Protective effect of the tachykinin NK2 receptor antagonist nepadutant in acute rectocolitis induced by diluted acetic acid in guinea-pigs.

We have evaluated the potential protective activity of nepadutant, a selective tachykinin NK2 receptor antagonist, in a model of acute rectocolitis induced by an enema with 7.5% acetic acid in guinea-pigs. The injury was quantified visually by using a macroscopic injury score, and histologically by using a necrosis score. In addition, changes in myeloperoxidase activity, a marker for neutrophil infiltration, and plasma protein extravasation were evaluated. The injury caused by 7.5% acetic acid was mild, affecting the superficial layers and producing a strong edema of the submucosa. A single administration of nepadutant (0.3-10 mg/kg s.c., 1 h before acetic acid) markedly reduced the macroscopic damage and necrosis score and the increase in plasma protein extravasation induced by 7.5% acetic acid in the early phase of the injury. Single administration of nepadutant (3 mg/kg s.c.) reduced the macroscopic score and myeloperoxidase activity at the top (24 h) of inflammation. Repeated administration (3 mg/kg s.c. three times during 24 h) or co-administration of the tachykinin NK1 receptor antagonist MEN 11467 (3 mg/kg s.c.) did not enhance the antiulcer effect obtained with the single treatment with nepadutant. These data suggest the involvement of tachykinin NK2 receptors in the first phases of inflammation induced by acetic acid.

Effect of MEN 11467, a new tachykinin NK1 receptor antagonist, in acute rectocolitis induced by acetic acid in guinea-pigs.

The aim of this study was to evaluate the effect of MEN 11467 (1R,2S)-2-N[1(H)indol-3-yl-carbonyl]-1-N{N-(p-tolylacetyl)-N-(meth yl)-D-3(2-Naphthyl)alanyl}diaminocyclohexane), a new potent tachykinin NK1 receptor antagonist, in an experimental model of acute rectocolitis induced by an enema with 7.5% acetic acid in guinea-pigs. This effect was compared to that of mesalazine (5-amino-2-hydroxybenzoic acid). The injury was quantified visually by using a macroscopic injury score and histologically by using a necrosis score. In addition, changes in myeloperoxidase activity, a marker for neutrophil infiltration, and plasma protein extravasation were evaluated. The injury caused by 7.5% acetic acid was mild, affecting the superficial layers and producing a strong edema of the submucosa. A single administration of MEN 11467 (0.3-10 mg/kg s.c., I h before acetic acid) reduced the macroscopic damage and necrosis score and the increase in plasma protein extravasation induced by 7.5% acetic acid in the early acute phase of the injury (death at 2.5 h). Mesalazine (100 mg/kg p.o., 1 h before) reduced the macroscopic score but not the plasma protein extravasation. Repeated administration of MEN 11467 (1-3 mg/kg s.c., -1, +6 and +23 h after 7.5% acetic acid) reduced the macroscopic score and myeloperoxidase activity but not the plasma protein extravasation induced in the late phase of acute injury (death at 24 h). At this time mesalazine markedly reduced the macroscopic score, myeloperoxidase activity and plasma protein extravasation induced by 7.5% acetic acid. These results suggest a greater involvement of tachykinin NK1 receptors in the early phase than in the late phase of colonic inflammation in response to chemical injury.

Is there a relationship between rat latent aggressiveness and susceptibility to convulsive crises?

Experiments were aimed at assessing a possible different sensitiveness to seizures in aggressive vs. nonaggressive rates. Thirty-nine muricidal rats were selected by using a sedated mouse. Six of these killer rats (K) showed electroencephalographic (EEG) spontaneous syncronous wave-and-spike discharges, 6-11 c/s. None of nonkiller animals (NK) showed a similar pattern. These 6 K were not used for the subsequent experiments. Intraperitoneal pentylentetrazole (PTZ; 10, 20, and 40 mg/kg) or bicuculline (BIC; 2 and 4 mg/kg) was given to both NK and K. K were more sensitive than NK to the epileptogenic effects of 20 mg/kg PTZ and 2 mg/kg BIC, as revealed by the significant increased number of convulsive rats and longer duration of EEG seizures. No difference in EEG or convulsant behavior was observed between K and NK after the administration of the lower dose of PTZ and the high dose of PTZ or BIC. The use of K rats as a possible new sensitive model of petit mal is discussed.

Electrocorticographic desynchronization after application of visceral and somatic noxious stimuli in urethane-anesthetized rats: effect of intrathecal administration of tachykinin (NK 1 or NK 2) receptor antagonists.

We investigated the electrocortical (E.Co.G) correlates of visceral (topical capsaicin application or overdistension of the urinary bladder) and somatic (perineal pinching) painful stimulation in urethane-anesthetized rats and their modulation by intrathecal application of selective tachykinins receptors (NK 1 and NK 2) antagonists. Vesical overdistension or topical capsaicin on the bladder serosal surface produced an immediate and lasting E.Co.G. desynchronization resembling a cortical arousal. A second application of capsaicin was ineffective. Bladder contraction induced by topical acetylcholine did not alter E.Co.G. A desynchronized E.Co.G. was also induced by pinching of the perineal area of the rat. Intrathecal administration of lidocaine at lumbosacral level abolished the E.Co.G. desynchronization induced by both visceral and somatic noxious stimulation. On the other hand capsaicin-induced or over-distension (but not pinching-induced) E.Co.G. desynchronization disappeared in animals systemically pretreated with capsaicin or after intrathecal administration of NK 1 tachykinin receptor antagonists such as the peptide GR 82334 or the nonpeptide RP 67580, whereas the inactive enantiomer RP 68651 or the nonpeptide NK 2 antagonists SR 48968 were ineffective. In conclusion, the experimental model described herein, allowing a quantitative analysis of the E.Co.G. correlates of visceral and somatic noxious stimulation in urethane-anesthetized rats, provides evidence for a specific neural pathway carrying bladder-arising visceral (both mechanical and chemical) nociception that uses pelvic capsaicin-sensitive afferents projecting to NK 1 (but not NK 2) bearing spinal neurons and that ultimately leads to activation of cortical areas.

Opioids and corticosteroids involvement in the regulation of the neocortical spindling episodes in DBA/2J mice.

The present study examined the effects of dexamethasone and RU-38486 on the spike-and-wave spindling episodes (S&W) which can be spontaneously recorded in the electroencephalogram (EEG) of DBA/2J mice. Our data indicated that dexamethasone (1-10-100 micrograms/kg, ip) in a time- and dose-related manner significantly reduce the S&W occurrence in freely-moving DBA/2J mice. Cycloheximide (10 mg/kg, ip), a protein synthesis inhibitor, by itself did not modify significantly the S&W occurrence in mice, but when injected two hours before DEX (100 mg/kg, ip), induced consistent delay of DEX effects. On the other hand, treatment of mice with RU-38486 (50 mg/kg, ip) induced, after a transitory decrease, a dramatic increase of the rate of S&W episodes. In addition, we performed a "chemical adrenalectomy" treating mice with RU-38486 (50 mg/kg, po/d) for 4 days, and also in this case we observed a significant increase of S&W 24 h after the 4th treatment. Finally a series of experiments indicated that low doses of morphine inhibited, whereas high doses of naltrexone strongly enforced S&W. The present results suggest that glucocorticoids are able to modulate inherited spindling episodes in DBA/2J mice and that this effect may be related to a genomic activation mechanism. Studies in this field may give, in the near future, some important contributions to the understanding of corticosteroids involvement in brain excitability, and of their relationships with the opioid system.

Differential effects of various xanthines on pentylenetetrazole-induced seizures in rats: an EEG and behavioural study.

The present study deals with the EEG (electroencephalogram) and behavioural effects of a subconvulsant dose (30 mg/kg i.p.) of pentylenetetrazole in freely moving rats pretreated (100 mg/kg p.o., 1 h before pentylenetetrazole) with two classic (theophylline and caffeine) and two new (enprofylline and isbufylline) xanthines. In rats treated with vehicle, pentylenetetrazole caused a slight desynchronization of the EEG, characterized by periods of 'wave discharges', and 'spike-and-wave discharge complexes'. In rats pretreated with xanthines (theophylline or caffeine) pentylenetetrazole produced a dramatic increase in ictal seizures with the appearance of continuous spikes; concomitantly animals experienced myoclonic jerks (100%) and in some cases (ca. 20%) the animals died. In contrast, in enprofylline-pretreated rats, pentylenetetrazole induced only brief periods of wave discharges and spike-and-wave discharge complexes whose duration was significantly reduced compared to that of controls, although these discharges were associated with mild epileptic behaviour. When isbufylline-pretreated rats were challenged with pentylenetetrazole, the EEG was characterized by a short run of wave discharges (whose duration was shorter than that of other groups). No enprofylline- or isbufylline-treated rats developed seizures or died. In conclusion, only xanthines with strong adenosine A1 receptor antagonism (theophylline and caffeine) markedly enhance the EEG and behavioural effects of a subconvulsive dose of pentylenetetrazole. The present experimental approach could be used to evaluate the pro-convulsive potential of new xanthine derivatives.

m-trifluoromethylphenylpiperazine and m-chlorophenylpiperazine-induced hypothermia in mice is reversed by tricyclic antidepressants and other drugs.

Many antidepressants reverse arylpiperazine-induced hypothermia after acute treatment by a mechanism that does not seem to implicate monoamine uptake inhibition. Activity is found in reversing 1-(m-trifluoromethylphenyl)piperazine (TFMPP)-induced hypothermia by desipiramine 5 and 10 mg/kg and not by maprotiline 10 and 20 mg/kg. Clomipramine and fluoxetine with comparable serotonin uptake blocking potential do not have comparable TFMPP-reversing effects. A dibenzothiadiazepine compound (IM/P/3/4), hypothesized to have antidepressant activity though devoid of uptake blocking properties, was active at 10 and 20 mg/kg. Other classes of tricyclics such as neuroleptics (clozapine 5 and 10 mg/kg) and chlorpromazine (2 and 10 mg/kg) and the H1 antihistamines, promethazine (20 mg/kg) and cyproheptadine (10 mg/kg) are active, as well as the calcium antagonists nifedipine (10 mg/kg) and verapamil (10 mg/kg). We hypothesize that properties other than monoamine-uptake block which these compounds share (such as calcium-uptake inhibition) could be involved. Activity was also seen with the 5-HT1A agonists 8-hydroxy-2-(di-n-propylamino)tetralin (8-OH-DPAT, at 0.05 and 0.25 mg/kg), and 5-methoxy-N,N-dimethyltryptamine (5-MeODMT at 3 mg/kg) as well as with the muscarinic agonist oxotremorine (0.1 mg/kg).

Potential antidepressant activity and enhancement of serotonin uptake of a new dibenzothiadiazepine derivative.

A molecule, 6-methyl-6,11-dihydro-11-[(N,N-dimethylamino) acetyl]dibenzo[c,fl-[1,2,5]thiadiazepine 5,5-dioxide, (IM/P/3/4, CAS 128377-70-8), was identified in a screening program, which had the scope of finding compounds with antidepressive potential without the common sideeffects of existing antidepressive medication. IM/P/3/4 was found active a) in antagonizing apomorphine (16 mg/kg) and reserpine-induced hypothermia in mice; b) in potentiating yohimbine-induced lethality in mice; c) in reducing immobility of rats forced to swim and of mice suspended by the tail. IM/P/3/4 does not affect a) apomorphine-induced stereotypy; b) amphetamine-induced hypermotility; c) haloperidol-induced catalepsy and water-induced grooming and d) does not induce stereotypy or alter motor activity. The compound also a) reduced the beating of rat right heart atria only at a concentration of 3 x 10-4 mol/l; b) had weak anticholinergic activity; c) antagonized electroshock-induced convulsions and d) prevented indometacin-induced duodenal ulcers. IM/P/3/4 does not have good affinity for noradrenergic, serotonergic, dopaminergic, histaminergic or muscarinic receptors and does not displace imipramine, desipramine and mianserine from their binding sites. IM/P/3/4 increases 5-hydroxyindolacetic acid content and 3H-serotonin uptake in the hypothalamus. The present results suggest that IM/P/3/4 is a potential antidepressant with reduced side effects and with a mechanism of action which is different from that of other antidepressants.

Pharmacological profile of the new anticonvulsant etazepine.

The pharmacological profile of the new anticonvulsant etazepine (5,6-dihydro-5-methyl-11H-11-ethoxy-dibenzo[b,e]azepin-6-one) was investigated. It protected mice and rats from a wide variety of convulsant agents (maximal electroshock, pentetrazol (metrazole), bicuculline, strychnine, 3-mercaptopropionic acid, nicotine, cefazoline and kainic acid) at doses about 16-45 times lower than those exerting neurotoxic effects (depending on the test used). The anticonvulsant effect of etazepine was long-acting (more than 24 h) and did not seem to develop tolerance. Moreover, etazepine did not prolong thiopental-induced sleeping time. Based on pharmacological studies etazepine seems to exert its anticonvulsant effects by activating the GABAergic system.

Experimental procedure to favor an otherwise undetectable potential rat muricidal behavior.

We hypothesized that variation in mouse aggressiveness could, at least in part, affect muricidal attitude of rats, therefore we introduced a sedated (diazepam 50 mg/kg/PO) instead of a normal (nonsedated) mouse into a cage with a rat. Rats were challenged with sedated or nonsedated mice for two-four days. It was found that a) the percentage (40-60%) of rats which killed a sedated mouse was higher than that (about 10%) of those which killed a nonsedated mouse; b) rats trained to kill a sedated mouse did not kill a nonsedated mouse and c) rats which did not kill a nonsedated mouse did not kill a sedated mouse. The present results indicate that the first experience in the presence of a sedated mouse uncovers a muricidal behavior which persists upon exposure to subsequent similar experimental conditions. This behavior undergoes seasonal variations, reaching a maximum in September-October and a minimum in February-March.

Experimental aluminium encephalopathy: quantitative EEG analysis of aluminium bioavailability.

Single oral doses of aluminium hydroxide (50 to 200 mg/kg) were found to induce in mice a dose-dependent diminution of the power of the 7.5 to 12 Hz frequency band, with a parallel dose-dependent increase of aluminium content in the brain, as early as 45 min after administration, and indicated that aluminium hydroxide is readily absorbed through an empty stomach or duodenum and is able to induce alterations of background EEG rhythms at doses equivalent to the ones used in human therapy. These data suggest that the EEG disturbances of the background type, (which are observed during the early stage of dialysis encephalopathy in man), may be partly due to a pharmacological and therefore reversible effect induced by an increase in aluminium level in the brain.