Food applications of Irvingia gabonensis (Aubry-Lecomte ex. O'Rorke) Baill., the 'bush mango': A review

Irvingia gabonensis, also known as 'bush mango', is a multipurpose fruit tree, native to tropical Africa. It is a priority indigenous fruit tree in western and central Africa since its wood is used for making utensils and fruits are mostly used as food and medicine. The objective of this work is to provide an updated review of the available knowledge about physicochemical characteristics of I. gabonensis fruit in order to evaluate its potential use in the food industry. The fruit mesocarp contains various phytochemicals and ascorbic acid concentration higher than some vitamin C rich fruits, then it is consumed fresh or dried, used to produce juice and wine, or as a flavourant. I. gabonensis fruit kernel is rich in oil (63%-69% crude fat), mainly composed of myristic and lauric acids. Its triacylglycerol composition and, resultantly, melting curve and polymorphism indicate an aptitude for diverse applications, as it is solid at room temperature. Forty-one phenolic compounds were identified in the seeds and derived extracts and supplements, being ellagic acid and its derivates the most present. This review enhances our knowledge about nutritional content and health benefits of I. gabonensis whole fruit, especially its pulp and seed, evidencing the need for safer and more efficient production of value-added products.

The acute impact of the intake of four types of bread on satiety and blood concentrations of glucose, insulin, free fatty acids, triglyceride and acylated ghrelin. A randomized controlled cross-over trial

The purpose of the present study is to compare the effects of four different breads (one commercial par-baked wheat bread, three sourdough breads prepared with commercial wheat flour, organic wheat flour, organic einkorn flour) in 16 healthy subjects. The primary outcome of this randomized cross-over trial was evaluating intra-individual changes in glycemic areas-under-the-curve (AUCs) after 50g carbohydrate portions of each bread; secondary outcomes were changes in insulin, fatty free acids (FFA), triglyceride, acylated ghrelin and satiety AUCs. Blood samples and satiety ratings were collected every 30-min for 2-h after the consumption of each bread. The einkorn flour showed the lowest amylase activity, the commercial flour the highest; commercial bread had the highest carbohydrate content and the lowest dietary fiber content. Glucose AUCs were significantly lower after the consumption of sourdough breads made with organic (12,754±1433mg/dL×h) and einkorn flour (12,216±1210mg/dL×h), with respect to the commercial bread (13,849±2193mg/dL×h). Insulin AUCs decreased after the consumption of all sourdough breads when compared to commercial bread. FFA and triglyceride AUCs did not differ by kind of breads. Median ghrelin AUC was significantly lower and satiety higher after the einkorn bread (3710pg/mL×h; 3225±2414, respectively) than after commercial bread consumption (4140pg/mL×h; 1706±1766, respectively), but not with other sourdough breads. In conclusion, the use of sourdough may improve the nutritional features of breads; einkorn bread induced the least disturbance in carbohydrate homeostasis and the greater satiety. If confirmed by further research, these results might have implications in the approach towards chronic dysmetabolic diseases.

Human papilloma virus infection and cervical intraepithelial neoplasia in transplanted patients

Progress in diagnosis and treatment has led to an increased number of transplantation patients who consequently have immunological depression and emergence of tumors. The incidence of cervical neoplasia, according to previous studies, is 11%; this tumor is the only one that can be investigated by screening before and after a graft. Our purpose was to evaluate whether transplanted patients showed an increased incidence of genital human papilloma virus (HPV) infection and whether this infection produced greater progression of disease in cases of low-risk HPV infections. Our study involved 151 transplant patients who underwent Papanicolaou (Pap) and HPV tests. Patients listed for grafts underwent Pap and HPV tests 6 months before and 6 months after transplantation. All patients had negative Pap tests before their grafts. After their grafts 16 patients (10.59%) had negative Pap tests, but positive viral typing. Eleven patients (7.28%) showed positive Pap tests, 6 of whom had low-grade squamous intraepithelial lesion (SIL) and 5 patients high-grade SIL. The final HPV infection incidence (15.23%) was consistent with the literature. The incidence of lower female genital tract intraepithelial lesions (7.28%) was higher than the healthy population or analogous studies (4.5%-8.5%). We showed a constant association between high-risk HPV infection and gynecologic intraepithelial neoplasia, whereas there was no association between low-risk broods HPV infection and neoplasia. In conclusion, screening should start at almost 6 months before grafting to avoid an irreversible situation that is difficult to treat.

Assessment of the safety, tolerability, and PK/PD properties of two new formulations of subcutaneously administered IFN-beta1a: a double-blind, placebo-controlled comparison with the currently available formulation

OBJECTIVE

Application-site disorders are well-known adverse events (AEs) associated with subcutaneous (s.c.) injection. With high-dose, high-frequency interferon (IFN)-beta1a (Rebif) these AEs are generally mild but may lead to the discontinuation of some patients. The objective of this study was to compare the safety, tolerability, and the pharmacokinetic (PK) and pharmacodynamic (PD) profiles of two new formulations of Rebif (Rebif New Formulation: RNF1 and RNF2) with the current formulation (hereafter referred to as R) and placebo.

METHODS

In this double-blind, placebo-controlled, parallel-group, Phase I study, healthy volunteers of both sexes were randomized 1:1:1:1 to receive a single 0.5 ml s.c. dose of RNF1, RNF2, R or placebo (normal saline). The three active treatments contained 44 microg IFN-beta1a. During the 24-hour post-dose period, safety and tolerability assessments were conducted and blood samples were taken at regular intervals for PK and PD analyses. Pain intensity on injection was measured using the short-form McGill questionnaire and a 100 mm visual analogue scale (VAS). Further safety assessments were performed and blood samples taken at 24-hour intervals until Day 7 post-dose, with a final post-study visit 10- 14 days after dosing.

RESULTS

A total of 48 subjects (22 men, 26 women) were recruited and allocated equally to each treatment (12 subjects per group). AEs were reported by 10 subjects in each active treatment group and by 3 subjects in the placebo group. All AEs were consistent with the known safety profile of R. The number of treatment-emergent AEs was lower in the RNF2 group than the RNF 1 or R groups (21, 31 and 33 events, respectively). Redness at the injection site was mostly mild and occurred in fewer subjects in the RNF2 group (n = 3) than the RNF 1 or R groups (n = 7 and n = 4, respectively). Injection site pain was reported by 1 subject in the RNF2 group, compared with 4, 6 and 3 subjects, respectively, in the RNF1, R and placebo groups. The worst pain intensity, as measured by VAS, was lower in the RNF2 and RNFI groups than either the R or placebo groups. There was considerable intersubject variability in the PK and PD profiles of the three formulations of IFN-beta1a. Nevertheless, the PK and PD characteristics of RNF2 were similar to those of R.

CONCLUSIONS

The results from this study suggest that RNF2 may offer improved tolerability compared with the current formulation of R, but retains comparable pharmacokinetic and pharmacodynamic characteristics.

Pharmacodynamic evaluation of a PEGylated analogue of human growth hormone releasing factor in rats and pigs

The aim of this study was to assess the in vivo efficacy of monoPEGylated GRF(1-29)NH(2) having one PEG(5000) chains attached to either lysine 12 or 21 as compared to the GRF(1-29)NH(2) in rats and pigs. This analogue termed GRF-1PEG(5000) was tested after a single intravenous administration in rats and after a single intravenous or subcutaneous injection in pigs. After 1 h administration, GH concentrations returned to values close to controls in the group of rats injected with GRF(1-29)NH(2). In animals injected with the same dose of GRF-1PEG(5000), the AUC values corresponding to the whole period 0.5-48 h and particularly to the 0.5-8 h period were higher than in the placebo or in the GRF(1-29)NH(2) groups. Interestingly, two additional peaks were observed at about 6 and 8 h following administration. An increase in the response of the endogenous GH peaks was also observed in pigs administered GRF-1PEG(5000) by intravenous route. When GRF-1PEG(5000) was administered subcutaneously to pigs, a significant increase, as compared to placebo and GRF(1-29)NH(2,) in both GH and IGF-I levels was observed. This new analogue might find therapeutic application in paediatric growth hormone deficiency or in aging.

Breakthrough pain characteristics and syndromes in patients with cancer pain. An international survey

Breakthrough pain (BKP) is a transitory flare of pain that occurs on a background of relatively well controlled baseline pain. Previous surveys have found that BKP is highly prevalent among patients with cancer pain and predicts more severe pain, pain-related distress and functional impairment, and relatively poor quality of life. An international group of investigators assembled by a task force of the International Association for the Study of Pain (IASP) evaluated the prevalence and characteristics of BKP as part of a prospective, cross-sectional survey of cancer pain. Fifty-eight clinicians in 24 countries evaluated a total of 1095 patients with cancer pain using patient-rated items from the Brief Pain Inventory (BPI) and observer-rated measures. The observer-rated information included demographic and tumor-related data, the occurrence of BKP, and responses on checklists of pain syndromes and pathophysiologies. The clinicians reported BKP in 64.8% of patients. Physicians from English-speaking countries were significantly more likely to report BKP than other physicians. BKP was associated with higher pain scores and functional interference on the BPI. Multivariate analysis showed an independent association of BKP with the presence of more than one pain, a vertebral pain syndrome, pain due to plexopathy, and English-speaking country. These data confirm the high prevalence of BKP, its association with more severe pain and functional impairment, and its relationship to specific cancer pain syndromes. Further studies are needed to characterize subtypes of BKP. The uneven distribution of BKP reporting across pain specialists from different countries suggests that more standardized methods for diagnosing BKP are needed.

Dextromethorphan and its metabolite dextrorphan block alpha3beta4 neuronal nicotinic receptors

Dextromethorphan (DM), a structural analog of morphine and codeine, has been widely used as a cough suppressant for more than 40 years. DM is not itself a potent analgesic, but it has been reported to enhance analgesia produced by morphine and nonsteroidal anti-inflammatory drugs. Although DM is considered to be nonaddictive, it has been reported to reduce morphine tolerance in rats and to be useful in helping addicted subjects to withdraw from heroin. Here we studied the effects of DM on neuronal nicotinic receptors stably expressed in human embryonic kidney cells. Studies were carried out to examine the effects of DM on nicotine-stimulated whole cell currents and nicotine-stimulated (86)Rb(+) efflux. We found that both DM and its metabolite dextrorphan block nicotinic receptor function in a noncompetitive but reversible manner, suggesting that both drugs block the receptor channel. Consistent with blockade of the receptor channel, neither drug competed for the nicotinic agonist binding sites labeled by [(3)H]epibatidine. Although DM is approximately 9-fold less potent than the widely used noncompetitive nicotinic antagonist mecamylamine in blocking nicotinic receptor function, the block by DM appears to reverse more slowly than that by mecamylamine. These data indicate that DM is a useful antagonist for studying nicotinic receptor function and suggest that it might prove to be a clinically useful neuronal nicotinic receptor antagonist, possibly helpful as an aid for helping people addicted to nicotine to refrain from smoking, as well as in other conditions where blockade of neuronal nicotinic receptors would be helpful.

14C-NaVP and 14C-PEV repeated dose study in rat. Pharmacokinetic study in rats after repeated oral administrations of 14C-valproic acid sodium salt and 14C-valproic acid pivaloyl oxymethyl ester

The absorption, excretion and tissue distribution of radioactivity after repeated oral equimolar doses of 14C-valproic acid sodium salt (NaVP) or 14C-valproic acid pivaloyl oxymethyl ester (PEV) was investigated in male rats treated once a day for 14 consecutive days. The 14th day plasma time-course of radioactivity after PEV administrations was characterised by a slow absorption rate with a delayed peak (tmax 2 h, Cmax 7.52 +/- 1.35 microg eq./ml), followed by a plateau lasting up to 8 h. After NaVP treatment, the main peak of radioactivity was observed 0.5 h after administration (Cmax 8.30 +/- 1.26 microg eq./ml) followed by a secondary peak due to biliary enterohepatic recycling. Starting from 4 h onwards, radioactivity levels after PEV treatment were higher than those after NaVP (AUCtau = 113.3 h.microg eq./ml after PEV vs 71.9 h.microg eq./ml after NaVP), but concentrations declined with similar terminal half-lives (52.8 h for PEV and 49.7 h for NaVP). Radioactivity recovered (0-432 h interval) in urine accounted for 79.3% (PEV) and 56.1% (NaVP) while, in faeces accounted for 9.1% (PEV) and 26.1% (NaVP) of total administered dose (14 days). The difference is attributable to a higher excretion of radioactivity in the bile for NaVP. The missing fraction in the total radioactivity balance is probably excreted in expired air, as observed in single dose studies. Radioactivity excreted in bile (0-8 h interval of the last 14th day) accounted for 5.1% (NaVP) and 0.23% (PEV) of the total administered dose (14 days). A possible explanation of this difference may be a different metabolism pattern for the two compounds. The negligible biliary excretion observed after PEV administration is probably due to an inhibition of the glucuronation of valproic acid (or other metabolites) caused by the pivalic acid. Due to the presence of the enterohepatic recycle, the radioactivity levels in intestine, 0.5 and 2 h after administration, were higher after NaVP administration. According to higher plasma levels, the radioactivity concentrations in liver, kidneys and some fat tissues were found to be slightly higher after PEV administration. At 120 h after the last treatment of both compounds, relevant tissue concentrations were observed in mesenteric lymphnodes, perirenal and brown fat. The tissue-plasma radio activity ratio appeared quite similar for the two compounds.

Pharmacokinetic study in dogs and monkeys after single intravenous and oral administrations of [14C]-ITF-296

Pharmacokinetics of [14C]-ITF-296 and its metabolites, ITF-1124 and ITF-1577, were studied in dogs and monkeys after a single intravenous (2.5 mg/kg) and oral (10 mg/kg) administration. Radioactivity was measured by LSC while unchanged drug and its metabolites in plasma were assayed by an HPLC-UV method. The absorption of [14C]-ITF-296 after oral administration is practically complete both in dogs and in monkeys. The determination of unchanged drug and its metabolites shows quite a similar profile in dogs and monkeys for ITF-296 and ITF-1124 and a different time-course for ITF-1577. Elimination of radioactivity occurs mainly in urine (namely 70-80%) for both species and the recovery of the dose (higher than 90%) takes place up to 96 h after both treatments.

Pharmacokinetic study in rats after single intravenous and oral administrations of [14C]-ITF-296

Pharmacokinetics of [14C]-ITF-296 and its metabolites, ITF-1124 and ITF-1577, were studied in rats after a single intravenous (2.5 mg/kg) and oral (10 mg/kg) administration. Radioactivity was measured by LSC while unchanged drug and its metabolites in plasma were assayed by an HPLC-UV method. The absorption of [14C]-ITF-296 after oral administration is practically complete. Elimination of radioactivity occurs mainly in urine (higher than 80%) and the recovery of the dose (higher than 95%) takes place up to 96 h after both treatments. Both by i.v. and p.o. route the results show that the radioactivity is largely excreted in the bile and reabsorbed in the intestine. The tissue distribution study indicates that there is no accumulation or localization of radioactivity in the major organs or blood and no radioactivity levels are found 96 h after either treatment. In addition, whole body autoradiography confirms the tissue distribution pattern, showing no differences between albino and pigmented rats.

Nicotinic receptor mediates spontaneous GABA release in the rat dorsal motor nucleus of the vagus

Spontaneous postsynaptic currents were investigated in neurons of the caudal portion of the dorsal motor nucleus of the vagus using the patch-clamp technique to study the effect of neuronal nicotinic acetylcholine receptor activation on synaptic transmission. In voltage-clamped neurons, bath application of nicotine (1-30 microM) elicited a concentration-dependent increase in the frequency of the spontaneous synaptic currents. The effect was also observed with application of the nicotinic receptor agonists epibatidine (10 nM) and cytisine (10 microM). Mecamylamine (20 microM) and curare (50 microM), two nicotinic receptor antagonists, both decreased the effect of 3 microM nicotine on the frequency of the spontaneous postsynaptic currents. This effect of 3 microM nicotine was also blocked by 20 microM bicuculline, a competitive antagonist of the GABA(A) receptor; in contrast, it was not affected by 1 mM kynurenic acid, an antagonist of the ionotropic glutamate receptor. In the presence of 1 microM tetrodotoxin, 3 microM nicotine was unable to affect the synaptic activity. Our findings suggest the existence of nicotinic receptors on GABAergic axons projecting to the vagal motoneurons. Because the effect is completely abolished by 1 microM tetrodotoxin, the nicotinic receptors are not localized on the presynaptic nerve terminal and their action on the GABA release requires the propagation of an action potential from their location to the synaptic terminal. This effect of nicotinic receptor activation on spontaneous GABA release in the dorsal motor nucleus of the vagus may have an important role in the regulation of gastrointestinal motility.

Presynaptic alpha2-adrenoceptors inhibit excitatory synaptic transmission in rat brain stem

The synaptic connection between the commissural portion of the nucleus tractus solitarius (ComNTS) and the dorsal motor nucleus of the vagus (DMV) was studied in rat brain stem slices, using the patch-clamp technique. The excitatory postsynaptic currents (EPSC) evoked by stimulation of the ComNTS were blocked by kynurenic acid (1 mM) and, in Mg2+-free solution, were sensitive to both the N-methyl-D-aspartic acid (NMDA) receptor blocker 3-[(RS)-2-carboxypiperazine-4-yl] -propyl-1-phosphonic acid (20 microM) and the non-NMDA receptor blocker 2,3-dihydro-6-nitro-7-sulfamoyl-benzo(f)quinoxaline (5 microM). Norepinephrine (NE, 1-100 microM) inhibited the EPSC, and the inhibition was attenuated by the alpha2-adrenoceptor antagonists idazoxan (1 microM) and yohimbine (10 microM) but not by the beta-adrenoceptor antagonist nadolol (50 microM). The NE-releasing agent tyramine (100 microM) reduced the EPSC, and the inhibition was attenuated by 1 microM idazoxan. NE (30 microM) did not affect the membrane input resistance but reduced the paired-pulse depression, demonstrating that NE acts on presynaptic alpha2-adrenoceptors. The results indicate the existence of a glutamatergic pathway from the ComNTS to the DMV neurons modulated by presynaptic NE receptors. This pathway might be a component of the vagovagal reflex regulating gastrointestinal function.

7-Chloro-3-methyl-3-4-dihydro-2H-1,2,4 benzothiadiazine S,S-dioxide (IDRA 21): a benzothiadiazine derivative that enhances cognition by attenuating DL-alpha-amino-2,3-dihydro-5-methyl-3-oxo-4-isoxazolepropanoic acid (AMPA) receptor desensitization

7-Chloro-3-Methyl-3-4-Dihydro-2H-1,2,4 Benzothiadiazine S,S Dioxide (IDRA 21), which attenuates the rapid autodesensitization of DL-alpha-amino-2,3-dihydro-5-methyl-3-oxo-4-isoxazolepropanoic acid (AMPA)-selective glutamate receptors and increases excitatory synaptic strength, improves cognition (learning and memory), as revealed by its ability to improve performance in water maze and passive avoidance tests in rats. Normal rats trained to (15-20 sec) reach the exit platform rapidly in a water maze that included four incorrect choices were given oral IDRA 21 (4-120 mumol/kg) or vehicle and then exposed to a delayed retention trial in a maze that included seven incorrect choices. In this retention trial, the IDRA 21-treated rats performed considerably better than those that received the vehicle. Moreover, oral IDRA 21 (ED50 = 7.6 microM) attenuated the performance impairment induced by the AMPA receptor antagonist 2,3-dihydroxy-6-nitro-7-sulfamoylbenzo (F) quinoxaline in the water maze test. In this test and in a passive avoidance test, the performance impairment elicited by alprazolam, a full allosteric modulator at gamma-aminobutyric acid-A receptors, or by scopolamine, a competitive muscarinic receptor antagonist, was also reduced by oral administration of IDRA 21 (ED50 = 13 and 108 mumol/kg, against alprazolam and scopolamine, respectively); in all these tests, IDRA 21 was 20- to 30-fold more potent than aniracetam. Because IDRA 21 is a racemic molecule; the two stereoisomers were isolated and studied behaviorally. Only the (+) form was found to be behaviorally active. These results indicate that IDRA 21 given orally to rats presumably crosses the blood-brain barrier and acts stereoselectively on specific receptors that were operative during this behavioral procedure. Because the activity of IDRA 21 on rat cognition tests appears to be related to its ability to potentiate AMPA-activated currents, one can suggest that IDRA 21 improves cognition by acting on a stereoselective site of AMPA receptor that is operative in attenuating the rapid autodesensitization of these receptors.

The assessment of constipation in terminal cancer patients admitted to a palliative care unit: a retrospective review

Constipation is a frequent and distressing complication in patients with advanced cancer. However, very few studies have reviewed the assessment and management of these patients. The purpose of this study was to review the documentation and assessment and diagnosis of constipation in patients admitted to a Palliative Care Unit, and the correlation between those findings and radiological evidence of stool in the colon. The records of 122 consecutive patients admitted to the Palliative Care Unit, Edmonton General Hospital were reviewed in order to assess the physician's and the nurse's record of symptoms, physical findings, and diagnosis and treatment of constipation. All patients also underwent a flat abdominal radiograph that scored for the presence of stool in the colon (0 = no stool; and 12 = stool occupying all the lumen of the four quadrants of the colon). The radiograph was scored blindly by two different physicians. Of 103 evaluable patients, a rectal exam was reported only in 42. Correlation between the assessment by the two physicians' radiograph score was high (0.78, P nd nurses' diagnosis of constipation, the presence of laxative treatment, the number of days since the last bowel movement, and the source of the admission (hospital vs home) were not associated with higher radiological scores for constipation. Assessment is insufficient in this population at high risk for severe constipation. Radiological examination may be necessary for adequate diagnosis in some patients. More research is needed in this area.

[Intrahepatic portosystemic shunts]

We want to present our experience performed at the Institute of Radiology of Turin: 98 TIPS in 97 patients (in 1 patient, twice). METHODS. From March 1992, 97 cirrhotic patients (18 Child A, 48 Child B, 31 Child C) underwent the TIPS procedure for portal hypertension. The indications were digestive hemorrhage in 81 patients (20 of which performed in emergency for acute bleeding), intractable ascites in 13 patients and bleeding prevention in 3 patients. RESULTS. Immediate technical success was obtained in 95/98 cases (96.9%). Patients were monitored by US-Doppler at 24 hours, 2 months and every 6 months and by esophagogastroscopy at 2 and 6 months. Major clinical complications included CID (2 cases), hepatic failure (3 cases), renal insufficiency (2 cases), heart failure (1 case), recurrent bleeding (6 cases) and encephalopathy (15 cases). We had 5 early occlusion and 17 late stenosis of the shunt; 21 patients in this group were successfully treated either by PTA or restenting; one patient underwent a surgical shunt. Mortality rate follow-up was 0/17 among Child A patients, 7/48 (14.5%) among Child B patients and 12/29 (41.3%) among Child C patients. CONCLUSIONS. TIPS is a safe and valuable method for the treatment of portal hypertension. Though shunt stenosis may occur with a certain frequency (22/95, 23.1% in our study), a second intervention is usually effective in reducing gastro-oesophageal varices and ascites.

Modulation of AMPA/kainate receptors by analogues of diazoxide and cyclothiazide in thin slices of rat hippocampus

Among the non-NMDA (non-N-methyl-D-aspartic acid) glutamate receptors, the AMPA (alpha-amino-2,3-dihydro-5-methyl-3-oxo-4-isoxazolepropanoic acid) selective receptors are characterized by a fast occurring desensitization. We and others have searched for specific modifiers of the rapid desensitization of AMPA responses in hippocampal slices using the patch-clamp technique. Aniracetam (1-(4-methoxybenzoyl)-2-pyrrolidinone) and diazoxide (7-chloro-3-methyl-2H-1,2,4-benzo-thiadiazine 1,1-dioxide) (1 mM) increased glutamate-activated currents recorded from voltage-clamped CA1 pyramidal neurons in presence of 5 microM MK-801 (dizocilpine; 10,11-dihydro-5-methyl-5H-dibenzo[a,d]cyclohepten-5,10-imine) by 2.5 fold. Cyclothiazide (3-bicyclo[2.2.1]hept-5-en-2-yl-6-chloro-3,4-dihydro-2H-1,2,4-benzoth ia diazine-7-sulfonamide 1,1-dioxide) (100 microM), a chemical congener of diazoxide, completely removed the desensitization of the AMPA response measured with fast application in excised outside-out patches. At this concentration cyclothiazide produced an 18 fold enhancement of the glutamate current. Eighteen diazoxide analogues (2H-1,2,4-benzothiadizines: IDRA 2-19) were then tested but none of them was as effective as diazoxide. Three analogues of cyclothiazide (3,4-dihydro-2H-1,2,4-benzothiadiazines: IDRA 20-22) were also tested and none of them were as potent as the parent compound. However, IDRA 21 produced a response 3 times larger than diazoxide. Moreover, while cyclothiazide and diazoxide potentiated kainate responses for all the doses that decreased AMPA receptor desensitization, IDRA 21, similarly to aniracetam, inhibited AMPA receptor desensitization preferentially. These results suggest that similarly to NMDA receptors the structure of AMPA receptors may include a center that regulates desensitization.

Amiloride blocks glutamate-operated cationic channels and protects neurons in culture from glutamate-induced death

The diuretic amiloride has been suggested as a specific inhibitor of T-type neuronal Ca2+ channels. The effects of amiloride on glutamate receptor-gated cationic channels and glutamate-induced. Ca2(+)-dependent neuronal death were investigated in primary neuronal cultures from neonatal rats. In primary cultures of cerebellar granule neurons of the rat, receiving 50 microM glutamate for 15 min, at 22 degrees C, in the absence of Mg2+, about 80% of neurons were killed in about 24 hr. Exposure of neurons to such a pulse of glutamate, in the presence of various concentrations of amiloride, resulted in a dose-dependent protection from neurotoxicity (EC50 300 microM, complete protection 1 mM). In voltage-clamped cortical and cerebellar neurons of neonatal rats in primary culture, 100 microM amiloride diminished (by about 25%) glutamate- and/or NMDA-evoked cationic currents, recorded in the whole-cell mode. About 80% of the NMDA-(20 microM) stimulated current was inhibited by 700 microM amiloride. The inhibitory effect of amiloride was not voltage-dependent. In outside-out membrane patches, excised from granule cells and held at -50 mV, 100 microM amiloride changed the NMDA-elicited single channel activity into a fast flickering between the open and closed states. The noise analysis of the data revealed that, although resembling the Mg2(+)-induced flickering, the amiloride-induced channel block was more similar to the effects described for the action of local anaesthetics on the nicotinic cholinergic channel. The pharmacological relevance of this action of amiloride requires further characterization; the data point out the necessity of a cautious use of amiloride in studying neuronal function.

Baclofen inhibits with high affinity an L-type-like voltage-dependent calcium channel in cerebellar granule cell cultures

In primary cultures of cerebellar granule cells, D,L baclofen (p-chlorophenyl-GABA) inhibited approximately 50% of the calcium-45 influx induced with cell depolarization. The half maximal effective concentration for baclofen was 4 nM. Basal calcium influx was not influenced by baclofen thus suggesting that its inhibitory action could be exerted via a voltage dependent calcium channel (VDCC). Whole-cell recordings by patch-clamp technique showed a calcium current that appeared to be similar to the reported L-type VDCC. Nanomolar concentrations of baclofen also inhibited this calcium current by about 60%. However, in order for baclofen to be active, it needed to be placed into the incubation buffer at least five minutes before patching a cell raising the possibility that baclofen may be acting to inhibit the VDCC via a second messenger system.

Down-regulation of protein kinase C protects cerebellar granule neurons in primary culture from glutamate-induced neuronal death

Exposing primary cultures of cerebellar granule neurons to 100 nM phorbol 12-myristate 13-acetate (PMA) for 24 hr decreases the Ca2+/phosphatidylserine/diolein-dependent protein kinase C (PKC; ATP:protein phosphotransferase, EC 2.7.1.37) by approximately 90% in the 100,000 x g supernatant and pellet fractions of neuronal culture homogenates. Immunoblot analysis of the homogenates with polyclonal antibodies raised against either the beta-type PKC peptide or total rat brain PKC reveals a virtual loss of 78-kDa PKC immunoreactivity in the supernatant and a marked decrease of PKC immunoreactivity in the pellet. Exposure of the cultures to 50 microM glutamate for 15 min (no Mg2+) induces the translocation of supernatant PKC immunoreactivity to the pellet. Such translocation persists after glutamate withdrawal and is followed by a progressive increase in neuronal death, which begins 2 hr later. Neuronal death approaches completion in about 24 hr. PMA-induced down-regulation of PKC decreases glutamate-elicited neurotoxicity. Yet, the culture exposure to 100 nM PMA fails to decrease the high-affinity binding of [3H]glutamate to neuronal membranes and does not reduce glutamate-induced activation of ionotropic or metabolotropic receptors (assayed as total membrane current measured in whole-cell voltage-clamped neurons, 45Ca2+ uptake in intact monolayers, inositolphospholipid hydrolysis, and transcriptional activation and translation of c-fos mRNA). Moreover, the immediate cell-body swelling and activation of spectrin proteolysis elicited by glutamate remain unchanged. On the other hand, PMA-induced PKC down-regulation reduces any increase in 45Ca2+ uptake or Ca2(+)-dependent proteolysis (measured as spectrin degradation) after glutamate withdrawal. These results support the view that PKC translocation is operative in glutamate-induced destabilization of cytosolic ionized Ca2+ homeostasis and neuronal death.

Kynurenic acid inhibits the activation of kainic and N-methyl-D-aspartic acid-sensitive ionotropic receptors by a different mechanism

The action of kynurenic acid on currents elicited by the activation of amino acid receptors was investigated in primary cultures of cortical neurons prepared from neonatal rats. Kynurenic acid was tested on currents elicited by both N-methyl-D-aspartic acid (NMDA) and kainate, using patch-clamp recording techniques in "outside-out" and "whole-cell" configurations. The inhibition by kynurenic acid was compared with that elicited by amino-phosphono-valeric acid (APV). Whole-cell currents, elicited by increasing doses of NMDA, were antagonized competitively by APV and non-competitively by kynurenic acid (ID50 70 microM); in contrast, kynurenic acid inhibited competitively the whole-cell currents elicited by kainic acid (ID50 500 microM). The non-competitive inhibition by kynurenic acid of the whole cell currents elicited by NMDA was antagonized competitively by glycine, a specific positive allosteric modulator of NMDA receptors; on the other hand glycine failed to change the inhibition by APV of the NMDA-elicited responses. Thus, kynurenic acid inhibits NMDA receptors allosterically (non-competitively) and kainic acid receptors isosterically (competitively).

Gangliosides prevent glutamate and kainate neurotoxicity in primary neuronal cultures of neonatal rat cerebellum and cortex

Using a sensitive histofluorescence staining method that allows for a quantitation of neuronal death, we compared the protective effects of gangliosides (a group of naturally occurring glycosphingolipids), phencyclidine (PCP), and MK-801 (dibenzocyclohepteneimine) on glutamate- and kainate-induced neuronal death in primary cultures of cortical and cerebellar neurons prepared from neonatal rats. PCP and MK-801 block neurotoxicity induced by glutamate doses 50 times higher than the LD50 (LD50 in Mg2+-free medium, 10 microM) but only partially block the kainate neurotoxicity (LD50 in presence of Mg2+, 100 microM). In contrast, pretreatment with gangliosides (GT1b greater than GD1b greater than GM1) results in complete and insurmountable protection against the neurotoxicity elicited by glutamate or kainate. In primary cultures of cerebellar granule cells gangliosides, unlike PCP and MK-801, fail to block glutamate-gated cationic currents and the glutamate-evoked increase of (i) inositol phospholipid hydrolysis (ii) c-fos mRNA content, and (iii) nuclear accumulation of c-fos protein. Protection of glutamate neurotoxicity by gangliosides does not require their presence in the incubation medium; however, it is proportional to the amount of glycosphingolipid accumulated in the neuronal membranes. The ganglioside concentration (30-60 microM) that blocks glutamate-elicited neuronal death also prevents glutamate- and kainate-induced protein kinase C translocation from cytosol to neuronal membranes.

Voltage-dependent block by strychnine of N-methyl-D-aspartic acid-activated cationic channels in rat cortical neurons in culture

Single-channel currents were recorded by means of the patch clamp method in outside-out patches excised from rat cortical neurons in primary culture. The excitatory amino acid N-methyl-D-aspartic acid activated mainly 40-50 pS conductance channels. Channel opening durations were characterized by a series of rapid openings and closures induced by the presence of Mg2+ ions. This inhibitory effect was voltage dependent. Strychnine, the antagonist of the glycine-gated Cl- channels, blocks the N-methyl-D-aspartic acid-activated cationic channel in cultured rat cortical neurons. Strychnine action is voltage dependent and it is not counteracted by ethylenediaminetetraacetic acid, ruling out Mg2+ contamination of strychnine. It has been reported recently that glycine increases the rate of openings of N-methyl-D-aspartic acid-activated channels. This action is not affected by the presence of strychnine. Our results show that 1) Mg2+ and strychnine have an apparently similar intermediate blocking action on the NMDA-activated channels, 2) strychnine presumably acts as a sequential open channel blocker producing a different type of block compared with the one reported for Mg2+ ions, and 3) the lack of effect of strychnine on the glycine potentiation of the N-methyl-D-aspartic acid response indicates that this alkaloid does not competitively antagonize glycine but acts as an open channel blocker.

Phencyclidine and glycine modulate NMDA-activated high conductance cationic channels by acting at different sites

Glutamate activates high (40-50 pS) and low (5-15 pS) conductance cationic channels in outside-out patches excised from cultured cortical and cerebellar granule neurons of neonatal rats. In these neurons, the excitatory amino acid N-methyl-D-aspartic acid (NMDA) activates mainly high conductance channels. Phencyclidine (PCP) at 2 microM selectively reduces the number of NMDA-activated channel openings, at 20 microM it reduces the channel open-time. Glycine increases the opening frequency of high conductance NMDA-activated channels. This action is counteracted by PCP. This inhibition by PCP can be eliminated by reversing the polarity of the membrane patch. However, the effect of glycine is voltage independent. These results imply different sites of action for these two modulators.

The action of AD6 on experimental arrhythmias and on action potentials of cardiac fibers

AD6 is a coumarinic derivative which increases both coronary blood flow and prostacyclin production, while it decreases platelet responsiveness. We tested its action on experimental cardiac arrhythmias. AD6 (2.5-10 mg/kg) was able to antagonize the arrhythmogenic action of aconitine in rats and of adrenaline in cats. AD6 action was also tested in vitro. The drug (20-50 microM) prolonged the functional refractory period of guinea-pig atrial and ventricular muscle and lengthened the refractory period shortened by hypoxia. Intracellular electrophysiological experiments showed that AD6 prolongs action potential duration (APD) of guinea-pig atrial myocardium, sino-atrial node and cat Purkinje fibers. The results obtained in vitro may explain the effect on experimental arrhythmias, therefore suggesting a protective action on cardiac rhythm disturbances.