healthy humans during the postprandial period.

Effects of an alpha(2)-adrenergic agonist on gastrointestinal transit, colonic motility, and sensation in humans

To characterize alpha(2)-adrenergic control of motor and sensory functions of gastrointestinal tract and colon, we studied dose-related effects of clonidine (placebo or up to 0.3 mg po) by random assignment in 55 healthy humans. Gastrointestinal transit was measured in all subjects; in 35, we assessed colonic compliance, tone, and sensations of gas and pain during phasic distensions. Clonidine did not significantly alter gastrointestinal or colonic transit, but it increased colonic compliance and reduced fasting tone without altering colonic response to a meal. Clonidine significantly reduced aggregate sensation to distensions overall and had significant linear dose-related sensory effects at 8- and 24-mmHg distensions. Effect on pain (including dose-response relationship) was due to 0.3-mg dose for distensions at 24 mmHg. We confirmed that clonidine relaxes fasting colonic tone and reduces sensation of pain. In this study, gut transit was not altered by clonidine, and novel dose-response characteristics and clonidine's effect on gas sensation are provided. Doses as low as 0.05 mg may be effective and potentially useful in reducing colonic tone and gas sensation.

Gender-related differences in slowing colonic transit by a 5-HT3 antagonist in subjects with diarrhea-predominant irritable bowel syndrome

OBJECTIVE

To evaluate the influence of gender on the effect of a 5-HT3 antagonist, alosetron, 1 mg b.i.d., on GI and colonic transit in D-IBS.

METHODS

Thirty patients (15 male, 15 female) with D-IBS received 1 mg b.i.d. alosetron for 6 wk. Transit was measured by scintigraphy at baseline and at the end of treatment.

RESULTS

Alosetron, 1 mg b.i.d., significantly retarded small bowel and, proximal and overall colonic transit in the 30 patients with D-IBS. The effect of alosetron on the primary endpoint, colonic geometric center at 24 h, was significantly greater in females than in males (p < 0.05). However, two females showed no slowing of colonic transit on treatment. Among male patients, two of 15 had a slowing of colonic transit at 24 h that was greater than the mean change in female patients, suggesting responsiveness to alosetron among a subgroup of males.

CONCLUSION

A 5-HT3 antagonist, alosetron, significantly retards small intestinal and colonic transit in diarrhea-predominant IBS patients, with significantly greater female to male responsiveness. Gender partly contributes to differences in the serotonergic control of intestinal and colonic transit in patients with D-IBS.

Prucalopride accelerates gastrointestinal and colonic transit in patients with constipation without a rectal evacuation disorder

BACKGROUND & AIMS

Prucalopride (PRU) is a selective benzofuran 5-hydroxytryptamine(4)-receptor agonist with gastrointestinal and colonic prokinetic activities. We evaluated the effects of PRU on gastrointestinal and colonic transit in patients with constipation.

METHODS

Gastrointestinal and colonic transit were measured over 48 hours in 40 patients who fulfilled modified Rome I criteria for functional constipation. Patients had no evidence of a rectal evacuation disorder. Subjects were randomized to receive a daily dose of 2 or 4 mg PRU or placebo in a double-blind, parallel-group design. Each treatment lasted 7 days. The transit test was performed over the last 48 hours of the study. Effects on gastric emptying, small bowel transit, and colonic transit were analyzed using Kruskal-Wallis and Wilcoxon rank sum tests.

RESULTS

Of 61 patients screened, 40 were eligible and randomized. Two patients withdrew because of adverse events. PRU accelerated overall gastric emptying and small bowel transit. PRU tended to accelerate overall colonic transit with significantly faster overall colonic transit and ascending colon emptying with the 4-mg dose.

CONCLUSIONS

PRU accelerates transit through the stomach, small bowel, and colon in patients with constipation unassociated with a rectal evacuation disorder.

Recombinant human neurotrophic factors accelerate colonic transit and relieve constipation in humans

BACKGROUND & AIMS

The aim of this study was to assess the effects of recombinant human brain-derived neurotrophic factor (r-metHuBDNF) and recombinant human neurotrophic factor 3 (r-metHuNT-3) on gastrointestinal motor functions in healthy people and in patients with constipation.

METHODS

Gastrointestinal and colonic transit was measured by scintigraphy before and after 2 weeks of treatment. Daily diaries documented symptoms over 6 weeks before, during, and after treatment. In a randomized study of healthy subjects, 40 received 100 microg/kg r-metHuBDNF or placebo subcutaneously (SC) daily. In a separate study, 8 healthy subjects and 8 patients with constipation received 300 microg/kg r-metHuNT-3 SC thrice weekly.

RESULTS

r-met-HuBDNF accelerated overall and proximal colonic emptying (P<0.05) in health. r-metHuNT-3 accelerated overall colonic transit in health and constipation (all P<0.05) and gastric and small bowel transit (both P<0.05) in health. r-metHuBDNF tended to increase stool frequency compared with placebo in health (P = 0.09). r-metHuNT-3 increased stool frequency (P = 0.05) and facilitated passage of stool (P < 0.01) in constipated patients. The effects on stool frequency started within 3 days of the beginning of neurotrophin administrations and lasted up to 5 days after treatment ended. r-metHu neurotrophic factors were well tolerated, although half of the participants in the 2 studies developed injection site reactions or paresthesiae.

CONCLUSIONS

Exogenous neurotrophic factors stimulate human gut motility in health and constipation.

Tegaserod accelerates orocecal transit in patients with constipation-predominant irritable bowel syndrome

BACKGROUND & AIMS

This study evaluated the effects of a partial 5-hydroxytryptamine (5-HT)(4) agonist, tegaserod, on gastric small bowel and colonic transit in constipation-predominant irritable bowel syndrome (IBS).

METHODS

After a 1 week run-in period, 24 patients with constipation-predominant IBS were randomized to 1 week of tegaserod, 2 mg twice daily, or placebo treatment. Scintigraphic gastric emptying, small bowel transit, and colonic transit were determined before administration of study drug and after 1 week on the medication. Colonic transit was also measured using radiopaque markers and a single radiograph on day 5.

RESULTS

Gastric emptying was unaltered by tegaserod. Proximal colonic filling at 6 hours, a measure of orocecal transit, was accelerated by tegaserod (70.4% +/- 1.3% [mean +/- SEM] vs. placebo, 46.4 +/- 1.9; P = 0.015). Proximal colonic emptying half-time and geometric center at 48 hours were also accelerated by tegaserod compared with baseline, but not compared with placebo. Mean colonic transit time was similar in both groups at baseline and after drug administration (tegaserod, 59.5 +/- 2.1 hours; placebo, 62.1 +/- 2.1 hours).

CONCLUSIONS

Tegaserod accelerates orocecal transit, tends to accelerate colonic transit, and deserves further study in patients with constipation-predominant IBS.

Selective stimulation of colonic transit by the benzofuran 5HT4 agonist, prucalopride, in healthy humans

BACKGROUND

Prucalopride (R093877) is a selective and specific 5HT4 agonist, the first of a new chemical class of benzofurans, with gastrointestinal prokinetic activities in vitro.

AIMS

To evaluate the effects of prucalopride on gastrointestinal and colonic transit.

METHODS

A validated scintigraphic technique was used to measure gastrointestinal and colonic transit over 48 hours in 50 healthy volunteers. For seven days, each subject received a daily dose of 0. 5, 1, 2, or 4 mg prucalopride, or placebo in a double blind, randomised fashion. The transit test was performed over the last 48 hours.

RESULTS

There were significant accelerations of overall colonic transit at 4, 8, 24, and 48 hours (p<0.05) and proximal colonic emptying t1/2 (p<0.05). The 0.5, 2, and 4 mg doses of prucalopride were almost equally effective and accelerated colonic transit compared with placebo. Prucalopride did not significantly alter gastric emptying (p>0.5) or small bowel transit (overall p=0. 12). The medication appeared to be well tolerated during the seven day treatment of healthy subjects.

CONCLUSION

Prucalopride accelerates colonic transit, partly by stimulating proximal colonic emptying, but does not alter gastric or small bowel transit in healthy human subjects. Prucalopride deserves further study in patients with constipation.

Lowered norepinephrine turnover as a sign of impaired ganglionic transmission after preganglionic lesioning by acetylcholinesterase antibodies

Monoclonal antibodies to acetylcholinesterase are known to destroy preganglionic sympathetic terminals in rats. To investigate resulting changes in sympathetic tone, turnover of norepinephrine (NE) was examined in five adrenergically innervated tissues: submaxillary salivary gland, heart, spleen, vas deferens and kidney. At time zero, 50 mu Ci of [3H]NE was injected into the tail vein; turnover rates were determined from the loss of radioactive NE between 2 and 24 hr later. Experiments with ganglionic blocking agents showed that most NE turnover was related to impulse traffic. Combined treatment with atropine (4 mg/kg/day) and chlorisondamine (20 mg/kg/day) reduced the apparent turnover rate constant by two thirds or more in all organs except vas deferens. NE turnover was likewise slowed after treatment with acetylcholinesterase antibodies (1.6 mg i.v., 5 days earlier): apparent rate constants fell 50% or more in submaxillary gland, heart and kidney. The reduced NE turnover in these end organs suggested that preganglionic immunologic lesions blocked synaptic transmission in the respective sympathetic ganglia. Sustained turnover in the spleen, however, suggested that certain pathways through the celiac ganglion resisted immunologic lesion or recovered quickly. Hence, there may be structural or functional differences among the sympathetic ganglia, especially between pre- and paravertebral groups.

Accumulation of enkephalin, proenkephalin mRNA, and neuropeptide Y in immunologically denervated rat adrenal glands: evidence for divergent peptide regulation

To investigate transsynaptic effects on peptides of adrenal chromaffin cells in the rat, presynaptic sympathetic terminals were destroyed by intravenous injection of monoclonal antibodies to acetylcholinesterase. At several times thereafter, neuropeptide Y (NPY)-like immunoreactivity (NPY-IR) and methionine-enkephalin-like immunoreactivity (Met-Enk-IR) were measured by radioimmunoassay. Within 2 days of antibody injection, adrenal Met-Enk-IR increased five- to 10-fold and NPY-IR increased 50%. These effects were accompanied by large increases in proenkephalin A mRNA assayed by polymerase chain reaction. The peptide responses could reflect either an acute activation, as presynaptic terminals degenerated, or a chronic synaptic inactivation after terminal degeneration. To test the possibilities, muscarinic and nicotinic receptors were inhibited by repeated injection of atropine (1 mg/kg) and chlorisondamine (5 mg/kg). Measurements of urinary free catecholamine excretion showed that this treatment prevented the paroxysmal release of norepinephrine and reduced the release of epinephrine that normally followed injection of acetylcholinesterase antibodies. When the drugs were given alone for 2 or 4 days, adrenal Met-Enk-IR increased modestly and NPY-IR remained steady or declined. When given together with acetylcholinesterase antibodies, the cholinergic antagonists blocked the increase of NPY-IR but not Met-Enk-IR. Adding naloxone (1 mg/kg) to the treatment regimen enhanced the blockade of epinephrine excretion and largely prevented the antibody-induced increase in Met-EnK-IR. These findings indicate that adrenal NPY and enkephalin are not regulated identically. Adrenal NPY behaves as though controlled by transsynaptic cholinergic input. On the other hand, adrenal enkephalin may be regulated by additional or different mechanisms, possibly involving peptidergic transmission or synaptic inactivation.