Effects of cadmium chloride inhalation on airflow limitation to histamine, carbachol and adenosine 5'-monophosphate assessed by barometric whole body plethysmography in healthy dogs

The effects of pharmacological bronchoprovocation on airflow patterns and surrogate respiratory parameters assessed by barometric whole body plethysmography (BWBP) were investigated in healthy dogs, previously exposed to cadmium chloride inhalation. BWBP-derived respiratory variables were calculated (1) at baseline and (2) following nebulisation of increasing concentrations of histamine, carbachol and adenosine 5'-monophosphate (AMP) until enhanced pause (PENH) increased to 300% of baseline (PCPENH300). Bronchoalveolar lavage fluid (BALF) cytology before (BCC) and after (ACC) cadmium chloride inhalation revealed cadmium-induced airway inflammation. Neutrophils increased from 6.7 +/- 7.3% (728 +/- 104/microL) BCC to 77.8 +/- 8.6% (3255 +/- 1407/microL) ACC. PCPENH300 for all three agonists significantly decreased ACC (means+/-SD) as follows: PCPENH300(histamine) 0.72 +/- 0.28 mg/mL BCC, and 0.35 +/- 0.31 mg/mL ACC (P<0.02); PCPENH300(carbachol) 0.34 +/- 0.16 mg/mL BCC, and 0.064 +/- 0.032 mg/mL ACC (P<0.02); PCPENH300(AMP) 1000 mg/mL BCC, and 415 +/- 398 mg/mL ACC (P<0.03). The only clinical sign shown was coughing. It was concluded that airway hyperresponsiveness after induced airway inflammation can be determined by BWBP in conscious small sized dogs. BWBP could be a suitable technique to study the respiratory effects of urban environmental pollution in pets.

Post-seizures amygdaloallocortical microvascular lesion leading to atrophy and memory impairment

Although the incidence of seizures after a cerebrovascular event including intracerebral hemorrhage has been widely recognized, the present studies have demonstrated that generalized convulsive seizures can cause multifocal amygdaloallocortical hemorrhage and tissue necrosis, the origin of which remains to be established. The seizure-elicited amygdaloallocortical injured area, which we refer to as a focal injury-prone area (FIPA), was caused by cholinergic stimulation of the ventroposterolateral and thalamic reticular nuclei. The amygdaloallocortical injury was preceded by focal absence of neuronal COX-2 and presence of microvascular immunoreactivity to the pro-inflammatory cytokines, IL-1beta and TNF-alpha. The microvascular inflammation was followed by edema and multifocal amygdaloallocortical microhemorrhages, leading to atrophy and cognitive impairment. On the basis of the present results, we conclude that generalized convulsive seizures may be at the origin of amygdaloallocortical microvascular injury suggesting that, in addition to anticonvulsant treatment, an appropriate clinical evaluation and therapy for seizures-associated cerebrovascular accidents should be considered.

Laxative and anti-diarrheal activity of polycarbophil in mice and rats

We investigated the laxative and anti-diarrheal activity of polycarbophil, an insoluble hydrophilic polymer, in comparison with other agents used for treating functional bowel disorder (FBD). In naive rats, polycarbophil (500 mg/kg) increased fecal weight and water contents without producing diarrhea. Carboxymethylcellulose (CMC) did not produce evident changes in bowel movement. Picosulfate markedly produced diarrhea. Loperamide, trimebutine and granisetron decreased stool output dose-dependently. Constipation, indicated by decrease in fecal weight, was produced by loperamide and clonidine in rats. Polycarbophil (500 mg/kg) and CMC increased fecal weight without diarrhea. Conversely trimebutine further decreased fecal weight in constipated rats. Polycarbophil (500 mg/kg) suppressed diarrhea induced by castor oil, and at 250-500 mg/kg, it produced shaped stools in animals with stools loosened by prostaglandin E2, serotonin or carbachol in mice. Polycarbophil (500 mg/kg) also reduced stools in rats with stool output increased by wrap restraint stress (WRS). CMC had no effect in the diarrhea models, except for carbachol-induced diarrhea, and WRS-induced evacuation. Loperamide, trimebutine and granisetron inhibited diarrhea production and WRS-induced evacuation, except for carbachol-induced diarrhea. The results show that polycarbophil prevents constipation and diarrhea without inducing diarrhea or constipation, which is different from the other agents. Hydrophilic polymers such as polycarbophil will be promising agents for the treatment of FBD.

Receptor mechanisms and circuitry underlying NMDA antagonist neurotoxicity

NMDA glutamate receptor antagonists are used in clinical anesthesia, and are being developed as therapeutic agents for preventing neurodegeneration in stroke, epilepsy, and brain trauma. However, the ability of these agents to produce neurotoxicity in adult rats and psychosis in adult humans compromises their clinical usefulness. In addition, an NMDA receptor hypofunction (NRHypo) state might play a role in neurodegenerative and psychotic disorders, like Alzheimer's disease and schizophrenia. Thus, understanding the mechanism underlying NRHypo-induced neurotoxicity and psychosis could have significant clinically relevant benefits. NRHypo neurotoxicity can be prevented by several classes of agents (e.g. antimuscarinics, non-NMDA glutamate antagonists, and alpha(2) adrenergic agonists) suggesting that the mechanism of neurotoxicity is complex. In the present study a series of experiments was undertaken to more definitively define the receptors and complex neural circuitry underlying NRHypo neurotoxicity. Injection of either the muscarinic antagonist scopolamine or the non-NMDA antagonist NBQX directly into the cortex prevented NRHypo neurotoxicity. Clonidine, an alpha(2) adrenergic agonist, protected against the neurotoxicity when injected into the basal forebrain. The combined injection of muscarinic and non-NMDA Glu agonists reproduced the neurotoxic reaction. Based on these and other results, we conclude that the mechanism is indirect, and involves a complex network disturbance, whereby blockade of NMDA receptors on inhibitory neurons in multiple subcortical brain regions, disinhibits glutamatergic and cholinergic projections to the cerebral cortex. Simultaneous excitotoxic stimulation of muscarinic (m(3)) and glutamate (AMPA/kainate) receptors on cerebrocortical neurons appears to be the proximal mechanism by which the neurotoxic and psychotomimetic effects of NRHypo are mediated.

A simple method to investigate the inhibitory effects of drugs on gastric emptying in the mouse in vivo

INTRODUCTION

The aim was to develop a simple method to study modification of gastric motility in the mouse in vivo.

METHODS

Mice were fed a hydrated diet in which the fluid content of standard laboratory chow was increased by adding water. Gastric emptying was assessed at specified times following a 1-h treatment period with orally administered pharmacological agents.

RESULTS

We demonstrated consistent and progressive gastric emptying over a 4-h period, stomach content being decreased from 7.52+/-0.90 at time zero to 2.80+/-0.25 mg/g body weight after 4 h. Results demonstrated typical effects of inhibitory agents (atropine and morphine) and showed inhibitory effects of three potassium channel opening agents, pinacidil, cromakalim, and SDZ PCO400: the residue remaining in the stomach was increased by 3.66+/-0.84, 6.56+/-1.35, and 5.68+/-1.33 mg/g body weight respectively 1 h after treatment with 10 mg/kg of these agents, compared to vehicle controls.

DISCUSSION

The inhibitory activity observed correlated well with previous studies on the effects of potassium channel opening agents on mouse gastrointestinal motility in vivo and in vitro. The present model may thus be of value in the pharmacological investigation of gastrointestinal motility owing to cost and convenience advantages, together with the possibility of its application to studies using transgenic animals.

Exposure to 60-Hz magnetic fields and proliferation of human astrocytoma cells in vitro

Epidemiological studies have suggested that exposure to electric and magnetic fields (EMF) may be associated with an increased incidence of brain tumors, most notably astrocytomas. However, potential cellular or molecular mechanisms involved in these effects of EMF are not known. In this study we investigated whether exposure to 60-Hz sinusoidal magnetic fields (0.3-1.2 G for 3-72 h) would cause proliferation of human astrocytoma cells. Sixty-Hertz magnetic fields (MF) caused a time- and dose-dependent increase in proliferation of astrocytoma cells, measured by (3)H-thymidine incorporation and by flow cytometry, and strongly potentiated the effect of two agonists (the muscarinic agonist carbachol and the phorbol ester PMA). However, MF had no effect on DNA synthesis of rat cortical astrocytes, i.e., of similar, nontransformed cells. To determine the amount of heating induced by MF, temperatures were also recorded in the medium. Both 1.2 G MF and a sham exposure caused a 0.7 degrees C temperature increase in the medium; however, (3)H-thymidine incorporation induced by sham exposure was significantly less than that caused by MF. GF 109203X, a rather specific protein kinase C (PKC) inhibitor, and down-regulation of PKC inhibited the effect of MF on basal and on agonist-stimulated (3)H-thymidine incorporation. These data indicate that MF can increase the proliferation of human astrocytoma cells and strongly potentiate the effects of two agonists. These findings may provide a biological basis for the observed epidemiological associations between MF exposure and brain tumors.

Myoclonic and tonic seizures elicited by microinjection of cholinergic drugs into the inferior colliculus

The inferior colliculus (IC) is the initiation site in the neuronal network for the epileptic audiogenic seizure (AGS). The present study investigates the effects of alteration of IC cholinergic transmission on the elicitation of epileptic seizures. Unilateral microinjections of carbachol (3 and 6 micrograms/0.2 microliter) into the IC elicited intense locomotor activity, contraversive rotations and myoclonic seizures. This result indicates that the IC is the initiation site for the induction of myoclonic seizures and suggests that these myoclonic seizures may result from activation of m1 muscarinic receptors. Microinjections of the nicotinic-muscarinic antagonist, gallamine (2 and 6 micrograms/0.2 microliter), into the IC induced AGS susceptibility. However, microinjections of muscarinic antagonists, atropine (15 micrograms/0.2 microliter) and scopolamine (12 and 20 micrograms/0.2 microliter), or the nicotinic antagonist, hexamethonium (12 and 20 micrograms/0.2 microliter), into the IC have no effect. Gallamine-induced AGS susceptibility may result from a selective blockade of m2 muscarinic receptors.

Interactions between limbic, thalamo-striatal-cortical, and central autonomic pathways during epileptic seizure progression

We used immunocytochemistry to determine the regional and temporal distribution of Fos protein expression in awake and unrestrained rats after a unilateral stereotaxic microinjection of a cholinergic agonist, carbachol, in the thalamic ventroposterolateral and reticular nuclei, previously shown to cause limbic and generalized convulsive seizures. The microinjection of carbachol elicits behavioral alterations including immobilization, staring, facial and jaw clonus, rearing, and falling, followed by recurrent generalized convulsive seizures, and a pattern of c-fos expression throughout the brain. In addition to the hypothalamic paraventricular and supraoptic nuclei, the initial induction of c-fos expression was observed as early as 15 minutes after the carbachol microinjection, in the piriform and entorhinal cortices, the thalamic paraventricular, the supramammilary, the lateral parabrachial nuclei, and the central gray. From 30 minutes to 2 hours, corresponding to the occurrence of motor expression of limbic and recurrent generalized convulsive seizures, Fos immunoreactivity was seen in a number of functionally related brain regions including the hippocampus, the amygdala, and the anterior thalamic nucleus (limbic system); the thalamus, the basal ganglia, and the cortex (thalamo-striatal-cortical system); and the hypothalamus, the central nucleus of the amygdala, the pons, and the medulla (central autonomic system). On the basis of the present results showing regional and temporal c-fos expression and well known neuroanatomical connections, we have constructed a neural network relating the limbic, thalamo-striatal-cortical, and central autonomic systems. This analysis provides, for the first time, neuronal circuits and pathways relating epilepsy-elicited behavioral expression of convulsive seizures and adaptive homeostatic responses and could serve as a basis for studying central autonomic regulation during epileptic disorders.

Selective, tight-binding inhibitors of integrin alpha4beta1 that inhibit allergic airway responses

Integrin alpha4beta1 mediates leukocyte recruitment, activation, mediator release, and apoptosis inhibition, and it plays a central role in inflammatory pathophysiology. High-affinity, selective inhibitors of alpha4beta1, based on the Leu-Asp-Val (LDV) sequence from the alternatively spliced connecting segment-1 (CS-1) peptide of cellular fibronectin, are described that employ a novel N-terminal peptide "cap" strategy. One inhibitor, BIO-1211, was approximately 10(6)-fold more potent than the starting peptide and exhibited tight-binding properties (koff = 1.4 x 10(-4) s-1, KD = 70 pM), a remarkable finding for a noncovalent, small-molecule inhibitor of a protein receptor. BIO-1211 was also 200-fold selective for the activated form of alpha4beta1, and it stimulated expression of ligand-induced epitopes on the integrin beta1 subunit, a property consistent with occupancy of the receptor's ligand-binding site. Pretreatment of allergic sheep with a 3-mg nebulized dose of BIO-1211 inhibited early and late airway responses following antigen challenge and prevented development of nonspecific airway hyperresponsiveness to carbachol. These results show that highly selective and potent small-molecule antagonists can be identified to integrins with primary specificity for peptide domains other than Arg-Gly-Asp (RGD); they confirm the generality of integrins as small molecule targets; and they validate alpha4beta1 as a therapeutic target for asthma.

Plasma protein extravasation induced in the rat dura mater by stimulation of the parasympathetic sphenopalatine ganglion

It has been proposed that migraine could result from a neurogenic inflammation of the dura mater. According to this theory, inflammation could be initiated by an axon reflex of nociceptive nerve fibers, but the trigger of this axon reflex remains poorly understood. Previous works have shown that parasympathetic agonists can activate mast cells and/or sensory C-fibers, inducing pain and inflammation. The aim of the present work was to determine whether the activation of intracranial parasympathetic nerve fibers could trigger an inflammatory mechanism within the rat dura mater. Activation of the intracranial parasympathetic system was achieved by electrical stimulation of the sphenopalatine ganglion (SPG). The development of a neurogenic inflammation was estimated either by microscopic examination or by quantitative measurement of plasma protein extravasation (PPE) in the dura. To determine the respective roles of the parasympathetic and sensory innervations, two groups of rats were pretreated either with atropine or with capsaicin. Stimulation of the SPG induced a PPE increase of about 200% in the stimulated side on the dura mater. Extravasated material was mainly concentrated around small blood vessels. This extravasation was significantly reduced by capsaicin pretreatment and completely abolished by atropine. Infusion of carbachol in the common carotid artery induced PPE in the ipsilateral dura comparable to that induced by electrical stimulation of the SPG. This extravasation was also blocked by atropine infusion. These data indicate for the first time that the parasympathetic nervous system can trigger a neurogenic inflammation in the dura via muscarinic cholinergic receptors. Sensory C-fibers seem to play a role in this phenomenon. With respect to the potential autonomic imbalance described in the etiology of various types of vascular headaches, such a mechanism could be important in inducing attacks.

Modulation of the pressor response elicited by carbachol and electrical stimulation of the amygdala by muscarinic antagonists in conscious rats

1. The nature of the muscarinic receptor involved in mediating cardiovascular changes caused by unilateral microinjection of carbachol (5 nmol) into, and electrical stimulation (200-300 microA) of, the amygdaloid complex was investigated in conscious, unrestrained female Sprague-Dawley rats. 2. Unilateral microinjection of carbachol (5 nmol; n = 6) and electrical stimulation (200-300 microA, 80 Hz, 30 s; n = 4) caused a significant rise in blood pressure of 21 +/- 4 mmHg and 25 +/- 5 mmHg, respectively. These changes were associated with no overall effect on heart rate. The effects of electrical stimulation were found to be repeatable. 3. Pretreatment i.c.v. with pirenzepine (5-20 mmol; n = 6-7 for each dose), dose-dependently inhibited the rise in blood pressure induced by carbachol, whereas AF-DX 116 (100 nmol; n = 6) failed to have any effect on the carbachol-induced pressure response. Neither antagonist alone had any effect on resting baseline variables. 4. Unilateral microinjections of atropine sulphate (1-100 nmol; n = 4-6 for each dose), pirenzepine (0.03-10 nmol; n = 4 for each dose) or AF-DX 116 (10-60 nmol; n = 4-5 for each dose), into the amygdala, dose-dependently inhibited the rise in blood pressure caused by electrical stimulation (200-300 microA). The ID50 values were 1.05, 0.23 and 39.5 nmol, respectively. Although pirenzepine seemed to be more potent than atropine, this difference was not significant. 5. It is concluded that the rise in blood pressure elicited by unilateral microinjection of carbachol into, or electrical stimulation of, the amygdaloid complex is mediated by M1-muscarinic receptors.

Pharmacological characteristics of BDTI, a new isoquinoline-derived beta 2-adrenoceptor agonist, in canine trachea and rat heart

The tracheal relaxing effects and beta 2-selectivity of BDTI (1-benzyl-6,7-dihydroxy-1,2,3,4-tetrahydroisoquinoline HBr) were investigated in canine trachea and rat heart by radioligand binding assay and pharmacological experiments in comparison with those of other beta-adrenoceptor agonists, salbutamol and isoprenaline. The potency of relaxing effect on carbachol-induced contraction in isolated canine trachea was in the order of isoprenaline (pD2 = 6.70 +/- 0.08) > BDTI (6.11 +/- 0.06) approximately salbutamol (6.14 +/- 0.08). ICI-118,551 (a selective beta 2-antagonist) and atenolol (a selective beta 1-antagonist) inhibited the relaxant action of BDTI with pKB values of 8.4 and 5.3, respectively, corresponding to high affinity for ICI-118,551 and low affinity for atenolol in antagonizing this response. The Kd values of radioligand ([3H]-CGP12177) were 453.3 +/- 30.8 and 563.4 +/- 96.7 pmol/l in cultured canine tracheal smooth muscle cells (TSMCs) and rat cardiomyocytes, respectively, and the Bmax values were 64.6 +/- 10.7 and 245.7 +/- 44.5 fmol/mg protein, respectively. BDTI, salbutamol and isoprenaline inhibited the binding of [3H]-CGP12177 in a concentration-dependent manner in cultured canine TSMCs (Ki 0.73 +/- 0.15, 0.75 +/- 0.21 and 0.24 +/- 0.05 mumol/l, respectively) and rat cardiomyocytes (Ki 2.76 +/- 0.36, 2.31 +/- 0.26 and 0.22 +/- 0.03 mumol/l, respectively). These results demonstrated that BDTI possessed moderate selectivity (3.8-fold) to beta 2-adrenoceptors as judged from the Ki (heart)/Ki (trachea) value (salbutamol 3.1-fold, isoprenaline 0.92-fold). BDTI and salbutamol also stimulated cAMP formation in a concentration-dependent manner in cultured canine TSMCs (EC50 0.5 +/- 0.2 and 0.4 +/- 0.1 mumol/l, respectively) and rat cardiomyocytes (EC50 6.2 +/- 0.5 and 5.7 +/- 0.6 mumol/l, respectively). The selectivity of BDTI and salbutamol for beta 2-adrenoceptors on the cAMP response were 12.4 and 14.3 times, respectively. It is concluded that BDTI is a beta 2-selective adrenoceptor agonist.

A central cholinergic link in the cardiovascular effects of the benzodiazepine receptor partial inverse agonist FG 7142

Previous work demonstrated that systemic administration of the benzodiazepine receptor (BZR) partial inverse agonist beta-carboline FG 7142 (FG) augments the cardiovascular response to non-signal stimuli, similar to the effects of an aversive context. Analysis of the parasympathetic and sympathetic contributions to the effects of FG prompted the hypothesis that increases in central cholinergic activity mediates the potentiation of the cardioacceleratory response by FG. Consistent with this hypothesis, the present experiments demonstrate: (a) intracerebroventricular (ICV) infusion of the cholinergic receptor agonist carbachol mimics the response-potentiating effects of FG; (b) this effect of carbachol was blocked by ICV co-administration of the muscarinic antagonist atropine; (c) ICV infusions of atropine blocked the potentiation of the cardioacceleratory response by systemically administered FG, but did not alter the basal response to the stimulus; and (d) 192 IgG-saporin-induced lesions of basal forebrain cholinergic neurons prevented the FG-induced potentiation of the cardioacceleratory response, again without altering the basal cardiac response. These data strongly support the hypothesis that the effects of FG on cardiac reactivity are mediated via an activation of central muscarinic cholinergic mechanisms.

Computer assisted recognition and quantitation of the effects of airborne chemicals acting at different areas of the respiratory tract in mice

The pattern and timing of a normal breath in unanesthetized mice was analyzed from measurement of inspiratory and expiratory airflows (VI and VE). Airflow was measured via a differential pressure transducer, attached to a pneumotachograph, which itself was attached to a body plethysmograph into which a mouse was placed. The analog voltage from the differential pressure transducer was digitized and stored for analysis on a microcomputer. Criteria were developed to classify each breath as normal (N) or belonging into one of seven abnormal categories. The abnormal categories were arrived at by computer analysis, recognizing specific modifications of the normal pattern into patterns of: sensory irritation of the upper respiratory tract (S), airflow limitation within the conducting airways of the lungs (A) or pulmonary irritation at the alveolar level (P). Combinations of these effects, i.e., S+A, P+A, P+S and P+S+A were also recognized. Computer analysis of each breath also permitted quantitative evaluation of the degree of S, A or P abnormalities. To induce each type of effect we used inhalation exposures to 2-chlorobenzylchloride, carbamylcholine or propranolol. We propose that this approach will permit rapid evaluation of the possible effects of airborne chemicals at three levels of the respiratory tract, with the classification of the type of effect easily obtained in an objective way using well defined criteria, followed by quantitation of the degree of each effect.

Chronic alcohol intake and carbachol-induced acute pancreatitis in the rat

Alcohol-induced changes in cholinergic and pancreozymin pathways regulating exocrine pancreatic secretion have been proposed to play a crucial role in the pathogenesis of acute alcoholic pancreatitis. In the present study we investigated the role of chronic alcohol intake in an experimental acute pancreatitis induced in rats by cholinergic hyperstimulation. Chronic alcohol intake interfered with the function of rat pancreatic muscarinic receptors in carbachol-induced acute pancreatitis. However, chronic alcohol intake did not sensitize the experimental animals to cholinergic hyperstimulation. Whether this increased resistance at the level of pancreatic muscarinic receptors contributes to acute alcoholic pancreatitis is discussed in the present article.

Involvement of M1 muscarinic receptors in the initiation of cholinergically induced epileptic seizures in the rat brain

The present study was designed to determine the types of acetylcholine receptors involved in the initiation of epileptic seizures from the zona incerta and surrounding structures by cholinergic stimulation in rats. Unilateral intracerebral microinjection of the mixed muscarinic and nicotinic agonist carbachol (3 micrograms) produced generalized seizures in 12 of 20 rats studied. Local pretreatment with equimolar doses of acetylcholine receptor antagonists was used as a method of determining the receptor type involved in the initiation of cholinergically induced seizures in the rat diencephalon. Pretreatment with the M1 muscarinic receptor antagonist, pirenzepine (7 micrograms), abolished carbachol-induced seizures in 91% of the animals tested. The M2 muscarinic receptor antagonist, methoctramine (12 micrograms) and the nicotinic receptor antagonist, mecamylamine (3 micrograms), were relatively ineffective in antagonizing seizures in 9% and 27%, respectively. The results suggest that M1 muscarinic receptors are preferentially involved in the initiation of generalized epileptic seizures in the basal diencephalon of the rat.

An in vitro system to screen for diarrheagenic chemicals

We examined an in vitro system to screen for diarrheagenic chemicals using an established intestinal cell line (T84 human colonic carcinoma). The cells were grown on Millicell-PCF (polycarbonate membrane) wells. The cells were seeded at approximately 5 x 10(6) cells/30mm well and incubated for 9-11 days in a 5% CO2 incubator saturated with water at 37 degrees C. The culture medium was a 1:1 mixture of Ham's F12 and Dulbecco's MEM with 5% fetal bovine serum and 25 micrograms/ml gentamicin sulfate. The well containing cells was removed from the incubator and mounted in a modified Ussing chamber for measurement of short-circuit current (ISC). Chemical-induced increases in ISC are usually indicative of electrogenic epithelial Cl- secretion, which is associated with diarrheagenic effects in animals and humans. T84 cells grown on Millicell-PCF membrane responded with an increase in ISC after basolateral addition of the cholinergic (muscarinic) agonist carbachol, prostaglandin E2, 16,16-dimethylprostaglandin E2, and forskolin, while non-diarrheagenic prostaglandin D2 did not affect ISC. Based on our results, this in vitro system has the potential to be adapted as a rapid screen for detecting diarrheagenic chemicals.

Susceptibility to seizures produced by chemical convulsants and maximal electric shock in rats after electrolytic lesions into the red nucleus

Bilateral electrolytic lesions into the red nucleus (RN) of rat elicit an increase in susceptibility to seizures induced by pilocarpine, kainic acid, isoniazid, pentylenetetrazole, bicuculline and maximal electric shock (MES). It was also observed that carbachol-induced wet-dog shakes were increased in the RN-lesioned rats. The brain acetylcholine (ACh) and gamma-aminobutyric acid (GABA) concentrations were significantly decreased in the striatum and substantia nigra, respectively. There were no changes in electroencephalogram (EEG) recordings in the RN-lesioned group compared with sham-operated rats. Based on the results it is proposed that the RN is involved in the generalization and acceleration of seizure activity through the cholinergic and GABA-ergic system.

Studies on the development of tolerance and potential spinal neurotoxicity after chronic intrathecal carbachol-antinociception in the rat

The antinociceptive effect in rats produced by chronic intrathecal administration of carbachol was studied for 14 days by the tail immersion test and the paw compression test. Daily injection of 10 micrograms carbachol intrathecally (lumbar level) to 8 rats produced an increase in latency times lasting from day 1 to day 4. The effect was statistically significant during the first 4 days, but not thereafter in both the tail immersion test and the paw compression test as compared to the rats (n = 6) injected with saline. Histopathological examinations of the lumbar spinal cord by light and electron microscopy revealed no signs of neurotoxic reactions of the neurons, nor the spinal tracts. Quantitative morphometric analyses were made by the "disector method", which is an unbiased stereological estimator of cell number and mean cell volume. In the laminae I-III of the L:1 segment, an average number of 88,000 cells/mm3 was found and the mean cell volume was calculated at 560 microns3. Comparison with untreated rats (n = 4) and those injected with saline showed no statistically significant differences. In the present study, the combination of different morphological analyses offers a sensitive method to trace toxic reactions of the nervous tissue. According to these results, intrathecal carbachol produces antinociception, and seems atoxic to spinal nervous tissue, but before intrathecal administration of carbachol to humans is considered, more neurotoxicological data must be obtained.

Aerosol deposition in the lung with asymmetric airways obstruction: in vivo observation

Both the total and regional aerosol deposition were measured in six adult sheep before and after an induction of asymmetric airway obstructions, either by local instillation of carbachol solution (CS, 0.1%) distal to the right main bronchus or inhalation challenge of the right lung with carbachol aerosol (CA, 10 breaths). Total lung deposition was determined by monitoring inert monodisperse aerosols [1.0 micron mass median aerodynamic diam (MMAD)] breath-by-breath, at the mouth, by means of a laser aerosol photometer. Cumulative aerosol deposition over the first five breaths as a percent of the initial aerosol concentration (AD5) was used as a deposition index. Regional deposition pattern was determined by scintigraphic images of sulfur-colloid aerosol (1.5 microns MMAD) tagged with 99mTc. Radioactivity counts in the right (R) and left lung (L) were expressed as a percent of the whole lung count. Half-lung AD5 was then determined by multiplying AD5 by fractional radioaerosol depositions in R or L. Pulmonary airflow resistance (RL mean +/- SE), as determined by an esophageal balloon technique, increased by 111 +/- 28 and 250 +/- 96% after CA and CS, respectively (P less than 0.05). AD5 also increased in all the sheep tested by 29 +/- 3 and 52 +/- 8%, respectively, after CA and CS (P less than 0.05). Radioaerosol deposition pattern was even at base line (R/L = 51:49) but shifted toward the unchallenged L after CS (R/L = 40:60). Deposition pattern after CA was variable: a shift toward L in three, no change in one, and a shift toward the R lung in two sheep.(ABSTRACT TRUNCATED AT 250 WORDS)

Prevention by prostaglandins of caerulein-induced pancreatitis in rats

Acute edematous pancreatitis was produced in rats by subcutaneous administration of caerulein. Pancreas weight, pancreas histology and plasma amylase were used as endpoints to quantitate the severity of the syndrome. A caerulein dose of 10 micrograms/kg.hour produced the most severe pancreatitis, whereas at 5 micrograms/kg.hour the values were half-maximal. The pancreatic lesions were characterized by edema, formation of cytoplasmic vacuoles, leukocytic infiltration, necrosis, and with time (12-hour caerulein infusion) dilated acini. Cholecystokinin octapeptide also produced pancreatitis when given at ten times the dose required for caerulein (50 micrograms/kg.hour instead of 5 micrograms/kg.hour). Carbachol did not induce pancreatitis. Two prostaglandins, 16,16-dimethyl prostaglandin E2 injected subcutaneously and prostaglandin E2 infused subcutaneously, dose dependently prevented caerulein-induced pancreatitis (pancreatic edema, leukocytic infiltration, and necrosis) and reduced the number and size of intracellular vacuoles. The ED50 were 15 to 25 micrograms/kg for 16,16-dimethyl prostaglandin E2 and 90 micrograms/kg.hour for prostaglandin E2. Neither prostaglandin, given at doses inhibiting the development of pancreatitis, prevented the retardation of gastric emptying caused by caerulein, a finding suggesting that the prostaglandins may act specifically on the effect of caerulein on the pancreas but not on caerulein receptors in gastric smooth muscle. Indomethacin, an inhibitor of prostaglandin synthesis, and methscopolamine bromide, an anticholinergic agent, had no effect on caerulein-induced pancreatitis. We concluded that prostaglandins of the E type prevent the development of caerulein-induced pancreatitis. The mechanism by which prostaglandins protect the pancreas may involve stabilization of lysosomes within the acinar cells and inhibition of intracellular activation of pancreatic digestive enzymes.

Anatomical analysis of frontal cortex sites at which carbachol induces motor seizures in the rat

High amplitude spiking representative of seizures, accompanied by an unusual motor behavior pattern of rearing and forelimbic clonus resembling "boxing," was elicited by microinjection of the cholinergic agonist, carbachol, 4 micrograms, into the medial prefrontal cortex of the rat. A rating scale devised to score the behavior revealed a motor pattern elicited by carbachol from the medial anterior cortex which was similar to that described by Racine for electrical stimulation of the amygdala. Topographical analysis of the areas surrounding the medial anterior cortex region revealed that the motor manifestations of seizures were elicited over a wide region of the anterior cortex, with scores significantly lower at carbachol microinjection sites greater than 1 mm rostral, 2 and 3 mm caudal, and 2 mm lateral to the standard medial prefrontal cortex site. Unilateral microinjection of carbachol yielded motor seizures primarily from the contralateral forepaw, suggesting involvement of a crossed pathway. Retrograde tracing with fast blue dye, combined with immunostaining for choline acetyltransferase and NADPH-diaphorase, found that the cholinergic neurons innervating the standard microinjection site were the dorsolateral tegmental cells, as previously reported, which have been shown to also contain substance P and corticotropin releasing factor. In addition, cholinergic neurons of the nucleus basalis of Meynert region were found to innervate the standard microinjection site. These findings implicate cholinergic innervation of the rostral cortex in classical limbic seizures.

Cholinergic induction of seizures in the rat prefrontal cortex

Intracerebral microinjection of the cholinergic agonist, carbachol, into the medial prefrontal cortex of the rat, induced a profound behavioral syndrome consisting of repetitive, stereotyped forepaw treading in an upright posture. Electroencephalographic analysis revealed multiple bursts of sharp waves, 200-300 microV, accompanying the carbachol-elicited motor behavior. Pretreatment with intraperitoneal doses of three anticonvulsant drugs, clonazepam, diazepam, and pentobarbital, blocked the manifestation of the motor behavior. These observations suggest that activation of cholinergically innervated regions of the rat medial prefrontal cortex induces an atypical form of seizures.

Studies on the mechanism of wet dog shakes produced by carbachol in rats

In an attempt to elucidate the mechanism of wet dog shakes (WDS) produced by carbachol administered into the rat lateral brain ventricle, the effects of blockade of muscarinic and nicotinic receptors on shaking response and the effects of carbachol on central catecholaminergic, serotonergic (5-HT) and GABAergic functions were studied in rats. The muscarinic receptor antagonists, atropine and scopolamine attenuated WDS produced by carbachol, whilst a peripherally active muscarinic receptor antagonist, scopolamine methyl nitrate, failed to influence WDS. The nicotine antagonist, mecamylamine, did not affect WDS caused by carbachol either. Carbachol dose dependently decreased brain concentration of noradrenaline (NA) but failed to affect the concentration of dopamine (DA). While the brain concentration of 5-HT was unchanged, the concentration of 5-hydroxyindoleacetic acid (5-HIAA) was increased in a dose-related manner. The catecholamine turnover times were unaffected whereas 5-HT turnover time was significantly prolonged. Atropine, but not mecamylamine, prevented the decrease in brain NA induced by carbachol. Consequently, the carbachol-induced enhancement in the level of 5-HIAA was completely blocked by atropine and only slightly influenced by mecamylamine. Neither brain GABA concentration nor glutamic acid decarboxylase activity were affected by carbachol. Behavioral and biochemical data suggest that WDS produced by carbachol may be mediated through the stimulation of central muscarinic receptors. The anatomical localization and exact mechanism of carbachol-induced WDS remain to be elucidated.

Induction of anticholinesterase tolerance in rats with doses of disulfoton that produce no cholinergic signs

The induction of anticholinesterase tolerance has, in the past, been achieved by using multiple doses of organophosphorus ester insecticides that initially caused cholinergic signs. The purpose of this study was to ascertain whether anticholinesterase tolerance could be induced with doses of an anticholinesterase that produced no overt cholinergic signs. Rats were fed diets containing 0, 7.5, or 20 ppm disulfoton. Animals fed at the 7.5 ppm level were without cholinergic signs throughout the period of feeding. Rats from this group were significantly more resistant to the lethal effect of carbachol than rats given the control diet after 58 and 62 d on the diet. Animals fed 20 ppm disulfoton in the diet initially showed signs that gradually disappeared with time on the diet. Rats fed at this level were more resistant to the lethal effect of carbachol than controls on all challenge dates (30, 45, 58, and 62 d on the diets) and more resistant than animals fed 7.5 ppm only on d 38 and 45. Thus the organophosphorus ester insecticide disulfoton, fed to rats in a dietary concentration that depressed acetylcholinesterase but was insufficient to cause cholinergic signs, induced tolerance to the lethal effects of carbachol. The length of time on an experimental diet before resistance to carbachol could be demonstrated was greater for the experimental group given 7.5 ppm disulfoton than the group given 20 ppm disulfoton in the diet.

Tolerance to the carbamate insecticide propoxur

Male mice were given the carbamate insecticide propoxur (2-isopropoxy phenyl methylcarbamate; Baygon) in the drinking water at weekly increasing concentrations (from 50 to 2000 ppm), for a period of 6 weeks. At the end of the treatment the LD50 for propoxur was significantly higher in the treated animals as compared with controls. Propoxur-treated animals were also resistant to the hypothermic effect of an acute administration of the same compound. Groups of mice were challenged with the cholinergic agonist carbachol at intervals during the drinking water dosing and at its end. No differences in sensitivity to carbachol acute toxicity were found between control and treated animals. Propoxur-tolerant animals were also not resistant to the hypothermic effect of oxotremorine, another cholinergic agonist. [3H]Quinuclidinyl benzilate ([3H]QNB) binding (a measure of muscarinic receptor density and affinity) in forebrain, hindbrain and ileum never differed in control and treated mice. The possibility that repeated administrations of propoxur induced increased metabolic inactivation was tested by measuring hexobarbital sleeping time and carboxylesterase activity in treated and control mice. No changes in tissue carboxylesterase activities occurred but hexobarbital sleeping time was significantly reduced in propoxur treated animals suggesting an induction of hepatic microsomal enzymes. These results suggest that tolerance to propoxur is not mediated by a decrease of cholinergic receptors, as reported for other acetylcholinesterase inhibitors, but possibly by an enhancement of its metabolism.

Commonly used intraocular medications and the corneal endothelium

Forty-one cats had balanced salt solution, chymotrypsin, epinephrine hydrochloride with preservatives in varying concentrations, acetylcholine chloride, and carbachol injected intracamerally to determine the toxic effects on the endothelium. Specular microscopy was performed both before and after injection, and for each of the medications, the cell densities were compared with the results obtained with the balanced salt solution. The mean postinjection density as compared with the preinjection density for the medications varied between 98% and 108%, and there were no statistically significant differences between each medication group and the balanced salt solution results. From the results of this study, it is believed that when indicated, these medications probably do not produce substantial toxic effects on the corneal endothelium.

[Effect of prostaglandin F2 alpha on the acute toxicity of cholinergic drugs in mice]

Studies on white mice of acute toxicity of cholinergic drugs (carbachol, physostigmine, pilocarpine) intraperitoneally made it possible to ascertain the magnitudes of DL50 as follows: 2.5 mg/kg for carbachol, 0.644 mg/kg for physostigmine and 150 mg/kg for pilocarpine. Intraperitoneal administration of prostaglandins F2 alpha (10 and 25 mg/kg) 15 min before carbachol, physostigmine and pilocarpine increased the toxicity of the drugs and considerably lowered their DL50, while the administration of the same doses of prostaglandins F2 alpha in control mice did not enhance side effects. The animals' survival after 24 hours elapsed was equal to 100%.

Secretagogue-produced duodenal ulcers in the rat

Duodenal ulcers were produced in rats by the subcutaneous infusion for 6-48 hours of two gastric secretagogues in combination: pentagastrin (2 or 4 microgram kg-1 min-1) and carbachol (0-4 or 0-8 microgram kg-1 min-1). With increasing duration of infusion and higher doses there were increases in the incidence, severity, number and perforation rate of duodenal ulcers, their caudad distribution and mortality from peritonitis. This method of producing duodenal ulcers may sufficiently resemble the clinical situation to provide a model for the study of anti-ulcer drugs and the natural history of duodenal ulcers.

Cholinomimetic teratogens. III. Interaction with amino acids known as neurotransmitters

The amino acids gamma-aminobutyric acid, taurocholate, guanidine, glycine, and beta-alanine, known to have putative functions as neurotransmitters, when given as supplement to carbachol or decamethonium, greatly reduced the incidence of malformations produced in chicken embryos by these depolarizing cholinomimetic teratogens. In combination with the nondepolarizing teratogens neostigmine and pyridostigmine similarly beneficial effects occurred only by supplementation with gamma-aminobutyric acid.