Co-administration Of Atropine Research Articles

Involvement of Acetylcholine Receptors in Cholinergic Pathway-Mediated Protection Against Autoimmune Diabetes.

Type I diabetes (T1D) is a T cell-driven autoimmune disease that results in the killing of pancreatic β-cells and, consequently, loss of insulin production. Using the multiple low-dose streptozotocin (MLD-STZ) model of experimental autoimmune diabetes, we previously reported that pretreatment with a specific acetylcholinesterase inhibitor (AChEI), paraoxon, prevented the development of hyperglycemia in C57BL/6 mice. This correlated with an inhibition of T cell infiltration into the pancreatic islets and a reduction in pro-inflammatory cytokines. The cholinergic anti-inflammatory pathway utilizes nicotinic and muscarinic acetylcholine receptors (nAChRs and mAChRs, respectively) expressed on a variety of cell types. In this study, we carried out a comparative analysis of the effect of specific antagonists of nAChRs or mAChRs on the development of autoimmune diabetes. Co-administration of mecamylamine, a non-selective antagonist of nAChRs maintained the protective effect of AChEI on the development of hyperglycemia. In contrast, co-administration of atropine, a non-selective antagonist of mAChRs, mitigated AChEI-mediated protection. Mice pretreated with mecamylamine had an improved response in glucose tolerance test (GTT) than mice pretreated with atropine. These differential effects of nAChR and mAChR antagonists correlated with the extent of islet cell infiltration and with the structure and functionality of the β-cells. Taken together, our data suggest that mAChRs are essential for the protective effect of cholinergic stimulation in autoimmune diabetes.

Efficacy of Recommended Prehospital Human Equivalent Doses of Atropine and Pralidoxime Against the Toxic Effects of Carbamate Poisoning in the Hartley Guinea Pig

Aldicarb and methomyl are carbamate pesticides commonly implicated in human poisonings. The primary toxic mechanism of action for carbamate poisoning is cholinesterase (ChE) inhibition. As such, it is logical to assume that the currently accepted therapies for organophosphate poisoning (muscarinic antagonist atropine and the oxime acetylcholinesterase reactivator pralidoxime chloride [2-PAM Cl]) could afford therapeutic protection. However, oximes have been shown to be contraindicated for poisoning by some carbamates. A protective ratio study was conducted in guinea pigs to evaluate the efficacy of atropine and 2-PAM Cl. The ChE activity was determined in both the blood and the cerebral cortex. Coadministration of atropine free base (0.4 mg/kg) and 2-PAM Cl (25.7 mg/kg) demonstrated protective ratios of 2 and 3 against aldicarb and methomyl, respectively, relative to saline. The data reported here show that this protection was primarily mediated by the action of atropine. The reactivator 2-PAM Cl had neither positive nor negative effects on survival. Both blood acetylcholinesterase (AChE) and butyrylcholinesterase (BChE) activities were significantly reduced at 15 minutes postchallenge but gradually returned to normal within 24 hours. Analysis of cerebral cortex showed that BChE, but not AChE, activity was reduced in animals that succumbed prior to 24 hours after challenge. The results suggest that coadministration of atropine and 2-PAM Cl at the currently recommended human equivalent doses for use in the prehospital setting to treat organophosphorus nerve agent and pesticide poisoning would likely also be effective against aldicarb or methomyl poisoning.

Carbon monoxide contributes to the constipating effects of granisetron in rat colon.

AIMTo investigate the mechanisms underlying the potential contribution of the heme oxygenase/carbon monoxide (HO/CO) pathway in the constipating effects of granisetron.METHODSFor in vivo studies, gastrointestinal motility was evaluated in male rats acutely treated with granisetron [25, 50, 75 μg/kg/subcutaneous (sc)], zinc protoporphyrin IX [ZnPPIX, 50 μg/kg/intraperitoneal (ip)] and hemin (50 μmol/L/kg/ip), alone or in combination. For in vitro studies, the contractile neurogenic response to electrical field stimulation (EFS, 3, 5, 10 Hz, 14 V, 1 ms, pulse trains lasting 10 s), as well as the contractile myogenic response to acetylcholine (ACh, 0.1-100 μmol/L) were evaluated on colon specimens incubated with granisetron (3 μmol/L, 15 min), ZnPPIX (10 μmol/L, 60 min) or CO-releasing molecule-3 (CORM-3, 100, 200, 400 μmol/L) alone or in combination. These experiments were performed under co-treatment with or without atropine (3 μmol/L, a muscarinic receptor antagonist) or NG-nitro-L-Arginine (L-NNA, 100 μmol/L, a nitric oxide synthase inhibitor).RESULTSAdministration of granisetron (50, 75 μg/kg) in vivo significantly increased the time to first defecation (P = 0.045 vs vehicle-treated rats), clearly suggesting a constipating effect of this drug. Although administration of ZnPPIX or hemin alone had no effect on this gastrointestinal motility parameter, ZnPPIX co-administered with granisetron abolished the granisetron-induced constipation. On the other hand, co-administration of hemin and granisetron did not modify the increased constipation observed under granisetron alone. When administered in vitro, granisetron alone (3 μmol/L) did not significantly modify the colon’s contractile response to either EFS or ACh. Incubation with ZnPPIX alone (10 μmol/L) significantly reduced the colon’s contractile response to EFS (P = 0.016) but had no effect on contractile response to ACh. Co-administration of ZnPPIX and atropine (3 μmol/L) abolished the ZnPPIX-mediated decrease in contractile response to EFS. Conversely, incubation with CORM-3 (400 μmol/L) alone increased both the contractile response to EFS at 10 Hz (10 Hz: 71.02 ± 19.16 vs 116.25 ± 53.70, P = 0.01) and the contractile response to ACh (100 μmol/L) (P = 0.012). Co-administration of atropine abolished the CORM-3-mediated effects on the EFS-mediated response. When granisetron was co-incubated in vitro with ZnPPIX, the ZnPPIX-mediated decrease in colon contractile response to EFS was lost. On the other hand, co-incubation of granisetron and CORM-3 (400 μmol/L) further increased the colon’s contractile response to EFS (at 5 Hz: P = 0.007; at 10 Hz: P = 0.001) and to ACh (ACh 10 μmol/L: P = 0.001; ACh 100 μmol/L: P = 0.001) elicited by CORM-3 alone. L-NNA co-administered with granisetron and CORM-3 abolished the potentiating effect of CORM-3 on granisetron on both the EFS-induced and ACh-induced contractile response.CONCLUSIONTaken together, findings from in vivo and in vitro studies suggest that the HO/CO pathway is involved in the constipating effects of granisetron.

Ghrelin protects the heart against ischemia-induced arrhythmias by preserving connexin-43 protein

Vagal nerve stimulation has been postulated to confer an antifibrillatory effect. We studied whether ghrelin administration would exert an antiarrhythmic effect via modulation of autonomic nerve activity in rats after acute myocardial ischemia (MI). Male Sprague-Dawley rats were exposed to 30 min of ischemia following ligation of the left coronary artery. Animals were then randomized to receive either ghrelin (n = 26) or saline (n = 26) during the period of coronary ligation. Power spectral analysis of heart-rate variability revealed that the administration of ghrelin increased the high-frequency (HF) power and decreased the low-frequency (LF)/HF ratio. Ventricular tachyarrhythmias were less frequent in rats after MI who received ghrelin in comparison with rats that received saline. Immunoblotting and immunohistochemistry revealed that rats given saline alone during MI exhibited a marked reduction in phosphorylated connexin-43 within the left ventricle, whereas those that received ghrelin displayed only minor reductions in comparison with sham-operated rats. These effects of ghrelin were diminished by the coadministration of atropine or the blockade of vagal afferents. These data demonstrate that the beneficial effect of ghrelin might be mediated by modulation of cardiac autonomic nerve activity.

Is prophylactic atropine necessary during ketamine sedation in children?

To quantify clinically significant hypersalivation and other adverse events requiring intervention, with and without the use of atropine during ketamine use, using a consensus-based, standardised terminology. This was a retrospective study based on paediatric patients who received ketamine for procedures done at the children's emergency department from July 2010 to September 2010. Patients who were given atropine were compared with patients who were not given atropine with regard to clinically significant hypersalivation. All other side effects of ketamine (airway, respiratory, cardiovascular, neurological and gastrointestinal side effects) were documented. Two out of the 164 (1.2%) patients who received atropine and 1 out of the 119 (0.8%) patients who did not receive atropine had desaturation (odds ratio (OR) 1.5; 95% CI 0.1-16.3). These three patients were all under 5 years old (P = 0.3) and had airway malalignment requiring repositioning. None had hypersalivation requiring intervention. Two out of 164 (1.2%) who received atropine and 3 out of 119 (2.5%) who did not receive atropine had vomiting (OR 0.5; CI 0.1-2.9). One patient who vomited did not receive atropine and was given ondansetron. The others had delayed discharges following a longer period of observation in the unit. There was no clinically significant hypersalivation in children given ketamine sedation, with or without the coadministration of atropine. Ketamine is a relatively safe drug for use in children with few intervention-based side effects.

Guinea pig ileum motility stimulation elicited by N-formyl-Met-Leu-Phe (fMLF) involves neurotransmitters and prostanoids

In guinea-pig ileum (GPI), the chemotactic peptide N-formyl-Met-Leu-Phe-OH (fMLF) possesses spasmogenic properties through the activation of formyl peptide receptors (FPRs). Despite this, the mediators involved remain to be elucidated. fMLF (1 nM–1 μM) induced a dose-dependent contraction of GPI (EC 50 = 24 nM), that is blocked by pre-treatment with the FPRs antagonist Boc 2. The pre-treatment with tetrodotoxin (TTX) atropine or with SR140333 reduced the fMLF-induced contraction, whereas with hexamethonium, MEN10627, SB222200, mepyramine, cimetidine, thioperamide or methysergide did not produce any effect. With DuP697 pre-treatment, but not with piroxicam, reduced the fMLF-induced contraction. After stimulation with 24 nM fMLF, a strong increase in the PGE 2 levels was observed. Finally, the concomitant blocking of the NK 1 receptor, the muscarinic receptors and COX-2 abolished the GPI contractions induced by fMLF. fMLF induced a concentration-dependent contraction of guinea-pig jejunum (EC 50 = 11 nM), proximal colon (EC 50 = 3.5 nM) and distal colon (EC 50 = 2.2 nM), with a time-course similar to that observed in GPI. In these preparations as well, the co-administration of atropine, SR140333 and DuP697 abolished the contractions induced by fMLF. Intraperitoneal injection of fMLF (0.1 or 1 μmol/kg) enhanced the gastrointestinal motility in mice, abolished by the co-administration of atropine, SR140333 and DuP697. In conclusion, we showed that fMLF exerts spasmogenic actions on guinea-pig intestine both in vitro and in vivo through the release of acetylcholine and substance P from myenteric motorneurons and through prostanoids, probably from the inflammatory cells of the enteric immune system.

Radish extract stimulates motility of the intestine via the muscarinic receptors.

The effects of radish (Brassica oleraceae, Cruciferae) on gastrointestinal motility were examined using rat intestinal segments with myenteric plexus in-vitro and measuring the intestinal transit of charcoal in-vivo. Radish extract (10 microg mL(-1) to 2 mg mL(-1)) caused a dose-dependent increase in contractions of the duodenum, jejunum and ileum, and 1 mg mL(-1) was the maximum effective dose. The largest contraction by the extract was found in ileal segments. The extract-induced (0.5 mg mL(-1)) ileal contraction was remarkably inhibited by pretreatment of segments with atropine (10(-7) M) for 10 min, but not by hexamethonium (0.5 mM). Moreover, antagonists of the muscarinic receptor reduced the radish-induced ileal contraction by a different ratio. The rank order of inhibitory effects was 4-diphenylacetoxy-N-methyl-(2-chloroethyl)-piperidine methiodide (90.5% of control) > tropicamide (67.4%) > pirenzepine (42.8%) > methoctramine (16.7%). Oral administration of radish extract (300-500 mg kg(-1) body weight) to mice remarkably improved the intestinal transit of charcoal, and this was significantly attenuated by co-administration of atropine (50 mg kg(-1)). Taken together, these results suggest that radish extract stimulates gastrointestinal motility through activation of muscarinic pathways.

Methylisogermabullone isolated from radish roots stimulates small bowel motility via activation of acetylcholinergic receptors

We have previously reported that extract of radish roots exhibits an increase in gastrointestinal motility through the activation of muscarinic acetylcholine (ACh) receptors. Based on the stimulatory activity-guided fractionation on rat ileal segments, this study isolated methylisogermabullone (MIGB, C23H31O5NS, MW 433) from methanol extracts of radish roots. MIGB caused a significant increase of the isolated rat ileal contraction in a concentration-dependent manner (23-693 microM), and the pattern of MIGB-induced ileal contraction was different in the time course to that produced by ACh. The EC50 value of MIGB, to produce 50% maximum ileal contraction, was estimated to be 45.5 microM. MIGB (230 microM)-induced ileal contractions were enhanced by pretreatment of segments with ACh (0.1 microM). Ileal contractions produced by MIGB (230 microM) or ACh (0.1 microM) at submaximal concentration were partially inhibited by pretreatment of hexamethonium (0.1 mM), a ganglionic blocker, whereas they were almost completely abolished by atropine (10 microM). Oral administration of MIGB to mice stimulated the small intestinal transit of charcoal in a dose-dependent manner (10-100 mg kg(-1)), and MIGB (100 mg kg(-1))-induced stimulation of small intestinal transit was significantly attenuated by co-administration of atropine (50 mg kg(-1)). Taken together, these results demonstrate that MIGB isolated from radish roots stimulates the small bowel motility through the activation of ACh receptors. These findings suggest that MIGB may become a potential regulatory agent for therapeutic intervention in dysfunction of gastrointestinal motility.

Investigating the role of protein kinase-G in the antidepressant-like response of sildenafil in combination with muscarinic acetylcholine receptor antagonism

The cGMP/PK-G pathway plays a crucial role in neuroprotection and neurotrophin support, and is possibly involved in antidepressant action. Recently we reported on a novel antidepressant-like response following simultaneous administration of sildenafil (phosphodiesterase 5 (PDE5) inhibitor, thereby increasing cGMP levels), and atropine (muscarinic acetylcholine receptor antagonist) in the rat forced swim test (FST). However, it is unclear whether the antidepressant-like activity of sildenafil + atropine is mediated via the activation of PK-G, an important down-stream effector for cGMP, and whether this may target known pathways in antidepressant action. We investigated whether the antidepressant-like response of sildenafil ± atropine could be reversed by Rp-8-Br-PET-cGMP, a PK-G inhibitor, and also whether a combination of 8-Br-cGMP (PK-G activator) ± atropine would likewise be active in the FST, and whether this combination could be attenuated by a PK-G inhibitor. 8-Br-cGMP alone, but not sildenafil alone, reduced immobility and selectively increased swimming in the FST. The antidepressant-like action of sildenafil was only evident following co-administration of atropine, and selectively increased climbing behaviour. Importantly, PK-G inhibition prevented the antidepressant-like effects of both 8-Br-cGMP and the sildenafil/atropine combination. These results confirm cholinergic-cGMP–PK-G interactions in the antidepressant-like effects of sildenafil, putatively acting via noradrenergic mechanisms, whereas direct PK-G activation induces antidepressant-like effects that are associated with enhancement of serotonergic neurotransmission.

Adjunctive Atropine Is Unnecessary during Ketamine Sedation in Children

The prophylactic coadministration of atropine or other anticholinergics during dissociative sedation has historically been considered mandatory to mitigate ketamine-associated hypersalivation. Emergency physicians (EPs) are known to omit this adjunct, so a prospective study to describe the safety profile of this practice was initiated. To quantify the magnitude of excessive salivation, describe interventions for hypersalivation, and describe any associated airway complications. In this prospective observational study of emergency department (ED) pediatric patients receiving dissociative sedation, treating physicians rated excessive salivation on a 100-mm visual analog scale and recorded the frequency and nature of airway complications and interventions for hypersalivation. Of 1,090 ketamine sedations during the 3-year study period, 947 (86.9%) were performed without adjunctive atropine. Treating physicians assigned the majority (92%) of these subjects salivation visual analog scale ratings of 0 mm, i.e., "none," and only 1.3% of ratings were >or= 50 mm. Transient airway complications occurred in 3.2%, with just one (brief desaturation) felt related to hypersalivation (incidence 0.11%, 95% confidence interval = 0.003% to 0.59%). Interventions for hypersalivation (most commonly suctioning) occurred in 4.2%, with no occurrences of assisted ventilation or intubation. When adjunctive atropine is omitted during ketamine sedation in children, excessive salivation is uncommon, and associated airway complications are rare. Anticholinergic prophylaxis is not routinely necessary in this setting.

Cutaneous Microdialysis as a Novel Means of Continuously Stimulating Eccrine Sweat Glands In Vivo

Previous studies of the pharmacological regulation of sweat gland function in humans have administered agonists or antagonists systemically, by local intradermal injection or by iontophoresis. This has not allowed prolonged or steady-state activation of sweat glands to be examined. In this study, we used the technique of dermal microdialysis to administer pharmacological agents singly and in combination for up to 5 hours. Muscarinic stimulation with pilocarpine nitrate (50 mug ml(-1) to 1.66 mg ml(-1)) produced a sigmoid dose response curve, with maximal sweating (measured as transepidermal water loss) (mean 70 g m(-2) hour(-1)) after 15 minutes. This was sustained at steady-state levels (55 g m(-2) hour(-1)) until perfusion stopped. Perfusion with atropine (0.003 mg ml(-1)) reduced sweating below baseline and blocked pilocarpine-induced sweating completely. Noradrenaline (0.005 mg ml(-1)) induced much lower sweat rates than pilocarpine (56.8+/-1.62 g m(-2) hour(-1) vs 8.2+/-1.2 g m(-2) hour(-1), respectively, P<0.001) and this was unaffected by co-administration of atropine. This method has made it possible to show that sweat glands are capable of sustaining near maximal activity for at least 5 hours. The method has future application in investigation of conditions with disordered sweat gland activity.

Noradrenergic and cholinergic neural pathways mediate stress-induced reactivation of colitis in the rat

Evidence to date suggests that stress-induced exacerbation or relapse of intestinal inflammation in inflammatory bowel disease requires both activation of the autonomic nervous system and the activation of the immune system by the presence of previously encountered luminal antigens. The aim of the present study was to further explore these associations and to determine the role of the autonomic nervous in modulating the intestinal inflammatory response to stress. Rats healed from an initial dinitrobenzene sulfonic acid-induced colitis were given a non-colitic dose of dinitrobenzene sulfonic acid (dissolved in saline) or 0.9% saline intra-rectally and then subjected to restraint stress. Cardiac sympathovagal balance was assessed by power spectral analysis of heart rate variability data collected from telemetric electrocardiogram recordings before, during and post stress. Only rats that were stressed and received dinitrobenzene sulfonic acid showed an inflammatory relapse characterized by significant macroscopic damage and elevated myeloperoxidase activity associated with a significant infiltration of mucosal and submucosal T lymphocytes. No difference in inflammatory markers was observed in animals that received intra-rectal saline and restraint stress. Rats subjected to stress and intra-rectal dinitrobenzene sulfonic acid demonstrated an increase in sympathetic activity with a nearly four fold increase in LF : HF ratio during stress and a significant increase in heart rate. Shortly after cessation of stress, the LF : HF ratio decreased significantly, returning to baseline levels, however the heart rate remained significantly elevated over baseline levels following stress, but decreased to a level that was significantly lower than during stress. The stress/dinitrobenzene sulfonic acid-induced relapses were preventable by pre-treating rats with hexamethonium (a nicotinic cholinergic ganglion blocking agent) or the co-administration of atropine (a muscarinic cholinoceptor antagonist) and bretylium (a noradrenergic ganglion blocking agent), but was not prevented when either atropine or bretylium were administered alone. This study utilizes an established model of chemically induced colitis that when integrated with stress results in relapsing inflammatory bowel disease. Moreover, this study demonstrates that noradrenergic and cholinergic neural pathways mediate the stress response critical for the relapse of colitis.

Generalized tetany: An unusual complication during dobutamine stress echocardiography

Dobutamine stress echocardiography is a frequently used noninvasive method for the evaluation of inducible myocardial ischemia, myocardial viability, and preoperative cardiac risk. Although its clinical safety has been validated, side effects and complications especially with the coadministration of atropine can occur. We report a case of generalized tetany in a 49-year-old woman undergoing dobutamine stress echocardiography. (J Am Soc Echocardiogr 2002;15:1414-6.)

Hypothalamic cholinergic regulation of body temperature and water intake in rats

Without disturbing the behavior of unanesthetized rats, the perfusion of neostigmine through microdialysis probe into the anterior hypothalamus (AH), paraventricular nucleus (PVN) and lateral ventricle (LV) decreased body temperature and increased water intake. On the other hand, the perfusion into the supraoptic nucleus (SON) increased the body temperature. The perfusion of neostigmine increased the extracellular concentration of acetylcholine in the perfusion sites except LV. Changes, both decrease and increase, in body temperature and increase in water intake were correlated with increases in c- fos-like immunoreactivity (Fos-IR) in the hypothalamus, pons and medulla. Distinct Fos-IR was found in the PVN, SON, median preoptic nucleus (MnPO), locus coeruleus (LC), area postrema and nucleus of the solitary tract (NTS). Co-administration of atropine with neostigmine completely suppressed the changes in the body temperature, water intake and Fos-IR, all of which were induced by the neostigmine perfusion into AH, PVN and SON. In the LV-perfused rats, on the other hand, co-administration of atropine and neostigmine only partially prevented body temperature reduction and still induced significant hypothermia. These results suggest that muscarinic receptor activation in specific regions of the hypothalamus and the activation of LC and NTS are implicated in the regulation of body temperature and water intake. Other receptor processes are involved in the LV-induced changes.

Exaggerated chronotropic and energetic response to dobutamine after orthotopic cardiac transplantation

Background: After heart transplantation, the transplanted denervated heart displays both an exaggerated chronotropic and an exaggerated inotropic response to circulating catecholamines. This study assessed whether denervated transplanted hearts also display an exaggerated energetic response when challenged with dobutamine. Methods and Results: A total of 18 heart transplant recipients and 14 normal volunteers underwent measurements of myocardial oxygen consumption (MVO 2), external work (EW), and pressure-volume area (PVA), at rest and during infusion of dobutamine. At rest, calculated myocardial (PVA/MVO 2) and mechanical (EW/MVO 2) efficiencies were similar among transplant recipients and normal volunteers. During low-dose dobutamine infusion (8 μg/kg/min), transplant recipients exhibited a larger increase in heart rate (to 126 ± 14 vs 87 ± 26 beats/min, p < 0.001) and MVO 2 (to 269 ± 43 vs 233 ± 19 J/min/100g, p < 0.05) and a smaller increase in EW (64 ± 18 vs 72 ± 13 J/min/100g, p < 0.05) and PVA (70 ± 16 vs 81 ± 13 J/min/100g, p < 0.05) than did normal volunteers. As a result, both myocardial (26 ± 4 vs 35 ± 4%, p < 0.05) and mechanical (23 ± 4 vs 30 ± 4%, p < 0.001) efficiencies were lower during dobutamine infusion in transplant recipients than in normal volunteers. During the infusion of a higher dose of dobutamine (19 μg/kg/min), the chronotropic and inotropic responses of heart transplant recipients were even more exaggerated. The fall in myocardial efficiency induced by dobutamine correlated with the increase in heart rate ( r = −0.58) and could be reproduced in normal volunteers by coadministration of atropine. Conclusions: Transplant recipients exhibit a larger fall in contractile efficiency and a larger oxygen-wasting effect during dobutamine infusion than do normal volunteers. Because normal volunteers pre-medicated with atropine presented with a similar increase in heart rate and a similar fall in efficiency, the exaggerated energetic response of transplanted hearts to dobutamine likely resulted from the same mechanisms as their chronotropic supersensitivity, i.e., the loss of inhibitory parasympathetic innervation.

Effects of neostigmine and atropine on basal and handling-induced acetylcholine output from ventral hippocampus

The involvement of muscarinic autoreceptors in the regulation of hippocampal acetylcholine levels during acetylcholinesterase inhibition was examined by perfusing the acetylhcolineterase inhibitor neostigmine bromide (10, 100 or 1 000 nM) alone and in the presence of the muscarinic receptor antagonist atropine methylnitrate (10 μM), in resting and behaviourally-activated animals. In resting animals, local perfusion of neostigmine caused a dose-dependent increase in acetylcholine levels. Coadministration of atropine did not affect basal levels in the presence of 10 nM neostigmine, but increased acetylcholine levels approximately four and 11-fold in the presence of 100 nM and 1000 nM neostigmine, respectively. In animals which were behaviourally activated by handling, acetylcholine levels increased two- to three-fold in the presence of all neostigmine concentrations. However, the handling-induced increase in acetylcholine levels was somewhat smaller with 1 000 nM neostigmine as compared to 10 nM neostigmine. Atropine had no effect on handling-induced acetylcholine output in the presence of 10 nM neostigmine, but caused greater and longer increases in the presence of 100 nM and 1 000 nM neostigmine. These data indicate that acetylcholine levels are greatly reduced by autoinhibition at higher levels of acetylcholine esterase inhibition. The handling-evoked increase in acetylcholine levels is only moderately affected by the level of acetylcholinesterase inhibition, despite the participation of autoreceptors in the handling effect at higher levels of acetylcholinesterase inhibition.

Coadministration of atropine, NBQX and TCP against soman-induced seizures.

The ability of relatively low doses of atropine, NBQX and TCP administered in combination to prevent or stop seizures induced by soman, was studied in rats. While these drugs injected together early after soman prevented the onset of seizures, their delayed concomitant administration after 5 or 30 min of epileptic activity only mildly attenuated the intensity of seizures. Conversely, a total arrest of epileptic activity was observed in 80 to 100% of animals when NBQX and TCP were given together after 5 to 50 min of seizures to atropine pretreated rats. The large time-window for antiepileptic effectiveness of this 'three drug treatment', provided that atropine is administered early after soman, is discussed in relation to reciprocal potentiations of the antiepileptic effects of atropine, NBQX and TCP in combination.

Adenosine A2 receptor regulation of apomorphine-induced turning in rats with unilateral striatal dopamine denervation.

The ipsilateral intrastriatal administration of the specific adenosine A2a receptor agonist, 2-[p-(2-carboxyethyl)phenethylamino]-5'-N-ethylcarboxamido adenosine (CGS 21680), produced a dose related decrease in apomorphine-induced rotation in the unilaterally 6-hydroxydopamine-lesioned rat. This effect could be reversed by intrastriatal infusions of the A2a antagonist, 4-amino-1-phenyl[1,2,4]triazolo[4,3-a]quinoxaline (CP 66,713). However, CP 66,713 had no significant effect when infused alone, neither did it influence the response to apomorphine in the absence of CGS 21680. The possible behavioural interactions between A2a receptors and striatal ACh activity were also investigated using this model. Atropine administered intrastriatally in a dose that had no effect on the response to apomorphine reduced the inhibitory effects of CGS 21680 on apomorphine-induced turning. Naloxone also reduced the effects of apomorphine, an effect which could be prevented by the co-administration of atropine, or CP 66,713. These results indicate that adenosine agonists can modulate apomorphine-induced turning by an interaction with both cholinergic and opioidergic mechanisms in the striatum.

Effects of intracerebroventricularly administered neostigmine on hypothalamic monoaminergic neuronal activities in awake rats

Hypothalamic neuronal activities of noradrenaline, dopamine and serotonin as well as serum glucose concentrations were simultaneously monitored 60 min after the third cerebroventricular injection of neostigmine, a cholinesterase inhibitor, in rats. Each neuronal activity was assessed from a ratio of the concentration of the major metabolite to that of its precursor monoamine itself by using the technique of gas chromatography-mass spectrometry. Neostigmine caused significant increases in serum glucose concentrations, hypothalamic noradrenergic and dopaminergic neuronal activities, and significantly suppressed hypothalamic serotonergic neuronal activity. All these responses to neostigmine were completely inhibited by the co-administration of atropine. These observations emphasize the important role of the interactions between cholinergic (muscarinic) and monoaminergic neurons in the brain.

Relative contribution of nervous system and hormones to CNS-mediated hyperglycemia is determined by the neurochemical specificity in the brain

To determine whether CNS regulatory pathways are organized so that differential sympathetic outflow patterns occur in response to stress, we injected various doses of neostigmine or bombesin into the third cerebral ventricle of fed rats, and then measured the hepatic venous plasma concentrations of glucose, glucagon, insulin, and epinephrine. The following four groups of rats were studied. Group 1 was intact rats. Group 2 comprised intact rats receiving the constant infusion of a) somatostatin to inhibit the endogenous secretion of insulin and glucagon, and b) insulin to maintain the plasma insulin concentration at basal levels. The infusion was started from −30 minutes and given via a catheter in the femoral vein. Group 3 consisted of rats that underwent bilateral adrenal medullectomy (ADMX) one week before the experiment. Group 4 was ADMX rats administered a constant infusion of somatostatin with insulin through a femoral vein, as above. The administration of 1 × 10 −9 mol neostigmine caused hepatic venous hyperglycemia mediated by three distinct pathways: 1) direct innervation of the liver, 2) a direct action of epinephrine on the liver, and 3) the action of glucagon on the liver. We estimated the relative contribution of these three factors to be about 47, 32, and 21%, respectively. Relative contributions of three factors of the doses of 5 × 10 −9 and 5 × 10 −8 mol neostigmine demonstrated an effect similar to that of 1 × 10 −9 mol neostigmine. Epinephrine was shown to be the only agent involved in the hyperglycemic response to intraventricular bombesin at doses of 1 × 10 −10, 1 × 10 −9, and 1 × 10 −8 mol. Coadministration of atropine with bombesin did not affect the bombesin-induced hyperglycemia. This evidence suggests that the relative contribution of the nervous system and hormones to CNS-mediated hyperglycemia is determined by the type of compound used to stimulate the CNS.