Brainstem nicotinic receptor subtypes that influence intragastric and arterial blood pressures.

The purpose of this study was to investigate the effect of microinjection of nicotine and nicotinic receptor antagonists into the dorsal motor nucleus of the vagus (DMV) or medial subnucleus of the tractus solitarius (mNTS) on intragastric (IGP) and arterial blood pressures (BP) in anesthetized rats. Nicotine microinjected into the DMV (10-300 pmol) produced dose-related increases in IGP (ED(50) = 89 pmol); no significant changes were noted for BP. Ipsilateral vagotomy abolished nicotine-induced increases in IGP. Nicotine microinjected into the mNTS in a dose range of 0.1 to 300 pmol produced dose-related decreases in IGP (ED(50) = 0.6 pmol) and BP (ED(50) = 5.4 pmol). Bilateral vagotomy abolished nicotine-induced decreases in IGP while having no effect on BP. In rats treated with daily s.c. injections of nicotine (0.8 mg/kg of base) for 10 days, microinjections of nicotine into the DMV produced similar increases in IGP. BP responses from the mNTS were not affected by chronic treatment. However, nicotine microinjections into the mNTS no longer produced a decrease in IGP in these chronically treated animals. alpha-Bungarotoxin (100 pmol) significantly blocked nicotine-evoked increases in IGP from the DMV while having no effect on nicotine-induced responses elicited from the mNTS. Hexamethonium (10 and 100 pmol) microinjected into the mNTS dose-dependently blocked nicotine-induced effects but did not interfere with the action of nicotine at the DMV. Our data indicate that nicotine-induced changes in IGP result from nicotine acting at two sites, the DMV and mNTS; and that at least three different nicotinic receptors in the dorsal medulla oblongata can influence gastrointestinal and cardiovascular function.

Respiratory depression produced by intravenously administered NBQX.

To determine whether blockade of non-N-methyl-D-aspartate (non-NMDA) excitatory amino acid receptors affects breathing, we administered the non-NMDA receptor antagonist, 2,3-dihydroxy-6-nitro-7-sulfamoyl-benzo(F)quinoxaline (NBQX), to anesthetized cats while monitoring phrenic nerve discharge, blood pressure and heart rate. NBQX, 3 and 10 mg/kg, i.v., reduced phrenic amplitude 59 +/- 20% (n = 3) and 88 +/- 6% (n = 5), respectively, and decreased respiratory rate. Phrenic activity was completely silenced in 3 animals. These effects were accompanied by decreased blood pressure and heart rate. Our data indicate that NBQX, a competitive antagonist of non-NMDA receptors, is a powerful depressant of cardiorespiratory activity.

Butyrylcholinesterase: an enzyme antidote for cocaine intoxication.

Cocaine-associated toxicity is the result of effects on the cardiovascular and central nervous systems. Since the primary route of cocaine inactivation is enzymatic degradation by butyrylcholinesterase (BChE), we sought to determine if the administration of purified human enzyme would ameliorate the lethal effects of cocaine. While the cardiovascular, autonomic or central nervous systems were unaffected by BChE, the enzyme reduced the adverse effects of cocaine including hypertension, hyperactivity and convulsions. BChE decreased both the brain and blood levels of cocaine and shifted the metabolites towards the production of the inactive product ecgonine methyl ester and away from the physiologically active metabolites, norcocaine and benzoylecgonine. We conclude that BChE would appear to be an ideal antidote in the treatment of cocaine intoxication and has potential therapeutic application.

Cocaine detoxification by human plasma butyrylcholinesterase.

The ability of human plasma butyrylcholinesterase (BChE) to detoxify cocaine in vivo was evaluated. Intravenous administration of BChE, at doses sufficient to increase the plasma levels of the enzyme as much as 800-fold, produced no adverse effects on the cardiovascular, autonomic, or central nervous systems of rats. Most of the enzyme could be recovered in the plasma immediately after administration and remained active with a beta-t(1/2) of 21.6 +/- 2.4 hr. Pretreatment of chloralose-urethane anesthetized rats with BChE, 0.1-7.8 mg/kg, decreased the hypertensive and arrhythmogenic effects produced by cocaine and increased the lethal dose of cocaine by three- to fourfold. Treatment of conscious rats with 1 and 10 mg/kg BChE decreased the incidence of seizures and deaths produced by a prior dose of cocaine (80 mg/kg, i.p.). These results suggest that BChE would provide a safe and highly efficacious treatment for cocaine intoxication.

Therapeutic use of butyrylcholinesterase for cocaine intoxication.

The most common complications of cocaine ingestion are on the cardiovascular and central nervous systems and produce chest pain and generalized seizures. In humans, decreased levels of butyrylcholinesterase (BChE) (EC 3.1.1.8) have been associated with sustained effects of cocaine and life-threatening complications. Administration of purified human BChE has previously been demonstrated to protect against cocaine-associated cardiovascular toxicity in rats. A shift in the metabolism of cocaine as well as enhanced metabolism may be the underlying mechanism of the enzyme. Therefore, levels of the parent drug and four metabolites were determined in rat plasma after i.p. administration of a lethal cocaine dose, followed by i.v. administration of BChE. Plasma and brain concentrations of cocaine were lowered by 80% after BChE administration. Furthermore, the metabolic profile of cocaine in the plasma was altered. The concentration of ecgonine methylester was doubled although the concentration of ecgonine, a secondary metabolite of cocaine, was reduced. The level of benzoylecgonine was reduced by one-half while norcocaine was absent. Cocaine-associated effects upon the central nervous system were also shown to be reduced by administration of BChE to conscious rats. Furthermore, our studies in the cat have also shown that purified BChE shifts the metabolic profile of cocaine (1 mg/kg) to the pharmacologically inactive products ecgonine methylester and ecgonine. Pretreatment with BChE (0.27, 1.0, and 10.0 mg/kg) ameliorated the hypertensive effects of cocaine (1 mg/kg) by reducing the duration and the extent of BP elevation by 66%. Administration of the enzyme, 1 min after cessation of cocaine infusion, resulted in an immediate attenuation in the cocaine-induced broadening of the QRS complex. These results suggest that BChE could be an effective and rapid therapy for the treatment of life-threatening cocaine-induced cardiovascular effects in human while clearing the total body burden of cocaine.

Potential role of the autonomic nervous system in the immunosuppressive effects of acute morphine administration.

These studies investigated the role of the autonomic nervous system in mediating the immunosuppressive effect of morphine on blood lymphocyte proliferation in rats. To determine the contribution of the autonomic nervous system, rats were pretreated with the ganglionic blocker chlorisondamine (5 mg/kg) prior to morphine (7 mg/kg) administration. Ganglionic blockade with chlorisondamine completely antagonized the inhibitory actions of morphine, suggesting that intact ganglionic transmission was required for the inhibition to occur. Blockade of postganglionic parasympathetic neurotransmission with atropine methylbromide (1 mg/kg) or blockade of sympathetic neurotransmission with the alpha-adrenoceptor antagonist phentolamine (1 mg/kg) did not attenuate the suppressive effect of morphine. Blockade of beta-adrenoceptors with propranolol (2.5 mg/kg) resulted in partial antagonism, but this action was not shared by the peripherally acting beta-adrenoceptor antagonist nadolol (6 mg/kg). These results suggest that the inhibitory effect of morphine on blood lymphocyte proliferation may be mediated through activation of the autonomic nervous system; however, individual blockade of either the parasympathetic or sympathetic division of the autonomic nervous system was not sufficient to antagonize this immunosuppressive effect.

Cocaine inhibits sympathetic neural activity by acting in the central nervous system and at the sympathetic ganglion.

The effects of cocaine on spontaneous pre- and postganglionic sympathetic nerve activity (SNA), mean blood pressure and heart rate were assessed in anesthetized cats. I.v. administration of 2 and 4 mg/kg decreased preganglionic SNA by -24 +/- 7% (n = 4) and -63 +/- 15% (n = 5), respectively. The 4 mg/kg dose produced a decrease in mean blood pressure (-49 +/- 6 mm Hg) with no change in heart rate. Similar sympathoinhibition was obtained in animals with denervated cardiovascular reflexes. Cocaine methiodide (4 mg/kg), a quaternary derivative of cocaine with limited central nervous system access, reduced mean blood pressure (-47 +/- 9 mm Hg) but did not inhibit preganglionic SNA. Cocaine (4 mg/kg) also reduced sympathetic discharge to the adrenal medulla as evidenced by a -62 +/- 6% (n = 5) decrease in splanchnic nerve firing. Cocaine, 2 and 4 mg/kg i.v., decreased postganglionic cardiac SNA by -54 +/- 5% (n = 7) and -60 +/- 13% (n = 4), respectively. The 2 mg/kg dose depressed postganglionic SNA to a greater extent that it did preganglionic SNA. Furthermore, cocaine methiodide (2 mg/kg) reduced postganglionic SNA by -85 +/- 15%. The depressant effect of cocaine (2 mg/kg) on postganglionic cardiac SNA was attenuated after treatment with phentolamine (5 mg/kg i.v.). Lidocaine administered in doses equimolar to those of cocaine did not significantly affect sympathetic discharge. These results indicate that cocaine acts in the central nervous system and at the stellate ganglion to inhibit sympathetic discharge and that these sympathoinhibitory effects are unrelated to cocaine's local anesthetic action.

Sympathetic nervous system mediated cardiovascular effects of cocaine are primarily due to a peripheral site of action of the drug.

Currently, augmentation of sympathetic nervous system function produced by cocaine is thought to be due primarily to stimulation of sympathetic centers in the brain (central effect) and to inhibition of catecholamine uptake into postganglionic sympathetic nerve terminals (peripheral effect). In this review of our work, we present the following evidence that cocaine-induced changes in cardiovascular function, particularly those that peak within 1 to 5 min after an i.v. bolus injection of the drug, are due to a peripheral effect of the drug: (1) In both dogs and cats, cocaine potentiates the tachycardiac effect of neurally-released and injected norepinephrine (NE). The time course of action and dosage range of cocaine that produces potentiation follows that which increases blood pressure (BP), heart rate (HR), rate-pressure product and coronary vasoconstriction. (2) Cocaine given in i.v. doses that increase BP in decerebrate cats (0.25-1.0 mg/kg) has no significant effect on directly monitored spontaneous cardiac sympathetic nerve activity (SNA). In fact, higher doses of cocaine (2-4 mg/kg, i.v.) consistently inhibit preganglionic cardiac and splanchnic nerve activity. (3) Cocaine (0.1-1.0 mg) administered directly into the blood supply of the hindbrain via the vertebral artery produces no increase in BP, HR or SNA in cats; instead, decreases in BP and sympathetic activity occur. The same dose (1 mg), injected i.v., does not depress BP or SNA. In addition, cocaine injected into the forebrain via the carotid artery or into the cerebral ventricles (0.1-1.0 mg) has very little effect on BP. Our results indicate that there is no significant excitatory effect of cocaine on CNS sympathetic centers, and that the sympathomimetic effects of cocaine on the cardiovascular system are likely to be mediated at peripheral sites.

Intravenous NBQX inhibits spontaneously occurring sympathetic nerve activity and reduces blood pressure in cats.

2,3-Dihydroxy-6-nitro-7-sulfamoyl-benzo(F)quinoxaline (NBQX) has been demonstrated to be a specific and competitive non-N-methyl-D-aspartate (non-NMDA) glutamate receptor antagonist. Our previous data obtained with the NMDA receptor antagonist MK-801 indicate that blockade of the NMDA receptor affects blood pressure. The purpose of this study was to determine whether the same is true with blockade of the non-NMDA receptor. For this purpose we administered three doses of NBQX (1, 3 and 10 mg/kg i.v.) to anesthetized, artificially ventilated and paralyzed cats while monitoring spontaneously occurring cardiac sympathetic nerve activity, arterial blood pressure and heart rate. The 1 mg/kg dose of NBQX i.v. reduced both sympathetic nerve activity (-29 +/- 7%, P < 0.05, n = 4) and blood pressure (-27 +/- 5 mmHg, P < 0.05). Injection of 3 mg/kg NBQX produced a greater decrease in sympathetic nerve activity (-78 +/- 11%, P < 0.01, n = 8) and mean arterial pressure (-47 +/- 5 mmHg) and also reduced heart rate (-11 +/- 2 beats/min, P < 0.01). The depressant effects of NBQX on sympathetic nerve activity, blood pressure and heart rate were similar regardless of whether activity was recorded from pre- or postganglionic cardiac nerves, or from animals subjected to baroreceptor denervation.(ABSTRACT TRUNCATED AT 250 WORDS)

Potentiation of MK-801-induced breathing impairment by 2,3-dihydroxy-6-nitro-7-sulfamoyl-benzo(F)quinoxaline.

The purpose of our study was to examine whether a significant interaction occurs between NMDA and non-NMDA receptor antagonists on respiratory function. For this purpose chloralose-anesthetized cats were used and respiratory minute volume (VE), tidal volume (Vt) respiratory rate (f), inspiratory and expiratory durations, and end tidal CO2 (FeCO2) were monitored. In some animals, phrenic nerve activity was also continuously recorded. In five spontaneously breathing animals, the NMDA receptor antagonist MK-801 was administered in a dose of 0.1 mg/kg i.v., and produced decreases in VE, Vt, f and increases in inspiratory duration and FeCO2. Using these five animals exhibiting respiratory effects from prior MK-801 dosing, we then administered the non-NMDA receptor antagonist NBQX (2,3-dihydroxy-6-nitro-7-sulfamoyl-benzo(F)quinoxaline) i.v. in a dose of 3 mg/kg. This dose is too low to produce a neuroprotective effect in animal models of brain ischemia. In each of the five animals NBQX administration produced an immediate impairment of respiration, culminating in apneusis within 55 s after i.v. injection. In terms of phrenic nerve discharge, inspiratory duration was increased approximately 4-fold by MK-801, and with the addition of NBQX, continuous discharge of the phrenic nerve occurred. Finally, NBQX given i.v. to animals not pretreated with MK-801 had only a slight depressant effect on respiratory activity. These results obtained with co-administration of low doses of two drugs that block NMDA and non-NMDA receptors raise the spector that combined use of these agents to ameliorate disorders in neurological function may be extremely deleterious to respiratory function.

Acute effects of calcitonin gene-related peptide on the mechanical and electrical responses of the rat hemidiaphragm.

Calcitonin gene-related peptide (CGRP) acutely augments the contractile response of skeletal muscle to both direct and indirect stimulation. However, studies in whole muscle tissues have produced extremely variable results. To determine if differences in stimulation parameters are the source of this variation, the effects of increasing stimulus duration were evaluated in the isolated perfused rat hemidiaphragm. The effect of CGRP on the maximum force of contraction (Fc) was dependent upon the stimulus duration. CGRP (10(-6) M) produced an 11% increase in Fc with a 0.1-msec duration stimulus and a 32% increase with a 1.0-msec stimulus. In contrast, CGRP decreased the time for twitch relaxation and this effect was independent of stimulus duration. Additional studies demonstrated that CGRP shortened the relative refractory period. Compound muscle action potential recordings revealed that stimulus durations greater than 0.5 msec produced a second peak of electrical activity with an associated increased Fc. The effects of CGRP on Fc corresponded to the effects of CGRP on this second peak of compound muscle action potential activity. We conclude that, by decreasing the relative refractory period of the muscle tissue, CGRP enhances the potential for repetitive stimulation with commonly used experimental parameters.

Cognitive dysfunction in a patient with long-term occupational exposure to ethylene oxide. Role of ethylene oxide as a causal factor.

This case illustrates a comprehensive approach to assessing causality in a woman with apparent cognitive dysfunction, as measured by neuropsychological testing, and a 10-year history of occupational exposure to ethylene oxide. The analysis included a multidisciplinary examination of the patient, which took place several years after the termination of her exposure. In addition, all of the patient's prior medical and psychiatric records were reviewed, as were the records of her employer to ascertain her exposure history. Our evaluation revealed a pattern of neuropsychological findings not consistent with nervous system damage secondary to an organic effect of ethylene oxide. A more likely causal hypothesis is adopted: the patient's apparent cognitive dysfunction had a psychiatric etiology. This case also illustrates the potential impact of a patient's involvement in legal proceedings related to claims of neurocognitive dysfunction.

Cocaine acts in the central nervous system to inhibit sympathetic neural activity.

Cocaine was administered i.v. to decerebrate cats while monitoring cardiac preganglionic sympathetic nerve activity (SNA), arterial blood pressure (BP) and heart rate (HR). Cocaine, 4 mg/kg i.v., reduced SNA by 55 +/- 6%, but did not significantly affect BP or HR. Cocaine, in doses that were ineffective by the i.v. route, was administered into the vertebral artery and produced decreases in SNA, BP and HR in anesthetized cats. Administration of cocaine into the carotid artery was without effect. Topical administration of cocaine to the intermediate area of the ventrolateral medullary surface (25 micrograms/side) evoked hypotension and bradycardia. Nisoxetine, an inhibitor of norepinephrine uptake, applied bilaterally to the intermediate area (30 micrograms/side) exerted a similar hypotensive effect. Lidocaine administered in doses equivalent to those of cocaine had no significant effect on SNA when given i.v. or on BP when given into the vertebral artery. These results indicate that cocaine inhibits central sympathetic outflow and that the site of action appears to be in the hindbrain at a site that is reached by placement of the drug at the intermediate area of the ventrolateral medulla. The data also indicate that the mechanism of action of cocaine to inhibit sympathetic outflow may be unrelated to its local anesthetic action and may involve inhibition of catecholamine uptake in the ventrolateral medulla.

Mechanisms of respiratory failure produced by neostigmine and diisopropyl fluorophosphate.

Acetylcholinesterase inhibitors produce diverse physiologic effects, but lethal exposure consistently produces respiratory failure due to neuromuscular paralysis or depression of respiratory control centers in the medulla. Simultaneous measurement of gastrocnemius muscle contraction and efferent phrenic nerve activity was used to determine the primary cause of respiratory failure produced by neostigmine and diisopropyl fluorophosphate (DFP) in anesthetized cats. Both neostigmine and DFP abolished phrenic nerve activity prior to producing neuromuscular blockade. Furthermore, neostigmine did not alter brain acetylcholinesterase activity and pretreatment with either atropine methylbromide or atropine increased the dose of neostigmine required to abolish phrenic nerve activity. In contrast, DFP abolished brain cholinesterase activity and only atropine inhibited its respiratory effects. Despite the loss of efferent phrenic nerve activity, there is no evidence of a direct effect of neostigmine on respiratory control centers. Neostigmine may instead alter afferent inputs which modulate respiration to produce a reflex respiratory failure.

Inhibition of brain choline acetyltransferase in vivo: (E)-1-methyl-4-(1-naphthylvinyl)-1,2,3,6-tetrahydropyridine hydrochloride (B115), a depot form of a potent inhibitor.

The quaternary ammonium salt (E)-4-(1-naphthylvinyl)pyridine hydroxyethyl bromide (B111) and the tertiary amine salt (E)-1-methyl-4-(1-naphthylvinyl)-1,2,3,6-tetrahydropyridine hydrochloride (B115), both previously shown to protect against organophosphate (OP) toxicity, were examined in vivo for effects on rat brain choline acetyltransferase (CAT) activity and acetylcholine (ACh) levels. When administered iv, but not when given ip, B111 was able to inhibit brain CAT 29% and reduce brain ACh levels 25%, yet was unable to prevent soman-induced increases in ACh. B115, which may serve as a depot form of a quaternary ammonium analogue, was able to decrease CAT activity as much as 80% upon multiple ip administration. This CAT inhibitory potency was unprecedented for a tertiary amine salt of its structure. However, ACh levels were reduced by no more than 25% and B115 was ineffective in preventing soman- and sarin-induced increases in ACh. Since the degree of inhibition of CAT activity produced by B111 and B115 was not accompanied by a corresponding decrease in ACh levels, the protection afforded by these compounds against OP toxicity is most likely not related to CAT inhibition. B115 was also tested for its ability to affect cholinergic receptor binding. B115 was administered to rats ip, twice daily, at low doses throughout a 3-week period. Analysis of cortex tissue revealed a 45% increase in nicotinic receptor binding with no change in either total muscarinic receptor binding (M-1 and M-2) or high-affinity muscarinic receptor binding (M-2 alone).

Toxicities in rats with free versus liposomal encapsulated cisplatin.

Wistar rats (five in each group) were given either 1 mg/kg of free cisplatin, 1 or 2 mg/kg of liposomal encapsulated cisplatin, or saline solution intraperitoneally biweekly for 15 injections. Rats in the free drug group showed significantly less weight gain; two rats died during the study. At necropsy, the free cisplatin--treated rats showed gross and microscopic evidence of peritoneal fibrosis that was not detected in any of the remaining groups. The free cisplatin--treated rats showed serum and histologic evidence of renal damage; all five rats had moderate or severe acute tubular necrosis. No renal abnormalities were detected in rats that received 1 mg/kg, and only focal or mild changes were found in rats that received 2 mg/kg of the liposomal preparation. Neurotoxicity, as determined by nerve conduction and inclined plane studies, developed in rats treated with free and liposomal cisplatin. These results are encouraging and warrant further investigation.

Comparison of midazolam and diazepam by the intramuscular route for the control of seizures in a mouse model of status epilepticus.

A model system is described in which sustained clonic seizures are produced by a combination of phenytoin (PHT) and pentylenetetrazol (PTZ) in the mouse, the former agent preventing the terminal tonic spasms produced by the latter. In this system, midazolam (MDL), a water-soluble benzodiazepine, was compared with diazepam (DZP), a sparingly soluble agent which is widely used to treat status epilepticus (SE) in humans. Both agents were administered intramuscularly (i.m.) in approximately equieffective doses in animals exhibiting clonic seizure activity. MDL proved to be about twice as potent as DZP. Whereas control animals convulsed for a period of approximately 90 min, those treated with DZP 0.2 and 0.4 mg/kg convulsed for 7.8 and 3.9 min, respectively; mice receiving MDL 0.1 and 0.2 mg/kg convulsed for 1.9 and 1.4 min, respectively. MDL arrested seizures substantially more rapidly than diazepam (p less than 0.05). These data suggest that MDL has sufficiently rapid anticonvulsant action to merit evaluation for control of SE in humans when a rapidly absorbed antiepileptic drug (AED) is needed and intravenous (i.v.) administration is not feasible.

Effects of calcium channel blocking agents on neostigmine-induced fasciculations.

Male Sprague-Dawley rats were anesthetized with pentobarbital and prepared for monitoring contractions of the gastrocnemius muscle evoked by stimulation of the sciatic nerve. Animals received atropine prior to a dose of neostigmine of 0.02 mg/kg i.v. The effects on contractile strength and the number of fasciculations in a 2-min period were assessed. Pretreatment with phenytoin, 20 mg/kg, reduced the number of fasciculations to 32% of control without altering contractile strength. Both nifedipine and nitrendipine, 1 mg/kg each, virtually abolished fasciculations without altering twitch strength. Verapamil, 4 and 8 mg/kg, depressed fasciculation frequency to 50% of control without affecting pre-neostigmine twitch height. The dihydropyridine calcium blocking agents did however reduce the neostigmine-induced augmentation of contraction strength. These data suggest that a calcium-mediated current at presynaptic motor endings participates in the generation of repetitive nerve terminal discharges leading to muscle fasciculations.

Cardiovascular effects of 1-methyl-4-(1-naphthylvinyl)piperidine hydrochloride.

1-Methyl-4-(1-naphthylvinyl)piperidine (B-120) produced a dose related decrease in blood pressure in cats. B-120 did not alter the cardiovascular response to acetylcholine or vagal stimulation. It did not affect the response of the nictitating membrane to both pre- and post-ganglionic stimulation. In isolated cortical synaptosomes, B-120 decreased calcium flux below basal levels. Thus, the blockade of calcium channels appeared to be related to the production of hypotension and may be the mechanism by which B-120 protected against organophosphate toxicity.