N-METHYL-d-ASPARTATE ANTAGONISTS, GLUTAMATE RELEASE INHIBITORS, 4-AMINOPYRIDINE AT NEUROMUSCULAR TRANSMISSION

It is thought that glutamate (GLU) and acetylcholine (ACh) are co-released in the neuromuscular junction (NMJ). Consequently, GLU is also a mediator or modulator of neuromuscular transmission (n-m) together with ACh. Therefore we decided to investigate the role of GLU in n-m by using isolated rat phrenic nerve–hemidiaphragm preparations. Since the GLU receptors present at NMJ have been reported to be predominantlyN-methyl-d-aspartate (NMDA) subtype, some non-competitive and competitive NMDA receptor blockers, MK801, ketamine, dextromethorphan and CGP 37849, and GLU release inhibitors, clonidine, guanfacine, tizanidine were used at their optimum concentrations in medium after having found them from dose–response curves. The preparations were first stimulated indirectly in the presence of the optimum concentrations of the drugs used and tensions developed were recorded isometrically through a force displacement transducer on a polygraph linked to a computer + Math coprocessor by an analog converter. All drugs at their optimum concentrations suppressed contractions significantly. Prolyl-glycinamide (PLG) or phenyl-succinate, both of which are the inhibitors of GLU production also suppressed the contraction significantly, following depletion of GLU stores by tetanic contraction in nerve endings. 4-Aminopyridine, which has been shown to release GLU augmented the contractions which were also completely abolished by the NMDA receptor antagonists or GLU release inhibitors at their higher concentrations than their optimum ones. The direct stimulation of the muscles elicited statistically insignificant but higher contractions than controls at the optimum concentrations of the antagonists or inhibitors in medium. The results were discussed and it was concluded that blockade of NMDA receptors, the inhibition of GLU release or the suppression of GLU production inhibit the contractions of the rat-isolated hemidiaphragms elicited by indirect electrical stimulation, without altering acetylcholinergic part of the contraction cascade.     

Calcium dependence of contractile activation of isolated sheep urethra. I: Responses to electrical stimulation

In isolated sheep urethral smooth muscle at resting tension, responses elicited by electrical stimulation of nerves were either contraction (40%), or contraction preceded by relaxation (60%). All responses were suppressed by tetrodotoxin (TTX), but at stimulation frequencies exceeding 16 Hz, there was a small TTX resistant contraction, which at the highest frequency used (50 Hz) amounted to about 15% of the total response. alpha-Adrenoceptor blockade suppressed the contractions, as did chemical sympathectomy with 6-hydroxydopamine. In calcium-free medium all electrically induced contractions were abolished. Nifedipine, verapamil, and lanthanum had concentration-dependent depressant actions, whereas Bay K 8644 (10(-6) M) significantly increased the responses. In preparations prelabelled with 3H-noradrenaline, electrical stimulation caused a release of 3H that could be blocked by TTX, and effectively reduced by calcium-free medium and lanthanum. However, the release was unaffected by nifedipine, and moderately reduced by high concentrations of verapamil (10(-5) M). It is suggested that contractile responses to electrical stimulation in isolated sheep urethral smooth muscle are mediated by the sympathetic nervous system, mainly through release of noradrenaline stimulating postjunctional alpha 1-adrenoceptors. The release of noradrenaline, as well as the action of released noradrenaline on postjunctional membranes are calcium-dependent. However, the calcium entry pathways used are partly different from those inhibited by organic calcium antagonists.     

Effects of diazepam and diphenylhydantoin on elicited and spontaneous seizures in kindled rats: a double dissociation

Diazepam (1 mg/kg) was more effective than diphenylhydantoin (100 mg/kg) in suppressing motor seizures elicited in kindled rats by amygdaloid stimulation; however, the effect of these drugs on the incidence of spontaneous motor seizures in rats kindled by amygdaloid stimulation was just the opposite. At the same doses, diphenylhydantoin effectively suppressed spontaneous motor seizures, but diazepam did not. This double dissociation suggests the need for caution in drawing inferences concerning spontaneously recurring seizures from studies of elicited seizures.     

Presynaptic, muscarinic inhibition of non-adrenergic, non-cholinergic neuromuscular transmission in the chicken rectum.

Cholinergic inhibition of the non-adrenergic, non-cholinergic ( NANC ) transmission was investigated in the chicken isolated rectum with Remak's nerve attached. Stimulation of Remak's nerve (RT stimulation) at frequencies higher than 5 Hz elicited a late, slow contraction of the rectum in addition to an initial, fast NANC contraction. The late, slow contraction was blocked by atropine (0.25 microgram ml-1), potentiated by physostigmine (50 ng ml-1) and accompanied by an overflow of acetylcholine into the vascular perfusate, indicating the existence of cholinergic innervation to the rectum via Remak's nerve. RT stimulation (10 pulses at 0.5-1.0 Hz) elicited NANC -mediated excitatory junction potentials (e.j.ps). The e.j.p. amplitude declined at the second stimulus and then increased to reach a plateau. Atropine, by abolishing this decrease in amplitude, increased the mean amplitude of the e.j.ps during trains of stimuli but atropine did not affect the amplitude of the first e.j.p. Physostigmine reduced the mean e.j.p. amplitude, and this action was readily antagonized by atropine. A single intramural nerve stimulation delivered 2s or less before RT stimulation with trains of stimuli, suppressed the amplitude of the first e.j.p. of the train. This effect was abolished by atropine. Atropine in concentrations high enough to affect the e.j.p. amplitude had no effect on the resting membrane potential, the threshold for generating an action potential, or membrane resistance of the smooth muscle. It is concluded that RT stimulation at low frequencies causes the release of acetylcholine simultaneously with the NANC transmitter. The released acetylcholine acts mainly on prejunctional muscarinic receptors and mediates an inhibitory effect on the release of the NANC transmitter.     

Calcium Dependence of Contractile Activation of Isolated Sheep Urethra I: Responses to Electrical Stimulation

In isolated sheep urethral smooth muscle at resting tension, responses elicited by electrical stimulation of nerves were either contraction (40%), or contraction preceded by relaxation (60%). All responses were suppressed by tetrodotoxin (TTX), but at stimulation frequencies exceeding 16 Hz, there was a small TTX resistant contraction, which at the highest frequency used (50 Hz) amounted to about 15% of the total response. α-Adrenoceptor blockade suppressed the contractions, as did chemical sympathectomy with 6-hydroxydopamine. In calcium-free medium all electrically induced contractions were abolished. Nifedipine, verapamil, and lanthanum had concentration-dependent depressant actions, whereas Bay K 8644 (10^?6 M) significantly increased the responses. In preparations prelabelled with³H-noradrenaline, electrical stimulation caused a release of ³H that could be blocked by TTX, and effectively reduced by calcium-free medium and lanthanum. However, the release was unaffected by nifedipine, and moderately reduced by high concentrations of verapamil (10^?5 M). It is suggested that contractile responses to electrical stimulation in isolated sheep urethral smooth muscle are mediated by the sympathetic nervous system, mainly through release of noradrenaline stimulating postjunctional α₁-adrenoceptors. The release of noradrenaline, as well as the action of released noradrenaline on postjunctional membranes are calcium-dependent. However, the calcium entry pathways used are partly different from those inhibited by organic calcium antagonists.     

Failure of isoprenaline and beta-receptor blocking drugs to modify depressor response and bradycardia induced by electrical stimulation of the anterior hypothalamus of cats

Summary The role of the hypothalamic betaadrenoceptors in the depressor response and bradycardia induced by stimulation of the anterior hypothalamus was studied in cats. In chloralose and urethane anaesthetized cats the anterior hypothalamus was superfused with artifical cerebrospinal fluid through a push-pull cannula. Electrical stimulation of the anterior hypothalamus with the tip of the cannula elicited a fall of systemic blood pressure and a decrease in heart rate. Superfusion of the anterior hypothalamus with isoprenaline did not change the depressor response and bradycardia induced by electrical stimulation of the anterior hypothalamus. Superfusion with atenolol or butoxamine also failed to modify the responses. Superfusion with (±)-propranolol significantly suppressed the responses. However, superfusion with (+)-propranolol suppressed the responses to the same extent. The resting systemic blood pressure and heart rate were not significantly changed by superfusion of the hypothalamus with these drugs. These results suggest that beta-adrenoceptors of the anterior hypothalamus are not involved in the depressor response and bradycardia elicited by hypothalamic stimulation.This work was supported by the Deutsche Forschungsgemeinschaft     

Electroencephalographic effect of quinupramine in the rabbit

Electroencephalographic (EEG) effect of quinupramine was investigated in unanesthetized rabbits with chronic electrode implants, and it was compared with those of imipramine and amitriptyline. Quinupramine (0.56-3.2 mg/kg) induced a marked drowsy pattern of spontaneous EEG: high voltage slow waves increased in the cortex, while the hippocampal theta rhythm was desynchronized. Imipramine (1.0-5.6 mg/kg) and amitriptyline (0.56-3.2 mg/kg) also elicited similar EEG effects. The EEG arousal response to auditory stimulation and to electric stimulation of the mesencephalic reticular formation, posterior hypothalamus and centromedian thalamus was markedly suppressed by quinupramine, imipramine and amitriptyline. The EEG arousal response induced by i.v. injection of physostigmine was markedly suppressed by quinupramine, amitriptyline and imipramine. Quinupramine showed no significant effect on the photic driving response and recruiting response. Quinupramine slightly enhanced the limbic afterdischarges elicited by either hippocampal or amygdaloid stimulation, while amitriptyline and imipramine caused an initial suppression followed by a quick recovery. The EEG effects of quinupramine were similar to those of amitriptyline in both qualitative and quantitative aspects.     

Enhancement of cocaine-induced hyperactivity in mice by benzodiazepines: Evidence for an interaction of GABAergic processes with catecholaminergic neurons?

The effects of nine benzodiazepines on the locomotor stimulation induced in mice by cocaine (4 mg . kg-1 i.p.) were studied. These benzodiazepines markedly enhanced cocaine-induced hyperactivity. This effect was observed at low doses, e.g. doses at least 8 times lower than those required to depress the stimulation caused by cocaine. Nitrazepam-induced enhancement of the hyperactivity elicited by cocaine was reduced or suppressed by blocking dopaminergic receptors with pimozide (0.015--0.03 mg . kg-1), by interrupting GABAergic transmission with picrotoxin (0.25--0.5 mg . kg-1) or blocking alpha- or beta-adrenergic receptors with prazosin (0.25 mg . kg-1) or dl-propranolol (4 mg . kg-1) respectively. At these doses, neither pimozide, picrotoxin, prazosin nor propranolol were able to modify the spontaneous locomotor activity or the stimulation elicited by cocaine alone. Strychnine (0.25--0.50 mg . kg-1) or methysergide (2 mg . kg-1) failed to alter the enhancement by nitrazepam of cocaine-induced hyperactivity. These results suggest that an interaction of benzodiazepines with some catecholaminergic processes, either directly or through the involvement of a GABAergic link, may account for their facilitatory activity on cocaine-induced locomotor stimulation.     

Antagonist discrimination of two muscarinic responses elicited by applied agonists and orthodromic stimuli in superior cervical ganglion of rabbit

Pirenzepine and gallamine selectively and differentially antagonized two muscarinic responses, in the superior cervical ganglion of the rabbit, whether elicited by the muscarinic agonist methacholine or by orthodromic stimulation. Methacholine elicited a biphasic ganglionic response, consisting of hyperpolarizing and depolarizing components that were the agonist-induced equivalents of the slow-inhibitory and slow-excitatory postsynaptic potentials elicited by orthodromic stimulation. Superfusion of ganglia with pirenzepine resulted in a concentration-dependent suppression of depolarization induced by methacholine with no suppressant action on ganglionic hyperpolarization. In contrast, superfusion of ganglia with gallamine resulted in a concentration-dependent suppression of ganglionic hyperpolarization and the slow-inhibitory postsynaptic potential. These effects occurred without appreciable suppression of ganglionic depolarization or the slow-excitatory postsynaptic potential. The action of gallamine was specific for muscarinic hyperpolarization. Hyperpolarizations produced by superfusion with dopamine or norepinephrine were unaffected by gallamine, at concentrations that suppressed the muscarinic slow-inhibitory post-synaptic potential. Incubation with anti-cholinesterases produced a parallel shift, to the right, of concentration-response curves for suppression by gallamine of the slow-inhibitory postsynaptic potential. This was presumably the consequence of an increase in the acetylcholine available for interaction with the muscarinic receptor. The evidence suggests that the ability of gallamine and pirenzepine to suppress selectively the slow-inhibitory and slow-excitatory postsynaptic potentials, as previously demonstrated, is through an action at muscarinic receptors. Furthermore, the data suggest that these pharmacological agents produce their effects by interaction at different muscarinic recognition sites.     

Potentiation by naloxone of pressor reflexes.

1 The effect of intravenous naloxone, and opiate antagonist, was studied on the pressor responses elicited by stimulation of afferent nerves (vagus and laryngeal superior nerves) in anaesthetized dogs. 2 Although naloxone (0.1 mg/kg i.v.) alone failed to modify basic blood pressure, the pressor responses induced by stimulation of either the vagus or laryngeal nerve were potentiated by naloxone. 3 Morphine (0.2 mg/kg i.v.) suppressed these two cardiovascular responses. These depressor effects of morphine were reversed by subsequent injection of naloxone (0.1 mg/kg i.v.). 4 The results suggest the involvement of endogenous opiate peptides in pressor reflexes elicited by stimulation of the afferent nerves.     

Modulation of GABAA receptor activity by alphaxalone.

The modulation of the gamma-aminobutyric acidA (GABAA) receptor by alphaxalone has been investigated by use of voltage-clamp recordings from enzymatically isolated bovine chromaffin cells maintained in cell culture. Alphaxalone (greater than 30 nM) reversibly and dose-dependently potentiated the amplitude of membrane currents elicited by locally applied GABA (100 microM). The potentiation was not associated with a change in the reversal potential of GABA-evoked currents and was not influenced by the benzodiazepine receptor antagonist, Ro15-1788 (300 nM). At relatively high concentrations (greater than 1 microM), alphaxalone directly elicited a membrane current. It is concluded that such currents result from GABAA receptor activation since they were reversibly suppressed by bicuculline (3 microM), dose-dependently enhanced by phenobarbitone (100-500 microM), and had a similar reversal potential (approximately 0 mV) to currents elicited by GABA. Additionally, on outside-out membrane patches, alphaxalone activated single channel currents with amplitudes and a reversal potential similar to those evoked by GABA. Alphaxalone (30 nM-1 microM) had no effect upon the amplitude of membrane currents elicited by locally applied acetylcholine (ACh) (100 microM). However, higher concentrations of alphaxalone (10-100 microM) reversibly suppressed ACh-evoked currents, the IC50 for blockade being 20 microM. The beta-hydroxy isomer of alphaxalone, betaxalone (100 nM-1 microM), did not potentiate GABA-induced currents, nor did higher concentrations of the steroid (10-100 microM) directly evoke a membrane current. However, over the latter concentration range, betaxalone suppressed the amplitude of currents elicited either by GABA or ACh. The relevance of the present results to the anaesthetic action of alphaxalone is discussed together with the broader implications of steroidal modulation of the GABAA receptor.     

Electroencephalographic effects of flurazepam in rabbits (author's transl)]

Electroencephalographic (EEG) effects of flurazepam were investigated in unanesthetized, unrestrained rabbits with chronic electrode implants and compared with those of diazepam. Flurazepam, at doses of 0.5 approximately 5 mg/kg i.v., induced a drowsy EEG pattern, i.e. high voltage slow waves in the cortex and amygdaloid complex and desynchronization of the hippocampal theta waves. In addition, low voltage fast waves were superimposed, especially on the cortical EEG. Flurazepam suppressed the EEG arousal responses induced not only by auditory stimulation but also by electrical stimulation of the mesencephalic reticular formation, posterior hypothalamus and centromedian thalamus. The EEG arousal response induced by i.v. injection of physostigmine was suppressed by flurazepam. Flurazepam depressed the photic driving response and the augmenting response. The recruiting response was slightly enhanced by flurazepam. The limbic afterdischarges elicited by either hippocampal or amygdaloid stimulation were suppressed by flurazepam. Flurazepam caused reductions of pressor responses to stimulation of the posterior hypothalamus and the mesencephalic reticular formation in anaesthetized rabbits. There was little or no effect on pressor responses to the injection of noradrenaline, carotid artery occulusion and asphyxia with flurazepam. In general, these effects of flurazepam were similar to those of diazepam, but the drug induced actions which differed from those of diazepam.     

Opiate and opiate antidiarrhoeal drug action on rat isolated intestine

1 Stimulation of segments of rat jejunum (2.5, 5, 10, 20 and 40 Hz for 8 s) and ileum (10 Hz) resulted in a fast atropine-sensitive contraction during stimulation and a non-cholinergic after-contraction. Stimulation of segments with single pulses at 0.1 Hz had no effect. The colon (10 Hz) usually responded only with single large atropine-sensitive contractions. 2 The responses of the jejunum (2.5–40 Hz, 8 s) were unaffected by the μ-receptor ligands morphine (0.3 μM) and RX 783006 (0.3 μM) or the k-receptor ligand, ethylketocyclazocine (0.3 μM). The cholinergic contraction of the colon was unaffected by ethylketocycazocine (0.3 μM), but was reduced slightly by morphine at high concentrations only. 3 The prototype δ-opiate receptor ligand D-Ala²-D-Leu⁵-enkephalin (DADLE; 30 nM) reduced the contraction during stimulation (2.5, 5, 10 and 20 Hz for 8 s) of the rat jejunum. The IC₅₀ value for inhibition of the contraction elicited by stimulation at 10 Hz was 3.2 in the jejunum and was 12 nM in the ileum. Contractions of the colon were only slightly inhibited at a high concentration of DADLE (1 μM). 4 DADLE had no effect on contractions elicited by acetylcholine, at a concentration of up to 3 μM in segments of jejunum. Naloxone (1 μM) abolished the inhibitory effect of DADLE on the cholinergic contraction of the electrically stimulated jejunum. In addition, naloxone caused a large enhancement of control responses to stimulation. 5 Only high concentrations of the antidiarrhoeals loperamide and diphenoxylate inhibited the contraction elicited at 10 Hz in the jejunum (IC₅₀, 1.3 and 7.1 μM, respectively) and ileum (loperamide IC₅₀, 0.5 μM). The same concentrations of these drugs also inhibited the effect of exogenously added acetylcholine. A similar pattern of findings was made in the colon. 6 The results show marked differences in responses to transmural stimulation and to opiate drugs compared to those previously obtained from guinea-pig ileum. Furthermore, it appears from the results that the cholinergic nerves of the rat jejunum and ileum possess non-μ, non-k, enkephalin-sensitive opiate receptors, which upon stimulation reduce the amount of depolarization-induced acetylcholine release. Finally, the opiate antidiarrhoeals appear to act postsynaptically.     

Relaxations of the isolated portal vein of the rabbit induced by nicotine and electrical stimulation

1. A pharmacological analysis of the inhibitory innervation of the isolated portal vein of the rabbit has been made.2. In untreated preparations, transmural stimulation elicited a long-lasting relaxation at low frequencies (0.2-1 Hz); at higher frequencies a contraction followed by a prolonged after-relaxation occurred. Tetrodotoxin abolished the contractions but a higher dose was required to abolish the relaxations. Veratrine lowered the threshold of stimulation for producing relaxations in the untreated vein. The relaxations were unaffected by hyoscine or hexamethonium. They were reduced or altered by antagonists of alpha-adrenoceptors for catecholamines and by adrenergic neurone blockade. They were sometimes slightly reduced by antagonists of beta-adrenoceptors.3. In the presence of antagonists of alpha-adrenoceptors, electrical stimulation elicited relaxations which increased with frequency of stimulation and became maximal at 20-30 Hz. These relaxations were partially reduced by antagonists of beta-adrenoceptors, or by adrenergic neurone block; the antagonisms were more pronounced at the higher frequencies of stimulation. Noradrenaline also caused relaxations which were abolished by beta-adrenoceptor blocking drugs. Cocaine increased the sensitivity to noradrenaline by 7-8 fold after alpha-adrenoceptor blockade but had little or no effect on the relaxations induced by electrical stimulation at high frequencies.4. In the presence of antagonists of alpha- and beta-adrenoceptors, or adrenergic neurone blocking agents, or in veins taken from rabbits pretreated with reserpine, electrical stimulation elicited rapid relaxations which were greatest at 20-30 Hz. These relaxations were increased by veratrine and abolished by tetrodotoxin or by storing the vein for 9 days at 4 degrees C. They were unaffected by antagonists of acetylcholine, or by dipyridamole.5. Prostaglandins E(1), E(2) and F(2alpha) inhibited contractions elicited by electrical stimulation and noradrenaline, but in higher doses caused contractions themselves.6. Nicotine (10(-6)-10(-5) g/ml) relaxed the portal vein; higher concentrations elicited mixed inhibitory and excitatory effects. All these effects were abolished by tetrodotoxin, cocaine, hexamethonium or storage. The contractor effects were abolished by drugs or procedures that blocked adrenergic mechanisms.7. The relaxations produced by nicotine in untreated preparations and in veins from rabbits pretreated with reserpine were mediated mainly by a non-adrenergic non-cholinergic nervous mechanism. Relaxations induced by nicotine in the presence of antagonists of a-adrenoceptors were only partially antagonized by antagonists of f3-adrenoceptors.8. It was concluded that all the effects of nicotine and transmural stimulation were mediated by nerves. Part of the inhibitory effects was mediated by non-adrenergic, non-cholinergic nerves.     

Contribution of glutamatergic systems in locus coeruleus to nucleus paragigantocellularis stimulation-evoked behavior.

The role of extracellular glutamate, within the locus coeruleus, in mediation of the behavioral signs elicited by electrical stimulation of the nucleus paragigantocellularis (PGi) was investigated in conscious, opioid-naive rats. Each rat was prepared with a chronically implanted unilateral electrode within the PGi and a microdialysis guide cannula directed at the ipsilateral locus coeruleus. Opioid withdrawal-like behaviors (rearing, teeth-chattering, wet-dog shakes, etc.) and increases in extracellular glutamate concentrations within the locus coeruleus were evoked, in a frequency-dependent (0.5-50 Hz) manner, during PGi stimulation. Reverse dialysis perfusion of the locus coeruleus with the nonspecific glutamate receptor antagonist, kynurenic acid (0.1, 1 mM), reduced the intensity of stimulation-induced behaviors by roughly 50%, but had no effect on the corresponding increases in glutamate concentrations. Perfusion of the locus coeruleus with the glutamate transporter inhibitor, L-trans-pyrrolidine dicarboxylic acid, at 1, but not at 0.1, mM significantly increased glutamate levels in dialysates. Neither concentration of the transporter inhibitor altered the behavioral score. The results indicate that the opioid withdrawal-like behaviors elicited by electrical stimulation of the brainstem at the site of the PGi are positively correlated with locus coeruleus levels of glutamate, and suggest further that the behaviors are partially mediated by release of glutamate within the locus coeruleus or its immediate vicinity.     

Frequency-dependent effects of bay K 8644 on tetanic contractions of frog skeletal muscle

• 1.1. The effects of the calcium channel agonist, Bay K 8644 (1–100 μM), on tetanic contractions, elicited by the stimulation frequencies of 100 Hz, 50 Hz and 25 Hz for 2 s, were investigated on frog skeletal muscle fibers.
• 2.2. Although the area under the tetanic force versus time curve was greatly reduced at the stimulation frequency of 100 Hz, this effect was significantly reversed at the lower stimulation frequencies of 50 and 25 Hz, at all concentrations tested.
• 3.3. During the intracellular recordings, it was revealed that the sodium action potentials elicited with the stimulation frequency of 100 Hz for 2 s were significantly blocked.
• 4.4. Similar to mechanical recordings, the blockade of repetitively elicited action potentials was also significantly reversed at lower stimulation frequencies of 50 and 25 Hz for all concentrations of Bay K 8644 tested
• 5.5. In conclusion, the results indicate that Bay K 8644 depresses both tetanic contractions and action potentials in a frequency-dependent manner in frog skeletal muscle fibers.

     

Stimulation of synaptosomal dopamine synthesis by corticotropin-releasing factor in rat striatum: role of Ca2+-dependent mechanisms

Corticotropin-releasing factor (CRF) stimulated synaptosomal dopamine (DA) synthesis in rat striatal homogenates. The stimulatory effect of CRF was antagonized by alpha-helical CRF 9-41 and was dependent on the extracellular Ca2+ concentration, being absent after removal of Ca2+ from the incubation medium and maximal at about 1.2 mM extracellular Ca2+. The stimulation of DA synthesis by forskolin (FSK) was less sensitive to a change of extracellular Ca2+ concentration. 3-Isobutyl-1-methylxanthine potentiated the FSK effect but did not affect the response to CRF. CRF stimulation was additive to that produced by 40 mM KCl and was little affected by the calmodulin inhibitor, W-7, which markedly suppressed the veratridine-induced stimulation of DA synthesis. Polymyxin B antagonized the CRF stimulation while it had a weaker effect on FSK-stimulated DA synthesis. Tolbutamide reduced the FSK stimulation more effectively than the CRF response. CRF elicited a non-significant increase of cyclic AMP formation by striatal membranes. These results indicate that CRF stimulates striatal DA synthesis by a Ca2+-dependent mechanism possibly involving the activation of the protein kinase C pathway.     

Action on ileal smooth muscle of synthetic detergents and pardaxin

Pardaxin (PX), a toxic and repellent substance isolated from the Red Sea flatfish, causes a sharp ball-like profile of drop of saline placed on a hydrophobic film to turn into a flattened one. This effect results with a decrease of the contact angle (theta) from 96 degrees to a maximum of 42 degrees at 10(-4) M of PX. The action of sodium dodecyl sulphate (SDS), a synthetic anionic detergent, benzalkonium chloride (BAC) cationic detergent and pardaxin (PX) a toxic protein with detergent properties, were studied in the ileal guinea-pig longitudinal smooth muscle preparation. SDS (4 X 10(-4) M) and PX (5 X 10(-6) M) diminished the muscle contractile response to field stimulation (0.1 Hz, 1 msec) and to acetylcholine (Ach) and to histamine and elicited a prolonged (4-6 min) TTX-insensitive muscle contraction. The dose dependence of muscle contraction to SDS and PX was found to be sigmoidal and occurred over a narrow range of concentrations. The SDS- but not PX-induced muscle contraction could be reduced by diphenhydramine (H1 antihistamine). BAC (10(-5)-10(-4) M) suppressed the muscle's contractile response to electrical stimulation (0.1 Hz, 1 msec), to Ach, histamine and 5-hydroxytryptamine but did not produce muscle contraction. PX at concentrations higher than 5 X 10(-6) M is a potent detergent and at this concentration shares several pharmacological similarities with SDS.     

Sodium excretion following central administration of an I1 imidazoline receptor agonist, moxonidine.

1. In anococcygeus muscles, ethanol (20-500 mM) slightly increased the tone and inhibited relaxations elicited by nitrergic nerve stimulation (0.5-5 Hz) in a concentration-dependent manner. 2. Other aliphatic alcohols decreased the tone but had inhibitory effects similar to ethanol on stimulation-induced relaxations, the EC50 (mM) values being: methanol 280, ethanol 80, propan-1-ol 20, propan-2-ol 55, propan 1,2-diol 135, butan-1-ol 120, butan-2-ol 15 and pentan-1-ol 3. 3. Relaxations induced by sodium nitroprusside (SNP, 10 nM) were inhibited by ethanol (20-500 mM) in a concentration-dependent manner and by propan-2-ol (100 mM). Relaxations induced by NO (1 microM) were inhibited by high concentrations of ethanol (200-300 mM) and by propan-2-ol (100 mM). 4. In gastric fundus strips, ethanol (60-200 mM) did not affect the resting tone but inhibited NO-mediated relaxations elicited by low frequency (1 Hz) field stimulation and reduced the initial relaxation by high frequency field stimulation (10 Hz) and by SNP (50 nM). The relaxant action of isoprenaline (10 nM) was not reduced although it was slightly slower in onset. Other aliphatic alcohols tested decreased the tone and inhibited relaxations elicited by field stimulation. 5. Acetaldehyde (1-10 mM) inhibited relaxations elicited by field stimulation and SNP in both the rat anococcygeus muscles and gastric fundus strips. The tone of gastric fundus strips was decreased by acetaldehyde but it was transiently increased in anococcygeus muscles.(ABSTRACT TRUNCATED AT 250 WORDS)     

Pharmacological evidence that at least two different non-adrenergic non-cholinergic inhibitory systems are present in the rat small intestine

The nature of the non-adrenergic non-cholinergic (NANC) relaxation was studied in the proximal (duodenum) and distal (ileum) regions of the rat small intestine. In rat duodenum ATP (1 microM-1 mM) produced a concentration-dependent transient relaxation. In ileal segments it produced a slight inhibitory effect at low concentrations (1-10 microM) and a powerful concentration-dependent contractile effect at concentrations equal to or higher than 100 microM. Relaxation similar to that elicited by ATP can be induced in rat duodenum with the nicotinic stimulant dimethylphenylpiperazinium (DMPP, 0.1 mM) and with gamma-aminobutyric acid (GABA, 1 mM). DMPP had a similar inhibitory effect on distal ileum while GABA barely affected spontaneous activity in this preparation. TTX (0.5 microM)-sensitive relaxation can be elicited in both duodenal and ileal tissues by field stimulation at 0.1 Hz. In the rat duodenum this nerve-mediated relaxation was sensitive to ATP desensitization, nucleotide pyrophosphatase (0.25 U/ml) but resistant to the proteolytic enzyme alpha-chymotrypsin (2 U/ml). On the other hand the field stimulation (0.1 Hz)-induced relaxation in the distal ileum was unaffected by ATP desensitization (by using both low or high concentration of ATP) and by incubation of the preparation with the two enzymes. These findings provide pharmacological evidence that low frequency field stimulation activates at least two different inhibitory NANC systems in the rat small intestine. Adenosine-5'-triphosphate (ATP) appears to be involved as a major transmitter in the duodenal but not in the ileal NANC inhibitory mechanism(s).