Muscarinic Agonists Evoke Neurotransmitter Release: Possible Roles for Phosphatidyl Inositol Bisphosphate Breakdown Products in Neuromodulation

Carbachol (CCh), a muscarinic agonist that elicits the formation of inositol trisphosphate (IP3) and diacylglycerol (DG), induces a calcium-dependent [3H]norepinephrine ([3H]NE) release [IC50 = (2.7 +/- 0.5) X 10(-4) M] in rat brain slices. Similarly, other muscarinic agonists evoke [3H]NE release which is specifically inhibited by muscarinic antagonists such as 3-quinuclidinyl benzilate, atropine, and N-methyl-4-piperidyl benzilate. The atropine-sensitive evoked release is effectively inhibited by neomycin (IC50 = 50 microM), a phospholipase C inhibitor that interferes with IP3-dependent cellular processes. In addition, polymyxin B, a rather selective inhibitor of protein kinase C (PK-C), abolishes the agonist-mediated release with a half-maximal effective concentration of 0.53 microM (750 ng/ml). These results have a significant implication for the mechanism by which agonists generating IP3 and DG act as inducers of neurotransmitter release in the CNS. However, since both neomycin and polymyxin B act also as N-calcium-channel blockers, other possible mechanisms are discussed. The CCh-induced release suggests that in the CNS an agonist-receptor interaction leads to a calcium-dependent neurotransmitter release, most likely via promoting the IP3/DG as second messengers followed by activation of PK-C.     

Effect of Nitrogen on Polysaccharide Production in a Porphyridium sp

Porphyridium cultures grown on either nitrate or ammonium as the nitrogen source showed similar patterns of growth and cell wall polysaccharide production. The effect of nitrogen on growth and cell wall polysaccharide production was studied by applying three regimens of supply: batch mode, in which nitrate was supplied at the beginning of the experiment and became depleted at day 6; continual mode, in which nitrate was added daily; and deficient mode, in which the cells were cultured in a nitrate-free medium. Growth was similar in the batch- and continual-mode cultures, whereas it was totally inhibited in the deficient-mode culture. Polysaccharide content (per volume) was highest in the batch-mode culture and lowest in the deficient-mode culture. However, polysaccharide production per cell was similar in the continual- and deficient-mode cultures, the highest value being found in the batch-mode culture. In addition to its effect on polysaccharide content, nitrogen affected the polysaccharide distribution between soluble and bound polysaccharides. In the deficientmode culture, most of the cell wall polysaccharide was dissolved in the medium.     

Do motilin and pancreatic polypeptide regulate duodenal bile acid delivery?

The plasma levels of the enteric hormones, motilin and pancreatic polypeptide, cycle in association with fasting intestinal motility and are altered by feeding. Intravenous administration of motilin causes gallbladder contraction and increased sphincter of Oddi phasic motor activity, whereas pancreatic polypeptide causes gallbladder relaxation. To determine if endogenous plasma levels of motilin and pancreatic polypeptide control sphincter of Oddi and gallbladder motility, and regulate duodenal bile acid delivery, we measured during fasting and after feeding the correlation between (a) changes in plasma motilin or pancreatic polypeptide, and (b) the duodenal delivery of a steady-state hepatic output of radiolabelled bile acid. Four dogs were prepared with duodenal cannulas. Duodenal motility was recorded manometrically. Plasma levels of pancreatic polypeptide and motilin were determined during a full cycle of the migrating myoelectric complex for 20 min before and 40 min after ingestion of a standard meal. To assess the effect of the sphincter of Oddi and the gallbladder together, or the gallbladder alone on duodenal bile acid delivery, the dogs received a continuous i.v. infusion of [14C]taurocholic acid (TCA); duodenal delivery of TCA was quantitated with the sphincter of Oddi intact using duodenal marker perfusion, or with the sphincter of Oddi cannulated and zero outflow resistance. In the interdigestive period with the sphincter of Oddi intact, only 0.1 (r2) of the variance of duodenal bile acid delivery can be predicted from the variance of motilin, and the correlation of plasma pancreatic polypeptide with duodenal TCA delivery is opposite that expected if pancreatic polypeptide caused gallbladder relaxation.(ABSTRACT TRUNCATED AT 250 WORDS)     

An endogenous brain substance, CDS (clonidine-displacing-substance), inhibits the twitch response of rat vas deferens

The effect of CDS, an endogenous brain substance that specifically displaces bound [3H]clonidine and [3H]rauwolscine in rat brain membranes and human platelets, has been tested in isolated, field-stimulated rat vas deferens. CDS, obtained after an extensive purification procedure as a single peak from an HPLC sizing column, inhibited the electrically stimulated rat vas deferens similarly to the inhibitory action of clonidine, an alpha 2-agonist. The effective dose of CDS as an inhibitor of the vas deferens is equivalent to its effective dose in displacing specifically bound [3H]-clonidine in rat brain membranes. Furthermore, the CDS inhibition of the twitch response is reversed by two alpha 2-adrenergic antagonists, yohimbine and phentolamine. From these results, it is suggested that CDS extracted from brain, with affinity for clonidine sites, may be involved in the nonadrenergic fast response of the sympathetic transmission of the vas deferens.     

Oesophageal peristalsis in the cat: the role of central innervation assessed by transient vagal blockade

Studies were performed on five cats to assess the role of extrinsic vagal innervation in the control of peristalsis in the smooth muscle oesophagus. Transient vagal nerve blockade was accomplished by cooling the cervical vagosympathetic nerve trunks previously isolated in skin loops on each side of the neck. Peristalsis throughout the body of the oesophagus was monitored using a continuously perfused multilumen manometry tube. Striated and smooth muscle portions of the esophagus were delineated by abolishing smooth muscle activity with atropine. Secondary peristalsis was assessed by intra-oesophageal balloon distension studies. The threshold volume for balloon-induced secondary peristalsis was lower in the smooth muscle oesophagus. Unilateral vagal blockade reduced the incidence of primary and secondary peristalsis in the striated muscle oesophagus but not in the smooth muscle oesophagus. Bilateral vagal nerve blockade abolished primary swallow-induced peristalsis and secondary peristalsis in both the smooth and striated muscle cat oesophagus. Administration of cholinergic agents or adrenergic blocking agents failed to restore secondary peristalsis in the smooth muscle oesophagus during vagal cooling. We conclude that connections to the central nervous system via the vagal nerve trunks are required for normal secondary as well as primary peristalsis in both the smooth and striated muscle portions of the cat oesophagus.     

Interaction of coupled nonlinear oscillators having different intrinsic resting levels

The interaction among coupled oscillators is governed by oscillator properties (intrinsic frequency and amplitude) and coupling mechanisms. This study considers another oscillator property, the intrinsic resting level, and evaluates its role in governing oscillator interactions. The results of computer experiments on a chain of either three or five bidirectionally coupled nonlinear oscillators, suggest that an intrinsic resting level gradient, if present, is one of the factors governing the interaction between coupled oscillators. If there is no intrinsic frequency gradient, then an intrinsic resting level gradient is sufficient to produce many features of interaction among coupled oscillators. If both intrinsic frequency and intrinsic resting level gradients are present, then both of them determine the manner in which the coupled oscillators interact with each other.     

Beta-endorphin and related peptides suppress phorbol myristate acetate-induced respiratory burst in human polymorphonuclear leukocytes

In the present study, the immunomodulatory effect of beta-endorphin (beta-E) and shorter pro-opiomelanocortin (POMC) fragments was evaluated by assessing their influence on respiratory burst in human polymorphonuclear leukocytes (PMN). The effect of the peptides (10(-17)M - 10(-10)M) on phorbol myristate acetate (PMA)-stimulated production of reactive oxygen metabolites was measured in a lucigenin-enhanced chemiluminescence (CL) assay. Both POMC peptides with opiate-like activity (i.e. alpha-endorphin (alpha-E), beta-E and gamma-endorphin (gamma-E] and their non-opioid derivatives (i.e. des-TYR1-beta-endorphin (dT beta E), des-TYR1-gamma-endorphin (dT gamma E), and des-ENK-gamma-endorphin (dE gamma E] were tested. With the exception of alpha-E, PMA-stimulated respiratory burst was suppressed by all POMC fragments tested. A U-shaped dose-response relation was observed. Doses lower than 10(-17)M and higher than 10(-8)M were without effect. beta-E and dT beta E both suppressed PMA-induced oxidative burst in human PMN at physiological concentrations (10(-16)M - 10(-10)M). gamma-E and dT gamma E proved to be less potent inhibitors, reaching maximal effect at higher concentrations (10(-12)M - 10(-10)M). DE gamma E exerted an even less pronounced but still significant suppressive effect at the concentration of 10(-10)M. None of the endorphins tested was shown to affect resting oxidative metabolism in the PMN. The modulatory effects of the opioid peptides could not be blocked by the opioid antagonist naloxone (10(-8)M). These data show that fragments derived from the POMC-precursor molecule modulate the activation of PMN by suppressing PMA-stimulated oxidative metabolism and that this activity does not involve a classical opiate-like receptor.     

Chronic toxicity of ammonia to juvenile gilthead seabream Sparus aurata and related histopathological effects

Effect of 20 days exposure of juvenile gilthead seabream ( Sparus aurata ) to elevated levels of ammonia on growth and survival was examined in a continuous flow system. Suppressed growth and reduced survival were observed at concentrations of 8.2 and 13 mg l⁻¹ total ammonia-N (0.5 and 0.7 mg l⁻¹ un-ionized ammonia-N, respectively) and higher. The maximum acceptable toxic concentration (MATC) for growth was between 4.8 to 8.2 mg l⁻¹ total ammonia-N (0.3 and 0.5 mg l⁻¹ un-ionized ammonia-N, respectively). Fish exposed to high ammonia levels (13 mg l⁻¹ total ammonia-N, 0.7 mg l⁻¹ un-ionized ammonia-N) displayed clear signs of liver pathology. Existing evidence suggests that S. aurata is less sensitive to ammonia than other reported marine and freshwater fish.
Under certain conditions ammonia concentration in the intensive fish ponds in Eilat may exceed the no observed effect concentration for S. aurata .     

Monogenean infestations and mortality in wild and cultured Red Sea fishes

Hyperinfection by the gill-infesting monogeneanAllobivagina sp. (Microcotylea) caused mass mortalities in juveniles ofSiganus luridus cultured in seawater earthen ponds and holding tanks in Eilat (Gulf of Aqaba, Red Sea). Other species ofSiganus and adults ofS. luridus cultured in the same systems acquired a low intensity of infestation. Most hyperinfected fish were emaciated and anaemic with hematocrit values below 10 %. Skin and mouth infestations by the monogeneanBenedenia monticelli (Capsaloidea) caused mass mortalities in grey mullets (Mugilidae). These mortalities occurred in large individuals in wild populations ofLiza carinata from lagoonal habitats in the Gulf of Suez and in most species of grey mullets cultured in Eilat. The intensity of infestation correlated positively with severity of infestation, and the common sites of infestation corresponded with areas of severe pathological alterations. Spontaneous recovery followed the climax of an epizootic, both for infestedS. luridus and infested grey mullets. Decline in infestation coincided with remission of the pathological signs.     

Symposium on diarrhea. 4. Diarrhea in the irritable colon syndrome.

The irritable colon syndrome comprises two predominant symptom patterns -- "spastic colon" with pain and constipation, and painless "nervous diarrhea". The two patterns frequently overlap. Low intake of dietary fibre is common to patients in both groups. Diagnosis of the irritable colon as a cause of diarrhea requires the characteristic symptom pattern and exclusion of organic disease. Management is based on common sense, careful reassurance of the patient, detailed explanation of the symptom pattern and explicit dietary advice. Increasing fibre in the diet is of prime importance in most patients.