Alberto Meli's research while affiliated with University of Rome Tor Vergata and other places

A new series of 11-[(aminoalkyl)carbonyl] derivatives of 6,11-dihydrodibenzo[c,f][1,2,5]thiadiazepine 5,5-dioxide (10-39) were synthesized and evaluated for potential antidepressant activity in the apomorphine-induced hypothermia (Apo 16) test. Effects on reserpine-induced hypothermia and toxicity for the most potent antagonists of Apo 16 hypothermia were also studied. Structure-activity relationships are reported. Anticholinergic effects were evaluated for compound 12, identified as the most potent and least toxic in this series, by assessing physostigmine lethality. Compound 12 was also subjected to X-ray analysis.

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.

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.

The anatomical localization of the binding sites of the spasmolytic drug octylonium bromide (OB) in the rat gastrointestinal tract was analyzed by use of light microscope autoradiography. The drug was visualized after in vitro incubation of frozen sections of the gastrointestinal tract with a 10 nM concentration of 14C-OB and after in vivo injection into the ascending, transverse, descending and sigmoidal portions of the colon. In vitro experiments demonstrated the specific accumulation of 14C-OB within the colonic and rectal smooth muscle. In contrast, no specific binding of the radiolabeled drug was noticeable in the stomach or in the small intestine. In vivo intracolonic injection of 14C-OB showed a significant accumulation of the drug in the colonic musculature 2 min after administration. The predominant localization of 14C-OB in the colonic and rectal musculature could explain its effectiveness in suppressing the amplitude and frequency of colonic contractions and in controlling the irritable bowel syndrome.

Tachykinins are a family of peptides which share the common C-terminal sequence Phe — x — Gly — Leu — Met NH2. Ample evidence, based on pharmacological, physiological, anatomical and neurochemical bases indicates that tachykinins, such as substance P (SP), play a physiological role as excitatory transmitters in the guinea-pig ileum (Costa et al., 1985; see also Barthó & Holzer 1985 for review). In the guinea-pig intestine, SP and other tachykinins, such as neurokinin A (NKA) are mainly stored in certain intrinsic neurons which are thought to play a role as final effectors of atropine-resistant peristalsis (Barthó and Holzer 1985 for review).

Stress-induced hyperthermia (SIH), which is seen in the last mice removed from the cage, is a novel animal model sensitive to anxiolytic drugs. SIH is antagonized by CL 218872 (25 and 50 mg/kg, os), by tracazolate (5 and 7.5 mg/kg, ip) and by 2-AP-5 (50 and 100 mg/kg, ip). At higher dose, CL 218872 (100 mg/kg, os) and tracazolate (12.5 mg/kg, ip) lose their activity. PK 9084 (5–40 mg/kg, ip) and CGS 9896 (2–20 mg/kg, both ip and os) were also ineffective in preventing SIH. The anti-hyperthermic effect of CL 218872 (25 mg/kg) and tracazolate (7.5 mg/kg) was blocked by the benzodiazepine antagonist Ro 15–1788 (15 mg/kg). CGS 9896 (10 mg/kg, os) also reversed the effect of CL 218872 (25 mg/kg) on SIH. Differently from anxiolytics, MK-801 (0.5–1 mg/kg, os), PCP (2.5 mg/kg, ip) and d-amphetamine (10 mg/kg, ip) evoked hyperthermia in the first set of mice and prevented a further stress-induced rise of body temperature in the last set of mice.

The effect of d- and l-enantiomers of propranolol on desipramine-induced anti-immobility effects and on brain desipramine levels was studied in the rat. Intraperitoneal propranolol and desipramine were administered three times, 25, 6, 2 and 24, 5, 1 h respectively, before the test. It was found that l-propranolol but not d-propranolol, at the same doses (2.5 and 5 mg/kg), antagonized 20 mg/kg desipramine without altering desipramine brain levels. It is suggested that blockade of beta-adrenergic receptors rather than membrane-stabilizing or pharmacokinetic effects is responsible for the antagonism of propranolol toward desipramine.

Capsaicin, the pungent ingredient of many red peppers, has been shown to possess a selective stimulant action on certain neuropeptide-containing primary afferents which are widely distributed in the gastrointestinal tract of several species (Maggi and Meli 1988 and Holzer 1988 for reviews). On isolated gut segments from rats or guinea pigs, capsaicin exerts a variety of motor responses (contraction, relaxation or both) which depend upon the release from sensory nerves of certain neuropeptides, such as tachykinins or calcitonin gene-related peptide (CGRP) (see as examples Barthó et al., 1987; Maggi et al., 1986; 1988a). A specific feature of the action of capsaicin on sensory nerves is represented by desensitization, which means that after a single application of a maximally effective concentration of capsaicin the sensory fibers become unresponsive to subsequent applications of this drug.

Thiorphan, a well known inhibitor of 'enkephalinase' (endopeptidase 24.11) potentiated and prolonged the contractile response to substance P (SP) and neurokinin A (NKA) on strips of the guinea-pig isolated urinary bladder and this effect was evident both in presence and absence of the mucosal layer. Thiorphan also enhanced and prolonged the capsaicin-induced contraction in strips from the bladder dome which is thought to be mediated by release of endogenous tachykinins. Exposure to capsaicin produced simultaneous release of SP- and tachykinin-like immunoreactivity both in presence and absence of mucosa. This effect of capsaicin was potentiated by thiorphan. Endopeptidase 24.11 activity was detected in the guinea-pig urinary bladder, being more concentrated in the mucosal than the muscular layer. These findings indicate that endopeptidase 24.11 terminates the activity of tachykinins in the guinea-pig urinary bladder and modulates the intensity of the biological response produced after their release from peripheral endings of sensory nerves.

We have studied the mechanical response of circular strips of the guinea‐pig ileum to tachykinins and characterized the receptors involved by means of receptor‐selective agonists. The strips responded to both substance P (SP) and neurokinin A (NKA), as well as to [Pro ⁹ ]‐SP sulphone (selective NK 1 ‐receptor agonist), [βAla ⁸ ]‐NKA(4–10) (selective NK 2 ‐receptor agonist) and [MePhe ⁷ ]‐neurokinin B (selective NK 3 ‐receptor agonist). The ED 50 s of the various peptides (calculated as the concentration of agonist which produced 50% of the response to 10 μ m carbachol) were similar, in the range of 40–200 n m , i.e. no clearcut rank order of potency was evident. The response to a submaximal (10 n m ) concentration of SP or NKA was unaffected in the presence of peptidase inhibitors (thiorphan, captopril and bestatin, 1 μ m each). The response to the NK 1 ‐agonist was totally atropine‐resistant, but was reduced (about 30% inhibition) by tetrodotoxin. The response to the NK 3 ‐receptor agonist was halved by atropine and abolished by tetrodotoxin. The response to the NK 2 ‐agonist was unaffected by either atropine or tetrodotoxin. The response to the selective NK 2 ‐agonist was unchanged after desensitization of NK 1 ‐ or NK 3 ‐receptors. The response to the NK 2 ‐selective agonist was strongly inhibited by [Tyr ⁵ , d ‐Trp 6,8,9 , Arg ¹⁰ ]‐NKA(4–10) (MEN 10,207) a selective NK 2 ‐receptor antagonist which did not modify the response to the NK 1 ‐selective agonist. Our findings indicate that all the three known types of tachykinin receptors mediate the contractile response of the circular muscle of the guinea‐pig ileum to peptides of this family. The response to activation of NK 3 ‐receptors is totally neurogenic and partially mediated by endogenous acetylcholine, the response to activation of NK 1 ‐receptors is partly neurogenic and largely myogenic and the response to activation of NK 2 ‐receptors is totally myogenic.