2-Amino/azido/hydrazino-5-alkoxy-5H-[1]benzopyrano[4,3-d]pyrimidines: synthesis and pharmacological evaluation.

New series of 5-alkoxy-benzopyranopyrimidine derivatives were developed from the chemical modulation of the substituent in position 2 of the scaffold, with the aim to produce analgesic/antiphlogistic agents more potent than analogues previously reported. The 2-hydrazino derivatives exhibited a good analgesic activity in writhing test; the analgesic doses of the compounds did not affect mice spontaneous locomotor activity thus any confounding sedative effect could be excluded. These derivatives revealed an aspirin-like profile with a strong inhibition of AA-induced platelet aggregation, probably due to a strong, non selective, inhibition of cyclooxygenases. In spite of the inhibition of COX activity displayed in vitro, the compounds did not cause gastric damage in rats after acute oral administration. A different pharmacological profile was observed for the 2-azido derivatives, particularly in vivo.

Effects of L-DOPA/benserazide co-treatment on colonic excitatory cholinergic motility and enteric inflammation following dopaminergic nigrostriatal neurodegeneration.

INTRODUCTION: The mainstay therapy for Parkinson's disease (PD) relies on L-3,4-dihydroxyphenylalanine (L-DOPA) plus a DOPA-decarboxylase inhibitor. However, their effects on colonic dysmotility and inflammation observed in PD are undetermined. This study examined the effects of L-DOPA plus benserazide (BE) on colonic motility and inflammation in rats with central nigrostriatal dopaminergic denervation. METHODS: Neurodegeneration was induced by 6-hydroxydopamine (6-OHDA) injection into the medial forebrain bundle (MFB). 6-OHDA animals were treated orally with L-DOPA/BE for 28 days, starting 28 days after 6-OHDA injection. At the end of treatment, in vivo colonic transit was evaluated by a radiologic assay. Electrically stimulated (ES) cholinergic contractions were recorded in vitro from colonic preparations, while acetylcholine release was measured in the incubation medium. Choline acetyltransferase (ChAT) and glial fibrillary acidic protein (GFAP) expression as well as eosinophil and mast cell density were examined in the colonic wall by immunohistochemistry. Colonic TNF and IL-1ß levels were also assayed. RESULTS: 6-OHDA animals displayed: 1) decrease in in vivo colonic transit; 2) impairment of ES-stimulated cholinergic contractions; 3) decreased acetylcholine release from myenteric nerves; 4) decrease in ChAT and increase in GFAP myenteric immunopositivity; 5) increase in eosinophil and mast cell density; 6) increase in TNF and IL-1ß levels. Treatment with L-DOPA/BE elicited an improvement of in vivo and in vitro colonic motor activity, a normalization of acetylcholine release, ChAT immunopositivity, as well as pro-inflammatory cytokine patterns, ganglionic GFAP levels, eosinophil and mast cell density. CONCLUSION: Under dopaminergic nigrostriatal denervation, treatment with L-DOPA/BE ameliorated colonic motility through a normalization of myenteric cholinergic neurotransmission, along with an improvement of colonic inflammation.

Plasticity of rat small intestine after removal of a chronic mechanical obstruction.

Chronic intestinal obstruction is associated with morphological changes and functional disorders clinically reported and experimentally documented in laboratory animals. In contrast, little is known about the properties of the hypertrophied intestine after removal of the obstruction. In the present study, we removed the ileal obstruction previously applied to the ileum of rats and, after 1 or 2 weeks, studied in vitro the motor responses of de-obstructed segments of intestine to pharmacological or electrical field stimulation (EFS). By 2 weeks after de-obstruction, maximal contractile responses to receptor (acetylcholine) and non-receptor (K(+)) mediated stimuli were comparable in operated and control tissues; furthermore, the loss of sensitivity to nitric oxide (NO) unmasked in obstructed tissues was, after de-obstruction, replaced by supersensitivity to exogenous NO and vasoactive intestinal polypeptide, probably acting through cyclic nucleotide-independent pathways. Despite the complete recovery of smooth muscle responses, neurogenic contractions remained impaired in de-obstructed tissue; however, the equal contribution of cholinergic/peptidergic components to EFS responses could represent a sign of gradual but delayed recovery of enteric neurotransmission.

Comparative screening of plant essential oils: phenylpropanoid moiety as basic core for antiplatelet activity.

Essential oils extracted from different plants (Anthemis nobilis L., Artemisia dracunculus L., Cannabis sativa L., Cupressus sempervirens L., Cymbopogon citratus (DC.) Stapf., Curcuma longa L., Foeniculum vulgare L., Hypericum perforatum L., Hyssopus officinalis L., Mentha spicata L., Monarda didyma L., Ocimum basilicum L., Ocotea quixos Kosterm., Origanum vulgare L., Pinus nigra J.F. Arnold, Pinus silvestris L., Piper crassinervium Kunth., Rosmarinus officinalis L., Salvia officinalis L., Salvia sclarea L., Santolina chamaecyparissus L., Thymus vulgaris L., Zingiber officinaie L.) were screened in guinea pig and rat plasma in order to assess antiplatelet activity and inhibition of clot retraction. The oils were chemically analysed and a relationship between components and ability to affect hemostasis was evidenced. O. quixos, F. vulgaris, and A. dracunculus showed the highest antiplatelet activity against ADP, Arachidonic Acid and the Thromboxane A2 agonist U46619 (IC50, 4-132 microg ml(-1)), and a good ability to destabilize clot retraction (IC50, 19-180 microg ml(-1)). For these oils a significant correlation between antiplatelet potency and phenylpropanoids content (54-86%) was evidenced thus suggesting a key role for this moiety in the prevention of clot formation. These findings provide the rationale to take in account the antiplatelet activity in the pharmacological screening of natural products containing phenylpropanoids.

Intestinal dysfunction in Parkinson's disease: Lessons learned from translational studies and experimental models.

BACKGROUND: Symptoms of digestive dysfunction in patients with Parkinson's disease (PD) occur at all stages of the disease, often preceding the onset of central motor symptoms. On the basis of these PD-preceding symptoms it has been proposed that PD could initiate in the gut, and that the presence of alpha-synuclein aggregates, or Lewy bodies in the enteric nervous system might represent one of the earliest signs of the disease. Following this hypothesis, much research has been focused on the digestive tract to unravel the mechanisms underlying the onset and progression of PD, with particular attention to the role of alterations in enteric neurotransmission in the pathophysiology of intestinal motility disturbances. There is also evidence suggesting that the development of central nigrostriatal neurodegeneration is associated with the occurrence of gut inflammation, characterized by increments of tissue pro-inflammatory markers and oxidative stress, which might support conditions of bowel neuromotor abnormalities. PURPOSE: The present review intends to provide an integrated and critical appraisal of the available knowledge on the alterations of enteric neuromuscular pathways regulating gut motor activity both in humans and preclinical models of PD. Moreover, we will discuss the possible involvement of neuro-immune mechanisms in the pathophysiology of aberrant gastrointestinal gut transit and neuromuscular activity in the small and large bowel.

H3-receptor antagonists: synthesis and structure-activity relationships of para- and meta-substituted 4(5)-phenyl-2-[[2-[4(5)-imidazolyl]ethyl]thio]imidazoles.

We report the synthesis, octanol/water partition coefficient (log P), dissociation constants (pKa), H3-receptor affinity (pKi in rat brain membranes, [3H]-N alpha-methylhistamine), and H3-antagonist potency (pA2 in guinea ileum, (R)-alpha-methylhistamine) of novel H3-receptor antagonists obtained by introducing a para or meta substituent on the phenyl ring of the lead compound 4(5)-phenyl-2-[[2-[4(5)-imidazolyl]ethyl]thio]imidazole (3a). The substituents were chosen to obtain broad and uncorrelated variation in their lipophilic, electronic, and steric properties. The log P values of the neutral species cover almost 3 orders of magnitude (from 1.40 to 4.11). The pKa,2 values (protonation of the 2-thioimidazole fragment) vary from 3.13 to 4.34, indicating that this fragment, which incorporates the so-called polar group common to many H3-receptor antagonists, is neutral at physiological pH. The compounds had pKi values in a range too narrow (from 7.28 to 8.03) to derive QSAR equations. In one case (3g), a biphasic displacement curve was observed (pKi,1 = 8.53; pKi,2 = 6.90). The pA2 values ranged 2 orders of magnitude (from 6.83 to 8.87) and yielded a QSAR model (PLS) indicating that antagonist potency depends parabolically on lipophilicity and is decreased by bulky para substituents. The compounds of this series, therefore, maintain a fair-to-good affinity for rat brain H3-receptor and a fair-to-good H3-antagonist potency on guinea pig ileum, although varying markedly in their lipophilicity. The series thus appears as a good candidate for pharmacokinetic optimization leading to brain-penetrating H3-receptor antagonists.

R-alpha-methylhistamine-induced inhibition of gastric acid secretion in pylorus-ligated rats via central histamine H3 receptors.

1. The effect of central H3 histamine receptor activation on gastric acid and pepsin production has been investigated in pylorus-ligated rats. 2. Intracerebroventricular injections (i.c.v.) of the selective H3 agonist, R-alpha-methylhistamine (0.5-50 nmol per rat) caused a dose-dependent inhibition of gastric acid secretion while intravenous administration (5-500 nmol per rat) was completely ineffective. 3. I.c.v. microinjections of mepyramine, tiotidine and thioperamide (51 nmol per rat), selective antagonists at H1-, H2- and H3-sites respectively, failed to modify the acid secretory response to pylorus ligation. 4. The antisecretory effect of R-alpha-methylhistamine (5 nmol per rat, i.c.v.) was selectively prevented by the H3-blocker, thioperamide (51 nmol per rat, i.c.v.), mepyramine and tiotidine pretreatment being completely inactive. 5. Unlike acid secretion, pepsin production was not significantly affected by all the tested compounds. 6. These findings provide the first pharmacological evidence that the activation of central H3 histamine receptors exerts a negative control in the regulation of gastric acid secretion in conscious pylorus-ligated rats.

Interaction of selective compounds with muscarinic receptors at dispersed intestinal smooth muscle cells.

1. The characterization of muscarinic receptors on single cells of the guinea-pig ileum longitudinal smooth muscle, devoid of neuronal elements, was functionally studied by estimating the affinities of muscarinic antagonists on acetylcholine-induced contractions. 2. Atropine (5 x 10(-11) to 5 x 10(-6) M), 4-diphenylacetoxy-N-methyl-piperidine methiodide (4-DAMP, 5 x 10(-8) to 5 x 10(-6) M), cyclohexyl(4-fluoro-phenyl) (3-piperidinopropyl) silanol (pFHHSiD, 5 x 10(-7) to 5 x 10(-5) M) as well as pirenzepine (5 x 10(-7) to 5 x 10(-5) M) competitively antagonized the acetylcholine-dependent contractions with different affinities (atropine > 4-DAMP > pFHHSiD > pirenzepine). 3. Methoctramine (5 x 10(-7) to 5 x 10(-5) M), and AF-DX 116 (5 x 10(-6) and 5 x 10(-5) M) also showed antagonist properties but these deviated from simple competition. These compounds, which discriminate between M2 and M3 receptors, showed a potency lower than that of pirenzepine, the rank order of potencies being pirenzepine > methoctramine > AF-DX 116. When concentrations of AF-DX 116, methoctramine and pirenzepine were increased an unspecific contractile effect occurred. 4. McN-A-343, a partial agonist on intact guinea-pig longitudinal smooth muscle strips, on this preparation induced a weak contraction (about 7% in comparison to control) that was not reversed by antimuscarinic agents. 5. These data indicate that M3 rather than M2 receptor sites are present on this tissue.

Motor responses of rat hypertrophic intestine following chronic obstruction.

The present work aims at investigating the changes in motor responsiveness of rat intestine hypertrophied by chronic mechanical obstruction. Motor responses to pharmacological agents and electrical field stimulation (EFS) were studied in hypertrophic ileal segments excised from rats subjected to experimental stenosis (n = 20) and compared with responses of control tissues from sham-operated animals (n = 20). Spontaneous motility and contractile responses to exogenous agents (KCl, acetylcholine and substance P) and EFS (10-s trains every minute, 120 mA, 0.5 ms, 1-10 Hz) were increased in hypertrophic longitudinal segments; however, normalization of motor responses to tissue wet weight revealed a remarkable reduction of contractile efficiency in hypertrophied tissues coupled with a loss of sensitivity to nitric oxide-mediated relaxation. Furthermore, EFS under non-adrenergic non-cholinergic (NANC) conditions unveiled a major role of the cholinergic component over the peptidergic one in the neurogenic contraction of hypertrophic intestine. On the whole, hypertrophic intestinal growth emerges as a dynamic process entailing adaptation of smooth muscle and neuronal structures to the increased functional load imposed by lumen obstruction.

Effects of two new pirenzepine analogs on the contractile response of the guinea-pig oesophageal muscularis mucosae to acetylcholine, bethanechol, histamine and high potassium.

The guinea-pig oesophageal muscularis mucosae was used to determine the affinity for muscarinic receptors of two new tricyclic compounds, DF 545 and DF 594, which are structurally related to pirenzepine. Both acetylcholine and bethanechol induced a concentration-dependent contraction of the muscularis mucosae. This contraction was competitively antagonized by DF 545 and DF 594 over the dose range 10(-7)-10(-5) M, while at higher concentrations both antagonists caused a depression of the maximal response to the cholinomimetics. The potency of DF 545 and DF 594 appeared to be comparable to that of pirenzepine and approximately 50 times lower than that of atropine. By comparing the affinities of DF 545 and DF 594 with those of selective antagonists (methoctramine and 4-DAMP) which discriminate between M2/M3 muscarinic receptor subtypes, it emerged that pirenzepine as well as DF 545 and DF 594 might act on M3 receptors, which seem to be predominant in the guinea-pig oesophageal muscularis mucosae. McN-A-343 exhibited no agonist activity while it acted as a competitive antagonist against acetylcholine and bethanechol. None of the compounds exhibited calcium antagonist properties. DF 545 inhibited the contractile responses to histamine, but DF 594 and pirenzepine did not.

Muscarinic M1 and M3 receptor antagonist effects of a new pirenzepine analogue in isolated guinea-pig ileal longitudinal muscle-myenteric plexus.

The new pirenzepine analogue DF 545 has been tested for its muscarinic M1 and M3 receptor antagonist properties in guinea-pig longitudinal muscle-myenteric plexus preparations. McN-A-343-induced inhibition of twitch contractions was taken as a parameter for muscarinic M1 receptor activation while electrical and acetylcholine-induced contractions were considered as a model for muscarinic M3 receptor stimulation. An unexpected contractile effect evoked by McN-A-343 was also investigated. In contrast to pirenzepine, DF 545 only weakly counteracted the M1-mediated McN-A-343 inhibitory effect but blocked M3-related twitch- or acetylcholine-stimulated responses with a 2-fold higher affinity than pirenzepine. Therefore, in this preparation, our findings suggest that DF 545 does not share the selectivity profile exhibited by pirenzepine at ileal muscarinic receptors. Studies on the McN-A-343 contractile effect provide evidence that this agonist may interact with ileal muscarinic effector sites in a different way from other cholinergic agents.

Evidence for specific analgesic activity of a muscarinic agonist selected among a new series of acetylenic derivatives.

The central and peripheral effects of a series of Oxotremorine/Oxotremorine-M derivatives, previously characterized as muscarinic agonists in isolated preparations, were investigated in in vivo experiments. The molecules were tested for their antinociceptive activity (formalin licking and acetic acid writhing tests) and for their ability to induce tremor in mice. Peripheral cholinergic effects such as salivation, bradycardia, hypotension and intestinal hypermotility were studied in anaesthetized rats. All of the acetylenic compounds acted as muscarinic analgesics displaying the same order of potency shown in in vitro studies. The Oxotremorine-like subset showed a clearer distinction between doses producing antinociception and doses exerting undesirable central/peripheral side effects compared to the Oxotremorine-M derivatives. The most promising profile was displayed by the isoxazolin-3-one Oxotremorine-like derivative (compound 1a), which was characterized by a wider therapeutic window than that of the parent molecule Oxotremorine. Indeed, it produced atropine-sensitive analgesia (ID50 about 0.1 mg/kg i.p.) in the absence of tremorogenic (EC50 2.73 mg/kg i.p.) and cardiovascular effects while lethality occurred only at higher doses (LD50 19 mg/kg i.p.). These results suggest that such a derivative could be a candidate for further development of selective muscarinic analgesics.

New analogues of oxotremorine and oxotremorine-M: estimation of their in vitro affinity and efficacy at muscarinic receptor subtypes.

Two subsets of tertiary amines (1a-6a) and methiodides (1b-6b) with a structural resemblance to oxotremorine and oxotremorine-M were tested at rabbit vas deferens (M1), guinea pig left atrium (M2), guinea pig ileum and urinary bladder (M3) muscarinic receptor subtypes. The pharmacological profile of the derivatives under study has been discussed by evaluating their potency, affinity and efficacy as well as the regional differences in muscarinic receptor occupancy.

Antinociceptive and gastroprotective effects of inhaled and orally administered Lavandula hybrida Reverchon "Grosso" essential oil.

In this study the antinociceptive and the gastroprotective effects of orally administered or inhaled Lavandula hybrida Reverchon "Grosso" essential oil, and its principal constituents linalool and linalyl acetate were evaluated in rodents. Either when orally administered (100 mg/kg) or inhaled for 60 min lavender essential oil significantly reduced the acetic acid-writhing response in a naloxone-sensitive manner. In the hot plate test, analgesic activity observed after oil inhalation was inhibited by naloxone, atropine, mecamylamine pretreatment suggesting the involvement of opioidergic as well as cholinergic pathways. Regardless of the administration route and the experimental model used both linalool and linalyl acetate did not produce significant analgesic response. Oral or inhalatory treatment with analgesic doses of essential oil did not affect mice spontaneous locomotor activity. Concerning the gastric effects, lavender oil, linalool and linalyl acetate oral administration protected against acute ethanol-induced gastric ulcers but did not prevent indomethacin-induced lesions indicating no interference with arachidonic acid metabolic cascade. In conclusion, besides this gastroprotection, lavender oil reveals an interesting analgesic activity mainly relevant after inhalation, at doses devoid of sedative side effect, suggesting the interest for potential application of this oil in aromatherapy.

Ligands of the histamine H3-receptor: new potent antagonists of the 2-thioimidazole type.

An overview of H3-receptor ligands is presented, with particular attention to antagonists. The protein binding of the classical H3-receptor antagonist thioperamide and its effect on in vivo distribution are discussed. A series of H3-receptor antagonists characterised by the presence of an imidazole ring, a spacer (ethylthio-, ethylamino-, propylthio- or propylamino-chain), a second heterocycle nucleus and a lipophilic group is described. Their H3-receptor antagonist potency has been measured on electrically stimulated guinea-pig intestine, and their affinity for central H3-receptor has been determined by competitive inhibition of [3H]N alpha-methylhistamine binding to rat cortex. Biphasic inhibition curves have been observed in some cases. Compounds endowed with interesting activity belong mostly to the class of 2-[[2-[4(5)-imidazolyl]ethyl]thio]imidazole, having a phenyl or a cyclohexyl group.

Plasma concentration and brain penetration of the H3-receptor antagonist thioperamide in rats.

Thioperamide is a potent and selective H3-receptor antagonist, whose in vivo effects have been reported after systemic administration. Some questions have arisen about its ability to cross the blood-brain barrier, since different experimental conditions have given different results in rats, namely a low brain/blood ratio at low doses (10 mg/Kg) and a much higher one at higher doses (60 mg/Kg). In this work we demonstrate the dose-dependence of thioperamide pharmacokinetics, measuring its plasma and cerebral levels after i.p. administration of different doses to rats. Both the plasma half-life and brain penetration of thioperamide resulted as being dose-dependent: when administered to 80 g body weight Wistar rats at 10 mg/Kg i.p., the drug has a short half life (120') and a rather poor brain penetration, but increasing the dose (to 20, 40 and 60 mg/Kg) gives rise to a prolongation of its persistence in the blood (up to 600' at highest dose) and a higher brain penetration. Also, the profile of the plasma concentration curve varies from the dose of 10 to that of 20 mg/Kg, passing from a mono-exponential decrease to a more complex one characterized by an apparent distribution phase. The different distribution processes can be interpreted in the light of thioperamide protein binding and affinity for lipophilic tissues: protein binding can prevent brain penetration (but not distribution to other tissues) at lower doses, while at higher doses the free plasma fraction increases and it can allow passive distribution to lipophilic tissues such as brain tissues. A re-distribution from these tissues and plasma is probably responsible for the strong increase in half-life at high doses.

In vitro characterization of potency, affinity and selectivity of H3-antagonists: from thioperamide to thioperamide unrelated imidazole derivatives.

This paper summarizes the findings obtained for three different series of original compounds designed as potential H3-antagonists starting from thioperamide structure. The compounds were tested in functional and binding assays to estimate their potency, affinity and selectivity for histamine H3 receptors. Among them, many non-thiourea/isothiourea derivatives acted as selective H3 competitive antagonists and, particularly, 4(5)-[2-[4(5)-cyclohexylimidazol-2-ylthio]ethyl] imidazole (dIII) proved to be the most potent H3 blocker vs (R)-alpha-methylhistamine in electrically-stimulated ileum. This imidazole derivative, devoid of thiourea dependent toxic effects, with high affinity displaced biphasically [3H]-N alpha-methylhistamine bound to rat brain H3 sites. Thus, such compound could be proposed as the prototype molecule for the development of new non-thiourea/isothiourea H3-antagonists and as experimental tool to explore the intriguing question of H3 receptor heterogeneity.

Synthesis and biological assays of new H3-antagonists with imidazole and imidazoline polar groups.

New histamine H3-receptor antagonists were synthesised and tested on rat brain membranes and on electrically stimulated guinea-pig ileum. The new compounds have a central polar group represented by a 2-alkylimidazole or a 2-thioimidazoline nucleus. The effect of the polar group basicity on the optimal length of the alkyl chain, connecting this group to a 4(5)-imidazolyl ring, was investigated. The best affinity values, obtained by displacement of [3H]-RAMHA from rat brain, were obtained for the 2-alkylimidazole derivatives (2a-f) with tetramethylene chain (pKi 8.03-8.97), having an intermediate basicity between that of the previously reported 2-thioimidazoles (1a-i) and that of 2-alkylthioimidazolines (3a-h). In contrast, a general lowering of affinity (pKi 5.90-7.63) was observed for compounds of the last series (3a-h), with a complex dependence on the terminal lipophilic group and chain length.

Intestinal chronic obstruction affects motor responsiveness of rat hypertrophic longitudinal and circular muscles.

Extensive morphological and neurochemical changes have been experimentally and clinically documented in the hypertrophied intestine located orally to a chronic partial stenosis of the lumen. Functional studies revealed not only disruption of the interdigestive motor complex in vivo and decreased efficiency of contraction but also preservation of the peristaltic reflex in vitro. Given the critical role played in intestinal peristalsis by the coordinated activity of the longitudinal (LM) and circular muscle (CM), this work focuses on the motor responses of LM and CM isolated from rat hypertrophied ileum following mechanical obstruction. Maximal contractions to both receptor (acetylcholine and substance P) and non-receptor (K+) mediated stimuli were up to 10-fold increased in hypertrophic CM rings compared with control tissues, while a higher potency of substance P was revealed in both hypertrophied muscle layers. Relaxations to vasoactive intestinal polypeptide and 8-Br-cGMP were more intense on prostaglandin F(2alpha)-contracted hypertrophic LM strips compared with control tissues and a general tendency towards increased relaxation was shared also by hypertrophic CM basal tone. The present results collectively suggest that hypertrophic growth leads to hyperresponsiveness to contractile agents, particularly evident in the CM, and to increased sensitivity to relaxing mediators, especially exhibited by the LM. In this regard, the complementary role exerted by each muscle layer and the plasticity of the intestinal tissue could both come into play to preserve the intestinal functions in a changing environment.

Pharmacological profile of new thioperamide derivatives at histamine peripheral H1-, H2-, H3-receptors in guinea-pig.

The recent availability of potent and selective ligands, namely R-(alpha)-methylhistamine and thioperamide, led to conclusive progresses as regards histamine H3-receptor knowledge. The aim of this work is to investigate by in vitro tests the pharmacological properties of new amino and methyl derivatives of the H3-antagonist thioperamide. Such original compounds, developed by the modulation of the thioperamide imidazolyl moiety, were assayed at guinea-pig ileal contractile H1-, atrial chronotropic H2- and enteric neuronal H3-receptors. None of the drugs exhibited interaction with H1 or H2 sites. On electrically stimulated ileum, two of the thioperamide methyl derivatives competitively antagonized the inhibitory effect of the H3-agonist R-(alpha)-methylhistamine. On the basis of the Schild analysis, the more active isomer (compound IV) displayed an affinity at H3-receptors only five times lower than thioperamide. These results could contribute to elucidate further the structural features required to develop potent and selective H3-antagonists. On the other hand, to prove the hypothesized apparent heterogeneity between peripheral and central H3-sites, as emerged by pharmacological and binding studies, autoradiographic investigations are in progress.